I cannot figure out how to find this problem:

**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.

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 in the far field, the Er=0 and other equations, but i cannot extract "r" from it because they are all in the product forms and lead me nowhere.

Also, i know the formula for the far field but the fact that we need to include the image element confuses me.

Please can I have some directions on how to solve it?

Thank you