Compact broadband waveguide diplexer for satellite applications

High-performance diplexers are frequently used in satellite systems to isolate the high-power wideband transmission band from the sensitive reception frequency range. A compact broadband waveguide diplexer to cover the Ku transmission and reception bands is proposed in this paper. The overall bandwidth of the diplexer is up to 50 %. The diplexer is composed of an E-plane T-junction which branches to a very compact Ku-band high-power low-pass filter and a band-pass filter based on inductive irises. The low-pass filter is based on λ/4-step-shaped bandstop elements separated by very short (ideally of zero-length) waveguide sections and provides the suppression of all higher-order modes. The size of the low-pass filter is dramatically reduced compared to a classical waffle-iron filter or a corrugated filter of narrowed width for the same frequency specifications. The band-pass filter has been also designed to minimize the overall footprint. The final diplexer has been manufactured by milling and the frequency response has been measured. A very good agreement between the measurements and simulations taking into account rounded corners effects has been obtained, demonstrating that this novel approach fulfills stringent specifications with a very compact implementation.