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.%该文提出一种新型阶跃阻抗谐振器(SIR)型低通滤波器.设计SIR开路枝节结构,使之具有二阶低通滤波器的特性,从而达到损耗低、阻带宽、结构紧凑,能很好地改善带外抑制,提高频率选择性.实验测得通带内的插入损耗均在-0.3 dB以内,插入损耗大于15 dB的阻带宽度达到9 GHz,而3 dB截止频率是7.2 GHz.这种谐振器可广泛用于各种微波系统中.给也了该二阶低通滤波器的等效电路和电路参数,电路仿真、全波电磁仿真和实测结果基本上吻合.为了进一步增加阻带带宽,抑制高次谐波,又提出一种带SIR开路枝节和倒T型开路枝节的三阶低通滤波器,它具有更宽的阻带特性.
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