The Simulation Of Radio Signal For Direction Finding System Of Communication Counter-Measures

Rests on the different direction finding principle, may divide into the existing correspondence direction finder the amplifier comparison direction finding system, the interferometer direction finding system, spatial spectrum estimate direction finding system, time difference direction finding system, Doppler direction finding system and so on. The scope comparison -like direction finding system is based on the electric wave in marching forward, the use direction finding antenna array or the direction finding antenna directional characteristic, comes the wave receive signal scope to the different direction the difference, determines the wave direction. The interferometer direction finding system uses changes the baseline technology, may use, the big foundation antenna array, uses the multi- channels receiver, the computer and the FFT technology, causes this system direction finding sensitivity high, direction finding accuracy high, the direction finding speed is quick, the observable elevation angle, has the certain anti- wavefront distortion ability. This system polarization error is insensitive. The spatial spectrum estimated the direction finding system has multi-element array, multi- channels receiver, digital signal processing equipment and the terminal demonstration unit four partial compositions. The spatial spectrum estimated the direction finding the basic principle for through carries on the enlargement, the frequency conversion, the sampling as well as A/D transformation to the multi-element array receive airborne radio signal After digital signal carries on mathematics to process estimated the signal comes the wave direction.The Amplifier comparison system direction finder gain azimuth information method is the signal which receives to various antennas carries on the high frequency signal processing, obtains to contain the azimuth information the high frequency profile, then delivers the direction-finding receiver to carry on the envelope detection. Must obtain contains the azimuth information the high frequency signal, so long as produces a high frequency signal, then low frequency uses its itself (angular frequency is W) the modulation signal carries on the precise phase shifting, obtains in front of the signal and the phase shifting the signal multiplications, then may obtain includes the azimuth information the high frequency signal.This supply oscillator for the amplifier comparison system direction finder was mainly composed by precise phase shifting unit, the microcomputer control unit, the duplicate frequency unit, the frequency demonstrated the unit as well as the power source unit compose.The improvement direction finder simulation supply oscillator design take the DDS module as the core,, This system uses PC machine + control module +DDS+I/O connection structure. But the control module (or embedded system) by the monolithic integrated circuit and the CPLD constitution, on thePC control software and the monolithic integrated circuit to the system core DDS chip management control mainly through the CPLD realization. The CPLD chip selects Altera Corporation MAX7000S in the series the EPM7256AE chip, 5,000 logical units, the great single number is 256, uses based on E2PROM in the system programmable structure, the system clock frequency may reach 172.4 MHz, between the pin 5.5 ns constant detention.The direct digital frequency synthesis (DDS) uses the digitized technology, produces each kind of different frequency code directly through the control frequency control word which needs. DDS mainly by reference frequency source, phase accumulator, sine ROM table, D/Composition and so on A switch' and filter. AD9954 is American AD Corporation uses the advanced DDS technology production the high integration rate frequency synthesizer. In it sets at high speed, high performance D/the A switch and the supervelocity comparator, may take the digital programming control the frequency synthesizer, can have the 200MHz simulation sine wave.Because DDS uses the entire digital structure, inevitably has introduced the stray. Its origin mainly has three: The phase accumulator phase shed position error creates stray; The stray which the amplitude quantizing error (causes by memory limited word length) which creates the stray and the DAC non- idealized characteristic creates. May enhance the phase interruption figure regarding the interruption phase stray to increase its SFDR, increases to be possible every time to make SFDR approximately to increase approximately 6 dB; Enhances clock frequency fc, was equal in has increased the noise bandwidth,Reduced the pass band noise power,Enhanced the signal to noise ratio; Regarding D/ A transformation stray,May use the hypothesis low pass filter to filter the stray,Also may enhance the system clock to cause the stray to be far away the signalling frequency,By reduces the stray to the output signal influence.In the noise frequency-modulated signal "the noise" by the pseudo-random sequence producer production, the pseudo-random sequence producer through to the CPLD programming production, the pseudo-random sequence and the DDS frequency control word which the pseudo-random sequence producer produces carries on the operation, produces the new frequency control word, CPLD delivers the DDS frequency register and the real-time renewal the current frequency control word, thus realization noise frequency modulation. The noise signal also may by the computer production, and stores SRAM, again reads by CPLD takes, or outputs the simulation noise after DAC.Increased based on the DDS technology direction finder simulation supply oscillator has had the signal modulation type, realized AM, FM, FSK, PSK, the noise frequency modulation continuous radio telegraph correspondence equisignal; The expansion signalling frequency scope to 120MHz, causes the simulation supply oscillator to contain the majoritymilitary station the signalling frequency; Uses the programmable logical component, causes parameter passable procedure close regulation and so on the phase, scope, may adapt the many kinds of direction finding system direction finding supply oscillator simulation; The use standard correspondence connection, facilitates realizes many machine interconnections and the computer long-distance control; Uses the open style software and hardware structure, after the system passable promotion has imitated the Doppler shift, the way declines, the multi- diameters effect, the many kinds of disturbances noise and so on approaches the battlefield actual electromagnetic environment.