This paper presents a novel quasi-elliptic function lowpass filter (LPF) by using quasi-lumped elements. The proposed LPF is firstly based on a seven-order Chebyshev response lowpass prototype. Then, a series branches of shunt resonant LC circuit is introduced in the filter design to provide a transmission zero close to the transition band, which can improve the roll-off rate of proposed LPF significantly. To implement the lumped elements of lowpass prototype, the high-impedance meander lines are employed to realized the inductors while inter-digital microstrip lines and the microstrip parallel-plate structures are used to realize the capacitors. To validate the proposed method, a LPF with 3 dB cutoff frequency fc at 1.9 GHz is designed and fabricated. The measured results show that the fabricated LPF has a sharp roll-off rate up to -142 dB/octave and -15 dB harmonic suppression from 1.1fc to 9.7fc. Moreover, the fabricated LPF also has a compact size of 0.1λgc × 0.11λgc. Good agreement can observed between the simulation and measurement.
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