Radar. Seminar report. Submitted in partial fulfillment of the requirement for the award of degree Of Mechanical

Transcription

1 A Seminar report on Radar Submitted in partial fulfillment of the requirement for the award of degree Of Mechanical SUBMITTED TO: SUBMITTED BY:

2 Preface I have made this report file on the topic Radar, I have tried my best to elucidate all the relevant detail to the topic to be included in the report. While in the beginning I have tried to give a general view about this topic. My efforts and wholehearted co-corporation of each and everyone has ended on a successful note. I express my sincere gratitude to..who assisting me throughout the prepration of this topic. I thank him for providing me the reinforcement, confidence and most importantly the track for the topic whenever I needed it.

3 Contents Introduction What is Radar Characteristics Types Application Principle Advantages Disadvantages Conclusion

4 Introduction Radar is an acronym for Radio Detection And Ranging. A radar is an electro-magnetic device capable of transmitting a electro-magnetic wave near 1 Ghz, receiver back a reflection from a target and based on the characteristics of the returned signal determine things about the target. Radars have become indispensable in several major fields of research and in commerce. The Federal Aviation Agency (FAA) makes extensive use of radars not only to track aircraft, but to make sure landings and take-offs are uneventful. Meteorologist use radars to track severe weather and to estimate the amount of rainfall. Radar meteorology means many things to many people. Depending on what your research interests is your definition may be very different from mine. As a working definition I will use the following.

5 What is Radar Radar meteorology is the study of the atmosphere using radar as a tool.radar Meteorology is not a true branch of meteorology because it is use by several true branches of meteorology, such as cloud physics and severe storms, as a tool for that particular branch. Radar meteorology is also not a branch of radio meteorology; Radio meteorology is the study of how electro-magnetic waves travel through the atmosphere. As such radio meteorology deal with refraction, reflection and propagation of electro-magnetic waves. Although these concepts are very important they are not the core of radar meteorology.

6 Characteristics Radar is a remote sensing tool in that it is not in contact with the object it is sensing Radar measures the characteristics of the atmosphere from a distance. Further, radar is an active sensor in that it modifies the atmosphere and then measures the atmospheres response. Radar is not a prognosticator, i.e. it does not make a forecast rather it samples the atmosphere from a close distance and there appears to make a very accurate forecast. Radar is a means of detecting locating identifying, measuring and then displaying the atmosphere and what is in it. Radar is useful because of the following characteristics: 1. Radar scans a three-dimensional volume and can be pointed any where in space. The scale of the smallest volume is meso-a. 2. Continuous scanning in space Typically with 5 -> 8 minutes between scans of the same volume. 3. Reasonable resolution. For a typical 2 msec pulse at 100 nm the volume is about 5 km x 5 km x 600m 4. Total variability of the atmosphere can be measured, i.e. Radar can measure all the components of the total derivative. 5. Radar can make in-storm measurements 6. Radar can measure the actual severity of the storm, since Z e is a measure of the number of hydrometers per cubic unit. 7. Radar, if coherent, can measure the three components of the wind. Thus from the meteorologists point of view a radar provides a large number of advantages over any other tool designed to look at the structure of severe storms and clouds. Much of what we know about the inner workings of thunderstorms and other precipitating cloud systems come from radar. Radar uses an antenna producing a narrow beam of energy to scan a volume of space until a reflection is obtained. The direction the antenna is pointing and the time interval between the transmission and reception determine the location of the reflection in space. Further the strength and polarization of the reflection determine the characteristics of the target.

7 Types of Radars Classification based on specific function Classification based on the primary function of radar is shown in the following figure: Primary Radar: A Primary Radar transmits high-frequency signals toward the targets. The transmitted pulses are reflected by the target and then received by the same radar. The reflected energy or the echoes are further processed to extract target information. Secondary Radar: Secondary radar units work with active answer signals. In addition to primary radar, this type of radar uses a transponder on the airborne target/object. A simple block diagram of secondary radar is shown below

8 The ground unit, called interrogator, transmits coded pulses (after modulation) towards the target. The transponder on the airborne object receives the pulse, decodes it, induces the coder to prepare the suitable answer, and then transmits the interrogated information back to the ground unit. The interrogator/ground unit demodulates the answer. The information is displayed on the display of the primary radar. The secondary radar unit transmits and also receives high-frequency impulses, the so called interrogation. This isn't simply reflected, but received by the target by means of a transponder which receives and processes. After this the target answers at another frequency. Various kinds of information like, the identity of aircraft, position of aircraft, etc. are interrogated using the secondary radar. The type of information required defines the MODE of the secondary radar. Pulsed Radar: Pulsed radar transmits high power, high-frequency pulses toward the target. Then it waits for the echo of the transmitted signal for sometime before it transmits a new pulse. Choice of pulse repetition frequency decides the range and resolution of the radar.

9 Target Range and bearings can be determined from the measured antenna position and time-ofarrival of the reflected signal. Pulse radars can be used to measure target velocities. Two broad categories of pulsed radar employing Doppler shifts are MTI (Moving Target Indicator) Radar The MTI radar uses low pulse repetition frequency (PRF) to avoid range ambiguities, but these radars can have Doppler ambiguities. Pulse Doppler Radar Contrary to MTI radar, pulse Doppler radar uses high PRF to avoid Doppler ambiguities, but it can have numerous range ambiguities. Doppler Radars make it possible to distinguish moving target in the presence of echoes from the stationary objects. These radars compare the received echoes with those received in previous sweep. The echoes from stationary objects will have same phase and hence will be cancelled, while moving targets will have some phase change. If the Doppler shifted echo coincides with any of the frequency components in the frequency domain of the received signal, the radar will not be able to measure target velocity. Such velocities are called blind speeds. Where, fo = radar operating frequency. Continuous Wave Radar: CW radars continuously transmit a high-frequency signal and the reflected energy is also received and processed continuously. These radars have to ensure that the transmitted energy

10 doesn t leak into the receiver (feedback connection). CW radars may be bistatic or monostatic; measures radial velocity of the target using Doppler Effect. CW radars are of two types 1. Unmodulated An example of unmodulated CW radar is speed gauges used by the police. The transmitted signal of these equipments is constant in amplitude and frequency. CW radar transmitting unmodulated power can measure the speed only by using the Doppler-effect. It cannot measure a range and it cannot differ between two reflecting objects. 2. Modulated Unmodulated CW radars have the disadvantage that they cannot measure range, because run time measurements is not possible (and necessary) in unmodulated CW-radars. This is achieved in modulated CW radars using the frequency shifting method. In this method, a signal that constantly changes in frequency around a fixed reference is used to detect stationary objects. Frequency is swept repeatedly between f1 and f2. On examining the received reflected frequencies (and with the knowledge of the transmitted frequency), range calculation can be done.

11 If the target is moving, there is additional Doppler frequency shift which can be used to find if target is approaching or receding. Frequency-Modulated Continuous Wave radars (FMCWs) are used in Radar Altimeters.

12 Application The information provided by radar includes the bearing and range (and therefore position) of the object from the radar scanner. It is thus used in many different fields where the need for such positioning is crucial. The first use of radar was for military purposes: to locate air, ground and sea targets. This evolved in the civilian field into applications for aircraft, ships, and roads. In aviation, aircraft are equipped with radar devices that warn of obstacles in or approaching their path and give accurate altitude readings. The first commercial device fitted to aircraft was a 1938 Bell Lab unit on some United Air Lines aircraft. They can land in fog at airports equipped with radar-assisted ground-controlled approach (GCA) systems, in which the plane's flight is observed on radar screens while operators radio landing directions to the pilot. Marine radars are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate, and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships. In port or in harbour, vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters. Meteorologists use radar to monitor precipitation and wind. It has become the primary tool for short-term weather forecasting and watching for severe weather such as thunderstorms, tornadoes, winter storms, precipitation types, etc. Geologists use specialised ground-penetrating radars to map the composition of Earth's crust. Police forces use radar guns to monitor vehicle speeds on the roads.

13 Principal of RADAR A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity especially by most metals, by seawater and by wet lands. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either toward or away from the transmitter, there is a slight equivalent change in the frequency of the radio waves, caused by the Doppler effect. Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended. Radar relies on its own transmissions rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, although radio waves are invisible to the human eye or optical cameras.

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15 Advantages and Disadvantages Advantages 1. The main advantage of RADAR, is that it provide superior penetration capability through any type of weather condition, and can be used in the day or night time. 2. Radar uses electromagnetic wave that does not require a medium like Sonar (that uses water) so can be used in space and air. Radar can be long range and the wave propagate at the speed of light rather then sound (like with sonar). It is less susceptible to weather conditions compared with Lasers.And be used at night unlike passive cameras. It does not require target cooperation to emit any signals or emission. 3. Very flexible - can be used in a number of ways! 4. Stationary mode 5. Moving mode 6. Two Directional mode 7. Beam spread can incorporate many targets! 8. Can often select fastest target, or best reflection! 9. Still very reliable. Disadvantages 1. Time - Radar can take up to 2 seconds to lock on! 2. Radar has wide beam spread (50 ft diameter over 200 ft range) 3. Cannot track if deceleration is greater than one mph/second! 4. Large targets close to radar can saturate receiver! 5. Hand-held modulation can falsify readings! 6. More interference sources.

16 Conclusion There are many improvements that we can make to our system in order to create better results. First of all, we need to increase the range of the detection, not having to limit our input signals as much to get accurate results. We need to adjust with the sampling rate that we use in order to be able to detect smaller velocities as well as more accurate ranges. We could optimize the algorithm for the peak locator in the velocity analysis to give more accurate results. In the end, we managed to create a system that created signals to send out with a RADAR, as well as simulate a returned signal for objects a specific distance away or moving at a certain velocity. We were able to detect the range for objects that were fairly close, and calculate the velocity for objects moving extremely fast.

17 Reference