Characteristics of the TE/sub 21//sup 0/ mode in circular apertures as used for satellite tracking

Monopulse tracking antennas are customarily used for tracking satellites subsequent to launch, in transfer orbit, and on station. A convenient means of obtaining a monopulse pattern is to couple to the null-on-axis TE/sub 21//sup 0/ mode of the tracking antenna's aperture in addition to the aperture's dominant mode. An expression is derived here for the polar-angular distance from the boresight of a circular-aperture antenna to the peaks of the TE/sub 21//sup 0/ null-on-axis lobe as a function of azimuthal angle. In addition, the relative levels of the peaks of the TE/sub 21//sup 0/ mode, relative to the mainlobe, are evaluated.