4阮明黄-外文翻译原文1.pdf

Car Collision Prevention Radar System Ni Guoqi Liu Changman Guan Yongjun Wang Mansheng Department of Fire Control 1 Medium I identification Concealment Medium Medium Air searching Good Under fog or dust 1 Good Medium Good circumstance 2 2 Transmitter 2 2 1 Frequency Selection The major factor that affects frequency selection is the radar functions what is required here of the radar is good searching high ranging accuracy adopt millimeter waver2 high ranging accuracy adopt millimeter wave because 1 It has shorter wave length The system will be compact and will possess high ranging accuracy 2 Its bandwidth is very wide There are four windows for atmospheric transmission near 8 6mm 3 2mm 2 lmm and 1 4mm within the millimeter the band The bandwidth of each window is very wide They are respectively 16 GHz 23GHz 26GHz and 70 GHz 3 Atmospheric attenuation and dissipation of the transmission windows are quite low The attenuation is low under the circumstance of suspended particles and dust and smoke and fog and a i r pollution Because of their low ground scattering the ground clutter and multi channel interference is low Two Americans Wicker and Webb have made a comparison between microwave radar and millimeter radar and optical radar Their condition is as shown in the following form 2 2 2 Oscillation Source Radar transmitter is mainly composed of radio frequency power source and modulator and power source There are two method of generate the radio frequency power the power oscillator and main vibration amplifier For the convenience of signal processing and light weigh and small volume the main power amplifier adopted in this system is used as oscillation source The main oscillator that may be applied in this system are crossed field amplifier and klystron and traveling wave tube and transistor amplifier etc Which are usually applied in such a occasions where the stable low power devices are needed For example they can be used as the terminal power amplifier in coherent movement target indication system pulse compression radar and pulse Doppler system 2 2 3 Transmittine Antenna Following the design principle of one certain tracing radar the orientation antenna is adopted to try to centralize its energy and cause the light beam into an acicular beam The mature technical Castigliano antenna is the ideal one The selection of an antenna depends on the systematic requirements the maximum number of targets to be detected at any time the number of targets to be tracked the speed and maneuver of targets and possible scope of angles of azimuth and elevation of targets These scanners range from the simplest and cheapest mechanical scanners to complicated and expensive electronic scanners The former can be used under a not demanding condition while the latter can be used under a highly demanding condition The ones between the two are mixed scanners and electromechanical scanners The simplest scanning type is the fixed beam system This type of system such as wake ranging radar does not require antenna beam scanning We adopt this type of scanning 2 3 Signal Processing System 7 3 1 Receiver 873 Through the reception and transmission transformation switch the reflected magnetic wave signal enters the receiver channel and gets the intermediate frequency after frequency mixing in the mixer and then the intermediate frequency signal is sent into the rectifier to detector out the video signal after being bipolarity amplification The superheterodyne receiver used in this system works smoothly with a higher sensibility and a modest cost In this system we adopt the no cooling millimeter wave heterodyne receiver in which the beam lead GaAs semi conductor devices are adopted It is very suit for the receiver which frequency range is between 30 to 100 gigahertz At present the wave guide component frequency over 100 gigahertz and its technology have found a wide application So many different transmitting vectors and technology also have found its application with the development of millimeter wave integrated circuit Many multifunction components have been adopted on suspension banded line and micro banded line and fin line and notched line and wave guide Their frequency is between 35 and 100 gigahertz The millimeter wave receiver can be made as the same as the structure of ordinary microwave receiver General speaking the millimeter wave receiver use the higher intermediate frequency but the millimeter wave receiver on the low frequency 30 gigaherz is adopted as the same as technology of the micro wave receiver Such as integrated circuit receiver gas discharge tube reception and transmission switch receiver protection device wave filter amplitude limited circulator isolator and PIN switch and so on 5J 2 3 2 DiPital P r o c e a Now the radar signal digital processing is becoming very popular It becomes the reality for us to generate the digital signal and to be filtered with the development of analog digital converter and integrated circuit technology and the appearance of the fast Fourier Calculation The digital processing has shown its advantages in its stability and repeatability and flexibility In theory no restriction is put on wave pattern and wave filter function With the appearance of the digital computer we can effectively deal with the continuous radar s signal according to the sampled theorem The frequency spectrum is calculated based on the sampled signal group 2 3 3 Digtal Pulse Comp ression The digital system provide us with a large capability to do processing in effective time The handled data can be stored in the memory after analogy to digital conversion processing and continue to carry out the processing in no real time rate faster or slower Why the pulse compression technology is adopted It is mainly because of its great improved test ability and less interference It will become serious problem for radar to interference one another in a very dense active electro magnetic environment So the pulse compression radar can be designed to reduce it interference by using different modulation codes and different matched wave filter 2 3 4 D i e i t w h e d F iltaig The ideal method of digital matched filtering is to adopt the weighted method of calculating tapped delay line But it is replaced recently by the fast Fourior transform for its peripheral convolution The wide dynamic state range and the high speed matched filter processing devices have come into being with the development of the assembly line faster Fourier transform technology and the development of the floating point equipment A new matched filter processing method called step transform use the Sub aperture processing and reduce the faster Fourier transform scale its hardware is not more than the half of the faster Fourier convolution processing 2 4 Indicator In this system the radar indicator is just kind of accessory equipment Which provide drivers the distance between two cars and display the speed We adopt the more popular plasma indicator which can complete the classical program with the microprocessor and precompiled program This plasma indicator can generate the dot line and special symbols such as small circles and blocks The plasma indicator has lots of advantages to have higher stability and longer lifetime than the cathedras tube to have brighter brightness than some cathode ray tube Take the cost into consideration another design to display sorts of data s is to adopt the light emitting diode array 2 5 Controlling and Readjustment Speed The car loader radar measures out the distance between two cars and converts it into digital signal and compare with he safe distance 150m If measured distance is shorter than the safe distance The radar will output a positive error signal to control the regulating system to reduce car s speed until the two cars is at the set up distance otherwise The radar will output a negative error signal to control and adjust the car s moving speed The car s speed can t be beyond the limited speed In addition if the drivers don t want to have such a high speed he can use he manual control The manual control will be out of caption when there is a negative error signal The speed will slow down automatically It is the best to use the infinitely variable speeds system as its adjustable speed sys