Radar System Engineering

SEC. 9.15] SCI HEIGHT FINDER 299
determination. The height-finder beam, at the 10-cm band, is 3.5° in
azimuth by 1.2° in elevation, and scans linearly one way for 10.5° in
elevation from the horizon up, ten times a second. It makes continuous
height-finding possible on small aircraft out to 50 miles, and farther on
larger planes.
FIG. 927.-Four-way
r-f switch usedin the AN/MPG-l.
The principal elements of the antenna are a 5- by 15-ft grating reflector
which stands on end, an 8- by 2- by l-ft convoluted parallel-plate
horn whose aperture is 5 ft from the reflector, and a rotating waveguide
feeding the horn. The feed, which does not show in Fig. 9.28, is driven
by a motor in the box attached to the horn. The parallel-plate horn
serves to transform the circularly moving waveguide feed into an apparently
linearly moving source. The beam scans 10.5° in elevation for
each rotation of the guide.
The principle may be better understood by considering a simplified
antenna which consists of a reflector and parallel trapezoidal plates with a
long flared base “illuminating” the reflector; the plates are fed with