Design of the Multipaction Free High Power Ka-band Diplexer with an E-plane T-junction

In this paper, the design and performance of a low-PIM and multipaction free Ka-band (20/30GHz) waveguide diplexer with an E-plane T-junction is described. The waveguide diplexer consists of a transmit filter and a receive filter combined to the antenna port via an E-plane T-junction. The reason why E-plane T-junction structure was selected is to reduce PIM (Passive Intermodulation) level. In order to handle high power the multipaction analysis was performed in design stage as the peak voltage in the resonator with minimum gap is much smaller than the threshold voltage recommended by ESA/ESTEC. The multipaction analysis margin is greater than 12dB. The manufactured diplexer has good pass band return loss (> 24dB) and high isolation (> 52dB) for both transmit and receive frequency bands. The diplexer does not need any post fabrication tuning. Those mean the analysis results of the waveguide diplexer are verified through the electrical performance test.