RU2347235C2 - Method of formation coherent frequency modulated signal for radar stations with periodic fm modulation and device for its realisation - Google Patents

Abstract

FIELD: physics; measuring.

SUBSTANCE: prospective invention concerns the radar-tracking measuring technics and range-frequency and also in radar measuring equipment and can be used in radar stations with the continuous periodic radiation with any triangular frequency modulation (FM), measuring a standing of the purposes in coordinates. The specified effect is reached at the expense of generating of digital read-out during the fixed moments of time, their transformation to discrete analogue readout and low-frequency filtration of discrete analogue readout with reception of analogue quarter-phase (sinus and cosine) FM on a video to frequency of signals with triangular frequency modulation with a demanded continuance of modulation and with deviation in m time of smaller demanded deviation of a sounding signal, transport quarter-phase FM on video frequency of a signal on higher carrier frequency with the help of the quarter-phase balancing mixer, multiplication of frequency of the gained signal in m time, amplification of a signal to demanded power in the given frequency band.

EFFECT: measurement accuracy increase in radar stations with periodic frequency - modulated (FM) signal with any triangular modulation at the expense of maintenance of high linearity of change of a carrier frequency in time with possibility of coherent accumulation between periods.

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Description

The present invention relates to radar measuring technology and can be used in radar with continuous periodic radiation with arbitrary triangular frequency modulation (FM), which measures the position of targets in the coordinates range - frequency, as well as in radar mapping type RSA.

Known radar range measuring devices using a continuous linearly frequency-modulated signal (LFM) as a probe signal, in which information about the measured range R is extracted from the frequency difference Δf of the probe signal and the signal reflected by the target [1, p. 289]. When working on one branch of the modulating signal, the estimate of the range from the radar to the target R is calculated by the formula:

R = cΔf / 2K _LChM

where K _LCHM = Δf _dev / T _and is the steepness of the frequency tuning of the probe signal in the measuring interval T _{and the} modulating function,

c is the speed of light

Δf _dev - the frequency deviation of the probe signal in the measuring interval.

Since the relative measurement error is also determined by the relative steepness error K _lm , it is obvious that the nonlinearity of the modulation of the frequency γ of the probing signal must correspond to the radar resolution in range δ _R :

γ <1 + δ _R / R _max ,

where R _max - the maximum measured radar range.

A known method of generating a periodic LFM signal in a radar measuring distance [2]. According to the LFM method, a probe signal is generated by a generator whose frequency is controlled by voltage. The current carrier frequency of the probe signal with the help of a local oscillator with a reference frequency is transferred to an intermediate one, divided by an integer, then it is measured and compared with the current calculated value. Based on the error signal, the processor corrects the digital sequence that is converted to an analog voltage that controls the frequency of the generator.

The disadvantage of this method is the inability to reproduce the law of modulation of the probing signals of different repetition periods accurate to phase, respectively, the impossibility of conducting inter-period coherent signal processing.

A known method of generating a chirp signal [3], in which the frequency of the output chirp signal is obtained by multiplying the frequency of the primary chirp signal with less deviation by an integer number of times. The primary LFM signal is generated using a voltage controlled oscillator. To control the law of modulation of the current frequency of the primary signal, it is divided by an integer number of times, measured, compared with the current calculated one, an error signal is generated and the digitized calculated sequence is corrected, which controls the frequency of the primary signal generator through digital-to-analog conversion.

The disadvantage of this method is the incoherence of the probe signals of different periods. Frequency feedback does not ensure the repetition of the law of modulation of the frequency of the primary signal with an accuracy of up to phase; accordingly, it does not allow for inter-period coherent signal processing, and clarifies the Doppler shift and range to the target.

In the method of generating a periodic FM probing signal with symmetric triangular modulation described in [4] and used in a radar measuring the range and speed of approach with a target, the frequency of the output generator is controlled by a periodic modulating voltage, which is calculated, entered into memory, and read at calculated times are converted to analog and filtered in a low-pass filter. The nonlinearity of the modulation characteristics of the output generator is compensated by the calculation of the shape of the modulating voltage. A feature of the method is that in order to reduce the amplitude of the ripples of the modulating analog voltage obtained from the digitized values, respectively the spurious components of the spectrum of the difference frequency of the probing and reflected signals, the memory is read at the calculated time points that are not equidistant from each other.

The disadvantage of this method is the neglect of possible departures of the modulation characteristics of the output generator associated with aging, changes in temperature, voltage. The inter-period coherent signal processing mode is also not possible here.

In the method of generating a periodic FM signal with symmetric triangular modulation [5], taken as a prototype, the modulation voltage of the carrier frequency of the output generator is generated by generating digital samples at fixed times, converting them to discrete analog samples and low-pass filtering, while digital The readings of the modulating voltage are made recursively as the sum of the current voltage of the previous period and the corrective one. To calculate the current correction voltage as a function of the relative deviation of the instantaneous period of the difference frequency from the average, measure the instantaneous and average period of the difference frequency.

The disadvantage of this method is that FM signals of different periods are not coherent and cannot be used with coherent inter-period accumulation. In addition, ensuring high linearity of the frequency modulation to reduce the error of range measurement is quite difficult, due to the need to obtain a reference signal delayed relative to the probing signal, from which the correction voltage is calculated. For a radar operating with a multipurpose reflected signal, including for an extended target, to create a reference signal, a probe signal delay device, a separate mixer for obtaining the difference frequency between the reference and probing signals, and devices for measuring the current instantaneous and average periods of the difference frequency are required. The relative measurement error of the order of 0.1% achieved by this method is insufficient when measuring large distances with high resolution and accuracy.

The aim of the invention is to increase the measurement accuracy in a radar with a periodic frequency-modulated signal with arbitrary triangular modulation by providing a high linearity of the carrier frequency in time with the possibility of inter-period coherent accumulation.

This goal is achieved by the fact that the method of generating a probe periodic FM signal for a radar measuring the position of targets in the coordinates range - frequency, including the generation of digital samples at fixed points in time, converting them into discrete analog samples and low-pass filtering of discrete analog samples, generating output frequency modulated probing signal, receiving the reflected signal, mixing it with part of the probing power, extracting the difference frequency signal and the measurement interval, which is part of the modulation period, is characterized in that the sequence of operations for generating digital samples at fixed points in time, converting them into discrete analog samples and low-pass filtering provides analog quadrature (sine and cosine) frequency-modulated signals with a triangular frequency modulation with the required modulation period and deviation Δω _is m times less than the required deviation of the probe signal Δω _s , where m is an integer lo, the formation of a frequency-modulated signal probing involves the transfer of quadrature frequency modulated signal at video frequency to a higher carrier using quadrature balanced mixer, frequency multiplication of the received signal in the m times, the signal gain to the desired power in a predetermined frequency band _of Δω.

To ensure fine tuning of the carrier frequency of the probe signal and increase the power of the signal supplied to the frequency multiplier by a factor of m, an additional shift of the carrier frequency of the multiplied signal is performed using a PLL shift mixer.

According to the proposed method, a sequence of quadrature (sine and cosine) digital samples of a periodic video frequency FM signal with a triangular modulation is formed, which at fixed times is converted into discrete quadrature analog samples and filtered by a low-pass filter. The frequency modulation period of the quadrature signals U _c (ω _in , t) and U _s (ω _in , t) corresponds to the required modulation period of the probe signal T _M. The frequency of quadrature signals is described by the expression:

where k ₁ and k ₂ are the steepnesses of the FM modulation of the signal on different sides of the triangle,

n is the number of the period of the modulation law of the probe signal,

-k ₁ T ₁ = k ₂ (T _M -T ₁ ).

In this case, the frequency deviation of the generated quadrature video signal Δω is selected m times less than the required deviation of the probing signal Δω _s , where m is an integer.

Of the quadrature analog voltages U _c (ω _a, t) and U _s (ω _a, t) and a voltage with a frequency offset _{U o (t) = cos (} ω _a t + φ _o) entering the quadrature balanced mixer formed primary FM signal at a frequency ω _kbs (t) = (ω _о + ω _в (t)

U _kbs (t) = cos [ω _kbs (t) t + φ _о ],

which is additionally shifted in frequency in the PLL shift mixer in order to both increase the spectral purity of the signal, its power, and provide the possibility of adjusting the output carrier frequency of the probe signal. The signal after the shear mixer is described by the expression:

U _sdv (t) = cos [(ω _sdv + ω _kbs (t)) t + φ _о + φ _sdv ].

Further, by multiplying the frequency m times in the power amplification and receive probe at a frequency ω _n = m (ω + ω _{sh about} + ω _a (t)) with _nine deviation Δω = 2π Δf = mΔω _{in nine.}

The invention is illustrated by a further description and drawings of the radar that implement this method:

Figure 1 - structural diagram of the radar.

In figure 1, the following notation:

1 - Shaper quadrature video frequency FM signal (FCFM),

2 - Quadrature balanced mixer (KBS),

3 - The first band-pass filter (PF1),

4 - Shear mixer (SMSD),

5 - Frequency Synthesizer (MF),

6 - Frequency Multiplier (Uch),

7 - Power Amplifier (Um),

8 - The second band-pass filter (PF2),

9 - Calculator (WU),

10 - low frequency amplifier (VLF),

11 - Mixer (cm),

12 - Directional coupler (BUT),

13 - Analog-to-digital Converter (ADC),

14 - The second (receiving) antenna (A2).

15 - The first (transmitting) antenna (A1),

The prototype of the radar shown in FIG. 1, which implements a method for generating a coherent periodic FM signal, is a radar [3, FIG. 14], comprising a directional coupler 12, a mixer 11, a low-frequency amplifier 10, an analog-to-digital converter 13, first ( transmitting) antenna 15, the input of which is connected to the first output of the directional coupler 12, the second (receiving) antenna 14, the output of which is connected to the second input of the mixer 11, characterized in that a frequency synthesizer 5 is connected in series with it, shear mixer 4, frequency multiplier 6, power amplifier 7, second bandpass filter 8, the output of which is connected to the input of the directional coupler 12, sequentially connected quadrature balanced mixer 2 and the first bandpass filter 3, the output of which is connected to the second input of the shear mixer 4, quadrature shaper video FM signal 1, the first and second outputs of which are connected to the inputs of the same name as the quadrature balanced mixer 2, calculator 9, the second output of which is connected to the second input of the quad shaper frequency video frequency FM signal 1, the first, second and fourth outputs of the frequency synthesizer 5 are connected to the first input of the quadrature video frequency FM signal shaper 1, the third input of the quadrature balanced mixer 6 and the second input of the analog-to-digital converter 13, respectively, the output of which is connected to the third input of the calculator, the first input - the output of the computer 9 is the input - output of the radar.

As the shaper of the quadrature video frequency FM signal 1, the AD9854 chip from Analog Devices can be used.

As a quadrature balanced mixer 2 can be used chip NMS 495 LP company Hittite Microwave Corp.

As a shift mixer 4, a PLL-based frequency shift scheme can be used [6, p. 63, Fig. 3.2 g].

Frequency multiplier 6 can be constructed according to the amplification-multiplier circuit [7].

The computer 9 can be performed on the basis of the on-board computer [8].

The remaining elements of the radar (frequency synthesizer 5, low-frequency amplifier 10, mixer 11, directional coupler 12, antennas 14 and 15) are widely used in radar and do not require explanation for implementation.

Radar (figure 1) works as follows. The reception of commands and information from an external control system, the organization of the preparation of the radar for operation, the secondary processing of the reflected signal with the assessment of the range and radial speed of the targets, the issuance of the measured information in the control system is performed by the calculator 9. The algorithm of its operation is shown in figure 2

Полученная матрица комплексных амплитуд Q(t_i,f_i) сигнала преобразуется в матрицу мощностей сигнала P(t_i,f_j) в тех же координатах по формуле:The start of the radar operation is initiated by the inclusion command, data on the angle between the direction of sight and the aircraft velocity vector coming to the first input - the output from the external control system (item 16, figure 2). The calculator 9 for the given operating conditions calculates the parameters of the frequency modulation of the probe signal (T _m , T ₁ , Δf _c ) and enters them into the shaper of the quadrature video frequency FM signal 1 through the second input (pos. 17, Fig. 2). In turn, the driver of the quadrature video frequency FM signal 1, using the clock frequency coming from the first output of the frequency synthesizer 5, generates analog quadrature voltages U _c (ω _in , t) and U _s (ω _in , t) coming in the first and second inputs of the quadrature balanced mixer 2. The quadrature balanced mixer 2 primary FM signal is formed by shifting the FM video signal to a frequency ω _2, coming from the second output of the frequency synthesizer 5. _kbs ω 2 = ω ₂ The output frequency of the quadrature balanced mixer + ω _in the first polo ovogo filter 3 is further shifted in frequency in the mixer 4, a shift to the frequency ω ₃ formed on the third output of the frequency synthesizer 5. The result of multiplying the output frequency shift of the mixer 4 in the m times 6 frequency multiplier, the gain in the power amplifier 7 and the band-pass filtering the output of the second bandpass filter 8 receive a probe signal at the frequency ω _n = m (ω _o + ω + ω _{sh in} (t)) with _nine deviation Δω 2 = m π Δ / f _B. The probe signal passing through the directional coupler 12 to the first (transmitting) antenna 15 is emitted in the direction of the target. The reflected signal is received by the receiving antenna 14, fed to the mixer 11, where it is mixed with a part of the sounding signal power taken from the second output of the directional coupler 12. As a result, the difference frequency signal (beat signal) is received at the output of the mixer 11, which after amplification in the low-frequency amplifier 10 is digitized by an analog-to-digital converter 13 with a clock frequency f ₄ coming from the fourth output of the frequency synthesizer 5, and is fed to the third input of the calculator 9, where it is memorized, its internal period the first and the interperiodic weight processing, the two-dimensional Fourier transform, as a result of the first transformation, the periodically compresses the signal in range over an interval of duration T _and starting from τ _о (maximum delay of the reflected signal) to T ₁ , after which the Doppler filtering (interperiodic accumulation) is performed by the second transformation signal) for N periods of signal modulation. The result is the complex amplitude Q (t _i , f _i ) of the reflected signal in coordinates time (t _i ) is the frequency (f _j ), i is the sample number of the beat signal on the interval T _and ,

The resulting matrix of complex amplitudes Q (t _i , f _i ) of the signal is converted to the signal power matrix P (t _i , f _j ) in the same coordinates by the formula:

P (t _i , f _j ) = | Q (t _i , f _j ) | ²

and is used for threshold detection of the target signal (pos.20 of figure 2):

For scene points (t _i , f _j ), where S (t _i , f _j ) = 1 (a signal is detected), the calculator 9 determines the range D _{i, j} and the radial velocity V _{i, j of the} detected target (item 21 of FIG. 2) according to the formulas:

D _{i, j} = c (t _i -f _j / k ₁ ) / 2,

V _{i, j} = f _j λ / 2,

where λ is the wavelength of the probe signal.

The measured coordinates of the detected targets (D _{i, j} , V _{i, j} ) are output to the control system through the information bus connected to the first input - the output of the calculator 9 (pos.22, Fig.2).

The technical advantage of the proposed method for generating an FM signal and a radar that implements it before the prototype is both the high linearity of the FM periodic signal with triangular modulation (correspondingly higher accuracy) and the coherence of the probe signal in different periods of repetition of the modulation (provided by highly stable frequencies of the frequency synthesizer and direct digital synthesis of a quadrature FM signal at a video frequency using digital samples in memory or calculated in real time). Changes in supply voltages, temperatures, and aging cannot lead to a relative change in the carrier frequency of the probe signal by more than 10 ^-4 (determined by the parameters of the quartz reference frequency in the frequency synthesizer), which is an order of magnitude less than in the prototype method. The modern element base allows you to receive a probing signal with a given linearity on the basis of microchips and nodes that have significantly lower overall mass characteristics than in the prototype (a reference signal is not required, for which a microwave device for delaying the probing signal is required, a separate mixer to obtain the difference frequency between reference and probing signals, devices for measuring the current instantaneous and average periods of the difference frequency.The proposed solution for the formation of the FM signal is not known but it also meets the criteria of novelty and inventive step.In particular, digital samples converted to analog voltage are not used in this method to modulate the frequency of the output generator, but are an FM video signal, which is converted by a frequency shift and subsequent multiplication by an integer number of times In this case, the probe signal is coherent in different repetition periods by ensuring the repeatability of the modulation law of the probe signal Ala accurate to phase.

Using the information presented in the application materials, the proposed radar can be manufactured according to the existing technology known in the radio industry, based on well-known components and used to measure the position of targets in the coordinates of the range - Doppler frequency.

Information sources

1. V.M.Svistov. Radar signals and their processing. M .: Sov. Radio. 1977, p. 289, Fig. 6.10.

2. US patent No. 5387918 from 05.07.95, CL. G01S 13/32. Method and Arrangement for measuring distances using the reflected beam principle.

3. US patent No. 5546088 from 08.13.96, cl. G01S 13/18. High-precision radar finder.

4. Japanese Patent No. 20002244918 of 08.25.2003, cl. G01S 13/34. Waveform generation method, waveform generation program, waveform generation cirquit and radar device.

5. Patent of Russia No. 2234716 dated 03/04/2003, cl. G01S 13/34. A method of generating a frequency modulated signal for a rangefinder with periodic frequency modulation.

6. A.V. Ryzhkov, Popov V.N. Frequency synthesizers in radio technology. M .: Radio and communication. 1991, p. 63, fig. 3.2 g

7. The UUTS-ARM module, MAVI 600-0672. OJSC "UPKB" Detail "Kamensk-Uralsky, Sverdlovsk region.

8. On-board computer VB-480-01. Operation manual NKShR.466535.020 RE.

Claims (3)

1. The method of generating a probing periodic frequency-modulated (FM) signal for a radar station that measures the position of targets in the coordinates range - frequency, which consists in generating a modulating signal in the form of its digital samples at fixed points in time, convert the digital samples into discrete analog samples of a modulating signal, low-pass filtering of discrete analog samples is carried out, an FM output probe signal is generated, characterized in that when generated The use of a modulating signal in the form of digital samples, converting digital samples to discrete analog signals of a modulating signal and performing low-pass filtering of discrete analog signals provides analog quadrature sine and cosine FM signals on the video frequency of signals with a triangular frequency modulation with the required modulation period and with deviation Δω _in , m at a time _of a desired deviation Δω probing signal, where m - is an integer, when forming the output signal of the FM sounding provide transfer quadrature sine and cosine FM signals at video frequency to a higher carrier frequency via the quadrature balanced mixer is multiplied by the frequency of the received signal at m time and amplify the signal to a desired power in a predetermined frequency band _of Δω. 2. The method according to claim 1, characterized in that, before multiplying the signal frequency by a factor of m, it is additionally shifted in frequency using a shift circuit based on a phase-locked loop. 3. The device that implements the method according to claim 2, containing a series-connected directional coupler and a transmitting antenna, characterized in that a frequency synthesizer is introduced in series, the third output of which is connected in series with a shift mixer, frequency multiplier, power amplifier, second band-pass filter, output which is connected to the input of the directional coupler, series-connected quadrature balanced mixer and the first band-pass filter, the output of which is connected to the second input of the mixture shifter, a shaper of a quadrature video frequency-modulated (FM) signal, the second input of which is the input of the frequency modulation parameters of the probing signal, and the first and second outputs of which are connected to the same inputs of the quadrature balanced mixer, the first and second outputs of the frequency synthesizer are connected respectively to the first input the shaper of the quadrature video frequency FM signal and the third input of the quadrature balanced mixer, the first output of the frequency synthesizer being the output of the clock signal, the second and third outputs of the frequency synthesizer are the outputs of the signals of the corresponding frequency shifts.

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