Compact ultra-wideband bandpass filter implemented with stepped impedance resonators and T-shaped line

A compact ultra-wideband (UWB) bandpass filter (BPF) is implemented with stepped impedance resonators (SIR) and T-shaped line. Fractional bandwidth (FBW) of the UWB BPF can be adjusted properly by changing the impedance ratio of the SIR. A transmission zero is created by the central open stub of the T-shaped line to suppress the second harmonic of the filter. In addition, the filter size is further reduced by introducing T-shaped transmission line. The resulting UWB filter indicates a FBW of 108% with three transmission zeros at 2.3, 11.1 and 13.4 GHz. Good agreement can be observed between simulated and measured responses.