A Miniaturized Bandpass Filter Based on Hexagonal Resonator

This paper proposes a miniaturized bandpass filter (BPF) based on hexagonal resonator. Compared with the rectangular filter structure the hexagonal structure is compact, which can realize the miniaturization of the filter. The Y-shape branches are added to the three inner corners of the hexagon which are not adjacent to each other. At the same time, the input/output ports (I/O ports) position of is changed, two transmission zeros (TZs) are introduced at the high frequency band, and the size of the filter is reduced to achieve further miniaturization. In order to obtain better selectivity at low frequency, a split-ring resonator (SRR) is etched on the ground plane, and a TZ is introduced at low frequency. The simulation results show that the filter designed in this paper has a center frequency of 7.3 GHz along with a fractional bandwidth of 7.8%, which achieves a minimum insertion loss of 0.43 dB in the passband and a return loss better than 20 dB, three transmission zeros are introduced at 6.61 GHz, 8.06 GHz and 10.04 GHz, respectively. The final size of this filter is $0.23\lambda_{g}*0.29\lambda_{g}$, a reduction of 48.2%.