A Novel Compact 2.4/5.2 GHz Dual Wideband Bandpass Filter with Deep Transmission Zero

In this study, a novel compact 2.4/5.2 GHz dual wideband bandpass filter was designed and fabricated on an Al2O3 ceramic substrate. First, a dual-band filter was designed based on two open-loop rectangular ring (OLRR) resonators, which were cascaded using a coupling connection in order to increase the bandwidths of the dual passbands. Diverging U-shaped dual feed input/output transmission lines were used for strong coupling. A shunt quarterwavelength open stub eliminated unwanted harmonic frequencies and transmitted the desired passbands. To achieve this, four open stubs were directly added onto the two OLRR resonators as bandstop resonators to reject undesired frequencies and improve the out-of-band rejection between the two resonant frequencies. The coupling sections between the two resonators were modified using a groove structure to regulate the coupling of the two modes and eliminate the ripple at the designed 5.2 GHz band. According to simulated and measured results, the proposed filter with optimized parameters exhibited dualwide passbands with bandwidths of 530 MHz (22.84%) and 650 MHz (12.29%) at 2.32 GHz and 5.29 GHz, respectively.

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