Design of the Compact Wideband Bandpass Filter With Low Loss, High Selectivity and Wide Stopband

In this letter, a novel compact wideband bandpass filter using the asymmetric stepped-impedance resonator (SIR) with one step discontinuity is designed and implemented to achieve characteristics of low loss, wide stopband and very high passband selectivity, simultaneously. The first two resonant modes of the asymmetric SIR are coupled together and applied to create a wide passband. The design procedure is discussed in detail. The proposed filter at center frequency f₀ of 4 GHz has very good measured characteristics including a low insertion loss of 0.5 plusmn 0.3 dB, the bandwidth of 2.9-5.3 GHz, sharp rejection due to two transmission zeros in the passband edge. Experimental results of the fabricated filter show a good agreement with the predict results.