Analysis of high power microwave Gaussian feed aperture field

A High Power Microwave square pyramidal Gaussian feed aperture field is analyzed by using the waveguide intrinsic mode expansion method. The key parameter is the Gaussian beam waist radius that is determinded by compromise of the radiation charateristics and breakdown avoidance. The mode ratios of the square waveguide multimodes can be calculated with the slected waist radius, that makes a base for designing a Gaussian feed by mode matching or coupling wave theory．