Compact bandpass filter using novel stepped impedance resonators

In this paper, a compact bandpass filter (BPF) with improved stopband characteristics using novel stepped impedance resonators (SIRs) is proposed. The conventional low-impedance stub of SIR is replaced by radial stubs, owing to its intrinsic wide stopband characteristics; the stopband rejection can be widened. A new BPF centered at 1.57 GHz has been designed and fabricated to verify the validity of the proposed method. Measured results are in good agreement with the electromagnetic simulation. The spurious frequencies of the upper stopband are suppressed below 20dB from 2.07 to 16.25GHz. And the circuit only occupies 0.09λ_g×0.09λ_g.