CN106405506A - High-frequency sky-ground wave MIMO radar realization method - Google Patents

Abstract

The invention discloses a high-frequency sky-ground wave MIMO radar realization method, and provides an effective solution for the problems of multipath and multi-mode effect and clutter Doppler expansion and the like for a sky-ground wave over-the-horizon radar. A radar system is formed by a plurality of sky wave transmitting stations and a plurality of ground wave receiving stations. Each transmitting station and each receiving station are formed by a plurality of antenna units, so that coexistence of distributed and intensive MIMO radars is realized, and spatial resolution is improved, and multi-angle observation can be realized. By allocating different frequency bands or phases to transmitting subunits, a multiplexed orthogonal effect of transmitting signals is realized. The receiving stations realize pulse compression through frequency mixing and filtering, so that separation of multipath orthogonal signals is realized. The multi-angle observation enlarges detection range and improves detection precision; and MIMO virtual array elements enable the sky-ground wave MIMO radar system to have flexible wave beam formation capability, and influence from different-spatial-orientation multipath and multi-mode effect and clutter expansion due to ionosphere contamination in the sky-ground wave radar can be eliminated properly.

Description

A kind of implementation method of high frequency sky earthwave MIMO radar

Technical field

The invention belongs to Radar Technology field, particularly to a kind of implementation method of high frequency sky earthwave MIMO radar, it is used for The problems such as solve multipath, multimode effect and the clutter dopplerbroadening that sky ground wave OTHR faces.

Background technology

Its earthwave integration over-the-horizon radar belongs to a kind of radar of New System, using bistatic system, works in sky wave Reflection/ground wave diffraction new biography broadcasts pattern, and high band radio wave is mapped to ionosphere, through ionospheric reflection by free space is oblique Afterwards ground (extra large) face is reached by free space, then travel to earthwave receiving point through ground (extra large) face with surface wave forms, receiver can To be remotely from the seashore of transmitter or on naval vessel, there is very big motility, and receiver distance objective is near, receives Target echo stronger.However, because ionosphere has the characteristics such as layering, non-stationary, the complexity of propagation channel makes a day earthwave Multipath, multimode propagation effect and spread clutter that the performance of radar is caused by ionosphere etc. are affected.Simultaneously because its echo Complexity so that de-electrifying absciss layer multipath, multimode effect become world wave radar system, sky earthwave mixed networking systematic study Difficult point.

Multiple-input and multiple-output (MIMO) radar is the study hotspot in current Radar Technology field, is characterized in that each launches sky Line can be with the different waveform of independent transmission, compared with array element transmitting identical waveforms all with phased-array radar, concentrated type MIMO thunder The waveform diversity ability reaching brings more transmitting degree of freedom, in aspect tools such as Faint target detection, AF panel, resolving power raisings There is obvious advantage；Distributed MIMO radar there is space diversity ability, realize multi-angle observation.Domestic at present existing with regard to The research of MIMO sky-wave OTH radar aspect, MIMO radar technology is excellent the aspects such as AF panel, spatial resolution raising Gesture is just gradually being applied in higher-frequency radar, is limited with the intrinsic bottleneck breaking through conventional highfrequency radar.

High frequency sky ground wave radar is in networking mode MODE of operation, it is possible to obtain more marine echo doppler datas. Compared with monotype radar system, this system has more preferable detection performance.However, in the wave radar system of the world, echo many Footpath effect, clutter extends, and still exists the problems such as the spatial resolution of wave beam difference.

Content of the invention

The present invention is directed to the problem that background technology exists, there is provided a kind of implementation method of high frequency sky earthwave MIMO radar, Wave beam forming the feature to different directions transmitting narrow beam can be carried out in sending and receiving end using MIMO radar, solve sky earthwave ultraphotic Away from the multipath that radar faces, multimode effect and clutter dopplerbroadening the problems such as.

For reaching above-mentioned purpose, the present invention adopts the following technical scheme that：

A kind of implementation method of high frequency sky earthwave MIMO radar, this implementation method mainly includes radar antenna formation and transmitting The design of waveform and Echo Processing, comprise the steps,

Step 1：The transmitting of design of Simulation sky earthwave MIMO and receiving antenna array.

Under the requirement of geographical environment permission and detection accuracy, the directional diagram with receiving antenna array is launched by emulation, really Ding Ge sky wave cell site and the element number of array of receiving station；And determine day operating frequency f for earthwave MIMO radar₀Battle array with antenna array Type and aperture.

Step 2：In conjunction with sky earthwave echo feature, selection signal modulator approach, provide ground wave radar system in sky under MIMO system The signal model of system.

The signal making different transmitting subelements by designing transmission signal waveform occupies different frequency ranges or phase place, realizes sending out The multichannel penetrating signal is orthogonal.

Step 3：Matched filtering process is carried out to receipt signal.

Technology using mixing and filtering to realize pulse compression, isolates and just has the multichannel of different initial Doppler frequencies Hand over signal.

The feature of technique scheme is：

Adopt 2 sky wave cell sites and 3 receiving stations in step 1, be the pitching angle information of sky wave direct wave and to transmitting Signal makees Wave beam forming, and design sky wave cell site formation and receiving station's formation are irregular face battle array.

In step 2 sky wave transmitting using Continuous Wave with frequency modulation (Frequency Modulated Continuous Wave, FMCW).The generation of orthogonal signalling can adopt orthogonal frequency linear FM signal (Orthogonal Frequency Division Multiplexing-Linear Frequency Modulated, OFDM-LFM), linear based on time warping Frequency modulation (Linear Frequency Modulated, LFM) signal or the LFM signal based on slow time domain phase code.

In sky earthwave networking, receive and adopt FMICW (Frequency Modulated Interruptrd Continuous Wave, FMICW) waveform, limited by interruption pulse frequency, maximum unam is limited, wrong based on the time The MIMO mechanism of position LFM is no longer applicable, and the MIMO mechanism receiving terminal based on OFDM-LFM is relative complex, therefore transmitted waveform reference Based on the MIMO mechanism of slow time domain phase code LFM, and designed according to sky earthwave echo feature.

Described signal modulating method is that the transmission signal to different transmitting array elements carries out different modulation, and different transmitting are single The signal of unit occupies different frequency ranges or phase place so as to orthogonal in Doppler domain, and the transmission signal of each transmitter unit is corresponding different Doppler frequency shift.

Mixing and filtering technology in step 3, launches the different frequency range of array element or phase value for sky wave, adopts in receiving station Different matched filters is realizing pulse compression.

Described step 2, the signal model process setting up world wave radar system under MIMO system is as follows：

Assume that there are M sky wave transmitting array element signals, each transmitter unit FMCW signal S in cell site 1_mT () represents, wherein m Value in 1～M；Transmitting frequency sweep cycle is T, launches N number of pulse altogether a coherent accumulation time, and repetition rate F is equal to 1/ (NT), in the MIMO mechanism based on slow time domain phase code LFM, using phase code so that difference launches the signal of subelement Occupy different frequency ranges, F is divided into M orthogonal subchannel, a width of F/M of band of each subchannel；

Assume m road transmission signal echo Doppler initial value be f_dm, its transmission signal initially differs as Δ θ_m, then it Meet following relation：

If transmission signal carrier wave is f₀, swept bandwidth is K, and the transmission signal in t n-th cycle of m-th array element is：

Wherein 0≤t<T, n=0～N-1.

Described step 3, the detailed process of mixing and filtering is as follows：

If a certain ground wave receiver has N root reception antenna, the local oscillation signal S of receiving terminal_LOT () is：

Wherein g (t) is interruption pulse；

If the far-field region of array has a point target, transmission signal runs into target and scatters, and echo is received sky Line receives, then the world wave path echo-signal in l array element on reception antenna is expressed as：

Wherein a_R=[a_R1,a_R2,...,a_RN]^T,a_T=[a_T1,a_T2,...,a_TM]^TIt is respectively earthwave receiving array and sky wave The steering vector of emission array, τ is to receive time delay, c_tComplex magnitude for reflected signal；

In receiving station, the form taking mixing and filtering, to realize pulse compression, obtains after mixing and filtering is processed：

Wherein

Corresponding to Doppler domain, the corresponding echo initial Doppler of m root sky wave transmission signal will be located at

For different sky wave transmission signals, its initial Doppler frequency is different, so realizes multichannel transmission signal Separation in receiving station.

Compared with prior art, advantage of the invention is that：

The implementation method of the high frequency sky earthwave MIMO radar that the present invention provides, by designing transmitting and the reception of MIMO radar Antenna array and Orthogonal injection waveform are it is achieved that application in the wave radar system of the world for the MIMO mechanism.This system achieves MIMO radar is distributed with concentrated type and deposits, not only can multi-angle observation but also improve spatial resolution.The observation of multi-angle is expanded Big investigative range simultaneously improves detection accuracy, and MIMO Virtual array enables world wave radar system to possess flexible Wave beam forming Power, can suitably eliminate multipath effect, multimode effect and the ionosphere contamination band being derived from different spaces orientation in day ground wave radar The impact of the spread clutter coming.

Brief description

Fig. 1 is transmitted waveform design diagram；

Fig. 2 is radar system operating diagram；

Fig. 3 is sky earthwave mixed networking echo range-Doppler spectrum during the transmitting of sky wave list station；

Fig. 4 is sky earthwave mixed networking system echoes range-Doppler spectrum during the transmitting of sky wave dual station.

Specific embodiment

With reference to example, the present invention is described in further detail, and enforcement example described herein is merely to illustrate With the explanation present invention, it is not intended to limit the present invention.

A kind of implementation method of high frequency sky earthwave MIMO radar, this implementation method mainly includes radar antenna battle array and transmitted wave The design of shape and Echo Processing, specifically include following steps,

Step 1：The transmitting of design of Simulation sky earthwave MIMO and receiving antenna array.Allow and detection accuracy in geographical environment Under requirement, by emulation transmitting and the directional diagram of receiving antenna array, determine the element number of array of each sky wave cell site and receiving station；And Determine operating frequency f of sky earthwave MIMO radar₀Formation and aperture with antenna array.

Experiment is related to 2 sky wave cell sites and 3 receiving stations, is the pitching angle information of sky wave direct wave and to transmission signal Make Wave beam forming, design sky wave cell site formation and receiving station's formation are irregular face battle array.

Step 2：In conjunction with sky earthwave echo feature, selection signal modulator approach, provide ground wave radar system in sky under MIMO system The signal model of system.Design transmission signal waveform makes the signal of different transmitting subelements occupy different frequency ranges or phase place, realizes The multichannel of transmission signal is orthogonal.

Assume that there are M sky wave transmitting array element signals, each transmitter unit FMCW signal S in cell site 1_mT () represents, wherein m Value in 1～M.Transmitting frequency sweep cycle (pulse repetition period) is T, in a coherent accumulation time (Coherent Integration Time, CIT) launch N number of pulse altogether, repetition rate F is equal to 1/ (NT), based on slow time domain phase code In the MIMO mechanism of LFM, using phase code so that the signal of different transmitting subelement occupies different frequency ranges, F is divided into M Individual orthogonal subchannel, a width of F/M of band of each subchannel.

Assume m road transmission signal echo Doppler initial value be f_dm, its transmission signal initially differs as Δ θ_m, then it Meet following relation：

Transmitted waveform design is as shown in Figure 1.

If transmission signal carrier wave is f₀, swept bandwidth is K, and the transmission signal in t n-th cycle of m-th array element is

Wherein 0≤t<T, n=0～N-1；

Step 3：Matched filtering process is carried out to receipt signal.Technology using mixing and filtering to realize pulse compression, point Separate out the multichannel orthogonal signalling with different initial Doppler frequencies.

Assume that a certain ground wave receiver has N root reception antenna, the local oscillation signal S of receiving terminal_LOT () is：

Wherein g (t) is interruption pulse.

Assume that the far-field region of array has a point target, transmission signal runs into target and scatters, and echo is received Antenna receives, then the world wave path echo-signal in l array element on reception antenna is represented by：

Wherein a_R=[a_R1,a_R2,...,a_RN]^T,a_T=[a_T1,a_T2,...,a_TM]^TIt is respectively earthwave receiving array and sky wave The steering vector of emission array, τ is to receive time delay, c_tComplex magnitude for reflected signal.

In receiving station, the form taking mixing and filtering, to realize pulse compression, obtains after mixing and filtering is processed

Corresponding to Doppler domain, the corresponding echo initial Doppler of m root sky wave transmission signal will be located at

Wherein

For different sky wave transmission signals, its initial Doppler frequency, by difference, so can achieve multichannel transmitting letter Number the separation in receiving station.

Radar system using up-to-date development carries out field test, and concrete approach is as follows：

Experiment is related to two folded Clutter in Skywave Radars stations and three ground wave radar stations, and sky wave cell site is located at Hubei Chongyang and lake respectively Northern Wuhan, distance about 100Km；Three earthwave erect-positions in Dongshan in Fujian, Longhai City and Chi Hu, apart from sky wave cell site about 900Km. Operation principle is shown in accompanying drawing 2.

Double frequency multichannel ground wave radar employed in experiment works in double frequency pattern, interrupts continuous wave using linear frequency modulation Waveform, system operating frequency is in 7.5～8.5MHz and two frequency ranges of 12～13.5MHz.Sky wave multichannel emission system has five Independent transmission channel, the transmitted waveform (comprising frequency, amplitude and phase place) of each passage can independent control, each passage is maximum Transmission power is 2Kw.

Sky wave transmitting adopts log-periodic antenna, and Wuhan Railway Station has 1 road transmitting antenna, and there are 5 road transmitting antennas, each sky in Chongyang station Line is spaced 20m, and earthwave transmitting adopts ternary yagi aerial.

Receiving array is located at ground wave radar station, receives radar echo signal using 8 yuan of face battle arrays.The swept-frequency signal cycle in experiment It is set to 0.125s, swept bandwidth is 30KHz.

Accompanying drawing 3 gives 20 days 10 January in 2015:The sky earthwave mixing group that during 41 points of sky wave list station transmittings, Longhai City station receives Net echo distance-Doppler figure.Five, Chongyang station antenna is launched simultaneously, forms centralized mimo system, and Longhai City station receives.Sky wave Operating frequency 12.47MHz, each 1Kw of transmission power, frequency sweep cycle is 0.125s, and the coherent accumulation time is taken as 64s.Each sky wave is sent out The initial difference penetrating channel signal is Δ θ_mIt is respectively -150 °, -90 °, -31 ° ,+27 ° ,+86 °, in the echo spectrum shown in accompanying drawing 3 In, corresponding sky earthwave Echo Doppler Frequency initial value is followed successively by -3.3Hz, -2Hz, -0.7Hz, 0.6Hz, 2Hz.

The ocean Bragg peak of world wave path is high-visible, and single order Bragg peak accounts for 12 distance elements, with respect to ground Ripple has obvious broadening.So, in receiving terminal, just it has been easily achieved the separation of transmission signal.

Accompanying drawing 4 gives 20 days 11 January in 2015:The sky earthwave networking that during 46 points of sky wave dual station transmittings, Longhai City station receives is returned The pitch of waves is from-image of colorful Doppler.

Chongyang sky wave cell site 4 antenna is launched simultaneously, and Wuhan sky wave cell site single antenna is launched, and is formed distributed Mimo system, Longhai City station internal loopback, Chi Hu station, Dongshan station receive simultaneously.Sky wave operating frequency 12.47MHz, transmission power is each 1Kw, frequency sweep cycle is 0.125s, and the coherent accumulation time is taken as 64s.The initial difference of Chongyang each transmission channel signal is Δ θ_mPoint Not Wei -150 °, -31 ° ,+27 ° ,+86 °, Wuhan Railway Station initially differ for -90 °, earthwave transmitting initial difference be+150 °, then exist In echo spectrum as shown in Figure 4, corresponding sky earthwave Echo Doppler Frequency initial value be followed successively by -3.3Hz, -2Hz, - 0.7Hz, 0.6Hz, 2Hz, the wherein left side the 2nd tunnel (- 2Hz) are the echo-signal of Wuhan Railway Station sky wave, and earthwave internal loopback echo is many General Le frequency initial value is 3.3Hz.

The ocean Bragg peak of world wave path is high-visible, and single order Bragg peak accounts for 20 distance elements, than earthwave Many.Due to the difference of Liang Ge sky wave cell site distance, their direct wave positions can be clear that on echo spectrum not With.

Field experimentation result illustrated above, preliminary experimental result is suitable to this signal model to sky earthwave mimo system ?.

Claims (6)

1. a kind of implementation method of high frequency sky earthwave MIMO radar is it is characterised in that comprise the steps：

Step 1：The transmitting of design of Simulation sky earthwave MIMO and receiving antenna array；

Under the requirement of geographical environment permission and detection accuracy, by the directional diagram of emulation transmitting and receiving antenna array, determine respectively Sky wave cell site and the element number of array of receiving station；And determine day operating frequency f for earthwave MIMO radar₀With the formation of antenna array with And aperture；

Step 2：In conjunction with sky earthwave echo feature, selection signal modulator approach, set up world wave radar system under MIMO system Signal model；

The signal making different transmitting subelements by designing transmission signal waveform occupies different frequency ranges or phase place, realizes transmitting letter Number multichannel orthogonal；

Step 3：Matched filtering process is carried out to receipt signal；

Technology using mixing and filtering to realize pulse compression, isolates the orthogonal letter of multichannel with different initial Doppler frequencies Number.

2. a kind of high frequency sky according to claim 1 earthwave MIMO radar implementation method it is characterised in that：

Described step 1, using 2 sky wave cell sites and 3 receiving stations, is the pitching angle information of sky wave direct wave and to transmitting letter Number make Wave beam forming；Sky wave cell site formation and receiving station's formation are irregular face battle array.

3. a kind of high frequency sky according to claim 2 earthwave MIMO radar implementation method it is characterised in that：

Signal modulating method described in step 2 is that the transmission signal to different transmitting array elements carries out different modulation, different transmittings The signal of subelement occupies different frequency ranges or phase place so as to orthogonal in frequency domain or Doppler domain, and the transmitting of each transmitter unit is believed Number different Doppler frequency shift of correspondence；Sky wave transmitting adopts Continuous Wave with frequency modulation FMCW.

4. a kind of high frequency sky according to claim 3 earthwave MIMO radar implementation method it is characterised in that：

Mixing and filtering technology described in step 3, launches the different frequency range of array element or phase value for sky wave, adopts in receiving station Different matched filters is realizing pulse compression.

5. a kind of high frequency sky according to claim 4 earthwave MIMO radar implementation method it is characterised in that：

Described step 2, the signal model process setting up world wave radar system under MIMO system is as follows：

Assume that there are M sky wave transmitting array element signals, each transmitter unit FMCW signal S in cell site 1_mT () represents, wherein m is in 1～M Interior value；Transmitting frequency sweep cycle is T, launches N number of pulse altogether a coherent accumulation time, and repetition rate F is equal to 1/ (NT), In MIMO mechanism based on slow time domain phase code LFM, using phase code so that the signal of different transmitting subelement occupies not Same frequency range, F is divided into M orthogonal subchannel, a width of F/M of band of each subchannel；

Assume m road transmission signal echo Doppler initial value be f_dm, its transmission signal initially differs as Δ θ_m, then they are expired Enough to lower relation：

$f_{dm}=\frac{{\mathrm{\&Delta;\&theta;}}_m}{2\mathrm{\&pi;}T}$

If transmission signal carrier wave is f₀, swept bandwidth is K, and the transmission signal in t n-th cycle of m-th array element is：

$S_m\left(t\right)=cos\&lsqb;2\mathrm{\&pi;}(f_0-\frac{Kt}{2})t+{\mathrm{n\&Delta;\&theta;}}_m\&rsqb;,$

Wherein 0≤t<T, n=0～N-1.

6. a kind of high frequency sky according to claim 5 earthwave MIMO radar implementation method it is characterised in that：

Described step 3, the detailed process of mixing and filtering is as follows：

If a certain ground wave receiver has N root reception antenna, the local oscillation signal S of receiving terminal_LOT () is：

$S_{LO}\left(t\right)=cos\&lsqb;2\mathrm{\&pi;}(f_0-\frac{Kt}{2})t\&rsqb;\&lsqb;1-g\left(t\right)\&rsqb;,0\&le;t<T$

Wherein g (t) is interruption pulse；

If the far-field region of array has a point target, transmission signal runs into target and scatters, and echo is connect by reception antenna Receive, then the world wave path echo-signal in l array element on reception antenna is expressed as：

$S_{Rl}\left(t\right)=c_t{a}_{Rl}\underset{m=1}{\overset{M}{\&Sigma;}}{a}_{Tm}{S}_m(t-\mathrm{\&tau;})\&lsqb;1-g\left(t\right)\&rsqb;$

Wherein a_R=[a_R1,a_R2,...,a_RN]^T,a_T=[a_T1,a_T2,...,a_TM]^TIt is respectively earthwave receiving array and sky wave transmitting battle array The steering vector of row, τ is to receive time delay, c_tComplex magnitude for reflected signal；

In receiving station, the form taking mixing and filtering, to realize pulse compression, obtains after mixing and filtering is processed：

$\begin{array}{c}{S}_{Il}\left(t\right)=lowpass\left\{S_{LO}\left(t\right)S_{Rl}\left(t\right)\right\}\\ =a_{Rl}\underset{m=1}{\overset{M}{\&Sigma;}}{c}_t{a}_{Tm}\cos \&lsqb;2\mathrm{\&pi;}(f_0\mathrm{\&tau;}-Kt\mathrm{\&tau;}+\frac{{\mathrm{K\&tau;}}^2}{2})+{\mathrm{n\&Delta;\&theta;}}_m\&rsqb;\\ =a_{Rl}\underset{m=1}{\overset{M}{\&Sigma;}}{c}_t{a}_{Tm}\cos ({\mathrm{\&phi;}}_{\mathrm{\&tau;}}+{\mathrm{n\&Delta;\&theta;}}_m)\end{array}$

Wherein

Corresponding to Doppler domain, the corresponding echo initial Doppler of m root sky wave transmission signal will be located at

$f_{dm}=\frac{d\&lsqb;({\mathrm{\&phi;}}_{\mathrm{\&tau;}}+{\mathrm{\&Delta;\&theta;}}_{m}n)\&rsqb;}{dt}=\frac{{\mathrm{\&Delta;\&theta;}}_m}{2\mathrm{\&pi;}T}$

For different sky wave transmission signals, its initial Doppler frequency is different, so realizes connecing of multichannel transmission signal Receive the separation at station.