Design of wide stopband lowpass filter using transformed radial stub based on substrate integrated suspended line technology

Abstract

A novel planar elliptic function lowpass filter (LPF) based on substrate integrated suspended line technology is developed and investigated. Transformed radial stub, stepped‐impedance resonators, and open stubs are cascaded to obtain sharp roll‐off and wide stopband. The proposed LPF produces six transmission zeros in the stopband, and the mechanism of the transmission zeros is studied. Both the simulation and measurement are conducted to verify the performance of the proposed filter, and good agreement between the simulated and measured results is observed. The filter shows attractive characteristics such as low insertion loss<0.6 dB, high return loss of 20 dB, wide stopband from 3.85 to 24 GHz with −20 dB attenuation level and a small area of 0.20 λg × 0.14 λg, where λg is the waveguide length at the cutoff frequency.