An Electrically Small, Pattern-Reconfigurable, HCP Antenna with Quasi-Isotropic Beam Coverage for Wireless Power Transfer Enabled IoT Applications

Wireless power transfer (WPT) technology holds the key to unlock the massive deployment of wirelessly powered battery-free Internet of Things (IoT) devices and has become an emerging topic in IoT applications. As IoT devices are distributed randomly in the environment, antennas featuring broad circularly polarized (CP) radiation coverage are highly promising as a power source to wirelessly charge them. Herein, in this article, an electrically small (ES) pattern-reconfigurable Huygens CP (HCP) antenna with quasi-isotropic beam coverage is presented for WPT-enabled IoT applications. It consists of a pair of orthogonally placed crossed Egyptian ax dipoles (EADs), customized reconfigurable capacitively loaded loops (CLLs), and an unbalanced reconfigurable crossed driven-dipole structure. Pattern reconfigurability is realized due to the phase reversal of the EADs by switching the diodes at the center of the additional crossed shorter strips beneath the upper section of the CLLs. Furthermore, to ensure overlapping bandwidths for impedance matching and axial ratio (AR), the effective lengths of the driven-dipole arms are reconfigurable by controlling the diodes. An optimized prototype was fabricated and validated, showing a peak realized gain (RG) of 2.45 dBic and a wide 3-dB AR beamwidth of more than 100° for both modes in an ES size (ka = 0.79).