INTRODUCTION TO RADAR TECHNOLOGY

SYED FAHAD RAZA L2F07BSEE0627WAQAS AMJAD L2F07BSEE0612

PRESENTED TOCOL.(Ret) SIKANDAR QAYYUM

Introduction

• RADAR stands for RADIO DETECTION and RANGING.

• Before World War II, experiments were performed with electronic systems to find the range of aircraft or other targets by transmitting radio pulses and measuring the time delay in receiving an echo back from the target.

• During the war, "radio detection and ranging (radar)" went through a rapid evolution and became an important weapon and tool in the conflict, with the opponents developing radars of increasing sophistication -- as well as "electronic intelligence (ELINT)" systems to spot enemy radars and "electronic countermeasures (ECM)" systems to jam them.

BASIC PRINCIPLE OF OPERATION

1)Reflection of electromagnetic waves:-The electromagnetic waves are reflected if they meet an electrically leading surface. If these reflected waves are received again at the place of their origin, then that means an obstacle is in the propagation direction.

2) Electromagnetic energy travels through air at a constant speed, at approximately the speed of light. This constant speed allows the determination of the distance between the reflecting objects (airplanes, ships or cars) and the radar site by measuring the running time of the transmitted pulses.

3) This energy normally travels through space in a straight line, and will vary only slightly because of atmospheric and weather conditions. By using of special radar antennas this energy can be focused into a desired direction. Thus the direction (in azimuth and elevation of the reflecting objects can be measured.

These principles can basically be implemented in a radar system, and allow the determination of the distance, the direction and the height of the reflecting object.

RADAR BASIC PRINCIPLES

The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device

The electrical signal picked up by the receiving antenna is called echo or return.

The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.

All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also called scattering. Backscatter is the term given to reflections in the opposite direction to the incident rays.

Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of targets.

SECTIONS OF RADAR BLOCK DIAGRAM

• Transmitter The radar transmitter produces the short duration high-power rf pulses of energy that are into space by the antenna.

• Duplexer The duplexer alternately switches the antenna between the transmitter and receiver so that only one antenna need be used. This switching is necessary because the high-power pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver.

• ReceiverThe receivers amplify and demodulate the received RF-signals. The receiver provides video signals on the output.

• Radar AntennaThe Antenna transfers the transmitter energy to signals in space with the required distribution and efficiency. This process is applied in an identical way on reception.

• IndicatorThe indicator should present to the observer a continuous, easily understandable, graphic picture of the relative position of radar targets.

PRINCIPLES OF MEASUREMENT DISTANCE DETERMINATION The distance is determined from the running time of the high-frequency transmitted

signal and the propagation c0.

The actual range of a target from the radar is known as slant range. Slant range is the line of sight distance between the radar and the object illuminated

While ground range is the horizontal distance between the emitter and its target and its calculation requires knowledge of the target's elevation.

R = c0· t /2

c0 = speed of light = 3·108 m/s

t = measured running time [s]R = slant range antenna - aim [m]

DIRECTION DETERMINATION• The angular determination of the target is determined by the directivity of the

antenna.• By measuring the direction in which the antenna is pointing when the echo is

received, both the azimuth and elevation angles from the radar to the object or target can be determined.

• The True Bearing (referenced to true north) of a radar target is the angle between true north and a line pointed directly at the target.

• This angle is measured in the horizontal plane and in a clockwise direction from true north.

CLASSIFICATION OF RADAR SYSTEMS

PRIMARY RADARThe radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device.

The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.

All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions.

Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems.

SECONDARY RADAR• The need to detect „hostile” aircraft led to a vast investment in intellect and

money to develop RADAR• If the „friendly” aircraft is fitted with a transponder (transmitting responder), then

it sends a strong signal back as an „echo”.• An active also encoded response signal which is returned to the radar set then is

generated in the transponder. • This proved very useful for the military in seeing their own aircraft clearly.

Continuous Wave Radar• CW radar sets transmit a high-frequency signal continuously. The echo signal is

received and processed permanently.

Speed gauges are very specialized CW-radars. A speed gauge uses the Doppler- frequency for measurement of the speed.

The figure shows the speed gauge „Traffipax Speedophot” produced by ROBOT Visual Systems GmbH . This radar uses a frequency of 24.125 gigahertz.

It can measure the speed of the incoming and the outgoing traffic, from the right or left border of the street. The radar can be mounted in a car or on a tripod.

The traffic offence can be circumstantiated by a photo camera with high resolution.

WEATHER RADARBASIC PRINCIPLE OF OPERATION

The basic concept of weather radar works off of the idea of a reflection of energy.

The radar sends out a signal, as seen to the right, and the signal is then reflected back to the radar.

The stronger that the reflected signal is, the larger the particle.

So the weather is determined by the reflection of the reflected waves.

SYNTHETIC APERTURE RADAR• A Synthetic Aperture Radar (SAR), or SAR, is a

coherent mostly airborne or space borne side looking radar system which utilizes the flight path of the platform to simulate an extremely large antenna or aperture electronically, and that generates high-resolution remote sensing imagery.

• SAR is usually implemented by mounting, on a moving platform such as an aircraft or spacecraft, a single beam-forming antenna from which a target scene is repeatedly illuminated with pulses of radio waves at wavelengths anywhere from a meter down to millimeters.

• The many echo waveforms received successively at the different antenna positions are coherently detected and stored and then post-processed together to resolve elements in an image of the target region.

Radar ScopesA-Scope

• A-scope presents only the range to the target and the relative strength of the echo.• Such a display is normally used in weapons control radar systems.• The bearing and elevation angles are presented as dial or digital readouts that

correspond to the actual physical position of the antenna.• In modern digital radar sets don't exist a similar video signal of the backscatter. The

target messages are transmitted to the displays as a digital word

Radar B-Scope

• The B-Scope shows a picture like a Cartesian diagram.• It provides a 2-D “top down” representation of space. • The horizontal axis (abscissa) typically represents the measurement of the azimuth

(bearing), and the vertical axis (ordinate) represents the measurement of the range.

• Signals appear as bright spots.

Range mark Azimuth mark

Targets

ground clutter

Radar PPI-Scope

• The PPI-scope is by far the most used radar display.• It is a polar coordinate display of the area surrounding the radar platform.• Own position is represented as the origin of the sweep, which is normally located

in the center of the scope, but may be offset from the center on some sets.• The ppi uses a radial sweep pivoting about the center of the presentation.• The sweep rotates on the display just as fast as the radar antenna. This results in a

map-like picture of the area covered by the radar beam.

RADAR APPLICATIONS

• Search radars scan a large area with pulses of short radio waves

• Targeting radars use the same principle but scan a smaller area more often

• Navigational radars are like search radar, but use short waves that reflect off hard surfaces. They are used on commercial ships and long-distance commercial aircraft

• Mapping radar scans a large regions for remote sensing and geography applications

• Wearable radar which is used to help the visually impaired

• Air traffic control uses radar to reflect echoes off of aircraft

• Weather radar uses radar to reflect echoes off of clouds

• Weather radars use radio waves with horizontal, dual (horizontal and vertical), or circular polarization

• Some weather radars use the Doppler effect

to measure wind speeds

REFERENCES

• www.haystack.mit.edu/edu/pcr/waves/Radar/Radar

• http://www.radartutorial.eu/10.processing/sp20.en.html

• www.radar04.org