Research Of Dual-Polarization Feed For Millimeter Wave Monopulse Antenna

Dual-polarization feed for millimeter wave monopluse radar is studied in this paper. Firstly according to the structure of feed, a new orthomode transducer (OMT)is designed, which is key component in feed system, and its operating principle is described. Then OMT is analyzed by a hybrid method that combines mode expansion and finite element method (FEM) based on Helmholtz equation weak form. Mode Expansion other than PML is applied to truncate the FEM computing domain into the finite and smaller one. The 3-dimension vector-FEM is used to model the OMT structure, while the computing space of finite element is truncated by Mode Expansion. A sparse matrix obtained subsequently is solved by SSOR-BCG algorithm to get S parameters of the OMT. The results accord with that computed by Ansoft HFSS.An unsymmetrical-branch OMT at Ka band is designed and analyzed in this paper. After structure parameters optimization, return losses of both orthomodes are better than 20dB over 11% frequency band, and its isolation is better than 60dB. Besides, W band un- symmetrical-branch and Ka band symmetrical-branch are designed and optimized. The computed S parameters are presented.In the end of this paper, a 3-dimension framework of dual-polarization monopulse antenna feed at Ka band is described, which is structured with five square horns, five OMTs, four Magic Tees and some waveguides. It has a whole dimension of about 200mm*200mm*300mm. The framework can be a reference for manufacture.