The Effect Of Antenna Sidelobe On The Radiometer And Low Sidelobe Antenna Design

This paper studies the radiometer performance influenced by antenna sidelobe, and how to reduce the antenna sidelobe level. In the millimeter wave radiometer, the antenna should have low sidelobes, high gain and narrow beam, ect. The main contents of research in this paper is three types of antenna, which are multimode conical horn antenna, cassegrain antenna and offset parabolic reflector antenna, which are needed by department of millimeter wave radiometer projects.Firstly, based on the working principle of millimeter wave radiometer, this paper analyzes which performance of the radiometer is affected by the antenna sidelobe, as well as the role of antenna sidelobe in antenna temperature obtained by the calibration equation inversion.Secondly, a low sidelobe multimode horn antenna is designed in this paper. It mainly introduces the flare-angle discontinuity to generate the high-order modes in conical horn, and adjusts the phasing-section length to abtain an appropriate phase distribution in the horn aperture. The simulated and measured results show that it observably reduces the antenna sidelobe level.Thirdly, it gives the way to reduce the sidelobe level in Cassegrain antenna. Due to the blockage of Cassegrain antenna, this paper designs a new type of conical hom feed instead of previous pyramidal horn feed. The simulated and measured results show that not only reduces the sidelob, also improves the gain.Finally, an offset parabolic reflector antenna is developed. It designs the asymmetry of the offset configuration to suppress sidelobe level, but this configuration results into higher cross-polarization. So it designs a mufli-mode matched feed, according to the characteristics of focal plane field in parabolic reflector surface, to reduce the cross-polarization level. The simulated and measured results show that it gets low sidelobe and cross-polarization simultaneously, so the effect is superior.