Radar. Joo Eun heui. Ⅰ.Introduction

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1 Radar Joo En hei Abstract Radar is the device sing the characteristics of the doppler effect of the EM waves, comprising transmitter composed of magnetron and plse modlator, receiver composed of mixer, amplifier and local oscillator, wavegide, antenna, display nit and radome. Radom is thedielectric shield to protect the antenna and its thicknessshold be controlled to improve the transmittance of EM waves. Recently,laser can be more applied to radar,so called lidar, and sch trend will be scceeded. Ⅰ.Introdction 1.Origin of the word The word radar comes from radio detection and ranging. The light radar operating in optical wavelength is called lidar(light detection and ranging). 2.Basic concept. Radar radiates EM waves to the object and can get the information abot object by detecting echoes received and reflected from the srface of the object, then the radial velocity of the moving object can be got by measring the Doppler freqency shift occrred in it and the shape and material of the moving object can be known by the shape and dimension of the reflected plse. 3.History The idea of getting information abot the object by sing the EM waves was first sggested by the American, N.Tesla in 1889, and then the German, C. Whilsmeier attained the patent of the ship crsh prevention device in In 1931 Taylor monitored the existence of the airplane in 65 km front by sing the 60MHz FM Doppler radar, and then G.Bright and M.A.Tbe shot p the 0.5 ms plse to observe the ionosphere, which was the origin of the plse radar. In the U.K. so as to correspond against the German airforce the plse radar was developed in 1934, which cold captre the aircraft in 120 km front and 450 m hight, and in 1939 the 200MHz (1.5 m wave) radar was developed, they intercept the German airforce by sing it. Dring the world war 2 the U.S.A. established the radar instittion in M.I.T. as the military aid for the U.K. and therein the magnetron technology was introdced and the PPI(propagation projection image) which cold display the object as if it moved on the map and the landing aid wave device were developed and accomplished in todays form of the radar. Now the radar is widely sed in air traffic control, aircraft navigation, speed gn, earth environment remote exploration, weather observation, car crsh prevention device, inside investigation of the concrete bridge, etc..

2 ⅡBasic Operation of the Radar system 1. fndamental principle of the radar fndamental principle of the radar is the Doppler effect which is described in or textbook section T T R sorce object Fig.1 fig.2 If the wave sorce velocity is and the freqency f, the freqency of the wave can be observed f =f(1+ cosθ/c)by the standing observer, which is different from the original freqency f. Also, while the wave sorce is standing, bt the object is moving, we can assme that the object is standing and the wave sorce is moving backward in the velocity at the θ=π, then f=-2f /c by the effect given by going and coming back(see or textbook problem P.8-3 and the above fig.2). Therefore if the shift of the freqency is measred, then the velocity of the moving object can be calclated by the term =2( f/f)c. This principle can be applied to the lidar sing the laser samely. 2. The Composition and Operation of the Radar 1 antenna synchronizer/ modlator 2 transimitter nit dplexer video processor receiver 8 video display nit 7 servo 1 The Synchronizer synchronizes the transmitter with the video display nit by the d.c. plse series. 2 The Transmitter makes the high power RF generator operate with the plse received from the synchronizer/modlator nit. 3 The Video display nit also receives the plse from the

3 synchronizer/modlator nit together with the transmitter at the same time. 4 The RF plse generated from the transmitter is provided to the antenna throgh the dplexer which enables the transmitter and the receiver to se commonly the only one antenna. The circlator can play the role of the dplexer. 5 The energy coming back by scattering from the object is captred by the antenna and transmitted to the receiver in which it is transformed to signals, then the exist, position, and velocity information of the object is extracted. 6 The receiver transforms the received RF signal into the lower video freqency signal, transmitting it to the video display nit which displays the signal in the preferred type. 7 The servo nit plays the part in controlling the beam direction of the antenna according to the controlling signal. 3.the Composite elements and the relation of the EM wave s characteristics. (1) Dplexer In monostatic radar sing the same antenna in transmitting and receiving, it is the dplexer that plays a part in separating the transmitting and the receiving signals and the circlator is the one of it. The circlator is the 3-port device sing the ferrite placed in the magnetic field by the permanent magnet, the signals can be transmitted only in the direction as the following, port 1 port 2 port 3 port 1,not in the reverse direction. Transmitter antenna receiver fig. 3. circlator If the antenna is connected to the port 1,the received singal is transmitted to only the port 2, no reflection to the port 3 from the port 2 nder the condition that the signals are well matched. If the transmitting signals are connected to the port 3, they are transmitted to the port 1 connected to the antenna. (2) Polarization diversity The radar receiver has the 12 channels throgh the mltiplexer, each channel being amplified and sent to the dplexer. The reason of comprising the mltiple channels is that they enable the radar to operate in spite of losing some channels de to the system breakdown. Then, if the polarization diversity is sed in the antenna, the nmber of channel can be increased to 24 channels. That is to say, thogh the freqency is the same, two different information can be sent by sing the RHCP and LHCP signal. This is related to or textbook section RHCP 1~12 CH receiver dplexer

4 LHCP 13~24 CH receiver dplexer (3) Radome Radome means the cover made of the dielectrics to protect the antenna of the radar. In transmitting/receiving of the inpt/otpt signals, the thickness of the radome shold be controlled to optimize the transmittance lest the reflection from the radome distort the signal. Assme the waves are normal incident on the radome srface, becase both the back and front of the radome is the air, thhe dome thickness d shold be integral mltiple of half of the wavelength(d=nλ /2), which can make the reflectance zero and the transmittance optimized. This is related to or textbook section 8-8,8-9,review qestion R8-35, and P.8-29.Recently, the elliptical radome thickness is calclated by genetic algorithm becase the optimizing process is very complex as the antenna moves. Ⅲ.Recent trend of the radar techniqe (1) Recently, laser beam is sed as the EM waves in the radar(lidar).the reason is that laser has good directivity. Especially in the case of the weather observing radar, Δ f of the Doppler effect is very small so that the backgrond effect of the snlight can be ignored, which made the the lidar more preferable. The lidar comprises the transmitter composed of laser generator, the laser amplifier, the wavelength modlator and the transmitting telescope, the receiver composed of the receiving telescope, the dispersion device, the detector and the signal modlator, and the display nit. (2) The measrment of the moon distance was achieved by sing the laser reflecting mirror installed by the Apolo 11 in 1969,the sattlite Japan shot p in 1986 had been eqipped with the laser beam reflecting prism to forecast earthqake and earthshell movement by lidar. (3) The sea bottom map can be made by sing the ble green laser(nd:yag laser 532 nm) which has good transmittance in sea water. The time difference of the reflective plses between the sea srface and the sea bottom can be measred, from which the depth of the sea can be calclated. (4) The Doppler effect and Raman scattering effect can be applied to the earth scale air observation. (5) The lidar is viewed to be sccessively preferred in ftre and reqired to be less weighted and shorter plse higher speed repitation. Ⅳ.Conclsion We had better stdy laser characteristics if wish to participate in the radar development. References 1. Field and wave electromagnetics by D.K. Cheng. 2. Dsan encyclopedia. 3. Laser application by Kim hee je. 4. Applied electromagnetic theory by Ulaby. 5. The radome thickness optimizing design by genetic algorithm by Pak chang sn.

Lecture 1 INTRODUCTION. Dr. Aamer Iqbal Bhatti. Radar Signal Processing 1. Dr. Aamer Iqbal Bhatti

Lecture 1 INTRODUCTION. Dr. Aamer Iqbal Bhatti. Radar Signal Processing 1. Dr. Aamer Iqbal Bhatti Lecture 1 INTRODUCTION 1 Radar Introduction. A brief history. Simplified Radar Block Diagram. Two basic Radar Types. Radar Wave Modulation. 2 RADAR The term radar is an acronym for the phrase RAdio Detection