مرکز منطقه ای اطلاع رساني علوم و فناوري - The circular loop antenna immersed in a dissipative medium

Abstract :

Investigations were made of the radiating and circuit properties of circular loop antennas when immersed in conducting media with various loss tangents. The following quantities were experimentally examined and compared with the available theoretical results. 1) Driving point admittance $Y_{\\in}$ of circular loops as a function of the circumference per wavelength, $2\\pi b/\\lambda = \\beta b$ . 2) Current amplitude and phase distributions. 3) Field patterns. In each case the loss tangent $\\sigma /\\omega \\epsilon_{r}\\epsilon_{0}$ of the medium (conductivity $\\sigma$ , permittivity $\\epsilon_{r}\\epsilon_{0}$ ) is taken as a parameter. The experimental results are in good agreement with the theory. A comparison between the behavior of the loop in a conducting medium and those of a linear dipole was made wherever possible. It was discovered that there is a cut off size beyond which the driving point admittance of a linear dipole is the same whether or not its ends are connected to form a loop. This particular loss tangent is 1.06, and the cut off size is $\\lambda /2$ . A circular loop antenna with $\\beta b= 1.0$ is excited predominantly in a dipole mode and its field pattern resembles that of a two element dipole array. A study was made to determine how this pattern becomes more like that of a monopole as the loss tangent of the solution is increased.