Radiation Properties of Pure Magnetic Dipole Antenna With Spherical Current Density via Exact Maxwell Solution

• Published in: IEEE transactions on antennas and propagation Vol. 70; no. 5; pp. 3469 - 3476
• Main Author: Garren, David Alan
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antennas; Current; Current density; Dipole antennas; Dipole moments; Electric currents; Exact solutions; Exponential functions; Loop antennas; low-frequency antennas; magnetic antennas; Magnetic dipoles; Magnetic moments; Magnetic properties; Magnetic resonance imaging; Mathematical analysis; Mathematical models; Maxwell's equations; Polynomials; Q factors; Q-factor; Radiation; radiation impedance; radiation resistance; Spherical antennas; Spherical shells; Trigonometric functions
• ISSN: 0018-926X; 1558-2221
• DOI: 10.1109/TAP.2021.3137470

A recent analysis has investigated a possible new type of magnetic antenna that is characterized by an electric current that flows azimuthally on the surface of a sphere with a density magnitude that scales as the sine function applied to the spherical polar angle. This analytic theory has yielded an exact solution of the Maxwell equations for the electromagnetic (EM) fields of the resulting radiation for all spatial regions, including that both interior and exterior to the spherical current shell. In the present investigation, the EM fields are expressed in terms of an alternative, and perhaps more intuitive, form such that the radial dependence varies as a product of polynomial and exponential functions. In addition, the subject spherical current density is shown to produce exactly the same purely dipole radiation fields exterior to the spherical current shell as that of an infinitely small magnetic dipole moment antenna. Furthermore, the present analysis calculates various radiation properties corresponding to the subject spherical current antenna concept, including the Poynting vector, radiation impedance, quality factor, and maximum effective area. Finally, the present investigation reveals that the subject spherical electric current density achieves the minimum quality factor that can be attained for all antennas.