Quality factor of an electrically small antenna radiating close to a conducting plane

Abstract

Expressions are derived for the smallest achievable radiation quality factor () of an electrically small antenna in front of a conducting plane. Applying the low-frequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane, an expression is formed for the field in the radiation zone. The contribution of nonpropagating energy in the near field is obtained explicitly using a spherical harmonics decomposition. The radiation is found to depend on the radius (relative to wavelength) of the smallest sphere that encloses the antenna and its image, the ratio of the vertical and horizontal dipole moments, as well as the positions of the dipoles relative to each other and to the plane. A number of simple wire structures are analysed with NEC (based on the Method of Moments), and the approximate obtained from their fractional bandwidth are compared to the corresponding theoretical minima.

A Novel Numerical Arithmetic of Calculating Bandwidth for a Giant T-Type VLF Antenna Array

“…Antenna input impedance at arbitrary frequency can be acquired by MOM and Lagrange multinomial with fewer operation amounts and enough precision. According to (4) and (5), the VLF antenna bandwidth in arbitrary frequency can be acquired easily as its input impedance. In the low end of the frequency band (less than 20 kHz), bandwidth calculate by classical and numerical arithmetic are very close.…”

Comparison of efficient small antennas for wireless microsensors through simulation and experiment

“…A method for calculating radius a was proposed by Sten [6] for printed elements operating near large ground planes. It was also discussed by Bancroft in [7].…”

Gain enhancement of low-profile, electrically small capacitive-feed antennas using stacked meander lines

“…The leakage current existing on the outer surface of a coaxial cable causes drastic changes in antenna characteristics [15,19,20] when the feed is unbalanced. Moreover, typical electrically small and low-profile antennas have disadvantages of low radiation efficiency [15,[21][22][23][24][25] and it is difficult to attain impedance matching characteristics [26]. The problems of the leakage current and the impedance matching can be improved by a capacitive feed (C-feed) technique in [27].…”