AP 3302 Pt. 3
Section 1
CHAPTER 3
Factors affecting the performance of Pulse-Modulated Radars
Radar
is used over a wide range of frequencies. For convenience, this range may be
split into bands, each band being given a letter (Table 1). These letters are
not internationally recognized; other countries may use other letters and also
different limits within each band.
There are considerable differences in the design of radars for use in the metric, centimetric and millimetric regions. These differences are mainly in circuitry, components and techniques and will be discussed in later chapters.
Shape of Radar Beam and Scanning Methods
We have already noted the need for narrow beams. The shape of the beam however will depend upon the requirement of the radar. The pencil beam, the shape we have been concerned with till now, gives a high precision of angle measurement, but the time taken to scan a given volume of sky may be too long for quick detection and tracking of a target. Very often other beam shapes and other scanning methods are used to determine quickly the required information about a target.
One quick method of scanning involves the full rotation of a fan beam about a vertical axis (Fig 11). Using a beam like this in conjunction with a p.p.i. gives accurate determination of range and bearing in azimuth once every revolution of the aerial. No indication of elevation is possible.
[In Fig 11 the range rings are calibrated at 50, 100 and 150 miles,
Ed.]
