Analysis of a four parallel wire anechoic chamber

An important electromagnetics problem in the VHF frequency range is to design an anechoic chamber for which an almost planar electromagnetic wave can propagate. This is a difficult anechoic chamber design problem because the free-space wavelength in this frequency range is exceedingly large; large and expensive anechoic chambers are required in order to create conditions for which a near electromagnetic plane wave can propagate. An anechoic chamber design which circumvents the problem of needing to use an exceedingly large anechoic chamber is described. It consists of placing four parallel wires within an anechoic chamber enclosure and exciting the four wires in such a way that a wave which is nearly a transverse electric and magnetic (TEM) wave will propagate from one end of the four-wire system to the other. The TEM nature of the wave accurately simulates the characteristics of a free-space plane wave. A simple model of a four-wire anechoic chamber without the inclusion of a matching taper at either end is shown.<>