A Tunable Quarter-Wavelength Coaxial Filter With Constant Absolute Bandwidth Using a Single Tuning Element

This letter presents a novel configuration high-
$Q$
coaxial tunable filter that employs a single rotational mechanism to tune the filter while using fixed
$\lambda $
/4 resonators. A prototype filter is designed for the proof of concept, which has a tuning range of 11.6% from 685 to 770 MHz, over which bandwidth (BW) variation is within 10.5 MHz ± 0.7 MHz. In addition, the proposed design methodology can be scaled to realize higher order filters. The proposed filter promises to be useful in a wide range of telecommunication applications, including flexible payload in aerospace applications.