Background technology
Radar is military and the important class of civil electronic equipment, from appearance more than 70 years so far, with its acquisition of information, armament systems guidance, measure assessment etc. in unique advantage, play an important role in World War II and each great local war after the war and national economy, Radar Technology has become the important symbol of a measurement National Electrical technical merit to a certain extent.
Along with radar system becomes increasingly complex, in design, manufacture, test and application stage, the analysis of radar equipment and research are also becomed increasingly difficult, particularly in development and the debug phase of radar, needing more and more urgently can be convenient effectively to the means that the Performance Characteristics of radar detects, how guinea pig environment and to carry out judgement to its Performance Characteristics be urgent problem.Current, along with the requirement of radar test, the imitation technology of radar signal also arises at the historic moment.General radar signal simulation is the product that imitation technology combines with Radar Technology.Produced by analog simulation method and comprise the echoed signal of target information, radar system is debugged, analysis and inspection, become the necessary means of modern radar system design.Particularly in the debug process of research of radar and production, radar target simulation is economical with it, flexibly, repeatable and controllability is good etc., and feature plays an important role in the research of sophisticated radar systems.
According to the principle of radar work, the simulation of target is based upon on following three analog platforms usually: frequency domain, time domain and amplitude analog platform, namely by realizing the emulation of the distance of radar echo signal, speed and amplitude (RCS value) three dominant motion parameters to the modulation of target time delay, Doppler shift and amplitude.
Radar target feature is mainly reflected in change along with the spacing of radar and target and the time delay feature changed in time domain, that is target echo pulsion phase has certain delay in time for transponder pulse, the size of time delay has reacted the distance of target relative to radar, and its relational expression is:
R＝cτ/2
In formula: R is the distance of target and radar, and unit is m;
C is propagation velocity of electromagnetic wave, and unit is m/s;
τ be echo-pulse relative to exomonental time delay, unit is s.
Echo character is mainly reflected in the change along with radial velocity between radar and target on frequency domain, form the Doppler shift of the relative radar carrier frequency of echoed signal frequency, especially concerning coherent system radar, adopt pulse Doppler technology, Doppler frequency domain finds and tracking target, will directly have influence on the detecting and tracking performance of radar.Doppler shift formula is:
fd＝2v/λ
F in formuladfor the Doppler shift of target echo, unit is Hz;
V is the radial velocity between radar and target, and unit is m/s;
λ is the operation wavelength of radar, and unit is m.
P in formularrepresent received signal power, unit is W;
Ptrepresent transmit signal power, unit is W;
G represents antenna gain, and unit is multiple;
λ represents the operation wavelength of emitting electromagnetic wave, and unit is m;
The target that represents R arrives the distance of emitting antenna, and unit is m;
σ represents that target radar scattering cross-section amasss, and unit is m2.
Radar target simulation signal generator is that one processes input wideband radar signal, after adding the simulated target representing certain distance and speed, under certain bandwidth, undistorted playback goes out the device of radar target signal, and can simulate very well and produce with coherent radar be the multiple radar target echo signal of representative.To the simulation of radar target distance, by store input radar signal and delayed playback realizes, the distance of distance that the length of time delay is corresponding, generally adopt now digital RF to store (DRFM) technology and realize.To the simulation of radar target speed, realize by producing Doppler shift, the size of frequency displacement is directly proportional to speed.To the simulation of target radar xsect (RCS), be that the power by changing output signal realizes, power is larger, and to represent radar cross section larger.
In view of the special role of radar target signal generator, the domestic research starting radar target signal generator and correlation technique very early, wherein main based on radar equipment research institute, a lot of unit has all set up special seminar and has been engaged in the development of radar target signal generator.Say to a certain extent, the development carrying out radar target signal generator has become gadget and has developed indivisible ingredient.But for various reasons, domestic radar target signal generator is still to be dedicated as master, technology path is also mainly simulated based on from intermediate frequency, and utilizes existing technology in radar as far as possible, adopts traditional optical fiber delay method to carry out radar target range simulation still very general.Carry out target range simulation from IF-FRE and digital signal and become radar self-inspection self-test function, from the simulation of radar transmitter frequency realize target still in lag line (comprising optical fiber) mode, namely by radar emission signal is carried out difference postpone after, feed back to radar receiving port and carry out realize target range simulation, the main deficiency of this type simulation device is that simulated range can not be arranged arbitrarily, volume ratio is huger, is difficult to the target simulating long distance.
Modern radar adopts multiple advanced technology counter radar to resist mostly, generally adopt the sophisticated signal treatment technologies such as pulse compression, phase encoding, correlation reception, pulse width discrimination, frequency agility, if curve does not have coherent pulse signalf maybe can not meet ultrasonic echo feature, just be easy to by enemy radar identification, and by the target as antitracking and strike.Along with computer technology particularly semiconductor device art develop rapidly, at present in radar target simulation, analogue technique, generally have employed digital RF and store (DRFM) technology, store after the radar pulse collection of reception, then it forwards by this signal of re invocation, produces disturbing pulse and carries out cheating interference to enemy radar.The undesired signal and the radar return that produce due to DRFM are coherents, thus to the various pulse signal that have employed complicated intra-pulse modulation and coding techniques all effectively, have the ability tackling these coherent waveforms, are therefore widely used in electronic countermeasure field.
External radar target simulation signal generator and correlation technique comparatively ripe, the different phases such as the digital RF memory technology that its technical scheme is most widely used till now from initial lag line, optical fiber delay.Wherein typical products has Agilent company of U.S. N5110B digital signal acquiring/playback system and Herley company of U.S. chameleon II radar simulator.N5110B digital signal acquiring/playback system block diagram as shown in Figure 1.This system mainly comprises data acquisition, data readback and master control system three parts, can form radar signal collection and the playback system of carrier frequency 100kHz ~ 6GHz frequency range with E4438 radio-frequency signal source (comprising 004 option) and down conversion module conbined usage.Master control system, by controlling the time delay of playback signal, can realize the simulation of radar target distance.Because this system configurations is desktop system, onsite application is very inconvenient, and therefore its application is still confined to, in laboratory or research of radar process, be difficult to meet army's request for utilization.
Herley company of U.S. chameleon II radar simulator adopts Double-number radio frequency memory channel, each passage has signals collecting and the copy function of 10 amplitude resolutions, radio-frequency channel reception carrier 1 ~ 18GHz radar emission signal, by down coversion carrier frequency moved on medium and low frequency and send digital RF memory channel, simulating signal is converted to digital signal store, master control system produces distance time delay according to the target range information that will arrange and velocity information control figure radio frequency memory module, controls Doppler source and produces Doppler frequency.And by up-conversion, the baseband signal uppermixing containing target range and target speed information is fed back to radar to radio frequency band.Owing to receiving lower mixing and playback uppermixing all adopts same local vibration source, playback is made to contain radar target signal and the radar emission signal coherence of simulated range and velocity information.This radar simulator is made up of two standard cabinets, volume and weight huge, expensive, maximum analog target range 262 kilometers.
The radar target signal generator of the domestic overwhelming majority, based on Special Signal-generator, is that frequency range covers, function setting is all for a certain concrete model radar system, its range of application is greatly limited.Therefore develop that a kind of compact integrated structure is applicable to onsite application, frequency coverage radar target simulation signal generator that is wide, highly versatile is very necessary.
Summary of the invention
The object of the invention is for existing radar target signal generator based on Special Signal-generator, no matter be that frequency range covers, function setting is all for a certain concrete model radar system, make the deficiency that its range of application is greatly limited, propose a kind of by adopting digital RF storage and reproduce, Doppler frequency simulation and suppress sideband, wide-band microwave mirror image suppresses (IQ) mixing and calibration, the technology such as miniaturization Low phase noise synthetic wideband local oscillator achieve wide frequency ranges in single desktop chassis, the reception playback of large bandwidth radar signal, simulate multiple Stand-Alone Radar target, its distance, speed, RCS (RCS) is isoparametric compact integrated, frequency coverage is wide, a kind of radar target simulation versatile signal generator of highly versatile.
The present invention specifically adopts following technical scheme:
A kind of radar target simulation versatile signal generator, comprise embedded main control computer, timing control unit, decay drives, filter and amplification amplitude limit power splitter, local oscillator module, multiple digital RF storage and reproduce module, multiple Doppler frequency analog module, RCS control module, noise modulated module and microwave down-conversion mixer, the modules such as IQ uppermixing, the output terminal of described microwave down-conversion mixer connects filter and amplification amplitude limit power splitter, described filter and amplification amplitude limit power splitter connects multiple digital RF storage and reproduce module, the output terminal of each described digital RF storage and reproduce module connects Doppler frequency analog module, described embedded main control computer connects decay respectively by bus and drives, local oscillator module, timing control unit and RCS control module, the output terminal of each described Doppler frequency analog module is connected same multiplier with the output terminal of a RCS control module, the output terminal ingoing power compositor of described multiplier, described IQ uppermixing module is made up of wide-band microwave vector modulator, 3dB/90 ° of power splitter is entered after the output signal of described power combiner mixes with the output signal of noise modulated module, the output terminal of described 3dB/90 ° power splitter connects wide-band microwave vector modulator, the output terminal of described wide-band microwave vector modulator connects power amplifier, the output terminal of described power amplifier connects programmable attenuator, described programmable attenuator is driven by bus be connected with decay.
Preferably, described digital RF storage and reproduce module comprises the limiting amplifier, analog to digital converter, reduction of speed circuit, memory module, raising speed circuit and the digital to analog converter that connect successively, described storage module by bus connects clock and delay control circuit, described clock and delay control circuit are connected with digital to analog converter respectively with limiting amplifier, analog to digital converter, reduction of speed circuit, raising speed circuit, described clock and delay control circuit are connected with clock phase-locked loop, described clock phase-locked loop are connected with 10MHz reference source.
Preferably, described memory module comprises multiple dual-port random access memory.
Preferably, described Doppler frequency analog module adopts mirror image to suppress frequency mixing technique and vector modulator, carry out a mixing, the input end of described vector modulator comprises I road input signal and Q road input signal, be provided with compensating circuit before described I road input signal and Q road input signal, described vector modulator be connected with wideband mirror image and suppress mixing calibration circuit.
Preferably, described wide-band microwave vector modulator is formed by a radio frequency vector modulator and a microwave vector modulator interlocking.
Preferably, described wideband mirror image suppresses mixing calibration circuit to comprise two programmable amplifiers and two digital phase shifters.
Preferably, described local oscillator module comprises reference plate, this vibration plate and frequency multiplication frequency division plate, realizes by Phase locking frequency synthesis and switch frequency multiplication frequency-division filter the signal exporting 1GHz ~ 20GHz.
Preferably, described vibration plate adopts 1GHz benchmark.
Preferably, described main control computer platform comprises control module, motherboard, keyboard, liquid crystal display, multiple communication interface and power module.
The beneficial effect that the present invention has is:
(1) by using the technology such as digital RF storage, Doppler frequency simulation and suppress sideband, wide-band microwave IQ mixing and calibration, miniaturization Low phase noise synthetic wideband local oscillator, electromagnetic compatibility and squelch, the reception playback of wide frequency ranges, large bandwidth radar signal is achieved in single desktop chassis, can simulate multiple Stand-Alone Radar target, the parameters such as its distance, speed, RCS can be established.Simulate four Stand-Alone Radar targets, the distance of each radar target, speed, RCS (radar cross section) are controlled.Owing to have employed Modular Structure Design, can insert multiple radar target simulation module in the chassis, system extension is convenient.This instrument of multiple stage conbined usage, can construct multiple different batches, and each batch of Complex Radar target simulation environment having multiple target.
(2) have employed cpci bus and modular construction, the versatility of instrument, extendability are strong, system upgrade, easy to maintenance.Control module, motherboard, machine cage adopt CPCI standard module, highly versatile, are convenient to upgrading.Each functional module adopts standard 6UCPCI wiring board size, and structure is reliable, and plug is easily, system upgrade, easy to maintenance.
(3) wide frequency range, versatility is good.Accurate playback radar target signal can be gone out in 1 ~ 20GHz frequency range, under more than 60MHz bandwidth, can very well trace simulation goes out with coherent radar is the multiple radar target echo signal of representative.Can simulate multiple Stand-Alone Radar target, the distance of each radar target, speed, RCS are controlled.
(4) small in volume, is applicable to onsite application.
In single desktop chassis, achieve wide-band radar target simulation function, volume weight greatly reduces compared with same kind of products at abroad, and price is its part, and cost performance is high.
Embodiment
Below in conjunction with the drawings and specific embodiments, the specific embodiment of the present invention is described further:
As shown in Figure 2, a kind of radar order local oscillator module, mark simulation versatile signal generator, comprise embedded main control computer, timing control unit, decay drives, filter and amplification amplitude limit power splitter, multiple digital RF storage and reproduce module, multiple Doppler frequency analog module, RCS control module, noise modulated module and microwave down-conversion mixer, the modules such as IQ uppermixing, the output terminal of microwave down-conversion mixer connects filter and amplification amplitude limit power splitter, filter and amplification amplitude limit power splitter connects multiple digital RF storage and reproduce module, the output terminal of each digital RF storage and reproduce module connects Doppler frequency analog module, embedded main control computer connects decay respectively by bus and drives, local oscillator module, timing control unit and RCS control module, the output terminal of each Doppler frequency analog module is connected same multiplier with the output terminal of a RCS control module, the output terminal ingoing power compositor of multiplier, described IQ uppermixing module is made up of wide-band microwave vector modulator, 3dB/90 ° of power splitter is entered after the output signal of power combiner mixes with the output signal of noise modulated module, the output terminal of 3dB/90 ° of power splitter connects wide-band microwave vector modulator, the output terminal of wide-band microwave vector modulator connects power amplifier, the output terminal of power amplifier connects programmable attenuator, programmable attenuator is driven by bus be connected with decay.
Compared with domestic and international existing radar target simulation signal generator, this radar target simulation versatile signal generator has following advantage: wide frequency range, and versatility is good.Accurate playback radar target signal can be gone out in 1 ~ 20GHz frequency range, under more than 60MHz bandwidth, can very well trace simulation goes out with coherent radar is the multiple radar target echo signal of representative.Can simulate multiple Stand-Alone Radar target, the distance of each radar target, speed, RCS are controlled.Use wide-band microwave mirror image to suppress (IQ) mixing and collimation technique, reduce microwave circuit complexity.Small in volume, is applicable to onsite application.In single desktop chassis, achieve wide-band radar target simulation function, volume weight greatly reduces compared with same kind of products at abroad, and cost performance is very high.Adopt cpci bus and modular construction, versatility, the extendability of instrument are strong, are convenient to the upgrading of system, maintenance.
The input and output frequency range of this radar target simulation versatile signal generator is 1 ~ 20GHz, can simulate multiple independently radar target.Use a microwave down-conversion mixer, the input radar signal of microwave frequency band is transformed to intermediate frequency, intermediate frequency realizes the simulation of digital RF storage and reproduce, Doppler shift, and the simulation of target RCS.The mistiming of control signal storage and reproduce, can the distance of guinea pig target.The size of control signal Doppler shift, can the radial velocity of guinea pig target.Intermediate-freuqncy signal after 90 degree of merits are divided, carries out IQ uppermixing to wide-band microwave vector modulator again, finally exports after power amplification, program control decay again.
So carry out signal transacting on intermediate frequency, because all radar signals have certain bandwidth, when meeting nyquist sampling theorem, intermediate frequency realizes digital RF storage and reproduce more convenient, and existing technology also cannot realize Direct Sampling and the process of microwave signal.
The method of brief description this instrument realize target speed simulation once.Suppose radar target simulation signal generator input point-frequency signal cos ωit, does not consider phase shift, becomes intermediate-freuqncy signal cos ω after lower mixingift, ωif=ωi-ωlo, wherein ωlofor local frequency.After Doppler shift circuit, intermediate-freuqncy signal becomes cos (ωi-ωlo+ ωc) t, wherein ωcfor Doppler frequency.Become after microwave vector modulator uppermixing:
VRF＝COSωlot·COS(ωi-ωlo+ωc)t-SINωlot·SIN(ωi-ωlo+ωc)t＝COS(ωi+ωc)t
That is, at radio frequency signal frequency ωion add Doppler frequency+ωc.In like manner, also can at radio frequency signal frequency ωion add Doppler frequency-ωc.For the radar signal having certain bandwidth, Doppler frequency+ω can be added in radiofrequency signal equallycor-ωc.
The simulation of radar target RCS is realized by the power of control objectives signal.Add distance, velocity information intermediate-freuqncy signal through a mlultiplying circuit, change the equivalent RCS that its gain can change simulated target.Add different RCS models, as various Swerling echo model, the simulation of dissimilar target and background signal can be realized.
Noise modulated module, can produce various undesired signal and false modulation signal, for electronic countermeasure field.Briquettability sine sweep signal, broadband white noise signal and false modulation signal can be produced, formed suppression jamming, range gate deception interference, velocity gate deception interference, distance and velocity gate deception interference, high density spurious pulse interference.
Instrument have employed new technologies and methods new technology, and in single desktop chassis, achieve the reception playback of wide frequency ranges, large bandwidth radar signal, versatility, extendability, maintainability is strong.
As shown in Figure 3, digital RF storage and reproduce module comprises the limiting amplifier, modulus (A/D) converter, reduction of speed circuit, memory module, raising speed circuit and digital-to-analogue (D/A) converter that connect successively, storage module by bus connects clock and delay control circuit, clock and delay control circuit are connected with digital to analog converter respectively with limiting amplifier, analog to digital converter, reduction of speed circuit, raising speed circuit, clock and delay control circuit are connected with clock phase-locked loop, clock phase-locked loop are connected with 10MHz reference source; Memory module comprises multiple dual-port random access memory (RAM).
Radar emission signal is mixed down intermediate-freuqncy signal through receiving cable and is converted by A/D, simulating signal is converted to high-speed digital signal, reduction of speed control circuit converts parallel data at a high speed the low-speed parallel data matched with memory read/write speed to, and stored in two-port RAM, the ablation process of settling signal.Signal read procedure is just in time with to write process contrary, namely the data stored in two-port RAM are under the synchro control of delay control circuit, require through certain time delay according to wanting simulated range, by first in first out order, after low-speed parallel data being converted into high-speed parallel data by rising film condensation circuit, be converted to analog if signal by D/A.The length of time delay determines simulated target distance range, and time delay, resolution determined the range resolution of simulated target.Will realize range simulation on a large scale conversely speaking, read after must postponing for a long time write data, this will increase data space.Realize high precision range simulation, just need improve memory read/write clock frequency, make the control accuracy of time delay higher, along with the raising of memory read/write clock frequency, make to need larger storage space under identical time delay condition.
According to existing device level and this instrument target call, sample frequency and storage space calculated and optimizes, adopting A/D and the D/A converter of 12 500MHz sampling rates, to meet instant bandwidth and quantizing noise requirement.In order to realize the simulation of maximum 300km target range, storer adopts the high-capacity and high-speed two-port RAM of 1024k × 16.High-speed data reception, reduction of speed process and two-port RAM management circuit adopt high speed FPGA to realize, and the 500Mbps data stream that A/D produces is divided into 4 tunnels, and timesharing is stored in 4 groups of dual-ported memories.Raising speed circuit is built suitable High Speed Multiplexer to realize by utilizing FPGA.
Doppler frequency analog module adopts mirror image to suppress frequency mixing technique and vector modulator, carry out a mixing, the input end of described vector modulator comprises I road input signal and Q road input signal, be provided with compensating circuit before described I road input signal and Q road input signal, described vector modulator be connected with wideband mirror image and suppress mixing calibration circuit.
The detection of radar target speed is realized by the Doppler shift of test target, the simulation of target velocity is just converted to the generation of Doppler frequency, and carries out modulated by frequency shift to radar transmitter frequency.In order to the simulation of realize target speed, Doppler signal source output signal is carried out mixing with the intermediate-freuqncy signal that digital RF memory module exports, because Doppler frequency is lower, according to conventional mixer mode, because two sideband frequencies are from obtaining very, the suppression that filtering mode carries out carrier wave and unwanted sideband cannot be applied.IQ mixing schemes only produces a useful sideband in theory, and therefore we have employed vector modulation technique.The theory diagram of vector modulator as shown in Figure 4, comprises 90 degree of power splitters, two frequency mixer and a combiner.
The simulation of intermediate frequency Doppler shift is by using direct digital synthesis technique (DDS) technology to produce the orthogonal Doppler signal of two-way, produce the intermediate-freuqncy signal with Doppler shift by vector modulator again, the Doppler frequency analog module theory diagram of design as shown in Figure 5.In order to improve the integrated level of system, adopting FPGA circuit and D/A converter to realize binary channels DDS, being combined with low-pass filter, producing highly purified Doppler frequency signal.This DDS frequency synthesizer circuit phase accumulator is 48, and D/A converter is 14, adopts the reference clock of 10MHz, meets velocity range and the velocity resolution requirement of this instrument requirements.Finally can realize frequency range from direct current to 4MHz, frequency resolution is better than 1uHz, phase noise is better than-130dBc/Hz10kHz and the spuious high-performance Doppler frequency being less than-70dB of near-end exports.
If intermediate-freuqncy signal is COS ωift, the I road of Doppler shift circuit exports as COS ωct, the Q road of Doppler shift circuit exports as SIN ωct, then by the signal after vector modulator be:
VOUT＝COSωct·COSωift+SINωct·SINωift＝COS(ωif-ωc)t
If the I road of Doppler shift circuit exports as COS ωct, the Q road of Doppler shift circuit exports as-SIN ωct, then by the signal after vector modulator be:
VOUT＝COSωct·COSωift-SINωct·SINωift＝COS(ωif+ωc)t
This shows, after Doppler shift circuit, IF signal frequency is by ωifbecome ωif+ ωcor ωif-ωc, that is create doppler shift effect.
Vector modulator I road input signal symbol I represents, Q road input signal symbol Q represents, local oscillator input signals symbol VlOrepresent, radio frequency output signal symbol VrFrepresent, then the transition function of desirable vector modulator can be expressed as:
VRF＝(I+jQ)·VLO
The main error of Vector Modulation is the amplitude imbalance on I road and Q road and the Phase-shifting Errors of 90 degree of power splitters, for the vector modulator of reality, be 1 by the gain normalization on I road, if the gain error k on Q road, the phase shift angle of actual 90 degree of power splitters is not 90 ° but 90 ° of+δ, δ is Phase-shifting Errors, then the transition function of actual vector modulator is:
VRF＝I·VLO+k·Q·VLO·ej(π/2+δ)＝I·VLO+k·ejδ·jQ·VLO
Drawn by the transition function of actual vector modulator, before the Q input end of vector modulator, increase a compensating circuit, the transition function of this compensating circuit is e-j δ/ k, namely a gain is 1/k, and phase shift angle is the circuit of-δ, can obtain the transition function formula of desirable vector modulator.
This radar target simulation versatile signal generator achieves the two-way doppler shifted signal source with phase compensation function.In order to produce the variable two-way doppler shifted signal of difference, need in common Direct Digital Frequency Synthesizers designed phase off-centre circuit, change the value of two phase offset registers, the relative phase difference of I road and Q road output signal can be changed, thus can the radial direction of guinea pig target.By the value of adjustment phase offset register, the phase differential of I road and Q road signal can also be finely tuned, to compensate the Phase-shifting Errors of 90 degree of power splitters in intermediate frequency vector modulator, by adjusting the value of gain register, the amplitude of I road and Q road signal can also be finely tuned, to compensate intermediate frequency vector modulator I road and Q road gain error, thus improve suppress sideband index.After calibration, the mirror image of IF output signal suppresses and carrier wave suppression index raising more than 10dB, and representative value is better than-50dB.
As shown in Figure 6, wideband mirror image suppresses mixing calibration circuit to comprise two programmable amplifiers and two digital phase shifters.Realize frequency range 1 ~ 20GHz broadband IQ mixing, because frequency coverage is too wide, segmented mode can only be adopted realize.Be specially the IQ mixing of employing 1 ~ 4GHz radio frequency and 4 ~ 20GHz microwave IQ mixing.1 ~ 20GHz broadband local oscillation signal selects 2 switches to deliver to radio frequency vector modulator and microwave vector modulator respectively through 1, and the radiofrequency signal that two modulators export 1 selects 2 switches interlockings to be that 1 ~ 20GHz broadband exports by another.Radio frequency vector modulator directly uses ripe MMIC product to carry out Two-level ensemble, microwave vector modulator designed, designed.
The design of wideband microwave vector modulator middle width strip directional coupler is the difficult problem that must solve.Require that directional coupler can realize the phase shift of 90 degree, and the degree of coupling will ensure as 3dB, such guarantee radiofrequency signal can produce power equal and the I of phase 90 degree and Q signal through directional coupler, can adopt reflected gradient coupling line coupler circuit.Mixting circuit adopts two double balanced mixers.An input channel for I signal, an input channel for Q signal.The circuit structure of double balanced mixer can ensure that signal and local oscillator port have good isolation, can reach multiple octave bandwidth simultaneously.The design of balanced-unbalanced transformer is also crucial.The Ba Lun of I and Q signal adopts the tap coupler coil form of lumped parameter, and dimension volume is little.High frequency adopts microstrip balun.External wide-band microwave vector modulator typical products has SM0218LC1CDQ, frequency range 2 ~ 18GHz, IQ modulation frequency range DC ~ 500MHz, linear modulation power is+5dBm to the maximum, carrier wave power input+13dBm, suppress sideband 20dB, carrier wave suppresses 25dB, quadrature phase accuracy representative value ± 10 °, quadrature amplitude accuracy representative value ± 1dB.Can find out that its technical indicator is poor.The wide-band microwave vector modulator frequency range 3 ~ 20GHz of our design, technical indicator is suitable with external product.
Due to wideband microwave vector modulator designing technique and process technology limit, the indexs such as its carrier wave suppression, suppress sideband are very undesirable.On microwave frequency band, directly compensating the amplitude imbalance of vector modulator especially Phase-shifting Errors is suitable difficulty.
The technical indicator of the technical indicator wider frequency microwave vector modulator of radio frequency vector modulator chip is well a lot, but also needs design compensation circuit.
For above technical barrier, propose a kind of method that wideband IQ mixing is calibrated.The error of the method radio frequency and microwave vector modulator on intermediate frequency compensates, and greatly can improve the technical indicator of equipment, improves the performance of equipment.
Based on above-mentioned analysis, we devise wideband IQ mixing calibration circuit, and its theory diagram as shown in Figure 6.This circuit comprises two programmable amplifiers, resolution reaches 0.1dB, respectively programming amplifying is carried out to I road input signal and Q road input signal, with the amplitude imbalance k of compensation vector modulator, this circuit also comprises two broadband digital phase shifters, respectively phase shift is carried out, with the Phase-shifting Errors δ of compensation vector modulator to I road intermediate-freuqncy signal and Q road intermediate-freuqncy signal.Regulate the IQ common mode input of vector modulator, carrier leak index can be improved, regulate the IQ of vector modulator to input differential mode voltage, mirror image can be improved and suppress index.
For intermediate-freuqncy signal, phase shift can be obtained by time delay.Design N position digitally programmable delayer, can realize the broadband digital phase shifter of N position.Every stage circuit is made up of two single-pole double-throw switch (SPDT)s, delay lines, by controlling, can select not time delay or time delay.The phase shift angle of every grade is multiple proportion.For intermediate-freuqncy signal centre frequency, if the phase shift of the first order is φ degree, then the phase shift of the second level is 2 φ degree, and the phase shift of the third level is 4 φ degree, and the phase shift of the fourth stage is 8 φ degree ..., the phase shift of N level is 2n-1 φ degree.As shown in Figure 7, attainable phase shift range is 0 ~ 15 φ degree to the theory diagram of quadravalence digital phase shifter, and phase shift resolution is φ degree.To different intermediate-freuqncy signals, phase shift resolution is different, and when frequency increases, the phase shift resolution of this circuit declines to some extent.The intermediate frequency broadband digital phase shifter exponent number of design is 4 grades, and bandwidth is an octave, and group delay characteristic is excellent, and attainable phase shift range is 0 ~ 15 degree, and phase shift resolution is 1 degree.
Under normal circumstances, the range error of vector modulator and Phase-shifting Errors have contribution to the distortion outputed signal, both weave ins, and they are decomposed out is a technical barrier, proposes a kind of measuring method for this reason.Thinking is, when measuring one of them error, manages the impact of another error to remove.
The gain error k of radio frequency and microwave vector modulator and the value of Phase-shifting Errors δ are obtained by following measuring method.
When carrying out IQ mixing calibration, instrument connection diagram as shown in Figure 8, the EXII input end of equipment to be calibrated and EXTQ input end are connected to the signal output part of two-way function generator, the output terminal of equipment is connected to the input end of frequency spectrograph, GPIB cable is connected, Vector Modulation calibration software in operational outfit, equipment carries out program control to the machine, function generator, frequency spectrograph respectively.Herein, equipment refers to radar target simulation versatile signal generator.
Then divide two steps to calculate, first step obtains Vector Modulation amplitude imbalance calibration data, and second step obtains Vector Modulation Phase-shifting Errors calibration data.Vector Modulation calibration algorithm software flow is as follows: the local oscillator that (one) equipment controls the machine carries out frequency sweep, to each Frequency point, control function generator exports sinusoidal signal, frequency is the centre frequency of equipment intermediate frequency, first export I road signal, close Q road signal, control frequency spectrograph to measure, obtain the general power that vector modulator outputs signal two sidebands, close I road signal, export Q road signal, control frequency spectrograph to measure, obtain the general power that vector modulator outputs signal two sidebands, ask the difference of these two power, the gain error k of vector modulator Q road relative to I road can be obtained.After obtaining the gain error k of vector modulator, be saved in amplitude calibration data, (2) local oscillator re-starts frequency sweep, control the programmable amplifier of Vector Modulation calibration circuit, the gain of each Frequency point is compensated, control function generator output signal frequency is the centre frequency of equipment intermediate frequency, two paths of signals exports simultaneously, phase differential 90 degree, control the relative phase of two-way 4 bit wide band digital phase shifter, scan from minimum value to maximal value, control frequency spectrograph to measure simultaneously, obtain the power of useful signal and image signal in vector modulator output signal respectively, ask the difference of these two power, vector modulator mirror image can be obtained and suppress index, index is suppressed to be retrieved to the repetitive measurement mirror image of same frequency, find the point that mirror image suppresses index maximum, the digital phase shifter relative phase of its correspondence is phase-shift compensation value-δ, so, obtain the phase-shift compensation value of each Frequency point, and be saved in phase shift calibration data.After completing above step, the testing tool be connected with equipment of dismantling.
The compensation method of radio frequency and microwave vector modulator gain error k and Phase-shifting Errors δ is as follows.After measuring gain error k and Phase-shifting Errors δ, the local oscillator of equipment often exports a frequency, just takes out amplitude calibration data 1/k and phase shift calibration data-δ, the control IQ mixing calibration circuit of this frequency, compensates the error of vector modulator.
The essence of the design is by carrying out pre-distortion to input signal, with the distortion of compensation vector modulator, by the pre-distortion to intermediate-freuqncy signal, reduces the distortion of radiofrequency signal.Solve on microwave frequency band, be difficult to the technical barrier directly amplitude imbalance and the Phase-shifting Errors of vector modulator compensated.
According to wideband IQ mixing calibration steps provided by the invention, after vector modulator is compensated, the mirror image of radio frequency vector modulator output signal suppresses and carrier wave suppresses target improvement 10dB, the mirror image of microwave vector modulator output signal suppresses and carrier wave suppresses target improvement 20dB, representative value is better than 40dB, substantially increases the technical feature of system.
As shown in Figure 9, local oscillator module comprises reference plate, this vibration plate and frequency multiplication frequency division plate, realizes by Phase locking frequency synthesis and switch frequency multiplication frequency-division filter the signal exporting 1GHz ~ 20GHz, and this vibration plate adopts 1GHz benchmark.Main control computer platform comprises control module, motherboard, keyboard, liquid crystal display, multiple communication interface and power module.
Minimized wide-band local vibration source is one of key modules part of this instrument, and requiring it to output signal in the whole frequency range of 1 ~ 20GHz has the higher purity of frequency spectrum, resolution and power, and its performance index directly have influence on the technical indicator of complete machine.Meanwhile, frequency synthesizer is the relatively independent part of in radar target simulation signal generator, requires that its volume is little, low in energy consumption.
Mainly comprise reference plate, this vibration plate, frequency multiplication frequency division plate, be provided for the local oscillation signal of Up/Down Conversion, require frequency range 1 ~ 20GHz, adopt Phase locking frequency synthesis to add switch frequency multiplication frequency-division filter technology.
10MHz, 1GHz Low phase noise reference signal that referrer module provides this vibration plate to need.In order to realize Low phase noise frequency synthesis, usually adopt sampling phase-looked, the technology such as twin crystal shakes, frequency multiplication realizes, but its circuit is more complicated.We used surface acoustic wave voltage controlled oscillator and conventional phase lock circuitry form in this instrument, achieve 1GHz Low phase noise reference signal and export.Make an uproar mutually curve combination 10MHz Low phase noise constant-temperature crystal oscillator and the 1GHz voltage controlled oscillator of composite signal are made an uproar the advantage of curve mutually.What final 1GHz outputed signal makes an uproar lower than-130dBc/Hz10kHz mutually.
In order to reduce the complexity of circuit, realize the miniaturization of local frequency synthesis, local oscillator have employed volume and the less 5 ~ 10GHz microwave broadband VCO of weight designs.But making an uproar mutually of broadband VCO is far short of what is expected compared with YIG oscillator, we carry out well-designed to the topological structure of local oscillation circuit, export compared with the signal of Low phase noise to reach.The local oscillation circuit theory diagram of instrument as shown in Figure 9.
This vibration plate adopts 1GHz benchmark, produces final output frequency via stepping ring and main ring two phaselocked loop synthesis.In stepping ring, 1GHz as stepping ring reference frequency, produces 500 ~ 1100MHz frequency by stepping ring phase-locked loop circuit through 10 frequency divisions.In main ring, 1GHz through DDS fractional frequency division as main ring reference frequency, main ring VCO module output frequency feeds back to phase frequency detector after 8 frequency divisions with after the mixing of stepping ring, filtering, obtains 5 ~ 10GHz output frequency via main ring phase-locked loop circuit, and ensures that frequency step is less than 1Hz in this frequency range.DDS adopts AD9912, and this DDS chip clock is 1GHz, and adopt 48 phase accumulators, composite signal exports through 14 D/A converters.When exporting 399MHz signal, make an uproar mutually up to-130dBc/Hz10kHz, ± 250kHz arrowband SFDR is-86dBc.
This instrument uses direct digital synthesis technique (DDS) to instead of the fractional frequency-division phase-locked loop (PLL) of classic method, makes circuit design more succinct.Adopt the method for direct digital synthesis technique excitation PLL frequency synthesize.Namely use DDS as reference signal source, the frequency synthesis scheme combined by DDS and PLL.It combines the advantage of DDS and PLL frequency synthesizer, has high frequency resolution, extremely short frequency converting time and good noiseproof feature, and wide frequency range, control are flexible, are the frequency synthesis techniques of a kind of advanced person.
Frequency multiplication frequency-division filter assembly comprises frequency multiplier, frequency divider, wave filter, amplifier, PIN modulator, and the 5 ~ 10GHz signal exported by this vibration plate is through frequency multiplication frequency-division filter, and produce 1 ~ 20GHz local oscillation signal, output power is greater than 16dBm.Consider the extensibility of instrument low end frequency, frequency multiplication frequency-division filter assembly comprises a frequency mixer, and when device is assembled complete, local frequency can reach 10MHz ~ 20GHz.
1 ~ 20GHz the broadband local oscillator designed based on the circuit topological structure of autonomous innovation is not when using YIG oscillator, routine YIG oscillator and the sampling loop technique index of making an uproar mutually that can reach are reached, under 10GHz, measure representative value be better than-92dBc/Hz10kHz, under 1.25GHz, measure representative value be better than-110dBc/Hz10kHz, frequency resolution is 0.000057Hz, eliminate fractional frequency division plate and the YIG drive plate of conventional implementation method, volume weight greatly reduces.
Delay line adopts microstrip transmission line, and as shown in Figure 10, the characteristic impedance of microstrip transmission line is:
Wherein Zf=376.8 Ω, effective dielectric constant εefffor:
As w/h<1, the characteristic impedance of microstrip transmission line is designed to 50 Ω, and according to the dielectric constant of printed board, the height h of printed board medium, by calculating the live width w that can obtain printed board, and meets w/h<1.
The phase velocity of microstrip transmission line is:
Its wavelength X is:
In formula, c is the light velocity, and f is frequency, and the distance of a wavelength represents the change of 360 ° of phase places, therefore the transmission line of a segment length, for certain frequency, and corresponding phase change necessarily, phase shift angle θ is expressed as:
θ＝360L/λ
In formula, the unit of θ is degree, and L is the length of transmission line, and λ is wavelength.
Under normal circumstances, the range error of vector modulator and Phase-shifting Errors have contribution to the distortion outputed signal, both weave ins, and they are decomposed out is a technical barrier, proposes a kind of measuring method for this reason.Thinking is, when measuring one of them error, manages the impact of another error to remove.
For the interference from power lead, the design of this equipment to electric power system takes into full account, power supply adopts independent shielding box, power switch to the line at the inner place such as fuse, power-supply filter away from printed board; Key position adopts shielding: strong signal wire and weak signal line are separated, and direct current signal line separates with alternating current line ball, avoids runs parallel, the independent cabling of feeder line of forceful electric power, does not share wire casing but along backplane routing, guarantees the security of system.
In addition, the method adding high-performance power-supply filter in the alternating current porch of instrument suppresses the interference from power lead effectively.Work due to power-supply filter is two-way, and the electromagnetic radiation produced when it also inhibits internal system work in fact is simultaneously to the interference of electrical network.Designing requirement can be reached completely for three aspects such as power lead conducted emission, power lead conducted immunity, power lead spiking conducted immunities.
The radiation source of radar target simulation versatile signal generator is mainly the data noise of the program operation generation of CPU board, the radiation of display cable, radiation external when high-frequency output circuit and the work of various digital circuit, the harmonic wave that various clock produces and the spark that relay contact produces etc.For this reason, when product design, we take appropriate measures for the different characteristics of each several part.In order to reduce one integral piece each several part electromagnetic interference (EMI) each other, corresponding Specification Design being pressed to the layout of instrument internal, adopts the designing techniques such as shielding, ground connection, decoupling, filtering.For phaselocked loop, Weak Signal Processing, the Simulation scale-up output of sensitivity, adopt can shielding, add diode at the control pin of relay and supply pin and suppress spike; For the big current such as power supply or high-voltage part also each personal metal cap shielding, the input end power-supply filter of power supply is isolated.In circuit layout, part and numerical portion isolation will be intended, and by two-part VDD-to-VSS line separately, to reduce the crosstalk between circuit.By good contact between the shell of instrument, guarantee good earth, the fan on side panel is added tinsel gauze pad, add wire netting bar in the contact position of machine shell and front panel, guarantee good contact.The employing of all these measures makes itself to have extremely low electromagnetic radiation, has again good anti-electromagnetic interference capability.
For the interference from space, this radar target simulation versatile signal generator mainly adopts the method for shielding to eliminate, and this is similar with the design of anti-electric field radiation-emitting.The metal shell of totally-enclosed and effective shielding in the product, ground connection can resist the interference of external electrical field radiation effectively.
The circuit worked under full clock status in radar target simulation versatile signal generator is a lot, as radar target simulation module high-speed a/d converter, high-speed d/a converter, reduction of speed circuit, raising speed circuit, phase regulator, signal framing and timing circuit etc., require that the frequency operation of these circuit is at more than 500MHz.This just brings high-speed digital signal integrity issue, typically has that crosstalk, reflection, transmission delay, time clock are asymmetric, noise margin exceeds standard; Also have the transport property of some resolution elements to worsen, the power gain of such as radio frequency amplifier also can with the rising of frequency lower degradation problem.The timing requirements of digital RF storage and reproduce circuit is very strict again simultaneously, this just requires will fully to keep during circuit design the time delay one of clock and data to make peace the complete of signal, high-speed data process can be completed under unified clock, realize accurate signal storage and playback.Use for reference our development Experience in high-speed data acquisition and process field, with high speed field programmable gate function (FPGA) for core, take to reduce circuit board distributed capacitance, adopt the measures such as topological wiring method to ensure the normal work of high-speed digital signal.In the intermediate-frequency circuit design of radar target simulation versatile signal generator, require that the noise figure of circuit is little as much as possible, to prevent the self-excitation of amplifying circuit and to introduce noise signal, and cause the signal to noise ratio (S/N ratio) of output signal to decline, parasitic increase.Therefore, for ensureing good noise suppression feature, when High-speed Board Design and PCB layout, take following several measure:
A, keep all PCB cabling short as far as possible, adopt the wiring technique that impedance is controlled;
B, select little as far as possible component size, select 0603 or 0402 packaging as far as possible;
The device of c, use high quality factor (Q) reduces the phase noise of high speed device, increases the transmission of output power simultaneously;
All components and parts of d, maintenance tuned circuit are close as far as possible, simultaneously as far as possible near integrated VCO;
E, decoupling capacitor near high speed device, and will be directly connected to ground, and all VCC connect provides independent decoupling capacitor;
Analog signal line interconnection between f, wiring board different units adopts 50 Ω characteristic impedance couplings as far as possible;
G, for exist parasitic parameter may need adjust some component values finely tune, to ensure optimal performance.
After adopting above-mentioned advanced technology and technique, the radar target simulation versatile signal generator of design, has the following advantages: wide frequency range, and versatility is good.Accurate playback radar target signal can be gone out in 1 ~ 20GHz frequency range, under 60MHz bandwidth, can very well trace simulation goes out with coherent radar is the multiple radar target echo signal of representative.Can simulate multiple Stand-Alone Radar target, the distance of each radar target, speed, RCS are controlled.Use wideband IQ mixing and collimation technique, reduce microwave circuit complexity.Small in volume, is applicable to onsite application.In single desktop chassis, achieve wide-band radar target simulation function, volume weight is the part of same kind of products at abroad, and cost performance is high.Adopt cpci bus and modular construction, versatility, the extendability of instrument are strong, system upgrade, easy to maintenance.
Certainly, above-mentioned explanation is not limitation of the present invention, and the present invention is also not limited in above-mentioned citing, and the change that those skilled in the art make in essential scope of the present invention, remodeling, interpolation or replacement also should belong to protection scope of the present invention.