A Compact Quarter-mode SIW Bandpass Filter for 5G Power IoT

A quarter mode substrate integrated waveguide (QMSIW) filter is proposed based on substrate integrated waveguide (SIW) technology. It involves implementing frequency-dependent coupling (FDC) to allow the classic triplet to be high selectivity where multiple transmission zeros (TZs) are achieved and independently controlled. First, two QMSIW resonators are cascaded to reduce the occupied area to one quarter. In order to further reduce size, the grounded coplanar waveguide (GCPW) is etched to form additional resonator without expanding the entire physical size, increasing the number of resonators. Hence, a cascaded triplet (CT) is obtained by coupling, where one transmission zero can be individually realized. Meanwhile, the proposed FDC is simultaneously implemented via inductive coupling iris of two QMSIW cavities and the coplanar waveguide to generate another TZ at upper stopband. It might be worth pointing out that TZ can thus be generated and be independently controlled by FDC without any auxiliary cross coupling or extracted-pole technique. In this particular case, the implementation of two TZs at upper stopband improves both out-of-band rejection and sharp skirt characteristic. The simulation result shows that the filter has the insertion loss of about 0.23 dB with the center frequency of 3.9 GHz, relative bandwidth of 30.5%, and return loss better than 21.8 dB. On the other hand, the transmission zeros are located at 4.7 GHz and 5.26 GHz, respectively, which is entirely consistent with the synthesized result. The filter shows the attractive characteristics of low insertion loss, miniaturization, high selectivity and easy fabrication, indicating the great potential applications in other devices such as multiplexers, antennas, low-noise amplifiers, and so on.