CN1295486C - Non-linear evolutional correction method for levelmeter of linear frequency-modulation radar - Google Patents

Non-linear evolutional correction method for levelmeter of linear frequency-modulation radar Download PDF

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CN1295486C
CN1295486C CNB2004100924472A CN200410092447A CN1295486C CN 1295486 C CN1295486 C CN 1295486C CN B2004100924472 A CNB2004100924472 A CN B2004100924472A CN 200410092447 A CN200410092447 A CN 200410092447A CN 1295486 C CN1295486 C CN 1295486C
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linear
frequency
controlled oscillator
signal
curve
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CN1632474A (en
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谢克明
阎高伟
谢刚
夏路易
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Taiyuan University of Technology
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Taiyuan University of Technology
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Abstract

The present invention relates to a non-linear evolutional correction method for a linear frequency modulation radar level meter, and belongs to the technical fields of signal processing and automatic measurement. A frequency sweep voltage curve for controlling a voltage controlled oscillator is segmented, characteristic information is extracted by using spectral analysis, end point coordinates of the segmenting curve are obtained through an evolutional calculation principle, and the non-linear frequency sweep curve is formed to compensate the nonlinearity of the voltage controlled oscillator. The present invention can generate linear frequency modulation signal with high linearity without measuring the frequency or the phase of a microwave signal with high frequency, solve the non-linear problem of the frequency modulation of the linear frequency-modulated radar, ensure the measurement precision, can be suitable for the measurement of various phases, have no need of adding special circuits for linearity correction, and have low cost.

Description

Non-linear evolutional correction method for levelmeter of linear frequency-modulation radar
One, technical field
Non-linear evolutional correction method for levelmeter of linear frequency-modulation radar of the present invention belongs to signal Processing and automatic measurement technology field, be a kind of spectrum analysis characteristic information extraction that utilizes specifically, adopt the principle of evolutionary computation to solve the nonlinear problem of linear FM radar frequency modulation.
Two, technical background
LINEAR CONTINUOUS frequency modulation radar body place meter has noncontact, resolution height in level gauging, the advantage of medium wide adaptability is widely used in various level gaugings.Because the voltage controlled oscillator that uses in the LINEAR CONTINUOUS ripple frequency modulated(FM) radar has the non-linear of essence, when adopting linear fully voltage to carry out frequency modulation (PFM), can make the frequency signal of final output present nonlinear characteristic, owing to there is frequency shift (FS), Beat Signal after the mixing is not the simple signal under the ideal linearity FM signal situation, frequency spectrum is with broadened, thereby cause LFMCW radar level gauge resolution to reduce, also can cause the decline of signal to noise ratio (S/N ratio) after the FFT spectrum analysis simultaneously, influence final computational accuracy.Non-linear in order to eliminate, generally adopt 2 kinds of methods: open loop correction and closed-loop corrected.Open loop correction is to measure the electric voltage frequency relation of VCO in advance, is stored in the storer, and the digital quantity by storage in advance during actual the use is carried out the output of sweep voltage by D/A converter.Or utilize potentiometer and amplifier to constitute the hardware circuit of the gamma correction of multistage, and to carry out hardware correctedly, the shortcoming of these two kinds of methods is that the characteristic of each VCO is all inequality, workload is very big in the production debug process, is difficult for mass production.Temperature influence is also very big in the actual use, is difficult to guarantee measuring accuracy.Closed-loop corrected method is that the measuring method of employing frequency or phase place is obtained the frequency under the corresponding voltage, then the digital quantity that produces control voltage is revised, and to obtain the satisfied linearity, this will increase the workload of hardware cost and software.
In order to address this problem, it is synthetic that the method that people adopt the synthetic and digital phase-locked loop of Direct Digital is carried out numeral to needed signal, but can not drop into the application of reality owing to following reason.At first adopt the synthetic method of Direct Digital also not reach the X-band of fill level radar work at present, can only adopt the method for frequency multiplication or up-conversion, this method one is that cost is too high, system complex, the 2nd, the microwave signal that produces through frequency multiplication has a lot of harmonic components, phase noise is big, can produce negative influence to measurement result.In addition, need a transient process when utilizing phaselocked loop to change frequency, so its frequency inverted time is longer, and can not satisfies the requirement of the high speed frequency sweep characteristic of linear frequency modulation ripple radar.
Three, summary of the invention
Non-linear evolutional correction method for levelmeter of linear frequency-modulation radar purpose of the present invention is: provide a kind of easy and need not increase the bearing calibration of the fm linearity of any hardware, solve the problem of the difficult and more complicated of present linearity correction, solve because the problem of the non-linear influence that measuring accuracy is brought of frequency modulation, a kind of radar levelmeter of producing and debugging be convenient to is provided.
Non-linear evolutional correction method for levelmeter of linear frequency-modulation radar of the present invention, utilize the evolution principle to the frequency modulation of the voltage controlled oscillator in the radar levelmeter non-linear carry out closed-loop corrected, it is characterized in that: the non-linear frequency modulation that remedies voltage controlled oscillator that utilizes the fm voltage curve is non-linear, the fm voltage curve is divided into plurality of sections, every section end points coordinate is divided certain region of variation, adopt the evolution principle to ask for the end points coordinate of corresponding best fm linearity, with the fm voltage curve after each end points connection can formation correction; Need not measure the frequency or the phase place of high-frequency microwave signal, ask for evaluation function in the evolution principle, realize the nonlinear correction of voltage controlled oscillator frequency modulation by extracting the difference frequency signal spectrum signature; Adopt the fm linearity of the method raising voltage controlled oscillator of overlapping analysis; Specifically, the hardware foundation of the linearity evolution bearing calibration of LFMCW radar levelmeter voltage controlled oscillator of the present invention mainly comprises digital signal processing unit and microwave unit [structure sees Fig. 1 for details], digital signal processing unit is by keyboard display communication interface module 1, D/A converter 2, digital signal processor 3, buffer amplifier 4, storer 5, wave filter 12, digital program controlled gain amplifier 13 and high-speed a/d converter 14 are formed, microwave unit is by voltage controlled oscillator 6, coupling mechanism 7, antenna 9, circulator 10 and frequency mixer 11 are formed, digital signal processor 3 output digital quantity signals are given D/A converter 2, convert voltage signal to, form the control voltage of the voltage controlled oscillator 6 of microwave unit through buffer amplifier 4, excitation voltage controlled oscillator 6 produces the microwave FM signal, the microwave FM signal is passed through coupling mechanism 7 after circulator 10 is launched by antenna 9, the signal that coupling mechanism 7 is coupled out is simultaneously delivered to frequency mixer 11 as the reference signal, target object 8 reflection echos receive through antenna 9, behind circulator 10, also be sent to frequency mixer 11 and reference signal mixing, signal after the mixing forms difference frequency signal by low-pass filter 12 backs, difference frequency signal is sampled by high-speed a/d converter 14 by digital program controlled gain amplifier 13 backs, converting Serial No. to is read by digital signal processor 3, storage in storer 5,3 pairs of sampled digital sequences of digital signal processor are carried out FFT or small echo computing and analysis, extract the non-linear characteristics amount of representing;
There is non-linear [the seeing Fig. 3] of essence in voltage controlled oscillator, among Fig. 3 desirable frequency modulation transmit 18 and desirable echoed signal 20 mixing after be point-frequency signal, actual frequency modulation transmits and 17 has nonlinear characteristic, actual ghosts signal 19 also has nonlinear characteristic, will make spectral aliasing after the two phase mixing, make the resolution of measurement reduce the position that maybe can't differentiate concrete target object, spectrum peak 21 is corresponding concrete thing positions among Fig. 4, there are two peak points 22 and 23 in adjacent very near position, might cause to differentiate concrete material position, this is a kind of reasonable situation in laboratory measurement, will be more serious in the actual measurement process, Fig. 5 is the frequency spectrum that adopts after method of the present invention is proofreaied and correct the linearity, except that the spectrum peak 24 of representative position, other composition is effectively suppressed, and the phase noise of VCO and the non-linear influence that brings are eliminated, and the non-linear evolution bearing calibration of linear FM radar level meter voltage controlled oscillator of the present invention is adopted based on the principle of evolvement method the frequency modulation voltage curve is carried out the piecewise linearity correction, concrete way is, the fm voltage curve is divided into plurality of sections, among Fig. 6 the frequency modulation curve is divided into six sections, be respectively line segment 25, line segment 26, line segment 27, line segment 28, line segment 29, line segment 30, have seven end points, be respectively starting point 31, terminal point 37 and the middle variable end-point 32 that is assigned Variable Area, 33,34,35,36, starting point 31 and terminal point 37 are changeless point, connect each end points and form a nonlinear fm voltage curve, the non-linear of voltage controlled oscillator compensated, every section end points adopts the method for evolving to obtain, and by the frequency spectrum after FFT or the small echo computing is analyzed, obtains to represent the characteristic quantity of non-linear and interfere information, the concrete thing position of 21 correspondences, spectrum peak among Fig. 4, be to need in the measuring process, and two other peak point 22 and 23 is phase noise and non-linear causing by VCO, need be inhibited, can select to compose in peak and spectrum both sides, the peak certain limit several peak values the merchant's and as estimating the non-linear evaluation function that impacts, make this function reach certain numerical value by evolvement method, can effectively suppress the phase noise and the non-linear influence that causes of frequency modulation of voltage controlled oscillator, the numerical value at spectrum peak 21 and spectrum peak 22 among for example optional Fig. 4,23 numerical value the merchant's and as evaluation function, evaluation to the evolution calibration result, the method of proofreading and correct of evolving sees Fig. 9 for details, the coding colony of variable end-point coordinate in the middle of first subprocess 43 after trimming process begins among Fig. 9 is used for producing at random in the variable end-point region of variation in the middle of each, and coding can adopt binary coding or other coding form, the figure place of coding can be determined as required, the quantity of individual in population is N, and the quantity of population determines that as required the quantity of variable is M in the individuality, quantity decision by curve segmentation, thereafter subprocess 44 is with the loop variable zero clearing, and subprocess 45 converts the encoded radio of each end points of curve in the individuality to coordinate figure, and subprocess 46 is with starting point, variable end-point in the middle of each, terminating point connects together, generate the sweep voltage curve, this curve is actually a digital quantity sequence, and subprocess 47 is exported the digital quantity sequence with predetermined speed continuously by D/A converter 2, produces the sweep voltage curve to voltage controlled oscillator 6, control voltage controlled oscillator 6 output microwave FM signal, through coupling mechanism 7, circulator 10, antenna 9 is transmitted into a planar metal thin plate, and the reflection echo signal that antenna 9 receives enters frequency mixer 11 and carries out mixing by the reference frequency signal that coupling mechanism 7 is coupled out through circulator 10, and the mixed frequency signal of generation forms difference frequency signal through wave filter 12 backs, after digital program controlled gain amplifier 13 amplifications or decay, carry out the Serial No. that sample quantization forms difference frequency signal by high-speed a/d converter 14 in subprocess 48, the Serial No. of 3 pairs of samplings of digital signal processor carries out FFT computing or wavelet analysis in subprocess 49, obtains spectrum curve, carry out the Characteristic Extraction of curve, thereafter subprocess 50 is used for calculating the performance evaluation function of this sweep voltage curve, and subprocess 51 judges whether evaluation function satisfies predetermined requirement, if meet the demands then by subprocess 52 saving results, finish trimming process, otherwise subprocess 53, the 54 pairs of loop variables increase progressively and judge, the curve of each individual representative can both be tested and estimate in the colony that guarantees to encode, and carry out evolutionary computation by evolutionary computation subprocess 55 after initial population test and evaluation are finished, the result clusters body weight that is produced is carried out above-mentioned test and evaluation procedure again, thick line sweep voltage curve 38 among Fig. 7 has been represented the sweep voltage curve after overcorrect, and sweep voltage curve 38 has been non-linear as can be seen, by the non-linear microwave FM signal of revising the non-linear acquisition high linearity of voltage controlled oscillator of sweep voltage curve 38, need to prove in the subprocess 55 and can adopt genetic algorithm, or other evolution algorithm is evolved such as thinking, evolutional programming, immunoevolution method etc., the selection of evaluation function also is diversified simultaneously, has divided 6 sections to the frequency modulation voltage curve among the present invention, the segmentation of adopting other quantity also is feasible, the many more calibration results of segmentation also can be got well, and improve the sampling rate of A/D conversion, obtain surpassing the sample sequence that FFT counts, employing is carried out overlapping FFT computing to original sample sequence, obtain a plurality of frequency spectrums of single frequency sweep curve, Fig. 8 has represented the crude sampling sequence is carried out overlapping segmentation thought in detail, for example can be divided into overlapped sequence length identical 39,40,41,42 data segments, each section is carried out the FFT computing, characteristic quantity on comprehensive a plurality of frequency spectrum is estimated, and can obtain the higher correction result of the linearity, but the increase that can bring operand.
Advantage of the present invention: be mainly used in industrial and mining enterprises various things position measurement and can be used for some range observation occasions.The correction of the linear frequency modulation linearity relies on level meter itself to carry out, need not external measurement devices and instrument, and correcting mode and algorithm are simple, proofread and correct back linearity height; The cost of instrument is low, produces and debugs simply, enhances productivity; The measuring accuracy height, error is little, antijamming capability is strong, adapt to abominable industrial environment, and is reliable and stable.
Four, description of drawings
Fig. 1 is the structural drawing of way of realization 1 of the present invention
Fig. 2 is the structural drawing of form 2 of the present invention
Fig. 3 is the nonlinear characteristic of voltage controlled oscillator
Frequency spectrum before Fig. 4 proofreaies and correct
Frequency spectrum after Fig. 5 proofreaies and correct
The segmentation of Fig. 6 sweep voltage curve
Fig. 7 proofreaies and correct back sweep voltage curve
The overlapping segmentation of Fig. 8 crude sampling sequence
Fig. 9 linearization correcting process figure
Figure 10 sweep voltage curve of correspondence as a result of evolving
Number in the figure
1, display keyboard communication interface 2, high-speed d/a converter
3, digital signal processor 4, buffer amplifier
5, storer 6, voltage controlled oscillator
7, coupling mechanism 8, target object or metal plate
9, antenna 10, circulator
11, frequency mixer 12, low-pass filter
13, digital program controlled gain amplifier 14, high-speed a/d converter
15, microwave delay line 16, microwave switch
17, the nonlinear properties 18 of actual transmission, desirable linearity transmit
19, the echo nonlinear properties 20 of actual reception, desirable echoed signal
21, the target peak in the spectrum curve 22, by the interference peak value of the non-linear generation of frequency modulation
23, by the interference peak value 24 of the non-linear generation of frequency modulation, the single peak value after the evolution linearity correction
25, sweep voltage curve segmentation 1 26, sweep voltage curve segmentation 2
27, sweep voltage curve segmentation 3 28, sweep voltage curve segmentation 4
29, sweep voltage curve segmentation 5 30, sweep voltage curve segmentation 6
31, in the middle of the sweep voltage curve starting point 32, sweep voltage curve variable end-point 1 and
Region of variation
33, in the middle of the sweep voltage curve in the middle of variable end-point 2 34, the sweep voltage curve variable end-point 3 and
And region of variation region of variation
35, in the middle of the sweep voltage curve in the middle of variable end-point 4 36, the sweep voltage curve variable end-point 5 and
And region of variation region of variation
37, the sweep voltage curve after sweep voltage curve terminating point 38, the correction
39, the overlapping segmentation 1 40 of crude sampling sequence, the overlapping segmentation 2 of crude sampling sequence
41, the overlapping segmentation 3 42 of crude sampling sequence, the overlapping segmentation 4 of crude sampling sequence
43, produce coding colony 44, the loop variable zero clearing of end points coordinate
45, the end points encoded radio converts end points 46 in the individuality, connection end point generates the frequency sweep curve
Coordinate figure
47, output sweep voltage curve 48, acquisition difference frequency signal sampled digital sequence
49, carry out the performance that frequency spectrum calculated and extracted spectrum signature 50, calculates the sweep voltage curve
Amount
51, judge whether the linearity reaches requirement 52, preserve and proofread and correct the result
53, loop variable increases progressively 54, whether judgement is estimated each individuality in the colony finishes
55, colony is carried out evolutionary computation
Five, embodiment
Embodiment 1 as shown in Figure 1, timing, before radar levelmeter, place a metal plate perpendicular to the antenna axial direction position, distance between radar levelmeter and the metal plate can be carried out preliminary surveying and is input to having in the related parameter of radar levelmeter, as a reference, can accelerate trimming process, digital signal processor 3 output digital quantity signals are given D/A converter 2, convert voltage signal to, form the control voltage of the voltage controlled oscillator 6 of microwave unit through buffer amplifier 4, excitation voltage controlled oscillator 6 produces the microwave FM signal, the microwave FM signal is passed through coupling mechanism 7 after circulator 10 is launched by antenna 9, the signal that coupling mechanism 7 is coupled out is simultaneously delivered to frequency mixer 11 as the reference signal, target object 8 reflection echos receive through antenna 9, behind circulator 10, also be sent to frequency mixer 11 and reference signal mixing, signal after the mixing forms difference frequency signal by low-pass filter 12 backs, difference frequency signal is sampled by high-speed a/d converter 14 by digital program controlled gain amplifier 13 backs, converting Serial No. to is read by digital signal processor 3, storage in storer 5,3 pairs of sampled digital sequences of digital signal processor are carried out FFT computing and analysis, the bearing calibration of the linear FM radar level meter that utilizes the present invention to evolve to proofread and correct by the keyboard input command is proofreaied and correct then, table 1 has provided the example of an initial population, binary-coded 16 shaping values of initial population by variable end-point X coordinate in the middle of 5 of 6 sections segmentations and Y coordinate, individual amount N=35, variable quantity M=10 in the individuality, variable end-point X in the middle of table 2 has provided 5 that obtain after the evolutionary computation, coordinate figure after the encoded radio of Y coordinate and process convert, and starting point coordinate (0,0) and terminal point coordinate (13383,13383).Figure 10 is the digital quantity preface that each end points coordinate is connected the control sweep voltage that generates
Table 1 initial population example
Sequence number Variable end-point 1 Variable end-point 2 Variable end-point 3 Variable end-point 4 Variable end-point 5
X1’ Y1’ X2’ Y2’ X3’ Y3’ X4’ Y4’ X5’ Y5’
1 16838 5202 26703 2750 28528 21293 1696 19975 413 23236
2 5758 9171 6270 879 23363 29441 18585 10519 26281 7254
3 10113 4434 13870 30989 21087 19484 13455 21472 12389 11688
4 17515 28317 11529 30134 19052 12759 92 19641 11357 5003
5 31051 24582 27499 29752 31235 15400 18288 9349 4887 32203
6 5627 6815 4500 28364 15109 6211 31755 23391 17532 8788
7 23010 4586 8607 4880 17075 4144 29167 30563 1555 23915
8 7419 9653 5808 5629 11755 15335 27412 22184 12299 1199
9 16212 26306 15725 2235 10675 22704 25030 19958 9490 13424
10 4086 7174 12457 21332 288 32520 31717 41 26460 24408
11 2749 18451 16542 24145 32053 23789 24842 27666 24911 6490
12 12767 23448 16474 3356 14157 32121 28572 23363 14183 27655
13 9084 6473 11531 5243 5758 21913 26393 25344 22704 21593
14 12060 32434 17222 3079 5222 23571 27828 2410 17412 13310
15 32225 8193 3952 3988 17488 12369 11805 28635 20961 3072
16 17543 14110 17024 807 18945 2770 3660 1006 20382 12038
17 25089 24748 19894 24979 10294 1594 5838 20068 3608 5087
18 21183 28210 24015 31357 11200 887 9046 26660 5811 1697
19 25137 29320 18247 914 5171 18093 18182 20562 7168 23526
20 25566 32049 11276 21187 14305 32317 23772 29323 20794 7448
21 26966 12956 26278 3540 7951 11188 12354 13764 12286 17497
22 4978 14162 19365 14022 6601 27640 15377 21307 13771 15802
23 20495 4166 8746 10149 23608 4295 14885 7773 27844 19649
24 10311 14997 21976 609 7214 12490 22759 10683 6684 30555
25 11367 7793 18092 29009 6377 25859 22934 9013 11255 25891
26 30054 32310 25851 24833 13865 3106 1903 8216 29227 1020
27 17031 21391 29088 16696 25369 24786 6159 28834 26960 18267
28 13145 19799 29163 5432 27215 17097 26145 15571 27448 14366
29 19882 7926 2231 24999 8030 5062 10045 15241 9086 23408
30 25736 14905 26233 28863 177 27943 26847 2303 8526 12848
31 30524 25885 29732 16369 16849 31247 17401 24754 1211 29762
32 28505 2582 21106 28676 11337 12292 29783 928 26131 22042
33 28394 15610 5411 24077 2699 16846 4167 3417 8645 23252
34 22102 5000 9874 7701 23099 3962 781 32048 11552 31440
35 24851 8052 5448 1691 8531 28479 24287 12018 18627 21810
The row curve.With these frequency sweep curve negotiating D/A converter 2 outputs, can obtain linear modulation frequency.Can enter normal metering system after proofreading and correct end, be installed to the scene.Therefore, adopting method of the present invention to proofread and correct at the scene also is very easily.During normal the use, calculate real material level signal, utilize the mode that shows via display keyboard communication interface unit 1, or export to outside Displaying Meter, or communicate the transmission data by communication interface and outside Displaying Meter by electric current;
Table 2 is proofreaied and correct the result
Starting point Variable end-point 1 Variable end-point 2 Variable end-point 3 Variable end-point 4 Variable end-point 5 Terminal point
X0 Y0 X1 Y1 X2 Y2 X3 Y3 X4 Y4 X5 Y5 X6 Y6
The shaping value of binary coding correspondence Do not have Do not have 13061 4002 3410 9286 11470 12125 5166 5896 15445 21762 Do not have Do not have
Coordinate 0 0 2170 2608 4223 4677 6601 6820 8714 9240 11133 10986 13383 13383
Embodiment 2 as shown in Figure 2, the linear FM radar level meter inside of proofreading and correct has increased microwave delay line 15 and microwave switch 16 evolving, 15 pairs of microwaves of microwave delay line produce certain delaying, and can simulate the echo signal of fixed range, therefore can realize online self-correcting.Digital signal processor 3 output digital quantity signals are given D/A converter 2, convert voltage signal to, form the control voltage of the voltage controlled oscillator 6 of microwave unit through buffer amplifier 4, excitation voltage controlled oscillator 6 produces FM signal, FM signal is passed through coupling mechanism 7 after circulator 10 is launched by antenna 9, coupling mechanism is coupled out two paths of signals simultaneously, one the tunnel delivers to frequency mixer 11 as the reference signal, after producing fixed delay, the delayed line 15 in another road delivers to microwave switch 16, the target echo that receives through antenna 9 also is sent to microwave switch 16 behind circulator 11, microwave switch 16 is subjected to the control of digital signal processor 3, select to the microwave signal of delayed line 15 with through the signal of circulator 10, allow one of them to pass through, signal by microwave switch 16 is in frequency mixer 11 and reference signal mixing, signal after the mixing forms difference frequency signal by low-pass filter 12 backs, difference frequency signal is sampled by high-speed a/d converter 14 by digital program controlled gain amplifier 13 backs, converting Serial No. to is read by digital signal processor 3, storage in storer 5, timing, microwave switch is switched to the state that the microwave signal that allows lag line 15 is passed through, can adopt method of the present invention to proofread and correct, during normal the measurement microwave switch switched to the state that the microwave signal that allows circulator 10 is passed through, 3 pairs of sampled digital sequences of digital signal processor are carried out FFT computing and analysis, after calculating real material level signal, utilize the mode that shows via display keyboard communication interface unit 1, or export to outside Displaying Meter by electric current, or communicate the transmission data by communication interface and outside Displaying Meter.

Claims (1)

1. non-linear evolutional correction method for levelmeter of linear frequency-modulation radar, utilize the evolution principle to the frequency modulation of the voltage controlled oscillator in the radar levelmeter non-linear carry out closed-loop corrected, it is characterized in that: the non-linear frequency modulation that remedies voltage controlled oscillator that utilizes the fm voltage curve is non-linear, the fm voltage curve is divided into plurality of sections, every section end points coordinate is divided certain region of variation, adopt the evolution principle to ask for the end points coordinate of corresponding best fm linearity, with the fm voltage curve after each end points connection can formation correction; Need not measure the frequency or the phase place of high-frequency microwave signal, ask for evaluation function in the evolution principle, realize the nonlinear correction of voltage controlled oscillator frequency modulation by extracting the difference frequency signal spectrum signature; Adopt the fm linearity of the method raising voltage controlled oscillator of overlapping analysis.
CNB2004100924472A 2004-12-23 2004-12-23 Non-linear evolutional correction method for levelmeter of linear frequency-modulation radar Expired - Fee Related CN1295486C (en)

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