Highly Selective Bandpass Filter for the Input Multiplexer of C-Band Satellite Communication

A channel bandpass filter of the satellite communication multiplexer has been developed around a design consisting of 12 coaxial resonators. To cut the group delay time and considerably improve the selectivity of the device, two additional inductive and two additional capacitive couplings between nonadjacent resonators have been applied. This makes it possible to provide two zero poles near the right and left edges of the passband. To reduce the spread of the passband’s transmission factor, a special method was applied that allows one to somewhat decrease reflection losses near the edges of the bandpass of the filter. This, in combination with the electrodynamic analysis of a 3D model developed for the given design, makes it possible to synthesize a small-size filter with the center frequency of the bandpass f0 = 4 GHz and its width Δf = 45 MHz measured at a level of 0.8 dB from minimal losses. The measured characteristics of the filter prototype are in good agreement with calculation data.