Some far-field studies of an offset launcher

An offset paraboloidal reflector illuminated by a balanced feed horn constitutes an efficient launcher for coupling microwaves into quasioptical beams. Measurements on a launcher with low blockage show low cross polarization. The amplitude, phase, and polarization characteristics are predicted by two gaussian beam modes, and the resulting formulas are found to agree well with measurements at 19 and 28 GHz. For example, with increasing offset angles, the ratio of the maximum cross-polarized signal in the radiation pattern to the on-axis co-polarized signal is observed to vary from −44 to −37 dB, within 1 dB of the predicted variation.