An Isolation Enhancement Method for a Circularly Polarized Shared-Aperture Array Using Rotating Feed

A novel isolation enhancement method for the shared-aperture antenna is proposed in this letter. When the high-frequency band (HB) antenna is arranged by rotation, the loop current can be excited, which reduces the mutual coupling between the HB antenna and the low-frequency band (LB) antenna. Based on this approach, a circularly polarized (CP) shared-aperture antenna array with high cross-band isolation is proposed. It consists of 2 × 2 cross-shaped patch antennas operating in the LB and 4 × 4 rectangular printed dipole antennas operating in the HB. The LB and HB antennas are etched on the same substrate. In this work, cross-band isolation in the LB is improved by more than 8.2 dB by an anticlockwise rotating feed for the HB antennas. For validation, an array prototype was designed and fabricated. The measured results demonstrate that the proposed array achieves an operating bandwidth (IBW) of 13.6% (2.6–2.98 GHz) in S-band and 30.0% (4.72–6.32GHz) in C-band, respectively. Furthermore, the antenna exhibits cross-band isolation exceeding 19.2 dB and 26.8 dB, along with aperture efficiency of 73.4% and 81.8% in S-/C-band, respectively. The proposed CP shared-aperture array has features of high cross-band isolation and high aperture efficiency with a simple structure.