| Cassegrain antennas have been widely used in long distance communication systems and high-resolution radars, because of its high-gain, low side lobe, and high resolution characteristics. With increasing demand of high precision detectors, the study and design of multi-beam antennas are of great significance nowadays. In this thesis, design of60GHz/78GHz dual-frequency, multi-beam Cassegrain antennas has been investigated according to the demand of a prescribed engineering application. The main research work is as follows:Firstly, the basic principle of Cassegrain antennas is interpreted. Parametric study on Cassegrain antennas characteristics has been conducted to obtain the effective design principle. A Matlab program is written to adjust the parameters of the Cassette antenna.Secondly, design of horn antennas is investigated to provide the source of Cassegrain antenna, in which calculation of the equivalent phase center of the horn antenna is emphasized. Based on above analysis, a single beam Cassegrain antenna with small diameter is developed at78GHz. Measured results agree well with simulated ones, which show that antenna has a good standing-wave ratio and a maximum gain of32.8dB, i.e., corresponding to aperture efficiency of58.8%.Based on the previous work, the optimized design of a60GHz/78GHz dual-frequency, multi-beam Cassegrain antenna has been implemented with a gain of32.8dB, i.e. the aperture efficiency of50%. The angle between two beams of±1.35°is achieved with1.9°beam width for a single beam.Finally, dielectric rod antennas are further considered to be feed antennas for multi-beam Cassegrain antenna in order to break through the limitation of the feed aperture size on the angle between beams. A dual-beam Cassette antenna with dielectric rod feed has been designed at78GHz, and the angle of±0.77°between two beams is achieved with single beam of1.7°, which is more suitable for the engineering application of detection systems. |
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