Radar System Engineering

CHAPTER 12
THE RECEIVING SYSTEM—RADAR RECEIVERS
BY L. J. HAWORTH AND W.
INTRODUCTION
BY L. J. HATVORTH
H. JORDAN
12.1. The Role of the Receiving System.—It is the purpose of the
receiving system to extract the information contained in the radiofrequency
echoes, to sort it in terms of the geometrical parameters
involved, and to present the results to the observer in a convenient and
useful form.
The data involved are in a variet y of forms. Most of them come from
the radar set itself. Ihrst in importance, of course, are the echo signals,
which may contain as many as several million separate pieces of information
each second. The exact instant at which the radar pulse is transmitted
is known by virtue of a pulse to or from the modulator. The
geometrical coordinate of range is proportional to the return time of the
echo pulses with respect to this pulse. The orientation of the antenna is
available in terms of the rotational positions of shafts geared to the
scanner axes. These direct data are often supplemented by others
(obtained from external sources or from observation of the composite
radar results), such as geographical information, the location and orientation
of the radar platform, if it is a moving one, and so on.
Within the limitations of these data and the requirements of the particular
situation, the equipment should present to the observer a continuous,
easily understandable, geometrical picture of the radar targets
under study, giving the location, size, shape, and, in so far as possible, the
nature of each to any desired degree of accuracy. In many cases, the
equipment should have provisions for instantaneous y determining in a
precise numerical way the exact position of each target with respect to
the radar set or to other targets, and often it should furnish means for
passing these results onto other devices in an automatic way. All of this
must be done in such a manner that the echo signals have optimum sensitivity
compared to internal system noise and to extraneous radiations.
The accomplishment of these objectives requires a considerable array
of equipment. The ultimate link with the observer is the indicator.
The indicator proper is usually supplemented by a considerable amount
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