
Array Antennas 185
!
!
(A)
DIFF
SUM
3 dB BW
(B) SUM (C) DIFFERENCE
(D) IMPROVED
Figure
9-11 A) Monopulse feed; B) sum pattern; C) difference pattem; D)
improved
pattern
due to adding sum
and difference.
(which has a lower temperature); on the negative side, galactic and solar noise may
be slightly higher on a Cassegrain dish.
Figure 9-11 shows the
monopulsefeed
geometry. In this system, a pair of radi-
ator elements is placed at the focal point and fed to a power splitter network that
outputs
sum
(Fig. 9-11B) and
difference
(Fig. 9-11C) signals. When these are com-
bined, the resultant beam shape has an improved-3-dB beamwidth ...