GB2227141A

GB2227141A - Integratable transceiver

Info

Publication number: GB2227141A
Application number: GB8900593A
Authority: GB
Inventors: Robert Neil Bates
Original assignee: Philips Electronic and Associated Industries Ltd
Current assignee: Philips Electronics UK Ltd
Priority date: 1989-01-11
Filing date: 1989-01-11
Publication date: 1990-07-18
Also published as: GB8900593D0

Abstract

An integratable transceiver comprises a Gunn diode harmonic oscillator whose output is coupled by way of a square waveguide section (14) and a circular polariser (48), interfacing with the square waveguide section (14), to an antenna. A return signal has its E field rotated through 90 degrees by the circular polariser (48) as it propagates into the square waveguide section. A receiver front end comprises a sub-harmonic mixer which has a first probe (50) projecting into the square waveguide for coupling-out the return signal and a second probe (56) for providing a local oscillator signal. The sub-harmonic mixer comprises a pair of anti-parallel connected diodes and the connection of the first probe is by way of suspended stripline. The described integratable transceiver can be used in FMCW radars and avoids the need for a circulator when using a single antenna. The Gunn diode is mounted in a harmonic oscillator cavity (14') and the local oscillator signal is produced by a parallel mounted fundamental cavity 32. The fundamental cavity (32) acts as a locking control on the harmonic cavity (14') via a coupling probe (30). <IMAGE>

Description

DESCR1PlrION INTEGRATABLE TRANSCEIVER The present invention relates to an integratable transceiver, more particularly to a crossed-circularly polarised mmrwave transceiver.

Conceptually one of the simplest radars is an FMOW radar in which a continuously energised oscillator has its output frequency modulated. The modulated output of the oscillator is supplied to an antenna by way of non-reciprocal means, such as a circulator.

The return signal having the same polarisation as the transmitted signal is detected by the antenna and is passed by the non-reciprocal means to a receiver, the front end of which comprises a frequency dcwnconverter formed by a mixer having a first input for the return signal and a second input for a local oscillator signal derived by coupling-out part of the oscillator signal. The IF signal produced by this operation is passed to a detector stage for subsequent processing.

The FMCW radar is capable of being integrated but it is desired to make it even more ccmpact without affecting its performance.

According to the present invention there is provided an integrated transceiver comprising a Gunn diode harmonic oscillator having a signal output for a signal to be transmitted, a square waveguide section coupled at one end to the signal output, a circular polariser interfacing with the other end of the square waveguide section, signal propagating and receiving means coupled to the circular polariser, a sub-harmonic mixer, a first probe in the square waveguide section for supplying a received signal to the mixer and means for supplying a local oscillator signal to the mixer, the mixer having an output for an intermediate frequency signal.

The transceiver made in accordance with the present invention is based on the realisation that it is possible to use cross circular polarisation for the transmission and reception of signals and be able to receive an adequate return fran the target. The square waveguide facilitates the propagation of both signals. By using a circular polariser, the transceiver can be integrated without a circulator and a load which reduces its cost and size.

In an ewtodiment of the present invention the Gunn diode harmonic oscillator comprises a second harmonic oscillator consisting of a harmonic oscillator cavity and a fundamental cavity, the harmonic oscillator cavity being coupled to the square waveguide section. A second probe disposed in the fndamental cavity, comprises the means for supplying the local oscillator signal. The mixer is located between the harmonic oscillator and fundamental cavities and comprises a pair of anti-parallel diodes. At least the first probe is connected to the mixer by suspended stripline.

The harmonic oscillator and fundamental cavities of the Gunn diode harmonic oscillator may comprise respective first and second waveguide sections. It has been noted that the brientation of the harmonic oscillator and fundamental waveguide cavities of a Gunn diode oscillator are parallel but have orthogonal E-fields. Consequently a linear and planar mixer (using suspended stripline or coplanar technology) can be placed between the two waveguides so that the fundamental local oscillator signal in the fundamental cavity couples strongly to the mixer whereas the (second) harmonic signal at the first probe (or signal port) of the mixer in the harmonic oscillator cavity does not couple. Hence all the (second) harmonic power is available for transnission.

If desired a backsnort is provided in the fundamental cavity of the Gunn oscillator at a distance fran the second, (local oscillator) probe corresponding to substantially a quarter of the wavelength of the fundamental frequency of the Gunn oscillator.

The provision of the backshort enables an open circuit to be presented at the plane of the second probe and avoids it being loaded by a short circuit or reactive impendance.

A post constituting a backsnort for the return signal may be located in the square waveguide on the opposite side of the first probe to the circular polariser and at a distance fran the first probe corresponding to substantially a quarter of the wavelength of the return signal. The provision of the post lying in the plane of the return signal prents the return signal fran propagating down the square waveguide section towards the Gunn diode whilst letting the signal to be transmitted propagate substantially unattenuated in the opposite direction.

The present ineention will now be described, by way of example, with reference to the accorpanying drawings, wherein: Figure 1 is a block schematic diagram of a transceiver made in accordance with the present invention; Figure 2 is a diagrammatic perspective view of an embodiment of the transceiver made in accordance with the present invention, Figure 3 is a longitudinal cross sectional view of the transceiver shown in Figure 2, Figure 4 is a cross sectional view on the line IV-IV of Figure 3, and Figure 5 is a perspective view on the line V-V of Figure 3.

In the drawings the same reference numerals have been used to indicate corresponding features. The drawings are not to scale.

Referring to Figure 1, the transceiver comprises an oscillator 10 for generating a signal 2FLo having for example a frequency of 94GHz. The signal 2FLo is transmitted to an antenna 12 by a square waveguide section 14 which is interfaced with a circular polariser (not shown in Figure 1). A return signal Fs pick-up by the antenna 12 is relayed by the circular polariser and the square waveguide section 14 to a receiver 16 in which it is frequency dcwn-converted using a fundamental frequency F0. An IF signal is produced which is processed further.

Referring now to Figures 2 to 5, the oscillator comprises a twin cavity, varactor tuned, second harmonic Gunn diode oscillator. A suitable oscillator is described and claimed in EurcEean Patent Specificaticn 0 114 437 (Applicants reference B 32947 EP). For the sake of ccmpleteness the oscillator will be described briefly.

The oscillator comprises a rectangular waveguide section 14' of standard cross-section terminated at one end by a movable non-contacting short-circuit 18 (Figure 3). The rectangular waveguide section 14 is of a cross-section suitable for propagating millimetre wavelengths. A Gunn diode 20 (Figure 4) designed for oscillation at a fundamental frequency FLo, for example 47GHz, below the cut-off frequency of the rectangular waveguide section 14 is mounted in a central longitudinal plane of the waveguide section on a heat-sink 22 received in a bore in the lower wall of the waveguide section.The diode 20 is coupled to the waveguide section 14 and to a D.C. bias supply by means of a resonant cap structure ccmprising a thin circular disc or cap 24 and a post 26 which extends to an R.F. choke 28 mounted in a bore in the upper wall of the waveguide section. The disc 24 is in contact with the upper terminal of the diode and extends parallel to the facing broad walls of the waveguide section. The R.F. choke 28 is of knawn construction and is dimensioned to have a cut-off frequency below the fundamental frequency of oscillation.

As so far described, when a suitable bias voltage is applied to the Gunn diode 20 via the choke 28, the diode generates microwave energy both at a fundamental frequency FL3 and at a second harmonic frequency 2Fw (and possibly also at higher harmonic frequencies), the values of the frequencies being mainly dependent on the resonant cap structure and particularly on the diameter of the disc 24; the position of the short-circuit 18 has little effect on the values of the frequencies but is adjustable to optimise the power output at FW.

An electric probe 30 extends linearly into the waveguide section 14' so as to be adjacent the disc 24. In this embodieent, the probe 30 extends above the disc 24 (i.e. on the side thereof remote fran the Gunn diode 20), and in the longitudinal direction, intermediate the short-circuit 18 and the transverse plane of the Gunn diode as to be close to the periphery of, and parallel to, the disc. The probe 30 can be used to couple to the diode 20, via the resonant cap structure, a locking signal supplied along a further, rectangular waveguide 32. The waveguide 32 extends parallel to the waveguide section 14' and is of a larger cross-section than the rectangular waveguide section 14'.The waveguide 32 has a cutoff frequency below the fundbmental frequency F of the Gunn diode 20 mounted in the rectangular waveguide section 14'. The relative positions of the two waveguides are such that the probe 30 projects into the waveguide 32. Where the probe passes through the cation wall of the two waveguides, it forms the central conductor of a coaxial line having longitudinally-successive portions 33 and 34 in which the outer conductor has larger and smaller diameters respectively. The impedance of the portion 33 of the coaxial line is higher than that of the adjacent portion 34 extending to the narrow wall of the waveguide section 14'.

This latter portion 34 of the coaxial line is approximately a quarter wavelength long at the second harmonic frequency 2Fm so that at that frequency, the impendance of the portion 33 is transformed to a very low impedance at the wall of the rectangular waveguide section 14 and thereby inhibits the leakage of energy at that frequency, F from the waveguide resection 14'.

The vqulde 32 is terminated in a fixed short-circuit 36 to form a resonant cavity. A varactor diode 38 is disposed adjacent to that broad wall of the further waveguide 32. The varactor diode 38 is coupled to said broad wall both at D.C. and at R.F. The varactor diode 38 is coupled to the resonant cavity at R.F. by way of a radial line transformer 39 and is biased with a direct voltage by means of a conductive post 40 which extends through the opposite broad wall of the waveguide 32 and is insulated therefrom at D.C. The resonant cavity also has a dielectric tuning screw 42 for mechanically adjusting the resonant frequency of the cavity.

In operation, a locking signal is supplied along the waveguide 32 in the direction of the arrow 44 (Figure 3) at a frequency which is at or fairly close to the fundbmental frequency Fw of the oscillator in the absence of the locking signal.

Energy at a frequency which is twice that of the locking signal will then propagate along the waveguide section 14 in the direction of the arrow 46. If the frequency of the locking signal is varied, the harmonic frequency 2FLo will ranain locked to twice the locking signal frequency over a tuning or locking range which increases as the power of the locking signal in waveguide 32 increases and as the extent to which the probe 30 projects into the waveguide section 14', and hence the magnitude of the coupling to the resonant cap structure, increases.

The harmonic frequency 2FLo propagates in the direction of the arrow 46 into a transceiver section in which the cross-section of the waveguide has changed fram rectangular (14') to square (14) by a variation in the height of the narrower wall of the waveguide. The square waveguide section 14 interfaces with a circular polariser 48 of conventional design and the polariser 48 in turn is connected to the antenna 12 (Figure 1).

The return signal F5 received at the antenna 12 passes through the circular polariser 48 which rotates its plane of polarisation so that it is at right angles to that of the transmitted signal.

The E-field directions for the transmitter Et and the receiver Er are shown in Figure 5.

The receiver section of the illustrated transceiver comprises a first probe 50 which ccuples-out the received signal fran the square waveguide section 14. This probe 50 is connected to a suspended stripline 52 which is used to drive a subbarmonic mixer cansisting of an anti-parallel pair of diodes 54 connected as shown in Figure 5.

A local oscillator signal, Fw, is applied to the diodes 54 by means of a second probe 56 which couples into the rectangular waveguide 32 to derive the fundamtntal frequency signal. An IF frequency signal is derived fran the mixer by a lead-out 58. A backabort 60 is positioned in the further waveguide 32 a quarter of a wavelength of the fundbmental frequency Fw beyond the second probe 58. The provision of the backsnort 60 enables an open circuit to be presented at the plane of the second probe 56 and avoids it being loaded by a snort circuit or reactive impedance. The length of the second probe 56 determines the degree of local oscillator coupling.The first and second probes 50, 56 and the mixer circuitry can be printed on a low dielectric constant (Duroid) substrate and manufactured using conventional photolithographic techniques. An insulating gasket 59 is provided between the side of the substrate having electrically conductive tracks thereon and the wall of the waveguide.

Optionally a post 61 can be mounted in the square waveguide section 14 at a quarter of a wavelength of the return signal, that is Fs/4 fram the first probe 50. The post 61 which is aligned with the E-plane of polarisation of the return signal in the square waveguide section 14 is used as a backshort and prevents the return signal fram propagating into the rectangular waveguide section 14' towards the Gunn diode 20. The positioning of the post 61 is such that it has no effect on the transmitted signal as its E-plane of polarisation is orthogonal to that of the return signal.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already knawn in the design, manufacture and use of mmrwave integrated transceivers and component parts thereof and which may be used instead of or in addition to features already described herein.

Although claims have been formulated in this application to particular coSbinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefran.

Claims

ClAIM(S)

1. An integrated transceiver catprising a Gunn diode harmonic oscillator having a signal output for a signal to be transmitted, a square waveguide section coupled at one end to the signal output, a circular polariser interfacing with the other end of the square waveguide section, signal propagating and receiving means coupled to the circular polariser, a sub-harmanic mixer, a first probe in the square waveguide section for supplying a received signal to the mixer and means for supplying a local oscillator signal to the mixer, the mixer having an output for an intermediate frequency signal.

2. A transceiver as claimed in Claim 1, wherein the Gunn diode harmonic oscillator comprises a harmonic oscillator cavity and a fundattaatal cavity, the harmonic oscillator cavity is coupled to the square waveguide section and wherein the means for supplying the local oscillator signal comprises a second probe disposed in the fundamental cavity.

3. A transceiver as claimed in Claim 1 or 2, wherein the mixer is located between the harmonic oscillator and fundamental cavities and comprises a pair of anti-parallel connected diodes and wherein the first probe is connected to the mixer by suspended stripline.

4. A transceiver as claimed in Claim 3, when appended to Claim 2, wherein the first and second probes and mixer circuitry are formed on a low dielectric constant substrate.

5. A transceiver as claimed in Claim 2 or 4 or Claim 3 when appended to Claim 2, wherein the harmonic oscillator and fundamental cavities comprise first and second rectangular waveguide sections, respectively, the Gunn diode is disposed in the first waveguide-section which is dimensioned to cutoff the fundarnantal frequency of the Gunn oscillator and wherein the second waveguide section is dinensicned to have a cut-off frequency below that of the fundamental frequency of the Gunn oscillator.

6. A transceiver as claimed in Claim 5, wherein a backshort is provided in the second rectangular waveguide section at a distance fran the second probe corresponding to substantially a quarter of the wavelength of the fundamental frequency of the Gunn oscillator.

7. A transceiver as claimed in any one of Claims 1 to 6, wherein a post constituting a backssort for the return signal is located in the square waveguide section on the opposite side of the first probe to the circular polariser and at a distance from the first probe corresponding to substantially a quarter of the wavelength of the return signal.

8. An integrated transceiver constructed and arranged to operate substantially as hereinbefore described with reference to and as shown in the accatpanying drawings.