Optimization of Resonator Couplings in Coaxial Bandpass Filters for Characteristic Stability Enhancing under Operational Impact

This study addresses the challenges of ensuring the stability of characteristics for volume-resonator coaxial band-pass filters with cross-couplings, designed for operation in spacecraft onboard equipment. Two key aspects are considered: the organization of a smoothly adjustable capacitive cross-coupling resistant to mechanical stress, and control of the band-pass filters characteristics sensitivity to its manufacturing tolerances. The study also analyzes the influence of realistic structural gaps during the implementation of an inductive autotransformer-type («wire-type») coupling on the symmetry of the pair of transmission zeros formed in the stop band by the capacitive crosscoupling. An original design for an adjustable capacitive coupling unit with backlash compensation is proposed, which ensures high parameter stability given the correct selection of manufacturing tolerances. The influence of linear and angular uncertainties in the coupling element’s position on filter characteristic variations was analyzed using the Monte Carlo statistical simulation method. A comparative analysis on the effect of manufacturing gaps in the wire-type coupling – often used instead of the more trivial inductive diaphragm type (window) coupling – considering quantitative requirements for the symmetry degree of the zero pairs on the amplitude-frequency response of the transmission coefficients for filters with different relative bandwidths was conducted. It is shown that the use of wire-type coupling significantly for wideband filters (relative bandwidth ~2,4%) reduces the sensitivity of the transmission coefficients amplitude-frequency response to the presence of manufacturing gaps, while for narrowband filters (~1%), and this effect is less pronounced over a wide frequency range. The study results have practical effect for the design of high-reliability microwave devices operating in conditions of the severe mechanical and thermal loads.