مرکز منطقه ای اطلاع رساني علوم و فناوري - Experimental verification of dipole radiation in a conducting half-space

Abstract :

A laboratory size model of the flat earth-air (two-layer) problem, constructed to verify certain proposed theories on electromagnetic propagation through the sea, is described. The modeling system is used in scaling and measuring electromagnetic field components of electric or magnetic antennas submerged in sea water. Specifically, the experimental results are compared with the theory of radiation from a horizontal electric dipole antenna submerged in the sea. The results presented here verify that 1) the cyclindrical coordinate $E_{r}$ , and $E_{\\phi}$ field components measured in the sea vary with radial distance from the antenna as $\\rho^{-3}$ in the near-zone and $\\rho^{-1}$ and $\\rho^{-2}$ , respectively, in the far-zone; 2) all field components vary with depth, $z$ , as exp ( $-z/\\delta$ ), where $\\delta$ is skin depth; 3) the $E_{r}$ , and $E_{\\phi}$ components vary with $\\phi$ as $\\cos \\phi$ and $\\sin \\phi$ , respectively; 4) all field components vary linearly with length $l$ and dipole current, $I$ . In addition, the $H_{\\phi}$ , $H_{r}$ , and $E_{z}$ components were measured in the air as a function of $\\rho$ for the static-zone, near-zone, and far-zone. The modeling system representing the sea includes a cylindrical tank 11.5 feet in diameter, 2-feet deep, containing a salt solution of 4 mhos/meter conductivity. The transmitting frequency varied from 100 to 400 Mc. For submerged antennas that can be validly scaled at least $10^{-2}$ in size and $10^{+4}$ in frequency, this model can conveniently be used to verify experimentally the radiation characteristics of these antennas.