REFSYN REFSYNThe example reflector is elliptical with dimensions of 28.58 by 8.90 wavelengths (horizontal by vertical dimensions). The focal length is 11.50 wavelengths and the reflector is a prime-focus paraboloid. A cosecant-squared radiation pattern between 5.0 and 55.0 degrees in Elevation is required from REFSYN. The feed radiation pattern taken as input is that provided by an E-field model for a rectangular aperture of 1.0 by 1.5 wavelengths (horizontal by vertical dimensions) which gives an edge taper of about -9.0 dB in both principal planes. The polarisation is vertical.
Figure 1 shows the initial geometry and Figure 2 shows the final geometry as an error from the initial paraboloidal surface. The computations in REFSYN are carried out in terms of relative dimensions and the actual wavelength is of no interest to REFSYN. However, when REFSYN has completed the shaping and the radiation pattern of the shaped reflector is computed, the rather small size of the vertical dimension in wavelengths is apparent in the slow roll-off (Figure 3 - F0 curve) rather than the sharp cut-off requested. On the other hand, if we use exactly the same shaped geometry with the same metric dimensions at a frequency ten times higher, the cut-off is much sharper (Figure 3 - 10*F0 curve). Note that the requested cosecant squared pattern is in terms of a normalised set of values (Figure 3 - TEMPLATE) and is not attached to any value of peak gain. The gains in Figure 3 for the two frequencies are in dBi and the peak gain is larger for the higher frequency as is expected for the same reflector aperture.
Figures 1 to 3 are below.
