Compact printed antenna with little radiation in elevation

0001The field of the invention is that of planar printed antennas transmit and / or reception of microwave signals.

0002More specifically, the invention relates to a planar antenna producing a maximum radiation at low elevations.

0003The antenna of the invention has many applications. It can for example be used in a network on the roof of a passenger car, in order to ensure satellite communications. Indeed, some mobile, particularly those linked with geostationary satellites in countries with average or high latitude (Europe North, for example) require planar antennas producing maximum radiation for low elevations.

0004Currently, for reasons of space and cost, are used in Mobile antennas printed type "patch". Indeed, these have particular the advantage of being planar and inexpensive.

0005In general, a printed antenna comprises a substrate plate dielectric, a ground plane (composed of a first deposited on a conductive deposit first face of the dielectric substrate plate), a radiating element (consisting a second conductive deposit deposited on a second face of the substrate plate dielectric) and the antenna feed means.

0006In their current operation, that is to say when they operate in their fundamental mode, these printed antennas generate a radiation pattern having a maximum in the direction perpendicular to the plane containing the antenna. For this type current operation, the length of the radiating element is very close to the half-length wave taking into account the permittivity of the dielectric substrate used.

0007To 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, printed antennas must operate in a higher mode whose current distribution can create this type of radiation.

0008The major problem lies in the fact that the higher modes of presenting interest appear to relatively high frequencies compared to those of fundamental mode. This means that to use this mode (top) for the desired frequency band (close to that corresponding to the fundamental mode) the antenna must be oversized very significantly.

0009This oversizing it virtually impossible integration of such network radiating elements in order to obtain high-gain antennas. This issue congestion is especially crucial for a network to generate a low elevation radiation, radiating elements must be placed very close each other in order to avoid major network lobes strongly deteriorate the antenna gain.

0010EP 0708492 (ASULAB SA) describes (see Figures 1-4 and page 4, lines 36-35) antenna comprising a conductor and slot pairs disc extending from the periphery towards the center of the disc, which control the resonant frequency. As regards the provision of slots (5 and 6) of the antenna according to this document, they extend from the periphery towards the center of disk driver (see Figures 3 and 4). Even if the slots are perpendicular to the current lines of TM21 mode, this document does not suggest in any way the use of these slots to control resonant frequency of the higher mode.

0011The invention particularly aims to overcome this major drawback of the state art.

0012More specifically, one of the objectives of the present invention is to provide a printed antenna to obtain radiation at low elevations while with a small footprint.

0013The invention also aims to provide an antenna that maintains all the advantages of printed antennas, including a low manufacturing cost.

0014These various objectives, and others that will appear later, are achieved according to the invention using a planar printed antenna emission and / or receiving microwave signals, comprising in particular<ul><li>a dielectric substrate board,</li><li>a ground plane formed by a first deposited on conductive deposit a first side of said dielectric substrate board,</li><li>a radiating element consists of a second deposited conductive deposit on a second side of said dielectric substrate board,</li><li>supply means of said antenna,</li></ul>   said antenna having a fundamental mode in which it generates a radiation pattern having 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    said antenna being characterized in that said radiating element has at least one notch arranged to control the resonant frequency of a mode Higher selected.

0015The chosen higher mode is one in which one wishes to see run the antenna, so that the maximum radiation is generated at low elevations.

0016Thus, the general principle of the invention, for a given higher mode, to reduce the resonance frequency only by making notches on the element radiant, that is to say without changing the overall antenna size. In other terms, for operation in the same higher mode, the printed antenna the invention has a smaller footprint than a conventional printed antenna.

0017Advantageously, the notch or notches are arranged substantially perpendicularly to the current lines of said chosen higher mode.

0018In this way, we increase the electrical length of these current lines, and thus decreases the resonance frequency of the chosen higher mode.

0019Advantageously, the dimensions (length, width) of the or notches are determined from a calculation technique based on an element method finished.

0020Preferably, said power-means implement a technical Power from 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>

0021Preferably, said radiating element is disc-shaped.

0022In a first preferred embodiment of the invention, the method Higher selected is the TM21 mode, whose current lines form a pattern that 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 slots being substantially perpendicular to the current lines in one of said quarters of the disc.

0023In a second preferred embodiment of the invention, said mode Higher selected is the TM01 mode, whose currents are arranged radially,    said radiating element having at least one circular notch, or the notches extending over at least a portion of the circumference of a circle contained in said disk and the same center as the latter.

0024Advantageously, each notch cooperates with annihilation means its effect, said antenna comprising means for activating / deactivating said means annihilation.

0025Preferably, said means of annihilation of the effect of a notch comprises a diode connecting the two edges of said notch.

0026In a first particular embodiment of the invention, said element radiating has a plurality of notches,    said means for activating / deactivating acting simultaneously on all 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>

0027This multimode operation can cover a large solid angle with a maximum radiation. Indeed, in the fundamental mode, a maximum of radiation in the direction perpendicular to the plane containing the antenna, and the chosen higher mode, there is a maximum of radiation to a lower elevation.

0028In a second particular embodiment of the invention, said element radiating has a plurality of notches,    said means for activating / deactivating acting on a variable number in the time of annihilation means associated with said plurality of slots, so as to allow multifrequency operation such that each distinct number of ways annihilation activated at a given instant corresponds to a resonant frequency Particular said chosen higher mode.

0029This allows a multifrequency operation for the same type of fashion superior.

0030The invention also relates to a dual-band antenna, characterized in that it includes two superimposed antennas, termed upper and lower antennas, the type of those presented above, the radiating element of said lower antenna forming the ground plane of said top antenna.

0031Other features and advantages of the invention will become apparent from 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 coaxial probe;</li><li>2 shows a curve of variation, as a function of frequency, the standing wave ratio (VSWR) of the conventional antenna of Figure 1;</li><li>3 shows a top view of one embodiment of a first antenna of the invention;</li><li>Figure 4 shows schematically the mode of the current lines TM21 for the first antenna of Figure 3;</li><li>5 shows a curve of variation, as a function of frequency, SWR of the first antenna of Figure 3;</li><li>Figure 6 shows the complete radiation pattern for the Etheta component, the first antenna of Figure 3;</li><li>Figures 7 and 8 each a sectional view for phi = 0 ° and 90 °, the radiation pattern of Figure 6;</li><li>Figure 9 shows the complete radiation pattern for the Ephi component, 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 of the invention;</li><li>Figure 13 shows schematically the mode of the current lines TM01 for the second antenna of Figure 12; </li><li>14 shows a curve of variation, as a function of frequency, VSWR of the second antenna of Figure 12;</li><li>Figure 15 shows the complete radiation pattern for the Etheta component of the second antenna of Figure 12;</li><li>Figures 16 and 17 each show a sectional view of phi = 0 ° and 90 °, the radiation pattern of Figure 15;</li><li>Figure 18 shows the complete radiation pattern for the Ephi component of the second antenna of Figure 12;</li><li>Figures 19 and 20 each show a sectional view of phi = 0 ° and 90 °, the radiation pattern of Figure 18;</li><li>Figures 21 and 22 each show a side view and respectively from above, of an antenna according to the invention fed by slot;</li><li>FIG 23 shows a top view of one embodiment particular of an antenna according to the invention comprising means annihilation of the effect of each notch; and</li><li>Figures 24 and 25 each show a side view and respectively from above, of a particular embodiment of a dual band antenna according to the invention.</li></ul>

0032The invention therefore relates to a planar printed antenna emission and / or receiving microwave signals.

0033Figure 1 shows a side view of a conventional antenna fed by probe coaxial. The antenna comprises:<ul><li>a dielectric substrate plate 1, thickness H = 2.28 mm and ε relative permittivity_r = 2.2, for example;</li><li>a ground plane 2 formed by a first conductive deposit, by example copper, deposited on a first face of the substrate plate dielectric 1;</li><li>a radiating element 3 consisting of a second conductive deposit, by example 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 a outer 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>

0034The antenna has a fundamental mode in which it generates a diagram radiation having 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.

0035With 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>

00362 shows a variation curve, as a function of frequency, standing wave ratio (VSWR) of the conventional antenna of Figure 1. This curve clearly shows the resonance frequencies F1 and F2.

0037According 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 remainder of the description, This information includes:<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>

00383 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 repeats 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 element radiating 30. In other words, each notch is substantially perpendicular to current lines in one of the quarters of the disk 30.

0039In this example, the length of the notches is Lo = 18,375 mm and the width La = 7.35 mm. In an optimization goal, these values ​​are preferably obtained using a computational technique (implemented by software) based on a method of elements finished.

0040The first antenna is designed to reduce the resonant frequency mode TM21 higher. 5 shows a curve of variation, depending on the frequency, SWR of the first antenna of the invention. This 5 shows clearly with the aid of the slots 31 to 34, the higher mode resonant frequency TM21 is reduced from F2 = 2.63 GHz 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).

0041The invention thus significantly reduces the size of the structure by compared to a conventional antenna. Indeed, for a TM21 working at fashion 1.662 GHz frequency would require a full disk with a diameter approximately 119 mm instead of 73.5 mm in diameter of the first antenna of the invention. So, in this specific example, the invention allows a reduction in the size of the antenna about 40%.

00426 and 9 each complete radiation pattern for the Etheta Ephi and components, respectively, of the first antenna of the invention. The Figures 7 and 8 each show a sectional view for phi = 0 ° and 90 °, the radiation diagram of the Etheta component (Figure 6). Figures 10 and 11 each present a sectional view of phi = 45 ° and 135 ° respectively, the radiation pattern of the Ephi component (Figure 9).

0043The radiation patterns were measured at the resonant 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), Z axis corresponding to the normal to the plane of the antenna.

0044The radiation patterns are in the form of "petals" having 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 mode TM21.

0045Figure 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 in parallel the circumference of the disc 40. As shown in Figure 13, for the second antenna of the invention, the current lines of the TM01 mode are circular (currents, shown in dotted lines being arranged radially). The notches 41-44 are placed to obtain a maximum interception of currents on the radiating element 40. other words, each notch is substantially perpendicular to the current lines in one of the quarters of the disk 40.

0046In this example, the inner radius of the notches is Ri = 23.52 mm, the radius external 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.

0047The second antenna is designed to reduce the resonant frequency mode TM01 higher. Figure 14 shows a variation curve, depending on the frequency, VSWR of the second antenna of the invention. This 14 shows clearly with the aid of the slots 41 to 44, the higher mode resonant frequency TM01 is reduced from 3.26 GHz to F3 = F3 = 2.104 GHz.

0048The invention thus significantly reduces the size of the structure by compared to a conventional antenna. Indeed, for a TM 01 mode working on the frequency of 2.104 GHz would require a full disk with a diameter approximately 117 mm instead of 73.5 mm diameter of the second antenna of the invention. So, in this specific example, the invention enables a new reduction in the size of the antenna of approximately 40%.

0049Figures 15 and 18 each have the full radiation pattern for Etheta Ephi and components, respectively, of the second antenna of the invention. Figures 16 and 17 each show a sectional view for phi = 0 ° and 90 ° respectively, of the radiation pattern of the Etheta component (Figure 15). The Figures 19 and 20 each show a sectional view for phi = 0 ° and 90 ° respectively, of the radiation pattern of the Ephi component (Figure 18).

0050The radiation patterns were measured at the resonant frequency of the TM01 mode. The radiation patterns are presented in the same way as those Figures 6 and 9.

0051It is found that the Etheta component is in the form of a torus having a maximum located around theta = 45 °. The directivity obtained for this antenna 6.31 dB. These radiation patterns correspond perfectly to those of a TM01 mode.

0052Figures 21 and 22 each show a side view and respectively above, 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 diameter W;</li><li>a first substrate layer 51, of height H1 and permittivity on 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 permittivity on ε_r2 ;</li><li>a supply line 55, whose end which extends beyond the slot 53 is a stub length adaptation Lstub;</li><li>a third layer substrate 56, height H3 and permittivity on ε_r3 ;</li><li>a second ground plane 57.</li></ul>

0053Was presented above two types of power supply, namely by coaxial probe and by coupling slot. It is clear however that the invention is not limited to these two types of power supply but can be used by any type of conventional feed (Proximity coupling, power line in the plane of the radiator, etc.).

0054Figure 23 shows a top view of a particular embodiment of a antenna according to the invention, wherein each notch cooperates with means 61 annihilation of its effect. The antenna also includes activation / Disabling these means 61 annihilation. These means (not shown) for activating On / off are, for example an electronic control device. In the example presented, the means of annihilation of the effect of a slot include a diode varactor 61reliant the two edges of this notch.

0055Thus, with these additional resources, we can consider other types of operation of the antenna of the invention, including a multimode operation and a multifrequency operation.

0056In 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 mode basic (having a maximum 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 for a low elevation).</li></ul>

0057In multifrequency operation to a higher mode selected, the means activation / deactivation act on a variable number in the time of diodes, such that each distinct number of diodes activated at a given instant corresponds to a particular resonant frequency of the chosen higher mode.

0058Figures 24 and 25 each show a side view and respectively above, a specific embodiment of a dual band antenna of the invention.

0059This 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.

0060The lower antenna 70 includes a 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), an element 75 and a second radiating coaxial feed 76.

0061Each antenna 70, 71 operates independently. The two discs 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 disturbance and made.