A Differential Filtering Microstrip Antenna Array With Intrinsic Common-Mode Rejection

A differential third-order Chebyshev filtering microstrip antenna array with high common-mode (CM) rejection is presented. The feeding structure consisting of one line resonator and one H-shaped resonator as well as the microstrip antenna elements together provide the three stages in the bandpass filter design. Under differential-mode excitation, the H-shaped resonator can be effectively coupled with the line resonator, and thus differential signals can be radiated. However, under CM excitation, the H-shaped resonator cannot be excited so that the CM suppression can be achieved. A prototype antenna array with center frequency at 3.5 GHz has been designed and fabricated to experimentally validate the principle and design approach. Experimental results exhibit that the proposed differential filtering antenna array features high CM rejection, low cross-polarization level, and good filtering response.