Differentially fed dual‐band circularly polarized printed slot antenna with high common‐mode rejection

This letter proposes a newly designed differentially fed dual‐band circularly polarized (CP) printed slot antenna (PSA). The antenna consists of two oppositely fed halberd‐shaped strips and an S‐shaped slot. By configuring the antenna structure in rotationally symmetric fashion, the fields radiated by any two rotationally symmetric parts of the CP PSA will be constructive when excited differentially and destructive when in common‐mode (CM) operation. Thus, good differential‐mode (DM) performance and high CM rejection can be achieved. In particular, in both CP bands the radiation patterns of the proposed antenna are of the same CP sense, and the CP beams are wide and stable. Measurement shows the proposed differentially fed dual‐band CP PSA has a lower (higher) 10‐dB DM impedance band of 2.09 to 2.85 (5.06‐5.89) GHz and a 3‐dB DM axial‐ratio band of 2.32 to 2.59 (5.13‐5.86) GHz, corresponding to a CP fractional bandwidth of 10.9% (13.3%). Besides, in the displayed frequency region of 2‐6 GHz, the CM signals can be effectively suppressed, with the measured CM return loss smaller than 2.96 dB. The conversion of DM input signals into CM reflected signals is even smaller, with the measured DM‐to‐CM conversion less than −32 dB.