Circularly polarized electrically small antennas for emerging wireless applications

This paper introduces three circularly-polarized (CP) electrically small antennas for emerging wireless applications including wireless power transfer (WPT), Internet-of-Things (IoT), and Device-to-Device (D2D) communications in future fifth generation (5G) systems. First, an electrically small Huygens CP (HCP) antenna operating at L-band frequencies is presented that is facilitated by two near-field resonant parasitic (NFRP) elements, a crossed Egyptian axe dipole (EAD) pair and a crossed capacitively loaded loop (CLL) pair. The HCP antenna is electrically small (ka = 0.73), low profile (~ 0.04°0), and has decent cardioid-shaped radiation patterns with a broad half power beamwidth (>120°). It is attractive for many WPT and body-centric wireless sensor network applications. Second, with the rapid development of 5G wireless networks, a corresponding 28 GHz electrically small HCP antenna is reported. The overall size of this antenna is only p (1.5)² × 1 ˜ 7 mm³ (ka = 0.94), which can be readily integrated into the various compact platforms anticipated for 5G IoT devices. Third, unlike the above two antennas that radiate uni-directional patterns, a compact 28 GHz omni-directional CP (OCP) antenna is presented for D2D communications in future 5G systems. It is electrically small (ka = 0.95), easy to fabricate, and its performance characteristics cover the entire FCC-specified 5G, 27.5 to 28.35 GHz band.