GB2235585A - A multiple-beam antenna system - Google Patents

Abstract

At the focal plane of a dish reflector, dielectric focussing lens 4 or like RF focussing element, there is placed a plurality of RF transmitter/receiver elements 3 each comprising a non-linear self-oscillating mixer device, for example an Impatt diode, transferred electron device, or a transistor. Each such device can be rendered operable both for generating an RF transmission signal and for mixing a received signal with the transmission signal to form, within the device itself, an i.f. signal. The devices may be comprised in a so-called integrated antenna unit coupled to respective ones of an array of antenna elements, e.g. dipoles, formed on a surface of a substrate. There is also disclosed an integrated antenna which may comprise only one antenna element formed on a substrate with a self-oscillator mixer device coupled to the element to enable the antenna to both transmit and receive RF radiation. <IMAGE>

Description

TITLE: R. F. RECEIVER/TRANSMITTER.

This invention relates to RF transmitter/ receiver systems, primarily, but not necessarily only, intended for operation at frequencies from some tens of Megahertz to several hundred Gegahertz or even beyond.

By way of example, such equipment may form the basis of or be used in equipment such as surveillance and tracking radar; active, semi-active, radiometric and anti-radar homing heads; ESM receivers and communication links.

Our patent application No. PCT/GB82/00029 discloses a target sensing system for a missile, which system comprises an RF transmit/receive antenna and, to supply an RF signal to the antenna, an oscillating mixer device, i.e. an active device (such as a Gunn effect device or an Impatt device) which has a nonlinear current/voltage relationship and which therefore, suitably biassed, is able to generate an RF signal and which also is operable to mix the return signal received by the antenna with part of the transmission signal being generated to produce a detectable i.f.

signal, if due to Doppler effect say, the return signal frequency differs from that of the transmitted signal.

According to one aspect of this invention, there is provided a multiple-beam antenna system comprising a focal plane defining element and, substantially in the region of said focal plane, a plurality of RF transmitter elements each comprising, for generating a transmission signal, a non-linear self-oscillating mixer device such as, for example, an Impatt diode, or transferred electron device, transistor or the like.

According to a second aspect of the invention there is provided an integrated high-frequency antenna system comprising at least one antenna-defining element provided on a surface of a dielectric substrate and, coupled to said element, a non-linear self-oscillating mixer device, such as for example an Impatt diode, transferred-electron device, a transistor or the like, for producing an RF signal to be radiated by the element and for mixing an RF signal received by the element with the signal to be radiated to produce, within the device itself, an i.f signal.

For a better understanding of the invention, reference will be made, by way of example, to the accompanying drawings, in which: figure 1 is a diagrammatic view of part cf a multiple-beam transmitter/receiver using a reflective antenna, figure 2 is a diagrammatic view of part of a multiple-beam transmitter/receiver using a transmissive focussing device, figure 3 shows diagrammatically part of an examplary form of an antenna array usable in the transmitter/receiver of figure 2.

In many applications, it is desirable to scan the transmit and receive antenna beams of a radar system say over a field of view which is wider than the antenna beam itself. This leads to complexity and cost. As an alternative to part or even all of the provisions for scanning the beams, the system can be operable to define a plurality of fixed, i.e.

'staring' beams focussed in different directions.

In the apparatus to be described, a multiplicity of staring transmission/reception beams are produced by grouping a plurality of semi-conductor self-oscillating mixers at the focus or focal plane of some radiating aperture, typically as a two-dimensional array. Two possible configurations are shown in Figs 1. and 2.

In figure 1, a composite feed 1 at the focus of a dish reflector 2 comprises a multi-section waveguide, each section containing a self-oscillating mixer element (not shown). In figure 2, a solid-state antenna array 3 comprising a plurality of self-oscillatiny mixer elements is positioned at the focal plane of a focussing element 4 or 'lens' made of suitable dielectric material.

In each case, each individual element of the array is in focus to signals arriving from a respective different direction and so multiple beams are generated. The beam width of each beam is governed by the total aperture dimensions and the number of beams corresponds to the number of elements.

Each self-oscillating mixer can transmit as well as receive in the direction corresponding to focus.

Thus, each individual semiconductor is a separate radar and the total array can cover a wide field of view simultaneously. Directional resolution to an accuracy greater than that of a single beamwidth may be obtained in a known way by processing the output from each element as a phase or amplitude comparison monopu1se as an interferometer, or by rotating the complete array in a conicalscan fashion or by other mechanical or electrical scanning techniques. In addition, the outputs from each individual radar element may be processed to give a degree of imaging capability.

The self-oscillating mixers are any non-linear device in which power generation and signal mixing can occur simultaneously. Typically such devices are IMPATT diodes, transferred electron devices, transistors. Any suitable form of transmission line may be used to conduct the radiation, some examples being metal waveguide, micrcstrip and dielectric image guide, freespace focussed systems.

The transmit signal may be modulated in any way by varying its amplitude, frequency and phase and information may be extracted from the received signal te give range and target characteristics, or the performance improved against clutter, precipitation or interference.

Thus, as will be realised, by grouping two or more self-oscillating mixers at the focus of a larger antenna system, there is produced an array of simple radars (which transmit as well as receive) each focussed in a particular direction, thus realising a very simple, staring radar array.

By way of example, the array 3 of figure 2 may be as shown in figure 3. This array comprises a substrate 5, made of alumina or quartz say, on one surface of which is provided a printed (or otherwise formed) array of half-wave dipoles 6 each comprising two dipole sections 7 and 8. Only one of the dipoles 6 is fully illustrated. On the top surface of dipole section 7, near the innermost end of the section, there is attached a semiconductor self-oscillating mixer element 9, a Gunn effect diode say. The section 7 is thus electrically connected to one side of device 9 while the other side of this device is connected to one side of a bias source 10. The other side of source 10 is connected via a printed resistive track 11 on substrate 5 to the dipole section 7.Due to the bias supplied by source 10, and the resonant situation or context within which device 9 is placed, i.e. its position in close association with dipole 6, the device 9 produces a transmission signal which is radiated from the dipole. The RF return signal received at the dipole becomes mixed with the transmission signal due to the non-linear characteristics of device 9 and the resultant appears as an i.f.

signal across the resistor formed by resistive track 11.

A portion of this signal is taken off via connections 12 to an i.f. amplifier 13.

As will be well appreciated by those skilled in the art, the arrangement of the tracks and connections and the position of the dipoles on substrate 5 have to be carefully designed and experimented with to obtain proper operation. Figure 3 has been drawn with a view to explaining the operation of the relevant embodiment of the invention - it does not necessarily illustrate an operable geometric design of interconnections and such.

It is not usually allowable for conductor tracks to connect directly to the dipole sections - this is why track 11 is made resistive. At the same time, because it is resistive, this track conveniently forms the resistor across which the i.f signal output is taken However, it is not essential that this particular arrangement be used.

The radiation pattern of each complete radar transmitter/receiver formed by each dipole/self-oscillating mixer device combination on substrate 5 comprises a relatively very small amount of energy emitted in the direction upwards (in the figure) and away from the dipole carrying surface of substrate 5. A much larger amount of energy is directed through the substrate and out from the other or lower surface.

Thus, translating the illustrated array to figure 2, this other surface is made to face the lens 4. This lens focusses the pattern from each dipole/device combination, of which there might be perhaps 100 in a 10 X 10 array, to form a multinlicity of transmission/ reception beams directed in different directions.

The divergence of the beam axes is chosen according to the desired purpose - for example it may be desirable for the areas covered by the respective beams at a particular distance from the apparatus to overlap or it may be required to look at quite separate areas at this distance.

For example, with overlapping beams a greater or lesser 'imaging' capability may be achieved whereby, with the resolution achievable with RF radiation, geometric information about an observed object is acquired.

The principle illustrated in figure 3 can also be extended to a Microstrip type of device or aerial i.e. a transmission line aerial or aerial array, in which generally a ground plane would be provided on the lower surface of substrate 5 - the transmission/ reception characteristics then of course become different to those described. Also, while figure 3 shows a hybrid device implementation, full-scale monolithic integration could be applied thereto - in this case, the substrate 5 might be made of say silicon, gallium arsenide or indium phosphide with the devices 9 doped into the substrate.

As mentioned earlier, a device such as that shown in figure 3 has to be carefullydesigned to achieve optimum operation or even any operation - the various factors to be considered will be known to those skilled in the art. Because of practical considerations which arise in connection with very high frequency signals, as opposed to theoretical considerations, for example the simple difficulty of getting a transmission signal in to a dipole such as the dipole 6 in figure 3 without so modifying its theoretical characteristics that it no longer works, a device of this kind has not generally been used as a transmitter - only as a receiving device.

Thus, within the context of a hybrid or monolithic integrated RF device of the general nature shown in figure 3, this invention is applicable even in the case where, instead of multiple beam producing antenna array, only a single antenna pattern is provided, e.g.

a single dipole1 patch antenna or the like.

Claims (7)

1. A multiple-beam antenna system comprising a focal plane defining element and, substantially in the region of the focal plane defined by said element, a plurality of RF transmitter elements each comprising, for generating a transmission signal, a non-linear self-oscillating mixer device.

2. A system according to claim 1, wherein each mixer device comprises an Impatt diode, a transferred electron device or a transistor.

3. A system according to claim 1 or 2, wherein said focal plane defining element comprises a dish reflector and wherein, substantially in the region of the focus of the reflector, there is provided a composite feeler including a multi-section waveguide and, contained in each section of the waveguide, a non-linear selfoscillating mixer device.

4. A system according to claim 1 or 2, wherein said focal plane defining element comprises a focussing lens made of dielectric material and wherein, substantially at the focal plane of said lens, there is provided a substrate supporting a planar array of non-linear selfoscillating mixer elements.

5. A system according to claim 4, wherein said mixer elements are connected to respective ones of an array of antenna elements formed on said substrate.

6. An integrated high-frequency antenna system comprising at least one antenna-defining element provided on a surface of a dielectric substrate and, coupled to said element, a non-linear self-oscillating mixer device, for example an Impatt diode, transferred electron device or a transistor, for producing an RF signal to be radiated by the element and for mixing an RF signal received by the element with the signal to be radiated to produce, within the device itself, an i.f.

signal.

7. An RF transmitter/receiver system substantially as hereinbefore described with reference to figure 1 or figure 2 and 3 of the accompanying drawings.

7. A multiple-beam antenna system substantially as hereinbefore described with reference to figure 1 or figures 2 and 3 of the accompanying drawings.

8. An integrated high-frequency antenna system substantially as hereinbefore described with reference to figure 3 of the accompanying drawings.

Amendments to the claims have been filed as follows 1. An RF transmitter/receiver system comprising a common RF radiation focusing element and a plurality of RF oscillator/mixer circuits at spaced positions within the focal region of the focusing element, to form, with the comnon focusing element respective ones of a plurality of RF transmitter/receivers for transmitting and receiving RF radiation beams extending in respective different directions from the focusing element, each oscillator/mixer circuit comprising a radiator element and, coupled thereto, a semi-conductor component having non-linear characteristics such that it is inherently capable of generating an oscillatory electrical signal in response to an applied bias signal and thereby, in association with the radiator element, feeding said focusing means with RF radiation to form the transmit beam associated with the circuit and it is also capable, sinultaneously and inherently, of producing an intermediate frequency output signal by mixing a portion of the generated oscillatory electrical signal with an oscillatory electrical signal applied to it from the radiator element and induced in said radiator element by the receiver beam associated with the circuit, each circuit further comprising bias signal applying means for biassing said component into the oscillatory region of its characteristics, and output means for extracting said intermediate frequency output signal from said component.

2. A system according to claim 1, wherein said common focusing means comprises a dish reflector, the radiator elements of the oscillator/mixer circuits comprises respective sections of a multiple-section waveguide of which the exit/entrance apertures lie within the focal plane of the dish reflector, and said semiconductor components are positioned inside respective ones of said sections.

3. A system according to claim 1, wherein said focusing means comprises a lens made of dielectric material and wherein, substantially at the focal plane of said lens, there is provided a substrate supporting a planar array of said oscillator/mixer circuits.

4. An RF transmitter/receiver system comprising an RF radiation focusing lens made of dielectric material, a dielectric substrate positioned with one face in the focal plane of said lens and its opposite face nearer said lens than said one face and, supported by said one face of the substrate, an array of spaced antenna/mixer/oscillator circuits each comprising an antenna defined by metallisation of said one face and, positioned at least close to the antenna and connected thereto, a semi-conductor component having non-linear characteristics such that it is inherently capable of generating an oscillatory electrical signal in response to an applied bias signal and hence causing RF radiation to be transmitted from the antenna via said substrate and said lens, and it is also capable, simultaneously and inherently, of producing an intermediate frequency output signal by mixing a portion of the generated oscillatory signal with an oscillatory signal induced in said antenna by radiation received via said lens and said substrate, each circuit further comprising bias signal applying means for biassing said component into the oscillatory region of its characteristics, and output means for extracting said intermediate frequency output signal from said component.

5. A system according to any preceding claim, wherein each semi-conductor component is one of an Impatt diode, a transferred-electron component, a Gunn-effect diode and a transistor.

6. An RF transmitter/receiver system comprising an RF radiation focusing lens made of dielectric material and an integrated antenna/mixer/oscillator circuit supported at the focus of said lens by a substrate, the circuit comprising an antenna defined by metallisation on a surface of the substrate and, positioned at least close to the antenna and connected thereto, a semi-conductor component having non-linear characteristics such that it is inherently capable of generating an oscillatory electrical signal in response to an applied bias signal and hence causing RF radiation to be transmitted from the antenna via said lens and it is also capable, inherently and simultaneously, of producing an intermediate frequency output signal by mixing a portion of the generated oscillatory signal with an oscillatory signal induced in said antenna by radiation received via said lens, the circuit further comprising bias signal applying means for biassing said component into the oscillatory region of its characteristics and output means for extracting said intermediate frequency output signal from said component.