RU2408030C2 - Radar system with prediction of missing targets in doppler resection zones - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: system has a radar unit, an indicator device whose first input is connected to the first output of the radar unit, a unit for calculating the time for entrance/exit of the target from the scanning zone, whose input is connected to the second output of the radar unit, a unit for calculating parametres of the resection zone, whose input is connected to the second output of the radar unit, and the second output is connected to the second input of the indicator device, a decision unit, whose first input is connected to the output of the unit for calculating parametres of the resection zone, and the second input is connected to the output of the unit for calculating the time for entrance/exit of the target from the scanning zone, an extrapolation unit, whose input is connected to the output of the decision unit and the second output is connected to the third input of the indicator device, a unit for identifying targets, whose first input is connected to the first output of the radar unit and the second input is connected to the first output of the extrapolation unit, the third input is connected to signals of targets from other carriers, and the output is connected to the fourth input of the indicator device.

EFFECT: high efficiency of operation of the radar unit and operators servicing the radar unit due to reduced loss of targets in Doppler resection zones.

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Description

The invention relates to radar and can be used for radar tracking of air and ground targets.

One of the effective methods for detecting and tracking low-flying aircraft (LA) is the use of pulsed-Doppler radar stations (radars) deployed on modern fighters [1, pp. 562-690] or special long-range radar detection aircraft (DRLs) [2, p. .449-479, 3, pp. 301-340]. The use of aircraft radars can increase the detection range of low-flying aircraft due to the expansion of the radio horizon in comparison with ground-based radars. However, the radar mobility and the need to accompany low-flying aircraft against the underlying surface make it necessary to use the Doppler principle of radar construction [4, p. 73-87], which determines the appearance of Doppler resection zones in which signals reflected from the tracked objects are not detected. Moreover, for aircraft moving along different trajectories, the presence of these zones manifests itself in different ways. For some aircraft, the tracking time is reduced, for others, there are interruptions in the flow of information, which in the general case reduces the effectiveness of guidance systems [5, pp. 12-22, 27-29].

When using the Doppler mode, reflected signals whose frequencies are close to the average frequency f _{s of the} signal reflected from the earth’s surface in the direction of the main beam of the antenna pattern are not detected due to the presence of a special filter in the radar (resection filter or free zone filter) [4 , pp. 243-248]. The frequency f _s depends on the frequency of the emitted signal and the Doppler shift caused by the movement of the aircraft on which the radar is installed.

The Doppler frequency shift is proportional to the radial component of the relative speed of the irradiated object (target or underlying surface) in the coordinate system associated with the mobile radar.

Closest to the described system is a radar system (PC), placed on an A-50 airplane (prototype) [2, p. 45 5-479], containing a radar and an indicator device (IU), the first input of which is connected to the first output of the radar. Measurements of range, speed and angular coordinates are received at this input from the radar, according to which marks of targets are formed in the indicator device (DUT) and traces of their movements in space are built. At the request of the operator, the digital values of range, approach speed and angular coordinates are displayed on the screen in the target form.

A systemic disadvantage of Doppler radars is the presence of resection zones, which cannot be eliminated within the framework of the used signal processing method. However, it is possible to increase the efficiency of target tracking and situational awareness of tracking and guidance operators [2, p. 470-479, 3, p. 225-228], if they are notified in advance about the possible loss of targets in the resection zones, indicating the expected entry time and exit of escorted objects from the resection zone.

The technical result that can be obtained by implementing the present invention is to predict the disappearance of targets in the areas of Doppler resection and their identification after leaving these areas, which will improve the efficiency of guidance procedures.

The specified technical result is achieved by the fact that in the pulse-Doppler radar system (PC) containing the radar, an indicator device (IU), the first input of which is connected to the first output of the radar, an additional unit for calculating the time of entry / exit of the target into the viewing area (BVVVZO) is introduced the input of which is connected to the second output of the radar, a block for calculating the parameters of the resection zone (BWPR), the input of which is connected to the second output of the radar, the first output is with the first input of the decision block, and the second output is with the second input of the DUT and the second input of the block extrapolation (BE), decision block (BPR), the first input of which is connected to the first output of the BVPZR, the second input - with the output of the BVVVZO, and the output - with the first input of the BE, the first input of which is connected to the output of the decision block, the second input - with the second BVPZR output, the third input - with the first radar output, through which the target’s range, speed of approach and angular coordinates of the target are received at the moment of its entry into the resection zone, the first exit - with the second input of the target identification unit (BIC), and the second output - with the fourth entrance of the IU, BIC, the first entrance is a cat It is connected to the first output of the radar, the second input - to the first output of the BE, if necessary, signals from other carriers are received at the third input, and the output is connected to the third input of the DUT.

The system operates as follows.

All reflective objects for which the radial component of the relative velocity V _rel differs from the radial component of the velocity of the underlying surface V _{s by} no more than a certain value V _min , i.e. for which the inequality holds

are invisible to radar due to contact with the resection area. The value of V _{min is} determined by the width of the spectrum reflected from the earth's surface of the signal received from the main lobe of the radiation pattern and is a parameter that is taken into account when choosing the bandwidth of the notch filter or the free zone filter [4, pp. 243-248].

From inequality (1) it follows that the resection zones have the form of sectors formed by intersecting straight lines. The intersection point of these lines (the common peak of two sectors) is located at the position of the aircraft’s onboard radar. The location of the sectors shown in figure 2. It follows from condition (1) that the general bisector of the resection sectors is always perpendicular to the flight direction of the aircraft, and the angular size α of each sector is determined by the formula

where V is the speed of the target.

In the case of rectilinear and uniform movement of the aircraft and the aircraft performing its radar tracking, the moments of crossing the zone boundaries by an air object can be calculated. To do this, consider the rectilinear motion of the aircraft in the coordinate system Z ₁ OZ ₂ associated with the onboard radar of the aircraft (figure 2). In this coordinate system, the position of the target z (t) at time t is described by the expression

where z ₀ is the initial position of the target.

Substituting expression (3) into the equations of boundaries (resection sectors) and solving them with respect to t, we find the moments of crossing the boundaries:

Here, the angles φ and φ _H , which determine the direction of movement of the radar carrier and the longitudinal axis of the followed aircraft, are counted from the axis OZ _{1 of the} moving coordinate system (in Fig. 2, the angle φ _H = 0), and V _H is the speed of the radar carrier.

In order to determine how short the duration of the tracking of an aircraft due to resection sectors is, it is necessary to know the moments when the trajectory of the aircraft intersects the radar detection zone. These points can be found under the following assumptions.

The radar detection zone is considered to be a circle whose center is located at the location of the aircraft equipped with the radar, and the radius of the circle R is determined by the detection range of the aircraft. The detection zone moves with the radar carrier (figure 2) in the direction of the carrier velocity vector V _H.

The escorted aircraft moves uniformly and rectilinearly, while its velocity vector has the form:

The movement of the aircraft in the coordinate system Z ₁ OZ _{2 is} described by expression (3). At the moments when the aircraft crosses the boundaries of the detection zone (including the moment it leaves it), the length | z (t) | vector z (t) is equal to the radius of the zone R or:

(z ₀ + V _rel · t, z ₀ + V _rel · t) = R ² ,

where the left side of the equality is the scalar product of vectors (3).

After completing the multiplication, we obtain a quadratic equation for determining the moments when an aerial object crosses the border of the detection zone:

.

.

The solutions of the equation that determine the moments of the aircraft entering and leaving the field of view are of the form

If one or both solutions are negative, then this means that the intersection of the detection zone boundary occurred in the “past”, i.e. until the aircraft was at the point defined by the vector z ₀ .

Expression (6) for calculating the moments of intersection of the aircraft trajectory of the boundary of the detection zone becomes especially simple if, at the initial moment (at t = 0), an air object, being at the boundary of the zone z (0) = z ₀ , moves deep into it.

Expressing V _rel through the parameters of the aircraft and radar motion (for φ _Н = 0) and taking into account that | z ₀ (t) | = R, we obtain the dependence

tracking time from the angles φ and β, which determine the movement of the aircraft and the point of its entry into the radar detection zone (see figure 2), where β is the angle between the line of sight of the target Oz ₀ and the vector V _relative relative speed (figure 3).

The numerator of this expression is the length of the chord cz ₀ along which the aircraft crosses the radar field of view, and the denominator shows the speed of the relative motion of the aircraft.

The presence of resection sectors in the detection area of the Doppler radar leads to interruptions in the receipt of information about the aircraft and a reduction in the time of their tracking. The nature of this effect and its degree depend on the parameters of the movement of the aircraft relative to the mobile radar.

Some of the possible options for the relative location of the trajectories of the aircraft and the resection zones in the moving coordinate system Z ₁ OZ ₂ shown in Fig.3. The location of the resection zones relative to the aircraft trajectory is determined by the position on the time axis of the moments t ₁ and t _{2 of the} intersection of the two boundaries of the resection zone with respect to the moment it enters the detection zone and the moment t _exits the detection zone. The moments t ₁ and t _{2 are} determined by formulas (4), and the moment t _o - by the formula (7).

Figure 3 a) and c) shows the trajectories that do not fall into the resection sectors within the detection zone. In the first case, this happens because the intersection of the trajectories of the aircraft within the detection zone with the boundaries of the resection sectors occurs before entering the detection zone. In the second case, the movement of the aircraft in the detection zone occurs after leaving one sector and ends before entering the second resection sector.

Trajectories similar to those shown in Fig. 3 b) are characterized by the fact that the duration of tracking the aircraft moving along them is reduced compared with the absence of resection sectors.

Finally, the variant of the trajectory shown in Fig. 3 g) is characterized by a break in the receipt of information about the aircraft due to the intersection of the resection sector within the field of view.

The frequency of occurrence of each type of track depends on the speeds of the aircraft and the radar carrier, as well as on the value of V _min .

Studies have shown that the presence of resection zones has a significant impact on the process of tracking aircraft. The main manifestation of this influence is a reduction in the time of their accompaniment and the appearance of gaps in the accompaniment of air objects. Gaps accompanied by aircraft can reach tens of minutes and should be taken into account in the process of controlling aircraft in the air.

After the disappearance in the resection zone and the appearance of the target beyond, it is necessary to identify the target. Identification, the meaning of which is to make a decision that this is a new goal or followed earlier, is carried out in the target identification unit (Fig. 1) and is performed according to well-known algorithms [6, p. 306-311, 323-327].

The results of calculating the time of entry and exit of the target into the resection zone and its extrapolation are sent to an indicator device for informing tracking and guidance operators.

Relations (1) - (7) allow:

- to determine in advance the moments of disappearance and the appearance of escorted targets in pulse-Doppler radars for various purposes and basing (air, ground, ship);

- evaluate the size of the resection zone, the absolute and relative time of loss of these objects;

- extrapolate the lost objects by measuring ranges, speeds and angular coordinates at the time of loss, or, if necessary, transfer tracking of these objects to other radars.

Figure 1 presents a block diagram of the proposed system.

The system includes: radar 1, a unit for calculating the entry / exit time of the target into the BVVVZO 2 viewing area, a unit for calculating the parameters of the BVPZR 3 resection zone, a decision making unit BPR 4, an extrapolation unit BE 5, a target identification unit BIC 6, an indicator device IU 7.

1. Radar - operates in the usual pulse-Doppler mode [1, pp. 314-404], by detecting targets, measuring the distance R to them, approach speed, airborne bearings, coordinates (z ₀₁ , z ₀₂ ) in a rectangular coordinate system, associated with the center of mass of the carrier, and the parameters of the absolute movement of targets φ, β, V (see figure 2). These data from the output 1 of the radar arrive in IU 7, BICB, BE 5. From the second output of the radar, in unit 2 of calculating the time of entering / leaving the target, the coordinates of the targets (z ₀₁ , z ₀₂ ) and the parameters of the absolute movement of targets φ, β , V, calculated in the channel for determining the parameters of the target’s own motion [6, p.276-298] and measuring the carrier’s own velocity V _H.

2. BVVVZO - unit for calculating the time of entry / exit of the target into the detection zone. The entry time is fixed at the moment of detection (trajectory setting time) [6, p. 300-306], and the exit time t _{o is} calculated by formula (7) according to the results of measuring the distance (R) in the rangefinder channel and target motion parameters φ, β, V and own speed V _{H of the} carrier coming from the second output of the radar.

3. BVPZR - unit for calculating the parameters of the resection zone, calculates the angle α of the resection sector according to formula (2) from measurements of the target velocity V from the channel for determining the parameters of the radar target’s movement and the known value V _min [1, p. 311-324], determined by the width of the spectrum reflections from the ground along the main lobe of the antenna radiation pattern, the position of the resection sector in the coordinate system associated with the center of mass of the carrier (Fig. 2, shaded areas) and the times t ₁ and t _{2 of} the target entering and leaving the resection zone according to formulas (4), calculated by measurements z ₀₁ , z ₀₂ , φ, β, V, V _H , gender learners from the second output of the radar, and issues forms of these goals to the second input of the indicator device IU indicating the time of their disappearance and appearance.

4. BDP - decision block according to the relation (t ₂ -t ₁ ) / t _o <1, where t _{o is} calculated by the formula (7), at ₁ , t ₂ - by formulas (4), generates an extrapolator trigger signal, or the start signal of the algorithm for transmitting tracking of an object to a radar located on another medium and capable of tracking a lost target over time t ₂ -t ₁ .

5. BE - an extrapolation unit that predicts the position of the target when it is in the resection zone by the start signal generated in the BPR and by measuring the range, approach speed, airborne bearings and their derivatives at the time the target disappears from output 1 of the radar. According to the extrapolation signals arriving at the fourth input of the indicator device, it continues to indicate the target that has fallen into the resection zone along with other targets, which ensures the continuation of the process of pointing fighters at it.

6. BIC — the target identification block performs, according to the well-known rules [6, pp. 306-311, 323-327], the extrapolated target is identified after it leaves the resection zone with the signals of real targets coming from the output of 1 radar. Based on the results of identification, a decision is made: whether the extrapolated mark belongs to a previously accompanied target, or is it a mark of a new target. In the first case, according to the signal from the second output of the BIC, arriving at the third input of the DUT, its display on the indicator continues, in the second case, its indication stops.

7. IU - an indicator device that displays the position of the target relative to the carrier of the radar and its form, which indicates the digital values of the distance to the target, the speed of approach with it and its airborne bearings coming from the output 1 of the radar, the position and size of the sectors of the resection with an indication in the goal form of the time remaining until the target enters the resection zone, the time of exit from the resection zone, and the estimated time spent in the resection zone according to the signals received at the second input of the DUT from the second output of the BHPR. In addition, in the DUT, the target, which fell into the resection zone, is displayed according to the signals of extrapolated range, speed of approach and angular coordinates received at its fourth input from the second output of the extrapolation unit. If in the BIC a decision is made that after leaving the resection zone the extrapolated target path does not correspond to the real marks coming into it from the first radar output, then in the BIC a prohibition signal is generated in the DUT of the extrapolated path display.

All the blocks entered into the PC are implemented on a microcomputer.

Thus, the implementation of the above-described features of the functioning of the new blocks introduced into the PC allows solving the problem of predicting the loss of targets in the Doppler resection zones, improving the situational awareness of the crew and reducing the time for setting goals at the exit from the resection zone.

Information sources

1. Dudnik P.I., Kondratenkov G.S., Tatarsky B.G. and others. Aviation radar systems and systems. - M.: VVIA, 2006.

2. Babich V.K., Bakhanov L.E., Karpeev V.I. and others. Air defense of Russia and scientific and technological progress. Combat systems and systems yesterday, today, tomorrow. / Ed. E.A. Fedosova. - M.: Bustard, 2001.

3. Willow V.S. Aviation complexes of radar patrol and guidance. Status and development trends. - M .: Radio engineering. - 2008.

4. Dudnik P.I., Ilchuk A.R., Tatarsky B.G. and other multifunctional radar systems. - M.: Bustard, 2007.

5. Merkulov V.I., Kanaschenkov A.I., Chernov V.S. and other Aviation systems of radio control. T.3. Command radio control systems. Autonomous and combined guidance systems. / Ed. A.I. Kanaschenkov and V.I. Merkulov. - M .: Radio engineering, 2004.

6. Merkulov V.I., Drogalin V.V., Kanaschenkov A.I. and other Aviation systems of radio control. T.2. Electronic homing systems. / Ed. A.I. Kanaschenkov and V.I. Merkulov. - M.: Radio Engineering, 2003.

Claims (1)

A radar system containing a radar, an indicator device, the first input of which is connected to the first output of the radar, characterized in that it further includes a unit for calculating the time of entry / exit of the target into the viewing area, the input of which is connected to the second output of the radar, a unit for calculating the parameters of the resection zone the input of which is connected to the second output of the radar, and the second output is to the second input of the indicator device, a decision block, the first input of which is connected to the output of the block for calculating the parameters of the resection zone, and the second input to the progress of the unit for calculating the time of entry / exit of the target into the field of view, the extrapolation unit, the input of which is connected to the output of the decision unit, and the second output is to the third input of the indicator device, the target identification unit, the first input of which is connected to the first output of the radar, the second input with the first output of the extrapolation unit, the third input with target signals from other carriers, and the output with the fourth input of the indicator device.

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