Miniaturized Wide-Stopband Filter Based on Quadruple-Mode FSIW-Patch-LC Resonator

In this letter, a new miniaturized wide-stopband filter with high-frequency selectivity based on the single-cavity quadruple-mode hybrid resonator is proposed. The modified patch with loading slot and metal via is first embedded in the folded substrate integrated waveguide (FSIW) to design the single-cavity quadruple-mode resonator (TM
₁₀₀
,
LC
, TE
₁₀₁
, and TE
₂₀₁
). Meanwhile, this embedded patch reduces TE
₁₀₁
and TE
₂₀₁
, while other high-order FSIW modes keep unchanged, so miniaturized size and wide stopband can be realized easily. Additional transmission zeros near the passband can improve the frequency selectivity by the cross coupling between FSIW modes and two other modes (TM
₁₀₀
and
LC
). In final, a prototype with 3-dB fractional bandwidth (FBW) of 11.2% is designed and fabricated at 5.94 GHz (
$f_{0}$
). The upper stopband of this filter is extended to 13.3 GHz (
$2.24f_{0}$
) with a rejection level of 24 dB. It occupies only
$0.165~\lambda ^{2}_{g}$
, where
$\lambda _{g}$
is the guided wavelength at
$f_{0}$
.