Ka-band Circularly Polarized Monopulse Antenna

This paper firstly explores the design of two sets of circular polarized monopulse horn antenna array with 28 radiating elements. The suggested antenna was fabricated, and measurement was conducted. The measured result had a good agreement with the theoretical results. Both the simulation and measurement results satisfied the design requirements.The key point of this design was how to obtain the circular polarized wave since the injected wave was linearly polarized. In our design, the radiated field from the horn antenna was a summation of two linearly polarized waves which transmitted in the horn antenna was named as TE10 mode and TE01 mode. If the phase difference of TE10 and TE01 modes was 90 deg, and their amplitudes were the same at the radiation port of the horn antenna, a circular polarized wave was constructed. The feed of the horn antenna was a waveguide which has only one mode that is TE10. To obtain the mentioned two modes, high modes which were filtered with a specified cross-section size of the horn except the required two modes were generated with an inclined-slot connecting the waveguide and horn antenna. The other way to generate the high modes that was studied in this thesis was adding a substrate sheet at the neck of the horn antenna.In this thesis, the classical theory was applied to verify the feasibility of the realization of the radiation characteristics of circular polarization with its far-field radiation performance especially the axial ratio. Then the physical structure of the dual-mode feeder to the pyramidal horn antenna was designed. Three different structures of the radiation element were designed with HFSS. From the three different radiation structures, two sets of the antenna array were composed. The array pattern synthesis was performed to calculate unit number"N", the unit distance"d", and the distribution of exciting current. Then the array was modeled and simulated with ideal distribution of exciting current loaded on each port. After that, sum-difference feed network with H-T cascade structure was designed. The sum-difference function was realized by a folded magic T to save space. The sum-difference network plays a vital role in the performance of monopulse antenna array, especially the puncture surplus of sum-difference beam. At last, the radiation part and feed network were joined together, and the whole simulation and optimization were conducted.Finally, the fabrication and measurement were carried out. The good agreement between the experimental and the simulation results shows the feasibility of the method adopted to the antenna system design.