Wide Stopband Bandpass Filter With Higher-Order Mode Suppression

To meet the requirement of band selection performance and low loss in wireless communication system, a wide stopband bandpass filter with higher-order mode suppression is proposed in this paper. The filter utilizes the high-pass characteristic of the Half Mode Substrate Integrated Waveguide (HMSIW) to produce a lower stop-band. A quarter-wavelength resonator is used to generate a transmission zero at the upper band. Thus, the bandpass effect is realized from 3.4 to 5.6 GHz. The 3 dB relative bandwidth reaches 46.7%, the in-band insertion loss is less than 0.7 dB, and the return loss is better than -15 dB. The transverse slots of the resonant part cut the surface current flow and effectively suppress the higher-order TE mode; the additional metal vias near the electric wall are equivalent to the inductors for storing magnetic energy, which reduce the harmonic interference of higher-order TM modes. The -25dB stopband of the filter is from 6.5 to 17 GHz, thus a wide stopband of 3.7 times of center frequency is realized. The measured results are well matched with simulated ones. The filter has the characteristics of simple structure, low profile, low loss, and easy fabrication, which provides a novel concept for the design of high-performance filtering devices in radar and aerospace systems.