US3500418A - Satellite antenna array with electrically adjustable beam shaping - Google Patents

Description

March 10, 1970 HANS-DIETRICH KUHNE ETAL 3,500,418

1 SATELLITE ANTENNA ARRAY WITH ELECTRICALLY ADJUSTABLE BEAM SHAPING Filed Aug. 29. 1966 3 Sheets-Sheet l Fig.7

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Inventors:

United States Patent 1 Claim ABSTRACT OF THE DISCLOSURE An antenna array is mounted on a satellite so as to direct the signals toward the earth in a uniform field. Each antenna in the array is angularly mounted with respect to the otherand has an electrically variable dielectric means mounted at the aperture. The means are electrically adjustable by a common control system to shape the beam. I

The present invention relates to an antenna system for an earthsatellite.

As is Well known, artificial communication satellites have recently been put into orbit around the earth. of the many possible tracks which such earth satellites can follow, the circular orbits are of particular interest, irrespective of whether the communication system uses one earth satellite, a plurality of earth satellites, or a socalled twenty J-four hour or synchronous satellite which appears to stand still over one point on the earth. In such systems, the'duration of one period, i.e., one orbit around the earth, the position of the satellite on the track, and the circular configuration of the track have to be maintained witha certain amount of accuracy. If the satellite occupies a given position with respect-to the earth, this has a greaf' -deal of influence on the expense and elab- Orateness of the communication efifiipment carried aboard the satellite, inasmuch as a satellite which occupies a given position with respect to the farth can utilize directional antennas. 1

Assuming that the main axis of the radiation pattern continuously points to the center of the-'earth, the electric field strength obtained at the edges of he surface portion of the earth which is visible from the satellite will be weaker inasmuch as the distance between a point near the center of the earths surface portion; seen from the satellite and the satellite is less than the distance between a point in the region of the edge of this...surface portion of the earth and the satellite. Furthermore, the radiation patterns of antennas which were up to now used in satellite antennas are generally lobe-shaped, and this also contributes to a decreased field strength in the region of the edges of that surface portion of the earth which is visible from the satellite. The amount of the decrease depends primarily on the directivity of the particular antenna system being used.

It will be appreciated that the above conditions are undesirable, and it is the primary object of the present invention to provide a way in which to eliminate the disadvantages of existing antenna systems used in satellites.

With the above objective in view, the present invention resides basically in an antenna system for an earth satellite having a directivity characteristic or radiation pattern which produces, over as large a portion of the earths surface as possible, the same electric field strength and as low an electric field strength as possible outside of such portion of the earths surface. In accordance with the present invention, the antenna system comprises an array of antennas, whose apertures preferably lie in the same plane, and which are so dimensioned and arranged,

3,500,418 Patented Mar. 10, 1970 and/or the phases of whose field strengths are so influenced, as to obtain the desired radiation pattern.

Additional objects and advantages of the present invention will becom'e'a'pparent upon consideration of the following description' when taken in conjunction with the accompanying drawings in which:

FIGURE 1 shows the optimal radiation pattern of an antenna array according to the present invention.

FIGURE 2 shows the radiation pattern of conventional satellite antennas.

FIGURE 3 shows two antennas whose axes are inclined with respect to each other.

FIGURE 4 is 'an end view of a four-antenna array according to the present invention.

FIGURE 5 shows an array of five antennas fed by a common feed.

FIGURE 6 shows an array of three antennas two of which are provided with phase shifting elements.

FIGURE 7 shows how the characteristic of a phase shifting element may be varied.

FIGURE 8 shows a metallized plastic antenna element.

FIGURE 9 shows in more detail the structure of the antennas of FIGURE 3 and the phase shifting arrangement used with these antennas.

Referring now to the drawings, FIGURE 1 shows the optimal directional characteristic of a satellite antenna, this being a characteristic which causes the electric field strength of the received field to be constant over a predetermined portion of the earths surface, in particular, a surface portion which subtends an angle a so that the radiation which strikes each point in this surface portion will be of the same field strength. By way of comparison, FIGURE 2 shows the directional characteristic of heretofore conventional satellite antenna systems.

In accordancewith one embodiment of the present invention, the desired dIrectional characteristic is obtained by positioning the individual radiators obliquely with respect to each other, Thus, as shown in FIGURE 3, multi-horn-type antennas are so arranged that their axes form an angle 1E? with each other which depends on the height of the satellite.

An array incorporating a plurality of individual reflectors makes it possible to use circularly polarized waves. Such an array is sit iown in FIGURE 4 which depicts four horns whose apertures lie in a common plane and together form a square. Here, too, the axes of the horns may be arranged obliquely with respect to each other. It will be understood, of course, that the array according to the present invention is not limited for use with circular y polarized waves in that differently polarized waves can be used.

In the embodiment of FIGURE 5, the antenna array comprises a plurality of dipoles D which are fed from a common feed S, there being interposed between the feed and the individual dipoles respective phase shifters P by means of which the phases of the individual antennas can be influenced. Feeding of the individual antennas will be chosen in a manner disclosed in our copending application Serial No. 575,669 filed August 29, 1966 for getting the desired lobe that means an oscillatory energy distribution with a maximum in the middle of the aperture and a decreasing amplitude towards the edge of the aperture. This means that an antenna arrangement from which FIG. 5 shows a side view consists of several circlelike zones the resulting phase of each changes by suitable choosing the phase shifters P.

A part of the array shown in FIGURE 6 comprises three individual parabolic reflectors which together form a common aperture area. In order to achieve the desired phase shift, elements E made of metallic or dielectric material are arranged in the vicinity of the aperture openings of the two outer antennas.

In the embodiment of FIGURE 7, there is shown how the dielectric constant and/or the permeability constant of a dielectric phase shifting element such as is shown at E in FIGURE 6 can be varied by applying a predetermined field, so that the phase can be shifted by varying the voltage which is put out by a voltage source U and applied across the dielectric element. In this way, any undesired change in position of the satellite, or change in the configuration of the orbit, can be compensated for. Such compensation can also be made if any given area within the portion of the earths surface illuminated by the array is, for any reason, to be excluded.

FIGURE 8 shows one antenna consisting, mainly, of plastic material F, the same being provided with a metallized coating M. In this way, the total weight of the antenna system is kept to a minimum which, it will be appreciated, is of considerable importance in the case of an antenna system that is to be carried aboard a satellite.

FIGURE 9 shows the variable dielectric phase shifting arrangement as disclosed in FIGURE 7 and the metallized plastic antenna structure as disclosed in FIGURE 8 applied to the antenna array as in FIGURE 3. Each of the antennas is formed of plastic material having a metallized coating. The aperture of each antenna has a phase shifting element E arranged in front of it. A variable voltage source V is connected across each of the elements B, so as to vary the dielectric thereof. Each of the variable voltage sources V is electrically connected to a phase shifter P, which in turn is connected to the common feed S.

It will thus be seen that, in accordance with the present invention, there is provided an antenna system in which the desired radiation pattern, namely, a radiation pattern that produces, over as large a portion of the earths surface as possible, the same electric field strength and as low an electric field strength as possible outside of such portion of the earths surface, is obtained by means of an antenna system which comprises an array of a plurality of individual antennas and means associated with these antennas for causing the array as a whole to produce the desired radiation pattern. That is to say, the desired radiation pattern is achieved by so dimensioning and arranging the individual antennas, and/or by so influencing the phases of the field strengths of the antennas, as to obtain the desired radiation pattern.

It is also pointed out that if the spin of the satellite is stabilized, the desired radiation pattern can be approximated by making the radiation pattern rotationally symmetrical with respect to the spin axis. This, however, means that most of the energy is radiated in directions which will result in most of the energy being lost, i.e., in not being picked up by the receiving stations on the earths surface. In order to avoid this, at least certain parts of the antenna system can be so influenced that energy is directed only toward a desired region on the earths surface. This can be done, as explained above, by electrically or mechanically switching the antennas, or by suitably controlling the phase of the energy coming in through the feed line.

The antennas themselves may be in the form of horns, spirals, longitudinal reflectors, or dipoles.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claim.

What is claimed is:

1. An antenna system comprising a satellite, a plurality of individual antennas mounted on the satellite, said antennas having their axes arranged at an angle with respect to each other whereby the antennas radiate signals in different directions, phase shifting means for varying the phase of the signal of each antenna comprising a variable dielectric element mounted in front of each antenna and means for varying the dielectric constant of each dielectric element to thereby vary the phase of the associated antenna signal.

References Cited UNITED STATES PATENTS 2,286,839 6/1942 Schelkunolf 343853 2,432,990 12/1947 Hansen 343-778 3,184,743 5/1965 Crawford 343-778 3,188,640 6/1965 Simon et al. 343-705 3,259,902 7/1966 Malech 343-754 3,339,275 9/1967 Anderson et al 343-786 ELI LIEBERMAN, Primary Examiner U.S. Cl. X.R. 343-754, 854

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