The term “Radar” stands for RAdio Detection And Ranging. Even though radar was being developed since the 1930s, it was first coined as radar in 1940 by the United States Navy. As the name suggests, radar transmission is dependent on the use of radio signals to transmit data. Radar systems work by sending or relaying electromagnetic waves much like wireless networks or computer networks. The radio signals from radar systems are sent out as short pulses and as they travel, they hit on objects along the path. These objects reflect the radio signals which are then taken back to the radar transmitters. As the radio signals are reflected back to the radar sensors, part of the energy may end up being scattered back as a result of precipitation in the atmosphere. However, some of the signals will be reflected all the way back to the radar antenna where it is processed and the details are then used to determine the characteristics of the object being detected.
Components of a RADAR system
Below is a list of a simple radar system.
A transmitter: The transmitter is responsible for the production of short duration high-powered pulses of energy that must be released into the air by the antenna.
The Duplexer: The duplexer is the device that alternately switches the antenna between the transmitter and the receiver. This is because only one antenna needs to be used at a time. This switching between the transmitter and the receiver is necessary because the receiver would be destroyed by the transmitter if the high powered pulses were allowed to move from the transmitter to the receiver.
The receiver: The purpose of the receiver is to amplify the radio frequency (RF) signals. This ends up giving video signals at the output.
Radar antenna: The antenna is responsible for the transfer of the transmitter energy into signals in space with the required efficiency and distribution. The same applies when the signals hit the receiver on the receiving end.
Indicator: The indicator is the device that indicates to the user or observer a continuous graphic representation of the relative positions of the radar targets.
Overview of the Pulse RADAR system
A pulse radar system operates on a simple principle of propagating high-frequency radio signals towards an object through the antenna. The waves or radio signals hit the object and are then reflected back to the objet. The transmitter has to wait for the radio signals sent out through the antenna to hit the object and be reflected back before they can send another signal. The range and resolution of the radar data will depend on how frequently the pulses are transmitted to the object. The antenna that was used to make the signal transmission to the object will again capture the returning signal and send it to the receiver. The range of the object can then be determined by timing the transmission and reception of the pulses.
Of importance to note is the fact that the radar must not be transmitted at the same time as when it is being received. This is because the transmitter transmits stronger pulses and signals that are then received by the weaker receiver that receives weaker signals. In this case, the receiver would be damaged if this were to happen.
Types of Pulsed RADAR
The pulse Doppler radar is responsible for transmitting high pulse repetition frequency. The signal being transmitted and the reflected signal are then mixed in a detector to get the shift in Doppler. The difference in signal is then filtered using a device known as the Doppler filter. It is at this point that the noise is filtered and removed to remain with a clear signal.
Moving target indicator radar (MTI)
The MTI radar transmits low pulse repetition frequency with an aim of avoiding the range ambiguities that are associated with radar. In an MTI radar system, the received radio signals that have been reflected from the object are directed towards a mixer and then mixed with a signal from a stable local oscillator to give the final Intermediate Frequency signal.