Quarter-Wavelength and Open-End Half-Wavelength Four-Section Coaxial Stepped Impedance Resonators for High-Power Space Bandpass Filters

This article focuses on the comparison of quarter-wavelength and open-end half-wavelength four-section coaxial stepped impedance resonators (SIRs) for the design of Tx bandpass filters with high multipactor thresholds. To obtain a half-wavelength configuration with open ends in an enclosed space, the coaxial sections are stacked on two levels. Despite the strong geometrical difference between the two structures, the same analytical formalism can be used to model their frequency behavior. The synthesis equations show that the first three frequencies (fundamental, first transmission zero, and second harmonic) are independent, making the three impedance ratios between two adjacent coaxial sections, very practical degrees of freedom. They impact sensitivity to technological variations in manufacture and misalignments, power handling, and quality factors. Moreover, the two-level topology makes it possible to obtain another shape factor, and thus, push back size and performance limitations. A comparison was made of the values of the quality factor, obtained with eigenmode and a numerical method. To compare the two configurations, we designed a quarter- and a half-wavelength four-section fourth-order filter in the
$L$
-band. These two four-section filters were also compared with their two- and three-section quarter-wavelength counterparts in terms of electrical performances, bulk, and multipactor threshold. Finally, a comparison with the state-of-the-art is given.