Quarter-Wavelength Two-Section Coaxial Stepped Impedance Resonators for Harmonics Suppression in Tx Bandpass Filters

This paper presents the implementation of two-section coaxial stepped impedance resonators (SIRs) solution to control the attenuated band of Tx bandpass filters. This type of resonator has two degrees of freedom, in the transverse and longitudinal dimensions. At a fixed fundamental frequency, this allows the dimensions of the resonators to be modulated to control both the location of the harmonics and the power handling for space applications. It is therefore possible to design a filter for which the harmonic frequencies of the resonators are not the same, leading to destructive recombinations in the attenuated band. This is illustrated through the design of a 6th order narrowband L-band bandpass filter with controlled attenuation up to $6.6\times $ F0 and a multipactor threshold of around 30 W. This filter was fabricated in aluminum and tested. The experimental results are presented and discussed. Finally, a comparison is made with the state-of-the-art.