Design And Development Of Millimeter Wave High Isolation, Orthogonal Polarization Cassegrain Antenna

Millimeter wave (MMW) radar has features such as short wavelength and narrow beam width. It is suitably used for detecting the structure and the dynamic characteristics of the cloud particles. As a kind of dual reflector antenna with high gain, Cassegrain antenna is widely used in radar detection system. Currently,35GHz (8.6mm) and 94GHz (3.2mm) MMW radars are commonly used in the meteorological observation. In order to satisfy the requirements of dual-frequency detection and extraction of cloud-phase, dual polarized antenna with high isolation shall be designed. In this paper, a 94GHz dual linear polarization Cassegrain antenna and a 35/94GHz dual frequency orthogonal linear polarization Cassegrain antenna were designed respectively.Firstly, the geometric parameters, working principle and engineering design methods of the typical parabolic antenna and Cassegrain antenna were introduced. Secondly, a new type of high isolation feed horn antenna was designed. Based on the H-plane forked magic T-junction, its orthogonal field feeding system adopted the waveguide feed to realize the couple of orthogonal dominant mode waves and high isolation; In order to achieve a high efficiency feed with equal E and H patterns, the design methods of conical horn and dual-mode conical horn were given. Finally, according to above basic theory, a 94GHz dual linear polarization Cassegrain antenna and a 35/94GHz dual frequency orthogonal linear polarization Cassegrain antenna were designed. The research results of 94GHz dual linear polarized Cassegrain antenna show that the gain are 47.4dB and 49.6dB at the two ports respectively, the first side lobe level are -19.2dB and -14.7dB respectively, the isolation between the two ports of the feed is better than -40dB,3dB beam width is less than 0.5°, the cross polarization is better than -30dB. The research results of 35/94GHz dual frequency orthogonal linear polarization Cassegrain antenna show that the isolation between the two ports of the feed is better than -40dB at 35GHz and 94GHz. The antenna gain and side lobe level at 35GHz are better than 40dB and-20dB respectively; The antenna gain and side lobe level at 94GHz are better than 50dB and -20dB respectively. Cross polarization at 35GHz and 94GHz are superior to -30dB.