Broadband balanced filter with high common-mode suppression and wide stopband based on SIW and SSPP

This paper introduces a novel balanced bandpass filter that utilizes the symmetrical F-shaped groove (SFG) substrate-integrated waveguide and spoof surface plasmon polariton (SIW-SSPP) structure. This design combines lowpass SSPP unit cells within a highpass balanced dual-layer SIW structure to realize bandpass filtering response. The SFG SIW-SSPP unit cell's superior dispersion properties contribute to broad bandwidth and extensive stopband. Additionally, the balanced dual-layer SIW structure, achieved by removing a rectangular aperture from the common ground, allows for high in-band common-mode (CM) suppression and a broad CM suppression range. The proposed filter offers multiple variables to regulate the passband's lower and upper cut-off frequencies independently. A fabricated prototype of the balanced filter is tested, demonstrating superior performance compared to previously reported balanced SIW and half-mode SIW BPFs. The filter achieves a broad 3-dB fractional bandwidth of 46.55% (6.33-10.17 GHz), a wide 20-dB stopband rejection up to 2 f(0) (f(0): the passband's center frequency), and simultaneous broad CM suppression range (24-dB up to 4.85 f(0)).