Prediction of range performance

Name – Bhupender SinghRoll no. – 13ECE06Subject- RADAR & SONAR engineering

Content

• Introduction to radar• Radar working• Radar equation • Use of radar equation• Prediction of range performance

Introduction to radar

• RADAR is acronym for Radio Detection and Ranging. • First successfully demonstrated in 1936. • It uses electromagnetic waves.• Large variety of application.

How weather radar works

Radar application

• Military • Air traffic control• Remote sensing• Ship safety• space

Radar equation• Perhaps the single most useful description of the factors influencing radar

performance is the radar equation which gives the range of a radar in terms of the radar characteristics.

• The radar range equation relates the range of the radar to the characteristics of the transmitter, receiver, antenna, target and the environment.

• The radar range equation represents the physical dependences of the transmit power, that is the wave propagation up to the receiving of the echo-signals.

• The radar equation is an important tool for following aspects1. Assessing the performance of radar2. Designing of new radar systems3. Assessing the technical requirements for new radar procurements

• -If the transmitter delivers ( ) Watts into an isotropic antenna, then the power density(W/m2) at a distance R from the radar is

• here the 4πR2 represents the surface area of the sphere at distance R

• the gain G of an antenna is the measure of the increased power radiated in the direction of the target, compared to the power that would have been radiated from an isotropic antenna.

Power density from a directional antenna =

• the measure of the amount of incident power by the target and redirected back in the direction of the radar is called the cross section σ.

• Hence the Power density of the echo signal at the radar =

• - the receiving antenna effectively intercepts the power of the echo signal at the radar over a certain area called the effective area Ae.

• Since the power density (Watts/m2) is intercepted across an area Ae, the power delivered to the receiver is

• - Now the maximum range Rmax is the distance beyond which the target cannot be detected due to insufficient received power Pr The minimum power which the receiver can detect is called the minimum detectable signal Smin.

• Setting Pr= Smin and rearranging the above equation gives

• Note here that we have both the antenna gain on transmit and its effective area on receive. These are related by:

• As long as the radar uses the same antenna for transmission and reception we have

Drawbacks of simple form of radar equation

• The fluctuation and uncertainties in target radar cross section.• The nature of minimum detectable signal, which is affected by

the receiver noise.• The losses experienced in the radar system• Displaying the locating targets is not clear

Prediction of range performance

• All of the parameters of the basic pulsed radar system will affect the performance in some way.

• Some basic factors – 1. Transmitter power2. Pulse width3. Pulse repetition frequency (PRF) and range ambiguities4. Radar operating frequency

Transmitter power

Pulse width ( PW )

• The duration of the pulse and the length of the target along the radial directions determine of the returned pulse.

• The range of values from the leading edge to the trailing edge will create some uncertainty in the range of the target.

If we designate the uncertainty in measured range as the range resolution, Rres, then it must be equal to the range equivalent of the pulse width.

To create perfectly formed pulse with a vertical leading edge would require an infinite bandwidth. In fact you may equate the bandwidth β, of the transmitter to the minimum pulse width, PW by :

Pulse repetition frequency (PRF) and range ambiguities

• PRF is crucial for systems and devices that measure distance.

1. RADAR2. LASER RANGE FINDER3. Sonar

• Different PRF allow systems to perform very different functions.

• A radar system uses a radio frequency electromagnetic signal reflected from a target to determine information about that target.

• PRF is required for radar operation. This is the rate at which transmitter pulses are sent into air or space.

Radar operating frequency

• The frequency of the radio carrier wave will also have some affect on how the radar beam propagate.

• For low frequency, at the high extreme, the radar beam will behave much like visible light and travel in very straight line.

• Very high frequency radar beams will suffer high losses and are not suitable for long range systems.

Thanky u