Miniaturized, Wide Stopband Filter Based on Shielded Capacitively Loaded SIW Resonators

Based on the full-mode capacitively loaded substrate integrated waveguide (SIW) resonator and the miniaturized shielded half-mode capacitively loaded SIW (S-HMCSIW) cavities, a novel compact high-performance filter is proposed. The footprint of the half-mode SIW (HMSIW) is further reduced due to the application of the capacitive-loading technique. By applying cross coupling, the proposed SIW filter’s transmission zero enhances the stopband rejection and shows excellent selectivity. For the bandpass filter, the measured |S₂₁| and |S₁₁| are better than 1.09 dB and −14 dB, respectively. And a 3-dB fractional bandwidth (FBW) of 9.14–10.76 GHz (FBW=16.2%) is also observed. The filter achieves a wide stopband with a −20 dB out-of-band rejection up to 2.69f₀ (f₀ = 10 GHz), with a size of 0.39λ_g × 0.51λ_g only. Good agreement between measurement and simulation is obtained.