Development of a two-way microwave communication system for traffic applications

Chan, Tak Kwong (1994) Development of a two-way microwave communication system for traffic applications. Doctoral thesis, University of Northumbria at Newcastle.

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Abstract

This thesis presents the results of the research that has been carried out in order to realise a highly reliable two-way microwave based digital communication link between a radio beacon and a moving vehicle. Such a system can be used for traffic applications such as automatic road and corridor (lane) tolling.
The emphasis of the research has concentrated on the design of the system in order to meet the required system specifications in terms of range, data rate and communication zone, etc. In particular the research has also focused on the design and realisation of the in-vehicle unit (called on-board-unit) which has to be small in size and inexpensive. To achieve the above objectives, novel designs have been produced for both a circularly polarised patch antenna and a single-diode approach for the on-board-unit. Circular polarisation is obtained using a microstrip square patch antenna and a 3dB two-branch coupler. In order to match the coupler to the antenna, the characteristic impedance of the matching line has to be very
high and this results in a very narrow microstrip line that is difficult to realise. Thus the design of the coupler has been modified in order to have a lower characteristic impedance of this matching line, making it wider and easier to realise.
In respect of the design of the road-side beacon's antennae, a 4 by 4 planar antenna array has been developed, including the effect of mutual coupling between the patches. The mutual coupling between two patches has also been studied in detail using both the transmission line
model and the cavity model. For the transmission line model, a new approach has been developed in deriving a simpler expression for the mutual conductance between the patches. The new derived formula for the mutual conductance can be readily evaluated.
Further, a unique method has been implemented for an ASK demodulation and a PSK modulation using a single diode at the on-board-unit. An analysis for a non-ideal PSK modulation was also presented. Finally a two-way microwave communication system has been successfully realised and evaluated. Good performance was achieved.
As a result of the above work, two reports have been published in the Commission of the European Communities documents (November 1992 and May 1994), one paper has been
published in the IEE Colloquium Proceedings (11 June 1993), one paper is to be published in the 24th Microwave Conference Proceedings (5-8 September 1994) and one paper is to be published in the Microwaves 94 Conference and Exhibition Proceedings (25-27 October 1994) and these are listed in Appendix M.

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