The invisible thing that saves planes from crashing between them and finds idiots who cause accidents with their ridiculous driving is none other than a most useful concept that is RADAR TECHNOLOGY…NASA uses radar to map the Earth and other planets; meteorologists use radar to track storms, hurricanes and tornadoes. You even see a form of radar at many grocery stores when the doors open automatically!


The three main uses of radar are…

  1. 1. To detect the presence of an object at a distance
  2. 2. To detect the speed of an object
  3. 3. To map something

These works of radar done with concepts of ECHO and DOPPLER SHIFT using radio waves…

What is an echo? :

When you shout into a well, the reflected sound waves you hear back is called an ECHO… it occurs because some of the sound waves in your shout reflect off of a surface (the water at the bottom of the well) and travel back to your ears…The length of time between the moment you shout and the moment that you hear the echo is determined by the distance between you and the surface that creates the echo…

What is meant by Doppler shift? :

Doppler shift is generated when sound waves are reflected by moving objects…here time interval plays an important role in defining this concept…Let’s say there is a car coming toward you at 60 miles per hour (mph) and its horn is blaring. You will hear the horn sound increasing as the car approaches, but when the car passes you the sound of the horn will suddenly shift to a lower note. It’s the same horn making the same sound the whole time. The change you hear is caused by Doppler shift.

You can combine echo and Doppler shift in the following way. Say you send out a loud sound toward a car moving toward you. Some of the sound waves will bounce off the car (an echo). Because the car is moving toward you, however, the sound waves will be compressed. Therefore, the sound of the echo will have a higher pitch than the original sound you sent. If you measure the pitch of the echo, you can determine how fast the car is going.

This is how we can detect presence and speed of object coming to us or going away from us…the same concept in radio waves form is used by radar….


Using the principles above a SOUND RADAR or SONAR can be built which is used by submarines and ships all the time. But when it comes to sound waves, those waves can disturb others and they fade out soon. And also they don’t travel distances in miles even. Hence in place of sound waves, radio waves are used… Radio waves travel far, are invisible to humans and are easy to detect even when they are faint.

Let’s take a typical radar set designed to detect airplanes in flight. The radar set turns on its transmitter and shoots out a short, high-intensity burst of high-frequency radio waves. The burst might last a microsecond. The radar set then turns off its transmitter, turns on its receiver and listens for an echo. The radar set measures the time it takes for the echo to arrive, as well as the Doppler shift of the echo. Radio waves travel at the speed of light, roughly 1,000 feet per microsecond; so if the radar set has a good high-speed clock, it can measure the distance of the airplane very accurately. Using special signal processing equipment, the radar set can also measure the Doppler shift very accurately and determine the speed of the airplane.


The power Pr returning to the receiving antenna is given by the radar equation:


  • Pt = transmitter power
  • Gt = gain of the transmitting antenna
  • Ar = effective aperture (area) of the receiving antenna
  • σ = radar cross section or scattering coefficient, of the target
  • F = pattern propagation factor
  • Rt = distance from the transmitter to the target
  • Rr = distance from the target to the receiver.

This shows that the received power declines as the fourth power of the range, which means that the reflected power from distant targets is very, very small.


Some of the de merits of radar communication are

  1. Beam path and range
  2. Noise
  3. Interference
  4. Jamming



Building blocks of RADAR are

  • A transmitter that generates the radio signal with an oscillator and controls its duration by a modulator
  • A waveguide that links the transmitter and the antenna.
  • A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations.
  • A receiver knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using
  • An electronic section that controls all those devices and the antenna to perform the radar scan ordered by software.
  • A link to end users.

This is just a basic explanation of antenna…as it is a vast concept, we will be explaining each concept of it in parts…

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