DK141221B - ROTATION SYMMETRIC CASSEGRAIN ANTENNA - Google Patents

Description

OD PUBLICATION MANAGEMENT 141221 DENMARK (int.ci.3 h 01 q 19/18 in (21) Application No 5095/75 (22) filed on 12 Nov 1975 (23) Race day 12. HOV 1975 (44) The application presented and

the petition published on Feb. 4; I98O

DIRECTORATE OF

PATENT AND TRADE MARKET (30) Priority requested from it

25 dec. 1974, 2461283, DE

(71) SIEMENS SHARE COMPANY, Berlin and Munich, 8 Mienchen 2, Wittels = 'Uacherplatz 2, DE.

(72) Inventor: Wolfgang Rebhan, 8000 Muenchen 90, Schoenetraese 62, JE.

(74) Plenipotentiary in the proceedings:

International Patent Office.

(64) Cassegrain rotary symmetric antenna.

The invention relates to a Cassegrain rotationally symmetric antenna having two mutually independent rotational axes for elevation and azimuth, wherein the transmit / receive apparatus for the information signal is stationary in the antenna base, where the azimuth axis and the main reflector oscillation axis are located in one plane, and where the rotary wave is transmit / receive equipment is connected to the central reflector central feed opening, on the transmit / receive side, an antenna's azimuthal motion accommodates microwave rotating joints, and on the main reflector side an antenna's elevation motion accommodates 2-mirror arrangement which includes a first outside azimuthal axis but on a student axis but placed second in the intersection of the elevation and azimuthal axes and the mirror rotating about the former axis. Antennas of this kind are particularly suitable for conveying the radio connection to bodies flying in outer space, where, due to the weak signals received, it is necessary to have an antenna with a sharply defined beam of radiation and with a large antenna gain available. The antennas built according to Cassegrain's principles, which are analogous to those in optics, require, above all, in connection with the frequencies often used in satellite communication between 2 and 6 GHz, a considerable technical effort due to the size of the main reflector with diameters. of up to 30 meters and above, and the requirements are further increased by the fact that an antenna in general must be traceable, ie. be movable about two mutually independent rotational axes for elevation and azimuth.

As is clear from messages from Siemens AG * s Central Laboratory of Transmission Technology "Nachrichtentechnische Fachberichte", Vol. 32, 1967, pages 23-33, a variety of considerations have been provided concerning a suitable way of constructing the microwave feed arrangement which forms the connection between the transmitting / receiving apparatus and the main reflector of the antenna. A waveguide swivel for the feed horn is sufficient when the space in which the transmitter / receiver is located participates in the azimuthal motion of the antenna. The same literature (Fig. 10 with accompanying description) and German publication publication 1,541,611 also provide solutions for how the control room containing the transmitting / receiving apparatus can be placed stationary in the antenna base. In this case, as a microwave feed arrangement, a broken horn satellite is used, which is provided between the crack and the satellite reflector with a second swivel joint for recording the movement of the antenna around the elevation axis. This constructive solution does reduce the technical range, but brings about disadvantages as far as the electrical properties of the antenna are concerned. In particular, in this case, certain asymmetries in the cornea's radiation field must be included, which causes, among other things, an unwanted radiation of the primary radiation beyond the rim of the Cassegrain antenna's auxiliary reflector, and causes larger side loops in the antenna radiation diagram. In addition, the gain and efficiency of the Cassegrain antenna deteriorates.

In the journal "Frequenz", year 22, 1968, booklet 5, pages 151-156 and in "IEEE Transactions on Antennas and Propagations", November 1973, pages 884-886, another solution to the design of a Cassegrain antenna's microwave feeding arrangement is given by which transmitting / receiving apparatus may also be stationary in the antenna base. This microwave feeding arrangement here constitutes a 4-mirror microwave conductor arrangement. It consists of a stationary primary beam located along the azimuth axis, the radiation of which is directed through the central aperture of the main reflector and onto the auxiliary reflector via four mirrors, each making a 90 ° deflection. The function of the rotary joints necessary for the feed arrangement for the elevation and azimuth movements of the antenna is handled by the separately rotatable pairs of the primary beam and the first mirror as well as the third and fourth mirrors. The 4-mirror microwave conductor arrangement allows for the radiation field to be approximately rotationally symmetrical in an appropriate design of the primary radiator. However, practice has shown that the 4-mirror microwave conductor arrangement requires a very extensive adjustment of the four mirrors, inaccuracies in the alignment are summed up, so radiation distortions in terms of amplitude, phase and polarization can assume a considerable extent even with small adjustment errors. Above all, polarization errors in connection with so-called double frequency utilization (radiation or reception of two orthogonally polarized signals) must be extremely small. Even with precise adjustment, such a mirror system, due to its principle asymmetries, still causes certain radiation distortions which increase with the number of mirrors. The losses in such a system also increase with the number of mirrors, since in practice, the radiations of the mirrors cannot be completely avoided.

It is the object of the invention in connection with a rotationally symmetric Casse-grain antenna, where the transmitting-receiving apparatus is stationarily arranged in the antenna base, to provide another solution to the microwave feeding arrangement, which combines the advantages given by the known solutions without having the associated disadvantages.

This object is achieved according to the invention in that the microwave feeding arrangement comprises a symmetrical radiation field producing horn rays which are connected via a waveguide piece to the microwave rotary joint and by free radiation and without own waveguides irradiate the first mirror and that the microwave beam radiation and the the central reflector's central feed opening via the second mirror is also directed solely by free beam propagation without the intervention of its own waveguides. In this way, the first mirror directs the radiation in the direction of the elevation axis towards the second mirror, which in turn directs the radiation through the central reflector's central feed opening and onto the auxiliary reflector.

Of course, from the journal "Japan Telecommunications Review", April 1973, pages 101-110, there is already known a rotationally symmetric Cassegrain antenna which uses a 2-mirror instead of a swivel to record the antenna's movement around the elevation axis. In this known embodiment, the primary beam which radiates the first mirror of the 2-mirror microwave conductor is also stationary in the antenna base adjacent to the transmitter / receiver apparatus. , that is, in this case, the two axes are not located in the same plane. This detail results in an exceedingly complicated construction which, in practice due to the special demands made on the stability and to the maximum circulation speed of the antenna, can in practice only be realized in connection with small antennas having a low guard.

141221 4

In the solution provided according to the invention, namely the combination of a 2-mirror microwave conductor and a microwave rotary joint, a microwave feed arrangement for Cassegrain antennas of any size and with a stationary transmitting / receiving apparatus which are the known solutions described is realized in a not insignificant manner. Scope 2 - The microwave conductor arrangement according to the invention ensures an optimal antenna gain due to very small losses and due to poor adjustment work in connection with the two mirrors due to the symmetry of the radiation field thus obtained. It also allows the azimuth axis and the axis of rotation of the antenna to be placed in one plane, which is of decisive importance for a favorable mechanical construction of the antenna structure. The reduced space requirements for the feeding system due to the small number of mirrors and correspondingly small number of adjustment mechanisms also have a favorable effect on the mechanical construction of the antenna.

It is convenient to place the first mirror in the 2-mirror microwave conductor in the near field of the horn. In a preferred embodiment of the 2-mirror microwave conductor arrangement, the horn jet is designed as a wave horn and the first mirror is an ellipsoid mirror. The other mirror can be either curved or flat. The waveguide piece is hereby composed of a curved waveguide piece and a straight waveguide piece attached thereto.

In order to achieve as small a loss as possible within the 2-mirror microwave conductor arrangement, it is advantageous to extend the cross-section of the straight waveguide piece relative to such a waveguide cross-section where only the principal oscillation can propagate. The transitions to the curved waveguide piece and to the horn beam are hereby arranged so that the appearance of higher vibration types becomes as small as possible.

The invention is explained in more detail below with reference to the drawing, in which fig. Fig. 1 shows a rotationally symmetrical Cassegrain antenna of known type with two mutually independent rotational axes for elevation and azimuth, and the transmitting-receiving apparatus being stationary in the antenna base; 2 is a modification according to the invention of the embodiment of FIG. 1.

In the embodiment shown in FIG. 1, the main reflector is denoted by 1, the auxiliary reflector by 2, the auxiliary reflector stand by 3, the central reflector feed opening by 4, the microwave feed arrangement in the form of a broken home parabolic with a round horn cross section with 5, There is, with 6, the waveguide access for the broken horn parabola in the form of a curved waveguide piece of 7, the waveguide swivel of 8, a control room of 9 and the one in con. the spell space provided transmit-receiving apparatus with 10. The elevation axis and azimuth axis are denoted by E and A. respectively.

5 141221

By moving the antenna around the azimuthake A, the rotational movement of the cracked horn parabola 5 is compensated by the waveguide rotary joint 8 above the ceiling of the control room 9. The swivel 6 at the crack of the homing ball 5 located in the elevation axis E compensates for the antenna's movement around the elevation axis.

As already mentioned, the cracked horn parabola 5 gives rise to a wide asymmetry in the radiation field around the central food aperture 4, which is primarily due to the horn parabola being fed with the non-rotationally symmetric H 2 head oscillation from the round waveguide. The essentially symmetrical structure of the total structure, about the azimuth axis A, provided by placing the azimuth axis and the axis of symmetry in a common plane, is enabled by this known construction, in that the horn of the horn parabola 5 at the lower end opens into the longitudinal azimuth. waveguide swivel joint via the curved waveguide piece 7.

According to the invention, as shown in FIG. 2, the cracked horn parabola 5, which is the microwave feed arrangement, replaced by a 2-mirror microwave conductor arrangement. To the curved waveguide piece 7, which has a round cross-section, and at the end facing away from the microwave rotating link 8, is connected a straight waveguide piece 11 with a possible round cross-section, which opens into the horn radiator 12. The horn radiator 12 is a so-called wave hom, of the kind described in the journal "Microwaves", January 1973 on * pages 44-49. In such a wave horn, hybrid oscillation types are produced which result in a highly symmetric radiation field for such a horn. The curved waveguide piece 7 defines a radiation direction for the horn radiator 12 which differs from the azimuth axis A's direction. The horn radiator 12 irradiates, with its radiation field, the first mirror 13 in the 2-mirror microwave conductor, which may thereby have an ellipsoid contour.

The first mirror 13 deflects the radiation in the direction of the elevation axis E of the second mirror 14 located at the intersection of the elevation axis and the azimuth axis and which in the embodiment described herein may be a slightly curved convex reflector. The second mirror 14, in turn, deflects the radiation through the central feed opening 4 of the main reflector 1 and onto the auxiliary reflector 2, as the dotted lines indicate. Furthermore, as can be seen from FIG. 2, the main reflector in the region of the central feed opening is provided with a tubular nozzle 15, which thereby exerts a shielding function towards the radiation deflected in the direction of the auxiliary reflector 2 by the second mirror 14.

Conveniently, the ellipsoidal contour of the first mirror 13 is dimensioned such that one focal point of the ellipsoid lies in the phase center of the horn radiator 12. The second virtual focal point is placed such that, as the course of the radiation passage suggests, a slightly convergent beam bundle is obtained, thereby causing losses due to the irradiation of the second mirror 14, as a result of the iMtå

Claims (2)

6 U1221 high-degree rotationally symmetrical cross-field itself can be kept small, reduced even more. By using a beam bundle that converges in the direction from the reflector 13 towards the reflector 14, it is further possible to make the reflector 13 larger than the reflector 14. This not only can further reduce the radiation losses at the reflector 13, but there is further the constructively favorable the possibility of increasing the distance between the wave horn 12 and the reflector 13, thereby reducing the length of the connecting waveguide piece 11. In FIG. 2 is the second mirror 14 plane. However, if a slightly convergent beam bundle is to be radiated in the direction of the auxiliary reflector 2, the mirror 14 is assigned a suitably slightly concave shape. The straight waveguide piece 11 then, because of its length, causes undesirable losses when its cross-section is dimensioned so that only the principal oscillation of the waveguide can propagate therein. These losses can easily be substantially reduced by expanding its cross-section relative to the above-mentioned cross section. In this case, to avoid the appearance of higher vibration types as much as possible, its transitions to the curved waveguide piece 7 and to the horn radiator 12 must be adapted. The conditions of movement applicable to the one shown in FIG. 2 shows the 2-mirror. microwave conductor arrangement, similar to those applicable to the one shown in FIG. 1 The broken 2-mirror microwave conductor arrangement participates in the azimuth movement, while only the second mirror 14 participates in the elevation motion. The FIG. 2 in relation to the embodiment shown in FIG. 1 shows not only the advantage of radiation asymmetry, but also the substantial advantage that in FIG. 1, and due to its large diameter, relatively expensive HF swivel joints 6 can be avoided. As shown in FIG. 2, in the transmission path between the straight waveguide piece 11 and the curved waveguide piece 7, another fitting link 13 'is needed, if the antenna is to be used simultaneously for bearing purposes. 1. Rotationally symmetric Cassegrain antenna with two mutually independent rotational axes for elevation and azimuth, wherein the transmit / receive apparatus for the information signal is stationary in the antenna base, where the azimuth axis and the main reflector axis of rotation are located in one plane, and the microwave feed station transmitting, / receiving apparatus communicates with the central reflector central feed opening, on the transmit / receive side has an antenna azimuthal motion receiving microwave (8) and on the main reflector side an antenna elevation motion receiving 2-mirror arrangement which includes a first off azimuth axis but on elevation axis 13 and another in the eleva-