CN105866743B - Radar clutter spectral characteristic simulation system based on reverberation chamber and method - Google Patents
Radar clutter spectral characteristic simulation system based on reverberation chamber and method Download PDFInfo
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- CN105866743B CN105866743B CN201610221233.3A CN201610221233A CN105866743B CN 105866743 B CN105866743 B CN 105866743B CN 201610221233 A CN201610221233 A CN 201610221233A CN 105866743 B CN105866743 B CN 105866743B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/023—Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
- G01S7/4082—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder
- G01S7/4086—Means for monitoring or calibrating by simulation of echoes using externally generated reference signals, e.g. via remote reflector or transponder in a calibrating environment, e.g. anechoic chamber
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- Radar Systems Or Details Thereof (AREA)
Abstract
The invention discloses a kind of radar clutter spectral characteristic simulation system and method based on reverberation chamber are related to using the reflection of radio wave or reradiative positioning or there are detection method technical fields.Described method includes following steps：Mathematical modeling is carried out to the sea clutter frequency spectrum of low sea condition using Allpole models, and mathematical modeling is carried out to the sea clutter frequency spectrum under high sea condition using combination Exponential models；Change the unitary sampling signal S of agitator speed and two spectral models of repeated acquisition several groupssample；Fourier transformation and normalized are made to obtained unitary sampling data, analyze its spectral characteristic.The method portrays the spectral characteristic simulation of radar clutter more fine, accurate.
Description
Technical field
The present invention relates to the reflection for using radio wave or reradiative positioning or there are detection method technical fields, especially
It is related to a kind of radar clutter spectral characteristic simulation system and method based on reverberation chamber.
Background technology
Modern war is the spaces union informationization operation of multidimensional one, and with the addition that " electromagnetism " is tieed up, war dimension obtains
To be promoted, war form is more concealed, and operation content is more abundant so that cruel military struggle becomes fiercer originally.
Information-based main battle weaponry forms Battle Field Electromagnetic in battlefield space radiation, and Battle Field Electromagnetic shows significant complexity,
By time domain, frequency domain, spatial domain and can on domain it is densely distributed, quantity is various, pattern is complicated, a variety of electromagnetic signals of dynamic random and spoke
Penetrate that source entity is overlapping to be formed, complex electromagnetic environment increasingly becomes the huge challenge of electronic equipment reliability service, to operational commanding
It is had a direct impact with fighting capacity performance.Therefore, see clearly that the critical role that complex electromagnetic environment is occupied in future battlefield, searching are ground
The inherent law for studying carefully it prevents it and endangers the influence that weaponry is brought, and obtaining battlefield supremacy using it has great meaning
Justice.
Radar applies to after modern war, and the various signals that radar emission generates are with the weight for becoming Battle Field Electromagnetic
Want component part.It is influenced by residing electromagnetic environment totality situation, radar is subject to also more tight from the test of electromagnetism ring condition
It is high.Complex electromagnetic environment influences radar to target real-time tracking, early warning discovery, azimuth caging, Threat verdict etc., directly restricts
Play to radar properties.
Clutter has consequence in Radar Electromagnetic Environment, it is both the important component of Radar Electromagnetic Environment,
It is an important factor for causing Radar Electromagnetic Environment to be different from other Battle Field Electromagnetics again.It is different from other weaponrys, clutter
Signal to radar equipment interferes especially prominent.Noise signal enters radar reception device together along with target echo signal,
It is difficult to be detached inhibition, always is the hot and difficult issue of radar signal processing field.Radar is when carrying out receiving processing
Directly influenced by the characteristic of clutter itself, for example, the amplitude scintillation characteristic of clutter and radar CFAR detection rate measurement processor
Performance is related；The power spectrum characteristic of noise signal is related with the Moveing target indication performance of filter of radar；The spatial extent of clutter
Characteristic is related with the signal-to-noise ratio test before radar clutter cancellation.Therefore, it can realize that the comprehensive simulated of radar clutter is structure thunder
Up to the key of Battle Field Electromagnetic.
In clutter simulation, conventional method includes：Battlefield clutter environment based on actual load reappears, based on computer software
Clutter electromagnetic property emulates and based in kind or half radar cluttcr simulator in kind.Reverberation chamber is tested as large space electromagnetism
Chamber has its unique advantage on the basis of traditional electromagnetic compatibility test function as clutter Simulator.Reverberation chamber is used
In clutter simulation, the radar clutter for meeting tested demand and solid can be simulated quickly, efficiently at low cost comprehensively
When being presented clutter, the multiple domains information such as frequency, sky, " omnidirectional's irradiation " solid radar clutter ring true to nature is formed in large-scale confined space
Border.
Sea condition ceases commonly used in characterization sea motion state and the surge degree of wave, the two parameter breaths in it and wave height and wind speed
It is related.Seawater motion state under the influence of the factors such as gravity, air-flow, the temperature difference rises and falls in real time just corresponds to different sea conditions.Different sea conditions
Corresponding different sea degree of roughness introduces side's wave height and correlation function and is described.
The unrestrained height in side is defined as：
In formula (1), h (r) indicates the high function of wave；P (h) indicates the high distribution of wave；<>sIt indicates to take mean value, h tables along tested extra large table
Show unrestrained height.
Correlation function is defined as：
In formula (2), R indicates two point distance of extra large table.
Under low sea condition sea situation, sea is tranquil, and surface is jolted, and degree is gentle, and the corresponding unrestrained high level in side is low, correlation function
It is slow with R increase decaying；On the contrary, under high sea condition sea situation, wave rolling degree aggravation, the corresponding unrestrained high level in side is high, correlation
Function is rapid with R increase decaying.
Different sea condition sea clutter characteristic
Different sea conditions, extra large table fluctuating quantity is different, and especially under the conditions of high sea condition, sea rolling is violent, ocean surface topography
It changes over time that scale is big, produces the seawater detailed structure of many complexity, cause extra large table mathematical model more complicated and changeable.Thunder
On the extra large table for acting on different structure up to wave beam, it is respectively IPIX thunders that echo scattering properties, which also has very big difference, Fig. 1 and Fig. 2,
Up to Observed sea clutter obtained under different sea conditions when, frequency domain characteristic figure：
In time domain, when low sea condition, it is small that swellings, heaving and subsiding, and side's wave is high small, and multipath effect is not notable, amplitude echo institute accounting
Example is larger, and amplitude distribution is more uniform；When high sea condition, it is big that swellings, heaving and subsiding, and side's wave is tall and big, and multipath effect is notable, small magnitude echo
Proportion increases, and amplitude distribution is into small magnitude segment set.
On frequency domain, when low sea condition, ocean surface wind speed is low, and clutter frequency domain energy is more concentrated, dopplerbroadening unobvious, both sides
Hangover length, spectral line are in sharp keen " herringbone ".When high sea condition, ocean surface wind speed is high, and clutter frequency domain energy is disperseed, Doppler's exhibition
Wide significantly lower frequency side and high frequency side spectral line fall off rate are inconsistent, and spectral line is in " the entering font " broadened.
Sea clutter Power Spectrum Model
Common sea clutter Power Spectrum Model has Gaussian (Gaussian), exponential type (Exponential) and full pole
Type (Allpole).Gaussian models in sea clutter Power Spectrum Model with the most extensively, good symmetry and double
The convenience of parameter regulation can clearly portray Doppler frequency shift and the broadening of radar sea clutter：
In formula (3), P0Indicate mean power；fdIndicate average Doppler frequency；σ indicates standard deviation.
Allpole models increase along with radar accuracy and generate, when radar beam acts on sea with low pitch angle, time
The power spectrum characteristic of wave can more accurately be portrayed with Allpole models, and probability density function is：
In formula (4), fcIndicate cutoff frequency.
Exponential model uses are less, and it is special to be generally not suitable for description radar clutter power spectrum under tranquility
Property, but due to the distinctive property of exp functions, have the advantage of its own, probability close describing high sea condition clutter power time spectrum
Spending function is：
If Fig. 3 is three kinds of typical sea clutter Power Spectrum Model curve graphs：
For above is referred to two kinds of typical sea conditions under sea clutter power spectrum, Gaussian types cannot all carry out well
It portrays.In low sea condition, although Gaussian spectrums can portray the dopplerbroadening of spectral centroid, spike both sides fall off rate
Relatively slow, both sides trailing length is also inadequate；When high sea condition, it is such asymmetric as portraying instead that Gaussian composes good symmetry
The bottleneck of spectral line.Allpole models can not only be fitted the kurtosis of low sea condition clutter power spectrum, long streaking characteristic well
Also preferably mutually agree with low sea condition situation, but it is not suitable for high sea condition.And the Exponential models of single parameter are not
High sea condition clutter spectrum can be fully described by.
Invention content
Technical problem to be solved by the invention is to provide a kind of, and the radar clutter spectral characteristic simulation based on reverberation chamber is
System and method, the method portray the spectral characteristic simulation of radar clutter more fine, accurate.
In order to solve the above technical problems, the technical solution used in the present invention is：A kind of radar clutter based on reverberation chamber
Spectral characteristic simulation system, it is characterised in that：Including combination signal generating module, RF Amplifier Module, mechanical agitation reverberation chamber
With output signal acquisition module, the signal input part of the signal output end and radio frequency method module of the combination signal generating module
Connection, the signal output end of the RF Amplifier Module and the signal receiving antenna of the mechanical agitation reverberation chamber carry out signal
Transmission, passes through the indoor transmitting antenna of the reverberation and the output signal acquisition module by the signal of mechanical agitation reverberation chamber
Signal input part connection.
Further technical solution is：The signal generating module includes that arbitrary waveform generator and analog signal occur
Device, write-in low frequency signal S in the arbitrary waveform generator0, by low frequency signal S0Occur as modulated signal feed-in analog signal
Device, analog signal generator generate modulated signal S through ovennodulation1。
Further technical solution is：The RF Amplifier Module includes AR power amplifiers and low loss coaxial line
Cable, modulated signal S1Radio-frequency input signals S is ultimately formed by the effectively amplification of AR power amplifiersinput, appropriate adjusting power amplifier
Amplification factor so that radio-frequency input signals SinputSignal had not only met reverberation chamber job requirement, but also made the S being agitated to formoutput
Signal does not injure output collecting device.
Further technical solution is：The mechanical agitation reverberation chamber includes chamber, blender, reception antenna and transmitting
Antenna, blender, reception antenna and transmitting antenna are located in the chamber, and inhomogeneity is realized by changing the rotating speed of blender
Maximum doppler frequency f under typedmaxSimulation, Receiving antenna selection log-periodic antenna as input, keep its position to fix,
It is directed at a certain corner of reverberation chamber, emitting antenna selecting electromagnetic horn, same holding position is fixed, radio-frequency input signals SinputThrough stirring
Radio frequency output signal S is formed after mixingoutputTo subordinate's module transfer.
Further technical solution is：The output signal acquisition module includes coaxial attenuator and oscillograph, is passed through
Radio frequency output signal S after reverberation chamberoutputPower is reduced by coaxial attenuator, obtains signal Slow, finally again by oscillograph
Output signal is acquired, unitary sampling signal S is obtainedsample。
The radar clutter spectral characteristic analogy method based on reverberation chamber that the invention also discloses a kind of, it is characterised in that including
Following steps：
Mathematical modeling is carried out to the sea clutter frequency spectrum of low sea condition using Allpole models, and using combination Exponential
Model carries out mathematical modeling to the sea clutter frequency spectrum under high sea condition；
Inverse Fourier transform is made to the above-mentioned spectral model built up, obtains corresponding time domain data, is selected different types of
Above-mentioned time domain data is stored respectively in spare in arbitrarily signal generating device by monocycle time domain waveform as input；
Monocycle time domain waveform is sent as input into analog signal generator and carries out carrier-signal amplitude modulation, is completed
The generation of am signals, then appropriate amplification is carried out by RF Amplifier Module, ultimately form radio-frequency input signals；
After radio-frequency input signals is ready, to being configured inside mechanical agitation reverberation chamber, fixed dual-mode antenna position
It is constant, and the motor control program of blender is set, allow reverberation chamber to work in continuous mode, the stir speed (S.S.) of blender is set as
Certain value；
The output signal of mechanical agitation reverberation chamber is sampled by output signal acquisition module, obtains unitary sampling letter
Number Ssample, the unitary sampling signal S of two spectral modelssampleIt is respectively included by a data cell, keeps input signal constant,
It repeats the above process, each unit surveys several groups data；
Change the unitary sampling signal S of agitator speed and two spectral models of repeated acquisition several groupssample；
Fourier transformation and normalized are made to obtained unitary sampling data, analyze its spectral characteristic.
Further technical solution is：The method further includes the steps that being calibrated to mechanical agitation reverberation chamber, is adopted
The chamber of the reverberation chamber is calibrated with unloaded form, the simulation system is configured after calibration and is accurately connected
Line.
Further technical solution is：The probability density function of the Allpole models is：
Wherein, P0Indicate mean power；fdIndicate average Doppler frequency；fcIndicate that cutoff frequency, f indicate frequency, n tables
Show positive integer.
Further technical solution is：The combination Exponential models obtain by the following method：
By the cutoff frequency f for controlling two single Exponential modelsc, different exp function curves is selected to distinguish
High and low frequency failing edge part when high sea condition is described, finally by the high and low frequency failing edge part group of two exponential models
It closes, the modeling of combination Exponential models is completed, to complete the modeling of high sea condition clutter power spectral curve.
Further technical solution is：The probability density function of the single Exponential models is：
Wherein, P0Indicate mean power；fcIndicate that cutoff frequency, f indicate frequency.
It is using advantageous effect caused by above-mentioned technical proposal：The method uses Allpole functions and combination
Exponential function founding mathematical models are reference to survey radar sea clutter, and clutter spectrum spy has been carried out in reverberation chamber
Property simulation reproduce, obtain to draw a conclusion：
(1) the sea clutter data for using IPIX radars obtain radar sea clutter spectral characteristic under two kinds of typical sea conditions.Low sea
When feelings, sea clutter spectral line is in sharp keen " herringbone ", meets Allpole models；When high sea condition, high and low frequency both sides spectral line declines
Rate is inconsistent, in " the entering font " of broadening, meets combination Exponential models.The model gram built by the method
The limitation for having taken Gaussian type spectral models portrays the simulation of radar clutter spectral characteristic more fine, accurate.
(2) under ideal conditions, reverberation chamber selecting frequency characteristic is good, only has response to export in resonant frequency, can be equivalent to
Comb filter；Under non-ideal condition, reverberation chamber selecting frequency characteristic declines, other frequency components are excited, and can be equivalent to high pass
Filter.Reverberation chamber used in this method has non-ideal characteristic, and the narrow band signal for not influencing injection passes through.
(3) simulation is focused on to the model and maximum doppler frequency f of sea clutter frequency spectrumdmaxOn, to survey Radar Sea
Clutter spectrum characteristic is reference, and maximum doppler frequency f under different type is realized by constantly changing agitator speeddmax's
Simulation.
(4) from the point of view of analog result, the reverberation chamber output spectrum characteristic simulated is consistent with measured result, spectral model with
Input model is consistent, does not change with stir speed (S.S.) and changes；Maximum doppler frequency fdmaxOnly influenced by stir speed (S.S.), and
It is unrelated with input model, maximum doppler frequency fdmaxIncrease with stir speed (S.S.) and increases.
Description of the drawings
Fig. 1 is the time domain waveform of sea clutter under low sea condition；
Fig. 2 is the time domain waveform of sea clutter under high sea condition；
Fig. 3 is the power spectral density plot of sea clutter under low sea condition；
Fig. 4 is the power spectral density plot of sea clutter under high sea condition；
Fig. 5 is Gaussian type sea clutter power spectral density plots；
Fig. 6 is Allpole type sea clutter power spectral density plots；
Fig. 7 is the Exponential type sea clutter power spectral density plots of single parameter；
Fig. 8 be under ideal conditions reverberation chamber working frequency be 1GHz near resonant frequency value spectrum；
Fig. 9 is reverberation chamber amplitude-frequency response figure under non-ideal condition；
Figure 10 is the structural schematic diagram of irregular blender；
Figure 11 is the functional block diagram of heretofore described system；
Figure 12 is the sea clutter power spectrum mathematical model of Allpole modelings；
Figure 13 is the sea clutter power spectrum mathematical model for combining Exponential modelings；
Figure 14-15 is stir speed (S.S.) Allpole modelings clutter power spectrum densogram once；
Figure 16-17 is two times Allpole modeling clutter power spectrum densograms of stir speed (S.S.)；
Figure 18-19 is three times Allpole modeling clutter power spectrum densograms of stir speed (S.S.)；
Figure 20-21 is that stir speed (S.S.) once combines Exponential modeling clutter power spectrum densograms；
Figure 22-23 is two times combination Exponential modeling clutter power spectrum densograms of stir speed (S.S.)；
Figure 24-25 is three times combination Exponential modeling clutter power spectrum densograms of stir speed (S.S.).
Specific implementation mode
With reference to the attached drawing in the embodiment of the present invention, technical solution in the embodiment of the present invention carries out clear, complete
Ground describes, it is clear that described embodiment is only a part of the embodiment of the present invention, instead of all the embodiments.It is based on
Embodiment in the present invention, it is obtained by those of ordinary skill in the art without making creative efforts every other
Embodiment shall fall within the protection scope of the present invention.
Many details are elaborated in the following description to facilitate a thorough understanding of the present invention, still the present invention can be with
Implemented different from other manner described here using other, those skilled in the art can be without prejudice to intension of the present invention
In the case of do similar popularization, therefore the present invention is not limited by following public specific embodiment.
The radar clutter spectral characteristic simulation system and method, the method that the invention discloses a kind of based on reverberation chamber make
It is carried out with the simulation system, the correlation theory of the present invention is illustrated below：
Reverberation chamber amplitude versus frequency characte under ideal conditions：
Resonant theory is applied into reverberation chamber, is started with from overall structure, ignores some internal non-linear factors to amplitude-frequency
The influence of characteristic, chamber body can be considered as a regular rectangular configuration, and ideally reverberation chamber resonant frequency is：
Wherein：L indicates that the length of reverberation chamber, W indicate that the width of reverberation chamber, H indicate the width of reverberation chamber, c0Indicate light
Speed, n, m, p are non-negative positive integer and are asynchronously 0.
Utilize 1 reverberation chamber relevant parameter of table：
1 reverberation chamber basic parameter of table
Table 1 Parameters of reverberation chamber
It is computed, it is as shown in Figure 8 for the resonant frequency value spectral line near 1GHz in working frequency：
As it can be observed in the picture that in the case where ignoring the influence conditions such as chamber loss, reverberation chamber resonant frequency ideally is one
The isolated interruption spectral line of root, with frequency constantly increases, and spectral density increases.Theoretically, only when input frequency is equal to humorous
The signal of vibration frequency could pass through.Therefore, ideal reverberation chamber has good selecting frequency characteristic, can be considered as ideal comb filtering
Device.
Reverberation chamber amplitude versus frequency characte under non-ideal condition
Quality factor q characterizes the ability of chamber loss, the inverse of Q can be considered as in chamber it is various be lost take down respectively it is folded
Add.Calculation formula is as follows：
In formula (7), ηTxFor transmitting antenna efficiency；ηRxFor reception antenna efficiency；Indicate power mean value；PRecTo receive work(
Rate；PInFor transmission power.
The value of quality factor q is in rising trend with working frequency raising, when reverberation chamber is operated in 1GHz or so, theoretical Q
Value is 105Magnitude, the variation of Q values impact chamber idealization degree.The it is proposed of quality factor q makes reverberation chamber that size be lost
There are a specific measurement index, the presence of loss that chamber idealization degree is declined, the influence brought therewith is embodied in
Be exactly in amplitude versus frequency characte resonant frequency change.Being lost for ease of analysis influences (only considering dielectric loss)：
In formula (8), βnFor characteristic value；anFor eigenfunction.
It is σ to enable conductivity, is then obtained：
In formula (9), εcIndicate multiple capacitance coefficient.
Assuming that(area is divided into 0), then formula (9) is substituted into (8), it obtains：
And then it obtains：
It enables：
∫E·anD τ=Ane-jωt (12)
A in formula (12)nFor constant；ω=ω1+jω2, then：
It enables again：
As Q ＞ ＞ 1, eigenfrequency is：
Then：
Formula (16) shows that the electromagnetic wave for making undamped oscillation in ideal reverberation chamber originally is made to occur due to loss
Formula (16) from the angle of damped oscillation can be written as integration type by damped oscillation phenomenon：
All frequency contents therein are showed in conjunction with inverse Fourier transform：
Formula (18) shows to make that the field intensity value E (ω) under a certain frequency content is highlighted, it is necessary to make j (ωn-ω)-
ωn/ 2Q ≈ 0, as quality factor q ＞ ＞ 1, it is desirable to ωn≈ω。
By the above theory analysis and emulation is combined, when reverberation chamber is operated in 1GHz, amplitude-frequency response is as shown in Figure 9：
As shown in Figure 9, when input service frequency is larger, reverberation chamber was in mould state, and the independence for including in chamber is humorous
Vibration frequency is more, and pattern density is big.If injecting a higher wideband-radar signal of centre frequency, at this time the frequency spectrum of output signal
Component extends to continuous frequency band by isolated frequency point.And under non-ideal condition it can be seen from formula (18), reverberation chamber frequency-selecting is special
Property be deteriorated, a large amount of other frequency components can be inspired around resonant frequency, and with the increase of quality factor q, resonance frequency
Frequency component around rate also constantly increases.Reverberation chamber may finally be considered as to a high-pass filter.
Reverberation chamber used herein is non-ideal type, therefore, can be smooth when inputting the narrow band signal of certain bandwidth
By by be not suppressed.
Reverberation chamber radar clutter spectral characteristic principle of simulation
Sea with one climax following another can be considered as the prevailing transmission channel between emitting radar waves reception, not due to shifting
Fixed, scattering table shape is different, along with wave interaction produces abundant fine structure so that the shape of transmission channel
Real-time change, characteristic of channel complexity is various, causes echo multipath effect notable.Time-varying caused by order to imitate ocean natural environment
Transmission characteristic, reverberation chamber introduce blender in structure design and are adapted therewith.The presence of blender makes script simple rule
Rectangular chamber internal structure become complicated and changeable, the main agitator of reverberation chamber blender employed herein in addition to regular shape
Outside, also irregular secondary agitator, since the unique sawtooth hatch frame (as shown in Figure 10) of secondary agitator increases chamber
The complexity of structure.
The presence of blender not only increases the complexity of reverberation chamber geometry, and the process of continuous rotation can also cause
Export the dopplerbroadening of response.In true Radar Clutter Background, sea clutter dopplerbroadening is mainly since wave exists
It is performed relative motion under the action of wind-force, gravity etc., caused by the speed of radar incidence wave radial direction is not zero.Equally
Ground, in reverberation chamber clutter simulation system, the continuous rotation of blender can be analogous to the rolling of wave, finally can also make defeated
Go out response and occurs Doppler effect on frequency spectrum.Doppler shift formula is caused by the rectangle good conductor of rotation：
In formula (19), f0Indicate carrier frequency；Expression source and conductor plate angle；R indicates conductor radius of turn；ωsIndicate conductor
Angular velocity of rotation.
Into the indoor electromagnetic wave of chamber between metal cavity wall and blender roundtrip, under the pattern of continuously stirring, electricity
The propagation path random time-dependent of magnetic wave forms a time-varying multipath modulation channel.Therefore, the process that continuously stirs of reverberation chamber can be with
It is considered as the generating process of time-varying Nakagami multidiameter fading channels.
In such multidiameter fading channel, steady narrowband complex signal can be expressed as：
In formula (20) A (t) andIt is the envelope and phase function of signal respectively.
Define S (t) auto-covariance function be：
2Bs(τ)=E [S*(t)S(t+τ)]-|E[S(t)]|2 (21)
S in formula (21)*(t) conjugation of S (t) is indicated.Therefore, n ranks spectral moment bnIt can be defined as：
As m >=1, Bs(τ) is expressed as：
B in formula (23)0Indicate 0 rank spectral moment；I0() indicates 0 rank modified Bessel function；fdmaxIndicate maximum Doppler frequency
It moves；κ >=0, μ ∈ [- π, π).Further push away to obtain 1,2 rank spectral moment b1、b2Respectively：
I in formula (24) and (25)1() and I2() indicates 1 rank and 2 rank modified Bessel functions respectively.
Formula (19) gives the general expression of Doppler frequency shift of the regular rectangular shape conductive plate caused by the radial rotary,
But there is no the situation for metal agitator continuous rotation in reverberation chamber, it cannot be directly used to doppler phenomenon in reverberation chamber
Quantitative calculating.Introduce N (ρ) (level crossing rate (lcr)), in isotropic scatterning model, κ=0, b1、b2It can be reduced to b1=
0,N (ρ) can be expressed as：
In formula (26)Indicate normalization envelope level.Therefore, maximum doppler frequency can be with table in reverberation chamber
It is shown as：
N (ρ) can measure S by the way that experiment is arranged in reverberation chamber21Parameter obtains, and Nakagami form parameters m can not
It directly acquires, but m and Rice factor K has following relationship：
Rice factor Ks can be measured by experiment, and calculation formula is as follows：
P in formula (29)dIndicate transfer function S21The power of mean value；PsIndicate transfer function S21Variance.
It can be in the hope of f by formula (27)-(29)dmaxQuantitative solution, but solution procedure is complex, especially m parameter are also
It needs to acquire indirectly by experiment, due to the presence of experimental error, computational solution precision is relatively low.Therefore, it is introduced into work(in reverberation chamber
The empirical equation that rate spectrum density calculates calculates to simplify, and in reverberation chamber, the power spectral density of region of acceptance can be expressed as：
δ (f in formula (30)d) indicate Dirichlet functions；Sin(fd) indicate the received spectrum of direct-coupling part.
When the frequency spectrum to receiving area is normalized using its maximum value, experimental result has very well with empirical model
Fitting degree, using exponential type delay be expressed as：
S(fd)=aexp (- b | fd|-1) (31)
In formula (31), a is constant；B is codetermined by configuration inside reverberation chamber and carrier frequency, can be calculated with b=β λ.
Wherein λ is operation wavelength；β is form parameter, and value depends on agitator speed.
As shown in figure 11, the radar clutter spectral characteristic simulation system based on reverberation chamber that the invention discloses a kind of, it is special
Sign is：Including combination signal generating module, RF Amplifier Module, mechanical agitation reverberation chamber and output signal acquisition module, institute
The signal output end for stating combination signal generating module is connect with the signal input part of radio frequency method module, the RF Amplifier Module
The signal receiving antenna of signal output end and the mechanical agitation reverberation chamber carry out the transmission of signal, by mechanical agitation reverberation
The signal of room is connect by the indoor transmitting antenna of the reverberation with the signal input part of the output signal acquisition module.
Using modular form to data stream carry out transmission process, according to built shown in Figure 11 simulation system and to experiment set
It is standby to carry out related setting.Using combination signal generating module-RF Amplifier Module-mechanical agitation reverberation chamber-output signal acquisition
Module, quaternary structure are completed the transmission to signal stream and are handled.The waveform that signal generating source generates will be combined and inject reverberation chamber, then is right
Fourier transformation is made in output response, observes influence of the different stir speed (S.S.)s to dopplerbroadening in output response spectrum characteristic.
(1) signal generating module is combined.The first order is combination signal generating module, it is mainly appointed by Agilent 33250A
Meaning waveform generator and Agilent 8257D analog signal generators are composed, and low frequency signal S is written in 33250A0, will
S0As in modulated signal feed-in 8257D, is modulated by AM and generate modulated signal S1.The signal power mistake generated due to 8257D
It is low, the power requirement of reverberation chamber input signal is cannot be satisfied, needs to be added secondary amplification module power is carried out to one stage signal and put
Greatly.
(2) RF Amplifier Module.The second level is RF Amplifier Module, it is mainly by AR power amplifier (hereinafter referred to as work(
Put) and low-loss coax cables composition.Modulated signal S1Radio-frequency input signals S is ultimately formed by effectively amplifyinginput, appropriate to adjust
Save the amplification factor of power amplifier so that radio-frequency input signals SinputNot only met reverberation chamber job requirement, but also to be agitated to form
Radio frequency output signal SoutputOutput collecting device is not injured.
(3) mechanical agitation reverberation chamber.Third extremely mechanical agitation reverberation chamber, including chamber, blender, reception antenna and hair
Antenna is penetrated, blender, reception antenna and transmitting antenna are located in the chamber.It selects log-periodic antenna as input, keeps
Its position is fixed, a certain corner of alignment reverberation chamber, emitting antenna selecting electromagnetic horn, and same holding position is fixed, radio frequency input
Signal SinputRadio frequency output signal S is formed after agitatedoutputTo subordinate's module transfer.
(4) output signal acquisition module.The fourth stage be output acquisition module, mainly include coaxial attenuator and
7254 oscillographs of Tektronix DPO.Since there are one amplification, general radio frequency output signals for meeting after reverberation chamber for signal
SoutputPower is larger, is unsatisfactory for the job requirement of oscillograph, and therefore, first passing through 20dB coaxial attenuators reduces power, obtains letter
Number Slow, finally output signal is acquired by DPO7254 oscillographs again, obtains unitary sampling signal Ssample。
The radar clutter spectral characteristic analogy method based on reverberation chamber that the invention also discloses a kind of, includes the following steps：
(1) it uses Allpole models to carry out mathematical modeling to the sea clutter frequency spectrum of low sea condition, as shown in figure 12, and uses
It combines Exponential models and mathematical modeling is carried out to the sea clutter frequency spectrum under high sea condition, as shown in figure 13；
The probability density function of the Allpole models is：
Wherein, P0Indicate mean power；fdIndicate average Doppler frequency；fcIndicate that cutoff frequency, f indicate frequency, n tables
Show positive integer.
The combination Exponential models obtain by the following method：By controlling two single Exponential
The cutoff frequency f of modelc, select different exp function curves to describe high and low frequency failing edge part when high sea condition respectively, finally
By the high and low frequency failing edge part combination of two exponential models, the modeling of combination Exponential models is completed, from
And complete the modeling of high sea condition clutter power spectral curve.
The probability density function of the single Exponential models is：
Wherein, P0Indicate mean power；fcIndicate that cutoff frequency, f indicate frequency.
(2) inverse Fourier transform is made to the spectral model built up, obtains its time domain data, select arbitrary waveform generator
Time domain data is respectively written into and is stored in spare in " the Stored Wform " of 33250A by " Arb " pattern in 33250A；
(3) reverberation chamber is calibrated, carries situation since this method is not related to band, chamber is interior to significantly affect electromagnetism without other
The geometric object of setback reflection, therefore cavity is calibrated using unloaded form, according to level Four modularization side after calibration
Formula is configured to experimental provision and accurate line.
(4) since the signal highest frequency that 33250A type arbitrary waveform generator generates (is unsatisfactory for mixing no more than 80MHz
Ring room fL≈ 79.83MHz requirements, wherein fLIndicate reverberation chamber lowest usable frequency, fL=3*f0, wherein f0M=is worked as by formula (6)
1, n=0, p=0 are obtained.), therefore low frequency signal is given as input and carries out carrier signal into 8257D type analog signal generators
Amplitude is modulated." AM " pattern is arrived into 8257D settings, incoming carrier frequency is 1GHz, and it is " OUT1 " to select modulation input port, complete
Appropriate amplification is carried out at the generation of am signals, then by power amplifier, ultimately forms radio frequency input.
(5) after radio-frequency input signals is ready, reverberation chamber inside is configured, the fixed aerial position that transmits/receives is constant,
Transmitting antenna pitch angle is about 60 °, and reception antenna keeps horizontal, and the motor control program of blender is arranged, reverberation chamber is allowed to work
In continuous mode, stir speed (S.S.) is set as 0.314rad/s (stir speed (S.S.) one).
(6) output signal is sampled, unitary sampling sample number is 100000, takes oscillograph to adopt with bandpass sample theory
Sample frequency fs=5KHz obtains unitary sampling signal Ssample.Two spectral models are respectively included by a data cell, keep defeated
It is constant to enter signal, repeats the above process, each unit surveys 50 groups of data.
(7) it is 0.628rad/s (stir speed (S.S.) two), 0.942rad/s (stir speed (S.S.) three) to change agitator speed, is repeated
Step (6).
There are two spectral models, three kinds of stir speed (S.S.)s to amount to 6 data sheets in radar clutter spectral characteristic analogy method
Member, 300 groups of data.
Fourier transformation and normalized are made to obtained unitary sampling data, analyze its spectral characteristic, Figure 14-19,
Figure 20-25 is under different rotating speeds respectively, is that the reverberation chamber that input obtains exports response spectrum curve with two kinds of models：
The maximum Doppler that under different rotating speeds, high and low sea condition model obtains is broadened into fdmaxList 2：
Maximum Doppler broadens f under 2 different rates of tabledmax
fdmaxUnit：(Hz)
The result shows that：It, can after input signal changes into the broadband signal with certain bandwidth by traditional simple signal
Effectively output is formed in reverberation chamber, does not influence its whole spectral characteristic, under this non-ideal condition with the above theory analysis
The theory that reverberation chamber can be considered as a high-pass filter is consistent.From Figure 14-25 as can be seen that after reverberation chamber stirs,
It is consistent when its global shape of output that two kinds of models obtain is with input, only broadens f in maximum DopplerdmaxOn not
Together.In addition, maximum Doppler broadens fdmaxIncrease with the increase of the blender speed of rotation, increase and decrease degree and input model without
It closes.
The method is with Allpole functions and combination Exponential function founding mathematical models, to survey Radar Sea
Clutter is reference, and clutter spectrum idiocratically simulation reconstruction has been carried out in reverberation chamber, has been obtained to draw a conclusion：
(1) the sea clutter data for using IPIX radars obtain radar sea clutter spectral characteristic under two kinds of typical sea conditions.Low sea
When feelings, sea clutter spectral line is in sharp keen " herringbone ", meets Allpole models；When high sea condition, high and low frequency both sides spectral line declines
Rate is inconsistent, in " the entering font " of broadening, meets combination Exponential models.The model gram built by the method
The limitation for having taken Gaussian type spectral models portrays the simulation of radar clutter spectral characteristic more fine, accurate.
(2) under ideal conditions, reverberation chamber selecting frequency characteristic is good, only has response to export in resonant frequency, can be equivalent to
Comb filter；Under non-ideal condition, reverberation chamber selecting frequency characteristic declines, other frequency components are excited, and can be equivalent to high pass
Filter.Reverberation chamber used in this method has non-ideal characteristic, and the narrow band signal for not influencing injection passes through.
(3) simulation is focused on to the model and maximum doppler frequency f of sea clutter frequency spectrumdmaxOn, it is miscellaneous to survey radar
Wave frequency spectral property is reference, and maximum doppler frequency f under different type is realized by constantly changing agitator speeddmaxMould
It is quasi-.
(4) from the point of view of analog result, the reverberation chamber output spectrum characteristic simulated is consistent with measured result, spectral model with
Input model is consistent, does not change with stir speed (S.S.) and changes；Maximum doppler frequency fdmaxOnly influenced by stir speed (S.S.), and
It is unrelated with input model, maximum doppler frequency fdmaxIncrease with stir speed (S.S.) and increases.
Claims (5)
1. a kind of radar clutter spectral characteristic analogy method based on reverberation chamber, it is characterised in that include the following steps：
Mathematical modeling is carried out to the sea clutter frequency spectrum of low sea condition using Allpole models, and using combination Exponential models
Mathematical modeling is carried out to the sea clutter frequency spectrum under high sea condition；
Inverse Fourier transform is made to the above-mentioned spectral model built up, obtains corresponding time domain data, selects different types of single-revolution
Above-mentioned time domain data is stored respectively in spare in arbitrarily signal generating device by phase time domain waveform as input；
Monocycle time domain waveform is sent as input into analog signal generator and carries out carrier-signal amplitude modulation, completes amplitude
The generation of modulated signal, then appropriate amplification is carried out by RF Amplifier Module, ultimately form radio-frequency input signals；
After radio-frequency input signals is ready, to being configured inside mechanical agitation reverberation chamber, fixed dual-mode antenna position is constant,
And the motor control program of blender is set, allow reverberation chamber to work in continuous mode, the stir speed (S.S.) of blender is set as certain
Value；
The output signal of mechanical agitation reverberation chamber is sampled by output signal acquisition module, obtains unitary sampling signal
Ssample, the unitary sampling signal S of two spectral modelssampleIt is respectively included by a data cell, keeps input signal constant, weight
The multiple above process, each unit survey several groups data；
Change the unitary sampling signal S of agitator speed and two spectral models of repeated acquisition several groupssample；
Fourier transformation and normalized are made to obtained unitary sampling data, analyze its spectral characteristic.
2. the radar clutter spectral characteristic analogy method based on reverberation chamber as described in claim 1, it is characterised in that the side
Method further includes the steps that being calibrated to mechanical agitation reverberation chamber, and school is carried out to the chamber of the reverberation chamber using unloaded form
Standard, is configured the simulation system after calibration and accurate line.
3. the radar clutter spectral characteristic analogy method based on reverberation chamber as described in claim 1, it is characterised in that described
The probability density function of Allpole models is：
Wherein, P0Indicate mean power；fdIndicate average Doppler frequency；fcIndicate that cutoff frequency, f indicate that frequency, n indicate just
Integer.
4. the radar clutter spectral characteristic analogy method based on reverberation chamber as described in claim 1, it is characterised in that described
Combination Exponential models obtain by the following method：
By the cutoff frequency f for controlling two single Exponential modelsc, different exp function curves is selected to describe respectively
The high and low frequency failing edge part of two exponential models is finally combined in high and low frequency failing edge part when high sea condition, complete
At the modeling of combination Exponential models, to complete the modeling of high sea condition clutter power spectral curve.
5. the radar clutter spectral characteristic analogy method based on reverberation chamber as claimed in claim 4, it is characterised in that described
The probability density function of single Exponential models is：
Wherein, P0Indicate mean power；fcIndicate that cutoff frequency, f indicate frequency.
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