A widely-tunable balanced bandstop filter with low reflections and separate stop-bands

A frequency-tunable bandstop filter (BSF) with low reflections, separate stop-bands, and more than one-octave tunable frequency range is proposed. The BSF consists of a pair of frequency-tunable shunt resonant circuits in a balanced configuration, which enables the low-reflection characteristics and a great deal of degree of freedom in its design, such as the separate stop-bands. An X- to Ku-band tunable BSF has been fabricated with a ceramic substrate and commercially-available varactor diodes, and its measured characteristics are presented in this paper.