Finite-width effect of an image plane in suppressing electromagnetic radiation from a long strip

The presence of an infinite plane perfect electric conductor beneath a strip carrying a current has an effect of producing an ideal image which nullifies the radiation below it. When the width of the image plane is finite, computing the radiated fields is an interesting problem in the realm of EMC. Analytical methods capable of giving an exact solution are not available. This paper discusses an application of the method of moments for finding the fields in such a situation. The structure is excited by a plane wave and the induced currents are found from the electric field integral equation. The ratio of the maximum electric field radiated from the strip with a finite image plane to that with an infinite plane is computed as a function of the image plane width in free space wavelengths. This ratio approaches zero dB after nearly one wavelength if the height of the strip is small. Also, the field from the strip in the total absence of the image plane when compared to that in its presence reveals how the field is attenuated due to the induced currents on the image plane