Dual-band dual-polarized antenna array

IS 2 287 124 T3

DESCRIPTION

Dual band and dual polarization antenna array.

Object of the invention

The present invention generally relates to a new family of antenna arrays that can operate simultaneously in two different frequency bands, exhibiting a dual polarization characteristic in both bands. The design is suitable for applications where the two bands are centered at two frequencies f1 and f2 so that the ratio of the higher frequency (f2) to the lower frequency (f1) is f2 / f1 <1.5. The dual-band, dual-polarization characteristic is achieved primarily through the physical position of the antenna elements within the array. Also, some particular antenna elements are described again to improve antenna performance.

Background of the invention

The development of dual band and dual polarization matrices is of the greatest interest, for example in cellular telecommunications services. Both second generation (2G) cellular services, both the European GSM900, GSM1800 and the American AMPS and PCS1900, and the third generation (3G) cellular services (such as UMTS) take advantage of the polarization diversity in their network of base station antennas (BTS) to improve service performance while reducing the size of the antenna array as much as possible. Preserving a minimum size for the antenna system in a BTS becomes a main issue when it is taken into account that the growth in the service demands that the operators strive to increase the number of BTS, which is beginning to produce a significant visual and environmental impact on rural and urban landscapes. The problem begins to be particularly significant when the operator has to provide both 2G and 3G services, because as both types of service operate in different frequency bands, the deployment of both networks using conventional single-band antennas implies doubling the number of antennas installed and the increase in the environmental impact of the installation. Therefore, the invention of dual-band, dual-polarization antennas, which can simultaneously occupy two services in two different bands, appears to be a matter of great interest.

The development of multiband antennas and antenna arrays is one of the main engineering challenges in the field of antennas. There is a well-known principle in the state of the art that shows that the behavior of an antenna or an array of antennas is completely dependent on its size and its geometry relative to the working wavelength. The size of an antenna is entirely dependent on the wavelength, and in an array of antennas, the spacing between the elements is generally fixed and retains a certain proportion with respect to the wavelength (typically between half and one wavelength ). Due to this very simple principle, it is very difficult to make an array to operate simultaneously at two frequencies or at two different wavelengths, as it is difficult to make the antenna element geometry adapt in size to two wavelengths. different and similarly, it is difficult to find a spatial arrangement of the antenna elements that meets the constraints of both wavelengths at the same time.

The first descriptions of the behavior of antenna arrays were developed by Shelkunoff (SA Schellkunhoff, "A Mathematical Theory of Linear Arrays," Bell System Technical Journal, 22.80). That work was aimed at single band antennas. In the 1960s, some first designs for frequency-independent matrices (the logarithm-periodic dipole matrices or LPDA) (VHRumsey, Frequency-Independent Antennas) were developed. New York Academic, 1966; RL Carrel, “Analysis and design of the log-periodic dipole array,” Tech. Rep. 52, Univ. Illinois Antenna Lab., Contract AF33 (616) -6079, October 1961; PE Mayes, "Frequency Independent Antennas and Broad-Band Derivatives Thereof," Proc. IEEE, vol. 80, number 1, January 1992). These LPDA matrices were based on a non-uniform spacing of dipole elements of different sizes and were designed to cover a wide range of frequencies, however, due to their moderate gain (10 dBi), these designs have a restricted range of application and do not they would be suitable for applications such as cellular services, where a higher gain (above 16 dBi) is required. Also, neither the horizontal beamwidth (too narrow for BTS) nor the polarization and mechanical structure of such LPDA antennas match the requirements for BTS.

Some examples of multiband antenna arrays have recently been described in the state of the art. For example, patent PCT / ES99 / 00343 describes a configuration of interleaved antenna elements for general purpose multiband arrays. A collinear antenna element system is described in this document, in which the use of multiband antenna elements is necessary in those positions where the antenna elements of different bands overlap. The general scope of that patent does not meet the requirements of some particular applications. For example, it is difficult to achieve dual-band behavior following the description of the patent PCT / ES99 / 00343 when the frequency ratio between bands is below 1.5, as intended for the designs described in the present invention. Also, that solution is not necessarily cost effective when a separate electrical down slope is required for each band. The present invention describes a completely different solution based on single band, dual polarization elements, which are spatially arranged to minimize the size of the antenna.

IS 2 287 124 T3

There are already existing examples of dual-band, dual-polarization antennas on the market that simultaneously handle 2G and 3G services, however, these are so-called 'side-by-side' solutions that simply integrate two separate antennas on a single ground plane. and radome (Fig. 1). The downside to these antenna configurations is the size of the entire package (at up to 12 inches wide they are typically twice the size of a single antenna) and the pattern distortion due to coupling between antennas. Some examples of these solutions can be found for example at http://www.racal-antennas.com/ and at http://www.rymsa.com/. The present invention describes a more compact solution that is achieved by means of a careful selection of the positions of the antenna elements and the shape of said antenna elements that minimizes the coupling between them.

For the particular case in which the spacing between f1 and f2 is very small, several broadband solutions are described in the prior art to operate simultaneously in both bands. However, such solutions are not suitable if an independent and different downward inclination is required for each band, which is something that can be easily solved according to the present invention.

Summary of the invention

The architecture of the antenna consists of an interleaving of two independent vertically linear arrangements of a single band so that the relative position of the elements minimizes the coupling between antennas. Such a spatial arrangement of the antenna elements helps to keep the antenna size reduced to a minimum extent. In a basic design scheme for the spatial arrangement (interleaving) of the antenna, the compact dots display the positions of the elements for the lowest frequency f1, while the squares display the positions for the antenna elements for the highest frequency f2. The antenna elements for the highest frequency band f2 are aligned along a vertical axis with the desired spacing between elements. Said spacing is slightly smaller than one wavelength (typically below 98% of the size of the shortest wavelength) for maximum gain, although it can be quickly seen that the spacing can be made shorter depending on the application. .

A second vertical column of elements for the lower frequency band f1 is aligned along a second vertical axis located next to said first axis and substantially parallel to it. In another particular arrangement of the invention, the low-frequency elements are placed along a left axis while the high-frequency elements are placed along a right axis, but obviously the position of both axes could be interchanged. so that the low frequency elements would be located on the right side and vice versa. In any case, the spacing between these axes is chosen to fall between 0.1 and 1.2 times the longest wavelength.

The shortest wavelength (corresponding to f2) determines the spacing between elements (11) on both axes. Generally, a spacing below 98% of said shorter wavelength is preferred to maximize gain, while at the same time avoiding the introduction of secondary lobes in the upper band; this is possible due to the spacing between frequency bands which is always f2 / f1 <1.5 according to the present invention.

Regarding the relative position of the elements, the elements for f2 are placed in certain positions along a vertical axis and horizontal axes so that the horizontal axes intersect both with the positions of said elements and with the midpoint between elements. on the neighboring axis; this ensures a maximum distance between elements and therefore a minimum coupling between elements of different bands.

Having independent elements for each band, the matrix can be easily fed by means of two independent distribution networks. Collective power or microstrip pointing waveguide networks, strip line, coaxial or any other conventional microwave network architecture described in the prior art may be used and does not constitute a characteristic part of the invention. However, it is interesting to note that by using independent networks, an independent phase of the elements of each band can be used within the present invention, which in turn is useful for introducing a fixed or adjustable electrical downward tilt of the diagram. radiation in each band independently. Optionally and depending on the particular set of frequencies of f1 and f2, it is clear to those skilled in the art that any other dual-band or broadband power network described in the prior art can be used within the spirit of the present. invention.

With regard to antenna elements, any dual polarizing antenna elements (e.g. crossed dipole elements, patch elements) can be used in accordance with the scope of the present invention, however a radiating element of size reduced to reduce coupling between them.

The same basic dual band array configuration described here characterizes different beam widths and shapes in the horizontal plane depending on the spacing between elements in the horizontal direction. For this purpose, various elements can be placed within the matrix in a horizontal position offset with respect to the left or right axis in accordance with the present invention. Typically, the offset from said axis is less than 70% of the longest operating length. A particular case of said displacement consists in tilting one or both reference axes by a few degrees (always below 45 °) so that the displacement is increased uniformly either upwards or downwards.

IS 2 287 124 T3

Brief description of the drawings

Figure 1 shows a conventional side-by-side solution (7) for a 2G + 3G dual band matrix (prior art). Two conventional single band arrays (5) and (6) are joined for each band within a single ground plane (8) and housed within a single radome. The horizontal width (9) of the resulting antenna system is inconvenient for aesthetic and environmental reasons. Note that the spacing between elements in each particular band (between dots and squares) is different for this prior art configuration.

Figure 2 shows a general spatial arrangement of the antenna elements for the dual-band, dual-polarization array. The compact dots (1) display the positions of the elements for the lower frequency f1, while the squares (2) display the positions for the antenna elements for the higher frequency f2. The elements are aligned along parallel axes (3) and (4). The spacing (11) between elements in the vertical position the same in both bands. Note that the horizontal axes (10) that define together with the axis (3) the position (2) of the elements at frequency f2, intersect with the axis (4) at the midpoint between the positions (1) for the elements at frequency f1. The sandwiched position on the vertical axis ensures minimal inter-band coupling while preserving the width (9) of the ground plane (8) and the antenna package with the minimum extension.

Figure 3 shows two particular examples 13 and 14 of dual polarization gap filling miniature patch antennas that can be used to minimize interband and withinband coupling within array elements. The white circles (15) with the inner center point indicate the feed positions for orthogonal double polarization.

Figure 4 shows an example in which some elements (15) are horizontally displaced with respect to the vertical axis.

Figure 5 shows an example in which one of the axes (3) is slightly inclined from the vertical position defining another axis (3 ') the elements (2) corresponding to f2 are aligned along it. This can be seen as a particular case of the general case described in figure 4 in which all the elements are sequentially displaced a fixed distance with respect to the upper neighbor.

Figure 6 shows a preferred embodiment of a dual-band, dual-polarization matrix for simultaneous operation in GSM1800 (1710 MHz -1880 MHz) and UMTS (1900 MHz - 2170 MHz). The antenna elements are dual polarization patches with a space fill perimeter as described in the figure.

3.

Detailed description of a preferred embodiment of the invention

Figure 2 shows a schematic of the basic design for the spatial arrangement (interleaving) of the antenna elements. The compact dots (1) display the positions of the elements for the lower frequency f1, while the squares (2) display the positions for the antenna elements for the higher frequency f2. The antenna elements for the highest frequency band f2 are aligned along a vertical axis (3) with the desired spacing between elements (11). Said spacing is slightly smaller than a full wavelength (typically below 98% of the size of the shortest wavelength) for maximum gain, although it can be quickly seen that the spacing can be made shorter depending on the app. A second vertical column of elements for the lower frequency band f1 is aligned along a second vertical axis (4) located next to said first axis (3) and substantially parallel to it. In the particular arrangement of figure 2, the low-frequency elements are located along the left axis (4) while the high-frequency elements are located along the right axis (3), but obviously the position of both Shafts could be interchanged so that the low frequency elements would be located on the right hand side and vice versa. In any case, the spacing (9) between said axes (3) and (4) is chosen so that it falls between 0.1 and 1.2 times the longest wavelength.

The shortest wavelength (corresponding to f2) determines the spacing between elements (11) on both axes. Generally, a spacing below 98% of said shorter wavelength is preferred to maximize gain while avoiding the introduction of secondary lobes in the upper band; this is possible due to the spacing between frequency bands which is always f2 / f1 <1.5 according to the present invention. In relation to the relative position of elements (1) and (2), the elements for f2 are located at positions (2) along the vertical axis (3) and the horizontal axes (10) so that the horizontal axes (10) intersect both with the positions of said elements (2) and with the midpoint (12) between elements (1) on the neighboring axis (4); this ensures a maximum distance between elements and therefore a minimum coupling between elements of different bands.

Having independent elements for each band, the matrix is ​​fed in an easy way by means of two independent distribution networks. Mass feed or microstrip pointing waveguide networks, strip line, coaxial cable or any other conventional microwave network architecture described in the prior art may be used and do not constitute a characteristic part of the invention. However, it is interesting to note that through the use of independent networks, an independent phase of the elements of each band can be used within the present invention, which in turn is useful for introducing a fixed or adjustable electrical downward tilt of the radiation pattern in each band independently.

IS 2 287 124 T3

Optionally, and depending on the particular set of frequencies of f1 and f2, it is clear to those skilled in the art that any other dual-band or broadband feed network described in the prior art can also be used within the spirit of the present invention.

With regard to antenna elements, any dual polarizing antenna element (e.g. crossed dipole elements, patch elements) can be used in accordance with the scope of the present invention, however a radiating element of size reduced to reduce coupling between them. A dual polarization small patch element with a space fill perimeter is proposed here as a particular example for a possible matrix implementation (Figure 3). For the same purpose, other dual polarization space filling miniature antenna elements can also be used, such as for example those described in patent PCT / EP00 / 00411.

The same basic dual band array configuration described herein characterizes different beam widths and shapes in the horizontal plane depending on the spacing between elements in the horizontal direction. For this purpose, various elements can be placed within the matrix in a horizontal position offset with respect to the axis (3) or (4) according to the present invention. Typically, the offset from said axis (3) or (4) is smaller than 70% of the longest operating wavelength. A particular case of said displacement consists in tilting one or both of the aforementioned reference axes by a few degrees (always below 45 °) so that the displacement is uniformly increased upwards or downwards. Figure 4 shows an example of a particular embodiment in which some elements are displaced from the axis, while in Figure 5, another embodiment is shown in which the axes (3) and (4) are slightly inclined. As would be obvious to those skilled in the art, other offset and tilt schemes can be used for the same purpose within the scope of the present invention.

As anyone skilled in the art can readily see, the number of elements and the vertical extent of the array is not a substantial part of the invention; any number of elements can be chosen depending on the desired gain and the directivity of the matrix. Also, the number of elements and the vertical extent of the array need not be the same; Any combination in number of elements or vertical extent can optionally be chosen for each band within the spirit of the present invention.

Beyond the specific coordinate position of the elements, the skilled person will realize that any rotation in the elements can also be applied to the present invention to for example obtain other kinds of polarization states or changes in antenna parameters. as described in the prior art.

A preferred embodiment of the present invention is a matrix that operates simultaneously in the GSM1800 (1710-1880MHz) and UMTS (1900-2170 MHz) frequency bands. The antenna is characterized by double polarization at ± 45 ° in both bands and finds a main application in cellular base stations (BTS) where both services are combined in a single site. Figure 6 shows the basic configuration of a particular embodiment for said configuration.

The antenna is designed with eight elements operating in GSM1800 (13) and with eight elements operating in UMTS (14) to provide directivity above 17 dBi. The elements are aligned along two different axes (3) and (4), one for each band. According to the present invention, the elements (13) for GSM1800 are interspersed in the vertical direction with respect to the elements for UMTS (14) to reduce the coupling between elements by maximizing the distance between them, always keeping a minimum distance. between said axes (3) and (4). For this particular embodiment, the spacing between axes (3) and (4) must be greater than 40 mm if isolation between input ports above 30 dB is desired (as is normal for cellular systems).

Depending on the required gain, it is clear to anyone skilled in the art that the number of elements can be increased or decreased beyond eight. The number of elements can even be different for each band in order to achieve different earnings. To operate on these particular bands, the vertical spacing between elements must be chosen to fall in the range of 100mm to 165mm. For a matrix of eight elements and a gain of 17 dBi, the elements are mounted on a substantially rectangular ground plane (8) with a total height within a range of 1100mm to 1500mm.

Any kind of single band dual polarization radiating element can be used for this array of antennas within the scope of the present invention, such as, for example, crossed dipoles or patches, square or octagonal, however, the innovative fill patches of the Spaces such as those shown in Figures 13 and 14 are preferred here, as they are characterized by a small size (height, width, area) compared to other prior art geometries. Such space-filling patches can be manufactured using any of the well-known conventional techniques for microstrip patch antennas and for example, can be printed on a dielectric substrate such as epoxy fiberglass (FR4) substrates or other microwave substrates. Specialists such as CuClad®, Arlon® or Rogers® to name a few. Said elements are mounted in parallel to a conductive ground plane (8) and are typically supported with a dielectric spacer. It is precisely the combination of the particular spatial arrangement of the elements (vertical interleaving and vertical axis proximity) together with the reduced size and the way of filling the space of the elements of the patch antenna with which the size of all the antenna. The size of the antenna is basically the size of the ground plane (8) that for

ES 2 287 124 T3 this particular embodiment should be wider than 140mm but can typically taper below 200mm, which is a main advantage for minimal environmental visual impact on the landscape compared to other conventional solutions such as described in Figure 1.

The elements can be fed into the two orthogonal polarization feed points located in the center of the circles (15) by means of several of the previous techniques for patch antennas, such as for example, a coaxial probe, a microstrip line under the patch or a slot on the ground plane (8) coupled with a distribution network beyond said ground plane. For dual-band, dual-polarization operation, four independent power and distribution networks can be used (one for each band and polarization). According to the preferred embodiment, said feeder networks are mounted on the rear side of the ground plane and any of the well-known configurations for matrix networks such as for example microstrip, coaxial or strip line networks can be used. since it does not constitute an essential part of the invention.

With regard to the relative position of the feeding points (15) on the patch, figure 6 shows an embodiment in which said feeding points are located on the inner side towards the center of the ground plane, that is, in the right side of the shaft (4) for the lower belt and on the left side of the shaft (3). Those skilled in the art will realize that any other embodiment may also be used within the scope of the present invention, such as for example: all elements with feed points on the left side of their respective axes, all feed points on the right side, some elements on the right side and some on the left side, or it is even possible within the scope of the present invention , some items with a feed point on each side of the corresponding shaft.

In the preferred embodiment, the entire array of antennas with the elements, the ground plane and the power supply network is mounted on a conventional shielded metal casing that encloses the rear part of the ground plane, said casing also acting as a support for the entire antenna. Also, a conventional dielectric radome is mounted and fixed to the housing that covers the radiating elements and that protects the entire antenna from weather conditions as in any conventional base station antenna.

The antenna would naturally include four connectors (typically 7/16 connectors), one for each band and polarization, mounted at the bottom of the ground plane. Each connector is then connected through a transmission line (such as for example a coaxial cable) to the input port of each power supply network.

Those skilled in the art will realize that other combinations of connectors are possible within the scope of the present invention. For example, a duplexer filter can be used to combine the input ports of the + 45 ° GSM1800 and UMTS networks on a single connector, and the -45 ° GSM1800 and UMTS networks on a single connector to give a total of just two connectors. . Said duplexer can be any duplexer with 30 dB isolation between ports and does not constitute an essential part of the present invention. Obviously, an alternative solution such as a broadband or dual-band network combining GSM1800 and UMTS for the + 45 ° polarization and another for the -45 ° polarization could be used instead of the diplexer, which also gives a two connector configuration.