RADAR (Radio Detection and Ranging)

If you have sometimes experienced the reflection of a sound due to the presence of a sound reflecting object like a canyon/ cave, etc. you have in a way experienced how radar functions. When you shout near towards a valley or a mountain, the reflection of a sound, i.e., the echo comes back. The time an echo requires to come back can be used to estimate the distance of the reflecting object, provided the speed of sound in air is known. Radar functions in a similar manner to find out the location of the reflection object using RF waves.

Radar is an acronym for RAdio Detecting And Ranging. The name itself suggests that the radars are used to detect the presence of object and determine its range, i.e., RADAR

distance and bearing, using radio frequency waves.

Radars are being used to measure different parameters

1. Range Using Pulse Delay

2. Velocity From Doppler Frequency Shift

3. Angular Direction Using Antenna Pointing

4. Target Size From magnitude of reflected energy

5. Target Shape Analyzing reflected signal as a function of direction

6. Moving Parts Analyzing modulation of the reflected signal

Cost and complexity of radar is dependent upon the number of functions it performs. Radars are used for various applications like Surveillance, imaging, remote sensing, altitude measurement, etc.

BASIC PRINCIPLE

Basic principle governing the functionality of radar is due to the properties of radiated electromagnetic energy.

· The electromagnetic energy travels through space in a straight line, at a constant speed (approximately the speed of light). The propagation of these waves differs slightly because of atmospheric effects.

· When the electromagnetic waves strike an electrically conductive surface, a part the energy is reflected back towards the source, rest of the reflected energy gets radiated in different directions.

· Receipt of reflected energy towards the source is an indication of the obstacle in the direction of propagation.

These basic principles are utilised in Radar to determine distance, and bearings of the target, i.e., a reflecting object.

The block diagram of a primary Radar is shown below:

· Transmitter

The radar transmitter produces microwave signal, which is typically short duration high-power RF- pulses of energy for a pulsed radar.

· Duplexer

Duplexer acts as a switch; it switches the antenna between the transmitter and receiver. This obviates the need for separate transmitting and receiving antennas. Duplexer prevents high power energy to go into receiver (high power pulses can damage the receiver) while transmission and prevents reflected signal to be fed to the transmitter during reception.

· Antenna

The transmitting antenna radiates the transmitting energy to signals in space, in desired directions.

The radiated energy propagates with constant velocity. When it finds the target, the energy is scattered, a part of which is reflected towards the transmitting antenna. The antenna receives the reflected energy and feed it to the duplexer. The duplexer directs this energy towards the receiver.

· Receiver

The receiver demodulates the received reflected energy and analyzes the signal to find target parameters.

· Display

The receiver sends the output to display, which shows the analyzed signal in an easily understandable user friendly manner.