Dual band bandpass filter based on semi‐circular mushroom loaded substrate integrated waveguide

Abstract

This paper presents a dual band bandpass filter by loading two semi‐circular mushroom resonators (ScMRs) inside the cavity of a circular substrate integrated waveguide (SIW). TM101 and TM201 modes of the mushroom resonator loaded circular SIW cavity are excited to generate the first and second passbands respectively. As the proposed bandpass filter is based on circular SIW cavity, the passbands of the filter undergo relatively low insertion loss (IL) compared to other referred works. The selectivity is improved by generating four transmission zeros (TZs); two TZs are generated in between the two passbands by cross coupling the excited modes of the resonators and other two TZs are generated in lower and upper stopband by the source to load coupling. The passbands of the proposed filter are centred at 2.24 GHz and 4.35 GHz with 13% and 6.2% fractional bandwidth (FBW) respectively. A prototype of the proposed dual bandpass filter occupying a compact area of 0.3λ0 × 0.3λ0 is fabricated in Rogers RT/Duroid 5880. The measured minimum insertion losses for the first and second passbands are 0.9 dB and 1.1 dB respectively with a good agreement observed between simulated and measured results.

Semi‐circular mushroom resonator loaded substrate integrated waveguide cavity based compact triple‐band bandpass filter with high selectivity

“…In the referred works, the passbands at higher order excited modes suffer high insertion loss relative to fundamental mode 8–10,13,14 . As a way out, mushroom resonators have been used to propose SIW‐based bandpass filters with less insertion loss, better selectivity, and improved out of band response 17–21 . Mushroom resonators being composite right/left handed (CRLH) transmission lines, benefit single as well as multiple bandpass filter with enhanced selectivity and improved out‐of‐band response.…”

“…Although, the multi‐mode passband is significantly flat with satisfactory insertion loss but the proposed filter generated single passband only 18 . Later, cascaded mushroom resonators of rectangular and semi‐circular shaped metal patches have been separately loaded in SIW cavities of rectangular and circular geometries in order to propose second order dual‐band bandpass filters 19,20 . In case of Reference 19, the rectangular cavity shaped SIW is loaded with two cascaded mushroom resonators of rectangular shape.…”

“…The offset feeding technique employed to excite the resonant modes and the weak source‐load coupling at the frequency of interest have resulted in the generation of single TZ between the two passbands 19 . Second‐order dual bandpass filter with better passband selectivity and reduced insertion loss in the passbands are proposed on the basis of two cascaded semi‐circular mushroom resonators (ScMRs) loaded into circular‐shaped SIW cavity 20 . Along with the generation of two TZs in the upper and lower stopbands of entire filter response, two more TZs are also generated in between first and second passbands, which have enhanced the entire passband selectivity.…”

“…Along with the generation of two TZs in the upper and lower stopbands of entire filter response, two more TZs are also generated in between first and second passbands, which have enhanced the entire passband selectivity. The cross‐coupling between the excited modes of two ScMRs are responsible for generating two TZs between two passbands and increase the frequency selectivity 20 . The dual bandpass filter proposed in Reference 20 utilizes the benefits of ScMRs and circular SIW cavity to easily excite the resonant modes and reduce the passband insertion loss due to relatively high unloaded quality factor of circular SIW.…”

“…The cross‐coupling between the excited modes of two ScMRs are responsible for generating two TZs between two passbands and increase the frequency selectivity 20 . The dual bandpass filter proposed in Reference 20 utilizes the benefits of ScMRs and circular SIW cavity to easily excite the resonant modes and reduce the passband insertion loss due to relatively high unloaded quality factor of circular SIW. Though loading of mushroom resonators into SIW cavities have been utilized to enhance the passband selectivity and improve the out‐of‐band response but till now it has been useful in proposing dual‐band bandpass filters 18–20 …”