A Differential Low-Pass Filter With Wide Upper Stopband and Excellent Common-Mode Suppression

A compact high-performance differential low-pass filter (LPF) based on the double-sided parallel-strip line (DSPSL) structure is proposed simultaneously, featuring a wide upper stopband and excellent common-mode (CM) suppression. The intrinsic CM noise suppression can be realized with a compact circuit size due to the DSPSL phase inverter. For the differential-mode signal excitation, the low-pass response with small insertion loss (IL) and superior out-of-band rejection is exhibited. For practice, the fabricated and measured differential LPF prototype with the 1-dB cutoff frequency $f_{\text {c}}$ of 1.0 GHz demonstrates up to $14f_{\text {c}}$ of a wide upper stopband rejection over 20 dB. In addition, the excellent CM suppression is better than 40 dB over the entire measured frequency range from 0 to $14f_{\text {c}}$ .