U.S. Philips Corporation

Stuart M Feeney

David Hillary Evans

Ian M Clarke

Kenneth Holford

In multiple-channel microwave transmitters and communications systems, such as multi-point video distribution systems operating at frequencies of around 29 GHz or 40 GHz, good frequency stability for each of the channel frequencies is achieved with a feed-back loop including an error detector circuit. The error detector circuit (39,29) is coupled between a sampler and an input circuit of the source. This detector circuit detects any drift or other error in the carrier frequency of the sample from the desired microwave frequency for that channel signal and provides a corrective signal to the input circuit. The part of the feed-back loop comprising at least a part of the detector circuit is common to a group of the channels. Switch means couple the common part of the feed-back loop between the sampler and the source input circuit of each channel, and so permit this common part to be time multiplexed between the respective feed-back loops of the group of channels. The input circuit for each source applies an up-datable bias signal for regulating the frequency of the source in accordance with the last corrective signal generated by the detector circuit for that source. By adopting such a stabilisation arrangement in accordance with the present invention, expensive component parts of the feed-back loop can be common to a group of the channels, so reducing the assembly cost of the multiple-channel transmitter. Good long-term frequency stability for all the channels can be obtained, including a reliably constant frequency relationship between the channels.

Microwave transmitter and communications system

In addition to a first opening (11) forming a primary output from a waveguide cavity (10) of a microwave oscillator, a coupling aperture (12) in a reflective wall (32) provides a secondary output which does not degrade the performance or tuning characteristics of the source. Less than -20 dB of the source power may be coupled out via the aperture (12) and is used in a feed-back loop (12,21,23,24,36) with an harmonic mixer (21) and frequency discriminator (24) to stabilize the source. The mixer comprises a further waveguide section (15) separated from the source cavity (10) by the reflective wall (32). An advantageous mixer assembly comprises a circuit substrate which is mounted across the further waveguide cavity (15) and which carries an inductive probe by which the signal from the coupling aperture (12) is fed to an antiparallel pair of mixer diodes on the substrate. The whole assembly may be bolted together through holes (34).

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Campbell, CA, United States of America

Stuart M Feeney