A compact dual-band bandpass filter for WLAN and 5G bands based on dual-mode resonators

To accommodate the simultaneous operation of WLAN and 5G in miniaturized communication devices, designing a compact dual-band bandpass filter (DBBPF) that supports both frequency bands within a constrained physical footprint is critically important. This paper presents a DBBPF based on the T-shaped short-circuit line loaded circular patch resonator (TSLCR) and the dual-mode coupled half-wavelength uniform impedance resonator (DCH-UIR). The source-load coupling feed technique is adopted to achieve independent control of the passbands, centered around WLAN frequency band (2.35 GHz) and 5G frequency band (3.65 GHz). The proposed design addresses two key limitations of prior works: (1) mutual coupling between passbands hindering independent adjustment, and (2) large footprint due to conventional resonator geometries. A coupling short-circuit line is used to enhance the source-load coupling strength, and one transmission zero at 4.1 GHz is introduced to improve the performance of the stopbands. The filter exhibits excellent performance in both WLAN and 5G frequency bands, with low insertion loss, high return loss and multiple transmission zeros. The DBBPF has been designed, manufactured and measured, and the simulation and measurement data are basically consistent, which proves the feasibility of flexibly adjusting the center frequency and bandwidth of the passbands during the design of this structure.