Radar System Engineering

CHAPTER 9
ANTENNAS, SCANNERS, AND STABILIZATION
BY W. M. CADY, C. V. ROBINSON, F. B. LINCOLN, AND
F. J. MEHRINGER
The antenna is the sensory organ of the radar set. Its function is to
accept r-f energy from the transmission line, to distribute this energy into
space as desired, to gather in the radar echoes of this energy,
and to direct
these echoes back into the transmission line. Since the nature of electromagnetic
radiation is such that a good transmitting antenna is also a
good receiving antenna, we need consider only the former function. In
most cases the antenna is required to form the energy into a sharp beam
which may be aimed in various directions. The supporting structure is
known as the “pedestal,” and the entire assembly is termed the “antenna
mount” or “scanner.” 1 Airplanes and ships are notoriously unsteady
vehicles, whose motions disturb the direction of a radar beam of energy
transmitted from them. The compensation for such motions is called
“stabilization.’ )
9.1. The Antenna Equation.’—Two of the salient requirements of
most radar sets are that they be able to reveal distant objects and be able
to give accurately the direction of such objects. The design of the
antenna has a great influence on the attainment of these requirements.
We have seen (Sec. 2.1) that under certain conditions the maximum range
of detection of a given target varies as the square root of the area of the
antenna. This is one reason for the use of large antennas. Another
advantage of large antennas, having to do with the resolution of the radar
set, is that the beamwidth varies inversely as the linear dimension of the
antenna. Mathematically the beamwidth e (degrees) is usually related
to the width D of the antenna and the wavelength 1 of the radiation by
the approximate formula
if D and X are measured in the same units. We see that shorter wavelengths
make possible sharper beams; this accounts for the very con-
(1)
1For a fuller account of radar scanners the reader is referred to Radar
cni Radornes, Vol. 26 of this series.
2Sees. 9.1 to 9.12 by W. M. Cady.
271
Scanners