RU2205416C1 - Procedure determining line of position of radio radiation source - Google Patents

Abstract

FIELD: radio engineering, passive direction finding systems determining lines of position of radio radiation sources and mounted on mobile platforms. SUBSTANCE: in correspondence with procedure determining line of position of radio radiation source monopulse direction finder of phase type moves along axis X of plane XY with constant speed V. Signals of radio radiation source are received by two antennas A₁ and A₂, spaced apart which axes are constantly directed along axis Y. Signals S₁(t) and S₂(t) received by antennas A₁ and A₂ are limited, complex coefficient of correlation F(t) between received signals is measured, time moment t₀, is determined by data F(t), p-th harmonics S $\genfrac{}{}{0ex}{}{\text{p}}{\text{1}}$ (t) and S $\genfrac{}{}{0ex}{}{\text{p}}{\text{2}}$ (t) are extracted from limited signals S₁(t) and S₂(t) correspondingly, instantaneous frequency Ω(t) of complex correlation coefficient F(t) is measured as well as time moment. Complex correlation coefficient F(t) is measured for signals S $\genfrac{}{}{0ex}{}{\text{p}}{\text{1}}$ (t) and S $\genfrac{}{}{0ex}{}{\text{p}}{\text{2}}$ (t) and time moment t₀ is measured when instantaneous frequency Ω(t) reaches its maximum value. EFFECT: elimination of ambiguity in determination of line of position of radio radiation source. 4 dwg

Description

 The invention relates to radio engineering and can be used in passive direction finding systems mounted on mobile platforms for determining the position line (PL) of radio emission sources (IRI).

 The well-known problem of determining the LP of IRI on the XY plane [1, p.182]. One of the solutions to this problem involves the use of goniometric (direction-finding) devices for measuring the direction to the detected IRI [1, p. 182-183]. As goniometer devices, in particular, direction finders with monopulse antenna sensors, i.e. monopulse direction finders (MP) [1, p. 405-413; 2].

 For goniometric LP devices, the IRI is a straight line passing through a specific point of the XY plane in the direction of the IRI. For MFs that are part of stationary radars of all-round visibility, such a point is the installation site of the MF, which, together with the axis of the MF antenna aimed at the IRI, determines the PL of the IRI.

Another, in a sense, the opposite, is the case when the MP is mounted on a platform that performs linear motion along the X axis with a constant speed V, and the axis of the MP antenna system is fixed constantly in the direction of the Y axis, perpendicular to the trajectory of its movement. The IRI itself is supposed to be motionless. This situation is typical for side-scan radars [1, p. 393-399]. When the side-scan radar is operating in the passive mode, the IRI can be uniquely determined by the moment t ₀ , at which the direction of arrival of the wave from the IRI coincides with the direction of the Y axis, i.e. along the axis of the MP antenna system. This moment t _{0 is} uniquely associated with the point of the trajectory of the MP, from which the IRI is visible at right angles to the course of the MP (in marine terminology, on the beam), and therefore completely determines the LP of the IRI.

The disadvantage of analogues, regardless of the way (circular or lateral) of the review of space, is the low accuracy of determining the LP of IRI under the existing restrictions on the design dimensions of antenna sensors MP. Let us explain what has been said on the example of an MP, in which a phase-type monopulse antenna sensor is used [2, pp. 67-68], consisting of two antennas spaced apart along the X axis of antennas A ₁ and A ₂ , whose axes are oriented in the direction of the axis Y. In a magnetic field of this type, the arrangement of the IRI along the axis of the magnetic field means that the IRI is equidistant from the centers of the antennas A ₁ and A ₂ , and the deviation of the IRI from the axis of the MP is determined by measuring the current values of the correlation coefficient between signals S ₁ (t) and S ₂ (t), received antennas A ₁ and A _2, respectively.

It is known that the sensitivity of the magnetic field to changes in the angle of arrival of radio waves from the IRI is proportional to the normalized base L / λ between the antennas, where λ is the wavelength of the IRI. This explains the desire to increase the direction finding accuracy by increasing L (for a given λ). At the same time, in order to fulfill another fundamental requirement — the unambiguity of measuring the bearing on the IRI — an increase in L should be accompanied by an increase in the diameter of the antennas A ₁ and A ₂ , which should not be less than the distance L between them. When the possibilities of creating such antennas are limited, the contradiction between the requirements of high accuracy and unambiguity of bearing measurement cannot be eliminated within the framework of traditional processing methods.

The severity of this contradiction can be partially smoothed out in the prototype method, which involves a side view of the space. For the proposed method, passive side-view radars with a monopulse phase-type antenna sensor are the basic radio engineering systems, and the corresponding set of operations performed in the MP over the received IRI signal for direction finding and determination of the IRI signal is a prototype method. In this case, we will assume that in the prototype MP two correlation coefficients are measured - real F * and imaginary F **, which together form the so-called complex MP correlation coefficient: F = F * + jF **. Its real component F * is obtained in the presence of a phase shifter at π / 2 in the signal processing channel S ₁ (t), and the imaginary F ** - in the absence of it [2, p.250].

 The disadvantage of the prototype is the ambiguity of determining the line of position of the IRI in the case when the distance between the antennas of the phase-type MP significantly exceeds the diameter of each of the antennas.

 The purpose of the invention is the elimination of the ambiguity of determining the line of position of the IRI.

To do this, in the prototype method, which is carried out:
- moving phase-type magnetic field along the X axis of the XY plane with a constant speed V;
- reception of IRI signals to two antennas A ₁ and A ₂ spaced apart along the X axis, the axes of which are directed constantly along the Y axis;
- restriction of the received signals S ₁ (t) and S ₂ (1) received by the antennas A ₁ and A ₂ ;
- measurement of current values F (t) of the complex correlation coefficient F between the received signals;
- determination by current values of the complex correlation coefficient F (t) of time t ₀ at which the IRI is equidistant from the antennas A ₁ and A ₂ , and which uniquely characterizes the LP of the IRI, is additionally carried out:
- selection of the limited signals S ₁ (t) and S ₂ (t) "p" -x harmonics S ₁ ^p (t) and S ₂ ^p (t), respectively;
- measurement of the instantaneous frequency Ω (t) of the complex correlation coefficient F (t);
- measuring the point in time when the instantaneous frequency Ω (t) reaches its maximum value Ω _max , and:
- measurement of the coplex correlation coefficient F (t) is performed for signals S ₁ ^p (t) and S ₂ ^p (t);
- at _{0 is} defined as the moment when the instantaneous frequency Ω (t) reaches its maximum value Ω _max
In FIG. 1 shows the geometric arrangement of the IRI and MP, as well as the phase Φ (x), instantaneous frequency Ω (x), the output signal of the comparator 20 and the sync pulse SI as a function of the spatial coordinate x = Vt.

 Figure 2 is an enlarged image of a phase-type MP antenna sensor and a phase front of the IRI signal in the vicinity of the MP antenna.

 Figure 3 shows a phase-type magnetic field diagram that forms the real F * (t) and imaginary F * (t) components of the complex correlation coefficient F (t). It is indicated here: 1, 2 - mixer; 3, 4 - UPCH; 5, 6 - amplifier-limiter with a band-pass filter tuned to a center frequency equal to ω; 7 - local oscillator; 8 phase shifter on π / 2; 9, 10 - phase detector. The scheme of figure 3 differs from the typical one by the presence of elements 5, 6.

In FIG. 4 shows a possible circuit implementation of the instantaneous frequency meter Ω (t) and moment t ₀ when the instantaneous frequency Ω (t) reaches its maximum value. It is indicated here: 11, 12 - multipliers; 13 - harmonic oscillation generator; 14 - adder, 15 - frequency detector; 16 - analog-to-digital Converter (ADC); 17 - block selection of the maximum (BVM); 18 - time recording unit (BRV); 19 - clock pulse generator (GTI); 20 - a comparator; 21 - differentiating chain, 22 - real-time counter.

Consider the transformations performed on the signals of the IRI according to the proposed method. Let the IRI be located at a point on the plane with coordinates: x = 0, y = R and emit a continuous harmonic signal. The phase front of this signal has the form of a circle centered at the point (0, R), and the phase distribution has the form:
φ (x, y) = (2π / λ) [x ² + (yR) ² ] ^-0.5 (1)
Let us temporarily assume that the MP is motionless and located at the observation point with coordinates (x, 0), i.e. at the point (x, 0) is the center of the phase-type MP base. Then the received signals S ₁ (t) and S ₂ (t) received by the antennas A ₁ and A ₂ differ in phase, which depends on the coordinate "x" of the observation point. Provided that the base L is not too large, so that the wave can be considered flat, the difference Φ (x) between the phase of the signal S ₂ (t) and signal S ₁ (t) can be calculated by the formula
Ф (x) = L∂φ / ∂x, (2)
which, after substituting into it the expressions (1) gives
Ф (х) = (2π / λ) L (x / R) [1+ (x / R) ² ) ^0.5 . (3)
The dependence f (x) is depicted in figure 1. Expression (3) did not include such a parameter as the size of the antennas themselves due to the fact that, under the initial assumptions, the antennas have a weak directivity, which makes it possible to select only one half-plane (Y≥0), i.e. detect IRI from only one (left or right) side of the MP carrier.

After limiting the signals S ₁ (t) and S ₂ (t) in elements 5, 6 with the allocation of their "p" -th harmonics S ₁ ^p (t) and S ₂ ^p (t) using the band-pass filters, their phase difference (3 ) also increases by "p" times. The real F * (x) and imaginary F ** (x) components of the complex correlation coefficient F (x), considered as functions of the spatial variable "x", are distinguished at the outputs of the phase detectors 10.9, respectively, and are expressed in terms of the phase difference pF (x) their input signals S ₁ ^p (t) and S ₂ ^p (t):
F * (x) = Cos [pF (x)]; F ** (x) = Sin [pF (x)]. (4)
The previously introduced assumption about the immobility of a magnetic field can be removed if formulas (3), (4) remain valid after replacing the spatial variable "x" in them with the product x = Vt. This takes place in many practical situations, since the time interval during which the phase difference of the RF (t) is considered as a function of time t changes by π / 2, significantly exceeds the time interval during which the phase difference rF is measured ( t).

 Therefore, in the future, for a moving MP, we will continue to use expression (4) for the real F * (x) and imaginary F ** (x) components of the complex correlation coefficient F (x), assuming that the variable "x" in them is equal to the product x = Vt . Further, when the complex correlation coefficient F, its real F * and imaginary F ** components will be considered not as functions of the spatial variable "x", but as functions of time t, the notation F (t), F * (t) is used for them and F ** (t), respectively.

The instantaneous frequency Ω (x) of the complex correlation coefficient F (x) is obtained by differentiating pF (x) with respect to time, taking into account the equality x = Vt:
Ω (x) = (2π / λ) (pLV / R) [1+ (x / R) ² ] ^-1.5 (5)
and this dependence is depicted in figure 1.

 The harmonic model of the IRI signal is obviously an idealization of real IRI signals. For a more general model of the IRI signal in the form of a continuous phase-shifted signal in the output signals F * (t) and F ** (t) of phase detectors 10, 9, considered as functions of time t, against the background of a regular law of change in time of the form (4) can pulsed emissions (of different polarity) are observed. However, if the duration of the chips of the phase-shifted signal significantly exceeds the propagation time of the radio waves along the base L, then, choosing the time constant of the smoothing filter at the output of the phase detectors 10, 9 is commensurate with the duration of the chips, the indicated emissions in the output signals F * (t), F * * (t) will be eliminated.

Observing the change in the instantaneous frequency Ω (x) and considering it as a function of Ω (t) of time t, we can determine the moment t ₀ at which it reaches its maximum value Ω _max . It is at this moment that the IRI is on the MP traverse, i.e. equidistant from antennas A ₁ and A ₂ . This can be done automatically using the device of figure 4. In it, from the two quadrature components of the complex correlation coefficient F (t) = F * (t) + jF ** (t) using a frequency generator 13 ω, multipliers 11, 12 and adder 14, a high-frequency signal S (t) is generated, modulated by phase pF (t):
S (t) = F * (t) Sinωt + F ** (t) Cosωt = Sin [ωt + pФ (t)] (6)
The instantaneous frequency Ω (t) of this signal is emitted by a frequency detector 15, built, for example, on detuned circuits, one of which is tuned to the frequency ω, and the other to the frequency ω + Ω _max , where Ω _max is the maximum frequency of the complex correlation coefficient F (t). The output signal of the frequency detector 15 repeats the shape of the dependence Ω (x) of FIG. 1. Moment t ₀ when it reaches its maximum value is determined using elements 16-22 of the circuit of FIG. 4.

The operation of the part of the device of FIG. 4, including elements 16, 17, 18 and 19, is described in detail in [3] and essentially reduces to measuring the delay time τ of the output signal of the frequency detector 15 (more precisely, its maximum value) relative to the auxiliary SI clock pulse supplied to the control inputs of blocks 17 and 18 before the appearance of this maximum value. Using SI, the registers 17 and 18 and the delay time counter τ are reset to zero. The moment t * of occurrence of SI can be fixed using the absolute time counter 22, and then the absolute time t _{0 of} reaching the maximum frequency Ω (t) of its maximum value is defined as
t ₀ = t * + τ. (7)
Thus, a pair of quantities τ and t * completely determine the moment t ₀ when the IRI is at equal distances from the antennas of the MP.

It is advisable to generate the SI clock pulse at time t * close to time t ₀ (but no later than it) in order to reduce the requirements on the volume (capacity) of the delay time counter τ included in the BRV 18. This is done by part of the circuit of Fig. 4, including elements 20 and 21. The output signal of the frequency detector 15, proportional to Ω (t), is supplied to the signal input of the comparator 20, to the reference input of which the reference voltage is selected, for example, at the level of 0.35 from the maximum value of Ω _max . At the output of the comparator 20, a constant-amplitude signal SC of FIG. 1 is generated, over which the frequency Ω (t) exceeds a threshold value of 0.35Ω _max . The sync pulse SI is formed at the output of the differentiating chain 21 and coincides in time with the leading edge of the output signal of the SC comparator 20.

 The measurement procedure τ ends after filling in the delay time counter τ in the BRV block 18. It is assumed that the volume of this counter is filled by the end of the IRI observation interval.

Let us explain what has been said with a concrete example, when the MP is placed on a car and carries out reconnaissance of Iran in urban conditions. We choose the following values of radio engineering and long-range speed parameters: p = 5-7, L / λ = 30-100; V = 20 m / s, R = 40 m. The maximum value of the frequency in this case is: (1 / 2π) Ω _max = 75-350 Hz. The linear observation interval of the IRI is chosen equal to the range to the IRI: x = ± R. The value of the instantaneous frequency Ω (x) at x / R = 1, corresponding, according to (5), to the level of 0.35Ω _max , lies in the interval: (1 / 2π) Ω) (= 26-125 Hz. Thus, during the observation time IRI equal to 2R / V = 4 s, the instantaneous frequency variation Ω (t) is either 26-75 Hz (p = 5, L / λ = 30), or 125-350 Hz (p = 7, L / λ = 100 )

According to the found value of t ₀ LP is determined in the relative (moving) coordinate system associated with the MP. In the presence of a single (absolute) time service and a navigation system that ensure the "linking" of the moving MP platform to the terrain, it is possible to determine the LP also in the absolute (earth) coordinate system.

 Note that the task of determining the IRI LP is often auxiliary in solving the more general problem of identifying the object on which the IRI is installed. We show how it can be solved without reference to the absolute coordinate system. Firstly, the instantaneous frequency variations Ω (t) can be recorded in real time by a human operator “by ear” without using additional devices of figure 4, for which it is enough to “voice” the time dependence of the complex correlation coefficient F (t) by connecting the output of one of the phase detectors 9, 10 to the headphone operator.

 If, on the other hand, it is possible to install an optical device for monitoring the terrain on the MP mobile platform, the axis of which is directed along the Y axis, then the operator can make a rough “snap” of the instant of passing its maximum value Ω (t) to a specific object on the ground ( car, building, window of the house, etc.) and thus identify the installation point or carrier of IRI.

 Secondly, the procedure for identifying the location of the IRI can be carried out more accurately in stationary conditions after conducting a space survey, for which a video camera should be installed on the MP platform, recording, in addition to the image of the terrain along the Y axis, also the absolute time t * from the counter 22. Having the data set obtained by the device of figure 4, consisting of different pairs of values {t *, τ} of the explored IRI, you can identify the carrier objects of the IRI when watching a video, by "linking" these data to the image of objects on the ground.

 In conclusion, we note the role of a priori information on the range of R to Iran. The technical implementation of the proposed method (figure 4) turned out to be quite simple precisely because the range to the IRI was assumed to be approximately known (with an accuracy of 30-50%), because information about R was used in the frequency detector 15, comparator 20, and also when choosing the volume (bit capacity) of the delay time counter τ included in the BRV 18.

 At the same time, in the considered situation — intelligence of the IRI in urban conditions — such an estimate of the range of R can be easily obtained, since Potential installation sites for reconnaissance Iran - buildings, cars, etc. located along the streets - are easily observed visually and the distance to them can be measured using auxiliary devices - either a passive optical system or an active radar system. Given that at sufficiently large intervals of the path, comparable with the length of the streets, the distance R remains approximately constant, updating data on R in the processing device should be carried out quite rarely.

Decoding of used lettering:
V is the speed of the platform on which the MP is installed;
L is the distance (base) between the antennas A ₁ and A _{2 of the} monopulse direction finder of the phase type;
S ₁ (t) and S ₂ (t) are the signals received by the antennas A ₁ and A _2, respectively;
S ₁ ^p (t) and S ₂ ^p (t) are the "p" -th harmonics of the signals S ₁ (t) and S ₂ (t), respectively, after limiting the signals S ₁ (t) and S ₂ (t);
S (t) is a high-frequency signal generated at the output of the adder 14 of the meter of figure 4;
F is the complex correlation coefficient between the signals S ₁ ^p (t) and S ₂ ^p (t);
F * is the real component of the complex correlation coefficient F;
F ** is the imaginary component of the complex correlation coefficient F;
F (t) is the complex correlation coefficient between the signals S ₁ ^p (t) and S ₂ ^p (t), considered as a function of time t;
F (x) is the complex correlation coefficient between the signals S ₁ ^p (t) and S ₂ ^p (t), considered as a function of the x coordinate;
F * (t) is the real component of the complex correlation coefficient between the signals S ₁ ^p (t) and S ₂ ^p (t), considered as a function of time t;
the same is the output signal of the phase detector 10;
F ** (t) is the imaginary component of the complex correlation coefficient between the signals S ₁ ^p (t) and S ₂ ^p (t), considered as a function of time t;
the same is the output signal of the phase detector 9;
F * (x) is the real component of the complex correlation coefficient F (x);
F ** (x) is the imaginary component of the complex correlation coefficient F (x);
Ω is the instantaneous frequency of the complex correlation coefficient F;
Ω (t) is the instantaneous frequency of the complex correlation coefficient F (t), considered as a function of time t. This is the output signal of the frequency detector 15;
Ω (x) is the instantaneous frequency of the complex correlation coefficient F (x), considered as a function of the x coordinate;
Ω _max is the maximum value of the instantaneous frequency Ω (t);
Ф (t) is the phase difference of the signals S ₁ (t) and S ₂ (t), considered as a function of time t;
Ф (х) is the phase difference of the signals S ₁ (t) and S ₂ (t), considered as a function of the x coordinate;
pФ (t) is the phase of the signal S (t), considered as a function of time t;
pF (x) is the phase of the signal S (t), considered as a function of the x coordinate;
λ is the wavelength of the IRI;
R is the distance measured from the MP in the direction perpendicular to the trajectory of the MP and coinciding with the axis of the MP. In another way: this is the distance between two lines, one of which is the trajectory of the MP, and the other is a set of points, in each of which the IRI can be located;
φ (x, y) is the phase distribution of the IRI signal on the XY plane;
t is the absolute time;
t ₀ - the point in time at which the IRI is equidistant from the antennas A ₁ and A ₂ and at which the instantaneous frequency Ω (t) reaches its maximum value Ω _max ;
t * is the moment of occurrence of SI;
τ is the time between the moment the output signal Ω (t) reaches the frequency detector 15 of its maximum value Ω _max and the time t * of the SI clock pulse occurs;
∂ / ∂x - operation of taking the partial derivative with respect to the variable "x";
x is the spatial coordinate.

Sources of information
1. Yu. P. Grishin et al. Radio engineering systems / Ed. Yu.M. Kazarinova. - M., 1990.

 2. Leonov A.I., Fomichev K.I. Monopulse radar. - M., 1984.

 3. Auth. testimonial. 1824596, G 01 R 29/02 (Pulse delay meter).

Claims (1)

The method of determining the position line of the radio emission source, in which the phase-type monopulse direction finder moves along the X axis of the XY plane with a constant speed V, receiving the signals of the radio emission source into two antennas A ₁ and A ₂ spaced apart along the X axis, the axes of which are directed constantly along the Y axis, the limitation of the signals S ₁ (t) and S ₂ (t) received by the antennas A ₁ and A ₂ , the measurement of the complex correlation coefficient F (t) between the received signals, the determination, from the data of F (t), of the time t ₀ at which the radio emission source is equally remote from the antennas A ₁ and A ₂ and which uniquely characterizes the position line of the radio source, characterized in that it additionally extracts from the limited signals S ₁ (t) and S ₂ (t) "p" -x harmonics S ₁ ^p (t ) and S ₂ ^p (t), respectively, measuring the instantaneous frequency Ω (t) of the complex correlation coefficient F (t), measuring the moment in time when the instantaneous frequency Ω (t) reaches its maximum value, and measuring the complex correlation coefficient F (t) produced for signals S ₁ ^p (t) and S ₂ ^p (t), and t ₀ is defined as the moment the instantaneous frequency Ω (t) reaches its maximum value.

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