Efficient Radiation from an Electrically Small Antenna

摘要

Applying the analytic technique, two antenna designs were found for which the radiation Q was below the limit determined by Chu for electrically small antennas. The simplest design is a turnstile antenna comprised of two perpendicularly oriented collocated electric dipoles that are phased to support circular polarization, for which the radiation Q is slightly less than a single electric dipole. The most intriguing antenna design consists of four spatially collocated equal power dipoles, a magnetic and electric dipole moment pair oriented along the x-axis, with the dipole pairs driven /2 out of phase to support circular polarization. For this source the analytically predicted radiation Q is zero independently of the relative electrical size ka of the antenna, where a is the radius of the smallest virtual sphere that circumscribes the antenna and k is the wave-number of radiation.