FR2545280A1 - Radiating element or receiver of orthogonally polarised microwave signals and flat antenna comprising an array of such elements juxtaposed - Google Patents

Abstract

Radiating element or receiver of orthogonally polarised microwave signals, this element comprising, on either side of a first layer with a first recess, first and second perpendicular microwave transmission lines and on the other side of the transmission lines, a second layer with a second recess and a third layer with a third recess situated opposite the other two but short-circuited so as to constitute a reflector plane, the transmission lines consisting of symmetric splines and conducting strips 21 and 31 carried in the middle plane of these lines and whose ends penetrate inside the recesses to constitute exciter probes 24 and 34 whose lengths differ and are chosen so that, for an arbitrary specified thickness of the first layer, the pairs of values end lengths of a probe/distance from the probe to the single reflector plane correspond to an experimentally maximum or almost maximum coupling between each of the probes and the propagation medium. Application: microwave transmission or reception antennas.

Description

1 -

  RADIANT ELEMENT OR RECEIVER OF POLAR- MICROWAVE SIGNALS

  ORTHOGONAL SATIONS AND FLAT ANTENNA INCLUDING A NETWORK OF SUCH

Juxtaposed elements

  The present invention relates to an element for receiving microwave signals with orthogonal polarizations or, according to the principle of reciprocity of antennas, a radiating element of such

  signals carried out in a similar manner, this element comprising respec-

  tively, on either side of a first layer in which is provided a first recess, the first and second lines of

  microwave transmission arranged along two perpendicular axes

  laires, and also comprising, on the other side of one of the

  transmission genes, a second layer with a second recess

  located opposite the first and, on the other side of the other li-

  transmission gene, a third layer with a third recess

  located opposite the other two but short-circuited at a distance

  tance of this other transmission line less than the thickness of this third layer so as to constitute a reflective plane, the first and second transmission lines being constituted on the one hand by grooves produced symmetrically in the adjacent layers and on the other hand of conductive tapes carried in the median plane of these lines and the ends of which penetrate along

  said axes inside the recesses to constitute sound-

  exciters achieving with the propagation medium a

  range which allows the reception or the radiation of said microwave signals.

  The invention also relates to a flat antenna comprising

  taking a network of such juxtaposed elements, and finds in particular

  an application in the field of reception of tear signals

  12 gigahertz revision retransmitted via satellite

  lites It goes without saying that given the reciprocity of an antenna, a receiving element (or an antenna composed of a network of receiving elements) is capable of functioning as a radiating element (as a radiating antenna) without no modification -2-

  of its characteristics This remark remains valid without exception

  tion throughout the following description, and the words re-

  reception, reception, receiver can always be replaced by

  the words emission, emit, radiating.

  Such an element and a flat microwave antenna include

  taking a whole network of these elements have been described in two French patent applications NO 81 08 780 and 82 82 252, filed by the plaintiff on May 4, 1981 and March 12, 1982 respectively and not yet published When these elements or networks elements are called to receive signals only on one side of the plane they define, it is planned to increase their gain by placing on the side opposite to that of reception a metal reflector parallel to this plane and located at a distance from this = this equal to a quarter of the wavelength of the signals useful to receive. The waves thus reflected reinforce the waves already received directly.

  In the first of the requests which have just been

  tees, two independent triplate lines constitute two separate supply networks occupying the same median plane of the antenna, and the action of the reflector placed on one side of the antenna is therefore as identical as possible with vis each of these two networks; the structure thus proposed is however relatively complex and delicate to carry out, precisely taking into account the density of the supply lines of these two distinct networks as soon as the number of receiver elements making up the antenna is high enough. In the second of these requests, the establishment of

  first and second supply networks in two planes at the same time

  milking completely separate and quite distant from each other solves the problem of line density mentioned above, but in return, with this arrangement, the action of the reflector, also placed on one side of the antenna, is only optimal

  for only one of these two networks.

  The object of the invention is to propose a receiving element.

  tor and an antenna (composed of a network of such elements) in which the action of the reflector is optimized vis-à-vis

  of either of the two supply networks.

  To this end, the invention relates to a receiver element,

  or radiant, as defined above in the introduction and character-

  laughed in that the lengths of these ends constituting said excitation probes are distinct and chosen so that, for

  any given thickness of the first layer, the

  ples of values length of end of a probe-distance from

  probe in the reflective plane correspond to an experimental coupling

  slightly maximum or close to this maximum between each of said

  probes and the propagation medium contained in the recesses.

  The structure thus proposed allows a meticulous realization

  very simple, while allowing the planes in which the two excitation probes are located to be fairly widely spaced, which in particular allows the placement, in the layers,

  grooves forming with the conductors the lines of trans-

  mission (this guidance in the air then makes it possible to use a dielect,

  ordinary quality stick from the point of view of its hy-

  frequencies, without its losses becoming annoying).

  The invention relates, on the other hand, to a flat microwave antenna composed of a whole network of such elements and produced with similar characteristics.

  and advantages of the element and the antenna thus concerned appear

  will now be explained more precisely in the description which

  follows and in the accompanying drawings, given by way of non-limiting example

  mitative and in which: Figure 1 shows an embodiment of the receiving element according to the invention;

  Figure 2 shows an arrangement of the exci-

  to obtain a high gain for the receiving element

  guardian; Figure 3 is a partial sectional view along the axis AA of Figure 1 and highlights the arrangement of

  transmission lines according to the so-called suspended substrate structure.

  This element has the following structure: on the one hand and

  on the other, a first layer 10, in which a pre-

  mier recess 11 (in this example, circular) of internal surface

  metallized, a first transmission line and a second transmission line 30 are provided, consisting of conductive strips 21 and 31 carried in the median plane of grooves 22 and 32 by a thin dielectric sheet 23 and 33 providing mechanical support for the conductors L ' end of the central conductors of

  these suspended ribbon microwave transmission lines referenced

  metered 24 and 34 penetrates along two axes perpendicular to the

  térieur of the recesses, thus constituting two excitation probes which carry out with the propagation medium a coupling allowing the reception of the microwave signals; these two ends have

  a penetration length opposite the recess which is

  tincture, as specified below The other end of each

  line constitutes its output, in the case of reception.

  On the other side of the line 20 is provided a second layer 40 also comprising a second recess 41 of metallized interior surface located opposite the first recess 11, and, similarly, on the other side of the line 30 is provided a third

  layer 50 with a third recess 51 of inner interior surface

  tallized located opposite the other two This recess 51 is short-circuited in a plane parallel to the faces of the layers, at a distance from the line 30 of course less than the thickness of the layer 50, so as to constitute a single reflecting plane for the microwave signals received The element thus described behaves like a waveguide-line transition with a substrate suspended in

  which the axis of the guide is perpendicular to the plane of the lines.

  The first, second and third layers 10, 40 and 50

  may be metallic, or else made of a dielectric material

  stick with metallization of the walls of the recesses 11, 41 and 51 which pass through them respectively Furthermore, the diameter of the recesses must be both sufficiently small, compared to

  the wavelength associated with the frequency of the microwave signals

  quences, to avoid the appearance or to attenuate the propagation of the undesirable higher modes and sufficiently high to authorize -5-

  the propagation of the main mode in the bandwidth considered.

  Finally the recess 41 ends with a truncated flare

  pic 61 possibly covered with a polyurethane-type screen, these provisions helping to increase gain and improve

radiation characteristics.

  Tests performed with a receiving element having the

  structure which has just been described led to study the

  influence, on the performance obtained, of the end length of lines 20 and 30 actually located opposite the recesses

  11, 41, 51 aligned These experimental measurements, carrying essentially

  tially on the coupling between these ends of lines 20 and 30 and the propagation medium, that is to say the cavity formed by all of the aligned recesses, have led to an optimization

  of this coupling when said two ends, or probes excite-

  trices, have a different length More precisely, for a determined length of one of the excitation probes, we search for the distance from this probe to the single reflective plane (constituted by the bottom of the layer 50) which provides a satisfactory and if possible maximum adaptation in the frequency band concerned (here substantially from 11.7 to 12.5 gigahertz); Figure 2 shows a

  example of arrangement of the two probes of different lengths.

  We can thus have connections between the long-

  probe probes and the distance to the reflector, giving the best

  their possible adaptations The distance between the probes then being fixed by the thickness of the layer 10 (chosen according to the electromechanical requirements imposed: mechanical production of the layer, placement on the one hand in layers 10 and 40 and on the other part in the layers 10 and 50 of the grooves of the transmission lines 20 and 30,) we look in such correspondence tables for two length values for which the associated values of distance to the single reflective plane different from this

  value of the thickness of the layer 10.

  In the context of tests carried out with receiving elements

  square tors with rounded tops, it was possible to obtain at the end of the transmission line whose end of the conductor -6-

  central constitutes the excitation probe a station wave rate

  less than 1.6 (which corresponds to trans-

  mission less than 0.25 d B) under the following conditions: side of the square equal to 0.31 g or here 15 millimeters (the wavelength Xg being that in the guide part of the receiving element) and radius of curvature rounded tops equal to 3 millimeters; probe distance from line 20 reflecting plane: 0.27 Àg; probe distance from line 30 reflecting plane: 0.17 Xg; end length of the probe of line 20 protruding into the recess: 0.12 Xg; end length of the probe of line 30 protruding into the recess: 0.10 Xg; vertical distance between these two probes: 0.10 g (i.e., at 12 gigahertz, 5 millimeters, which is sufficient for the

  establishment, by machining, of the splines of the transmission lines

sion 20 and 30).

  These values, corresponding to the example of square elements

  with rounded tops as specified, are valid for an impe-

  line dance of approximately 70 ohms, corresponding to a width of the central conductors of 1.4 millimeters, in grooves of

dimensions 2.5 x 1.8 millimeters.

  For the installation of lines 20 and 30 between the

  ches 10 and 40 on the one hand, 10 and 50 on the other hand, note that the

  grooves mentioned above, generally rectangular in shape

  ral, are known for example from FIG. 4 of the patent of the United States of America NO 3,587,110 issued on June 22, 1971 in the name of the company RCA Corporation, a figure whose principle is repeated in FIG. 3 of the present application (we can also refer to the article "Careful MIC design prevents waveguide modes", published in the review Microwaves, May 1977, p 188 and following, figure 1) We will also note that at the end of these lines 20 and 30, to allow the reconstruction of the signals with right circular polarization and with left circular polarization, a 3 d B hybrid coupler can be provided, with its two inputs connected respectively to the outputs of lines 20 and 30 and its two outputs providing said signals to right or left circular polarization We can also, instead of

  coupler, provide a depolarizing structure in front of the element

  finally, without a coupler or depolarizing structure,

  holds signals having two linear polarizations perpendicular to

  laires. Of course, the present invention is not limited to the receiving or radiating element described above, from which variants can moreover be proposed without departing from the scope of the invention In particular, the 'invention

  also relates to a planar microwave antenna which is

  laid of a whole network of such receiving elements, the conditions seen above and relating to the diameter of the recesses being

  then supplemented by the fact that, for a placement of the elements

  satisfactorily next to each other, this diameter must be small enough (compared to the wavelength in vacuum associated with the frequency of microwave signals) so that the distance between the elements can be less than

  said wavelength It is indeed only at this latter con-

  the avoidance of unwanted side lobes

rables, called lobes of the network.

  The structure of this radiating or receiving antenna

  is quite similar to that of the radiating or receiving element

  and everything that has been said above about this can

  be transposed as is in the case of the antenna, except as regards

  identifies the transmission lines Indeed, the antenna no longer comprises only two transmission lines leading from the receiving element to two output connections but, more precisely,

  two networks of microwave, electric-

  ment independent like lines 20 and 30 and intended, like them, to ensure the transmission of the microwave signals received towards the electronic circuits external to the antenna In this case, it is now at the output of these two networks that can be -8 -

  provided with a 3 d B hybrid coupler (or, instead of the coupler, a struc-

  depolarizing ture in front of the whole antenna) for the

  signal titration with left and right circular polarization.

  These networks are each composed, in a manner well known in numerous embodiments (see in particular the network structure represented in FIG. 1 of French patent application No. 7011449), of a succession of combination stages If the antenna

  includes N receiving elements, the N first ends of each

  that network serve, as already described for a single receiving element

  on coupling with the propagation space of the signals to be received

  see, while the opposite single end of each of the two re-

  buckets, point of convergence of all transmission lines to

  through the successive combination stages, is connected to the circuits

  electronic receiving circuits outside the antenna (and, for example, first of all at one of the two inputs of the

  coupler 3 d B which allows the reconstruction of the polarized signals

  right and left circular positions).

  An antenna made in this way is suitable for 8

  especially good at a low cost modular realization, in

  which of the elementary blocks forming subsets of elements

  Receiving elements can be used in an appropriate number and by joined assembly for the constitution of antennas of well-defined dimensions, gain and directivity diagram, either for example a symmetrical antenna of square shape, or more generally

  asymmetrical antennas, in particular of rectangular shape, pre-

  feeling different radiation patterns in two orthogonal planes This last characteristic is particularly interesting for the antennas for receiving television signals at 12 gigahertz retransmitted by satellites, since an opening at 3 d B less than 2 is in this case, essential

  that in the equatorial plane to separate the signals from two satel-

  "distant" lites, in this plan, of 3 (see the recommendations of

C.C I R, Geneva, 1977).

  Another modular type embodiment can also be advantageously proposed: if it is desired to have a planar antenna which should receive or transmit microwave signals only

  of a single type of polarization (linear, or circular in main-

  nant a depolarizing structure), said antenna can be obtained from that described above simply by omitting the central layer 10 and one of the two supply networks 20 or 30.

  Finally, it is clear that the application of the invention

  tion at the reception of 12 gigahertz television signals re-

  transmitted by satellites is not limiting, although the antenna described is in fact mainly intended for coupling with one or more reception heads of such signals (an example of these reception heads is described in particular in the review "Onde Electrique ", volume 62, no 3, March 1982, pages 39 and 40); on the one hand the invention is applicable to all kinds of purely terrestrial microwave transmission networks, and on the other hand the choice of an example of application at the frequency of 12 gigahertz

  is not exclusive of any other possible operating frequency-

  in the microwave range, linked to the application in

visaged.

-10-

Claims (2)

  1 Receiver element for microwave polarized signals   orthogonal or, according to the principle of reciprocity of antennas   nes, radiating element of such signals produced in a similar manner, this element comprising respectively, on either side of a first layer in which a first recess is provided,   first and second microwave transmission lines available   located along two perpendicular axes, and also comprising, on the other side of one of the transmission lines, a second layer with a second recess located opposite the first and, on the other side of the other transmission line , a third layer with a third recess located opposite the other two but short-circuited at a distance from this other transmission line   less than the thickness of this third layer so as to   tituer a reflective plane, the first and second transmission lines being constituted on the one hand by grooves produced symmetrically in the adjacent layers and on the other hand by conductive tapes carried in the median plane of these lines and whose ends penetrate along said axes inside the recesses to form excitation probes carrying out a coupling with the propagation medium which allows the reception or the radiation of said microwave signals, characterized in that the lengths of these ends constituting said excitation probes are distinct and chosen so that , for any given thickness of the first layer, the pairs of end length values of a probe - distance from the probe to the single reflective plane correspond to an experimentally maximum coupling or close to this maximum between each of said probes and the medium of propagation contained in recesses.   2 flat microwave antenna for reception, or   the emission of orthogonal polarization microwave signals   nales, characterized in that it is composed of a whole network of elements according to claim 1, juxtaposed and arranged so that this antenna comprises, on either side of a -11-   first layer in which are provided the first recesses   first and second networks of transmission lines   microwave ensuring through a suc-   transfer of combination stages the link, for each of the two   networks, between the receiving or radiating elements and a   corresponding single output nexion, and so that it   also includes, on the other side of one of these li-   transmission genes, a second layer o are provided with second recesses located opposite the first and, on the other side of the other network of transmission lines, a third layer o are provided with third recesses located in   look of the first and second but shorted to a dis-   tance of this other network of transmission lines less than the thickness of this third layer so as to constitute a plane   reflector inside each element, the diameter of the recesses   Furthermore, the elements being sufficiently small compared to the wavelength associated with the frequency of the microwave signals so that   the distance between the elements may be less than said length wave gueur.