Small Circular Loop Antenna Research Articles

Far-fields Radiated of a Small Circular Loop Antenna Utilized in Remote Probing of the Earth

In a recent study, the classical problem of a circular loop antenna carrying a uniform current on the Earth's surface has been revisited, with a scope for deriving Closed-form formulae for the generated magnetic and electric far fields by a vertical magnetic dipole (VMD) located at certain height above the surface of a planar two-layer conducting earth, with a high degree of accuracy. The solution is obtained by reducing the field integrals to combinations of known Sommerfeld integrals (SIs), which is advantageous over the previous numerical and analytical-numerical approaches, and its usage takes negligible computation time. Numerical simulations are performed and illustrated by figures for different values of the frequency to show the accuracy of the obtained field expressions and to investigate the behavior of the above surface ground fields in a wide frequency range. Results can be used to evaluate numerical solutions of more complicated modeling algorithms, for application to mobile communication and will be useful for remote sensing especially when the transmitter is close to the surface.

On the Surface Fields of a Small Circular Loop Antenna Placed on Plane Stratified Earth

An analytical method is presented which makes it possible to derive exact explicit expressions for the time-harmonic surface fields excited by a small circular loop antenna placed on the top surface of plane layered earth. The developed procedure leads to casting the complete integral representations for the EM field components into forms suitable for application of Cauchy’s integral formula. As a result, the surface fields are expressed as sums of Hankel functions. Numerical simulations are performed to show the validity and accuracy of the proposed solution.

Electromotive Force Induced in and Inductance of an Electrically Small Circular Loop Antenna

Exact formulas are here given for 1) the electromotive force induced in a circular loop antenna by a quasi-static and uniform magnetic field perpendicular to the plane of the loop, and 2) the inductance of the loop. The loop consists of one turn of perfectly conducting round wire. Formulas are general in that they are valid for any possible value of the wire radius. Comparison with the results of numerical simulations is offered in order to let the reader appreciate the degree of accuracy obtainable through computational electromagnetics modeling of this canonical problem.

Reference Calibration Methods for Small Circular Loop Antenna in Low-Frequency Band

In this paper, we propose two reference calibration methods (RCMs) for small circular loop antennas. Generally, the standard field method is widely employed in loop antenna calibration at many national metrology institutes and calibration laboratories. In this method, a thermocouple is employed as a current sensor on an antenna element of a transmitting loop antenna to calculate the magnetic field strength at an antenna under calibration. This method has certain disadvantages: The standard transmitting antenna is complicated, cumbersome, and fragile. On the other hand, a calibration method is necessary to be reasonably traceable to the standard of the magnetic antenna factor. Our proposed methods can establish and keep traceability to it. We also compare the two proposed RCMs and show that they are efficient in calibrating the loop antennas.

Method of Moments Analysis of Active Thin Circular Loop Antennas With Closed-Form Currents and Validity

This paper presents an analysis of electromagnetic radiation due to thin circular loop antennas of arbitrary radii a. The electric type of dyadic Green's function expanded in terms of spherical wave functions is employed in this study. The Galerkin's method of moments is applied in the derivation of current distributions along the thin circular loop wires. With an advantage over others, the present analysis is quite general, compact and straightforward; most importantly, the current distributions are obtained analytically and expressed in a closed and simple form. Resulted from these currents, radiated fields in both near- and far-zones and both inside and outside the sphere of radius a are expressed in terms of the spherical vector wave functions. Also discussed in this paper is the validity of definitions of far-zone and electrically small size. The maximum radius of an electrically small circular loop antennas is found from a quantitative error analysis of both loop currents and the far-zone fields.

The Near and Far Field Distributions of a Thin Circular Loop Antenna in a Radially Multilayered Biisotropic Sphere - Abstract

In this contribution the technique of dyadic Green's function in terms of the normalized spherical vector wave functions is adopted for investigating the radiation of a thin circular loop antenna in a radially multilayered biisotropic sphere, and the current on the loop antenna is supposed to be a uniform, a sinusoidal as well as a generalized Fourier series distribution, respectively. The radiated fields in both near and far field zones for circular loop antenna of arbitrary radius are derived and expressed as a superposition of the right- and left-handed circularly polarized waves. Numerical results are presented to demonstrate the constitutive parameter effects of the two- and four-layer biisotropic spheres on the resonant characteristics of near fields as well as the radiated power and polarized state of the far fields for electrically large and small thin circular loop antennas excited by a uniform current, respectively.

Transient response computation of spheroidal objects using impedance boundary conditions

The transient response of imperfectly conducting and permeable spheroidal objects is determined using the impedance boundary conditions. Since the impedance boundary conditions are not known in the time domain, the frequency domain analysis is used to formulate the problem. The use of impedance boundary conditions relates conveniently the solution to the object's physical parameters and simplifies the computations. For highly conducting objects a simplified method is used to determine numerically the frequency domain data, which utilizes the numerical code for perfectly conducting objects. The excitation is assumed to be due to a periodic pulse train and generated by a small circular loop antenna. The procedure for the computation of the transient response, at very low excitation frequencies, is presented and the response forms for different object parameters and orientations are computed.

On the electrically small bare loop antenna in a dissipative medium

Two approximate methods for analyzing the electrically small circular-loop antenna in a dissipative medium have been presented in the literature. Admittances calculated by these methods are compared with the twenty-term Fourier series results which are known to be in good agreement with experimental data. The conductance predicted by both methods is in poor agreement with the Fourier series results. The reason for this difference is determined and a simple, accurate formula obtained for the admittance. The far-zone electric field maintained by the current on the loop is determined, and the accuracy of assuming a uniform current on the loop for field calculations is discussed.

On the receiving properties of a small horizontal bare circular loop antenna buried in the ground

It is shown that when a small bare circular loop antenna is buried in the ground it will respond to a vertically ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</tex> field) polarized ground-wave or sky-wave source with a directional azimuthal pattern. The response to a horizontally polarized skywave source is greatly enhanced by burying the antenna and is also shown to be far from omnidirectional in azimuth. These results depend upon the presence of a relatively small departure from a constant current distribution on the loop when it is regarded as a driven element. The current distribution formulas of Chen and King permit easy analytical estimates of these effects.

The near-zone magnetic field of a small circular-loop antenna

The near-zone magnetic field of a small circular-loop antenna

Admittance of insulated loop antennas in a dissipative medium

A small circular loop antenna is located in an insulating layer within a dissipative medium. The admittance of the loop is calculated using a two-term trial function for the loop current in a variational formulation. Thin insulating layers tend to maintain a nearly uniform current around the small loop, in particular for highly lossy surrounding media. The assumption of a uniform loop current is shown to be justified for a range of antenna parameters.

The small bare loop antenna immersed in a dissipative medium

The input admittance of a small thin-wire circular loop antenna, driven by a slice generator, immersed in a dissipative medium, is considered. It is found that the solution given by Storer for the loop antenna in a lossless medium can be carded over readily by replacing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\zeta_{0}</tex> by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\zeta</tex> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k_{0}</tex> by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> . The numerical values of the normalized input conductance and input susceptance of a small loop antenna, namely <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\beta b \leq 0.3</tex> , <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Omega = 10</tex> , are calculated. It is to be noted that the input susceptance is practically independent of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> while the input conductance changes as much as seventeen times in this special case.