Radar Systems  Overview
RADAR is an electromagnetic detection system that works by radiating electromagnetic waves and then studying the echo or reflected waves.
The full form of RADAR is RA dio D etection Un nd R anging. Detection refers to the presence or absence of the target. The target can be fixed or mobile, that is to say not stationary. Telemetry refers to the distance between the radar and the target.
Radars can be used for applications are listed below.
 Air traffic control
 Ship safety
 Detection of distant places
 Applications military
In any Radar application, the basic principle remains the same. Now let's talk about the principle of radar.
Prinbasic radar concept
Radar is used to detect objects and find their location. We can understand the basic principle of radar from
As shown in the figure, radar mainly consists of a transmitter and a receiver. It uses the same antenna to transmit and receive signals. Function of the transmitter is to transmit the radar signal in the direction of the present target.
The target reflects this received signal in different directions. The signal, which is reflected towards the antenna, is received by the receiver .
Radar Systems Terminology
These are the basic terms, which are useful in this tutorial.
 Range
 Pulse repetition frequency
 Maximum unambiguous range
 Minimum Range
Now let's talk about these basic terms one by one.
Range
The distance between Radar and targ andis called Range of target or simply range, R. We know that the radar transmits a signal to the target and as a result the target sends an echo signal to the radar with the speed of light, C.
Let “T” be the time it takes for the signal to pass from the radar to the target and back to the radar. The bidirectional distance between the radar and the target will be 2R, since the distance between the radar and the target is R.
Now here is the formula for Speed .
$$ Speed = frac {Distance} {Time} $$
$$ Rightarrow Distance = Speed times Time $$
$ $ Rightarrow 2R = C times T $$
$$ R = frac {CT} {2}::::: Equation: 1 $$
We can find the range of the target by substituting the values of C & T in equation 1.
Pulse repetition frequency
Radar signals must be transmitted at each clock pulse. The duration between the two clock pulses must be suitableIt is chosen so that the echo signal corresponding to the current clock pulse is received before the next clock pulse. A typical radar waveform is shown in the following figure.
As shown in the figure, the radar emits a periodic signal. It has a series of narrow pulses of rectangular shape. The time interval between the successive clock pulses is called pulse repetition time , $ T_P $.
The inverse of the pulse repetition time is called pulse repetition frequency , $ f_P $. Mathematically, it can be represented by
$$ f_P = frac {1} {T_P}::::: Equation: 2 $$ Therefore, the pulse repetition frequency is nothing other than the frequency at which the radar transmits the signal.
Maximum unambiguous range
We know that radar signals must be transmitted with every clock pulse. If we select une shorter duration between the two clock pulses, then the echo signal corresponding to the current clock pulse will be received after the next clock pulse. For this reason, the target's range appears to be smaller than the actual range.
So we have to select the duration between the two clock pulses in such a way that the echo signal corresponding to the current clock pulse will be received before the start of the next one clock pulse. Then we will get the true range of the target and it is also called the maximum unambiguous range of the target or just maximum unambiguous range .
Substitute, $ R = R_ {un} $ and $ T = T_P $ in equation 1.
$$ R_ {un} = frac {CT_P} {2 }::::: Equation: 3 $$
From equation 2, we will get the pulse repetition time, $ T_P $ as the reciprocal of the pulse repetition frequency, $ f_P $. Mathématically , it can be represented by
$$ T_P = frac {1} {f_P}::::: Equation: 4 $$
Substitute, equation 4 in equation 3.
$$ R_ {un} = frac {C left (frac {1} {f_P} right)} {2} $$
$$ R_ {un} = frac {C} {2f_P}::::: Equation: 5 $$
We can use equation 3 or equation 5 to calculate the maximum unambiguous range of the target.

We will get the value of the target's maximum unambiguous range, $ R_ {a} $ by replacing the values of $ C $ and $ T_P $ in equation 3.

Likewise, we will get the value of the maximum unambiguous range of the target, $ R_ {a} $ by replacing the values of $ C $ and $ f_P $ in equation 5.
Minimum range
We will get the minimum range of the target, when we consider the time required for the echo signal to receive at the radar after the signal transmitted by the radar comme pulse width. This is also called the shortest range of the target.
Substitute, $ R = R_ {min} $ and $ T = tau $ in equation 1.
$$ R_ {min} = frac {C tau} { 2}::::: Equation: 6 $$
We will get the value of the minimum range of the target, $ R_ {min} $ by replacing the values of $ C $ and $ tau $ in equation 6.