A Compact Independent Triple-Band Bandpass Filter Using Mode Splitting

In this paper, a compact tri-band bandpass filter (TBPF) is proposed. The proposed TBPF employs a multicoupled-line structure to achieve an independence between the inter-passbands. In addition, the triple-band bandpass characteristics are generated separately and independently using two pairs of quarterwavelength resonators with L- and U-shaped configurations. The two pair of resonators were set backto-back creates a second order filter and coupling to the stub transmission lines. The pairs of U resonators create mode splitting results two resonances frequency at 1.87 GHz and 5.82 GHz while two pairs of L resonator create bandpass with a wide$-3$dB bandwidth of 21.6% at 3.35 GHz center frequency. The two of three passband frequencies can be set and designed independently. Consequently, the proposed TBPF achieves a 46.4% size reduction compared to the previously reported TBPF. To validate its performance, the filter was fabricated and measured. The measurement results are in close agreement with the simulations. Overall, the proposed TBPF exhibits compact dimensions and independently controlled inter-passband characteristics.