Compact printed antenna with little radiation in elevation

p0001The field of the invention is that flat printed antenna transmission and / or reception of microwave signals.

p0002More specifically, the invention relates to a planar antenna producing a maximum radiation at low elevations.

p0003The antenna of the invention has many applications. It can for example be used in a network on the roof of a passenger car to ensure satellite communications. Indeed, some mobile, including those in connection with geostationary satellites in countries with medium or high latitude (Northern Europe, for example) require planar antennas producing maximum radiation at low elevations.

p0004Currently, for reasons of space and cost, are used in mobile antennas printed type "patch". Indeed, they have in particular the advantage of being planar and inexpensive.

p0005In general, a printed antenna includes a dielectric substrate board, a ground plane (consisting of a first conductor layer deposited on a first face of the dielectric substrate plate), a radiating element (constituted by a second conductive deposit deposited on a second face of the dielectric substrate plate) and the antenna feed means.

p0006In their current operation, that is to say, when operated in their fundamental mode, these printed antennas generate a radiation pattern with a maximum in the direction perpendicular to the plane containing the antenna. For this type of current operation, the length of the radiating element is very close to the half wavelength taking account of the permittivity of the dielectric substrate used.

p0007In order to generate radiation having a maximum for low elevations, that is to say, in directions away from the axis perpendicular to the plane containing the antenna, the printed antennas must operate in a higher mode of which the current distribution creates this type of radiation.

p0008The major problem lies in the fact that the higher modes of interest appear for relatively high frequencies compared to the fundamental mode. This means that to use this mode (top) to the desired frequency band (close to that corresponding to the fundamental mode), the antenna must be oversized very significantly.

p0009This oversizing it virtually impossible integration into network of such radiating elements to obtain high gain antennas. This problem of congestion is particularly crucial for a network to generate a low elevation radiation, radiating elements must be placed very close to each other in order to avoid major network lobes strongly deteriorate the antenna gain.

p0010The invention particularly aims to overcome this major drawback of the prior art.

p0011Specifically, an objective of the present invention to provide a printed antenna to obtain radiation at low elevations while having a small footprint.

p0012The invention also aims to provide an antenna that retains all the advantages of printed antennas, including a low manufacturing cost.

p0013These various objectives, and others which will become apparent hereinafter are achieved according to the invention with a printed planar transmitting antenna and / or reception of microwave signals, comprising in particular:<ul><li>a dielectric substrate board,</li><li>a ground plane formed by a first conductor layer deposited on a first face of said dielectric substrate board,</li><li>a radiating element formed by a second conductor layer deposited on a second face of said dielectric substrate board,</li><li>supply means of said antenna,</li></ul><ul><li>said antenna having a fundamental mode in which it generates a radiation pattern with a maximum in the direction perpendicular to the plane containing the radiating element, and at least one higher mode in which it generates a low elevation radiation pattern</li><li>said antenna being characterized in that said radiating element has at least one notch for controlling the resonant frequency of a chosen higher mode.</li></ul>

p0014The chosen higher mode is one in which the antenna is desired to view function, so that the maximum radiation is generated at low elevations.

p0015Thus, the general principle of the invention consists, for a given higher mode, to reduce the resonance frequency only by making notches on the radiating element, that is to say without changing the overall size of the antenna. In other words, for operation in an even higher mode, the printed antenna of the invention has a smaller footprint than a conventional printed antenna.

p0016Advantageously, the notch or notches are arranged substantially perpendicularly to the current lines of said chosen higher mode.

p0017In this way, we increase the electrical length of these flow lines, and thus decreases the resonance frequency of the chosen higher mode.

p0018Advantageously, the dimensions (length, width) of the or slots are determined from a calculation technique based on a finite element method.

p0019Preferably, said feeding means use a feed technique belonging to the group comprising:<ul><li>by the coaxial probe feed;</li><li>the feeding coupling slot;</li><li>food by proximity coupling;</li><li>by supply line feeding in the plane of the radiating element.</li></ul>

p0020Preferably, said radiating element is disc-shaped.

p0021In a first preferred embodiment of the invention, said chosen higher mode is the TM21 mode, whose current lines form a pattern that is repeated in each quarter of said disc,    said radiating element Presentan four radial slots, spaced two by two angularly by about 90 °, each of said notches being substantially perpendicular to the current lines in one of said quarters of the disc.

p0022In a second preferred embodiment of the invention, said chosen higher mode is the TM01 mode, whose currents are arranged radially,    said radiating element having at least one circular notch, the notch or notches extending over at least a portion of the circumference of a circle contained within said disc and the same center as the latter.

p0023Advantageously, each notch cooperates with means annihilation of its effect, said antenna comprising means for activating / deactivating said means annihilation.

p0024Preferably, said means of annihilation of the effect of a slot include a diode connecting the two edges of said notch.

p0025In a first particular embodiment of the invention, said radiating element has a plurality of notches,    said activation / deactivation means acting simultaneously on all the annihilation means associated with said plurality of slots, so as to allow a multimode operation such that:<ul><li>when all the means of annihilation are activated, the antenna operates in said fundamental mode,</li><li>when all the means of annihilation are turned off, the antenna operates in said chosen higher mode.</li></ul>

p0026This multimode operation can cover a large solid angle with maximum radiation. Indeed, in the fundamental mode, it has a maximum radiation in the direction perpendicular to the plane containing the antenna and the higher mode selected, it has a maximum of radiation to a lower elevation.

p0027In a second particular embodiment of the invention, said radiating element has a plurality of notches,    said activation / deactivation means acting on a variable number in the annihilation time means associated with said plurality of slots, so as to allow a multifrequency operation such that each distinct number of annihilation means activated at a given time corresponds to a particular resonant frequency of said chosen higher mode.

p0028This allows a multifrequency operation for the same type of higher mode.

p0029The invention also provides a dual band antenna, characterized in that it comprises two superimposed antennas, termed upper and lower antennas, such as those presented above, the radiator of said lower antenna constituting the ground plane of the said upper antenna.

p0030Other characteristics and advantages of the invention will appear on reading the following description of several preferred embodiments of the invention, given by way of indicative and non-limiting examples and the accompanying drawings, in which:<ul><li>1 shows a side view of a conventional antenna fed by a coaxial probe;</li><li>2 shows a curve of variation, as a function of frequency, the standing wave ratio (SWR) of the conventional antenna of Figure 1;</li><li>3 shows a top view of one embodiment of a first antenna according to the invention;</li><li>Figure 4 shows schematically the TM21 mode of the supply lines for the first antenna of Figure 3;</li><li>5 shows a curve of variation, as a function of frequency, the SWR of the first antenna of Figure 3;</li><li>Figure 6 shows the complete radiation pattern for Etheta component of the first antenna of Figure 3;</li><li>Figures 7 and 8 each a sectional view for phi = 0 ° and 90 ° respectively, the radiation pattern of Figure 6;</li><li>Figure 9 shows the complete radiation pattern for Ephi component of the first antenna of Figure 3;</li><li>Figures 10 and 11 each show a sectional view of phi = 45 ° and 135 ° respectively, the radiation pattern of Figure 9;</li><li>12 shows a top view of one embodiment of a second antenna according to the invention;</li><li>Figure 13 shows schematically the current lines of the TM01 mode for the second antenna of Figure 12; </li><li>14 shows a variation curve, as a function of frequency, VSWR of the second antenna of Figure 12;</li><li>Figure 15 shows the complete radiation pattern for Etheta component of the second antenna of Figure 12;</li><li>Figures 16 and 17 each show a sectional view for phi = 0 ° and 90 ° respectively, the radiation pattern of Figure 15;</li><li>Figure 18 shows the complete radiation pattern for Ephi component of the second antenna of Figure 12;</li><li>Figures 19 and 20 each show a sectional view for phi = 0 ° and 90 ° respectively, the radiation pattern of Figure 18;</li><li>Figures 21 and 22 each show a side view and top respectively, of an antenna according to the invention fed by slot;</li><li>FIG 23 shows a top view of a particular embodiment of an antenna according to the invention comprising means for annihilation of the effect of each notch; and</li><li>Figures 24 and 25 each show a side view and top, respectively, of a particular embodiment of a dual band antenna of the invention.</li></ul>

p0031The invention therefore relates to a planar printed antenna for transmission and / or reception of microwave signals.

p0032Figure 1 shows a side view of a conventional antenna fed by a coaxial probe. The antenna comprises:<ul><li>a dielectric substrate plate 1, thickness H = 2.28 mm and a relative permittivity ε_r = 2.2, for example;</li><li>a ground plane 2 formed by a first conductive deposit, e.g., copper, deposited on a first face of the dielectric substrate plate 1;</li><li>a radiating element 3 consisting of a second conductive deposit, such as a copper disk of 73.5 mm diameter, placed on a second side of the dielectric substrate plate 1; and</li><li>4 a coaxial probe for feeding the antenna and comprising an external conductor 5 soldered to the ground plane 2 and an inner conductor 6 welded to the radiating element 3. The positioning of this coaxial probe 4 provides the adaptation of the antenna.</li></ul>

p0033The antenna has a fundamental mode in which it generates a radiation pattern with a maximum in the direction perpendicular to the plane containing the radiating element, and at least one higher mode in which it generates a low elevation radiation pattern.

p0034With the previously mentioned dimensions for the various elements 1, 2, 3 of the antenna, is obtained:<ul><li>a resonant frequency F1 = 1.57 GHz for the fundamental mode TM11;</li><li>a resonant frequency F2 = 2.63 GHz for the higher mode TM21;</li><li>a resonant frequency F3 = 3.26 GHz for the higher mode TM01.</li></ul>

p00352 shows a variation curve, as a function of the frequency, the standing wave ratio (SWR) of the conventional antenna of Figure 1. This curve clearly shows the resonance frequencies F1 and F2.

p0036According to the invention, the radiating element 3 (that is to say the copper disc in this example) is not full but has one or more notches for controlling the resonant frequency of a chosen higher mode . In the following description, it has in particular:<ul><li>in relation to Figures 3 to 11, a first antenna according to the invention, for which the chosen higher mode is the TM21 mode;</li><li>in relation to Figures 12 to 20, a second antenna according to the invention, for which the chosen higher mode is the TM01 mode.</li></ul>

p00373 shows a top view of the first antenna according to the invention. The radiating element 30 has four radial slots 31 to 34, spaced apart in pairs angularly by about 90 °. As shown in Figure 4 for the first antenna of the invention, the current lines of the TM21 fashion form a pattern that is repeated as a quarter of the disc (the currents being shown in dotted lines). The notches 31 to 34 are placed to achieve maximum interception of currents on the radiating element 30. In other words, each notch is substantially perpendicular to the current lines in one of the quarters of the disc 30.

p0038In this example, the length of the notches is Lo = 18,375 mm and the width A = 7.35 mm. In an optimization goal, these values ​​are preferably obtained by using a calculation technique (implemented by software) based on a finite element method.

p0039The first antenna is designed to reduce the resonance frequency of the higher mode TM21. 5 shows a curve of variation, as a function of frequency, the SWR of the first antenna of the invention. This figure 5 clearly shows that, using the notches 31 to 34, the resonant frequency of the higher mode TM21 is reduced from 2.63 GHz to F2 = F2 '= 1.662 GHz. Note also that the frequency of the fundamental mode is now at F1 = 1.325 GHz (instead of 1.57 GHz without the slots).

p0040The invention thus significantly reduces the size of the structure compared to a conventional antenna. Indeed, for a TM21 fashion working at a frequency of 1.662 GHz would require a full disk having approximately a diameter of 119 mm instead of 73.5 mm diameter of the first antenna of the invention. Thus, in this specific example, the invention allows a reduction in the size of the antenna by about 40%.

p00416 and 9 each complete radiation pattern for Etheta components and Ephi respectively, of the first antenna of the invention. Figures 7 and 8 each a sectional view for phi = 0 ° and 90 ° respectively, the radiation pattern of the Etheta component (Figure 6). Figures 10 and 11 each a sectional view for phi = 45 ° and 135 ° respectively, the radiation pattern of the Ephi component (Figure 9).

p0042The radiation patterns were measured at the resonance frequency of the TM21 mode. To be very speaking, the results are shown for both components and Etheta Ephi (with phi = 0 corresponding to the X axis of the antenna (see fig.3), the Z axis corresponding to the normal to the plane of the antenna.

p0043The radiation patterns are in the form of "petals" with a maximum located around theta = 45 °, with a spatial rotation phi = 45 ° between the two radiation patterns associated with the two components. Directivity of 5.56 dB. These radiation patterns perfectly match those of a TM21 mode.

p0044Figure 12 shows a top view of the second antenna according to the invention. The radiating element 40 has four circular grooves 41 to 44, arranged parallel to the circumference of the disc 40. As shown in Figure 13 for the second antenna of the invention, the TM 01 mode of the current lines are circular (the currents, shown in dotted lines being arranged radially). The notches 41-44 are placed to achieve maximum interception of currents on the radiating element 40. In other words, each notch is substantially perpendicular to the current lines in one of the quarters of the disc 40.

p0045In this example, the inner radius of the notches is Ri = 23.52 mm, the outer radius Re = 25.72 mm and the angular displacement Da = 70 °. In an optimization goal, these values ​​are preferably obtained using the aforementioned calculation technique based on a finite element method.

p0046The second antenna is designed to reduce the resonance frequency of the higher mode TM01. Figure 14 shows a variation curve, as a function of the frequency, the SWR of the second antenna of the invention. 14 This figure clearly shows that using the notches 41 to 44, the resonance frequency of the TM01 higher mode is reduced from 3.26 GHz to F3 = F3 = 2.104 GHz.

p0047The invention thus significantly reduces the size of the structure compared to a conventional antenna. Indeed, for a TM 01 mode working at the frequency of 2.104 GHz would require a full disk having approximately a diameter of 117 mm instead of 73.5 mm diameter of the second antenna of the invention. Thus, in this specific example, the invention allows a new antenna size reduction of about 40%.

p0048Figures 15 and 18 each have the complete radiation pattern for Etheta components and Ephi respectively, of the second antenna of the invention. Figures 16 and 17 each show a sectional view for phi = 0 ° and 90 ° respectively, the radiation pattern of the Etheta component (Figure 15). Figures 19 and 20 each show a sectional view for phi = 0 ° and 90 ° respectively, the radiation pattern of the Ephi component (Figure 18). The radiation patterns were measured at the resonance frequency of the TM01 mode. The radiation patterns are presented in the same way as those of Figures 6 to 9.

p0049It is found that the Etheta component is in the form of a torus having a maximum located at about theta = 45 °. The directivity obtained for this antenna is 6.31 dB. These radiation patterns perfectly match those of a TM01 mode.

p0050Figures 21 and 22 each show a side view and top respectively, of an antenna according to the invention fed by slot. This antenna includes bunk following:<ul><li>a radiating element 50 of the type shown in Figure 3 (with four radial notches) and W diameter;</li><li>a first substrate layer 51, of height H1 and relative permittivity ε_r1 ;</li><li>a first ground plane 52 having a coupling slot 53;</li><li>a second substrate layer 54, of height H2 and relative permittivity ε_r2 ;</li><li>a supply line 55, whose end which extends beyond the slit 53 constitutes an adaptation stub length Lstub;</li><li>a third layer substrate 56, height H3 and relative permittivity ε_r3 ;</li><li>a second ground plane 57.</li></ul>

p0051Was presented above two types of power supply, namely by coaxial probe and coupling slot. It is clear however that the invention is not limited to these two types of food but can be used by any type of conventional power (proximity coupling, power line in the plane of the radiating element, etc. ).

p0052Figure 23 shows a top view of a particular embodiment of an antenna according to the invention, wherein each notch cooperates with means 61 annihilation effect. The antenna also includes activation / deactivation of the means 61 of annihilation. These means (not shown) on / off are, for example an electronic control device. In the example shown, the means of annihilation of the effect of a slot include a varactor diode 61 connecting the two edges of this notch.

p0053Thus, with these additional means, is possible to envisage other types of operation of the antenna of the invention, and in particular multi-mode operation and a multifrequency operation.

p0054In multimode operation, the activation / deactivation means act simultaneously on all the diodes, so that:<ul><li>when all the diodes are activated, the antenna operates in the fundamental mode (having a maximum of radiation perpendicular to the antenna),</li><li>when all the diodes are deactivated, the antenna operates in a chosen higher mode (having a maximum radiation to a low elevation).</li></ul>

p0055In multifrequency operation for a chosen higher mode, activation / deactivation means act on a variable number of diodes in time, so that each distinct number of diodes activated at a given instant corresponds to a particular resonant frequency of the higher mode selected.

p0056Figures 24 and 25 each show a side view and top, respectively, of a particular embodiment of a dual band antenna of the invention.

p0057This dual-band antenna comprises two antennas (below 70 and above 71) superimposed. The radiating element (e.g. a disc) 72 of the lower antenna 71 is the ground plane of the upper antenna 71.

p0058The antenna 70 comprises a lower ground plane 73, a substrate plate (not shown), a radiating element 72 and a first coaxial feed 74. The upper antenna 71 comprises a ground plane (formed by the radiating element 72 of the lower antenna 70), a substrate plate (not shown), a radiating element 75 and a second coaxial feed 76.

p0059Each antenna 70, 71 operates independently. The two disks 72, 75 are offset so that the attack of the upper disc 75 passes through the lower disc 72 in the middle, so as to minimize the disturbance thus made.