Radar System Engineering

SEC. 4.2] POWER AND INFORMATION RATE 121
separate transmitter and receiver. The V-beam radar is thus an authentic
example of the use of a separate radar system to overcome a scanning
speed limitation.
In a certain sense, however, the use of the second channel in this
way more than doubles the number of angular elements searched in a
given time. That istosay, anisolated target can relocated in azimuth
and in elevation with an accuracy that would ordinarily require a sharp
“pencil” beam. But to scan the whole region with such a pencil beam
would take, according to the earlier discussion, a very much longer time.
It might therefore appear that the V-beam system eludes the very
restrictions which have been claimed to be fundamental. This is to be
explained by the fact that the V-beam height-finding method works
only if relatively few targets appear on the screen at one time; otherwise
there is essential ambiguity in the interpretation of the picture. The
system is, therefore, not fully equivalent to a pencil-beam scan of the
same angular region.
Actually more than two separate radar sets are involved in the
V-beam system, for both the vertical and the slant beams are themselves
composite. This, however, has nothing to do with the scanning speed
limitation, but is required merely to get adequate range and vertical
coverage. It is a consequence, in other words, of the radar equation
for fan beams discussed in Sec. 2.5.
4.2. Bandwidth, Power, and Information Rate.—If a radar system
were used to find only the direction of a target, range information being
suppressed, it would be operating very much like a television camera.
The picture so obtained would, in effect, be divided into a number of
elements equal to the ratio of the total solid angle scanned to the solid
angle included in the beam itself. Thus the number of pieces of information
that the system can collect per second is simply the number of
picture elements multiplied by the number of complete scans per second,
exactly as in television. In the radar system giving hemispherical
coverage which was used as an example in the preceding section, this
number comes to 1500 elements per second, which is not very impressive
by television standards. The type C indicator already mentioned in
Sec. 2“11 and described in more detail in Sec. 6.6 gives information of
just this sort. It has not found wide use fort wo reasons: (1) the accompanying
increases in minimum detectable signal power, explained in
Sec. 211, and (2) the fact that the method discards a large fraction of the
information available in the radar system, the range information.
An even closer approach to the television method has been visualized,
in which the proposed radar receiving system is built something
like a television camera. A mosaic of microwave-sensitive elements
located at the focal surface of a receiving antenna would be scanned by an