JP2003344518A - System and method for tracking target - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for tracking target by which the level fluctuation of received signals can be suppressed. <P>SOLUTION: At the time of driving a movable antenna which is periodically driven under a step tracking system, the step-driving angle θ at every driving time is calculated by using a function using the difference between the reception level P2 of radio waves when the antenna is step-driven the last time and the reception level P1 of radio waves when the antenna is step-driven one time before the last time as an argument. In addition, the magnitudes of the levels P1 and P2 are compared with each other, and, when P1>P2, the antenna 2 is inversely driven by the step driving angle θ when the antenna is step-driven before the last time, because the reception level of radio waves drops after the antenna is step-driven. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target tracking system and a target tracking method for tracking a pointing direction of an antenna to a target that emits radio waves. In particular, the present invention relates to improvement of a method of tracking a target by the step track method.

[0002]

2. Description of the Related Art A step track system is known as one of the systems for tracking the pointing direction of an antenna to a target such as an orbiting satellite that emits radio waves. This method can track the radio source without the need for a guide signal,
Moreover, since it is a comparatively simple method compared to the currently mainstream monopulse roving method, it has an advantage of high reliability.

In the step track method, the directional direction of the antenna for tracking a target is physically changed in a stepwise manner, and the position of the radio wave source is estimated from the change in the intensity of the received signal before and after that. That is, when the signal strength increases after driving the antenna, the direction of change of the angle is maintained and the antenna driving process is performed next time. On the contrary, when the signal strength decreases, the direction of change of the angle is reversed. The moving target is tracked by repeating such processing periodically, for example, in the order of 1/100 second.

[0004]

By the way, in the conventional step track system, the step drive angle of the antenna is fixed. Therefore, depending on the moving speed of the target, the driving angle of the antenna is too large or too small, and the radio wave from the target is received at a position off the center of the antenna beam directivity pattern, and the strength of the received signal is increased. May fluctuate significantly.

If the fluctuation amount of the received signal strength is large, the effective antenna diameter becomes small, so that the received data may be missed. In principle, the step track method cannot avoid a change in the reception level, but there is a need to minimize the fluctuation amount of the reception signal level in order to avoid the above problems.

The present invention has been made under the above circumstances.
It is an object of the present invention to provide a target tracking system and a target tracking method that suppress fluctuations in received signal level.

[0007]

In order to achieve the above object, a target tracking system according to the present invention comprises a movable antenna which is tracked and controlled by a step track method toward a target, and which captures radio waves radiated from the target. Receiving means for receiving the electric waves captured by the movable antenna, level measuring means for measuring the receiving level of the electric waves received by the receiving means, and storage means for storing the receiving level data measured by the level measuring means. And a calculation means for adaptively calculating the step drive angle of the movable antenna from the history of the reception level data stored in the storage means, and a cycle of the movable antenna based on the step drive angle calculated by the calculation means. Drive to cause the movable antenna to track the target while changing the pointing direction of the movable antenna stepwise. Characterized by comprising a control means.

In particular, in the present invention, in the process of driving the movable antenna which is carried out periodically, the step driving angle θ at each time is set to the radio wave reception level P2 at the immediately preceding step driving, and the previous step driving time. The calculation is performed using a function that takes the difference from the reception level P1 of the radio wave in the above as an argument.

By taking such a means, in the target tracking system for tracking the target by the step track method, the step drive angle of the movable antenna is adaptively calculated from the reception level history data. That is, the step drive angle of the antenna is optimized according to the change in the reception level. As a result, it becomes possible to always capture the target in the maximum gain direction (bore sight) of the movable antenna, and thus it becomes possible to suppress the fluctuation of the received signal level.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a system configuration diagram showing an embodiment of a target tracking system according to the present invention. This system is an observation satellite (hereinafter referred to as satellite) that observes various objects on the earth in orbit.
And a ground station. The satellite 1 moves at various speeds depending on the distance to the ground station and the time. The ground station includes an antenna 2 that receives radio waves from the satellite 1 and a control station 3 that controls the antenna 2, and analyzes the received information to obtain knowledge about the object. The antenna 2 has its pointing direction controlled by the control station 3 in order to maintain a good reception state, and tracks the satellite 1. Antenna 2 by control station 3
The control system is a step track system, and therefore the antenna 2 is periodically step-driven and its pointing direction changes.

FIG. 2 is a functional block diagram showing the structure of the ground station shown in FIG. In FIG. 2, the radio wave transmitted from the satellite is received by the reception unit 31, and the reception level thereof is measured by the power meter 32. The reception level is measured each time the antenna 2 is step-driven.

The measured reception level is stored in the storage unit 33, and its history is accumulated. In this embodiment,
The reception level P2 measured during the previous antenna drive processing and the reception level P1 measured during the previous antenna drive processing are stored in the storage unit 33 while being updated over time. Since P1 is earlier than P2 in terms of time, subscripts 1 and 2 are added according to the order.

Both the data P1 and P2 are read by the arithmetic unit 34 and used to calculate the step drive angle θ at the next step drive of the antenna 2. Computing unit 34
Calculates θ using a function with the difference between P1 and P2 as an argument. As the function, for example, a function of θ = k (P1-P2) obtained by multiplying (P1-P2) by a constant term k is used. Alternatively, if the pattern function indicating the directivity pattern of the antenna 2 is known, (P1-P2) may be substituted into this pattern function as an argument to calculate θ.

The step drive angle θ thus obtained
Are provided to the antenna drive unit 35. The antenna drive unit 35 drives the antenna 2 periodically based on the step drive angle θ under the step track method. As a result, the antenna 2 follows the target while changing its pointing direction stepwise. The step drive angle θ is
It is updated every time the step drive process is performed.

FIG. 3 is a flow chart showing a processing procedure executed in the ground station 3 shown in FIG. Figure 3
In step S1 of, an initial value is given to the step drive angle θ. In the next step S2, the value of d indicating the initial driving direction of the antenna 2 is set. For example, if the sign of d is positive, the antenna 2 is driven in the forward direction, and if the sign of d is negative, the antenna 2 is driven in the reverse direction.

In the next step S3, the reception level of the radio wave at that time is measured, and the result is substituted into P1 and stored in the storage unit 33. In the next step S4, the antenna 2 is step-driven with the step drive angle θ and the drive direction d.

In step S5, the reception level of the antenna 2 whose directional angle has changed is measured, and the result is substituted into P2 and stored in the storage unit 33. In step S6, the reception levels P1 and P2 are compared, and the processing procedure branches according to the result. If P1 is less than or equal to P2, the processing procedure proceeds to step S10, and the step drive angle θ at the next step drive is newly calculated by the predetermined function f having (P1-P2) as an argument.

In step S11, the value of P2 is substituted for P1, and the value of P1 is updated accordingly. This updated P1
Is the next step drive angle θ with P2 measured next.
It is used to calculate Then, the processing procedure shifts to the step S4 again, and the driving processing of the antenna by the step track method is repeated with the passage of time.

On the other hand, when it is determined in step S6 that P1 is larger than P2, the processing procedure proceeds to step S7, and the sign of the driving direction d is reversed. In the next step S8, the antenna 2 is step-driven under the inverted sign d and the step drive angle θ. Here, the step drive angle θ calculated at that time is used.
That is, the step drive angle θ does not change, and only the antenna drive direction 2 is reversed. Therefore, the pointing direction of the antenna 2 returns to the state before the previous step driving. Then, after the reception level P2 of the antenna 2 is measured in step S9, the processing procedure reaches step S11.

In step S10 of the above processing procedure, the function f indicating the directivity pattern of the antenna beam formed by the antenna 2 can be used. The function f is
It can be obtained from a theoretical formula of antenna beam directivity, or can be obtained by actual measurement. When the directivity pattern of the antenna beam is known, it is possible to estimate which part of the directivity of the antenna beam caused the level change by (P1-P2).

Therefore, by using the directivity pattern of the antenna beam as the function f, the step drive angle θ corresponding to the drive error of the antenna can be obtained from (P1-P2). The step drive angle θ obtained by this method means the amount of deviation angle from the directivity center of the antenna beam to the direction in which the antenna is actually facing. Therefore, by driving the antenna in the driving direction d with this step driving angle θ, the satellite can be always captured at the center of the directivity of the antenna beam.
As a result, it becomes possible to suppress variations in the received signal level.

As described above, in this embodiment, when the movable antenna is periodically driven under the step track method, the step driving angle θ is set to the radio wave reception level at the immediately preceding step driving. The difference between P2 and the reception level P1 of the radio wave at the previous step drive is used for the calculation. Further, the magnitudes of P1 and P2 are compared, and if P1> P2, the reception level has decreased after step driving, so the antenna 2 is driven in reverse by the previous step driving angle θ.

Since this is done, the step drive angle θ is variably controlled to an optimum value. That is, when the fluctuation of the reception level before and after the step driving is small, the antenna 2 is driven with a relatively small step driving angle θ. On the contrary, when the fluctuation of the reception level is large, the antenna 2 is driven with a relatively large step drive angle θ. In this way, the step drive angle θ of the antenna 2 is optimized from the values of P1 and P2, so that the satellite 1 can always be captured at the center of the directivity of the antenna 2, thus suppressing fluctuations in the reception level. It will be possible.

Further, according to the present invention, since the satellite capturing position is always maintained near the center of the directivity of the antenna 2, the driving amount of the antenna 2 can be minimized. This means that if the driving moment of the antenna 2 is constant, the antenna 2 can be driven at a higher speed than in the conventional case. That is, the step cycle can be shortened. Therefore, according to the present invention, even if the target moving speed is higher, data is not lost,
It is possible to accurately track the target.

The present invention is not limited to the above embodiment. For example, a system for tracking the satellite 1 is assumed in the present embodiment, but the present invention can be applied to any other system as long as it is a system for tracking a target that generally emits a radio wave. Examples of this type of system include a system for tracking an aircraft or a flying object, a system for tracking a mobile mobile terminal, and the like.
In short, the present invention can be applied to any system as long as it is required to track a target that radiates a radio wave without a guide signal.

The object of tracking in the present invention is not limited to the moving target. The present invention can be applied to, for example, applications in which the directivity of an antenna is aligned with a geostationary satellite as a target. In such an application, if the directivity of the antenna on the ground is first roughly adjusted to the stationary target and the antenna is operated by the method of the present invention in the fine adjustment stage, the target is automatically captured at the center of the directivity. It Therefore, the labor of position adjustment can be greatly saved. It is very convenient for installing ground antennas that receive radio waves from broadcasting satellites.

Further, the present invention can be similarly applied to an application in which a stationary target is tracked by a mobile station. The present invention can be applied to, for example, the purpose of tracking a geostationary satellite from a ship. Furthermore, the present invention can be applied to a system in which both the target and the moving body move with each other.

In addition to the above, regardless of the form of the function for calculating the step drive angle θ or the antenna system such as a prime focus antenna, a Cassegrain antenna, an offset Cassegrain antenna, etc., various variations are possible within the scope of the present invention. Modifications can be made.

[0029]

As described above in detail, according to the present invention, it is possible to provide a target tracking system and a target tracking method in which variations in the received signal level are suppressed.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of a target tracking system according to the present invention.

FIG. 2 is a functional block diagram showing the configuration of the ground station 3 shown in FIG.

FIG. 3 is a flowchart showing a processing procedure executed in the ground station 3 shown in FIG.

[Explanation of symbols]

1 ... Observation satellite (satellite) 2 ... antenna 3 ... Control station 31 ... Receiver 32 ... Power meter 33 ... Storage unit 34 ... Calculation unit 35 ... Antenna driver

Claims (6)

[Claims] 1. A movable antenna, which is tracking-controlled toward a target by a step-track method and captures a radio wave radiated from the target, a receiving unit which receives the radio wave captured by the movable antenna, and a receiving unit which receives the radio wave. Level measuring means for measuring the reception level of the received radio wave, storage means for storing the reception level data measured by the level measuring means, and history of the reception level data stored in the storage means Calculation means for adaptively calculating the step drive angle, and the movable antenna is periodically driven based on the step drive angle calculated by the calculation means to move the movable antenna while changing the pointing direction of the movable antenna stepwise. A target tracking system comprising: a drive control unit that causes an antenna to track the target. 2. The calculation means sets a step drive angle at the next step drive of the movable antenna as θ,
The reception level of the electric wave at the time of the last step driving is set to P2.
The target tracking according to claim 1, wherein θ is calculated using a function having the difference between P1 and P2 as an argument, where P1 is the reception level of the radio wave in the previous step drive. system. 3. When the pattern function indicating the directivity pattern of the movable antenna is known, the calculating means is
The target tracking system according to claim 2, wherein θ is calculated by substituting the difference between P1 and P2 as an argument into the pattern function. 4. The calculating means sets θ = k, where k is a constant.
The target tracking system according to claim 2, wherein θ is calculated using a function of (P1-P2). 5. The drive control means, when P1> P2, reverses the pointing direction of the movable antenna by the step drive angle θ calculated at that time. The target tracking system described in any of 1. 6. A method of tracking a target by a step track method, wherein a step drive angle of an antenna for tracking the target is set between a received signal level at the immediately preceding step drive and a received signal level at the previous step drive. A target tracking method characterized by being calculated using a function having a difference as an argument.