TABLE OF CONTENTS In its simplest form radar senses only the energy backscattered by its target(s) and reaching its receiver via its antenna (Colour Plate 5). Any inference that can be drawn about the nature of target(s) is based only on the amount of this energy, taking into account the parameters of the radar system.
In the more common role of the radar as a point-target observer, the direction of the target relative to the radar can be inferred by noting the pointing direction of the antenna for which the echo power received by the radar is maximum. The distance of the target from the radar is ascertained from the time taken by the electromagnetic waves to travel from the antenna to the target and back, measured as the time difference between the instant of the waves leaving the antenna, and the instant of the corresponding echo arriving at the antenna. Such correspondence is difficult to establish without time marks (or modulation) on the transmitted signal. To provide the time marks, and for other important advantages, radar signals are most commonly transmitted in the form of short, high-power pulses, typically of the order of 1 ?s in duration, spaced relatively wide apart in time, the interpulse interval often being of the order of 1 ms. Such radars are called pulsed radars. The structure of pulsed transmitted signals is shown schematically in Fig. 6.1, and the important parameters of pulsed radars are listed in Table 6.1 along with...
