To address the trade‐off between the poor integration of traditional waveguides and the severe high‐frequency radiation loss of microstrip lines, a novel bandpass duplexer is proposed based on substrate integrated waveguide (SIW) hexagonal resonators. The design integrates the flexibility of a rectangular resonator with the high quality factor characteristics of circular cavities. By constructing SIW resonators with a hexagonal geometric configuration and combining a three‐cell cascaded structure with cross‐coupling theory, transmission zeros are introduced at the passband edges to regulate the electromagnetic field distribution. A duplexer is designed and fabricated for center frequencies of 6.8 and 7.9 GHz, with relative bandwidths of 3.5% and 7.5%, respectively. The measured results show that the isolation between passbands reaches −55 and −43 dB, the out‐of‐band rejection is better than −40 dB, and the measured results are in good agreement with the simulation results. This scheme combines the advantages of low radiation loss, high power‐handling capability of SIW structures, and the integration advantages of planar technology, providing a new path for the design of high‐performance duplexers in microwave and millimeter‐wave frequency bands.
Liu et al. (2026) studied this question.