On-axis fields of small grid paraboloid by moment method

The currents flowing along each element of a small grid paraboloid are calculated using the method of moments and are shown graphically. A comparison is made using the J = 2 (n ¿¿ H) approximation and taking the appropriate spacing between grids to give an equivalent grid current, for a range of F/D values. Although the currents are markedly unlike in the two cases, the on-axis fields are very similar for large F/D values. It is shown that in the receiving situation the position of maximum electric field strength for the grid paraboloid considered is a function of F/D, and can exist on either side of, or at, the geometrical focus.