Wideband Dual-Circularly Polarized Antennas Using Aperture-Coupled Stacked Patches and Single-Section Hybrid Coupler

This paper presents a dual-circularly polarized (dual-CP) antenna with simple configuration, low-profile, and wide bandwidth. Its primary radiating element is an aperture-coupled patch loaded with a stacked patch for a wide operational bandwidth. A single-section hybrid coupler is utilized as a feeding structure of the antenna to generate dual-CP radiation. Different from the priors normally requiring both wideband radiator and wideband feeding structure, this work demonstrates that the wideband dual-CP radiation can be obtained by combining a wideband radiator and a conventional hybrid coupler. A design operating at the center frequency of 5.5 GHz has been fabricated and tested. The measurements result in a -10-dB reflection coefficient bandwidth of 30.0% (4.66 - 6.31 GHz), a 10-dB isolation bandwidth of 30.9% (4.66 - 6.35 GHz), a 3-dB axial ratio (AR) bandwidth of 29.1% (4.70 - 6.30 GHz), and a realized broadside gain of 5.5 - 7.05 dBic. For a more robust dual-CP radiation, a low-sidelobe 4 × 4 element array of the proposed antenna has been designed, fabricated, and measured. Compared to the single element design, the array prototype yields similar impedance and 3-dB AR bandwidths, but a higher isolation. The measurements on the array prototype result in an isolation of ≥ 14 dB, a peak gain of 16.3 dBic, a side-lobe level of ≤ -20 dB, and a cross-polarization of ≤ -16 dB across the frequency range of 4.7 - 6.3 GHz (29.1%).