Multi-layer waveguide antenna with metasurface

MULTI-LAYER WAVEGUIDE ANTENNA WITH METASURFACE

TECHNICAL FIELD OF THE INVENTION

[001] The present invention relates to an antenna arrangement formed by multi-layer waveguides, and particularly to antennas with multiple sets of antenna slots.

BACKGROUND OF THE INVENTION

[002] Antennas for transmitting and receiving electromagnetic radiation are of great importance in modem society. For example, antennas are essential for wireless communication and are also used in RADAR applications for transmitting and detecting RADAR signals. To this end, multiple antennas are integrated into most modem automobiles (as well as other vehicles) for both wireless communication purposes and RADAR detection of the surroundings to e.g. achieve autonomous driving or safety features such as automatic speed or cmise control and automatic stop functionality.

[003] In many applications, and especially for automotive, it is important the antennas are cost efficient to manufacture, made small and thin to enable simple integration and offer excellent radiation performance at high frequencies. These requirements have made waveguide stmctures utilizing multi-layer structures with gap waveguides popular.

[004] In some gap waveguide designs a first layer with a metamaterial structure of protruding pins (sometimes referred to as a bed of nails) is arranged with the pins defining a channel and with the pins facing a second flat layer, whereby electromagnetic waves can propagate along the channel between the first and second layer. This layout has proven to be associated with many benefits, including offering better performance (e.g. lower leakage) and being easy to manufacture.

[005] However, a problem lies in coupling the gap waveguide structures to antennas for conveying electromagnetic signals between the gap waveguides and free space. In some solutions, the gap waveguides are coupled to traditional antennas (e.g. horn antennas) using a transformation structure for achieving impedance matching. While acceptable performance in terms of radiation pattern and losses may be achieved this solution is bulky and ill-suited for integration into e.g. automobiles. Other solutions have been proposed involving integrating antenna openings in the multi-layer structure used to form the gap waveguides whereby the waveguide structure doubles as an antenna. However, it has proven difficult to achieve high performance with this type of antenna since it is not obvious how e.g. antenna openings should be arranged to minimize cross-talk and/or improve the directivity.

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GENERAL DISCLOSURE OF THE INVENTION

[006] It is a purpose of the present invention to overcome at least some of the shortcomings of the prior solutions and provide a multi-layer antenna that offers improved performance, even at high frequencies, while being simple to manufacture and small.

[007] According to a first aspect of the invention there is provided a center-fed multilayer antenna arrangement comprising, a top layer, a bottom layer, at least one intermediate layer arranged between the top layer and the bottom layer. The center-fed antenna arrangement further comprising an aperture forming a channel provided in the at least one intermediate layer, the channel comprises a first elongated portion, a second elongated portion and a common portion between the first elongated portion and the second elongated portion. Wherein a metasurface is arranged between the top layer and the at least one intermediate layer and between the bottom layer and the at least one intermediate layer, the metasurface being arranged to surround the channel and comprises thick and thin sections. Wherein the top layer comprises at least one antenna slot above the first and second elongated portion of the channel, respectively, and wherein the first and second elongated portions extend away from the common portion in substantially opposite directions.

[008] According to the first aspect of the invention, at least two antenna slots are fed by two channel portions that extend away from the common feeding portion. The antenna slots will cooperate together to form an antenna arrangement that is compact and easy to manufacture while at the same time offering excellent radiating performance. The first and second channel may extend symmetrically away from the common portion.

[009] Additionally, the multi-layer arrangement allows use of sub-quarter wavelength thick and thin sections forming the metasurface. For example, the height difference between the thick and thin sections in the metasurface is less than one fifth of an operational wavelength, preferably less than one eighth of the operational wavelength, and most preferably less than one tenth of the operational wavelength. This allows each layer to be made very thin which makes the antenna arrangement compact and cost efficient to produce. The sub-quarter wavelength thick and thin sections have also shown to offer excellent performance even when the separation distance between adjacent layers varies due to e.g. manufacturing tolerances.

[010] In some implementations, the common portion of the channel is elongated and extends substantially perpendicular to the first and second elongated portions.

[Oil] Accordingly, electromagnetics signals can be conveyed to/from the radiating/receiving elongated channel portions along an elongated common portion that extends away in a plane parallel to the layers.

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[012] In some implementations, the at least one intermediate layer comprises a central conductor arranged in the channel portions. That is, the radiating elongated channel portions and common portion can be realized as a rectangular coaxial waveguide with the central conductor defining the coaxial waveguide together with the channel, the top and bottom layer and the metasurface.

[013] The central conductor has a width defined in a plane parallel to the at least one intermediate layer, and optionally, the width of the central conductor is greater in the common portion than in the first and second elongated portions. A wider common portion central conductor has shown to improve matching which facilitates improved antenna performance. [014] In some implementations, the bottom layer comprises at least one feeding aperture arranged below the common portion of the channel.

[015] Thereby, electromagnetic signals can be conveyed to/from the radiating/receiving elongated channel portions through the feeding aperture arranged in the bottom layer, below the common portion. To this end, the common portion can be made very small allowing the antenna arrangement to be made very compact with a small footprint in a plane parallel to the layers. A radiating and/or receiving element can be arranged below the bottom layer in electromagnetic communication with the feeding aperture allowing the antenna arrangement to be stacked on top of e.g. a waveguiding structure and/or a printed circuit board, PCB.

[016] In some implementations, the top layer comprises at least one aperture forming a corrugation extending through the top layer, the corrugation being separated from, and extending substantially parallel to, the first and/or second elongated portion.

[017] With corrugations integrated in the top layer, the surface currents of the top layer are reduced which enhances antenna performance. The corrugations could be arranged in different patterns in the top layer. Preferably, the corrugations extend parallel to the elongated radiating/receiving channels, for example the top layer comprises at least two corrugations, a first corrugation being separated from, and extending substantially parallel to, at least a portion of the first elongated portion and at least a portion of the second elongated portion, and a second corrugation being separated from, and extending substantially parallel to the first or second portion on the opposite side of the first or second portion from the first corrugation

[018] Preferably the corrugations in the top layer extend without crossing the common channel portion as such a corrugation would effectively form a radiating/receiving aperture that may deteriorate the antenna pattern.

[019] In some implementations, the at least one intermediate layer comprises a corrugation corresponding to each corrugation in the top layer. With matching corrugations

546 210 present also in the at least one intermediate layer surface currents are suppressed further. Since each layer can be very thin, e.g. below one eight of an operational wavelength matching corrugations that extend through at least two layers forms a quarter wavelength deep chamber which acts as a quarter wavelength stub transforming an open circuit end to a short circuit impedance which helps attenuating surface currents along the top layer. Alternatively, the antenna arrangement comprises a corrugation layer arranged above the top layer, the corrugation layer comprising at least one corrugation, and a metasurface arranged between the top layer and the corrugation layer, wherein the corrugation layer comprises a radiating aperture overlapping the at least one antenna slot.

[020] With a dedicated corrugation layer, the antenna structure grows in stack height due to the addition of at least one layer. On the other hand, the corrugation layer can be made very thin and allows free placement of the corrugations. In addition, the corrugation layer aperture has been found to influence the radiation properties (e.g. the radiation pattern) of the antenna slots. To this end, the shape and size of the aperture in the corrugation layer can be selected to achieve a desired antenna performance.

[021] Additionally, in some implementations the arrangement of the thick and thin sections of the metasurface on the corrugation layer differs from the arrangement of thick and thin sections of the other metasurface in the antenna arrangement. For example, the at least one corrugation is arranged between two rows of thick sections of the metasurface between the top layer and the corrugation layer, wherein the distance between two rows of thick sections is between an operational wavelength divided by six and the operational wavelength divided by ten, preferably about the operational wavelength divided by eight. By e.g. adjusting the spacing between adjacent rows of thick sections for the metasurface on the corrugation layer, it is possible to create a space between the corrugation layer and the top layer which acts as quarter wavelength stub transforming an open circuit impedance to a short circuit impedance which helps attenuating surface currents along the corrugation layer.

[022] In some implementations, the channel further comprises a third elongated portion and a fourth elongated portion, wherein the third and fourth elongated portions extend away from the common portion in substantially opposite directions, while being separated from, and substantially parallel to, the first and second portion, respectively, and wherein the top layer further comprises at least one antenna slot arranged above the third and fourth elongated portion of the channel.

[023] Accordingly, an antenna arrangement with four radiating/receiving elongated channel portions is provided which may have beneficial radiating performance compared to an

546 210 antenna arrangement with two elongated channels. Similarly, an antenna arrangement is preferably provided with six or more, eight or more or even ten or more elongated channels extending away pairwise in opposite directions from the elongated common portion.

According to a second aspect of the invention there is provided an end-fed multi-layer antenna arrangement comprising, a top layer, a bottom layer, and at least one intermediate layer arranged between the top layer and the bottom layer. The end-fed antenna arrangement further comprises an aperture forming a channel provided in the at least one intermediate layer provided in the at least one intermediate layer, the channel comprising an elongated first portion, an elongated second portion and an elongated third portion, a waveguiding portion and a manifold portion between the first, second and third elongated portion on one side, and the waveguiding portion on the other side, a metasurface is arranged between the top layer and the at least one intermediate layer and between the bottom layer and the at least one intermediate layer, the metasurface being arranged to surround the channel and the metasurface comprises thick and thin sections, the top layer comprises a plurality of antenna slots distributed above the first, second and third elongated portion of the channel, respectively, and wherein the first, second and third elongated portions extend substantially in parallel with each other, the manifold portion of the channel has three separate channels, each channel connecting to one of the elongated channel portions, respectively, and a common channel connecting to the waveguiding portion.

[024] In addition to the center-fed antenna arrangement described above an end-fed antenna arrangement is also provided wherein the elongated channels are fed from the same side. Depending on the application, an end-fed antenna arrangement may be preferred over a centerfed antenna or vice versa, depending e.g. on the space available for the antenna arrangement. For example, an end-fed antenna arrangement will in general be longer and thinner compared to a center fed antenna arrangement which can be made approximately square shape.

[025] The end-fed antenna arrangement according to the second aspect shares the same or equivalent benefits and features as the center-fed antenna arrangement according to the first aspect. For example, the end-fed multi-layer antenna arrangement may comprise a central conductor arranged in the channel of the at least one intermediate layer.

[026] For any of the above antenna arrangement various antenna slot shapes are envisaged. For example, each antenna slot may comprises an elongated slot portion extending along an axis oblique to the elongated first or second portion and/or each antenna slot is Sshaped.

[027] Similarly, the thick and thin sections of the metasurface of the antenna arrangements can also be the same. For example, the height difference between the thick and thin

546 210 sections in the metasurface may be less than one fifth of an operational wavelength, preferably less than one eighth of the operational wavelength, and most preferably less than one tenth of the operational wavelength.

[028] The total layer thickness (e.g. the total layer thickness) may also be much smaller than the operational wavelength. For example, the layer thickness may be less than one fifth of the operational wavelength or preferably less than one eighth of the operational wavelength. [029] As an example, at 77 GHz the operational wavelength is about 3900 pm and each layer has a thickness of about 400 pm. Accordingly, the layer is very thin compared to the operational wavelength, being less than one fifth, or even less than one ninth of the operational wavelength. The thin sections are formed as 300 pm deep recesses in the layer to outline the thick sections. Accordingly, the thick sections may have a height of about 300 um which is less than one tenth, even less than one twelfth, of the operational wavelength.

[030] At the thin sections, the local layer thickness may be about 400 - 300 = 100 pm. For example, the local thickness of the layer, at each thin section, may be smaller than one tenth, preferably smaller than one twentieth or most preferably smaller than one thirtieth of the operational wavelength.

[031] The above mentioned layer thicknesses are merely exemplary and one example of dimensions suitable for 77 GHz. It is understood that other layer thicknesses can be used and that the dimensions can be scaled alongside the frequency if operational frequencies other than 77 GHz are to be used.

[032] Each layer in any of the above antenna arrangements can be made of a metal material and/or a non-metal material coated with a metal layer.

[033] In some implementations a feeding aperture is provided in the bottom layer of the common portion or waveguiding portion in any of the above described antenna arrangements. In such implementations, an antenna system comprising the antenna arrangement a multi-layer waveguiding arrangement arranged below the bottom layer can be provided. The multi-layer waveguiding arrangement comprising: a feeding bottom layer, and at least one feeding intermediate layer arranged between the bottom layer and the feeding bottom layer. Wherein the at least one feeding intermediate layer comprises an elongated feeding channel and the metasurface is arranged between the bottom layer and the at least one feeding intermediate layer and between the feeding bottom layer and the at least one feeding intermediate layer, wherein the feeding aperture is arranged so as to overlap with the elongated feeding channel of the waveguiding arrangement.

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[034] The feeding bottom layer and the feeding intermediate layer form an example of a radiating and/or receiving element in the form of a waveguide that is arranged below the antenna arrangement in a stacked manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[035] Aspects of the present invention will be described in more detail with reference to the appended drawings, showing currently preferred embodiments.

[036] Figure la is a perspective view of an elongated antenna element with three layers.

[037] Figure lb is a cross-sectional view of an elongated antenna element with three layers.

[038] Figure lc is a cross-sectional view of an elongated antenna element with five layers.

[039] Figure 2a-f depict examples of different arrangements of antenna slots.

[040] Figure 3a shows a top-down view of the intermediate layer of a center-fed antenna arrangement with three parallel columns of slots.

[041] Figure 3b shows a top-down view of the intermediate layer of a center-fed antenna arrangement with a central conductor according to some implementations.

[042] Figure 3c shows a top-down view of the intermediate layer of a center-fed antenna arrangement with the metasurface outlined.

[043] Figure 3d shows a perspective view of a center-fed antenna arrangement according to some implementations.

[044] Figures 4a-c are graphs showing different properties of the radiation performance of the center-fed antenna arrangement shown in fig. 3d.

[045] Figure 5a shows a top-down view of the intermediate layer of an end-fed antenna arrangement with three parallel central conductors combined with a 3-way power combiner.

[046] Figure 5b shows a top-down view of the intermediate layer of an end-fed antenna arrangement with the metasurface outlined.

[047] Figure 5c shows a perspective view of an end-fed antenna arrangement according to some implementations.

[048] Figures 6a-b are graphs showing different properties of the radiation performance of the end-fed antenna arrangement shown in fig. 5c.

[049] Figure 7a shows a top-down view of the intermediate layer of a center and bottom fed antenna arrangement with the antenna slots, feeding aperture and metasurface outlined.

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[050] Figure 7b is a perspective view of a center and bottom fed antenna arrangement coupled to a waveguiding structure arranged below the center and bottom fed antenna arrangement.

[051] Figures 8a-d show different layers of a waveguiding structure and center and bottom fed antenna arrangement.

[052] Figures 9a-d show features of a bottom-center-fed antenna arrangement with a feeding aperture suitable for enabling usage of an antenna slot layout of the side-fed antenna arrangement with enhanced matching.

[053] Figure 10a shows a cross-sectional view of a waveguiding structure and center and bottom fed antenna arrangement with a common bottom/top layer.

[054] Figure 10b shows a cross-sectional view of a waveguiding structure and center and bottom fed antenna arrangement with separate bottom and top layers.

[055] Fig. 1 la-c shows another example of a center and bottom fed antenna arrangement according to some implementations.

[056] Figure 12a shows a cross-sectional view of an antenna arrangement with a corrugated layer.

[057] Figure 12b shows a cross-sectional view of an antennae arrangement with corrugations provided in the top and at least one intermediate layer.

[058] Figure 13a is a perspective view of an antenna arrangement with a corrugation layer according to some implementations.

[059] Figure 13b is a top-down view of the antenna arrangement from fig. 13a.

[060] Figure 13c is a top-down view of the at least one intermediate layer of the antenna arrangement from fig. 13a and fig. 13b with the metasurface and antenna slots outlined.

DETAILED DESCRIPTION OF CURRENTLY PREFERRED EMBODIMENTS

[061] Fig. la depicts a multi-layer elongated antenna element 100 according to some implementations. The elongated antenna element 100 is formed by a top layer 1 and a bottom layer 3. Between the top layer 1 and the bottom layer 2 there is arranged at least one intermediate layer 2. Each of the top layer 1, the bottom layer 3 and the at least one intermediate layer 2 is a physical layer. For instance, at least one, or all, of the layers 1, 2, 3 is/are made of a respective metal material, such as brass, copper or aluminum. Additionally or alternatively, at least one of the layers 1, 2, 3 is made of a non-metal material (such as plastic or ceramic material) and coated with a metal on at least one side. It is also envisaged that different layers are made of different materials. For example, at least one of the layers may be made of a first metal material (or coated

546 210 with a first metal material) whereas at least one different layer 1, 2, 3 may be made of a second metal material (or coated with a second metal material) that is different from the first metal material.

[062] For example, the top and bottom layer 1, 3 are made of brass and the at least one intermediate layer 2 is made of copper. As most losses will occur in the at least one intermediate layer 2 it is preferable to use the metal material with the highest conductivity in the at least one intermediate layer 2 whereas the top and bottom layers 1, 3 can be made of a cheaper, less conductive, metal material, such as brass. In addition to brass and copper, another metal material that is suitable for making at least one of the layers 1, 2, 3 is aluminum.

[063] The thickness of each individual layer is preferably less than 1 mm, although larger thicknesses are possible. In some implementations, the thickness of each layer is between 500 pm and 300 pm. All layers could have the same thickness, but it is also envisaged that the layers 1, 2, 3 may have different thicknesses. For example, the top layer 1 and bottom layer 3 has a same thickness between 500 pm and 300 pm and the at least one intermediate layer 2 is thinner, such as a thickness between 50 pm and 200 pm, e.g. about 100 pm. The above exemplary thicknesses are suitable for simple and cost effective manufacturing but are merely exemplary and can vary outside of these ranges, e.g. depending on the operational frequency. The above exemplary thicknesses are suitable for an operational frequency around 77 GHz.

[064] With further reference to fig. lb, it is shown that the at least one intermediate layer 2 is provided with an elongated opening 22, also referred to as a channel 22, which defines a waveguide 45 together with the top and bottom layers 1,3. The extent and path of the channel 22 defines the extend and path of the elongated antenna element 100. Optionally, a central conductor 21 is arranged in the channel 22 such that a coaxial waveguide 45 is formed by the top and bottom layers 1, 3, the channel 22 and the central conductor 21. The central conductor 21 may be attached to the intermediate layer 2 via one or more supporting stubs as will be described in further detail below.

[065] Between each two adjacent layers 1, 2, 3 (e.g. in the space between the bottom layer 3 and the intermediate layer 2) there is arranged a metasurface 4. The metasurface 4 prohibits electromagnetic waves of an operational frequency from propagating in a direction from along the waveguide 45 in the space between adjacent layers 1, 2, 3. The metasurface 4 is a textured surface arranged on at least one of two adjacent layers so as to face the space between the two adjacent layers. That is, for each pair of adjacent layers, a metasurface 4 is formed on a surface of a first layer, the surface facing the second layer of the pair of adjacent layers. The surface on the second layer may be substantially flat. A metasurface 4 could also be arranged on

546 210 the second layer of each pair of adjacent layers, but this is entirely optional and its fully sufficient that only one metasurface 4 is arranged between each pair of adjacent layers. [066] The metasurfaces 4 may be provided in various arrangements. For example, metasurface 4 is made of thick sections 41 and thin sections 42 wherein the thick sections 41 form what is commonly referred to as pins. The difference in height between thick sections 41 and thin sections 42 is less than the wavelength at the operational frequency divided by four, preferably less than the wavelength divided by five and most preferably less than the wavelength divided by ten. With sub-quarter wavelength thick and thin sections 41, 42 the antenna arrangement can be made much thinner while also the electromagnetic leakage is reduced. Each thick section 41 may have the same thickness as the physical layer, whereas the thin sections are formed as recesses in the layer. In some implementations, each metasurface 4 is surrounded with a substantially flat portion having a thickness substantially equal to that of the thick sections 41. [067] The metasurface 4 is arranged to surround the waveguide channel in the at least one intermediate layer 2, to confine and guide electromagnetic waves along the extension of the waveguide 45.

[068] As illustrated in fig. la and lb, one or more antenna slots 11, 11a, lib, 1 lc are provided in the top layer 1, distributed along the extension of the waveguide channel 22 in the at least one intermediate layer 2. Each antenna slot 11, 11a, lib, 1 lc is in the form of an opening extending fully through the top layer 1. Different shapes of each antenna slot 11, 11a, lib, 11c are envisaged. For example, the antenna slots 11, 11a, lib, 11c may be rectangular, S-shaped, Zshaped, or dumbbell shaped.

[069] In fig. la, the antenna slots 11a, lib, 11c are elongated and substantially rectangular. Each elongated antenna slot 11a, lib, 1 lc is arranged in the top layer 1 so as to extend along an axis oblique to the waveguide channel 45. The elongated antenna slot 1 la, 1 lb, 11c could alternatively extend parallel to the waveguide channel 45. Different arrangements of the antenna slots 11a, lib, 1 lc are described in further detail in connection to fig. 2a-f below. [070] In fig. lc an antenna arrangement with more than one intermediate layer 2, 201, 202 is shown. Intermediate layer 201 is provided between the top layer 1 and intermediate layer 2 and intermediate layer 202 is provided between the bottom layer 3 and the intermediate layer 2. Additional intermediate layers could also be added in a similar fashion to form antenna arrangements with even more intermediate layers 2, 201, 202. Each intermediate layer 2, 201, 202 has an aperture 22 forming a channel 22 corresponding with the elongated channel of the intermediate layer 2. In this way, the intermediate layers 2, 201, 202 define the waveguide channel together with the top layer 1 and the bottom layer 3. As shown in fig. lc, a metasurface

546 210 is arranged between each pair of adjacent layers and this also applies to pairs of intermediate layers 2, 201, 202. In the example illustrated in fig. lc, a metasurface 4 arranged on a flat side of the intermediate layer 202 facing the intermediate layer 2. The opposite, a metasurface 4 on the intermediate layer 2 facing intermediate layer 202, is also possible. It is also envisaged that both the intermediate layer 2 and the intermediate layer 202 could comprise a respective metasurface 4 facing each other. The same applies to the space between the intermediate layer 201 and intermediate layer 2 which also is provided with a metasurface 4. In fig. lea metasurface 4 is arranged on the intermediate layer 201 on a surface facing the intermediate layer 2, but the opposite arrangement is also possible.

[071] Fig. 2a-f depict different shapes and arrangements of antenna slots 11a, lib, 11c that can be used for any of the antenna arrangements described herein.

[072] In fig. 2a a plurality of antenna slots 11a, lib, 11c are arranged in the top layer above the elongated channel 22 and central conductor 21 of the intermediate layer. Each of the antenna slots Ila, lib, 1 lc is substantially rectangular and elongated extending along a respective elongation axis. The elongation axis of each antenna slot 11a, lib, 1 lc is arranged oblique from the axis along which the channel 22 of the intermediate layer extends. In fig. 2e the elongation axis Bi of the rectangular antenna slots 11a, lib have been plotted relative an antenna axis A along which the elongated antenna portion and channel 22 extends. Rectangular antenna slot Ila extends along elongation axis Bi forming an angle of ai with respect to the antenna axis A. Neighboring antenna slot 1 lb is equivalent to antenna slot 1 la with the difference being that antenna slot 1 la is rotated clockwise with respect to antenna slot 1 lb so as to form an angle of ai degrees with respect to the antenna axis A. This arrangement is repeated for the remaining antenna slots 11c with every second slot 11a, 11c forming an angle of ai with respect to the antenna axis and every other antenna slot lib forming an angle of -ai degrees with respect to the antenna axis A.

[073] Fig. 2b and 2e depict another exemplary arrangement of the antenna slots 1 la, 1 lb, 11c. The antenna slots 11a, lib, 1 lc are rectangular antenna slots 11a, lib, 11c extending parallel with the antenna axis A, wherein every second antenna slot 11a, 1 lc is displaced a distance d from the antenna axis A on a first side of the antenna axis A and every other antenna slot 1 lb is displaced a distance d from the antenna axis A in the opposite direction. Optionally, the displacement of fig. 2b and fig. 2e can be combined with alternating oblique arrangement of the antenna slots as shown in fig. 2a and fig. 2d.

[074] Fig. 2c and fig. 2f depict yet another example of antenna slot arrangements that can be used for any of the antenna arrangements described herein. The antenna slots 11a, lib, 11c

546 210 are provided with at least one curve so as to form a shape which is referred to as an S-shape, or Z-shape or “crank” shape. Generally, the S-shape can be described with a sigmoid function. [075] Fig. 2f shows a detailed view of antenna slot 11a and it is understood that each antenna slot in fig. 2c may have a shape corresponding to antenna slot 11a. Antenna slot 1 la is formed of a slot having a width W. The slot has a main portion that has a length Li and extends along a main axis Bi. The main axis Bi may be parallel to the antenna axis A, or oblique to the antenna axis A, so as to form an angle of ai between the antenna axis A and the main axis Bi. [076] The main portion of the antenna slot 1 la is connected to a first slot portion at first end and a second slot portion at a second end extending along a respective first and second axis Ba, Bb. Together, the main portion, first portion and second portion form a single slot having a curved shape. The first and second axis Ba, Bb form a respective angle aA, aB with the main axis Bi. In some embodiments, angles aA, and aB are selected such that the first and second axis Ba, Bb extend in parallel to the antenna axis A as shown in fig. 2f. It is also envisaged that the angles aA and aB are selected such that the first and second axis Ba, Bb are not parallel, but oblique, to the antenna axis A. The first and second slot portion have a respective length La, Lb and these lengths may be equal or different from each other. The lengths La and Lb may also be equal to, greater than, or smaller than the length Li of the main portion.

[077] The elongated antenna element 100 shown in fig. la comprises one linear array of antenna slots fed by the same waveguide 45. That is, a multi-layer waveguide extending along an antenna axis with one or more antenna slots 11a, 1 lb, 11c arranged in the top layer 3, so as to overlay the waveguide 45 forms an elongated antenna element 100. As will now be described, two or more elongated antenna elements 100 can be combined to form an antenna arrangement 101 that is center-fed via a common portion.

[078] The intermediate layer of a center-fed antenna arrangement is shown in fig. 3a. The at least one intermediate layer 2 comprises an elongated aperture 22a-g forming a channel 22a-g having a plurality of elongated channel portions 22a-g, wherein some of the channel portions 22a-f contributes to forming the different elongated antenna elements 100a-e. The elongated channel also comprises a common channel portion 22g that branches of into a plurality of elongated channel portions 22a-f that form the respective elongated antenna elements 100a-f. [079] A first channel portion 22a extends in a first direction away from the common channel portion 22g and a second channel portion 22b extends in the opposite direction, away from the common channel portion 22g. Each channel portion 22a-22f forms a respective elongated antenna element 100a-f together with the top and bottom layer arranged above and below the intermediate layer and the antenna slots in the top layer. Electromagnetic signals in a

546 210 frequency band of operation can be received by the antenna slots above each elongated channel 22a-f and guided into the common waveguide (formed in part of the common channel portion 22g). Analogously, electromagnetic signals for transmission can be injected into the waveguide formed in part by the common channel portion 22g to be conveyed into the elongated antenna elements 100a-f so as to be transmitted via the antenna slots in the top layer (see fig. 2a-f). The intermediate layer 2 may be formed from a substantially flat layer wherein all channel portions 22a-g are formed by providing an opening in the layer, e.g. by means of stamping.

[080] Optionally, as shown with further reference to fig. 3b, a central conductor 21a-g is arranged in each channel portion 22a-g. Accordingly, the waveguide of the common portion 101 and each elongated antenna element 100a-f effectively becomes a coaxial waveguide with the central conductor 21a-g acting as a central conductor which may facilitate coupling and reduce reflections etc. To support the central conductor 21a-g, one or more supporting stubs 27 may extend between the periphery of the channel 22a-g and the central conductor 21a-g to support the central conductor 21a-g. As mentioned in the above, the intermediate layer 2 may be formed by providing a substantially flat layer 2 and providing openings in the intermediate layer 2 to form the elongated channels 22a-g and central conductor 21a-g. The central conductor 21a-g, and any supporting stubs 27, may also be formed in the same piece of material as the intermediate layer 2.

[081] As shown in fig. 3a and fig. 3b each channel portion 22a-g, except the common channel portion 22g, contributes to forming a respective elongated antenna element 100a-f. The first and second elongated channel portion 22a, 22b defines a respective first and second elongated antenna element 100a, 100b together with the top and bottom layer and the antenna slots provided in the top layer. Additionally, a third and a fourth elongated antenna element 100c, lOOd is arranged parallel to the first and second elongated antenna element 100a, 100b on opposite sides of the common portion 101. A fifth and sixth elongated antenna element lOOe, lOOf is arranged parallel to the third and fourth elongated antenna portion 100c, lOOd on opposite sides of the common portion 101. Thus the common portion 101 extends along a common portion axis and the first, third and fifth elongated antenna elements 100a, 100c, lOOe extend away perpendicular from the common portion 101 on a first side thereof and the second, fourth and sixth elongated antenna elements 100b, lOOd, lOOf extend away perpendicular from the common portion 101 on a second side thereof, opposite to the first side of the common portion 101.

[082] The intermediate layer 2 further comprises one or more corrugations 23a, 23b, 23c corresponding to matching corrugations provided in the top layer (see fig. 3d). Corrugation 23a

546 210 extends parallel to, and is arranged next to, the first and second channel portion 22a, 22b of the first and second elongated antenna element 100a, 100b. Corrugation 23b and 23c are elongated and arranged to be aligned with each other. The corrugations 23b and 23c are also parallel to the fifth and sixth elongated channel portion 22e, 22f of the fifth and sixth elongated antenna portion lOOe, lOOf, respectively. Each corrugation 23a, 23b, 23c effectively reduces surface currents from propagating along the intermediate layer 2.

[083] The intermediate layer 2 of fig. 3a or fig. 3b is arranged between a top layer and a bottom layer. In fig. 3c, the arrangement of a metasurface 4 surrounding the elongated channel portions 22a-g forming the elongated antenna elements 100a-f and common portion 101 is shown. The metasurface 4 comprises thick section 41 and thin sections 42 arranged so as to surround the elongated channels 22a-g. For instance, the metasurface 4 extends between adjacent elongated antenna portions 100a, 100c, lOOe on the same side of the common portion 101 so as to prevent electromagnetic signals from one elongated antenna portion 100a to couple to another elongated waveguide portion 100b.

[084] A metasurface 4 is arranged between the intermediate layer and the bottom layer and a metasurface 4 is arranged between the intermediate layer 2 and the top layer. For instance, the metasurface 4 is arranged on the top layer and bottom layer, respectively, and arranged to face the intermediate layer 2.

[085] In fig. 3d a top layer 1 has been arranged above the intermediate layer 2 from fig. 3a or fig. 3b, and a bottom layer 3 has been arranged below the intermediate layer 2. The top layer comprises six antenna arrays one array for each elongated antenna element 100a-f, and each array comprising at least two antenna slots 11a, lib, 11c. Antenna slots 11a, lib, 11c are arranged above the first channel portion 22a forming the first elongated antenna element 100a. Similarly, other sets of antenna slots arranged above each of the other elongated channel portions 22b-f forming the other elongated antenna elements 100b-f.

[086] Fig. 3d shows the top layer 1 of the antenna arrangement from fig. 3a with six elongated antenna elements 100a-f. To improve efficiency and mitigate surface currents in the top layer 1 corrugations 12a, 12b, 12c are provided in the top layer 1. Each corrugation 12a, 12b, 12c is an aperture formed in the top layer 1 that extends along at least two antenna slots 1 la-c. The corrugation 12a extends parallel to the first and second elongated antenna elements and has an extension exceeding that of the extension of six antenna openings. The corrugation 12a mitigates surfaces currents on one side of the antenna arrangement 100. To further mitigate surface currents corrugations 12b, 12c are also provided next to, and parallel with, the fifth and sixth elongated antenna portions. However, since the common portion must cross the corrugation

546 210 the corrugation on this side is split into two parts, a first corrugation part 12b arranged next to the sixth elongated antenna portion and a second corrugation part 12c arranged next to the fifth elongated antenna portion. Preferably, no corrugation 12a-c should cross the common portion since this would cause leakage of the signal being conveyed to/from the antenna openings 11a, 11b, lie.

[087] In some implementations, the top layer 1 is provided with a metasurface 4 on a bottom surface thereof, the bottom surface facing the at least one intermediate layer. Preferably, the corrugations are arranged in a space between two neighboring sets of thick sections (i.e. the corrugations are arranged in thin sections). This allows the corrugations 12a-c to be placed close to the waveguide channels without noticeably disrupting the functioning of the metasurface. Preferably, the thick and thin sections are arranged in grid pattern wherein at least two rows of thick sections separate each corrugation 12a-c from the closest waveguide channel.

[088] In some implementations, the arrangement of the antenna slots 11a, lib, 1 lc in each of the first and second elongated antenna element 100a, 100b may be mirrored in the common axis of the common portion. For example, the antenna slots 11a, lib, lie arranged above the second elongated antenna element 100b are mirrored in the axis of the common portion 101 but otherwise identical to the antenna slots of the first elongated antenna element 100a.

[089] In addition to the antenna slots being mirrored in the common portion 101, the antenna slots of neighboring elongated antenna elements provided on the same side of the common portion (such as the first and third elongated antenna portions) are also mirrored with respect to each other.

[090] In fig. 3d, each elongated antenna element 100a-f comprises three antenna slots, giving a total of 18 antenna slots distributed over the six elongated antenna elements 100a-f. It is envisaged that the elongated antenna elements 100a-f may be provided with more or less than three antenna slots Ila, lib, lie, such as two, four or five antenna slots 11a, lib, lie, giving in total 12, 24 or 30 antenna slots 1 la, 1 lb, lie. Additionally, it is envisaged that more than six elongated antenna portions can be used, such as eight, or ten, or twelve or more elongated antenna portions.

[091] In some implementations, the common portion 101 is devoid of antenna slots 1 la-c in the top layer 1. Alternatively, the antenna slots 1 la-c of each elongated antenna element 100af may extend at least partially over the common channel 22g. Experiments have shown that antenna slots 1 la-c overlapping partially with the elongated common channel 22 do not degrade performance while at the same time allowing for a smaller antenna arrangement to be

546 210 manufactured, as the antenna slots 1 la-c of the first and second elongated antenna elements 100a, 100b can be placed closed together.

[092] Fig. 4a-c depicts experimentally measured antenna characteristics of the center—fed antenna arrangement depicted in fig. 3d having six elongated antenna elements and 3x6 S-shaped antenna slots. In fig. 4a, the isotropic gain is depicted in azimuth and elevation respectively. Lines Ga76 and Ga77 depict the isotropic gain for azimuth angles in the range from -90° to 90° at an operational frequency of 76 GHz and 77 GHz respectively. As seen, the antenna achieves an isotropic gain of above 17 dBi at 0° azimuth. Lines Ge76 and Ge77 depict the isotropic gain for elevation angles in the range from -90° to 90°.

[093] As seen the antenna achieves a side lobe level (SLL) exceeding 15 dB and performs similarly at both 76 and 77 GHz. The antenna arrangement has also proved to be comparatively broadband. With reference to fig. 4b line GF shows the isotropic gain as function of frequency, and with this antenna an intrinsic gain of 17 dB or above is obtained over frequencies ranging from 75.5 GHz to 78.5 GHz.

[094] Additionally, the antenna offers a low insertion loss as shown in fig. 4c. In fig. 4c, line L indicates the Su parameter as a function of frequency as measured at an interface with the common portion. The Su parameter is below -10 dB for frequencies between 75 GHz and 78.5 GHz, below -15 dB from 76 GHz to 77.5 GHz and even below -22 dB for frequencies around 76.5 GHz.

[095] In some implementations, the elongated antenna elements are arranged so as to form an end-fed antenna arrangement 300. One exemplary embodiment of an end-fed antenna arrangement 300 is shown in fig. 5a-5c.

[096] The intermediate layer 2 of the end-fed antenna arrangement 300 is shown in fig.

a. Three elongated channel portions 22a-c are arranged side by side in parallel and each elongated channel portion is part of an individual elongated antenna element 100a, 100b, 100c. A central conductor 21a-21c is arranged in each elongated channel portion 22a-c so as to form a coaxial waveguide channel together with the top layer and bottom layer. It is also envisaged that the antenna arrangement 200 can be realized without a central conductor 2la-c wherein each elongated channel 22a-c forms a hollow waveguide channel together with the top and bottom layer.

[097] The intermediate layer 2 further comprises a manifold channel portion forming a manifold portion together with the top and bottom layer. The manifold channel portion may be formed of a channel having substantially the shape of a trident or fork. That is, a shape having a common channel that splits into three or more channels wherein each of the three or more

546 210 channels are connected to a respective elongated channel portion 22a-c. The common channel is connected to a waveguiding channel 103 which together with the top and bottom layer forms a waveguide for conveying electromagnetic signals to and/or from the elongated antenna elements 100a-c formed in part by the elongated channel portions 22a-c.

[098] The waveguiding portion 103 may be equivalent to an elongated antenna element 100a-c without the antenna slots. The waveguiding portion 103 is connected to the common channel of the manifold channel portion 102. The manifold channel portion 102 acts as a power splitter/power divider wherein at least three separate and equivalent channel portions diverge from the common channel portion. Each of the at least three diverging channel portions are connected to a respective elongated channel portion 22a-22c.

[099] Fig. 5b shows the intermediate layer 2 of the antenna arrangement from fig. 5a with the thick sections 41 and thin sections 42 of the metasurface 4 highlighted. The metasurface 4 surrounds each channel so as to prohibit electromagnetic signals from propagating parallel to the intermediate layer in directions other than the along the elongated channel portions 22a-c, between the intermediate layer 2 and the bottom layer or between the intermediate layer 2 and the top layer.

[100] With further reference to fig. 5c there is depicted the end-fed antenna arrangement 300 with the top layer 1 arranged above the intermediate layer 2 and a bottom layer 3 arranged below the intermediate layer 2. The top layer 1 comprises, arranged above each elongated channel portion 22a-c, a plurality of antenna slots 1 la-c. In the embodiment depicted, a total of six antenna apertures 1 la-c are arranged above each of the three elongated aperture channels 22a-c giving a total of 3x6 antenna slots 1 la-c arranged in three columns. There are no antenna slots arranged above the manifold channel portion 102 or the waveguide channel portion 103 in the intermediate layer meaning that these channel are mainly for guiding and distributing electromagnetic signals to/from the elongated channel portions 22a-c and not for radiating and/or receiving electromagnetic signals.

[101] A line along which a mirroring plane P_m intersects the top layer is also shown. The mirroring plane P_m divides the antenna slots into two groups (with half of the antenna slots in each group) wherein the antenna slots of each group are mirrored images of each other in the mirroring plane P_m.

[102] Preferably, an elongated corrugation 12 is provided in the top layer on either side of the antenna slots 1 la-c of the at least three elongated antenna elements 100a-c. The corrugations 12 mitigate surface currents and improve antenna performance.

546 210

[103] Fig. 6a-b depict some measured antenna characteristics of the antenna arranged depicted in fig. 5c having three parallel elongated antenna portions with six S-shaped antenna slots respectively wherein the elongated antenna portions are arranged side by side and fed with via a trident shaped manifold portion. In fig. 6a, the isotropic gain is depicted in azimuth and elevation respectively. Lines G2a76 and G2a77 depict the isotropic gain for azimuth angles in the range from -90° to 90° at an operational frequency of 76 GHz and 77 GHz respectively. As seen, the antenna archives an isotropic gain of above 17 dBi at 0° azimuth. Lines G2e76 and G2e77 depict the isotropic gain for elevation angles in the range from -90° to 90° at an operational frequency of 76 GHz and 77 GHz respectively. As seen the antenna achieves a side lobe level (SLL) exceeding 16 dB and performs similarly at both 76 and 77 GHz. Compared to the elevation radiation pattern of the antenna shown in fig. 4a and 4b (having elongated antenna portions on opposite sides of the common portion) the elevation radiation pattern of the antenna from fig. 6a and fig. 6b (having multiple elongated antenna portions arranged side by side and fed with a manifold second) is less symmetric. For example, the sidelobe level at 30 degrees elevation is about 2 dB higher compared to the sidelobe level at - 30 degrees.

[104] Fig. 6b shows the sidelobe level varies with varying operational frequencies. Lines G2e76, G2e76, G2e76, G2e76, G2e76, G2e76 show the antenna elevation pattern for frequencies 76, 77, 78, 79, 80 and 81 GHz respectively. As seen, the SLL at 30 degrees elevation increases as the frequency increases, from approximately 17 dB at 76 GHz to about 14 dB at 81 GHz whereas the SLL at - 30 degrees elevation sees a more limited reduction in SLL between 76 GHz and 81 GHz with the SLL increasing with less than 2 dB.

[105] Fig. 7a and fig. 7b depict a bottom-center-fed antenna arrangement 400. The bottom-center-fed antenna arrangement 400 is fed from the bottom instead of from the side as for the antenna arrangements 200, 300 described in connection to fig. 3a-3d and fig. 5a-5c in the above. A bottom-center-fed antenna system is formed by providing a multi-layer feeding arrangement 401 arranged below the bottom-center-fed antenna arrangement 400.

[106] The bottom-center-fed antenna arrangement 400 comprises a first elongated antenna element and a second elongated antenna element wherein the elongated antenna elements extend in opposite directions away from a common portion. At the common portion, a feeding aperture 31 is formed in the bottom layer forming an opening through which electromagnetic signals to/from the elongated antenna elements are conveyed. Instead of providing the port for connecting the antenna arrangement to an external device at a side of the arrangement (i.e. in a plane perpendicular to the layers) as is the case for the side fed antenna

546 210 arrangements shown in fig. 3d and fig. 5c it is possible to provide the feeding port 31 in the bottom layer instead, as shown in the bottom-center-fed antenna arrangement 400 in fig. 7a.

[107] In fig. 7a the antenna slots 1 la-d of the top layer are depicted overlayed the central conductor 21 and elongated channel 22 of the intermediate layer. The feeding aperture 31 of the bottom layer is also shown. The feeding aperture 31 overlaps with the common portion of the elongated channel 22 in the intermediate layer. A first and second elongated antenna element extends away in opposite directions from the common portion, each elongated antenna element comprises a plurality of antenna slots in the top layer for transmitting/receiving electromagnetic signals.

[108] The feeding aperture 31 is connected to an external device such as an external waveguiding structure 401 arranged below the bottom layer. The waveguiding structure 401 may be a waveguide, such as a rectangular waveguide coupled to the feeding aperture 31 arranged in the bottom layer. The waveguiding structure 401 may also be a multilayer waveguide comprising at least an external device bottom 3’ layer and an external device intermediate layer 2’ as shown in fig. 7b.

[109] Preferably, the shape and/or orientation of the feeding aperture 31 is different from the shape and/or orientation of the antenna slots 1 la-d. The feeding aperture 31 and each of the antenna slots 1 la-d are preferably both generally S-shaped as described in connection to fig. 2f above. However, the angle ai between the antenna axis A and the main slot portion may be greater for the feeding aperture 31 compared to the antenna slots 1 la-d. Additionally or alternatively, the length La, Lb of the first and second slot portion of the feeding aperture 31 may be greater than the lengths La, Lb of the antenna slots. This shape of the feeding aperture 31 has shown to facilitate accurate impedance matching which enhances performance.

[110] In some implementations, the feeding aperture 31 overlaps at least partially with at least one antenna slot 1 la-d. That is, it is not necessary to displace the antenna slots 1 la-d from the feeding aperture 31 which saves space and enables compact antenna design.

[Ill] In fig. 7b the mirroring plane P_m is also outlined. The mirroring plane P_mis perpendicular to the top layer 1 (and the intermediate layer 2 and bottom layer 3) and has a normal parallel to the channel above which the antenna slots 1 la-h are arranged. The mirroring plane P_m divides the antenna slots into two groups, a first group 1 la-d on a first side of the mirroring plane P_m and a second group 1 le-h in a second opposite side of the mirroring plane P_m. For at bottom-center-fed antenna arrangement 200 with an S-shaped feeding aperture 31 the first and second group of antenna slots are not mirrored in the mirroring plane Pm. Rather, the second group of antenna slots 1 le-h are flipped (around a plane perpendicular to the mirroring plane)

546 210 with respect to a mirrored image of the first group of antenna slots in the mirroring plane P_m. By comparing fig. 7b with fig. 5c it is seen that the layout of the antenna slots therefore differs between the end-fed antenna arrangement (in fig. 5c) and the bottom-center-fed antenna arrangement (in fig. 7b). This is difference in antenna slot layout (mirror or non-mirroring in the mirroring plane P_m) is to ensure good matching. However, as will be described in the below in connection to fig. 9a-d, it has been found that using a particular feeding aperture layout enables excellent matching for the bottom-fed-antenna arrangement with an antenna slot layout identical to that of the end-fed antenna arrangement.

[112] With reference to fig. 8a-d and fig. 10a the layers of the bottom-center-fed antenna arrangement 400 and multi-layer feeding arrangement 401 will now be described in detail.

[113] Fig. 8a and fig. 10a depict the at least one feeding intermediate layer 2’ of the multi-layer feeding arrangement 401. Fig. 8a also indicates the position of the thick sections 41 and thin sections 42 forming the metasurface 4 between the feeding bottom layer 3’ and the feeding intermediate layer 2’ of the multi-layer feeding arrangement 401 which surrounds the elongated channel 22’ of the feeding intermediate layer 2’. While the embodiment shown in fig. 10a has the metasurface 4 arranged on the bottom layer 3’ it is understood that the metasurface 4 may be arranged on the feeding intermediate layer 2’ instead. The feeding intermediate layer 2’ may also comprise a metasurface 4 facing the bottom layer 3 of the multi-layer feeding arrangement 401.

[114] Fig. 8b and fig. 10a show the bottom layer 3 of the bottom-center-fed antenna arrangement 400 according to some implementations. The bottom layer 3 is arranged above the feeding intermediate layer 2’ of fig. 8a such that the feeding aperture 31 lies above the elongated channel 22’ of the feeding intermediate layer 2’. Accordingly, electromagnetic signals are guided along the elongated channel 22’ of feeding intermediate layer 2’ and are coupled into the bottomcenter-fed antenna arrangement 400 via feeding aperture 31. The bottom layer 3 comprises one metasurface 4 facing the intermediate layer 2 above and one metasurface 4 facing the intermediate layer 2’ below.

[115] Fig. 8c and fig. 10a show the intermediate layer 2 that is arranged above the bottom layer 3 which in turn is arranged above the feeding intermediate layer 2’. The intermediate layer 2 comprises an elongated channel 22 and a central conductor 21 arranged in the elongated channel 22. Electromagnetic signals that exit the feeding aperture 31 in the bottom layer 3 are guided along the elongated channel 22. Additionally, as the feeding aperture 31 is arranged in the middle of the elongated channel, the electromagnetic signals will be split and propagate in opposite directions in the elongated channel 22. Similarly, electromagnetic signals that are

546 210 received are combined at the middle and exit into the multi-layer feeding arrangement 401 via the feeding aperture 31.

[116] Fig. 8d and fig. 10a also show the top layer 1 of the bottom-center-fed antenna arrangement 400. In fig. 8d the position of the thick sections 41 and thin sections 42 forming the metasurface 4 are indicated. The metasurface 4 is formed on a bottom surface of the top layer 1, that faces the intermediate layer 2 shown in fig. 8c.

[117] By comparing fig. 7b (showing the antenna slot layout of a bottom-center-fed antenna) and fig. 5c (showing the antenna slot layout of an end-fed antenna) it is seen that the layout of the antenna slots 1 la-f are not identical between these two types of antennas. For example, both antennas comprise an even number of antenna slots 1 la-f but for the bottomcenter-fed antenna in fig. 7b a first half of neighboring antenna slots 1 la-d on one side of the mirroring plane P_m are not mirrored with respect to the second half of neighboring antenna slots 1 le-h on the other side of the mirroring plane P_m. This is not the case for the end-fed antenna shown in fig. 5c wherein a first half of neighboring antenna slots 1 la-c are mirrored with respect to the second half of neighboring antenna slots 1 le-h.

[118] It has been found that for bottom-center-fed antennas with an S-shaped feeding aperture 31 (see fig. 8b) the antenna slots 1 la-f should not be identical to that of the end-fed antenna arrangement if good matching and low reflection should be obtained. More specifically, the antenna slots on one side of the mirroring plane P_m for the bottom-center-fed antenna arrangement should be mirrored with respect to the antenna slots on a corresponding side of the mirroring plane P_m for the end-fed antenna arrangement.

[119] In some implementations, for example when an antenna must be realized within a limited space, end-fed and bottom-center-fed antennas are combined wherein it is desirable to obtain a similar or identical radiation pattern from both the end-fed and bottom-center-fed antennas. However, since the antenna slot layout differs between these two types of antennas the resulting antenna pattern will be slightly different between these two types.

[120] With reference to fig. 9a-d, it has been found that by using a different type of feeding aperture 3Γ, namely a feeding aperture 31’ which is substantially straight, extends parallel to the channel 22 and is offset from the center-line of the channel 22 allows the antenna slots 1 la-d of a bottom-center-fed antenna to be arranged with the same pattern as for an end-fed antenna with excellent matching and low reflections.

[121] In fig. 9a multiple features of the top, intermediate and bottom layer of a bottomcenter-fed antenna are shown. As seen, the feeding aperture 3 Γ is shaped like an elongated slit that extends along and in parallel to the channel 22 while being offset from the center of the

546 210 channel 22. The feeding aperture 22 may overlap partially with the optional central conductor 21 arranged in the channel 22. With this type of feeding aperture 3 Γ the antenna slots 1 la-d of the bottom-center-fed antenna can be arranged identical to the end-fed antenna arrangement to exhibit an identical or highly similar antenna pattern to the end-fed antennas. Fig. 9a also shows the thick and thin sections 41, 42 of the metasurface between two adjacent layers and the corrugations 12, optionally provided in the top layer or top and bottom layer.

[122] With further reference to fig. 9b and fig. 9d it is shown that the matching properties of the feeding aperture 31 ’ can be further improved by providing a matching supporting stub 28 connecting the central conductor 21 to the intermediate layer 2 at a point overlapping with the feeding aperture 3Γ. As seen in fig. 2, the intermediate layer 2 may further comprise corrugations that correspond to the corrugations 12 in the top layer.

[123] The feeding aperture 31 ’ may be offset on either side of the center line of the channel 22. This is demonstrated in fig. 9c wherein the feeding aperture is placed on the opposite of the center line compared to the embodiment shown in fig. 9a and 9b. In fig. 9c another structure for improving matching is shown in the form of an additional pin 410 arranged at the bottom layer and facing the intermediate layer so as to overlap with the channel 22. The pin 410 is placed along the center line of the channel 22 and enhanced matching and reduces reflection.

[124] Fig. 10a depicts a cross-sectional view of the bottom-center-fed antenna arrangement 400 connected to a waveguiding structure 401. The waveguiding structure 401 comprises at least a feeding bottom layer 3’ and a feeding intermediate layer 2’ arranged between the feeding bottom layer 3 ’ and the bottom layer 3 of the antenna arrangement. The feeding intermediate layer 2’ is provided with an elongated channel 22’ forming a waveguide channel, much like the elongated channel provided in the intermediate layer 2 as described in connection to fig. 5a.

[125] To prevent electromagnetic signals from propagating between the intermediate layer 2’ of the waveguiding structure 401 and the bottom layer 3 of the antenna arrangement 400 a metasurface 4 is arranged between these two layers. The metasurface 4 is arranged in the bottom side of the bottom layer 3 of the antenna arrangement so as to face the upper surface of the external device intermediate layer 2’. To this end, the bottom layer 3 may comprise a metasurface 4 on both sides, one metasurface 4 facing the feeding intermediate layer 2’ and one metasurface 4 facing the intermediate layer 2.

[126] When the antenna arrangement is used to transmit electromagnetic signals, the electromagnetic signals are injected into the waveguide channel 45’ of the waveguiding structure formed by the external device bottom layer 3’, the external device intermediate layer 2’ and the

546 210 bottom layer 3 of the antenna arrangement. The electromagnetic signals will propagate in the waveguide channel 45’ of the waveguiding structure 401 until it reaches the feeding aperture 31 formed in the bottom layer of the antenna arrangement 400. The electromagnetic signals enter into the antenna arrangement via the feeding aperture 31 and are transmitted into the environment via the antenna slots in the antenna arrangement.

[127] When the antenna arrangement is used to receive electromagnetic signals the electromagnetic signals are received by the antenna slots and enter into the waveguide channel 45 of the antenna arrangement 400. The electromagnet signals propagate along the waveguide channel and through the fed aperture 31 to enter into the waveguide channel 45 ’ of the external device. From here the electromagnetic signals can be led to e.g. a receiver or a component mounted on a PCB.

[128] Also shown in fig. 10a is the pin 410 used to enhance matching when the off-center feeding aperture 31’(see fig. 9c) is used.

[129] An alternative design of the bottom-center-fed antenna system is shown in fig. 10b. Instead of the bottom layer 3 acting as a bottom layer for the antenna arrangement and a top layer for the waveguiding structure it is envisaged that the waveguiding structure is provided with a feeding top layer Γ. The feeding top layer 1 ’ is provided between the feeding intermediate layer 2’ and the bottom layer 3 of the antenna arrangement. The feeding top layer 1 ’ comprises a metasurface 4 facing the external device intermediate layer 2’ to confine electromagnetic signals to the waveguiding channel 45 ’ of the waveguiding structure.

[130] Fig. 1 la-c show yet another embodiment of a center-bottom-fed antenna arrangement 400 fed by a multi-layer feeding arrangement 401. The multi-layer feeding arrangement 401 will be described in further detail in the below and this arrangement conveys electromagnetic signals to/from the feeding aperture 31 (see fig. 11a) provided in the bottom layer 3 of the center-fed antenna arrangement.

[131] An intermediate layer 2 is arranged on top of the bottom layer 3 and provided with an elongated aperture forming a channel 22. The intermediate layer 2 is also provided with a metasurface 4 facing the bottom layer 3. As seen clearly in fig. 1 lb, the channel 22 forms a confined space (together with top layer 1 from fig. 5c) in which electromagnetic waves can propagate. The intermediate layer 2 further comprises corrugations 23 being separate from, but extending parallel to, the channel 22.

[132] In fig. 5c the top layer 1 has been arranged on top of the intermediate layer 2. Although not seen, the top layer 1 also comprises a metasurface facing the intermediate layer 2. The top layer 1 also comprises a plurality of antenna slots 1 la-c arranged so as to overlap with

546 210 the channel 22 in the intermediate layer 2. A first plurality of antenna slots 1 la-c are arranged on one side of the feeding aperture 31 and a second plurality of antenna slots 1 la-c are arranged on the opposite side of the feeding aperture 31. The top layer 1 also comprises a plurality of corrugations 12 that preferably overlap with the corrugations 23 of the intermediate layer to quarter wavelength grooves having a depth of at least the operational wavelength divided by four to dampen surface currents.

[133] A difference between the center-fed antenna arrangement 200 of fig. 1 la-c and the center-fed antenna arrangement of fig. 8a-d, is that the intermediate layer of the arrangement in fig. 8a-d comprises a metasurface 4 whereas the intermediate layer of the arrangement in fig. Safi comprises no metasurface. Additionally, the arrangement of fig. 8a-d comprises a central conductor whereas the arrangement of fig. 5a-c does not comprise central conductor. As described herein, the person skilled in the art will realize that the metasurface can be arranged on different layers as long as a metasurface is provided between any two neighboring layers.

[134] Fig. 12a depicts a corrugation layer 5 that can be placed above the top layer 1 of any of the antenna arrangements described in the above. The corrugation layer 5 comprises a radiating aperture 52 that overlaps with one or more antenna slots 11 of the top layer 1. For example, the radiating aperture 52 covers at least two or all antenna slots 11 arranged in the top layer 1. The corrugation layer 5 further comprises at least one corrugation 51 a-d extending parallel to, but displaced from, the radiating aperture 52. Each corrugation 51 a-d extends between two rows of thick sections 41 forming a metasurface 4. The metasurface 4 also surrounds the radiating aperture 52 to prohibit electromagnetic waves from propagating along the corrugation layer 5, between the corrugation layer 5 and the top layer 1.

[135] The corrugations 51 a-d reduce surface currents and the size and shape of the radiating aperture 52 can be shaped and formed to enhance matching and/or vary the radiation pattern. Each corrugation 51 a-d opens into a chamber that forms an approximate quarter wavelength stub. The quarter wavelength stub is about one fourth of the operational wavelength long, such that an electromagnetic signal would round-trip travel a distance of a half wavelength. To form such a chamber between the top layer 1 and the corrugation layer 5 the corrugations 5 la-d are arranged in the corrugation layer 5 along a thin section 42 in the metasurface 4 and between two rows of thick sections 41 of the metasurface 4. Preferably, the thin section 41 has a width that is larger than the width of the corrugation 5 la-d and the corrugation 5 la-d is arranged next to one of the thick sections 41. This forms an L-shaped chamber between the corrugation layer 5 and the top layer 1 delimited by the thick sections 41 of the metasurface suitable for acting like a quarter wavelength stub. For example, the thin sections 42 in which the corrugations

546 210 la-d are arranged may be wider compared to the thin sections 41 of the metasurface 4 between the top layer 1 and at least one intermediate layer 2.

[136] In fig. 12b an alternative arrangements of the corrugations is depicted and, as also described in connection to fig. 3a-3d in the above, the corrugations may also be arranged in the top layer 1 and intermediate layer 2 of the antenna arrangement without needing a corrugation layer. The corrugations in the top layer 1 and corresponding corrugations in the intermediate layer 2 form a quarter wavelength groove (with an electromagnetic round trip propagation distance of about half a wavelength) that is suitable for damping surface currents. The quarter wavelength groove is formed by the corrugations 12a-c, 12a-c and the metasurface prohibiting electromagnetic signals from escaping between the layers. As seen in fig. 12b an electromagnetic signal entering through a corrugation 12a-c in the top layer 1 and propagating through the corresponding corrugation 23a-c in the intermediate layer propagate approximately one quarter of a wavelength prior to meeting the bottom layer 3.

[137] Alternatively, the corrugation layer 5 does not comprise any metasurface and is arranged as flat layer directly on top of the top layer 1. The corrugations 5 la-d may be provided as grooves formed in the corrugation layer 5 wherein the depth of the groove is adapted to form a quarter wavelength stub. Optionally, each groove comprises at least one bend, allowing a part of the groove to extend parallel with the corrugation layer 5. For example, each groove is L-shaped and provided with one substantially right angled bend. This enables the corrugation layer 5 to be made thinner.

[138] Fig. 13a shows a perspective view of an antenna arrangement with three layers 1, 2, 3 and a corrugation layer 5 arranged above the top layer 1. Fig. 13b shows a top-down view of the same antenna arrangement. The antenna slots 11a, 1 lb of the top layer 1 are visible through the radiating aperture 52 of the corrugation layer 5 and there is a metasurface 4 between each pair of adjacent layers (e.g. between the top layer 1 and the corrugation layer 5).

[139] Notably, the antenna arrangement of fig. 13a and fig. 13b only has two antenna slots 1 la, 1 lb. In fig. 13c the intermediate layer 2 of this antenna arrangement is shown in further detail. As seen, the antenna arrangement is similar in structure to the end-fed antenna arrangement shown in fig. 5a-5c, however, compared to the end-fed antenna arrangement of fig. 5a-5c the antenna arrangement of fig. 13c comprises has two, comparatively short channels and a manifold portion that splits a waveguiding channel to two channel portions. Additionally, antenna slots Ila, 1 lb of the top layer are also outlined illustrating that the antenna slots 11a, 1 lb of this embodiment are elongated and extend perpendicular to the axis of elongation of each channel portion. Fig. 13c also shows an outline of the thick and thin sections of the metasurface

546 210

4, however it is understood that the metasurface 4 may be arranged on the top and or bottom layer above or below the intermediate layer 2.

[140] Accordingly, the antenna arrangement of fig. 13c is very space efficient compared to the antenna arrangement of fig. 5a-5c. On the other hand, the larger surface area and higher number of antenna slots of the antenna from fig. 5a-5c may entail enhanced performance in terms of greater gain and smaller side lobes. To enhance performance of the antenna arrangement of fig. 13c a corrugation layer 5 with a radiating aperture 52 is provided, wherein the size and shape of the radiating aperture 52 can be selected to increase gain and reduce or modify the side lobes.

[141] The corrugation layer 5 depicted in fig. 12a-b and fig. 13a-b can be used for a large variety of antenna structures not necessarily limited to the examples described above. For example, a simple antenna structure can be realized with at least one antenna aperture. The antenna structure comprises a top layer 1, a bottom layer 3, and at least one intermediate layer 2, 201, 202 arranged between said top layer 1 and said bottom layer 3. Wherein an aperture forming a channel is provided in the at least one intermediate layer 2. A metasurface 4 is arranged between the top layer and the at least one intermediate layer and between the bottom layer and the at least one intermediate layer, said metasurface 4 being arranged to surround the channel and comprises thick and thin sections. The top layer 1 comprises at least one antenna slot 11 arranged above the channel and wherein a corrugation layer 5 is arranged above the top layer. The corrugation layer comprising at least one antenna aperture arranged to overlap with the antenna aperture of the top layer and at least one corrugation groove which, optionally, extends fully through the corrugation layer. The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the corrugation layer 5 shown in fig. 13a and fig. 13b can be combined with any antenna arrangement, such as the center-fed antenna arrangement from fig. 3a-d, the end-fed antenna arrangement from fig. 5a-c or the bottom-center-fed antenna arrangement of fig. 7a-b, fig. 8a-d, fig. 10a or fig. 10b.