Horn for Ka dual-band circularly polarized satellite antenna

Abstract

An antenna horn includes a waveguide having an open end and an end allowing access to transmitted signals, the widest opposite walls constituting a first pair of walls, two first ridges inside the waveguide, in the middle and over the whole length of the walls of the first pair of walls, a flat central wall connecting the walls of the second pair of walls at their midpoints at the level of the accesses, stopping in the direction of the open end so as to polarize signals transmitted by the two accesses according to orthogonal circular polarizations, and forming two ridges in the middle of the walls of the second pair of walls from the side of the open end, and with an antenna, an item of radio communication equipment and a method using the horn.

Claims

1. An antenna horn, comprising: a waveguide extending along a longitudinal axis, the waveguide having an open end and an end allowing access to signals transmitted in the waveguide, the widest opposite walls of the waveguide constituting a first pair of walls of the waveguide and the other two walls of the waveguide constituting a second pair of walls of the waveguide, the antenna horn comprising: two first ridges extending along the longitudinal axis inside the waveguide, in the middle and over the whole length of each of the walls of the first pair of walls, a flat central wall extending in the waveguide along the longitudinal axis, the central wall being configured so as, at the end allowing access to the signals transmitted in the waveguide, to connect the two walls of the second pair of walls at their midpoints, thus forming two separate accesses to said signals, and at the open end of the waveguide to stop so as to polarize signals transmitted by the two accesses according to orthogonal circular polarizations, the central wall forming two second ridges extending along the longitudinal axis in the middle of each of the walls of the second pair of walls from the open end of the waveguide.

2. The antenna horn according to claim 1, wherein the waveguide has a square cross section, either two opposite walls of the waveguide constituting the first pair of walls and the other two opposite walls of the waveguide forming the second pair of walls.

3. The antenna horn according to claim 1, wherein the waveguide, the first pair of ridges and the second pair of ridges have dimensions adapted for the propagation of electromagnetic waves according to the modes of propagation TE10 and TE01 in the frequency band of the transmitted signals, and wherein the two accesses have dimensions adapted for the propagation of electromagnetic waves according to the mode of propagation TE10.

4. The antenna horn according to claim 1, moreover comprising a layer of dielectric material positioned so as to cover the open end of the waveguide and configured to perform the matching between propagation inside the waveguide and propagation in free space.

5. The antenna horn according to claim 1, wherein the first and second ridges extend outside the waveguide through its open end while having a flared shape outside the waveguide.

6. The antenna horn according to claim 1, wherein the two first ridges have identical heights and widths and wherein the two second ridges have identical heights and widths.

7. The antenna horn according to claim 1, wherein one of the accesses formed by the central wall and the waveguide is used to inject a first signal at a first frequency, and wherein the other access is used to extract a signal at a second frequency, which is different from the first frequency, the first frequency and the second frequency belonging to the Ka band of the electromagnetic spectrum.

8. The antenna horn according to claim 1, wherein the waveguide has a cross section with sides having a size less than λ/2, where λ is the wavelength of the signals to be transmitted.

9. An antenna comprising at least one antenna horn according to claim 1.

10. An antenna comprising a network of at least two antenna horns according to claim 1, which are arranged in a mesh of regular pitch, wherein the first and second ridges extend outside the waveguides through their open ends while having a flared shape, the adjacent antenna horns being connected by the end of one of their ridges outside the waveguides.

11. A radio communication equipment comprising an antenna according to claim 9.

12. A telecommunication method, between two stations, the method comprising the use of an item of radio communication equipment according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood, and other features, details and advantages will become more apparent, on reading the description that follows, which is provided without limitation, and by virtue of the appended figures that follow, which are provided by way of example.

(2) FIG. 1a shows an antenna horn based on the prior art that simultaneously polarizes the signal and radiates it in a mesh of reduced dimensions.

(3) FIG. 1b shows an exploded view of the various elements from FIG. 1a.

(4) FIG. 2a shows an antenna horn according to a first embodiment of the invention, in a three-quarter rear view.

(5) FIG. 2b shows the antenna horn from FIG. 2a in a three-quarter front view.

(6) FIG. 2c shows the antenna horn from FIGS. 2a and 2b in a three-quarter front sectional view along a vertical plane situated in the middle of the horn.

(7) FIG. 2d shows the antenna horn from FIGS. 2a and 2b in a three-quarter front sectional view along a horizontal plane situated in the middle of the horn.

(8) FIG. 3 shows another embodiment of an antenna horn according to the invention, in a three-quarter front view.

(9) FIG. 4 shows a network of antenna horns according to an embodiment of the invention.

(10) Identical references are used in various figures when the denoted elements are identical.

DETAILED DESCRIPTION

(11) FIG. 2a shows an antenna horn according to a first embodiment of the invention, in a three-quarter rear view.

(12) The antenna horn 200 according to the invention comprises a waveguide 201, of rectangular section, which extends along a longitudinal axis zz′. The waveguide 201 is open through an end at the front, which is the end through which the horn radiates. The other end of the waveguide 201 has accesses 202 and 203 through which the signals transmitted by the horn are injected/extracted.

(13) The two widest opposite walls 204 and 204′ of the waveguide constitute a first pair of walls. The other two opposite walls 205 and 205′ constitute a second pair of walls. When the waveguide has a square section, which is a characteristic rectangle, the first pair of walls may be constituted by the opposite walls 204 and 204′ or the opposite walls 205 and 205′ equally.

(14) The antenna horn according to the invention comprises two ridges 206 and 206′, which are situated inside the waveguide and form a protuberance in the middle and over the whole length of each of the walls of the first pair of walls 204 and 204′. The two ridges 206 and 206′ are of identical width and height.

(15) Finally, the antenna horn according to the invention comprises a flat central wall that extends along the longitudinal axis zz′. From the accesses, the central wall 207 connects the middles of the walls of the second pair of walls 205 and 205′. It also forms two independent accesses 202 and 203 with the waveguide 201. These accesses each form a waveguide of rectangular section, of width a and of height b.

(16) As a result of the ridges 206 and 206′, each of the accesses 202 and 203 forms a ridged waveguide whose electrical dimension is reduced in relation to the wavelength, which makes the antenna horn compact. The choice in particular of the width a, of the height and of the width of the ridges 206 and 206′ determines the propagation of electromagnetic waves in the waveguides 202 and 203, according to rules that are known to persons skilled in the art, as described for example in the article W. J. R. Hoefer and M. N. Burton, “Analytical Expressions for the Parameters of Finned and Ridged Waveguides,” 1982 IEEE MTT-S International Microwave Symposium Digest, Dallas, Tex., USA, 1982, pp. 311-313.

(17) The dimensions of the accesses 202 and 203 are chosen to allow the propagation of electromagnetic waves according to the fundamental mode of propagation TE10 in the frequency band of interest. Advantageously, in the case of an antenna for a satellite link, the frequency band of interest is the Ka band. In particular, the accesses may be adapted for propagation in the frequency band 17.3-31 GHz, which covers the transmission and reception bands for satellite transmissions in Ka band. In a particular instance of application, one of the accesses can be used to inject a signal to be transmitted into the horn and the other access can be used to recover a signal received by the horn, the two signals being transmitted at the same frequency or at different frequencies in the same frequency band.

(18) The ridged waveguides involve no additional losses compared with conventional waveguides. The format of the waveguide 201 is directly linked to the format of the two accesses 202 and 203, as the distance between its walls 205 and 205′ is equal to the width a of the accesses 202 and 203. The internal height of the waveguide 201 is twice the height b of the waveguides 202 and 203, plus the thickness of the central wall 207. This wall will therefore advantageously be chosen to be small in view of b. Typically, commercial waveguides have a ratio of height b to width a of ½, but the antenna horn according to the invention can be implemented whatever the ratio a/b.

(19) FIG. 2b shows the antenna horn from FIG. 2a in a three-quarter front view, that is to say from side of the opening of the waveguide 201. It depicts the ridges 206 and 206′, which in fact extend all along the walls 204 and 204′ of the waveguide along the longitudinal axis. It can also be seen that the central wall ends in the form of two ridges 208 and 208′ that form a protuberance in the middle of each of the walls of the second pair of walls 205 and 205′ at the level of the open end of the waveguide. The two ridges 208 and 208′ are of identical width and height.

(20) In this embodiment the ridges 206, 206′, 208 and 208′ extend outside the waveguide 201, where they take on a flared shape so as to perform the matching between guided propagation inside the waveguide 201 and propagation in free space. An elliptical shape is used in the illustrations, but any shape allowing a progressive change of dimensions to be produced between the inside and the outside of the horn is suitable. In particular a stepped progressive flaring can allow fine matching in the two frequency bands.

(21) In the example in FIG. 2b, the ridges form a semicircle and overlap on the outside of the waveguide 201. This manifestation is advantageous for the networking of antenna horns, but the shaded part of the ridges is not essential for implementing an elementary horn according to the invention.

(22) FIG. 2c shows the antenna horn from FIGS. 2a and 2b in a three-quarter front sectional view along a vertical plane situated in the middle of the horn. It depicts the waveguide 201 and the ridge 206′. At the back of the antenna horn, at the end used to access the signals, the central wall 207 connects the two walls 205 and 205′ of the waveguide in continuous fashion at their midpoints. At the front of the antenna horn, at the open end through which the horn radiates, the central wall forms the two ridges 208 and 208′. Between the two, the central wall is interrupted in the direction of the open part of the waveguide 201, so as to form a septum polarizer allowing the signals transmitted in the two accesses 202 and 203 to be polarized in orthogonal circular polarizations. In particular, the polarization function is performed by designing the central wall so that it transfers part of the energy from the vertical mode to the horizontal mode while applying a delay equal to λ.sub.g/4 between these two modes, where λ.sub.g is the guided wavelength of the frequency band of interest taking into account the presence of the ridges. Such a result can be obtained by using a central wall, interrupted at its centre, that has a plurality of teeth, such as the teeth 209 and 209′ in FIG. 2c.

(23) The dimensions of the waveguide 201 are chosen so that it is adapted for the propagation of electromagnetic waves according to the modes of propagation TE10 and TE01 in the frequency band of interest at the level of its open end, specifically in reduced dimensions on account of the ridges arranged on each of its walls. Thus, the first ridges 206 and 206′ positioned against the first pair of walls of the waveguide and the second ridges 208 and 208′ positioned against the second pair of walls of the waveguide are not necessarily of identical height and width, the first ridges being sized on the basis of the width a of the walls 204 and 204′ for the mode of propagation TE10, the second ridges being sized on the basis of the width of the walls 205 and 205′, which is equal to 2b plus the height of the central wall 207, for the mode of propagation TE01. The height of the central wall 207 is therefore linked to the width of the ridges allowing propagation according to the TE01 mode in the waveguide 201.

(24) The central wall therefore plays a triple role: it allows the accesses 202 and 203 to be delimited, the circular polarization function to be performed by forming a quarter-wave septum, and the propagation of circularly polarized waves in a waveguide of reduced dimensions to be made possible on account of its ends 208 and 208′.

(25) FIG. 2d shows the antenna horn from FIGS. 2a and 2b in a three-quarter front sectional view along a horizontal plane situated in the middle of the horn. It can be seen in particular that the ridges 206 and 206′ form protuberances positioned along and in the middle of opposite walls 204 and 204′ of the waveguide 201.

(26) According to one embodiment of the invention, the waveguide 201 is of square section. In this case, the walls to which the ridges 206 and 206′ are attached can be chosen to be the opposite horizontal walls 204 and 204′ or the opposite vertical walls 205 and 205′ equally. In the second case, this entails the central wall 207 extending vertically along the longitudinal axis zz′, so as to connect the middles of the walls 204 and 204′ at the level of the accesses.

(27) By choosing the waveguide 201 to be of square section, the ridges 206 and 206′ of the horizontal walls and the ridges 208 and 208′ of the vertical walls can have the same heights and widths. In this case, the ellipticity rate of the transmitted signals is optimum and the circular polarization is very pure.

(28) The waveguide 201 can be chosen to have a non-square rectangular section so as for example to have standard-format accesses 202 and 203 with a ratio a/b equal to ½, or for a mesh of restricted size so as to meet requirements concerning the maximum scanning angle and the maximum operating frequency.

(29) The waveguide according to the invention allows transmission and reception to be performed simultaneously, for example in the Ka band for satellite communications, using a single antenna horn of reduced dimensions, thus satisfying a need to reduce the mesh pitch of networks of horns in scanning antennas. It has numerous advantages compared with the prior art: it is very compact, due to the use of ridged waveguides, it comprises no dielectric elements, which makes it simple to assemble, inexpensive to manufacture, and allows it to have homogeneous performance over time and during temperature variations; it has no losses linked to the use of dielectric materials, which allows a maximum antenna gain to be obtained; the dimensions of the antenna horn or of the operating frequency band are very easily adjustable since they are linked to the size of the ridges situated in the waveguide. It is therefore compatible with the continual need to increase the operating frequency; it can be integrated into a mesh of smaller size than the antenna horns of the prior art, in particular a mesh having a pitch size less than λ/2, and therefore allows wider-angle scanning antennas to be manufactured; it is totally metal and can be manufactured by machining or by additive manufacture (3D printing). The latter method of manufacture allows antenna horns or networks of horns to be produced rapidly and inexpensively, using simple three-dimensional modelling; the ends of the ridges 206, 206′, 208 and 208′ situated outside the waveguide 201 allow certain adverse effects to be prevented during heightened scanning: a drop in gain (scan loss), blind spot (loss of the beam), depolarization (effects usually promoted by the presence of a dielectric).

(30) FIG. 3 shows another embodiment of an antenna horn according to the invention, in three-quarter front view. This embodiment differs from the one shown in FIGS. 2a to 2d in that the ridges 206, 206′, 208 and 208′ do not extend outside the waveguide 201. In this embodiment, a dielectric layer such as the layer 115 needs to be added to the open end of the antenna horn 300 in order to perform the matching between guided propagation inside the horn and propagation in free space.

(31) This embodiment has the defect of requiring a layer of dielectric material to be assembled with the metal part of the horn. However, the layer of dielectric 115 is deposited over the opening of the waveguide 201. It is then simple to assemble and can be adjusted in one piece for all of the horns of a network of horn antennas according to the invention, thus limiting the costs of manufacture.

(32) FIG. 4 shows a network of antenna horns according to an embodiment of the invention, implementing elementary antenna horns such as the one described in FIGS. 2a to 2d.

(33) The network 400 has a mesh of pitch α along one dimension and of pitch β along the other dimension, corresponding exactly to the outer dimensions of the waveguide 201. Each antenna horn then totally fits the space assigned to it, which is optimal in regard to occupation.

(34) In the embodiment in FIG. 4, the adjacent ridges of adjacent horns, such as the ridges 401 and 402, are connected so as to form just a single continuous ridge. The absence of discontinuities allows, among other things, a reduction in the radar cross section (RCS) of the network antenna.

(35) The invention is therefore concerned with a compact antenna horn that can be integrated into a network of elementary antennas. The horn is described in relation to the instance of application represented by satellite communications in the Ka band, but could be used for any type of communications in a given frequency band involving the transmission of two circularly polarized signals.

(36) The invention is also concerned with an item of radio communication equipment comprising an antenna horn or a network of antenna horns according to the invention. The radio communication equipment may be installed on a terrestrial or aerial vehicle, for example.

(37) Finally, the invention is concerned with a telecommunication method, in particular a satellite telecommunication method, between two items of radio communication equipment according to the invention. The method comprises the transmission and/or reception of signals using an antenna horn or a network of antenna horns according to the invention.