A compact three stub-loaded open-loop resonator-based tri-band bandpass filter with better out-of-band suppression is presented. The position and length of the three stubs loaded to an open-loop resonator determine the position of the three passbands. Mathematical analysis has also been performed to calculate the resonance condition of the proposed resonator. To demonstrate the concept, two second-order filters are fabricated having three passbands centred at f o = 1.93 GHz, f 1 = 3.6 GHz, f 2 = 4.89 GHz and f o = 1.59 GHz, f 1 = 3.12 GHz, f 2 = 4.02 GHz, respectively. The fabricated filters show better 3 dB bandwidth as well. The simulation and measured results are in good agreement.

Open-loop resonators (OLRs) are loaded with one or two stubs to design a compact bandpass filter (BPF) with a wide stopband by creating extra transmission zeros. By properly selecting the length of the stubs and their positions, extra transmission zeros are created in the stopband before the spurious passband, thus giving wide stopbands. Mathematical analyses are performed to show the effect of open stubs on the OLR. A two-stub-loaded BPF is designed and fabricated, which shows a harmonic suppression of up to 3.2f o by creating five transmission zeros and 44% size reduction as compared with a simple OLR-based filter without stubs. Measured results are in good agreement with the theoretical analysis and simulation results.

No abstract

No abstract

Stub-loaded split-ring resonators (SRRs) are presented for the design of a compact tri-to dual-band bandpass filter (BPF). The length of the two concentric split-rings having splits on the opposite sides, the gap between the two concentric split-rings and the length of the stub determine the positions of the three passbands. Switchability has been achieved by controlling the closing and opening of the inner ring of the SRRs using pin diodes. The responses of the BPF depend upon the condition of the switch. Moreover, lumped coupling capacitors are connected between the two SRRs to enhance the bandwidths of the passbands of the BPF. It also permit a greater coupling-gap between the SRRs which further reduces the challenges of fabrication.