LAUSR

This paper presents a miniaturized resonator achieved by incorporating metal‐insulator‐metal (MIM) capacitors into a quarter‐mode substrate integrated waveguide (QMSIW) resonator. The resonant condition of the resonator is analyzed by equivalent model of the resonator. Additionally, a miniaturized bandpass filter utilizing the proposed capacitive‐loaded quarter‐mode substrate integrated waveguide (CL‐QMSIW) resonator is introduced. This filter comprises four CL‐QMSIW resonators, with magnetic coupling facilitated by short‐circuit striplines. A flexible and adjustable transmission zero (TZ) was achieved by introducing mixed electromagnetic coupling between resonators. A circuit model that represents the filter is developed, and the underlying mechanism for the transmission zero is analyzed and validated. The filter's size is only 6.1 mm*6.1 mm (0.31 λ g ${\lambda }_{g}$ *0.31 λ g ${\lambda }_{g}$ ), where λ g ${\lambda }_{g}$ is the waveguide wavelength in the medium at the center frequency. The center frequency of the filter is 7.3 GHz, the fractional bandwidth (FBW) is 13.7% and the minimum insertion loss (IL) is 1.7 dB. The filter exhibits a TZ at a frequency of 8.95 GHz, thereby enhancing its selectivity. The measurement results confirm that the filter is characterized by its small size and high selectivity, making it well‐suited for integration within RF microsystems.