Gantry frame type pan-tilt platform for antenna testing and control method thereof

Abstract

The present invention relates to a gantry-frame gimbal for antenna testing and a control method thereof. The gimbal comprises a base, an azimuth control motor, a roll control motor, a gantry, a pitch control unit disposed below the gantry, and an antenna mounting unit disposed on the pitch control unit. The antenna mounting unit comprises an antenna polarization direction control motor, a central axis, and an antenna mounting base. The gimbal of the present invention utilizes an azimuth-pitch control mode during the ascent and descent phases of a drone's vertical semicircular flight, and a roll-pitch control mode during the overhead phase, with smooth switching of control modes during the transition phase. The present invention utilizes a gantry-frame gimbal to resolve the problem of existing drones' directional test antennas being unable to consistently align with a target during vertical semicircular flight. This allows the test antenna to more accurately point to the target being tested while maintaining its polarization direction. During the overhead phase, singularity issues can be avoided.

Description

Technical Field

[0001] The present invention relates to a pan / tilt platform carried by an unmanned aerial vehicle (UAV) and a control method thereof, and in particular to a pan / tilt platform for testing antennas of an UAV and a control method thereof. Background Art

[0002] The paper "How Drone Technology Will Transform Satellite Antenna Testing," Microwave Journal, September / October 2020, pp. 8-14, describes a case study of drone technology used in satellite antenna testing. The paper demonstrates a drone for satellite antenna testing in motion. The drone is equipped with a standard two-degree-of-freedom azimuth-pitch gimbal, equipped with a directional horn antenna covering both the X-band and Ku-band. This drone is capable of completing commercial satellite antenna testing in accordance with SOMAP requirements. However, the antenna test drone presented in the paper suffers from two issues in its gimbal design and application. First, large roll angles due to wind interference during testing affect the pointing accuracy of the test antenna. Even rapid azimuth control to redirect the test antenna toward the target can cause changes in the polarization direction of the test antenna. Second, during vertical semicircular overhead flight tests, the gimbal antenna test system exhibits singularity issues. Specifically, even slight roll or lateral deviations near the antenna under test can cause large jumps in the gimbal's azimuth control angle, preventing accurate pointing of the test target. Summary of the Invention

[0003] The present invention aims to provide a gantry-frame pan-tilt platform for antenna testing and a control method thereof, which solves the technical problems that the existing test pan-tilt platform cannot accurately control the polarization direction of the test antenna and cannot accurately point to the target under test during overhead testing.

[0004] The technical solution of the present invention is:

[0005] A gantry-frame pan-tilt platform for antenna testing is characterized in that it includes a base, an azimuth control motor and an azimuth axis vertically mounted on the base, a roll control motor mounting bracket fixedly connected to the azimuth axis, a roll control motor and a roll axis horizontally mounted on the roll control motor mounting bracket, a gantry mounted on the roll axis, a pitch control unit mounted below the gantry, and an antenna mounting unit mounted on the pitch control unit. The gantry includes a gantry crossbeam and two gantry columns; the gantry crossbeam is fixedly connected to the roll axis vertically; the pitch control unit includes a pitch control motor and a middle frame; the pitch control motor is fixed to the lower end of one of the gantry columns; one side frame of the middle frame is fixedly connected to the output shaft of the pitch control motor; the other side frame of the middle frame is rotatably connected to the lower end of the other gantry column; the antenna mounting unit includes an antenna polarization direction control motor, a middle axis, and an antenna mounting base connected in sequence; the antenna polarization direction control motor is fixed to the rear frame of the middle frame; the middle axis passes through the front frame of the middle frame and is fixedly connected to the antenna mounting base; and the antenna mounting base is used to mount a test antenna.

[0006] In order to adapt to test antennas of different specifications, the antenna installation unit may further include a counterweight disposed in the middle frame.

[0007] In order to facilitate the rapid replacement of test antennas of different specifications, the antenna mounting base can be a quick-release mounting base.

[0008] The control method of the gantry-frame gimbal for antenna testing is as follows: the gimbal adopts an azimuth-pitch control mode during the ascent and descent stages of the vertical semicircular flight of the UAV, and adopts a roll-pitch control mode during the overhead stage, and smoothly switches the control mode during the transition from the ascent stage to the overhead stage and from the overhead stage to the descent stage.

[0009] In the control method of the gantry-frame pan-tilt head for antenna testing described above, the range of each stage is as follows: with the angle directly above the target being measured as 0°, the range of the ascending stage is 90° to A, with A ranging from 55° to 10°; the range of the descending transition stage is B to -90°, with B ranging from -10° to -55°; the range of the transition from the ascending stage to the overhead stage is A to A+C, with C not exceeding 6°; the range of the transition from the overhead stage to the descending stage is B to BD, with D not exceeding 6°.

[0010] In the control method of the gantry-frame pan-tilt platform for antenna testing, the preferred values ​​of the interval ranges of each stage are: A=60°; B=-60°; C=5°; D=5°.

[0011] In the control method of the gantry-frame pan-tilt platform for antenna testing, the azimuth-pitch control mode is specifically as follows:

[0012] Desired gimbal pitch angle θgd Calculate according to the following formula

[0013]

[0014] Desired gimbal azimuth ψ gd , calculated as follows

[0015]

[0016] Expected gimbal roll angle φ gd Calculate according to the following formula

[0017]

[0018] The above roll-pitch control mode is specifically as follows:

[0019] Desired gimbal azimuth ψ gd , calculated as follows

[0020]

[0021] Desired gimbal pitch angle θ gd Calculate according to the following formula

[0022] θ gd =arcsin(xcosψ g -ysinψ g );

[0023] Expected gimbal roll angle φ gd Calculate according to the following formula

[0024]

[0025] in:

[0026] ψ vhc is the expected azimuth angle for the vertical semicircle mission;

[0027] R ij is the i-th row and j-th column element of the UAV direction cosine matrix R;

[0028] φ g is the current gimbal roll angle;

[0029] ψ g is the current gimbal azimuth;

[0030] x, y, z are the desired test antenna pointing vectors z P The three coordinate components of ;

[0031] z P is the desired test antenna pointing unit vector, calculated as follows

[0032]

[0033] Where, B O a The coordinates of the origin of the test antenna coordinate system in the body coordinate system; B P t is the position of the antenna under test in the body coordinate system.

[0034] The above-mentioned smooth switching of control modes specifically includes:

[0035] When transitioning from the ascending phase to the overhead phase, the desired azimuth angle of the gimbal is calculated according to the azimuth-pitch control mode and is recorded as ψ gdy At the same time, the desired azimuth angle of the gimbal calculated according to the roll-pitch control mode is denoted as ψ gdr , then the expected gimbal azimuth angle in this transition phase is ψ gd =kψ gdy +(1-k)ψ gdr , where the coefficient k changes from 1 to 0 over time within N seconds; then, under the current gimbal azimuth angle, the gimbal desired roll angle φ is calculated according to the roll-pitch control mode gd and the desired pitch angle θ gd ;

[0036] When transitioning from the overhead phase to the descent phase, the desired gimbal roll angle calculated according to the roll-pitch mode is denoted as φ gdr At the same time, the expected gimbal roll angle calculated according to the azimuth-pitch mode is denoted as φ gdy , then the expected gimbal roll control angle in this transition phase is φ pzt =kφ gdr +(1-k)φ gdy , where the coefficient k changes from 1 to 0 over time within N seconds; then, under the current gimbal roll angle, the desired gimbal azimuth angle ψ is calculated according to the azimuth-pitch control mode gd and the desired pitch angle θ gd .

[0037] The coefficient k changes from 1 to 0 within 1 second according to the normal flight speed of the UAV.

[0038] The present invention provides a simplified gantry frame type pan-tilt platform for antenna testing, which is special in that it includes a base, an azimuth control motor and an azimuth axis vertically arranged on the base, a roll control motor fixing bracket fixedly connected to the azimuth axis, a roll control motor and a roll axis horizontally arranged on the roll control motor fixing bracket, a gantry arranged on the roll axis, a pitch control unit arranged below the gantry, and an antenna mounting unit arranged on the pitch control unit; the gantry includes a gantry beam and two gantry columns; the gantry beam is fixedly connected to the roll axis vertically; the pitch control unit includes a pitch control motor and a middle frame; the pitch control motor is fixed to the lower end of one of the gantry columns; a side frame of the middle frame is fixedly connected to the output shaft of the pitch control motor; the other side frame of the middle frame is rotatably connected to the lower end of the other gantry column; the antenna mounting unit includes an antenna mounting seat; the antenna mounting seat is arranged on the front frame of the middle frame; the antenna mounting seat is used to mount a test antenna.

[0039] Beneficial effects of the present invention:

[0040] 1. The gantry frame type gimbal for antenna testing of the present invention adopts a four-axis or three-axis gantry frame type gimbal, which solves the problem that the directional test antenna of the existing UAV cannot always aim at the target and maintain the desired polarization direction when flying in a vertical semicircle. The gimbal realizes ±180° rotation of the pitch axis through the outer frame gantry design, which can make the test antenna continuously and uninterruptedly aim at the target and accurately maintain the desired polarization direction in the vertical semicircle test. Specifically, in the non-overhead flight stage, it can quickly compensate for the rolling motion of the UAV, so that the test antenna can point to the target more accurately, and at the same time accurately maintain the polarization direction of the test antenna; in the overhead flight stage, it can avoid the singularity problem, so that the test antenna can also accurately, smoothly and smoothly point to the target when it is near the target above the test antenna; it can continuously control the polarization direction of the test antenna during the test process to meet the needs of certain special antenna testing tasks.

[0041] 2. The gantry-frame gimbal for antenna testing of the present invention has a roll axis and a pitch axis that are simultaneously used to compensate for the attitude changes of the UAV, thereby improving the pointing control accuracy of the test antenna and overcoming the control singularity problem existing in a single azimuth-pitch control mode.

[0042] 3. The control method of the gantry-frame gimbal for antenna testing of the present invention adopts an azimuth-pitch control mode during the ascent and descent stages of vertical semicircular flight, and a roll-pitch control mode during the overhead stage. The transition stage is smoothed, thereby ensuring continuous control and improving control stability.

[0043] 4. The gantry-frame gimbal used for antenna testing of the present invention has an antenna polarization direction control motor and a test antenna connected by a central axis, which also acts as a counterweight, allowing the test antenna to protrude as far forward as possible and thus as far away from the drone as possible. Therefore, the antenna test data has lower background interference noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural schematic diagram of the gantry frame type pan-tilt platform for antenna testing of the present invention;

[0045] Figure 2 This is a schematic diagram of the position of the antenna on the gimbal of the present invention pointing straight ahead;

[0046] Figure 3 This is a schematic diagram of the position of the antenna on the gimbal of the present invention pointing directly downward;

[0047] Figure 4 Schematic diagram of the position of the antenna on the gimbal of the present invention pointing backward and downward at 45 degrees;

[0048] Figure 5 It is a schematic diagram of the partition control of the pan-tilt platform of the present invention when it is flying in a vertical semicircle.

[0049] Figure 1: 1-base; 2-azimuth control motor; 3-roll control motor; 4-gantry beam; 5-roll control motor fixing bracket; 6-gantry; 7-gantry column; 8-antenna polarization direction control motor; 9-pitch control motor; 10-middle frame; 11-middle axis; 12-antenna mounting base; 13-test antenna. DETAILED DESCRIPTION

[0050] Reference Figure 1 The gantry frame type pan-tilt platform for antenna testing of the present invention is composed of a base, a roll control motor fixing frame, a gantry, a middle frame, a middle axis, an azimuth control motor, a roll control motor, a pitch control motor, an antenna polarization direction control motor, and an antenna mounting base.

[0051] The gimbal base is fixed on the drone's load shock absorber frame. The gimbal base is equipped with thin-wall bearings to bear the weight of the gimbal and antenna. The gimbal gantry frame structure is designed to ensure that the antenna pointing can be continuously changed by nearly ±180°, such as Figure 2 、 Figure 3 、 Figure 4 shown.

[0052] The gimbal's azimuth axis is designed to compensate for changes in the aircraft's yaw angle and steer the antenna horizontally toward the target. The gimbal's roll axis compensates for changes in the aircraft's roll attitude, maintaining a horizontal gimbal gantry frame. It also controls the antenna's direction during lateral deviation during vertical semicircular flight. The gimbal's pitch axis primarily steers the antenna toward the target and compensates for changes in pitch attitude. The gimbal's center axis controls the antenna's polarization.

[0053] An antenna mount is designed at the end of the gimbal to accommodate various test antennas. The antenna mount can be connected using standard connections or with quick-release springs and clips, allowing for tool-free replacement of test antennas. The antenna polarization control motor is located farther from the gimbal's pitch axis to provide balancing. If necessary, add additional counterweights to the antenna or motor.

[0054] The control process of the present invention:

[0055] 1. Roll motion compensation

[0056] First, define φ g ,θ g ,ψ g Define φ as the current gimbal roll angle, current gimbal pitch angle and current gimbal azimuth angle. gd ,θ gd ,ψ gd are the desired gimbal roll angle, desired gimbal pitch angle, and desired gimbal azimuth angle.

[0057] Reference Figure 5 In the azimuth-pitch control range, we hope to compensate the UAV motion by rolling the axis to keep the gantry beam level at all times. The vector of the gantry beam in the ground coordinate system is expressed as

[0058]

[0059] in B y R is the representation of the beam vector in the body coordinate system, W y R is the representation of the beam vector in the ground coordinate system, and R is the direction cosine matrix of the drone. The gantry beam remains horizontal. W y R (3)=0, the expected gimbal roll angle is

[0060]

[0061] Where: R ij Represents the element in row i and column j of the direction cosine matrix R of the drone.

[0062] 2. Test antenna pointing calculation

[0063] Calculate the position of the antenna under test in the body coordinate system

[0064] B P t =R T ( W P t -t) (3)

[0065] Where: W P t Indicates the position coordinates of the antenna under test in the ground coordinate system, which is input into the UAV as a mission parameter before takeoff. B P t Indicates the position coordinates of the antenna under test in the body coordinate system, R T represents the transpose of the direction cosine matrix of the UAV, and t represents the coordinate transformation translation vector, that is, the position of the UAV in the ground coordinate system.

[0066] According to the positive kinematic relationship of the gimbal, the position coordinates of the origin of the test antenna coordinate system in the body coordinate system can be calculated according to the rotation angle of each axis of the gimbal. B O a

[0067]

[0068] Among them L a L is the distance from the upper surface of the base to the origin of the body coordinate system, b L is the distance from the gantry beam to the upper surface of the base, c L is the distance from the gimbal pitch axis to the gantry beam. d is the distance from the center of the antenna mount to the pitch axis of the gimbal. From this, we can get the desired test antenna pointing unit vector in the body coordinate system

[0069]

[0070] 3. Gimbal Azimuth-Pitch Control Mode

[0071] Reference Figure 5 In the azimuth-pitch control range of vertical semicircular flight, the azimuth-pitch control mode is used, and the gimbal roll axis rotation is used to compensate for the aircraft's roll motion. First, the gimbal roll angle φ g In the case of certainty, let ψ gd ,θ gd is the desired gimbal azimuth angle and the desired gimbal pitch angle, and the antenna pointing vector z can be obtained through the gimbal forward kinematics equation P , making it equal to the above formula, we can get

[0072]

[0073] Where: x, y, z represent the desired antenna pointing vector z P Solving this equation yields

[0074]

[0075] 4. Gimbal roll-pitch control mode

[0076] Reference Figure 5 , in the roll-pitch control range of vertical semicircular flight, the roll-pitch control mode is used. First, at the gimbal azimuth angle ψ g When determined, the antenna pointing vector equation is

[0077]

[0078] Solving this equation easily yields the desired gimbal roll angle and desired gimbal pitch angle.

[0079]

[0080] Solve the desired gimbal azimuth angle. It is hoped that after the gimbal azimuth axis rotates, the gimbal roll axis points to the desired direction of the vertical semicircle task ψ t (The direction from the vertical semicircle starting point to the vertical semicircle end point) is consistent. First, calculate the position vector of the gimbal roll axis in the body coordinate system:

[0081]

[0082] Convert to ground coordinate system

[0083] W x R =R B x R (11)

[0084] Make the azimuth of the projection of this vector on the ground equal to the desired azimuth ψ of the vertical semicircle mission vhc Consistent, available

[0085]

[0086] The desired gimbal azimuth angle is obtained as

[0087]

[0088] 5. Smooth switching of motion control modes

[0089] If the azimuth-pitch control range and the roll-pitch control range are switched directly, the gimbal will have obvious jitter. It is necessary to add a transition range to smooth the control mode switch. In the azimuth-pitch target tracking mode, the gimbal roll control maintains the gantry level, the gimbal azimuth controls the lateral deviation, and the gimbal pitch controls the longitudinal deviation. In the roll-pitch target tracking mode, the gimbal azimuth is controlled to face the semicircle direction, the lateral deviation is controlled by rolling, and the longitudinal deviation is controlled by pitch. Figure 5 The azimuth-pitch control range is 90° to 30° and -35° to -90°; the roll-pitch control range is 25° to -30°; there is a transition range between the two, and each transition range is 5°.

[0090] 1) From the azimuth-pitch control range to the roll-pitch control range

[0091] The desired azimuth angle of the gimbal calculated according to the azimuth-pitch control mode during the transition process is recorded as ψ gdy , the desired azimuth angle of the gimbal calculated according to the roll-pitch control mode is recorded as ψ gdr , then the expected gimbal azimuth angle in this transition phase is

[0092] ψ gd =kψ gdy +(1-k)ψ gdr (14)

[0093] Where: the coefficient k changes from 1 to 0 over time within 1 second.

[0094] Then, under the current gimbal azimuth angle, calculate the gimbal desired roll angle φ according to the roll-pitch control mode gd and the desired pitch angle θ gd .

[0095] 2) Roll-pitch control range to azimuth-pitch control range

[0096] The expected gimbal roll angle calculated according to the roll-pitch mode during the transition process is recorded as φ gdr At the same time, the expected gimbal roll angle calculated according to the azimuth-pitch mode is recorded as φ gdy , then the gimbal roll control angle is:

[0097] φ pzt =kφ gdr +(1-k)φ gdy (15)

[0098] The coefficient k changes from 1 to 0 over time within 1 second. Then, under the current gimbal roll angle, the desired gimbal azimuth angle ψ is calculated according to the azimuth-pitch control mode. gd and the desired pitch angle θ gd .

[0099] Design principle of the present invention:

[0100] (a) The gantry-frame pitch axis design enables continuous rotation of the pitch axis within ±150°, facilitating the test antenna's tracking of the target below.

[0101] (b) The roll axis is designed in the middle of the upper part of the gantry frame, perpendicular to the pitch axis but not intersecting at a point. When the target is located in front or behind, it is mainly used for roll motion compensation of the UAV. When the target is located below, it is used for both roll motion compensation and target tracking control.

[0102] (c) The end of the gimbal is designed with an antenna polarization direction control axis to facilitate the change of the test antenna polarization direction. In certain special tests, it can achieve continuous control of the polarization direction of the aerial test antenna.

[0103] (d) During vertical semicircular flight, there is a gimbal mode transition interval between the ascent phase and the overhead phase, and between the overhead phase and the descent phase. To prevent gimbal jitter caused by switching gimbal control modes, gimbal commands are smoothed within the transition interval.

Claims

1. A gantry-frame pan / tilt platform for antenna testing, characterized by: The invention comprises a base (1), an azimuth control motor (2) and an azimuth axis vertically arranged on the base (1), a roll control motor fixing frame (5) fixedly connected to the azimuth axis, a roll control motor (3) and a roll axis horizontally arranged on the roll control motor fixing frame (5), a gantry (6) arranged on the roll axis, a pitch control unit arranged below the gantry (6), and an antenna mounting unit arranged on the pitch control unit; The gantry (6) comprises a gantry crossbeam (4) and two gantry columns (7), forming an open structure; the gantry crossbeam (4) is vertically fixedly connected to the rolling axis; The pitch control unit comprises a pitch control motor (9) and a middle frame (10); the pitch control motor (9) is fixed to the lower end of one of the gantry columns (7); a side frame of the middle frame (10) is fixedly connected to the output shaft of the pitch control motor (9); the other side frame of the middle frame (10) is rotatably connected to the lower end of the other gantry column (7); the roll axis is perpendicular to the central axis of the pitch control motor (9) and does not intersect at a point; The antenna mounting unit comprises an antenna polarization direction control motor (8), a central axis (11), and an antenna mounting seat (12) which are connected in sequence; the antenna polarization direction control motor (8) is fixed at the rear frame of the central frame (10); the central axis (11) passes through the front frame of the central frame (10) and is fixedly connected to the antenna mounting seat (12); the antenna mounting seat (12) is used to mount a test antenna (13).

2. The gantry-frame type pan / tilt platform for antenna testing according to claim 1, characterized in that: The antenna installation unit also includes a counterweight arranged in the middle frame (10).

3. The gantry-frame type pan / tilt platform for antenna testing according to claim 1 or 2, characterized in that: The antenna mounting seat (12) is a quick-release mounting seat.

4. The control method of the gantry-frame pan / tilt platform for antenna testing according to any one of claims 1 to 3, characterized in that: The gimbal is in vertical semicircular flight of the drone: The range of the overhead phase is A to B, using the roll-pitch control mode; With the angle directly above the target as 0°, the range during the ascent phase is 90° to A, with A ranging from 55° to 10°; the range during the descent phase is B to -90°, with B ranging from -10° to -55°. Both the ascent and descent phases adopt the azimuth-pitch control mode. The range of the overhead phase is A to B, using the roll-pitch control mode; When transitioning from the ascending phase to the overhead phase, the transition range is A to A+C, where C is no more than 6°. The control mode is switched smoothly during the transition phase. The desired azimuth angle of the gimbal is calculated according to the azimuth-pitch control mode and is recorded as ψ gdy At the same time, the desired azimuth angle of the gimbal calculated according to the roll-pitch control mode is denoted as ψ gdr , then the expected gimbal azimuth angle in this transition phase is ψ gd =kψ gdy +(1-k)ψ gdr Here, the coefficient k changes from 1 to 0 over time in N seconds; When transitioning from the overhead phase to the descent phase, the transition range is B~BD, D is no more than 6°, and the control mode is smoothly switched during the transition phase. The desired gimbal roll angle calculated according to the roll-pitch mode is first recorded as ψ gdr At the same time, the expected gimbal roll angle calculated according to the azimuth-pitch mode is denoted as φ gdy , then the expected gimbal roll control angle in this transition phase is φ pzt =kφ gdr +(1-k)φ gdy The coefficient k changes from 1 to 0 over time within N seconds.

5. The control method of the gantry-frame pan / tilt platform for antenna testing according to claim 4, characterized in that: A=60°; B=-60°; C=5°; D=5°.

6. The control method of the gantry-frame pan / tilt platform for antenna testing according to claim 4 or 5, characterized in that: The azimuth-pitch control mode is: Desired gimbal pitch angle θ gd Calculate according to the following formula Desired gimbal azimuth ψ gd , calculated as follows Expected gimbal roll angle φ gd Calculate according to the following formula The roll-pitch control mode is: Desired gimbal azimuth ψ gd , calculated as follows Desired gimbal pitch angle θ gd Calculate according to the following formula i gd =arcsin(xcosψ g -ysinψ g ); Expected gimbal roll angle φ gd Calculate according to the following formula in: ψ vhc is the expected azimuth angle for the vertical semicircle mission; R ij is the i-th row and j-th column element of the UAV direction cosine matrix R; φ g is the current gimbal roll angle; ψ g is the current gimbal azimuth; x, y, z are the desired test antenna pointing vectors z P The three coordinate components of ; z P is the desired test antenna pointing unit vector, calculated as follows Where, B O a The coordinates of the origin of the test antenna coordinate system in the body coordinate system; B P t is the position of the antenna under test in the body coordinate system.

7. The control method of the gantry-frame pan / tilt platform for antenna testing according to claim 6, characterized in that: Said N=1.

8. A gantry-frame pan / tilt platform for antenna testing, characterized by: The invention comprises a base (1), an azimuth control motor (2) and an azimuth axis vertically arranged on the base (1), a roll control motor fixing frame (5) fixedly connected to the azimuth axis, a roll control motor (3) and a roll axis horizontally arranged on the roll control motor fixing frame (5), a gantry (6) arranged on the roll axis, a pitch control unit arranged below the gantry (6), and an antenna mounting unit arranged on the pitch control unit; The gantry (6) comprises a gantry crossbeam (4) and two gantry columns (7); the gantry crossbeam (4) is vertically fixedly connected to the rolling axis; The pitch control unit comprises a pitch control motor (9) and a middle frame (10); the pitch control motor (9) is fixed to the lower end of one of the gantry columns (7); a side frame of the middle frame (10) is fixedly connected to the output shaft of the pitch control motor (9); the other side frame of the middle frame (10) is rotatably connected to the lower end of the other gantry column (7); the roll axis is perpendicular to the central axis of the pitch control motor (9) and does not intersect at a point; The antenna mounting unit comprises an antenna mounting seat (12); the antenna mounting seat (12) is arranged on the front frame of the middle frame (10); and the antenna mounting seat (12) is used for mounting a test antenna (13).

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