JP6678789B1 - Radar test equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radar test apparatus used for absolute calibration of a radar image captured by a synthetic aperture radar R mounted on a flying object. A radar test device used for calibrating a synthetic aperture radar mounted on a flying object, the radar test device supporting an antenna part for transmitting and receiving pulsed radio waves to and from the synthetic aperture radar, and supporting the antenna part. It has a movable arm for rotating the movable arm and a rotating shaft for rotating the movable arm. This is a radar test device installed at approximately the same height. [Selection diagram]

Description

  The present invention relates to a radar test apparatus used for absolute calibration of a radar image captured by a synthetic aperture radar mounted on a flying object such as an aircraft or an artificial satellite.

  A radar test apparatus is used for absolute calibration of a radar image of a synthetic aperture radar (SAR). FIG. 7 schematically shows the relationship between a synthetic aperture radar R mounted on an artificial satellite and a conventional radar test apparatus 300 installed on the earth surface G. In FIG. 7, S is the traveling direction of the artificial satellite.

  The conventional radar test apparatus 300 transmits and receives a pulse radio wave between the synthetic aperture radar R mounted on an artificial satellite and the radar test apparatus 300 mounted on the earth surface G. An amplifier for amplifying a received pulse signal and a variable attenuator for setting a radar cross-sectional area of the radar test apparatus 300 are provided.

  The pulse radio waves from the synthetic aperture radar R mounted on the artificial satellite are received by a receiving antenna in the radar test apparatus 300 installed on the earth surface G, and then amplified to a predetermined level by an amplifier. The attenuation amount of the amplified received pulse signal is adjusted by the variable attenuator so that the radar cross-sectional area of the radar test apparatus is set to a predetermined value. Thereafter, the received pulse signal is amplified to a predetermined level by an amplifier, and then a pulse radio wave is transmitted from the transmitting antenna to the synthetic aperture radar R. Such processing is realized by the RF circuit of the radar test apparatus 300.

  In the radar test apparatus 300, a signal transmission time determined from the configuration of the RF circuit is required from the reception to the transmission of the pulse radio wave, so that a delay time Δt is generated. Then, due to the influence of the delay time Δt of the radar test device 300, the point image position of the radar test device 300 appearing on the radar image is shifted (shifted) in the range direction (the direction orthogonal to the traveling direction of the artificial satellite (azimuth direction)). Would. This is shown in FIG. In FIG. 8, the point Q is the position where the radar test apparatus 300 is installed, but due to the influence of the delay time Δt, the point image position of the radar test apparatus 300 shifts to the position indicated by the point P or the point P ′. appear. For example, if the delay time Δt in the radar test apparatus 300 is about 10 nanoseconds, a position shift of about 1 to 2 meters occurs.

  Therefore, as a radar test apparatus for solving the above technical problem in the radar test apparatus 300, there is one described in Patent Document 1 below.

JP 2012-208043 A

  According to the radar test apparatus 300 described in Patent Document 1, the delay time Δt of the radar test apparatus 300 can be canceled by the time advance Δt depending on the installation position of the radar test apparatus 300, and the point image position of the radar test apparatus 300 The displacement can be eliminated.

  However, since it is necessary to bring the antenna unit close to the synthetic aperture radar by a distance that substantially matches the delay distance, it is necessary to increase the length of the movable arm when the frequency is low. When the movable arm is tilted in the direction of the synthetic aperture radar, the heavy antenna part is located at the tip, so that the balance of the radar test device is not stable and it becomes difficult to tilt the antenna part. Issues arise.

  Therefore, it is conceivable to shorten the length of the movable arm to make it easier to balance the radar test apparatus. In this case, the time advance Δt due to the installation position of the radar test apparatus 300 is larger than the delay time Δt of the radar test apparatus 300. Is also small, so that a point image position shift occurs.

  In view of the above technical problem, the present inventor has set the rotating shaft in the radar test apparatus at an appropriate position, thereby making the length of the movable arm shorter than before and the radar test apparatus when the antenna unit is tilted. In addition to solving the operational problem that it is difficult to achieve a balance between the points, we have invented a radar test apparatus that can keep the deviation of the point image position within a practically acceptable range.

A first invention is a radar test device used for calibrating a synthetic aperture radar mounted on a flying object, wherein the radar test device transmits and receives a pulse radio wave to and from the synthetic aperture radar, a processing unit for executing processing on the pulse signal received by the antenna portion, and a movable arm which supports the antenna unit includes a, a rotary shaft to be rotatable with the movable arm, the length of the movable arm Has a length shorter than the distance corresponding to the delay time of the processing unit, and the rotation axis has a point image position where the off-nadir angle is the maximum and a point image position where the off-nadir angle is the minimum. This is a radar test device installed at a height that approximately matches.

  By configuring the radar test apparatus as in the present invention, it is possible to solve the operational problem by shortening the length of the movable arm and to keep the deviation of the point image position within a practically acceptable range. it can.

  In the above invention, the radar test apparatus positions the reference axis near the center of the appearance range of the point image position when the off-nadir angle is the maximum and the point image position when the off-nadir angle is the minimum. It can be configured like a radar test device.

  The reference axis of the radar test device corresponding to the ground reference point may be located as in the present invention. In particular, the reference axis may be located near the center of the appearance range of the point image position where the off-nadir angle is the maximum and the point image position where the off-nadir angle is the minimum.

  In the above invention, the radar test apparatus calculates a tilt angle of the movable arm based on an off-nadir angle of the synthetic aperture radar, and tilts the movable arm at the calculated tilt angle with respect to a normal. It can be configured like a test device.

  The deviation of the point image position of the radar test equipment depends on the off-nadir angle. Therefore, by tilting the movable arm as in the present invention, it is possible to prevent deviation of the point image position of the radar test apparatus.

  In the above invention, the radar test apparatus further includes an auxiliary arm connected at one end to the movable arm, rotatable at a connection point, and supporting the movable arm when the movable arm is tilted. It can be configured like a radar test device having:

  When the movable arm is tilted, a load is generated on the rotation shaft that is the center of rotation, and the rotation shaft may be loosened. Therefore, by supporting with the auxiliary arm as in the present invention, loosening of the rotating shaft can be prevented.

  According to the present invention, the rotating shaft in the radar test apparatus can be provided at an appropriate position. This solves the operational problem of making the length of the movable arm shorter than before, making it difficult to balance the radar test device when the antenna is tilted, and also reduces the deviation of the point image position in practical use. It can be within an acceptable range.

It is a side view of the radar test device of the present invention. It is a top view of the radar test device of the present invention. FIG. 1 is an example of a simplified configuration diagram of a radar test apparatus including the function of an RF circuit of the radar test apparatus of the present invention. FIG. 4 is a diagram illustrating that a rotation axis and a reference axis are determined in the radar test apparatus of the present invention. FIG. 9 is a diagram illustrating an example of a positional shift of a point image. FIG. 4 is a diagram schematically illustrating a relationship between an off-nadir angle θ _off of a synthetic aperture radar and a tilt angle of a movable arm. FIG. 9 is a diagram illustrating an example of a configuration of a conventional radar test apparatus. FIG. 9 is a diagram showing that a position shift of a point image occurs on a radar image by a conventional radar test apparatus.

  1 and 2 show an example of a radar test apparatus 1 according to the present invention. FIG. 1 is a side view of the radar test apparatus 1, and FIG. 2 is a top view of the radar test apparatus 1.

  The radar test apparatus 1 of the present invention has a housing 2, an antenna unit 3, a movable arm 4, a rotating shaft 5, a level base 6, a reference shaft 7, and an auxiliary arm unit 8.

  The housing 2 includes a control circuit (processing unit) for performing signal processing in the radar test apparatus 1, preferably an RF circuit therein. FIG. 3 is a diagram schematically showing a simplified configuration diagram of the radar test apparatus 1 including the function of the control circuit of the housing 2. The RF circuit includes at least the amplifier 3c, the variable attenuator 3e, and the amplifier 3d, but may include other devices according to the purpose. In the following description, the case of an RF circuit will be described, but other circuits may be used.

  An antenna unit 3 is provided on the upper surface of the housing 2. The antenna unit 3 transmits and receives radio waves to and from a synthetic aperture radar R mounted on a flying object such as an airplane or an artificial satellite. The antenna unit 3 includes a receiving antenna 3a and a transmitting antenna 3b.

  The antenna unit 3 and the RF circuit are electrically connected inside the housing 2. A pulse radio wave from a synthetic aperture radar R mounted on a flying object such as an artificial satellite is received by a receiving antenna 3a in an antenna unit 3 of the radar test apparatus 1, and then received by an amplifier 3c of an RF circuit to a predetermined level. The signal is amplified. Then, the attenuation is adjusted by the variable attenuator 3e of the RF circuit so that the radar cross-sectional area of the radar test apparatus 1 is set to a predetermined value, and the signal is amplified to a predetermined level by the amplifier 3d. 3 is transmitted from the transmitting antenna 3b to the synthetic aperture radar R in the form of pulse radio waves. The configuration of the RF circuit is the same as the conventional one.

  On the earth surface G, a level base 6 for setting the azimuth and maintaining a horizontal plane is installed. Above the level board 6, there is a rotary shaft 5 that allows the movable arm 4 for setting the direction of the antenna section 3 to be rotatable. The lower end of the movable arm 4 is connected to the rotary shaft 5. The upper end of the movable arm 4 is joined to the bottom surface of the housing 2 at a joint 41. The joining method between the housing 2 and the movable arm 4 may be any method, and various joining methods such as screwing and welding can be adopted. The length Lr of the movable arm 4 is shorter than the distance corresponding to the delay time Δt in a processing unit such as an RF circuit.

  The bench 6 is provided with a reference shaft 7. The reference axis 7 is an axis 81 indicating the GCP (ground reference point) of the synthetic aperture radar R. The GCP is a coordinate point on the reference map corresponding to specific image information. The reference axis 7 is set in a vertical direction from a point of contact with the earth surface G (ground reference point). The reference shaft 7 is preferably formed of a metal needle or rod that can be embedded in the earth surface G for the purpose of specifying the position, but is not limited thereto. The indication indicating the reference axis 7 may be displayed on the upper surface of the level base 6. The bench 6 is preferably installed on the earth surface G such that the reference axis 7 provided on the bench 6 coincides with the ground reference point on the earth surface G in latitude and longitude. In this case, the latitude and longitude of the reference axis 7 provided on the level base 6 and the latitude and longitude of the ground reference point on the earth surface G do not have to exactly match, and there is no problem in practical accuracy. It may be a degree match, that is, a rough match.

  The material of the movable arm 4 may be made of metal such as iron or aluminum, or may be made of graphite. It is preferable to use graphite as a material because the influence of radio waves can be reduced. Further, the influence of radio waves may be reduced by wrapping a radio wave absorbing material around the movable arm 4. Examples of the radio wave absorber include a rubber sheet-like ferrite and carbon. Further, the movable arm 4 may be made of a conductive radio wave absorbing material, a magnetic radio wave absorbing material, or the like, such as made of graphite. Further, similarly to the movable arm 4, the level base 6, especially the upper surface thereof can be made of a conductive radio wave absorbing material, a magnetic radio wave absorbing material, or the like.

  The upper end of the auxiliary arm 8 is connected to the movable arm 4, and the other end is in contact with the earth surface G, so that when the movable arm 4 is tilted, the housing 2, the antenna unit 3, the movable arm 4 Support 4 The auxiliary arm unit 8 includes an auxiliary arm 80, a shaft 81, and a stopper 82. It is preferable that the length of the auxiliary arm 80 be adjustable. This is for adjusting the length of the auxiliary arm 80 when the movable arm 4 is tilted. The connection between the auxiliary arm 80 of the auxiliary arm portion 8 and the movable arm 4 is stopped by a shaft 81. As a result, the auxiliary arm unit 8 can rotate around the shaft 81. A stopper 82 is provided at the other end of the auxiliary arm 80.

  When the antenna unit 3 is tilted in a desired direction, the movable arm 4 rotates about the rotation shaft 5, and the tilted movable arm 4, the antenna unit 3, and the housing 2 are supported by the auxiliary arm unit 8. However, in the radar test apparatus 1 of the present invention, the length Lr of the movable arm 4 corresponds to the delay time Δt in the processing unit such as the RF circuit in order to secure the balance of the radar test apparatus 1 when the antenna unit 3 is tilted. The length is shorter than the distance to be performed. As a result, the operational problem caused by tilting the movable arm 4 can be solved, but a positional shift of the point image occurs.

  Therefore, the height of the rotation axis 5 (the height H from the earth surface G) in the radar test apparatus 1 is defined by the point image position when the off-nadir angle is the maximum and the point image position when the off-nadia angle is the minimum. The position between the point images when the off-nadir angle is maximum and the point image position when the off-nadir angle is minimum coincide with each other. be able to. This is schematically shown in FIG. It should be noted that the coincident positions do not need to be exactly coincident, and may be coincidences at which there is no problem in practical accuracy, that is, approximate coincidences.

The height H from the earth surface G to the rotation axis 5 and the point image position of the earth surface G where the point image when the off-nadir angle is the maximum and the point image when the off-nadia angle is the minimum coincide with each other are P ₀ , If the distance from the axis of rotation 5 to the position P ₀ from the intersection Q of the perpendicular and the earth surface G for the Earth's surface G was X, the point image position in addition to the off-nadir angle other than off-nadir angle of minimum or maximum P _The range in which the point image deviates from ₀ is within the range of ΔX shown in FIG. Therefore, if the level base 6 is installed so that the reference axis 7 is located at the center of the range ΔX in which the point image is shifted, the positional deviation of the point image from the reference axis 7 is within ± ΔX / 2. FIG. 5 is a diagram illustrating an example of a positional shift of a point image. The center may not be strictly at the center, but may be at the center where practical accuracy does not cause a problem, that is, near the center.

  As described above, the height H of the rotating shaft 5 is set so that the point image position when the off-nadir angle is the maximum and the point image position when the off-nadir angle is the minimum coincide (including a position where the off-nadir angle approximately matches). By doing so, the positional shift of the point image of the radar test apparatus 1 can be suppressed to within about one-fifth of the resolution of the synthetic aperture radar R which is a practically allowable range.

In FIG. 4, the length Lr of the movable arm 4, the length Lv of the virtual movable arm on the earth surface G side from the rotation axis 5, the delay time of the radar test apparatus 1 is Δt, and c is the speed of light (= 3 × 10 ⁸ km / sec), Equation 1 holds.
(Equation 1)

The length Lr of the movable arm 4 is as shown in Expression 2.
(Equation 2)

  When the length Lr of the movable arm 4 is determined in advance, the height position H of the rotating shaft 5 can be set by calculating Expression 2.

  The delay time Δt of the radar test apparatus 1 can be predicted at the design stage and its value can be used. However, after the RF circuit and the antenna unit 3 of the radar test apparatus 1 are manufactured, the delay time Δt is actually used by using them. Is measured, the movable arm 4 having the length Lr is manufactured based on the actually measured delay time Δt, and the positioning of the rotating shaft 5 can further improve the accuracy.

Further, the directional direction of the radar test apparatus 1 changes depending on the off-nadir angle θ _off of the synthetic aperture radar R. However, as for the pointing direction, if the set angle of the movable arm 4 is changed to a predetermined angle in accordance with the off-nadir angle θ _off , even if the off-nadir angle changes from θ _off to θ ′ _off , the radar test apparatus 1 Is not shifted.

で表される。ここで，飛翔体の高度Ｈ，地球半径Ｒ_０およびオフナディア角θ_ｏｆｆは既知の値であるから，オフナディア角θ_ｏｆｆが与えられれば，可動アーム４の傾き角θ_ｉは数３により算出できる。たとえば飛翔体の高度Ｈ＝５００キロメートル，オフナディア角θ_ｏｆｆを３０度とした場合，可動アーム４の法線方向からの傾き角θ_ｉは数３により３２．６度となる。 FIG. 6 schematically shows the relationship between the off-nadir angle θ _off of the synthetic aperture radar R and the tilt angle of the movable arm 4. When the height of the flying object equipped with the synthetic aperture radar R is H, the radius of the earth is R ₀ , the off-nadir angle of the synthetic aperture radar R is θ _off , and the inclination angle of the movable arm 4 from the normal direction is θ _i. The relationship between the off-nadir angle θ _off of the synthetic aperture radar R and the tilt angle θ _i of the movable arm 4 is as follows:
(Equation 3)

It is represented by Here, since the altitude H of the flying object, the earth radius R _0, and the off-nadir angle θ _off are known values, if the off-nadir angle θ _off is given, the inclination angle θ _i of the movable arm 4 is calculated by Expression 3. it can. For example, when the altitude H of the flying object is 500 km and the off-nadir angle θ _off is 30 degrees, the inclination angle θ _i of the movable arm 4 from the normal direction is 32.6 degrees according to Equation 3.

As described above, shortening of the movable arm 4 of the length Lr radar test apparatus 1, by inclining at the inclination angle theta _i from the normal direction calculated by the number 3, the length of the movable arm 4 than the conventional As a result, the operational problem of the radar test apparatus 1 can be solved, and the deviation of the point image position can be kept within a practically allowable range.

  The rotating shaft 5 may be provided directly on the level base 6, or a rod-shaped support member made of metal or the like may be projected vertically upward from the level base 6, and the rotating shaft 5 may be provided on the supporting member.

As described above, the inclination of the housing 2, the antenna unit 3, and the movable arm 4 may be manually performed, but may be realized by an inclination control unit (not shown) that controls the inclination by a computer. The tilt control unit is attached to a position where the tilt control is performed (the above-described rotation shaft 5 or the like), calculates the tilt angle θ _i by the above-described equation 3, and automatically combines the motor and the gear by a known method to automatically control the tilt. Can be controlled.

  Furthermore, if the latitude and longitude of the position of the reference axis 7 on the bench 6 of the movable arm 4 on which the radar test apparatus 1 is installed are measured using a GPS receiver, the point image P on the radar image and the latitude and longitude are measured. The correspondence with longitude can be associated.

  When the position of the transmitting antenna 3b in the radar test apparatus 1 is offset from the synthetic aperture radar R in the azimuth direction (the direction of travel of the artificial satellite S), the movable arm 4 is considered in consideration of the offset. The latitude and longitude of the level bench 6 of the section are measured.

  According to the radar test apparatus 1 of the present invention, the radar test apparatus 1 in which the position is not shifted in the range direction on the radar image can be realized. Further, the radar test apparatus 1 of the present invention can also be used as a ground reference point.

R: Synthetic aperture radar G: Earth surface 1: Radar test equipment 2: Housing 3: Antenna unit 3a: Receiving antenna 3b: Transmitting antenna 4: Movable arm 5: Rotating axis 6: Level base 7: Reference axis 8: Auxiliary arm 41: Joint 80: Auxiliary arm 81: Shaft 82: Stopper

Claims (4)

A radar test device used for calibrating a synthetic aperture radar mounted on a flying object,
The radar test device includes:
An antenna unit for transmitting and receiving pulse radio waves to and from the synthetic aperture radar;
A processing unit that performs processing on the pulse signal received by the antenna unit;
A movable arm supporting the antenna unit;
A rotating shaft that makes the movable arm rotatable.
The length of the movable arm is
A length shorter than a distance corresponding to the delay time of the processing unit,
The rotation axis is
The point image position when the off-nadir angle is the maximum and the point image position when the off-nadir angle is the minimum are set at a height that approximately matches.
A radar test apparatus characterized in that: The radar test device includes:
Positioning the reference axis near the center of the appearance range of the point image position when the off-nadir angle is the maximum and the point image position when the off-nadir angle is the minimum;
The radar test apparatus according to claim 1, wherein: The radar test device includes:
Calculating a tilt angle of the movable arm based on an off-nadir angle of the synthetic aperture radar, and tilting the movable arm at the calculated tilt angle with respect to a normal line;
The radar test apparatus according to claim 1 or 2, wherein: The radar test apparatus further comprises:
An auxiliary arm connected at one end to the movable arm, rotatable at a connection point, and supporting the movable arm when the movable arm is tilted;
The radar test apparatus according to any one of claims 1 to 3, wherein:

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