The Effect of the Source Distribution on Antenna Patterns

The response pattern of an antenna is modified when the source subtends an appreciable angle. Under these conditions the observed or resultant pattern is a function of both the true antenna pattern and the source distribution. This problem is important in radio astronomy and in radar. The general problem is formulated and solved for the particular case of a radio telescope antenna consisting of a 40 wavelength broadside array. Graphs are presented showing the effect of sources of various widths on the observed patterns. Using such graphs it is possible to deduce the approximate source extent from an observed pattern. The direct analytical solution for the source distribution from the observed pattern is also considered and the limitations of the various methods are discussed.