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Develop the theory of the offset phase correcting zoneplate based on dielectric tiles; investigate the limitations of the technique in terms of size, mechanical tolerances, effects of discontinuity etc; design, build and test a prototype unit. Progress:Initially, various dielectric tile configurations, which included the multilayered tiles, tiles with the same thickness but different permittivity, and tiles with the same permittivity but different thickness were considered. Owing to its flexibility, low cost and availability to the investigators, the multilayered configuration was chosen. Then, the research was carried out in parallel in the following three directions: 1 Offset Zoneplate Antennas:An offset Fresnel lens and an offset multilayered zoneplate reflector have been designed and tested [1,2]. A method for predicting the radiation field of offset zoneplates was proposed [1]. This led to the publication of three journal papers.2 Experimental Study:A set of multilayered tiles, 8mm square, with five discrete phase shifts were fabricated and glued to LEGOTM bricks. These bricks were mounted to a LEGOTM baseplate to produce a reconfigurable antenna. Such antennas with various offset angles were produced by re-arranging the positions of bricks. Based on the measurement of a number of small prototypes, two conference papers have been published [3]. A large prototype is being fabricated at our workshop and will be tested in the remaining seven months of the project.3 Theoretical Study on Reflective Arrays:The zoneplate reflector based on tiles is basically a reflective array. The influences of quantisation errors, mechanical tolerances etc. on the antenna efficiency have been analysed through focal fields [4]. Presently, the contribution of these effects to radiation patterns is being investigated. [1] Y.J. Guo, I.H. Sassi and S.K. Barton, Offset Fresnel Lens Antenna , Proceedings of IEE (H), vol. 141 no 6, December 1994.[2] Y.J. Guo, I.H. Sassi and S.K. Barton, Multilayer Offset Fresnel Zone Plate Reflector , IEEE Microwave and Guided Wave Letters, vol. 4, no 6, June 1994.[3] Y.J. Guo, I.H. Sassi and S.K. Barton, A New Flat Reflector with Phase Shifting Tiles Proc of Progress in Electromagnetics Research Symposium (PIERS94), the Netherlands, July 1994.[4] Y.J. Guo and S.K. Barton, Phase Efficiency of the Reflective Array Antenna , Proceedings of IEE (H), to appear.
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