22 May 2019

RADAR Block Diagram and Working (Bistatic Radar and Monostatic Radar) - Types of RADAR

What is a RADAR?

RADAR stands for "Radio Detection and Ranging" as it uses radio waves (electromagnetic waves) to detect and find the range of an object (target).
The transmitting antenna of the radar transmits radio waves towards the object and analyzes the reflected waves from the target object. After analyzing the reflected waves (echo signal) it can calculate target's distance (range), angle and velocity (if it is moving).
Radars can be classified into two broad categories, based on the number of Antennas used-
Bistatic Radar and Monostatic Radar

Watch the Complete RADAR Video Here

Bistatic RADAR (Block Diagram)

Here you can see the block diagram of Bistatic radar.

Bistatic RADAR Block Diagram

You can observe in this diagram that, the bistatic  radar contains a radar display, a transmitter and a receiver. Transmitting antenna is attached to the transmitter and receiving antenna is attached to the receiver of the radar. 
The job of the transmitting antenna is to transmit radio waves (electromagnetic waves) towards the target that we want to detect. The target object intercepts some part of the transmitted signal and reflects it back towards the receiving antenna. This receiving signal is known as the echo signal. 
Now the Radar receiver analyses these received signals. The radar display shows the information in the raw form, that needs to be analysed by an skilled person. 
The receiver of the radar must be very sensitive to receive weak signals, as the signals get very weak because of the attenuation of the radio waves in the forward and reverse path.
Also the radar transmitter should have high directivity and gain. Directivity of antenna is it's ability to transmit radiations in a particular direction. It should also have high gain since it has to counter losses in the forward and reverse path (before and after reflection from the target).
Now we will understand why it is known as bistatic radar and how it is different from the monostatic radar.
Actually the bistatic radar uses two antennas for transmission and reception purpose separately, that's why it is known as bistatic radar. 

Monostatic RADAR (Block Diagram)

Monostatic radar is the most commonly used form of the radar. Here you can see the block diagram of monostatic Radar-

Monostatic RADAR Block Diagram

As you can see in this block diagram that monostatic radar uses only one antenna for transmission and reception purpose, that's why it is known as monostatic radar (Mono means single and bi means double).
In this block diagram of monostatic radar you can see that it has an indicator, a transmitter and receiver, a duplexer and a single antenna. Observer that here we have not used two separate antennas as the transmitting antenna and receiving antenna. Only one antenna can function as the transmitting and receiving antenna.
Actually the basic working principle of both types of radars (Bistatic and monostatic) is same with some differences.
The radar transmitter transmits electromagnetic waves (radio waves). At the time of transmission the antenna of the monostatic radar works as the transmitting antenna and when these signals are reflected back (echo signal) from the target, the same antenna works as the receiving antenna. This received signal is analysed by the receiver circuitry and the data is shown on the indicator of the radar. 
Now we will understand the role of the duplexer in the monostatic radar-

Functions of the Radar Duplexer

  • The Radar duplexer makes it possible to use single antenna for transmission and reception purpose.

  • The duplexer helps in protecting the sensitive receiver from the high power transmitter.

  • The radar duplexer keeps the transmitter and receiver separate (isolated) at the time of transmission and reception.

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