Optimum Antenna Characteristics for Maximally Harvesting Ambient RF Energy

Abstract

This paper investigates the best antenna characteristics to harvest ambient RF waves maximally. The proposed approach analyzes and compares key design aspects, including multi-polarization, multi-port, multi-band, omnidirectional, quasi-isotropic, and non-quasi-isotropic pattern options, over the same antenna size defined by the enclosing sphere radius. First, the ideal isotropic and the Dirac-directive antennas are theoretically analyzed and compared within a general Gaussian channel to derive the most suitable design options. Then, several test antennas, covering the design options, are designed, fabricated, characterized, and compared within a full-wave antenna simulator under spherical incidences and polarizations. Further experiments in real ambient environments complete the tests. Two optimum antenna solutions emerge from the results: the quasi-isotropic antenna and the collocated LP-port diversity system with a power combiner. The crucial feature is optimizing antenna solutions for lower frequency bands with significant power densities that compensate for the available power ${\lambda }^{2}$ -factor.

Keywords

• Dipole antennas
• directive antennas
• isotropic antennas
• energy harvesting
• receiving antennas