GB2189650A - Steerable beam transmitters - Google Patents

Abstract

A steerable beam transmitter comprises a focussing device, e.g. dielectric lens 21, and a phased array comprising a large number of separate radiators, in the form of dipoles 20 or horns, lying in a non- focal plane. The contributions from each radiator combine constructively to supply to the focussing device a beam which appears to originate from a point in the focal plane. The large number of separate radiators permit a very much higher power to be radiated then would be possible from a single radiator located physically at the focal point. <IMAGE>

Description

SPECIFICATION Improvements in or relating to steerable beam transmitters This invention relates to steerable beam transmitters and seeks to provide a transmitter which can radiate relatively high power levels whilst permitting the direction of a transmitted beam to be precisely controlled.

The invention is suitable for transmitting microwave electromagnetic energy at frequencies which are typically used in radar applications or for certain communications purposes.

According to this invention a transmitter includes means for forming and transmitting a focussed steerable beam of electromagnetic energy; a plurality of radiator elements positioned in a non focal plane of the beam, forming means and means for controlling the relative phases of the energy rndiated by the plurality of elements so that the energy combines to constructively produce a beam lying in a predetermined direction, and which appears to originate from a focus.

Conventionally, only a single radiator element would be positioned physically at the focus, and in this invention since the total energy content of the beam receives contributions from a plurality of individual radiator elements, the total energy transmitted can be very greatly in excess of that which any one radiator can produce, and in practice, the plurality of elements may be quite large.

In order to optimise the form and profile of the transmitted beam, it is preferable to also provide means for controlling the amplitude of the energy radiated by the individual elements.

Adjustment of both amplitude and phase of the radiated electromagnetic energy permits a very precise control to be exercised on the boresight direction and width of the transmitted beam.

Each radiator may be associated with a separate oscillator which generates the energy to be radiated at the required high frequency.

In this case the oscillators are locked together so that each has a required frequency and phase relationship with respect to the other oscillators. Generally, the oscillators will all be required to operate at the same frequency, but with a relative phase which determines the direction of the beam.

Alternatively, a high power single oscillator may be provided from which selected proportions of energy can be branched off and fed to selected radiators. Typically, each radiator would receive a specified proportion of the total energy. Again precise control of the phase will be required, and this alternative arrangement is useful in those cases where the power handling capability of the individual radiators is significantly less than that of the oscillator.

The individual radiators can take any convenient form. For example, they may comprise individual waveguide horns arranged to illuminate a concave reflector which is so shaped as to form a beam of the required shape and direction. Alternatively, the individual radiators may comprise dipoles formed upon the surface of a dielectric body which itself, or in combination with another body, comprises a lens which shapes the electromagnetic energy into the required beam.

The invention is further described by way of example with reference to the accompanying drawing in which: Figure 1 is a block diagram indicating the principle of the invention, Figure 2 shows an array of radiators in the form of dipole antennas, and Figure 3 shows an array of radiators in the form of waveguide horns.

Referring to Fig. 1, there is shown therein an array of individual radiator elements 1 each of which is associated with transmitter channel 8; only one of which is shown in detail, but all channels are similar. Each channel 8 includes a microwave frequency oscillator 2 which feeds the radiator 1 via a controllable phase shifter 3 and a controllable attenuator 4 which determine the amplitude of the radiated electromegnetic energy. The radiators 1 are placed relatively close to each other so that the signal from each combine in a manner which is determined by their relative phases, i.e., they combine constructively in certain directions and destructively in other directions.

The relative phases are so chosen that the energy combines constructively in a predetermined direction. The relative phases necessary to achieve this constructive combination are produced by a control circuit 5 which sets the required phases for the various phase shifters.

All of the oscillators 2 operate at the same frequency.

In order to provide fine control of the constructive combination, to adjust the width of the transmitted beam and to minimise the generation of the undesirable side lobes, the amplitudes of the individual signals are also set by the adjustable attenuator 4, again under the control of the control circuit 5.

In this way, a very large number of individual radiators can be fed from separate oscillators 2 and a very high power beam can be generated by constructively combining the energy from all of the transmitter channels 8. In general, the power handling capability of individual radiators and their associated phase shifters can be rather limited and the invention permits the transmitted power to be increased without regard to those particular constraints, as additional energy can be obtained by adding radiators without sacrificing beam width requirements.

One form of the invention is illustrated in Fig. 2, in which a number of individual dipole radiators 20 are formed upon a flat surface of a dielectric body 21. The dipole radiators could be formed as an integral part of a monolithic microwave integrated circuit which includes at least the final stage of amplification, and would could be constructed of gallium arsenide or silicon. The dielectric body itself is formed as a lens which refracts the energy generated at the individual radiators 20. The properties of the dielectric lens are such that the beams formed by the individual radiators 20 appear to originate from a point source, or focus, lying in a focal plane 22.

The combined power of all of the radiators 20, which are located in a non-focal plane, is very much greater than could be generated by a single radiator positioned precisely at a focus lying in the plane 22. These dipole radiators can take any convenient form in which the dipoles are formed as metal de-positions upon localised surface regions of the dielectric lens. As is known, the energy radiated by the dipoles propagates preferentially into the dielectric material and can be shaped by the lens action of the outer curved surface 23 of the lens. By altering the relative phases of the energy radiated by the radiators 20 the position of the focus within the plane 22 is shifted.Thus it can be shifted from an on-axis point 24 to point 25 which causes the transmitted beam to point in a different direction, the angular shift 6 being dependent on the lateral shift A of the focal point. This shift of direction is obtained solely by adjusting the phase and amplitude of the different radiators 20 in accordance with the explanation given with reference to Fig. 1.

An alternative embodiment of the invention is shown in Fig. 3 in which a plurality of individual radiators 30, in the form of waveguide horns, are positioned in a single plane lying in front of a curved antenna reflector 31. Again, the phases and amplitudes of the signals radiated by the individual radiators are controlled so that the energy appears to originate from a point source of energy, or focus, lying in a plane 32. By altering the phase and amplitude of the radiated energy the focus can be shifted within the plane 32 from point 33 to point 34 so as to cause the beam to be transmitted in a different direction. The position of the radiators 30 can be offset from the axis of the beam formed by the reflector 31 so that it does not obstruct or block the radiated energy. If convenient, a Cassegrain system using a sub-reflector may be employed.

In both the cases illustrated in Figs. 2 and 3 the phase and amplitudes can be adjusted over a very wide range so that the position of the focus can likewise be altered by a great extent. As a very large number of radiating elements can be provided, the total transmitted power is correspondingly great.

Claims (5)

1. A transmitter including means for forming and transmitting a focussed steerable beam of electromagnetic energy; a plurality of radiator elements positioned in a non-focal plane of the beam forming means, and means for controlling the relative phases of the energy radiated by the plurality of elements so that the energy combines to constructively produce a beam lying in a predetermined direction, and which appears to originate from a focus.

2. A transmitter as claimed in claim 1 and wherein means are provided for controlling the amplitude of the energy radiated by the individual elements.

3. A transmitter as claimed in claim 1 or 2 and wherein each radiator is associated with a separate oscillator which generates the energy to be radiated.

4. A transmitter as claimed in claim 1 or 2 and wherein a high power single oscillator is provided from which selected proportions of energy are branched off and fed to selected radiators.

5. A transmitter substantially as illustrated in and described with reference to Figs. 1 and 2.

5. A transmitter as claimed in any preceding claim and wherein the radiators comprise individual waveguide horns arranged to illuminate a concave reflector which is so shaped as to form a beam of the required shape and direction.

6. A transmitter as claimed in any of claims 1 to 4 and wherein the radiators comprise dipoles formed upon the surface of a dielectric body which itself, or in combination with another body, comprises a lens which shapes the electromagnetic energy into the required beam.

7. A transmitter substantially as illustrated in and described with reference to Figs. 1 and 2 or 3 of the accompanying drawing.

CLAIMS Superseded claims 1-7 New or amended claims: 1-5 A transmitter including a plurality of dipole radiators positioned upon the surface of a dielectric body which forms at least part of a lens which combines electromagnetic energy radiated by said radiators into a required beam, the said surface of said body lying in a non-focal plane of said lens; and means for controlling the relative phases of the energy radiated by the plurality of dipole radiators so that said beam lies in a predetermined direction.

2. A transmitter as claimed in claim 1 and wherein means are provided for controlling the amplitude of the energy radiated by the individual radiators.

3. A transmitter as claimed in claim 1 or 2 and wherein each radiator is associated with a separate oscillator which generates the energy to be radiated.

4. A transmitter as claimed in claim 1 or 2 and wherein a high power single oscillator is provided from which selected proportions of energy are branched off and fed to selected radiators.