EP0527417A1 - Miniaturized radio frequency antenna element - Google Patents

Abstract

The antenna is designed to operate well below resonance, and includes a small flat cavity (1) on the surface (1) of which is made at least one radiating slot (3) of much smaller dimensions than those of a normally resonating slot. On the other hand, an impedance-matching circuit is often required at the feed-ins (5) of this antenna. <IMAGE>

Description

The present invention relates to a miniaturized elementary radio antenna, intended in particular for VHF waves. and U.H.F., that is to say the waves included in a frequency range covering from the small hundred megahertz up to a few Gigahertz only. Such an antenna is in particular intended to equip a radio communications satellite.

V.H.F. or U.H.F. the most formerly used are the wire antennas. At these relatively low frequencies, these antennas have large dimensions, which is very penalizing in terms of weight and size for a satellite. In addition, precisely because of this large size, they must be folded for storage and when launching the satellite, then deployed when the latter is finally in orbit. This necessitates the provision of a complex, expensive, bulky, heavy deployment mechanism, and moreover subject to a risk of breakdown when it is actuated once the satellite is put into orbit.

où L est la longueur d'onde de l'onde émise ou captée par cette antenne imprimée.It therefore seems ultimately very desirable to miniaturize these antennas as much as possible for VHF and UVF, and a solution that may come to mind for this is to use the technique, now very popular, of antennas printed on substrate, of the " patch "consisting of a conductive square separated from a ground plane by a thin dielectric substrate with Er permittivity. This conductive square is deposited on the substrate by a conventional printed circuit technique, and its side conventionally has the approximate length:

$\text{L / 2 .√}\overline{\text{Er}}$

where L is the wavelength of the wave emitted or picked up by this printed antenna.

In the air, we get for these antennas, and at frequencies that interest us here, dimensions still far too important.

The use of a substrate with a high dielectric constant Er, such as Alumina, makes it possible to reduce these dimensions, but still insufficiently. In addition, a high permittivity considerably penalizes the radiation qualities of such an antenna, so that such a solution is ultimately questionable.

There are many dielectrics of even higher permittivity, such as sintered ceramics, but the use of such materials is absolutely not currently possible on an industrial level. In addition, the radiation performance of such antennas would be even more degraded.

• . en ce qu'elle se compose d'une ou plusieurs fentes rayonnantes de dimensions très inférieures à celles des fentes rayonnantes résonnantes pour la ou les fréquences de fonctionnemehnt de cette antenne, et donc fonctionnant bien en deça de la résonance, cette ou ces fentes étant pratiquées sur une des deux grandes faces d'une cavité, cette cavité étant elle-aussi de dimensions très inférieures à celle d'une cavité résonnante pour cette ou ces fréquences de fonctionnement;
• . et en ce que son ou ses accès est ou sont chacun couplés à la ligne correspondante à travers au moins un circuit d'adaptation d'impédance.

The invention aims to remedy these drawbacks. To this end, it relates to a miniaturized elementary radio antenna, in particular for VHF and UHF wave ranges, which is characterized:

• . in that it consists of one or more radiating slots of dimensions much smaller than those of the radiating resonant slots for the operating frequency or frequencies of this antenna, and therefore operating well below resonance, this or these slots being practiced on one of the two large faces of a cavity, this cavity also being of dimensions much smaller than that of a resonant cavity for this or these operating frequencies;
• . and in that its access (es) is or are each coupled to the corresponding line through at least one impedance matching circuit.

• . Figure 1 est une vue en plan d'une forme simple de réalisation de cette antenne élémentaire;
• . Figure 2 représente ce même élément rayonnant, en coupe selon II-II de Figure 1 ;
• . Figure 3 est un schéma synoptique de branchement de cette antenne ;
• . Figures 4,5, et 6, montrent, de même façon qu'en Figure 1, trois autres configurations utilisant plusieurs fentes parallèles sur une même cavité;
• . Figures 7 à 10 montrent de même façon des possibilités de réalisation et excitation d'un élément rayonnant comportant deux fentes orthogonales;
• . Figure 11 montre de même une configuration bi-polarisation et comportant plusieurs fentes pour chaque polarisation; et
• . Figure 12 montre enfin une configuration multi-fentes, bi-polarisations, et bi-fréquences.

In any case, the invention will be well understood, and its advantages and other characteristics will emerge during the following description of a few nonlimiting examples of the construction of this miniaturized non-resonant antenna, with reference to the appended drawing in which:

• . Figure 1 is a plan view of a simple embodiment of this elementary antenna;
• . Figure 2 shows the same radiating element, in section along II-II of Figure 1;
• . Figure 3 is a block diagram of the connection of this antenna;
• . Figures 4,5 and 6 show, as in Figure 1, three other configurations using several parallel slots on the same cavity;
• . Figures 7 to 10 show similarly possibilities of realization and excitation of a radiating element having two orthogonal slots;
• . Figure 11 similarly shows a bi-polarization configuration and comprising several slots for each polarization; and
• . Figure 12 finally shows a multi-slot, bi-polarization, and bi-frequency configuration.

Referring to Figures 1 and 2, this miniaturized elementary antenna consists of a flat cavity 1, for example of Aluminum and of rectangular section, with for example 10 to 15 centimeters on a side and a low height (to minimize the bulk ) of for example 5 centimeters, and one of the large faces of which, for example the upper face 2 is perforated with a fine radiating slit 3 which is, according to the invention, dimensioned totally below the resonance: instead of have a length equal to half the wavelength, that is L / 2, its length is a much smaller fraction of it, for example of the order of L / 10 or even L / 20.

It can be seen that the radiation characteristics of such a slot 3, coupled to this cavity 2, whatever the dimensions of the latter precisely, remain very acceptable although the assembly operates completely below the resonance.

The excitation of the slot 3 is carried out in a conventional manner, for example by a probe 4 which extends the core a tri-plate line 5 connected to the cavity 1 via a connector 6.

Of course, such an antenna is, unlike the resonant antennas of the prior art, mismatched in impedances, and according to the invention, an impedance matching circuit, in itself being able to be very conventional, is provided between the antenna and the corresponding main supply line.

FIG. 3 represents the block diagram of the circuit for connecting this antenna 1.3 to its main line 7, represented in the form of a quadrupole. An impedance matching circuit 8 is therefore provided between the antenna 1.3 and this main line 7, to remedy the mismatch in impedance of this antenna.

A priori, the dimensions of the slot 3 and of the associated cavity 1 can be any, provided that they are much smaller than those which correspond to the resonance condition. However, the layout of the radiation diagrams of this antenna for various frequencies included in the VHF-UHF range shows that there are frequencies for which this diagram presents a dip in the axial direction of the radiation, and a preponderant lobe on both sides. other of it, about 40 to 60 degrees.

Such a characteristic is particularly advantageous in the case of antennas on board a satellite, because it then coincides with the optimal radiation pattern, so that ultimately it will sometimes be wise to choose a slot length which provides, for the frequency or frequencies VHF or UHF used, a diagram of this type, that is to say having a hollow for the direction of axial radiation, this hollow defining two lateral lobes on either side at about 40 to 60 degrees.

There is no simple calculation method for determining optimal dimensions satisfying this condition, but these can be easily optimized by laboratory tests and measurements.

The basic device which has just been described is, of course, not the only one that can be envisaged, and FIGS. 4 to 12 which will now be described illustrate some alternative embodiments of this antenna among many others.

The embodiment according to FIG. 4 differs from that according to FIG. 1 by the fact that the single slot 3 is replaced by a network of five parallel and identical slots 3A to 3E, which makes it possible to obtain an antenna with better gain and better management of the radiation pattern.

• . une première paire de fentes identiques 3G,3H;
• . une seconde paire de fentes identiques 3I,3J; et
• . une troisième paire de fentes identiques 3K,3L.

The antenna according to FIG. 5 has seven parallel slots, including a central slot 3F which is the longest of all and, arranged symmetrically on either side thereof, three pairs of slots of decreasing length as as we move away from this central slot 3F:

• . a first pair of identical 3G, 3H slots;
• . a second pair of identical slots 3I, 3J; and
• . a third pair of identical slots 3K, 3L.

An antenna of this type can be used either to obtain a distribution law corresponding to a well determined diagram, or to radiate on four determined frequencies with a single and same impedance matching circuit.

According to FIG. 6, a multi-slot antenna can comprise, for example to obtain a determined radiation diagram, several parallel slots 3M, 3N, 3P, 3Q, which are offset with respect to each other in the lateral direction, i.e. in the direction orthogonal to probe 4.

The antennas described so far are made to radiate a linear polarization. It is also possible, according to Figures 7 to 10 for example, to carry out an antenna according to the invention and intended to radiate a circular polarization.

According to FIG. 7, the cavity is perforated with two identical slots 3R, 3S which are orthogonal to one another and arranged in a Greek cross, the center of which coincides with that of the square surface 2.

The slot 3R is supplied by a probe 4A which is orthogonal thereto, while the slot 3S is similarly supplied by another probe 4B. The two probes 4A, 4B are therefore orthogonal. So that the wave radiated by the cross slit 3R, 3S is of circular polarization, these two probes 4A, 4B are supplied by waves of the same frequency and in phase quadrature.

Note that disturbances are to be feared due to the collinearities of the probe 4A and of the slot 3S on the one hand, as well as of the probe 4B and of the slot 3R on the other hand.

• . selon Figure 8, les sondes 4A et 4B précitées sont décalées d'un angle a par rapport à la normale à la fente, respectivement 3R et 3S, qu'elles alimentent. Par exemple, cet angle a est de l'ordre de 45 degrés.
• . Selon Figure 9, les sondes d'alimentation 4A et 4B sont décalées latéralement par rapport au point milieu de la fente, 3R et 3S respectivement, qu'elles alimentent et à laquelle elles sont respectivement orthogonales.
• . Enfin, selon Figure 10, l'optimum est atteint pour éviter toute interférence par le fait qu'en outre, par rapport à la figure 9, les fentes 3R et 3S sont elles aussi décalées l'une par rapport à l'autre de manière à ne plus être sécantes, bien que restant orthogonales.

To avoid these disturbances, several variants of the antenna according to Figure 7 are possible:

• . according to Figure 8, the aforementioned probes 4A and 4B are offset by an angle a relative to the normal to the slot, respectively 3R and 3S, which they supply. For example, this angle a is of the order of 45 degrees.
• . According to Figure 9, the supply probes 4A and 4B are offset laterally relative to the midpoint of the slot, 3R and 3S respectively, which they supply and to which they are respectively orthogonal.
• . Finally, according to Figure 10, the optimum is reached to avoid any interference by the fact that in addition, compared to Figure 9, the slots 3R and 3S are also offset relative to each other so to no longer be intersecting, although remaining orthogonal.

FIG. 11 shows another variant of this antenna, which comprises two orthogonal supply probes 4A, 4B each supplying a network 3T, 3U of parallel and all identical slots. We thus obtain a bi-polarization and multi-slot antenna.

Finally, FIG. 12 shows a variant of this antenna with two polarizations and two networks 3T, 3U of slots, for which the slots of the 3T network are significantly shorter than those of the 3U network. Such an antenna is desirable in the case of an antenna intended to radiate two waves of very different frequencies and with orthogonal polarizations.

It goes without saying that the invention is in no way limited to the exemplary embodiments which have just been described. Thus, for example, it is possible to further miniaturize this elementary antenna by completely or partially filling the cavity 1 with a dielectric material, such as Alumina for example. The section of this cavity can of course be circular, or other, instead of rectangular.

Claims (12)

Miniaturized elementary radio antenna, in particular for VHF and UHF waves, characterized: . in that it consists of one or more radiating slots (3) of dimensions much smaller than those of the normally resonant slots for the operating frequency or frequencies of this antenna, and therefore operating well below resonance, this or these slots (3) being formed on one of the two large faces (2) of a cavity (1), this cavity also being of dimensions much smaller than that of a resonant cavity for this or these operating frequencies; and . in that its access (es) (5) is or are each coupled to the corresponding line (7) through at least one circuit (8) for impedance matching. Radio antenna according to claim 1, characterized in that it comprises several parallel slots (3A to 3E). Radio antenna according to claim 2, characterized in that the parallel slots (3F to 3L) are of selected lengths, in order to produce, for example, an antenna operating at several determined frequencies, but with a single adaptation circuit (8) impedances. Antenna according to one of claims 2 or 3, characterized in that these parallel slots (3M, 3N, 3P, 3Q) are offset from one another. Antenna according to claim 1, this antenna being able to radiate a circular polarization, characterized in that it comprises two identical slots (3R, 3S) arranged in Greek cross. Antenna according to claim 5, characterized in that the respective feeds (4A, 4B) of these two slots (3R, 3S) are angularly offset with respect to normal to the slot (3R, 3S) which they supply respectively. Antenna according to claim 6, characterized in that this angular offset (a) is of the order of 45 degrees. Antenna according to claim 5, characterized in that the respective supplies (4A, 4B) of these two slots (3R, 3S) are offset laterally with respect to the midpoint of the slot (3R, 3S) which they supply respectively. Antenna according to claim 1, this antenna being able to radiate a circular polarization, characterized in that it comprises two identical 3R, 3S slots, orthogonal, and non-intersecting. Antenna according to claim 1, this antenna being with orthogonal polarizations, characterized in that it comprises a network of parallel slots (3U, 3T) by polarization. Antenna according to one of claims 1 to 10, characterized in that its cavity (1) is completely or partially filled with a dielectric material. Antenna according to one of claims 1 to 11, characterized in that the dimensions of the slot (s) (3) are chosen to obtain a radiation diagram having a hollow for the direction of axial radiation, this hollow defining two lateral lobes to about 40 to 60 degrees on either side of this axial direction.

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