An Ultracompact Shared-Radiator Electrically Small Huygens Dual-Circularly Polarized Antenna

A novel electrically small shared-radiator Huygens dual-circularly polarized (HDCP) antenna is developed that features an ultracompact size, i.e., $\pi $ ( $0.12\lambda _{\text {c}}$ ) ${}^{2} \times 0.06\lambda _{\text {c}} = 0.0027\lambda _{\text {c}}^{3}$ ( $ka =0.78$ ) at 915 MHz. A shared radiator is formed by a pair of orthogonally placed Huygens linearly polarized (HLP) antennas. HDCP beams, i.e., left-hand CP (LHCP) and right-hand CP (RHCP) Huygens beams, can be simultaneously excited by an “8”-shaped feed line as the driven element. To compensate for the inductive impedance, an innovative and compact LC matching network is developed to match both ports to standard 50- $\Omega $ transmission lines. The measured results of the prototype agree reasonably with the simulated ones. The results showcase good isolation lower than −16 dB between the two input ports and a wide measured (simulated) 3-dB axial ratio (AR) beamwidth of 120° (144°). Additionally, the measured peak realized gain values for LHCP and RHCP beams are consistent, e.g., 2.8 and 2.6 dBic, respectively. As an ultracompact dual-CP (DCP) antenna, it is an ideal candidate for wireless applications that require DCP performance along with compact system size, e.g., battery-free Internet of Things (IoT) ecosystems with simultaneous wireless power and data transmission.