Compact printed antenna with little radiation in elevation

The invention relates to planar printed antennas for transmitting and / or receiving microwave signals.

In particular, the invention relates to a planar antenna whose emission is maximum at low EI (elevation) angle.

The antenna of the invention has a variety of applications. It can be used, for example, with a roof-mounted vehicle-mounted circuit to secure satellite communications. In fact, certain moving objects, and in particular those associated with geostationary satellites in countries of medium or low latitudes (for example, Northern Europe), require planar antennas whose emission is maximal at a low EI angle.

Currently in vehicles, for reasons of space requirements and cost reasons, printed antennas of the type "patch" are used. These have the particular advantages of being even and inexpensive.

In general, a printed antenna includes a dielectric substrate plate, a ground plane (consisting of a first deposition of a conductive material deposited on a first surface of the dielectric substrate plate), a radiating element (formed by a second conductive deposit deposited on a second surface of the substrate) dielectric substrate plate is applied) and means for feeding the antenna.

In normal operation, ie in fundamental mode, these printed antennas produce a radiation pattern which has a maximum in the direction perpendicular to the plane containing the antenna. In this type of normal operation, the length of the radiating element is very close to half the wavelength, taking into account the dielectric constant of the dielectric substrate used.

In order to generate radiation having a maximum at low EI angle, ie, in directions away from the axis perpendicular to the plane containing the antenna, the printed antennas must be operated with a harmonic whose current distribution enables the generation of such radiation.

The main problem is that the interesting harmonics occur at frequencies that are relatively high compared to the fundamental frequency. That is, around this harmonic for the required frequency band (which is close to the frequency band corresponding to the fundamental frequency), the antenna must be very oversized.

This oversizing makes the incorporation of such radiating elements in a network with the aim of achieving high-gain antennas almost impossible. This space problem is all the more serious because, for a network that needs to produce low EI angle radiation, the radiating elements must be close together to avoid large network lobes that severely weaken the antenna gain.

Document EP 0 708 492 (ASULAB SA (CH) in Figs. 1-4 and on page 4, lines 35-36) shows an antenna comprising a conductive disk and pairs of slots extending from the periphery to the center of the Extend disk and allow the control of the resonant frequency. As regards the arrangement of the slots (5 and 6) of the antenna presented in this document, they extend from the periphery to the center of the conductive disk (see Figures 3 and 4). Even if the slits are perpendicular to the flow lines of the vibration region TM21, this document contains no indication of the use of the slits for controlling the resonance frequencies of this harmonic.

In particular, the invention aims to counteract this disadvantage of the prior art.

More specifically, it is an object of the invention to provide a printed antenna that provides low EI angle radiation while requiring little space.

A further object of the invention is to provide an antenna which has all the advantages of the printed antennas, in particular the low production costs.

These various objects, as well as others which will become apparent hereinafter, are achieved according to the invention with the aid of a planar printed antenna for transmitting and / or receiving microwave signals, of the type comprising in particular:

a dielectric substrate plate,

a ground plane consisting of a first deposition of a conductive material deposited on a first surface of the dielectric substrate plate,

a radiating element formed from a second conductive deposit deposited on a second surface of the dielectric substrate plate,

Means for feeding the antenna,

wherein the antenna has a fundamental vibration in which it generates a radiation pattern having a maximum in the perpendicular direction to the plane containing the radiating element and at least one harmonic in which it generates a radiation pattern with a weak EI angle,

the antenna being characterized in that the radiating element has at least one notch or notches designed to control the resonant frequency of a selected harmonic.

The selected harmonic is the one at which the antenna should operate, so that the maximum radiation is generated for low EI angles.

Thus, the general principle of the invention is to reduce the resonant frequency for a given harmonic only by cuts in the radiating element, ie, without changing the overall footprint of the antenna. In other words, when operating with the same harmonic, the antenna according to the invention requires less space than a conventional printed antenna.

Advantageously, the incision or the incisions are approximately perpendicular to the flow lines of the selected harmonic.

Thus, these streamlines are lengthened, reducing the resonant frequency of the selected harmonic.

Advantageously, the dimensions (length, width) of the incision or incisions are determined on the basis of a finite element method-based calculation technique.

Preferably, the feeds employ a feed-in technique from the group comprising:

- Infeed by coaxial probe;

- Infeed by slot coupling;

- Infeed by close coupling;

- Infeed through feed line in the plane of the radiating element.

Preferably, the radiating element has the shape of a circular disk.

In a first preferred embodiment of the invention, the selected harmonic is the harmonic TM21 whose streamlines form a pattern that repeats in each quarter of the disk,

the radiating elements having four radial cuts separated in pairs by an angle of about 90 °, each of the cuts being approximately perpendicular to the streamlines in one quarter of the circular disk.

In a second preferred embodiment of the invention, the selected harmonic is the harmonic TM01 whose streamlines are radial,

wherein the radiating elements have at least one circular cut where the cuts extend over at least part of the circumference of a circle contained in and concentric with the circular disk.

Advantageously, each incision cooperates with means for exterminating its effect, the antenna comprising means for activating / deactivating the said annihilation means.

Preferably, the destruction means comprise the action of an incision of a diode connecting both edges of the incision.

In a first particular embodiment of the invention, the radiating element has a plurality of cuts,

wherein the means for activating / deactivating act simultaneously on all the annihilation means associated with the plurality of sipes to enable a multi-shaft operation such that

if all the means of destruction are activated, the antenna is operated in the fundamental frequency mentioned,

- When all means of destruction are deactivated, the antenna is operated in the selected harmonic.

This multi-vibration mode allows you to cover a large solid angle with maximum radiation. In fact, at the fundamental, one has a maximum radiation in the direction perpendicular to the plane of the antenna, while in the chosen one, there is a radiation peak for a small EI angle.

In a second particular embodiment of the invention, the radiating element has a plurality of cuts,

wherein the means for enabling / disabling acts on a time-varying number of annihilation means associated with the plurality of incisions to enable multi-frequency operation, which is arranged such that each different number of annihilation means activated at a given time , corresponds to a specific resonant frequency of the selected harmonic.

This allows a multi-frequency operation for a same harmonic.

The invention also relates to a dual-band antenna, characterized in that it comprises two superposed antennas, called lower antenna and upper antenna, of the type already explained above, wherein the radiating element of the lower antenna forms the ground plane of the upper antenna.

Further characteristics and advantages of the invention will become apparent upon reading the following description of several preferred embodiments of the invention, given by way of example for illustration and without limitation, and upon consideration of the accompanying drawings, in which:

FIG. 1 shows a side view of a conventional antenna powered by a coaxial head; FIG.

Fig. 2 is a variation curve of the standing wave ratio (ROS) of the classical antenna of Fig. 1 as a function of frequency;

Fig. 3 is a plan view of an embodiment of a first antenna according to the invention;

Fig. 4 shows a schematic representation of the flow lines of the vibration region TM21 for the first antenna of Fig. 3;

Fig. 5 is a variation graph as a function of the frequency of the standing wave ratio of the first antenna of Fig. 3;

FIG. 6 illustrates the complete radiation diagram for the ethetah component of the first antenna of FIG. 3; FIG.

Figures 7 and 8 each show a section for phi = 0 ° and 90 °, respectively, of the radiation pattern of Figure 6;

FIG. 9 illustrates the complete radiation pattern for the Ephi component of the first antenna of FIG. 3; FIG.

Figures 10 and 11 each show a section for phi = 45 ° and 135 °, respectively, of the radiation pattern of Figure 9;

Fig. 12 is a plan view of an embodiment of a second antenna according to the invention;

Fig. 13 is a schematic representation of the flow lines of the vibration region TM01 for the second antenna of Fig. 12;

Fig. 14 shows a variation curve as a function of the frequency of the standing wave ratio of the second antenna of Fig. 12;

FIG. 15 illustrates the complete radiation pattern for the ethetah component of the second antenna of FIG. 12; FIG.

FIGS. 16 and 17 each show a section for phi = 0 ° and 90 °, respectively, of the radiation diagram of FIG. 15;

Fig. 18 shows a complete radiation pattern for the Ephi component of the second antenna of Fig. 12;

Figures 19 and 20 each show a section for phi = 0 ° and 90 °, respectively, of the radiation diagram of Figure 18;

FIGS. 21 and 22 show, respectively, a side view and a plan view, respectively, of a slot-fed antenna according to the invention;

Fig. 23 is a plan view of a particular embodiment of an antenna according to the invention having means for annihilating the effect of each cut, and

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

The invention accordingly relates to a planar printed antenna for transmitting and / or receiving microwaves.

Fig. 1 shows a side view of a fed via a coaxial head classical antenna. The antenna includes:

a dielectric substrate plate 1 having a thickness H = 2.28 mm and a relative dielectric constant of, for example, εr = 2.2;

a ground plane 2 formed by a first deposition of a conductive material, for example copper, deposited on a first surface of the dielectric substrate plate 1;

a radiating element 3 formed from a second conductive deposit, for example a 73.5 mm diameter copper disc applied to a second surface of the dielectric substrate plate 1, and

- A coaxial probe 4, with which the antenna can be fed and which has an external conductor 5, which is soldered to the ground plane 2 and an inner conductor 6, which is soldered to the radiating element 3. The positioning of this coaxial probe 4 allows the adjustment of the antenna.

The antenna has a fundamental, 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 harmonic, where it generates a radiation pattern with weak EI angles.

With the dimensions previously given for the various elements 1, 2, 3 of the antenna, one obtains:

a resonance frequency F1 = 1.57 GHz for the fundamental TM11;

a resonance frequency F2 = 2.63 GHz for the harmonic TM21;

a resonance frequency F3 = 3.26 GHz for the harmonic TM01;

Fig. 2 shows a variation curve of the standing wave ratio (ROS) of the classical antenna of Fig. 1 as a function of frequency. The resonance frequencies F1 and F2 can be clearly seen on the curve.

According to the invention, the radiating element 3 (the copper disc in this example) is not solid, but has one or more incisions that allow controlling the resonant frequency of a selected harmonic. In the following description, the following is particularly shown:

in relation to FIGS. 3 to 11, a first antenna according to the invention, in which TM21 was chosen as a harmonic;

in relation to FIGS. 12 to 20, a second antenna according to the invention, in which TM01 was chosen as a harmonic.

Fig. 3 shows a plan view of the first antenna according to the invention. The radiating element 30 has four radial recesses 31 to 34, which are each separated in pairs by an angle of approximately 90 ° from each other. As seen in Figure 4 for the first antenna of the invention, the streamlines of the vibration region TM21 form a pattern that repeats on each quarter of the disk (the streams being dotted). The cuts 31 to 34 are arranged so that a maximum detection of the currents on the radiating element 30 is achieved. That is, each cut is approximately perpendicular to the streamlines in each quarter of the disk 30.

In this example, the length of the cuts is Lo = 18.375 mm and the width La = 7.35 mm. For the purposes of optimization, these values ​​are determined from a finite element method based (using a computerized program) calculation technique.

The purpose of the first antenna is to reduce the resonant frequency of the harmonic TM21. Fig. 5 shows a variation curve of the standing wave ratio of the first antenna according to the invention as a function of frequency. It can clearly be seen in FIG. 5 that the resonant frequency of the harmonic TM21 is reduced from F2 = 2.63 GHz to F2 '= 1.6262 GHz by means of the cuts 31 to 34. It can also be seen that the frequency of the fundamental is now F1 '= 1.325 GHz (instead of 1.57 GHz without cuts).

Thus, the invention allows a significant reduction of the structure in relation to a classical antenna. In fact, to obtain a TM21 vibration region operating at a frequency of 1.662 GHz, a massive disc having a diameter of about 119 mm would be required while the first antenna according to the invention would have a diameter of 73.5 mm. In this case, the termination allows a reduction in the antenna dimensions of about 40%.

FIGS. 6 and 9 respectively show the complete radiation pattern for the components Etheta and Ephi of the first antenna according to the invention. Figs. 7 and 8 respectively show a sectional view for phi = 0 ° and 90 ° of the radiation pattern of the component eteta (Fig. 6). Figs. 10 and 11 respectively show a sectional view for phi = 45 ° and 135 ° of the radiation pattern of the component Ephi (Fig. 9).

The radiation patterns were measured at the resonance frequency of the vibration region TM21. To give them a special meaning, the results for the two components Etheta and Ephi are shown (where phi = 0 corresponds to the axis X of the antenna (see Fig. 3) and the axis Z corresponds to the perpendicular to the antenna plane).

The radiation patterns appear in the form of "lobes", with a maximum at about theta = 45 °, where the spatial rotation between the two radiation patterns associated with the two components is phi = 45 °. The directional characteristic is 5.56 dB. These radiation patterns correspond exactly to those of the vibration region TM21.

Fig. 12 shows a plan view of the second antenna according to the invention. The radiating element 40 has four circular recesses 41 to 44, which are mounted parallel to the circumference of the disc 40. As can be seen in Fig. 13 for the second antenna according to the invention, the current lines of the oscillation region TM01 are circular (with the dotted currents being radial). The cuts 41 to 44 are arranged so that a maximum detection of the currents on the radiating element 40 is achieved. In other words, each cut is approximately perpendicular to the streamlines in a quarter of the disk 40th

In this example, the inner radius of the cuts is Ri = 23.52 mm, the outer radius Re = 25.72 mm and the angular displacement Da = 70 °. For the purpose of optimization, these values ​​are determined from an already mentioned calculation technique based on a finite element method.

The purpose of the second antenna is to reduce the resonant frequency of the harmonic TM01. Fig. 14 shows a variation curve of the standing wave ratio of the second antenna according to the invention as a function of frequency. It can clearly be seen on this Fig. 14 that the resonant frequency of the harmonic TM01 is reduced from F3 = 3.26 GHz to F3 '= 2.104 GHz by means of the cuts 41 to 44.

The invention thus enables a significant reduction in the structure size compared to a conventional antenna. Namely, to obtain a vibration region TM01 operating at a frequency of 2.104 GHz, a massive disk having a diameter of about 117 mm instead of the diameter of 73.5 mm of the second antenna according to the invention would be required. Thus, in this particular example, the invention again enables about a 40% reduction in antenna dimensions.

FIGS. 15 and 18 each illustrate a complete radiation pattern for the components of the second antenna of the invention, Etheta and Ephi, respectively. Figs. 16 and 17 each show a sectional view of the radiation pattern of the component Eheta (Fig. 15), for phi = 0 ° and 90 °, respectively. Figures 19 and 20 are each a sectional view of the radiation pattern of component Ephi (Figure 18) for phi = 0 ° and 90 °, respectively.

The radiation patterns were measured at the resonance frequency of the vibration region TM01. The radiation patterns are presented like those of FIGS. 6 and 9.

It is noted that the component Etheta occurs in the form of a torus, with a maximum at about theta = 45 °. The directional characteristic obtained for this antenna is 6.31 dB. These radiation patterns correspond exactly to those of the vibration range TM01.

Figs. 21 and 22 respectively show a side view and a plan view of a slot-fed antenna according to the invention. This antenna comprises the following superimposed elements:

a radiating element 50 of the type shown in Fig. 3 (with four radial cuts) of diameter W;

a first substrate layer 51 having the height H1 and the relative dielectric constant εr1;

a first ground plane 52, with a coupling slot 53;

a second substrate layer 54 having the height H2 and the relative dielectric constant εr2;

a feed line 55 whose end extending beyond the slot 53 forms a matching stub of length Lstub;

a third substrate layer 56 of height H3 and relative dielectric constant εr3;

a second ground plane 57.

Two types of feed have been shown above, namely by coaxial probe and by slot coupling. It is nevertheless clear that the invention is not limited to these two types of feed, but that it is applicable to any type of classical feed (neighborhood coupling, feed line in the plane of the radiating element, etc.).

Fig. 23 is a plan view of a particular embodiment of an antenna according to the invention, each notch cooperating with means of exterminating its effect 61. The antenna also comprises means for activating / deactivating these destruction means 61. These activation / deactivation means (not shown) consist for example of an electronic control device. In the example presented, the means for canceling the effects of an incision comprise a reactance diode 61 connecting both edges of the incision.

Thus, additional modes of the antenna according to the invention are conceivable with these additional means, in particular a Mehrfachschwingungsbereich- and a multi-frequency operation.

In the case of operation after the multiple oscillation region, the activation / deactivation agents act simultaneously on all diodes such that:

when all diodes are activated, the antenna is operating in fundamental mode (having a maximum radiation perpendicular to the antenna);

- When all diodes are deactivated, the antenna operates in a harmonic mode (with a radiation maximum at a low EI angle).

In the case of multi-frequency operation at a selected harmonic, the enable / disable means acts on a time varying number of diodes so that each different number of diodes activated at a given time corresponds to a particular resonant frequency of the selected harmonic.

Figs. 24 and 25 respectively show a side view and a plan view of a particular embodiment of a dual-band antenna according to the invention.

This dual-band antenna comprises two superimposed antennas (a lower antenna 70 and an upper antenna 71). The radiating element (for example, a disk) 72 of the lower antenna 70 forms the ground plane of the upper antenna 71.

The 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 includes a ground plane (formed of the radiating element 72 of the lower antenna 70), a (not shown) ) Substrate plate, a radiating element 75 and a second Koaxialspeisung 76th

The two antennas 70, 71 function independently of each other. The two discs 72, 75 are offset from one another such that the suspension of the upper disc 75 passes through the lower disc 72 in the middle to minimize the interference thus introduced.