This article presents a dual band bandpass filter by loading two cascaded mushroom resonators inside the cavity of a rectangular substrate integrated waveguide (SIW). The passbands are generated by exciting TE101 and TE201 modes of dual mushroom structures loaded inside SIW cavity. The fundamental mode, that is, TE101 of the entire filter structure is utilized to create the first passband and the next higher order mode, that is, TE201 of the filter structure is employed for the generation of second passband. Due to the incorporation of mushroom resonators into SIW, which are composite right/left handed transmission lines, the anticipated frequency response represents highly selective passbands with three transmission zeros (TZs) and an improved out‐of‐band response beyond the second passband. The effects of some structural parameters of the filter on the control over coupling parameters (k101 and k201) and quality factor (Q) are studied. This modified SIW based dual bandpass filter is fabricated and measured to verify two passbands centered at 2.25 and 4.1 GHz with 12.9% and 10.8% fractional bandwidth (FBW) and minimum insertion loss of 0.86 dB and 1.6 dB, respectively. Mobile satellite communications, weather radar systems and Wi‐Fi technology are the actual fields where such bandpass filters can be thoroughly applied.
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.
A compact dual‐mode bandpass filter adapted from circular substrate‐integrated waveguide (SIW) is presented in this paper. The excited modes of the cavity are controlled by introducing metal vias and loading complementary split ring resonators (CSRRs) to the cavity. Higher order dual resonant modes are used to generate the passband response. Single ring CSRRs with double splits are loaded in the SIW cavity to provide independent control over the passband resonant modes. The loading of CSRRs contributes to further size reduction of the cavity. The fundamental mode of the cavity is controlled by using optimally configured metal vias. Thus, a nearly symmetric passband response and an improved out‐of‐band response below the dual‐mode passband are achieved by suppressing the fundamental mode. The modified SIW cavity loaded with CSRRs reduces the size of the standard circular cavity by 83%. The proposed bandpass filter has center frequency at 8.7 GHz with 14% fractional bandwidth. 0.7 dB is the measured minimum insertion loss with a return loss better than 20 dB.
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