Page 188 - Satellite Communications, Fourth Edition

168 Chapter Six

focal points, one of which is made to coincide with that of the main
reflector and the other with the phase center of the feed horn, as shown
in Fig. 6.23a. The Cassegrain system is equivalent to a single parabo-
loidal reflector of focal length
e 1
h
f f (6.35)
e
e 1
h
Main reflector
(paraboloid)

Subreflector
(hyperboloid)
S 2 S 1

(a)

Main reflector
(paraboloid)

Subreflector
(ellipsoid)
S 2 S 1

Figure 6.23 Ray paths for (a) Cassegrain
antenna. (b) Gregorian antenna.
(b)