Design of a Capacitive Gap-Coupled Filter Based on Metal Micro-Coaxial Structure

This paper presents the design of a copper-based micro-coaxial structure applied to a K-band capacitive gap coupled narrowband filter. The filter features a passband center frequency of 22.7 GHz with a fractional bandwidth of 4.6%, achieving a return loss greater than 13 dB over the frequency range of 22.2-23.15 GHz. Its dimensions are 0.6 mm ×0.5 mm ×26.7 mm. Compared to the conventional planar narrowband filters, this filter can effectively balance bandwidth and insertion loss with a limited number of filter stages, which demonstrates significant potential for integrated applications.