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Radar Systems for Technicians

# Chapter 4: The Basic Principles of Radar

## Overview

This chapter is a very basic introduction to the principle of pulsed radar. Obviously, getting a beginning concept of the main principle is one objective. Another is to introduce many terms commonly used in the radar language. Those which are the most essential to remember are printed in bold italics to assist you.

See figure 4 1. The basic principle of pulsed radar is not complex. A transmitter emits a burst of rf energy, and objects in its path will reflect the pulse back to the transmitting antenna as an echo. A steering device, called a duplexer, allows the transmitter burst to go to the antenna without damaging the receiver, then isolates the transmitter during a listening time. The listening time is usually called, live time. During live time, the echoes from any objects, called targets, are routed into the receiver.

Figure 4 1: Basic Components of a Radar System.

The time required for an echo is measurable, and representative of target range, the distance from the radar antenna to the target. The transmitted burst travels at the speed of light, and the distance of the target may be calculated by the basic Physics formula, distance=rate x time (d=rt). Since the transmitter burst is echoed, the two-way travel requires that the speed of light be halved in using it as r in the d=rt equation. Thus, d=rt becomes d=(c/2)t.

Radar ranges are usually expressed in either meters or nautical miles, depending upon the radar application.

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