Secondary Patterns

The antenna pattern at 327 MHz as computed using geometric optics is shown in Figure 19.5. More rigorous analytical models (the Uniform Theory of Diffraction [7]) gives the pattern shown in Figure 19.6.

Figure 19.5: Computed pattern (using geometric optics) of a GMRT antenna at 327 MHz.

Figure 19.6: Computed pattern (using uniform theory of diffraction) of a GMRT antenna at 327 MHz.

There is a pronounced difference seen at the side-lobe structures between these two models, while the primary beam shows near-identical shapes and the HPBW value matches to a second decimal accuracy. The computed HPBW also agrees to within measurement errors with the observed HPBW of the actual GMRT antennas.