RU2066060C1 - Method of map-making with the aid of synthetic aperture - Google Patents

Abstract

FIELD: medicine, generation of picture of section of internal organs of man and of media and volumes of matter opaque in optical range to expose their internal structures. SUBSTANCE: proposed method of map-making consists in probing of space with relative motion by monochromatic continuous signal, in separation of signal reflected from object by K range owing to sliding convolution of received Doppler signal with K reference signals presenting signals specularly inverted in time, reflected from point objects from different K ranges. Amplitudes of signals distributed by K ranges are re-coded into contrast or color signals and are slewed around in coordinates of distance from trajectory of relative motion and distance covered by trajectory. EFFECT: improved authenticity of method. 3 cl, 11 dwg

Description

 The invention relates to locations in the ultrasonic or radio range, and can be used to obtain a picture of the cross section of the internal organs of a person for the purpose of diagnosis, as well as for mapping opaque media in the optical range or volumes of a substance, to identify their internal and hidden from the eyes structure.

 Currently, the method of mapping the earth's surface using a synthesized aperture is widely known (A. P. Reutov, B. A. Mikhailov, G. S. Kondratenkov, B. A. Boyko. Side-scan radars. M. Sov. Radio, 1970 ; V.N. Antipov, V.T. Goryainov, I.N. Kulik, et al. Radar stations with digital synthesis of the antenna aperture. M. Sov. Radio, 1988; US patent N 3392385, class 343-5).

 The known method of mapping the earth’s surface, used in side-scan radars (radars), involves emitting a coherent pulse sounding signal, gating the reflected signal over time, that is, distributing the signal over the range channels, compressing the processed signal (synthesizing the aperture) in each range channel, modulating beam brightness and the scan image in the coordinates of the distance from the projection of the trajectory onto the ground and the distance along the trajectory.

 This method is described in the book of A.P. Reutov, B.A. Mikhailov, G.S. Kondratenkov, B.V. Boyko. Side-view radars. M. Sov. radio, 1970, p. 98 107, and a digital device that implements the well-known mapping method is described in detail in the book of V. N. Antipov, V. G. Goryainov and others. Radar stations with digital synthesis of the antenna aperture. M. Radio and Communications, 1988, p. 61, fig. 28. This device is adopted as a prototype of the proposed method of mapping. The device diagram is shown in FIG. 1, where indicated: 1 receiver; 2 5 gating cascades; 6 9 - analog-to-digital converters; 10 memory; 11 block fast Fourier transform (FFT); 12 sample multiplier; 13 memory with reference coefficients of the function; 14 block inverse fast Fourier transform (OBPF); 15 block calculating the model of complex samples; 16 is a digital display circuit; 17 emitter; 18 modulator.

 The device of FIG. 1, implementing the known method, works as follows.

 The pulse signal received by receiver 1 is distributed over the range channels using gate stages 2 5. Then, in each channel, using analog-to-digital converters (ADCs) in 6 9, the signals are converted into digital samples, and a sample of N-samples is entered into memory 10. V each range channel fast Fourier transform unit (FFT) 11 converts the samples of the signal into samples of the spectrum.

 In the multiplier 12, the same samples of the input spectrum and the support function coefficients are multiplied from block 13. The result of the multiplication of the same samples is subjected to the inverse fast Fourier transform (IFFT) in block 14 and the resulting complex convolution signal samples are taken modulo. Then the samples go to the digital display system 16 (DSI).

The known method, which is implemented by the described device, provides for the emission of a coherent probe signal, separation of the beat signal between the probe and reflected signal (Doppler signal), distribution of the beat signal over the distance channels using time gating, analog-to-digital signal conversion, convolution of the beat signal with the reference signal of the form S (t) H (t) • exp (j • 2 • n • v _from • t / l • r) and converting the convolution signal into an image using a digital display circuit.

 In this case, the convolution of the signal at each range provides a fast Fourier transform (FFT) from the selected beat signal, FFT from the reference signal, multiplication of the FFT results of the selected and reference signals, and the inverse Fourier transform of the multiplication results.

 The disadvantages of this method include the fact that the range resolution is set in advance by the duration of the probe signal and cannot be changed during operation. It is practically impossible to vary the resolution in range, because this will require the restructuring of the modulator and the restructuring of the entire receiving path, since it is usually designed in accordance with the probing signal.

Another significant drawback is that a satisfactory relative resolution at long ranges ΔR / R _max does not satisfy at short ranges ΔR / R _min , especially when R _min <ΔR, because ΔR is constant at all ranges and is determined by the duration of the probe pulse τ. and the propagation velocity of the sounding wave ΔR = c • τ, where c is the wave propagation velocity.

 Another significant drawback is that there is a dead zone near the locator due to the blinding of the location receiver at the time of sensing and the final time of the entire recovery.

 In addition, an endless decrease in the duration of the probe pulses, in order to increase the resolution in range, is prevented by a drop in the energy of the probe signal and the expansion of the band of the receiving path along with a deterioration in its sensitivity. In the limit, the duration of the probe pulses should not be less than 200 periods of the carrier frequency of the probe signal. This actually puts a limit to increasing the resolution over the range of the pulse method.

 The purpose of the invention is to increase the resolution in range in the direction away from the trajectory during deep penetrating mapping at small and ultra-small ranges. High resolution allows you to enlarge the image of the object and consider its details. High resolution in range at close range, as well as the ability to control this resolution, allows the use of aperture synthesis for tomography of the internal organs of a person.

 The goal in the proposed method is achieved by using the property of the synthesized aperture to focus on the desired range and obtain the necessary range resolution by controlling the dimensions of the synthesized aperture and long wavelength, for which, in a known method involving the emission of a sounding signal, beats are distinguished between the probe and reflected signals, formation reference signal, discretization of the beat signal and reference signal with conversion to digital form, distribution of the beat signal About K-channels of range.

,
где S₁1, S₂, S_i,S_k опорные сигналы для активного метода локации;

опорные сигналы для полуактивного метода локации;
a_max максимальное расстояние по перпендикуляру от траектории до картографируемых точек, т. е. максимальный промах;
a₁, a₂, a_i, a_k конкретные промахи следующие, с шагом Δa;
·γ· показатель степени, выравнивающий амплитуды сигналов с разных дальностей для активного метода локации, играющий роль автоматической регулировки усиления;
Wβ· показатель степени, выравнивающий амплитуды сигналов с различных дальностей при полуактивном методе локации

текущее расстояние от приемника до объекта при их относительном движении;
I 1, 2, 3, N отсчеты опорного сигнала;
N 2^м число отсчетов опорного сигнала и БПФ;
м 1, 2, 3, степень двойки (задается экспериментатором);
DT (л/5) • v_oт интервал дискретизации по времени;
(ALN)_i=a_i/tgΦ_ср+(N/2)•DT отсчитываемое от промаха расстояние по траектории, с которого начинается синтезирование апертуры;
T_o DT • (N+1) длительность синтезирования апертуры во времени;
n 3,1415;

постоянный коэффициент;
v_от относительная скорость приемника и картографируемого объекта;
л длина волны;
Φ_ср угол наклона середины диаграммы направленности антенны приемника и передатчика к траектории;
G_изл коэффициент направленного действия антенны;
б эффективная отражающая поверхность картографируемого объекта;

,
где G_изл коэффициент направленного действия излучающей антенны;
G_пр коэффициент направленного действия приемной антенны;
R_изл расстояние от картографируемого объекта до излучателя зондирующего сигнала
Полученные цифровые отсчеты амплитуды К сигналов скользящей свертки перекодируют в контрастные или цветовые символы и разворачивают все К-контрастных сигналов в порядке их нумерации в виде К-параллельных строк из N-контрастных или цветовых символов в координатах промаха и расстояния по траектории.Sounding of the surrounding space is carried out by a continuous monochromatic signal, and the beat signal is separated after discretization of the beat signal by sliding convolution of the beat signal with each of the K-reference signals of the same duration:
S ₁ = ((AK ₁ / R $\genfrac{}{}{0ex}{}{\text{4}}{\text{1}}$ ) • cos ((4 • n / l) • R ₁ • (a ₁ / a _max ) ^γ
S ₂ = ((AK ₁ / R $\genfrac{}{}{0ex}{}{\text{4}}{\text{2}}$ ) • cos ((4 • n / l) • R ₂ • (a ₂ / a _max ) ^γ
S _i = ((AK ₁ / R $\genfrac{}{}{0ex}{}{\text{4}}{\text{i}}$ ) • cos ((4 • n / l) • R _i • (a _i / a _max ) ^γ
S _k = ((AK ₁ / R $\genfrac{}{}{0ex}{}{\text{4}}{\text{k}}$ ) • cos ((4 • n / l) • R _k • (a _k / a _max ) ^γ

,
where S ₁ 1, S ₂ , S _i , S _{k are} reference signals for the active location method;

reference signals for a semi-active location method;
a _max maximum distance perpendicular from the trajectory to the points to be mapped, i.e. maximum miss;
a ₁ , a ₂ , a _i , a _{k the} specific misses are as follows, in increments of Δa;
· Γ · exponent leveling the amplitudes of signals from different ranges for the active location method, playing the role of automatic gain control;
Wβ · exponent leveling the amplitudes of signals from different ranges with a semi-active location method

the current distance from the receiver to the object during their relative movement;
I 1, 2, 3, N reference signal samples;
N 2 ^{m the} number of samples of the reference signal and FFT;
m 1, 2, 3, the degree of two (set by the experimenter);
DT (l / 5) • v _from the sampling interval over time;
(ALN) _i = a _i / tgΦ _sr + (N / 2) • DT is the distance measured from the miss along the path from which the synthesis of the aperture begins;
T _o DT • (N + 1) the duration of the synthesis of the aperture in time;
n 3.1415;

constant coefficient;
v _{from the} relative speed of the receiver and the object being mapped;
l wavelength;
Φ _{cf the} angle of inclination of the middle of the radiation pattern of the antenna of the receiver and transmitter to the trajectory;
G _rad directivity antenna;
b effective reflective surface of the mapped object;

,
where G is _radial directional coefficient of the radiating antenna;
G _pr the directional coefficient of the receiving antenna;
R _rad distance from the object being mapped to the probe signal emitter
The obtained digital samples of the amplitude K of the signals of the convolution are converted into contrasting or color symbols and deploying all the K-contrasting signals in the order of their numbering in the form of K-parallel lines of N-contrasting or color symbols in the coordinates of the miss and distance along the path.

The proposed method differs from the prototype in that:
1. The sounding of the surrounding space is carried out by a continuous monochromatic signal.

 2. Separation of the beat signal by the K-channels of range is carried out by sliding convolution of the beat signal from the object being mapped with K-reference signals corresponding to the beat signals from the point reflectors, each of which is located at the ith distance from the receiver trajectory.

 Note the fundamental difference in the formation of the reference signal in the proposed method compared to the known one.

In the known method uses a signal of the form
S (t) = H (t) • exp (j • 2 • n • v $\genfrac{}{}{0ex}{}{\text{2}}{\text{from}}$ • t ² ) / (l • r _o ) ,,
in which there is a linear approximation of the law of change of frequency,
where Φ = 2 • n • v $\genfrac{}{}{0ex}{}{\text{2}}{\text{from}}$ • t ² / (l • r _o ) phase of the reference signal.

This is not difficult to show if we take the derivative of the phase and obtain the frequency of the Doppler signal
f (t) = dФ / dt = - (2 • v $\genfrac{}{}{0ex}{}{\text{2}}{\text{from}}$ / l • r _o ) • t, (2 • v $\genfrac{}{}{0ex}{}{\text{2}}{\text{from}}$ / l • r _o ) = Const
From the last expression it is clear that frequency is a linear function of time (see V. N. Antipov, V. G. Goryainov et al. Radar stations with digital synthesis of the antenna aperture. M. Radio and communications, 1988, p. 13 15, Fig. 1.6).

A linear approximation of the law of variation of the beat signal frequency (Doppler frequency) when synthesizing an aperture is permissible only under the condition L <r _o (see Antipov V.N. et al. Radar stations, p. 11, formula 1.7), where L is the length of the synthesized aperture; r _o distance to the reflected object.

 At close distances, this condition is not fulfilled and a linear approximation of the law of variation of the Doppler frequency is unacceptable. In addition, the generated reference signals by a known method allow you to synthesize the radiation pattern of the synthesized antenna at right angles to the aperture, i.e. to the trajectory of movement.

 Reference signals in the proposed method allow to synthesize an antenna beam at any angle of inclination to the path.

 3. Sounding and reception are carried out only in the direction of the secant plane passing through the mapped object and the trajectory of the receiver.

 This allows us to conclude that the proposed method meets the criteria of the invention of "novelty."

 Comparison of the proposed method with other known solutions in this area shows that the above distinguishing features provide the proposed method with a new property of the ability to focus the synthesized aperture at specific ranges, thereby providing high resolution in range.

 High resolution in range due to focusing of the synthesized aperture is possible only at short ranges with the ratio of the length of the synthesized aperture to the distance to the object being mapped from 1 to 100 or more. This ratio does not hold in long-range radar, so the focusing properties of the synthesized aperture (SA) have never been used in long-range radar. They fought with him as with an undesirable phenomenon, choosing such modes where focusing can be neglected.

 Technical solutions with marked features providing the described properties were not found, therefore, the proposed method can be considered as corresponding to the criteria of the invention "significant differences".

 The invention is illustrated by drawings (Fig. 1 to 8).

 In FIG. 1 shows a device that implements the method; in FIG. 2 schematic side view of the earth's surface; in FIG. 3 principle of sweep of the area map (a) on the screen of a cathode ray tube; b) on film); in FIG. 4 ring resolution region of the near-radar system (RRF) for a continuous sounding signal with a dispersion filter.

 The use of a dispersion filter implemented in the form of a rolling convolution allows synthesized apertures of the antenna to be focused with the desired range, that is, with an annular resolution region (see G. Kondratenkov, V. A. Potekhin and others. Earth observation radar, with . 122, Fig. 1.6).

In this case, the near-radar system (RBS) should be understood not as an airplane with a radar installed on board, but as an ultrasonic emitter with a microphone or an ultrasonic transducer of acoustic waves into electrical signals that move relative to the object under study at a constant speed v _from .

 If we are talking about an ultrasound scanner for diagnosing the internal organs of a person, then RRF means an ultrasonic emitter in conjunction with a transducer of acoustic waves into electrical signals moving at a constant speed through the human body.

 In FIG. 5 shows a method for dividing the space into resolution zones around the RRF.

 In FIG. Figure 6 shows a scan of the space with an object moving a RRF using the generated resolution regions with isotropic radiation and the reception of a sounding signal.

 In FIG. 7 shows a scan of a space with an object moving a RRF using the generated resolution regions with directional radiation and the reception of a sounding signal.

 In FIG. Figure 8 shows a detailed image of an object in the form of lines of contrasting characters.

 In FIG. 9 shows a functional diagram that implements the proposed method of mapping and image acquisition of the object, where it is indicated: 1 - receiver; 2 memory; 3 and 10 FFT blocks; 5 block OBPF; 6 block computing the module of complex samples of the convolution signal; 11- block with reference signal samples; 16 digital display circuit; 17 emitter; 18 ADC.

 In FIG. 10 is a receiver block diagram showing: 1 a microphone or a piezoelectric transducer of an acoustic wave into electrical signals; 2 - frequency converter, consisting of a nonlinear element; 3 Doppler frequency filter; 4 Doppler frequency amplifier; 5 object of study; 6 emitter.

 In FIG. 11 shows a block diagram of a radiator, where it is indicated: 1 - a converter of electrical signals into acoustic vibrations (piezoelectric transducer); 2 power amplifier of ultrasonic vibrations; 3 - preliminary amplifier of ultrasonic vibrations; 4 master oscillator of ultrasonic vibrations.

 Schematic or structural diagrams of blocks 2, 3, 10, 5, 6, 11 and 18 (Fig. 9) are not given in the application materials, since they are widely known and their selective description can be found in the literature. For example, FFT blocks 3, 10 and 5-IFFT indicated in FIG. 9 are described in detail in the book by V. N. Antipov, V. G. Goryainov and others. "Radar stations with digital synthesis of the antenna aperture", p. 203, fig. 6.13 is a structural diagram of a device that implements the butterfly algorithm, which can be performed on the K1815 BFZ chip. In the same book on p.204, fig. 6.14 shows the structural diagram of a specialized processor on the elements of the "butterfly", which implements the operation of the FFT and IFFT.

 In addition, the structural diagram (Fig. 9), consisting of blocks 2, 3, 6, 10, 11 and 16, can be organized programmatically on a personal computer such as IBM PS.

 It is known from the theory of aperture synthesis that the resolution region for a signal without modulation (probing with a monochromatic signal) has the form of a ring symmetrical with respect to the trajectory of the receiver. Such a resolution region allows you to organize a scan of the surrounding space without resorting to modulation of the probe signal with a very high resolution of FIG. 6. In this case, the space around the receiver of the moving RRF is divided into annular resolution regions, as shown in FIG. 5. In order to obtain an image of an object in the mapping plane of FIG. 7, it is necessary to localize the radiation and reception in the mapping plane. This is especially necessary when obtaining a tomogram section of the internal organs of a person.

 Let us dwell in more detail on the technical solution of the problem of obtaining a cartogram of a section of objects at close range.

 Mapping in the radio range is carried out in two stages. The first step is to obtain a beat signal between the probing and reflected signals (Doppler signal).

 Technically, the Doppler signal is obtained in the RRB receiver by mixing the probe and reflected signals on a nonlinear element after filtering the difference signal of the beats.

 Then this signal is input into a digital computer (digital computer) for which the Doppler signal is discretized in accordance with the Kotelnikov theorem and converted using an analog-to-digital converter (ADC) into digital samples.

 Similarly, a beating signal is obtained in the ultrasonic range when locating the internal organs of a person. To do this, the receiver with the emitter of ultrasonic vibrations is carried out at a constant speed over the surface of the human body over the diagnosed organs and the received beat signal is recorded on magnetic tape or directly through the ADC is entered into the memory of a digital computer in the form of digital readings.

 The second stage consists in the fact that the input Doppler signal is processed programmatically and the cartogram or tomogram of the section of the object is constructed.

 The following is an algorithm for processing the beat signal and constructing a cartogram of a section of objects or a tomogram of a section of internal organs for the active location method.

The initial data for the program are the wavelength of the probe signal and the relative velocity v _of .

1. Defined by the minimum and maximum misses a _max and a _min and the miss resolution a.

3. Определяется число отсчетов сигнала на интервале синтезирования апертуры D

,
где DT л/5•v_от.2. Determine the required length of the synthesized aperture D (distance along the trajectory at which the synthesis of the aperture takes place), providing the required resolution

3. The number of signal samples in the aperture synthesis interval D is determined

,
where DT l / 5 • v _from .

 4. The final number of samples is selected according to the number of FFT samples.

N 2 ^m , where m 1,2,3,4,5. N ^* <N
The larger the number of samples N, the greater the length of the synthesized aperture, the greater the miss resolution.

6. Определяется начальное расстояние по траектории, с которого начинается синтезирование апертуры для каждого промаха

7. Определяется время синтезирования апертуры
T_o DT * (N+1)
8. Определяется коэффициент АК₁, учитывающий мощность зондирующего сигнала Р_изл, отражающие свойства объекта б, диаграммы приемной и передающей антенн G_пр, G_изл

9. Определяются отсчеты дальности для каждого из К опорных сигналов

,
где I 1, 2, 3, 4, 5, N
10. Каждая из К опорных сигналов определяется по формуле
S_i= (AK₁/R $\genfrac{}{}{0ex}{}{\text{4}}{\text{i}}$ )•cos((4•n)•R_i)•(a_i/amax)^γ,
где γ коэффициент, выравнивающий амплитуды сигналов, пришедших с разных дальностей.5. The number of misses K (the number of scan lines of the image) is determined

6. The initial distance along the trajectory from which the synthesis of the aperture for each miss begins is determined

7. The aperture synthesis time is determined
T _o DT * (N + 1)
8. The coefficient AK _{1 is} determined taking into account the power of the probing signal P _rad , reflecting the properties of the object b, the diagrams of the receiving and transmitting antennas G _CR , G _rad

9. The range samples for each of the K reference signals are determined.

,
where I 1, 2, 3, 4, 5, N
10. Each of the K reference signals is determined by the formula
S _i = (AK ₁ / R $\genfrac{}{}{0ex}{}{\text{4}}{\text{i}}$ ) • cos ((4 • n) • R _i ) • (a _i / amax) ^γ ,
where γ is a coefficient equalizing the amplitudes of signals arriving from different ranges.

 11. Take the N-first samples of the beat signal and produce FFT with it.

 12. N-samples of the FFT from the reference signal are produced; as a result, its spectrum is obtained.

 13. The same samples of the spectra of the reference signal and the beat signal are multiplied.

 14. The inverse FFT is produced from the result of the multiplication of samples and a convoluted signal consisting of 2 * N samples is received.

 Only the Nth sample of the received convolution signal is taken.

 15. Again, a sample of the N-samples of the beat signal is taken, shifted by 1 or more samples, and the convolution is repeated according to paragraphs. 11-14 and again only the Nth sample is taken from the received convolution signal.

 Thus, from the N-th samples of each convolution, discrete samples of the signal of the rolling convolution are formed, that is, the set of operations 11 15 is called the sliding convolution.

 16. The described process of paragraphs. 9-16 is repeated for all K-reference signals and K-signals of the rolling convolution are received. The sliding convolution operation, like the gating operation by time (range), allows you to distribute the received beat signal over different ranges (misses).

 17. Of all the K-received signals of the rolling convolution, a reference is found with the maximum value of the amplitude.

18. They are set by the level from the found value of 0.1 0.9 and find the minimum value of the amplitude corresponding to the lower limit of contrast
A _min A _max • (0.1 0.9),
where A is the amplitude of the signal.

19. Set the number of gradations of contrast L and partition the interval from A _max to A _min into L-levels.

 20. Sort the samples of each of the K-signals of the rolling convolution according to the level of contrast L with the assignment to each sample of a certain contrast symbol or color depending on the level of amplitude. As a result, the samples of the amplitude of the signals of the rolling convolution are transcoded into contrasting symbols or colors for each Kth miss. Operation 17-20 is essentially one operation of transcoding the amplitude of the signals into contrast symbols.

 21. Expand all the K-signals in the form of parallel lines of contrasting symbols and get a picture of the cross section of the object of FIG. 7 or a tomogram of the internal organs of a person.

;
где R_изл расстояние от подсчитывающего излучателя до картографируемого объекта;
β коэффициент, компенсирующий изменение амплитуды сигнала при различных промахах.The same algorithm is preserved with the semi-active location method. A slight difference will only be in the mathematical recording of reference signals
S _i = ((AK ₂ / R _i ) • cos ((2 • n / l) • R _i ) • (a _i / amax) ^b ,
Where

;
wherein R _rad counting the distance from the source to the object being mapped;
β coefficient, compensating for the change in the amplitude of the signal for various misses.

 The device of FIG. 9, implementing the proposed method, works as follows.

 The continuous signal received by the receiver 1, after mixing it with the probing signal of the receiver 17, is converted into a beat signal (Doppler signal). The beat signal is sampled and converted from analog to digital using ADC 18. The first N-samples are sent to memory block 2 and converted into 2 • N-samples of the spectrum using FFT block 3. Further, the distribution of the beat signal over the range channels is carried out using a sliding convolution, that is, by multiplying in the block 4 samples of the spectrum of the beat signal by the spectral coefficients of the reference signal and IFFT in block 5. The spectral coefficients of the reference signal are obtained in blocks 10 and 11. In the block 11, the samples of the reference signal are formed according to a predetermined algorithm in accordance with the mathematical notation given in the claims, and in block 10 these samples are converted into spectral coefficients using BP F.

 Complex convolution samples in block 6 are converted into real samples, that is, the module of complex samples is determined.

 Block 16, when constructing an image, uses only the Nth convolution samples. Then, the input signal is re-sampled from memory N from the N-samples with a shift of 1 or several samples and the shifted signal is convolved in blocks 3, 4, 5, 6, 10, and 11, and again only the Nth block is selected in the 16th block countdown for image building.

 As a result, to build an image in the 16th block, a signal of convolution convolution is formed, consisting of N-th convolution samples. Then, the samples of the amplitude of the signals of the rolling convolution are transcoded into contrasting or color symbols, and the printing device on moving paper prints along the lines of the encoded signals. As a result, the cartogram of the object under investigation unfolds.

The mapping based on the proposed method is based on the property of the synthesized aperture to focus on a certain range. It is supposed to use the property of the synthesized aperture to allow objects at different distances from the trajectory of the receiver (see Karavaev V.V. Sazonov V.V. Fundamentals of synthesized antennas. M. Sov. Radio, 1974, p. 14, 2nd paragraph). On p. 15 (the first paragraph) states that in the long-range radar, range resolution using aperture synthesis is practically impossible to realize due to the large ratio R _o / D, where R _{o is the} distance to the target; D is the length of the section of the trajectory on which the synthesis of the aperture is carried out.

 In this regard, they resort to pulse modulation of the probe signal to create the possibility of range resolution.

In near radar, the R _o / D ratio is small and therefore there are no restrictions on range resolution using aperture synthesis, and you can do without using pulsed modulation of the probe signal, i.e., a continuous monochromatic signal is suitable for sounding.

 We illustrate the advantages in the range of the proposed method in comparison with the known pulsed method.

We set the wavelength l 3 cm. Then the achievable range resolution DR of the pulse method, taking into account the fact that the duration of the probe pulse must contain at least 200 periods of the carrier frequency, will
R = c • τ = c • 200 • T _carried • 200 • l = 6 m ,,
where T _{carried the} period of the carrier frequency of the probe signal.

For the range resolution obtained using the synthesized aperture, we will have
ΔR = 0.8 • l • R $\genfrac{}{}{0ex}{}{\text{2}}{\text{o}}$ / D ²
(see Karavaev V.V. Sazonov V.V. Fundamentals of the theory of synthesized antennas, p. 55, formula 2.42), where D _vot * T is the path along the path traveled by the receiver during the time T of synthesizing the aperture, i.e., during Doppler signal observations. Then when R _o <= 50 m, D 25 m, l 3 cm
ΔR = 0.8 • l • (R $\genfrac{}{}{0ex}{}{\text{2}}{\text{o}}$ / D ² ) = 0.8 • 3 • (50/25) ² = 9.6 cm,
and when
R _o = 1 m. ΔR = 0.8 • 3 • (1/25) ² = 4 • 10 ^-3 cm
This range resolution is not achievable with a pulsed probe signal.

Take the formula for range resolution in aperture synthesis
ΔR = 0.8 • l • (R _o / D) ² .
Let's move on to the notation used in the application materials.
Δa = 0.8 • l • (a _i / D) ² ,,
- where D is the length of the synthesized aperture of the antenna.

It can be seen from the formula that in order for the resolution Δa to remain the same at any ranges a, the ratio a _i / D must be kept constant.

Поскольку длина синтезированной апертуры D_i определяется числом отсчетов опорного сигнала, то определим необходимое число отсчетов N_i, обеспечивающих эту длину

,
где DT л/5 • v_от
Таким образом, если необходимо иметь постоянное разрешение Δa на всех удалениях a_i, то следует пропорционально a_i увеличивать длину синтезированной апертуры согласно выражения

,
а число отсчетов БПФ нужно выбирать в зависимости от D_i согласно выражения

Так как все алгоритмы БПФ работают с числом отсчетов N=2^м, т. е. отсутствуют алгоритмы БПФ на произвольное число отсчетов, то следует брать число отсчетов БПФ с запасом N_бпф > N_i, располагая выборку из отсчетов сигнала посередине выборки отсчетов БПФ, обнуляя лишние отсчеты M_бпф на концах.For this, it is necessary that D change proportionally to a _i , i.e., transforming the last expression, we obtain

Since the length of the synthesized aperture D _i is determined by the number of samples of the reference signal, we determine the necessary number of samples N _i providing this length

,
where DT l / 5 • v _from
Thus, if it is necessary to have a constant resolution Δa at all distances a _i , then the length of the synthesized aperture should be increased proportionally to a _i according to the expression

,
and the number of FFT samples must be selected depending on D _i according to the expression

Since all FFT algorithms work with the number of samples N = 2 ^m , i.e., there are no FFT algorithms for an arbitrary number of samples, you should take the number of FFT samples with a margin of N _FFT > N _i , placing the sample from the signal samples in the middle of the sample of FFT samples, zeroing the extra M _{ff counts} at the ends.

 Using new operations, in particular, probing with a continuous monochromatic signal, distributing the range of the Doppler signal using a sliding convolution, transcoding the signals of the sliding convolution into contrast symbols and their sweep in the coordinates of the miss and distance along the path, as well as directional sensing and reception in the plane passing through the mapped object and the trajectory of the receiver, allows you to increase the resolution when mapping at small and ultra short distances, and Also, if you removed tomograms of internal organs.

 More detailed mapping with high resolution of individual elements is necessary for better recognition of objects and more accurate diagnostics using the constructed tomogram.

 In addition, receiving and transmitting units are simplified because modulators and complex broadband receivers become unnecessary. YYY2 YYY4 YYY6 YYY8 YYY10

Claims (3)

1. A method of mapping using a synthesized aperture, which consists in emitting a sounding signal, receiving a reflected signal, extracting a beat signal between the probing and reflected signals, generating a reference signal, distributing the beat signal over K ranges, characterized in that the sounding is performed by a continuous monochromatic signal, distribution the beat signal at K ranges is carried out by sliding convolution of the beat signal with each of the K generated reference signals, for which over N the first digital samples of a discrete beat signal produce a fast Fourier transform (FFT), determine digital samples for each i-th of the K reference signals according to the formula
S _i = (AK ₁ / R $\genfrac{}{}{0ex}{}{\text{4}}{\text{i}}$ ) • cos (4 • π • R _i / λ) • (a _i / a _max ) ² ,
where i 1, 2, 3, 4, 5, K, K the number of ranges

i 1, 2, 3, 4, 5, N;
1 reference signal reference number;
N is the number of samples of the reference signal;
a _i specific distance from the trajectory of the receiver;
DT time sampling interval
(ALN) _i = a _i / tgΦ _cp + (N / 2) • DT
the initial distance of the synthesis of the antenna aperture;
T0 DT • (N + 1) aperture synthesis time;
λ wavelength;
v _{cp is the} average beam angle of the transmitting and receiving antennas;
_P G _p, G _{and L} coefficients _of directional receiving and radiating antennas;
δ effective reflective surface of the mapped object;
P _EM radiated power
then, the FFT of each i-th reference signal is performed, the same samples of the spectra of the reference signal and the beat signal are multiplied, the FFT of the multiplication result is inverse, from the obtained convoluted signal consisting of 2N samples, only the N-th sample is selected, a new sample of N samples of the beat signal shift by one sample, repeat the described convolution operations and select only the N-th sample, then from the N-x samples of each convolution form the samples of the signal of the rolling convolution, the process of obtaining the sliding convolution is repeated for all K reference signals, after which K received discrete signals of the rolling convolution, each of which corresponds to a specific distance from the trajectory of the receiver, is converted into an image.  2. The method according to claim 1, characterized in that the sensing and reception are carried out in the direction of the secant plane passing through the mapped object and the trajectory of the receiver. 3. The method according to claim 1, characterized in that the number of samples N _{i of the} reference signal at each range is taken in proportion to the specific distance from the path a _i according to the formula

the number of FFT samples N _{B P F} must be greater than the number of samples N _{i of the} reference signal, for which a sample of the samples of the reference signal is located in the middle of the sample of FFT samples, zeroing the extra samples N _{B P F} at the ends of the beat signal sample, and the initial aperture synthesis distance antennas are taken equal
(ALN) _i = a _i / tgΦ _cp + (N _i • DT / 2)

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