Introduction To Radar

Radar is basically a means of gathering information about distant object or targets by streaming electromagnetic waves at them and analyzing their echoes (reflection). It was evolved during the years just before World War II independently and more or less simultaneously in Great Britain, the United States, Germanyand France. At first it was used as an all weather method of detecting an approaching aircraft and for detecting anti-aircraft weapons and later for many other purposes. The words ‘RADAR’ is an acronym coined from the words Radio Detection And Ranging (means target is detected with the help of radio waves and also it measures distance). It was radar that gave birth of microwave technology. It was seen that the higher frequencies gave the most accurate results.

Basic Types of Radar. There are mainly two types of radar systems, Primary and secondary radar. The Primary radar is an independent radar works on echo principle. In this the transmitter transmit EM energy in the space. If there is any object in the direction of the energy transmitted the object simply reflects the incident RF energy. The reflected energy known as echo pulse is being received by the highly sensitive radar receivers and processed. In the case of secondary radar object is caused automatically re-transmit the radio wave on the same frequency or some other frequency. Further the radar system is classified into two main category i.e., Pulse Radar and Continuous Wave radar (CW Radar).

Primary Radar

Search Radar. These are mainly primary pulse radar sets. These sets need not to have exceptional accuracy or resolution but are expected to detect enemy aircrafts at the greatest possible range to present a picture of the naval or air situation on which tactical decisions can be made. These sets have high power output and large antennae, which are rotated 360° for search purposes.  (For example Ground Radars i.e. THD – 1955, TRS, P-40, etc.)

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Tracking (Fire Control) Radar. These are also primary pulse radars, but these sets emphasis on the accuracy of range and angle information. These sets operate on high frequencies and have short pulse with the receivers having high bandwidth. In these sets a single object is tracked. The tracking is either manual or automatic. In auto tracking mode the error signal is derived from the echo pulse which actuates servo-mechanism that causes the antenna and range gate to follow the object co-ordinates faithfully for the purpose of aiming anti-aircraft missiles and guns. Airborne fire control radars are for interception and automatic searching and tracking of targets and launching air-to-air missiles. For Example Missile Guidance Radar,R2L (MiG), etc.

Secondary Radars

This refers to radars, which works along with the primary radar i.e., IFF, Beacons etc. Secondary radars are extensively used in navigational aids i.e., Homing Equipment and IFF Equipment (Identifying Friend or Foe).

Pulse Radar.  The essential function of radar set is to fix the co-ordinate of a material object in space with reference to the radar set.  The range, azimuth height and speed of the target can be determined with this.  Position of an object can be completely determined if the radar slant range ‘r’, bearing and the angle of elevation from the radar set are accurately measured. For this purpose the radar set sends a narrow beam of EM energy in the form of short bursts of pulses. The target, which is illuminated by radio wave, reflects some of these radio waves in all possible directions.  A small portion of this reflected energy called Echo Pulse, is being received and processed by highly sensitive receivers located at the radar sets.  If the time interval between the instances when the RF energy leaves the transmitter and the echo pulse arrival at the receiver is measured accurately the range ‘r’ of the target can be computed from the formula:-

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Where C is velocity of the EM energy in free space, which is equal to 1,86,000 miles per second or 3 X 108metre per second.

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