U.S. Philips Corporation

Kenneth Holford

David Hillary Evans

Alan F Dadds

Stuart M Feeney

Brian J Stocker

David M Nugent

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).

Microwave oscillators and transmitters with frequency stabilization

Information is communicated by microwave radio between transponders (9,10) carried by vehicles (7,8) travelling on a road (1) and a station (22) adjacent the road. The communications from the transponders are effected by the transponders suitably modulating their reflections of beams of microwave energy transmitted by the station from aerials (B) mounted on a gantry (11) above the road, these aerials irradiating respective communication areas (28,29,30). In order to prevent communications from different transponders overlapping and hence interfering with each other the transponders are enabled for their communications by microwave energy from further aerials (A), which energy has a higher frequency to enable it to be beamed at relatively small respective activation areas (23-27) the sizes of which are such that they can each only contain one vehicle and hence one transponder at any given time. The further aerials are activated, one at a time, successively and cyclically, so that the transponders are necessarily enabled in succession, the activation rate being, moreover, sufficient to ensure that all transponders passing through the relevant stretch of road are in fact enabled. During each interval between the activation of each further aerial and the next the station transmits a command from the aerial(s) (B) associated with the further aerial (A) which has just been activated ordering any transponder which has just been enabled to communicate its presence. If it receives such a communication the station transmits an address code from the relevant aerial(s) (B) which is stored in the relevant transponder and used subsequently to selectively address that transponder for further communication.

Communicating information by radio

A device for indicating whether a target is approaching or receding from a Doppler radar or the like comprising a length of wave-guide having a reflective termination at the end at which microwave energy is introduced into the guide, and two mixer diodes spaced along the guide. The diodes are spaced apart along the guide axis by an odd number of quarter-wavelengths and spaced from the termination by an odd number of eighth-wavelengths. Suitably, the diodes are positioned so as to be loosely-coupled to signals within the guide, thereby rendering the selection of suitable diodes much less critical.

Doppler radar device

A Doppler radar system for controlling portable traffic signals in response to on-coming traffic. Each of two channel amplifiers of the system is fixed at high gain and passes both noise signals and Doppler signals to a phase detector. A threshold element provides a control signal when the average level of the phase detector output between high and low levels changes sufficiently, due to the presence of Doppler signals, from a mean level which is due to noise alone.

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Crawley, United Kingdom

Kenneth Holford