# Image Theory of an Antenna

Discussion in 'Homework Help' started by xz4chx, Feb 11, 2015.

1. ### xz4chx Thread Starter Member

Sep 17, 2012
71
1
An infinitesimal electric dipole of length l = λ/50 is placed horizontally at a
height of h = 2λ above a flat, smooth, perfect electric conducting plane which
extends to infinity. It is desired to measure its far-field radiation characteristics
(e.g. amplitude pattern, phase pattern, polarization pattern, etc.). The system
is operating at 300 MHz. What should the minimum radius (in meters) of the
circle be where the measurements should be carried out? The radius should
be measured from the origin of the coordinate system, which is taken at the
interface between the actual source and image.

I know that far field in books calculates the far field area as (2D^2)/λ

How is this effected with the image theory of a PEC?
I assume that the D (maximum dimension of antenna) is different then λ/50 because of the image theory effect.

But how exactly is this effected and a little more concept information would be nice.

Thank you

r = (2D^2)/λ
λ = 3*10^8/3*10^8 = 1 m

2(D^2)/1 = r