Compact Electrically Steerable Tracking Antenna Feed System

Abstract

Described is an electrically steerable tracking antenna feed system employing a pair of ferrite phase shifters, one of which produces positive phase shift and the other of which produces negative phase shift with increasing applied magnetic field. The ferrite phase shifters, arranged in side-by-side relationship in a bifurcated wave guide, are surrounded by a common electromagnet.

Description

BACKGROUND OF THE INVENTION

As is known, longitudinally magnetized reciprocal ferrite phase shifters show anomalous behavior in that some show increasing phase shift with increasing applied field while others show decreasing phase shift with increasing applied field. In this respect, there are two competing mechanisms which govern the type of phase shift. These can be termed ".mu.-effective" and "suppressed Faraday rotation." The latter sets in when the guide is thick enough to support a cross-polarized electric field of the same order of magnitude as the incident electric field and results in increasing phase shift with increasing applied field. The ".mu.Aeffective" mechanism, on the other hand, results when the guide is of such thickness that it will not support a cross-polarized electric field of the same order of magnitude as the incident electric field and results in decreasing phase shift with increased applied magnetic field.

SUMMARY OF THE INVENTION

As an overall object, the present invention seeks to provide a new and improved electrically steerable tracking antenna feed system employing ferrite phase-shifting devices, at least one of which will produce an increasing negative phase shift with increasing applied magnetic field and the other of which will produce an increasing positive phase shift with increasing applied magnetic field.

More specifically, an object of the invention is to provide an electrically steerable tracking antenna feed system of the type described wherein the ferrite phase shifters are arranged in side-by-side relationship in a bifurcated waveguide and surrounded by a common magnetizing coil.

In accordance with the invention, an electrically steerable tracking antenna feed system is provided comprising at least one pair of antennas, a waveguide having one end adapted for connection to a source of wave energy for both of said antennas, a wall dividing the waveguide into two separate wave energy transmission paths, one of which is wider than the other, and ferrite slabs in the respective wave energy transmission paths, one slab being wider than the other.

A common magnetic coil surrounds both of the wave energy transmission paths to produce a magnetic field extending along the axis of the waveguide. With this arrangement, and assuming that the thickness of the wider slab is great enough to support a cross-polarized electric field of the same order of magnitude as the incident electric field while the thinner slab is not, the phase shift experienced by the wave energy in passing through the thin ferrite slab will decrease with applied magnetic field; while the passing through the wide ferrite slab will increase with applied field. The system is completed by connecting the respective wave energy transmission paths to two antennas which are spaced apart such that upon variation of the magnetic field applied to both ferrite slabs, the composite radiation pattern produced by the antennas will be caused to scan back and forth.

Further, in accordance with the invention, the wave energy in separate ferrite-filled transmission paths, having experienced different phase shifts, may be further divided into portions which pass through thick and thin ferrite slabs, under the influence of an axial magnetic field, for the purpose of producing four or more separate antenna feeds.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a cross-sectional schematic view of one embodiment of the invention for feeding two separate antenna elements;

FIG. 2 is a schematic illustration of another embodiment of the invention for feeding four separate antenna elements;

FIG. 3 is a cross-sectional view of a system in accordance with the invention for providing single-axis scanning employing a Cassegrain antenna feed; and

FIG. 4 illustrates the manner in which the device of FIG. 3 is employed.

With reference now to the drawings, and particularly to FIG. 1, the system shown includes a waveguide 10 having an inner wall 12 which divides it into two parallel wave energy transmission paths 14 and 16. The wave energy path 14, it will be noted, is much thinner than the path 16. Both path 14 and path 16 are filled with ferrite slabs 18 and 20, the slab 18 being much thinner than slab 20. Both slabs 18 and 20 are surrounded by an electromagnetic coil 22 connected to a control circuit 23 and adapted to produce an axial magnetic field along the length of the waveguide 10. The wall 12 separating the two wave energy paths is closely adjacent the top wall in waveguide 10 as shown in FIG. 1 but is bent inwardly as it passes through matching transformers 24 and 26 until it assumes a central position where it divides the wave energy passing through the waveguide 10. Similarly, the other end of the wall 12 is bent inwardly as it passes through matching transformers 28 and 30 until it assumes a central position. At this point, the center wall is connected, as a common wall, to two waveguide sections 32 and 34 which are, in turn, connected to antennas 36 and 38, respectively.

As was mentioned above, when the waveguide section within which the ferrite slab is disposed is thick enough to support a cross-polarized electric field of the same order of magnitude as the incident electric field, phase shift occurs by virtue of "suppressed Faraday rotation," in which case the phase shift experienced by the wave energy in passing through the ferrite increases with increased applied magnetic field. This is the case with the ferrite slab 20. On the other hand, when the slab is not thick enough to support a cross-polarized electric field of the same order of magnitude as the incident electric field, the phase shift decreases as the applied magnetic field increases. This is the case with the ferrite slab 18. Hence, as the magnetic field applied by the coil 22 increases, the phase shift experienced by the wave energy in passing through ferrite slab 18 will decrease while that experienced in passing through slab 20 will increase. The result is that the wave energy applied to the two antennas 36 and 38 will always be out of phase; and as the applied magnetic field is varied, so also will be the phases of the energy applied to the antennas 36 and 38 to cause the composite radiated beam to scan back and forth.

In FIG. 2 another embodiment of the invention is shown wherein wave energy is fed to four antennas 40-46. In this case, the wave energy is divided into two parallel paths and passed through two ferrite slabs 48 and 50, the thinner ferrite slab causing a negative phase shift and the thicker slab 48 causing a positive phase shift. The wave energy which has experienced a positive phase shift in passing through slab 48 is then fed into a second bifurcated ferrite phase shifter comprising a thin ferrite slab 52 and a relatively wide slab 54. The wave energy from slabs 52 and 54 is then applied to the antennas 44 and 46, respectively.

The same is true of the wave energy which experienced a negative phase shift in passing through slab 50, i.e., it is passed through a second bifurcated chamber having a thin ferrite slab 56 in side-by-side relationship with a relatively wide slab 58. Wave energy passing through slab 56 is applied to antenna 40; while that passing through slab 58 is applied to antenna element 42. In this manner, various scanning arrays or radiation patterns can be achieved from the antennas 40-46 which need not be arranged in line as shown in FIG. 2.

In FIGS. 3 and 4, another embodiment of the invention is shown in which elements corresponding to those shown in FIG. 1 are identified by corresponding reference numerals. In this case, however, the wave energy, after passing through matching transformers 28 and 30, is fed through a split feedhorn 60 and then reflected from a reflector 62 back onto a parabolic dish 64. The wave energy fed to one side of the dish 64 is, of course, out of phase with respect to that fed onto the other side; and the two signals combine to produce a directional effect which will cause scanning of the beam when the magnetic field applied by the coil 22 is varied.

The device shown in FIG. 1 can also be used as a microwave switch or amplitude modulator. In switching, the phase-shifting elements 18 and 20 go between .-+.90.degree. relative phase shift and .+-.90.degree. , switching the energy between the two output ports. For modulation, one output port can be terminated while the other port receives the modulated wave. Modulation is achieved by varying continuously the phase at the two ports between zero relative phase shift and .+-.90.degree. relative phase shift.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Claims

I claim as my invention:

1. In an electrically steerable tracking antenna feed system, the combination of a pair of antennas, a waveguide having one end adapted for connection to a source of wave energy for both of said antennas, a wall dividing said waveguide into two separate wave energy transmission paths one of which is wider than the other, ferrite slabs in said separate wave energy transmission paths, one slab being wider than the other, a common magnetic coil surrounding both of said wave energy transmission paths to produce a magnetic field extending along the axis of said waveguide, one of said ferrite slabs producing increasing positive phase shift as said magnetic field is increased and the other of said ferrite slabs producing increasing negative phase shift as said magnetic field is increased, first antenna means connected to one of said wave energy transmission paths, and second antenna means connected to the other of said wave energy transmission paths.

2. The tracking antenna feed system of claim 1 wherein said wide slab produces increasing positive phase shift as said magnetic field is increased and said narrow slab produces increasing negative phase shift as said magnetic field is increased.

3. The tracking antenna feed system of claim 1 including matching transformer means at opposite ends of said ferrite slabs.

4. The tracking antenna feed system of claim 1 wherein said first and second antenna means each comprise a plurality of antennas, and ferrite phase-shifting devices interposed between each of said first and second antenna means and said narrow and wide ferrite slabs.

5. The tracking antenna feed system of claim 4 wherein said latter-mentioned ferrite phase-shifting devices comprise ferrite slabs in a bifurcated waveguide divided into wide and narrow wave energy paths.

6. The tracking antenna feed system of claim 1 wherein said first and second antenna means comprise devices for feeding wave energy to opposite sides of an antenna reflector in a Cassegrain antenna feed system.