Abstract:

A novel two-order lowpass filter with a stepped impedance resonator (SIR) open-stub is proposed. The
filter improves performance of out-band rejection and cutoff frequency response by using an SIR open-stub, having
advantages of low loss, wide stop band and compact structure. The measured insertion loss in pass band is below
?0.3 dB and the rejection bandwidth at insertion loss greater than 15 dB is 9 GHz. The measured 3 dB cutoff
frequency of the two-order lowpass filter is 7.2 GHz in the pass band. It can be widely used in various microwave
systems. Circuit simulation results, EM simulation, and experimental results of the two-order lowpass filter are in
good agreement, showing feasibility of the lumped-element equivalent circuit. In order to broaden stop band and
suppress high order spurious signals, a three-order lowpass filter loaded with open SIR-stub and reverse T-stub is
also proposed.

Key words: SIR open-stub, lumped elements equivalent circuit, resonator, lowpass filter