Design of miniaturized quad-mode wideband bandpass filter with multiple transmission zeros

Abstract In this paper, a miniaturized wideband bandpass filter based on transversal signal interference technique is proposed. By introducing two independent signal transmission paths, a highly selective and compact design is achieved. The filter utilizes a combination of two paths to excite four controllable resonant modes, which helps to generate a wide passband. Besides, phase cancellation between the two paths yields five transmission zeros on both sides of the passband, which greatly improves frequency selectivity. The proposed wideband filter has very compact dimensions, where the overall circuit size is only 0.39 λ g × 0.13 λ g ( λ g is the guided wavelength). The center frequency of the designed filter is 4.38 GHz with 3-dB fractional bandwidth of 71.2 %. The design concept has been effectively validated through the experimental results of the fabricated filter, which are in good agreement with the simulated results.