Design and Implementation of Monopulse Antenna for Submillimeter Wavelengths Application

This communication presents the methodology design and implementation of a monopulse antenna based on quasi-optical (QO) technology at submillimeter wavelengths. The designed monopulse antenna consists of QO sum-difference comparator, beam-waveguide (BWG) feed systems and Cassegrain dual reflector. The BWG system between the feed horn and QO sum-difference comparator is composed of spherical thin lens, ellipsoid reflector mirrors, and plane mirrors. Four ellipsoid reflector mirrors are employed for the BWG feed system between QO sum-difference comparator and Cassegrain dual reflector. The parameters of all components are determined by using Gaussian beam theory. Then, the antenna configuration is simulated and slightly optimized by finite-difference time-domain (FDTD) method combining with Stratton-Chu formulas. The simulated results have good performance at the center frequency of 375 GHz, with the sidelobe levels below -15.4 dB in sum patterns, the maximum null depth is approximately -34.0 dB and lower than 0.05-dB amplitude imbalance in difference patterns. A prototype of the proposed monopulse antenna was manufactured and measured in the radiating near-field zone. The presented measurement results agree well with the corresponding simulated results and validate the correctness of design indirectly. It indicates that this type of monopulse antenna presents an excellent candidate for tracking systems at submillimeter wavelengths.