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Radar Systems

  • RADAR stands for Radio Detection and Ranging System.
  • It is basically an electromagnetic system used to detect the location and distance of an object from the point where the RADAR is placed. 
  • It works by radiating energy into space and monitoring the echo or reflected signal from the objects. It operates in the UHF and microwave range.


  • The RADAR system generally consists of a transmitter which produces an electromagnetic signal which is radiated into space by an antenna. 
  • When this signal strikes any object, it gets reflected or reradiated in many directions.
  • This reflected or echo signal is received by the radar antenna which delivers it to the  receiver, where it is processed to determine the geographical statistics of the object. 
 Types of Radar:
  • There are basically three types of Radars
  1.Continuous Wave Radar (CW Radar):
  • A block diagram of simple CW radar is shown in below figure.
  • The transmitter generates a continuous (unmodulated) oscillation of frequency F0, which is radiated by the antenna. 
  • A portion of the radiated energy is intercepted by the target and is scattered, some of it in the direction of the radar, where it is collected by the receiving antenna.
  • If the target is in motion with a velocity Vr relative to the radar, the received signal will be shifted in frequency from the transmitted frequency F0 by an amount ±Fd  .
  • The plus sign associated with the doppler frequency applies if the distance between target and radar is decreasing (closing target), that is, when the received signal frequency is greater than the transmitted signal frequency.
  • The minus sign applies if the distance is increasing (receding target). 
  • The received echo signal at a frequency F0 ± Fd enters the radar via the antenna and is heterodyned in the detector (mixer) with a portion of the transmitter signal/o to produce a doppler beat note of frequency Fd. The sign Fd is lost in this process. 


 2.Pulse Radar:
  • Pulse radar that extracts the Doppler frequency-shifted echo signal.
  • A simple way to convert the CW radar to the pulse radar by turning on and off CW oscillator to generate pulses. 
  • This way of generation of pulses removes the reference signal, which is required to  recognize the Doppler shifts.
  • One way to introduce the reference signal is shown in below figure. Here the power amplifier is turned on and off to generate the high power pulses. 
  • The received echo signal is mixed with the output of CW oscillator, which acts as coherent reference to allow the recognition of any change in the frequency. 
  • Here coherent means that the transmitted pulses are synchronously used as reference signal. The change in frequency is detected through Doppler filter.


 3.Moving Target Radar (MTI Radar):
  • The doppler frequency shift produced by a moving target may be used in a pulse radar. just as in the CW radar, to determine the relative velocity of a target or to separate desired moving targets from undesired stationary objects (clutter).
  • Such a pulse radar that utilizes the doppler frequency shift as a means for discriminating moving from fixed targets is called an MTI (moving target indication) or a pulse doppler radar.
  • The block diagram of MTI Radar system is shown below, the significant difference between this MTI configuration is the manner in which the reference signal is generated.
  • The coherent reference is supplied by an oscillator called the coho, which stands for coherent oscillator.
  • The coho is a stable oscillator whose frequency is the same as the intermediate frequency used in the receiver. In addition to providing the reference signal. the output of the coho. fc is also mixed with the local-oscillator frequency fl.
  • The local oscillator must also be a stable oscillator and is called stalo, for stable local  oscillator.
  • The stalo, coho, and the mixer in which they are combined plus any low-level amplification are called the receiver-exciter because of the dual role they serve in both the receiver and the transmitter.
  • The characteristic feature of coherent MTI radar is that the transmitted signal must be coherent (in phase) with the reference signal in the receiver. 
  • The reference signal from the coho and the I F echo signal are both fed into a mixer called the phase detector. The phase detector differs from the normal amplitude detector since its output is proportional to the phase difference between the two input signals.


Applications of Radar Systems:
Used in Military for Target Detection, Target Tracking and Weapon Control
Used in Air Traffic Control
Used to Avoid Collisions in Ships
Used in Submarines