Design of a Miniaturized Cavity Bandpass Filter

A novel design of a miniaturized cavity filter structure is proposed in this paper. The filter adopts a combination of interdigital and combines coupling structures instead of the traditional filter structure to reduce the filter size while ensuring excellent performance. The size is further reduced by adding metal rectangular blocks on the filter covers to increase the capacitance between the open end of the resonant rod and the ground and the coupling between the resonant rods. The critical parameters were designed and optimized by CST Studio Suite. Consequently, a nine-stage bandpass filter was fabricated and realized at 4.75 GHz with a fractional bandwidth of 10.5% and insertion loss of less than 0.7 dB.