Suppression of RF interference using balanced filter in communication system

A new differential feeding scheme is proposed to degrade the influence of common-mode noise on antennas in the communication system. The investigation of the impact of the common-mode noise on quasi-Yagi antenna is presented. The radiation pattern of the antenna becomes asymmetrical as the common-mode noise coupled to the antenna. The conventional differential feeding line is replaced with a balanced filter to improve the performance of the antenna. The compact balanced filter is proposed to transmit the differential-mode signal within the desired passband and significantly suppress the unwanted common-mode noise around the differential-mode passband. The balanced filter is designed at 3.8 GHz and can provide over 40 dB common-mode rejection level. By incorporating the proposed balanced filter into the antenna, the radiation pattern of the antenna becomes symmetrical and the cross-polarization level is also reduced over 25 dB at 3.8 GHz.