Miniaturized Wide Stopband Half-Mode SIW Bandpass Filter

Miniaturized four pole Half-mode substrate integrated waveguide (HMSIW) bandpass filter is designed with wide stopband and high skirt characteristics. Due to the absence of even harmonics, HMSIW gives wide stopband behaviour. A quarter wavelength resonator is loaded to the filter. It adds a transmission zero (TZ) where this length equals to quarter wavelength and also adds one reflection zero to the filter. To improve the performance at the lower side of the passband, a halfwavelength resonator is arranged in U-shape around the quarter wavelength resonator. It provides bypass coupling and generates a TZ at the lower side of the passband. A four pole HMSIW bandpass filter is fabricated on RT/Duroid 5880 substrate using normal PCB etching process. The simulated insertion loss, return loss, and fractional bandwidth are 1.64 dB, better than 19 dB and 8.8%, respectively.