The Radiation Pattern of an Antenna over a Circular Ground Screen

In a previous paper [The Input Impedance of an Antenna Over a Finite Ground Screen, Technical Report No. 119 (Cruft Laboratory, Harvard University, November 30, 1950)] the author treated the problem of the input impedance of an antenna erected over a large circular screen. Using the formulation developed therein, an expression is obtained for the entire radiation pattern of an antenna over a large circular screen. The most important difference between the pattern of an antenna over a large screen and an antenna over an infinite screen is the presence of lobes over the antenna. From the expression for the radiation pattern, simple formulas are obtained for: (a) the number of lobes, (b) the angular position of the lobes, and (c) the angle, βmax, within which the lobes occur. One important result obtained is that θmax∼(1/d12),where d is the diameter of the screen. It is apparent that the effects of a finite screen decrease very slowly as the diameter of the screen is increased.