VE4MA and Chaparral feeds with Septum polarizers - W1GHZ

Chaparral vs super VE4MA0.71lambda horn diameter, 1.9 lambda total blockage80Dish Efficiency (%)7570650 0.1 0.2 0.3 0.4 0.54 ring 0.15 x 0.333 ring 0.20 x 0.332 ring 0.30 x 0.33VE4MA 0.6 x 0.45Ring position - wavelengths behind rimFigure 22The radiation patterns from the Chaparral-style feeds do not demonstrate the large dip inthe center that seems to provide improved efficiency for the best VE4MA variations. Theadditional rings seem to simply reduce radiation in undesired lobes and put more evenenergy over a wide angle on the reflector, as seen in Figure 23, a 3D pattern for the feedin Figure 22 with 3 rings 0.20λ wide and 0.33λ deep, 0.25λ behind the rim. The result isthe high efficiency plotted in Figure 24.Figure 23. 3D pattern for Chaparral feed with 3 rings 0.20λ wide and 0.33λ deep, back 0.25λThe advantage of the Chaparral-style feeds over the simpler VE4MA is high efficiencyover a wider range of f/D, and probably over a broader bandwidth. The bandwidth wasnot investigated since all amateur operation is in relatively small bandwidths.