Generic UHF Bandpass Filter with Air-Filled SIR Coaxial Resonators

In this paper we present how we designed and fabricated a UHF cross-coupled 6^th-order bandpass filter able to address central frequencies from 430 MHz to 1.1 GHz. The filter is based on miniature two-section SIR (Stepped Impedance Resonators) built from air-filled coaxial structures fitted inside one another. This particular geometry makes the resonators, and thus the filter, very flexible in terms of central frequency adjustment over a large range of frequencies. The architecture makes it possible to inexpensively build a generic band pass filter, on which we can continuously select the central frequency, with the relative bandwidth remaining constant, over more than an octave, while maintaining an acceptable quality factor.