A Miniaturized Eighth-Mode Substrate-Integrated Waveguide Filter With Both Tunable Center Frequency and Bandwidth

This letter presents a miniaturized eighth-mode substrate-integrated waveguide (EMSIW) filter with tunable center frequency and variable bandwidth. The filter uses a stub-capacitor-loaded EMSIW structure which not only achieves miniaturization but also tunes the center frequency. The edge electrical coupling strength between the two resonators can be adjusted by loading varactor to achieve the bandwidth tunability. In addition, two transmission zeros are introduced to improve the upper stopband rejection. Both the simulated and measured results show a center frequency tuning range of 2.17-2.72 GHz, as well as demonstrate a 3-dB BW tuning range of 140-208 MHz around 2.17 GHz, 231-355 MHz around 2.45 GHz, and 314-435 MHz around 2.72 GHz. The measured insertion loss is 1.7-4.8 dB, and the return loss is better than 10 dB for all tuning ranges.