A Quad-Operation-Mode Tunable SISL Bandpass Filter With Compact Size and Self-Packaging

This letter presents a quad-operation-mode tunable bandpass filter (BPF) using substrate integrated suspended line (SISL). The filter combines separate electric and magnetic coupling paths (SEMCP) with varactor loaded, which realizes the tuning of frequency and bandwidth. Source–load coupling and stub loaded are introduced to filter to increase the number of transmission zeros (TZs) and achieve a wide stopband. The measurement results, which agree well with the simulations, show that the frequency and bandwidth tuning ranges are 0.6–1.32 GHz and 50–190 MHz, respectively. The stopband of better than 18 dB is more than
$6\times $
the center frequency. In particular, the circuit size is only
$0.09\lambda _{g} \times 0.07\lambda _{g}$
(
$\lambda _{g}$
is the guided wavelength at 0.96 GHz, which is the center of the frequency tuning range).