GB2320368A - Three axis controller for a directional antenna - Google Patents

Abstract

A three axis AZ, X, Y control method or system, suitable for an antenna mounted on a mobile platform, comprises inputting target coordinates 100, detecting the angle of the antenna on each axis relative to the platform and detecting the roll angle and pitch angle of the mounting platform relative to the horizontal level. From the above data control signals * capital Greek phi *xtd, * capital Greek theta*x, * capital Greek theta*y are derived for compensating the errors present in the three axis angles. The target coordinates 100 may be obtained using a locate and tracking facility which includes trial and error steptrack 104 adjustments until a signal of an acceptable quality is obtained. The bearing of the mobile platform 106 may be obtained from a gyrocompass whilst potentiometers may be used to detect the angle of the antenna on each axis. Inclinometers may be used to derive the roll and pitch angle of the platform.

Description

3-AXIS CONTROLLER FOR DIRECTIONAL ANTENNA Background of the Invention Field of the Invention This invention relates to a directional antenna apparatus comprising a directional antenna and an AZ-X-Y mount for supporting the directional antenna, which is suitable for use in the communications through INMARSAT (International Maritime Satellite Telecommunication Organization). More specifically, this invention relates to a 3-axis controller for the above-mentioned directional antenna apparatus. Certain prefered elTbodirnents of the present invention provide an improvement in a function to stabilize the directional antenna against the inclination of the moving platform such as a ship and a function to track a target such as an artificial satellite using the directional antenna, by steering the directional antenna about an AZ axis, an X axis, and a Y axis.

Description of the Related Art At certain times, in order to secure high quality signal reception from a target by using a directional antenna mounted on a moving platform, it is expedient to control the beam direction of the antenna according to the relative motion of the moving platform with respect to the target and according to the inclination of the moving platform. One means of controlling the beam direction known in the art is an antenna mount or a pedestal comprising a plurality of steerable mechanical axes which pivotally supports the antenna on the moving platform so that it can control the beam direction by causing them to rotate as appropriate about the mechanical axes. Accordingly, by steering the mechanical axes based on information relating to the direction of the target (azimuth and elevation), the bearing of the moving platform, the roll angle and pitch angle of the moving platform, and the angular positions of the mechanical axes, the beam direction of the directional antenna may be kept in a target direction, regardless of the inclination of the moving platform ("stabilization") and regardless of the movement of the moving platform ("tracking").

Compared to the conventional X-Y-Az-E 1 mount, an AZ-X-Y mount has a smaller number of mechanical axes, and consequently, it has a simpler mechanism and can be more economically manufactured. The AZ-X-Y mount has three mechanical axes, i.e. an AZ axis arranged on the deck of the moving platform. along the direction of the vertical when the moving platform is not inclined, an X axis supported by the AZ axis so as to direct horizontally when the moving platform is not inclined, and a Y axis for supporting the directional antenna and supported by the X axis which is perpendicular to the Y axis. In a directional antenna system using the AZ-X-Y mount, the beam of the directional antenna is controlled to point the target by controlling the AZ (or traverse)-axis in azimuth direction, the X (or cross-elevation, or cross-level)-axis in level and the Y (or elevation)-axis in elevation and level. The following references by Harries et al, and SR145 and SR150, are examples of prior art technology related to AZ-X-Y mounts.

Harries et al.: "Naval Satellite Communications Tenninals", G.Harries and J.W.Heaviside, IEE "Satellite Systems for Mobile Communications and Surveillance" Conference Publication, No. 95, 1973-03, pp.48-51.

SR145: "Study Report related to Geostationary Weather Satellite Climate Information Automatic Transmitting and Receiving System", 145th Study Group Meeting of Shipbuilding Research Association of Japan, Research Data No. 227, p.29-32, esp. p.29. Table 4.1 and p.32, Fig. 4. 11, March, 1975 SR150: "Study on Ship Navigation Systems and Ship Onboard Equipment using Satellites", 150th Study Group Meeting of Shipbuilding Research Association of Japan, Research Data No. 246, p.140- 150, March, 1976 In these references, Harries et al. and SR145 mention SCOT I and SCOT II which contain azimuth (or traverse) axis, cross-level (or X) axis and elevation (or Y) axis for each. These antenna systems were developed by The Admiralty Surface Weapons Establishment, Portsmouth and others. In SCOT I, as mentioned on page 49 of Harries et al., and in Fig. 4, 11 of SR145, the antenna is free to move +l- 30 degrees about the cross-level axis and - 20 degree to +120 degree in elevation. A stabilized platform on the elevation gimbal carries the gyros and two accelerometers to provide the reference signals which allows the servo system to maintain the pointing angle of the antenna. This package contains a small instrument servo which maintains the perform vertical about the elevation axis, three gyros and two accelerometers and a printed board carrying buffer amplifiers. Also SCOT I, as mentioned on page 51 of Harries et al., the antenna adopt a "conical scan" autotrack system which causes the antenna to scan with the circular motion at the frequency of 1 Hz. Any offset from the direct line of the sight to the satellite causes 1 Hz modulation of the received signal, which can be employed to derive error signal which causes a small signal servo to correct the demand pointing angles about the azimuth (or traverse) axis and the elevation axis (or Y-axis).

However, a complex antenna structure is usually required for a conical scan autotrack system because the antenna beam is offset by tilting either the feed or the subreflector with respect to one another and rotated continuously about a rotation axis. As a result, conical-scan antenna systems are usually rather costly.

As mentioned in p.140, lines 8-10, SR 150 utilizes a sensor for detecting the inclination angle of the moving platform on the AZ axis and enables reducing the azimuth tracking error from the inclination of the moving platform. The tracking error mentioned here is tracking error which occurs because data concerning the azimuth of the target is used to control the antenna mount, and in particular its angular position on the AZ axis, although the plane in which the data are obtained (horizontal plane) and the plane in which the antenna mount is disposed (deck plane) are not the same. When the inclination angle of the moving platform is large, this azimuth tracking error is more evident. Fig. 7 shows the results of a simulation performed by the inventor of the invention claimed in this application. According to this simulation, when the elevation of the directional antenna is as low as 5 degrees, the azimuth tracking error increases conspicuously when the roll angle exceeds 25 degrees. The horizontal axis in the figure is the azimuth of the target relative to the moving platform according to the virtually horizontal deck coordinate system, and the vertical axis in the figure is a value obtained by subtracting the aforesaid relative azimuth from the ideal value of the bearing angle of the AZ axis according to deck coordinate system, i.e. the azimuth tracking error (these coordinate systems will be defined hereafter).In SR150, the inclination angles of the ship about the X and Y axes are detected by a pair of inclination sensors on an AZ platform, the detected values of inclination angle are used to perform X/Y axes control, and the azimuth tracking error according to the inclination of the moving platform is derived based on these detected values. Next, yaw angle of the ship is detected by a yawing detector installed on the ship hull, and a value obtained by subtracting the detected value of yaw angle from the azimuth tracking error is taken as a control variable of the AZ axis (AZ axis control error signal). It might therefore be expected that, since the relative variation of the target azimuth due to inclination of the moving platform has been taken into account, there is not likely to be a severe azimuth tracking error.

However, whereas the azimuth tracking error due to the inclination of the moving platform is a quantity defined in the deck coordinate system, yaw angle is a quantity defined in the horizontal coordinate system, hence the physical meaning of the AZ axis control variable which is the difference between these two quantities is unclear. Furthermore, it appears that the X axis is assumed to be correctly oriented in the direction of the azimuth of the target when computing the azimuth tracking error a cb i due to the inclination of the moving platform by E g. (11.1.17). In practice, since the relative azimuth of the target varies dynamically due to rolling and pitching, the control error in the angular position of the AZ axis due to factors such as the delay in the AZ axis drive motor servocontrol system cannot be ignored. There is therefore a problem as to whether or not it is possible to use an AZ axis control error signal of the quality obtained by the method of SR150, in applications which demand high precision tracking. In other words, this may lead to an increase of mean square tracking error under severe conditions.

SUMMARY OF THE INVENTION It is therefore desirable to enhance the quality of an error signal for AZ axis control, to reduce a target tracking error and in particular an azimuth tracking error A rtd or A for AZ axis control, and to enhance steptrack performance by using the error signal enhanced in its quality.

Certain prefered embodiments of the invention address this object by providing a specific method for precisely estimating the azimuth tracking error A iLd or h 1* due to an error in the servo-control system a residual error in steptrack, and so forth.

It is further desirable to benefit from the advantage of a smaller number of mechanical axes offered by an AZ-X-Y mount in comparison to an X-Y-AZ-El mount.

It is further desirable to stabilize an antenna and rapidly capture a target even when a target direction is not initially given, and to enhance tracking precision, by utilizing target searching and steptrack operations.

It is further desirable to provide a specific method of target searching applicable for the case where a moving platform is inclined.

A preferred embodiment of this invention is a controller which controls the mechanical axes of an AZ-X-Y antenna mount for supporting a directional antenna. In the present application, the AZ-X-Y mount is defined as a mount having an AZ axis arranged on a moving platform along a direction which would be coincide with the direction of the vertical when the moving platform is not inclined, an X axis arranged on the AZ any so as to direct horizontally when the moving platform is not inclined, and a Y axis supported by the X axis and which is perpendicular to the X axis. Fig. 1 and Fig. 2 show examples of antenna mounts complying with this definition. In these figures, the AZ-X-Y mount comprises an AZ axis 10 arranged on a mounting plane of the moving platform (a deck in the case of a ship), an X axis 12 arranged on the AZ axis 10 such that it is perpendicular to the AZ axis 10, and a Y axis 14 arranged on the X axis 12 and being perpendicular to the X axis 12. This mount pivotally supports a directional antenna having a beam shown by A in the figures. The difference between the mounts shown in Fig. 1 and Fig. 2 is a difference in the way the axes are steered, i.e. whereas in Fig. 1 a structure on each of the axes is rotated by a rotation of the corresponding axis, in Fig. 2 the structure is rotated about the corresponding one of the axes without rotating the axis itself. In the context of this application, these steering systems are both referred to by the expression "a rotation about axes". Moreover, it should be understood that Fig. 1 and Fig. 2 are merely examples.

A preferred embodiment of this invention is a controller comprising a target direction input means, moving platform bearing input means, mechanical axes angular position detection means, inclination angle detection means, AZ axis control means and XTY axes control means. To better describe the functions of these various means, the coordinate systems and variables used in this application are defined in Table 1 - Table 6 along with Fig. 3 in which the relations between these coordinate systems and variables are shown schematically. To simplify the following description, all axes are assumed to be perpendicular to one another and the true north N is taken as a reference azimuth in horizontal coordinate system, however it shall be understood by those skilled in the art that this is done only for the sake of convenience. For example, instead of true north N, the magnetic north NM may be used. Instead of righthand coordinate systems having a common origin 0, left-hand coordinate systems may be used. In the following description, variables relating to azimuth are expressed in the form of the deviation from axes denoted by the letter "X" in a reference coordinate system, and variables relating to elevation are expressed in the form of the deviation from a plane which is defined by two axes which begin with the letters "X" and "Y' in a reference coordinate system. Coordinate systems such as horizontal true-north coordinate system, for which both of the "X","?' axes are horizontal, are referred to by the general name "horizontal coordinate system". Further, in this application, the term "roll" shall be taken to mean the inclination (angle) of the moving platform about an Xd axis, X axis or Xtd axis, while the term "pitch" shall be taken to mean the inclination (angle) of the moving platform about a Ydh axis, Yb axis or Yth axis.

TABLE 1 Coordinate Definitions (a) Horizontal true north coordinate system Xo Yo Zo Properties: Coordinate system fixed in the horizontal plane Definitions of axes: Xo: true north (N) direction Yo: perpendicular to Xo and horizontal Zo: perpendicular to Xo and Yo (b) Moving platform coordinate system Xd Ya Zd Properties: Coordinate system fixed on the moving platform Definitions of axes: Xd: direction of front end of moving platform Yd: perpendicular to Xd and parallel to mounting plane Zd: perpendicular to Xd and Yd (c) AZ platform coordinate system X Y Z Properties: Coordinate system fixed on AZ platform Definitions of axes:X: direction of X axis 12 Y: direction of Y axis 14 Z: direction of AZ axis 10 (d) Moving platform horizontal coordinate system Xdh Ydh Zdh Properties: Coordinate system obtained by rotating Xd Yd Zd by -rd about Xd, and rotating the resulting coordinate system by -pd about Ydh Definitions of axes: Xdh: axis which was Xd prior to rotation by -pd axis axis which was Yd prior to rotation by -rd, XdbYdh plane = horizontal Zdh=Zo TABLE 1 (Cont'd) (e) Name: Antenna horizontal coordinate system Xh Yb Zb Properties: Coordinate system obtained by rotating X Y Z by -rx about X, and rotating the resulting coordinate system by -py about Yh Definitions of axes: Xh: axis which was X prior to rotation by -py Yh: axis which was Y prior to rotation by -rx, Zh = Zo (f) Name: Target horizontal coordinate system Xth Yth Zth Properties: Virtual coordinate system based on azimuth of target Tin horizontal plane Definitions of axes: Xth: azimuth of target T in horizontal plane Yth: axis in horizontal plane and perpendicular to Xth (not shown in figures) Zth = Zo TABLE 2 Variables Related to Inclination Angle of Moving Platform Roll Pitch Reference Coordinate system Brief Description rd pd Xd Yd Zd Roll and pitch about Xd, Ydh rx py X Y Z Roll and pitch about X, Yh rsdet pydet X Y Z Detected values of roll and pitch about X, Yb rtd ptd X Y Z Roll and pitch about Xtd, Yth.

Xtd is the azimuth line of the target T on the mounting plane.

The azimuth line perpendicular to Xtd is referred to as Ytd.

TABLE 3 Variables Related to Front End Direction of Moving Platform Variable Name Reference Plane Brief Description # xdd Mounting plane Bearing of Xd based on Xod X0d is a line corresponding to X0 on mounting plane o xdh Horizontal plane Bearing of Xdh based on X0 # g e.g. Mounting plane e.g. Value of 4 xdd detected on mounting plane TABLE 4 Variables Related to Direction of Target T Azimuth Elevation Reference Coordinate svstem Brief Description 0 th tb X0 Yo Zo True or searched value O tvh E tvh X0 Yo Zo Variable utilized for searching and step-tracking # tbd Xd Yd Zd Azimuth of Xtd relative to Xd O tbh Xdh Ydh Zdh Azimuth of Xth relative to Xdh TABLE 5 Bearing Reference Coordinate system Brief Description o xbd Xd Yd Zd Bearing angle of X axis 12 # tbddet Xd Yd Zd Value of # xbd detected on mounting plane # xbh Xdh Ydh Zdh Value corresponding to # xbd on horizontal plane # # xtd Xd Yd Zd = # xbd - # tbd Azimuth tracking error on mounting plane # # xth Xdh Ydh Zdh = # xbh - # tbh Azimuth tracking error on horizontal plane TABLE 6 Variables Relating to Mechanical Axes Az axis 10 X axis 12 Y axis 14 # xbd X y Angular position Q xbddet Xdet ydet Detected value of angular position # # xtd # # x # # y Control error Signal According to one embodiment of the present invention, # tb and tb are input by a target direction input means which may be implemented by a unit for holding and storing th and/or E th supplied from an external device, such as a keyboard. The target direction input means may comprise a target direction search means which searches for unknown 9 th and/or E th, and a steptrack means which performs tracking by trial and error using tb and/or E th obtained by searching as a starting point. The target direction search means gradually updates azimuth and/or elevation variables # tvh and/or E tvh until the quality of a signal from the target received by the directional antenna exceeds a predetermined level.

Accordingly, even when # th and/or th are initially completely unknown, it is possible to detect the target direction th and/or th, from the variables # tsh and/or E tvh when the signal quality exceeds the predetermined level. Also, the steptrack means sets the searched # th and/or E th as a start point of varying the values of azimuth and/or elevation variables # tvh and/or E tvh and starts steplike-updating # tvb and/or E tvh by trial and error by incremental small angle(s) so as to detect a direction in which reception quality is enhanced, and inputs thus-obtained # tvb and/or @ tloh as the true # th/ E th. Whether or not "the receiving signal quality exceeds the predetermined level", is detected by comparing the detected level of the received signal from the directional antenna (or a signal which has been amplified or frequency converted) with a predetermined threshold, comparing the detected carrier-to-noise power ratio C,No of the received signal in a specified frequency band with a predetermined threshold, or determining the presence or absence of a synchronization signal indicating that a demodulator has synchronized with the frequency or the phase of the received signal. By performing this search and step track on the inclined moving platform, the target can rapidly be captured and the antenna can be stabilized, and can be performed with high precision, even when the target direction is not initially known, or the position of the target is somehow lost.

The moving platform direction input means moving platform direction data (e.g. # xdh, # xdd or incremental value of them). When xdd is input, it is converted to 9 xdh for precision antenna pointing, or represented as # ulh. The mechanical axis angular position detecting means detects rbd, X andy while the inclination angle detection means detects a level and py. More speciflally, the inclination angle detection means is fixed to the X axis 12 or X axis structure, and detects the inclination angle Axievel from the level about X axis and the pitch angle py, which is the inclination angle of the moving platform from the level in the X axis direction. According to this embodiment, as X axis null control is performed based on level as described hereafter, a detected value xQL of x obtained by the mechanical axis angular position detecting means, or a value obtained by adding A level from Xdet, may be considered as rx. Therefore, the input processing performed by these three means may be represented by the equations below. The moving platform bearing input means may be implemented by a navigation device which outputs o, e.g. a gyrocompass, a magnetic compass, an inertial navigation system, a radio navigation unit or a processor which inputs signals from these devices. The mechanical axis angular position detecting means may be implemented by angle sensors such as potentiometers fixed to the AZ axis 10, X axis 12 and Y axis 14, and a processor which inputs signals from these sensors. The inclination angle detection means may be implemented by a combination sensor of a vibratory gyro and a pendulum inclinometer, or an accelerometer, or a processor which inputs signals from these sensors.

# xdd = # g detection of moving platform bearing O xbd = S xbddet detection of antenna bearing angle #Xlevel = #Xlevel detection of inclination from level of X axis y = ydet detection of angular position of Y axis 14 r1 = Xdet detection of roll angle about X axis 12 py = pydet or detection of pitch angle about Yh axis = Xdet+#Xlevel Eqns.(l) In these equations, variables having the suffix det, and # e and # level are input values, e.g. output by a navigation system or sensors. Also, in these equations, # g g indicative of # xdd is input as the moving platform bearing data, however data not indicative of # xdd but indicative of # xdh, or other data relating directly or indirectly to the moving platform bearing may also be input. For example, a pulse generated each time the bearing increases or decreases by 1/6 degree, may also be input as the moving platform bearing data. The structure or output format of the device which supplies the moving platform bearing data (e.g. a vibratory gyro or navigation system)decides the format or nature of the moving platform bearing data and the conversion processing method.

The AZ axis control means derives # tbb based on # th and moving platform bearing data, derives # xbh based on Q xbd, rx and py, generates an AZ axis control error signal indicating A # xth or A # xtt, and causes a rotation about the AZ axis 10 in such a direction as to compensate for A # xtb or a # ztd based on the generated AZ axis control error signal to track the target in azimuth by the beam of the directional antenna. An example of a method performed by the AZ axis control means wherein # xdd is input as the moving platform bearing data is shown by the next equations. In this application, the cosine function cos is denoted by the operator c, the sine function sin is denoted by the operator s, and the tangent function tan is denoted by the operator t. rd = s-1 (spy . crx . s # xbd-srx . s # xbd) pd = t-1 {(srx . s # xbd+spy . crx . c # xbd)/(crx . cpy)} # xdh = t-1 {(s # xdd . crd)/(c # xdd . cpd-S # xdd . STd . spd)} # tbh = # th- # xdh # xbh = t-1 {s # xbd . cpy/(crx . c # xbd-Srx . spy . s # xbd)} # # xth = # xbh- # tbh # # xtd = t.1{s# # xth . cpy/(c# # xth . crx+s# # xth . srx . spy)} Eqns.(2) Finally, the X/Y axes control means generates an X axis control error signal and a Y axis control error signal. Specifically, the X/Y axes control means generates an X axis control error signal indicating #Xlevel, and a Y axis control error signal indicating an error A 0 y in y derived based at least on py causes a rotation about the X axis 12 in a direction which makes #Xlevel 0 based on the generated X axis control error signal (X axis null control) to stabilize the directional antenna against the inclination of the moving platform about the X axis 12, and causes a rotation about the Y axis 14 in such a direction as to compensate for A o y based on the Y axis control error signal to track the target in elevation by the beam of the directional antenna and to stabilize the directional antenna against inclination of the moving platform about the Y axis 14. An example of a method performed by the X/Y axes control means is shown by the following equations. In the expression for o " y, the error A 0 yin y is used as the Y axis control error signal, however the Y axis 14 may also be controlled so that the elevation error is made to gradually approach 0. #/2 which appears in the expression for A 0 y is used to convert 8 0 y to a declination angle. A # xtb may also be used as an approximate value for azimuth tracking instead of a # # # x = #Xlevel Stabilization about X axis a 0 # y = = -(p/2- # th-py) Elevation angle tracking + stabilization about Y axis Eqns.(3) Hence according to this embodiment, by performing a coordinate transformation between the moving platform coordinate system and horizontal coordinate system, to obtain high quality control error signals, specifically the AZ axis control error signal, the azimuth tracking error is reduced. Further, according to this embodimenimoving platform bearing data (e.g. # xbd) are converted into or input as # xdh represented according to the moving platform horizontal coordinate system, and a rotation is given to the AZ axis 10 based on # xdh (more specifically, by using xtd or xth) so that the azimuth tracking error in moving platform horizontal coordinate system is suppressed. As the step track is performed to track the target while the control regarding the AZ axis 10 using the control error signal having improved signal quality, according to this embodiment precise tracking can be performed under actual conditions wherein the relative azimuth # xbd of the target varies dynamically.

As the X axis null control is performed, there is no need to use a sensor having a linear characteristics in a wide range of inclination but being expensive to detect A Xievel, and hence the use of an economical sensor is allowed. An even more precise control may be performed by inputting d xbd as the moving platform bearing data, having the AZ control means derives rd and pd based on # xbd, rx and py, converts moving platform bearing data to 9 xdh based on derived rd and pd, and use the result to deduce # tbh. In addition, the target tracking error can be reduced by generating A y y using py together with precise control about the AZ axis.

According to this embodiment moreover, as the mount is an AZ-X-Y mount, there is the advantage of a smaller number of mechanical axes than in the conventional X-Y-Az-E 1 mount.

This invention can be implemented not only as a "controller", but also as a "control method" and a "3-axis directional antenna apparatus". Modifications to effect these changes may easily be made by those skilled in the art by referring to the details given in this application.

BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a schematic view of the ans-arrangement in an antenna mount to which the present invention may be applied.

Fig. 2 is a schematic view of the axis-arrangement in an antenna mount to which the present invention may be applied.

Fig. 3 is a coordinate diagram for describing the principle of this invention.

Fig. 4 is a block diagram showing the construction of a device according to one embodiment of this invention.

Fig. 5 is a schematic view of axis-arrangement in a gyroscope which may be used in this embodiment of the invention.

Fig. 6 is a block diagram showing the functions of an arithmetic and control unit for a 3-axis antenna mount according to this embodiment.

Fig. 7 is a figure showing the result of a simulation performed by the inventor in order to clarify azimuth tracking error problems in the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: A preferred embodiment of the invention will now be described with reference to the drawings. Coordinate systems, variables and their symbols defined in the section "Summary of the Invention" will be used also in the following description. Further, in the following description, a mount as shown in Fig. 1 or Fig. 2 will be assumed in order to simplify understanding.

The construction of a device according to one embodiment of this invention is shown in Fig. 4. According to this embodiment, a parabolic antenna 16 having a beam A is used as a transmitting/receiving antenna to transmit a signal to and to receive a signal from a target. An antenna of a different type from the parabolic antenna 16 may be used, or may be used only as a receiving antenna instead of as a transmitting/receiving antenna. A diplexer 18 is a means which enables the parabolic antenna 16 to be used for both transmitting and receiving and has a function of supplying a transmitting signal supplied by a transmitter, not shown, to the parabolic antenna 16, and a function of supplying a received signal from the parabolic antenna 16 to an amplifiertfrequency conversion circuit 20. The amplifier/frequency conversion circuit 20 amplifies the received signal, and converts it from a radio frequency to a lower intermediate frequency and supplies the amplified-and-frequency-converted received signal to an IF amplifier 22 for amplification. The amplified signal is then supplied to a demodulator 24. The demodulator 24 demodulates data from the received signal, supplies the demodulated data to a circuit at a later stage, not shown, and outputs a receiving level signal indicating the level of the received signal and/or a synchronization detecting signal indicating that a built-in synchronizing circuit has synchronized with the frequency and phase of the received signal.

The parabolic antenna 16 is pivotally supported on the moving platform by an AZ-X-Y mount having an AZ axis 10, Taxis 12 and Y axis 14 on which an AZ axis structure28, an X axis structure 30 and a Y axis structure 32 are provided respectively. These structures 28, 30, 32 includes members, such as frames or gimbals and motors, which rotate when the corresponding axes are steered. The AZ axis structure 28 is referred to also as an AZ axis platform. An AZ axis motor 34, an X axis motor 36 and a Y axis motor 38 are the members of these structures and cause antenna rotation respectively about the AZ axis 10, X axis 12 and Y axis 14. A 3-axis arithmetic and control circuit 40 supplies an AZ axis control error signal A ztd, an X axis control error signal a 6 @ and a Y axis control error signal A 6 y, respectively to an AZ axis motor driving circuit 42, an X axis motor driving circuit 44 and a Y axis motor driving circuit 46 which respectively drive the motors 34, 36 and 38 based on corresponding one of the control error signals A # ztd, A # x, and A 6 y. To supply xbddet, Xdet and Ydet as feedback signals to the 3-axis arithmetic and control circuit 40, potentiometers 48 50, and 52 for detecting xbddec, Xdet, or ydet are provided on the AZ axis 10, X axis 12, and Y axis 14 or corresponding structures 28, 30, and 32, respectively.

Further, this embodiment utilizes two inclinometers, one of which (56) is mounted on the X axis 12 or the X axis structure 30 for detecting Pydet to supply it to the 3-axis arithmetic and control circuit 40. The 3-axis arithmetic and control circuit 40 supplies the AZ axis control error signal A Q xtd derived based for example on zbddet to the AZ axis motor driving circuit 42, and supplies the Y axis control error signal A 6 y derived based for example on Ydet to the Y axis motor driving circuit 46.

Another inclinometer 54A arranged on the X axis 12 or X axis structure 30 detects n xl,,,l and supplies it to the 3-axis arithmetic and control circuit 40 which generates and supplies A 0 x to cancel Axieyel to the X axis motor driving circuit 44 (X axis null control). Therefore, according to this embodiment, an Xdet which can be treated as rx is obtained from the potentiometer 50 installed on the X axis 12 or X axis structure 30. According to this embodiment, the stabilization of the parabolic antenna 16 about the X axis 12 is performed in accordance with the X axis null control method and detection of rx are performed under the control, by using the detected rx for generating the AZ axis control error signal according to the method enables a highly reliable AZ axis control error signal is obtained. Further, as the X axis null control requires relatively narrow linear domain, the inclinometer having relatively narrow band of linear characteristics may be used as the inclinometer 54A, enabling reducing the component cost for implementing the present embodiment.

A device for supplying 9 g to the 3-axis arithmetic and control circuit 40, e.g. various types of navigation system or compass, may also be mounted on the moving platform. Fig. 4 shows a gyrocompass 26 as an example of such a device and Fig. 5 shows a typical construction of the gyrocompass 26. The gyrocompass 26 of this figure comprises an AZ axis 58, X axis 62 and Y axis 66,pivotally supports by the AZ axis 58 a directional frame 600n the plane on which the AZ axis 10 of the antenna mount is supported, pivotally supports by the X axis 62 an outer gimbal 640n the directional frame 60, pivotally supports by the Y axis 66 an inner gimbal 68 on the outer gimbal 64, and has a rotor 70 disposed inside the inner gimbal 68. In this gyrocompass, the rotor 70 tends to orient towards the true north N and thus g, which is supplied by the gyrocompass 26 to the 3-axis arithmetic and control circuit 40 therefore corresponds to a difference xdd between the orientation of the rotation axis of the rotor 70 and the moving platform bearing. Herein, it is assumed that 6 I coincides with the true xdd at the high precision causing no problem in normal practice.

Fig. 6 shows the functions of the 3-axis arithmetic and control circuit 40 according to this embodiment. This figure has been designed as a block diagram for the sake of ease of functional description, but this should not be understood to mean that the invention cannot be implemented at the software level.

In the 3-axis arithmetic and control circuit 40 according to this embodiment, a target direction input unit 100 is provided for inputting d th and E tb to the 3-axis arithmetic and control circuit 40, # th and th being input from an external device (not shown) and stored in or held by the target direction input unit 100. The target direction input unit 100 comprises a target direction searching unit 102 for searching an initial direction of the target, and a steptrack unit 104 for performing steptracking. The target direction searching unit 102 is activated when the position of the target T ( # th and 0 th) is unknown or have not yet been supplied from an external device, such as right after power is switched on, and searches for # th and th at which the quality of the signal from the target T exceeds a predetermined level, using the receiving level signal and/or the synchronization detection signal from the demodulator 24.

Specifically, the target direction search unit 102 gradually changes the values # tvb and E tvh until a sufficient receiving signal level is obtained or until the demodulator 24 synchronizes with the received signal, and sets the values # tvh and E tvh as the searched th and E th, when the sufficient receiving signal level is obtained or the synchronization is established. To gradually vary tvh and tvh, registers may be provided to hold, increment/decrement, and supply d tvh and E rvh to a later stage. A plurality of such registers may be provided so as to store plural sets of the aforesaid data along a time axis in order to perform statistical processing, to search the target direction precisely. The values of # tYh and # tvh after search is complete may be taken as the true 4 th and th. The steptrack unit 104 gradually changes the values # tvb and E tvh by trial and error after inputting or searching # th and th has been completed, so as to detect the changing direction in which change of < P tvh and E rvh gives an enhancement of signal reception quality and to change # tvh and # tvh by a predetermined angle in that direction. The methods used to detect and evaluate signal reception quality, and to gradually vary # tvh and E tvh, are identical or similar to those used for search.

The 3-axis arithmetic and control circuit 40 in this embodiment further comprises a moving platform bearing input unit 106 for inputting d g and supplying it as # xdd to a later stage, a moving platform inclination angle input unit 108 for inputting #Xlevel SO as to generate A # x for performing X axis null control, and for inputting Xdet, pydet and outputting them as respectively rx, py to a later stage, and a mechanical axes angular position input unit 110 for inputting # xbddet, order, and outputting them as respective # xbd and y to a later stage. The 3-axis arithmetic and control circuit 40 further comprises an AZ axis control unit 112 for imputting # th, # xdd, rx, py, and # xbd, and for generating and outputs # xtd based on these values, and an X/Y axes control unit 114 for generating and outputting a 0 y based on py, E th, and y, and for outputting A # x. The functions of these units were explained above. A both xth may be used as a control error signal instead of A # xtd.

The aforesaid construction, and in particular the procedure for generating the AZ axis control error signal performed by the AZ axis unit 112, offers the features and advantages described above.

Claims (8)

1. CLAIMS: 1. A controller for use in conjunction with an antenna mount having an AZ axis, an X axis, and a Y axis, said AZ axis being arranged on a moving platform along the direction which would be coincide with the direction of the vertical when said moving platform is not inclined, said X axis being supported by said AZ axis so that it is horizontal when said moving platform is not inclined, and said Y axis being supported by said X axis so that it is perpendicular to said X axis, said Y axis pivotally supporting a directional antenna, wherein: said controller comprises: target direction input means for inputting an azimuth th and elevation E th of a target according to the horizontal coordinate system; moving platform bearing input means for inputting moving platform bearing data which represent or can be converted to a bearing xdh of said moving platform in said horizontal coordinate system; and mechanical axis angular position detecting means for detecting angular positions xbd, X, and y of said AZ, X, and Y axes; inclination angle detection means fixed to said X axis or X axis structure thereon for detecting an inclination angle a level from the level about said X axis and a pitch angle py which is an inclination angle of said moving platform from the level in the direction of said X axis, AZ axis control means for deriving a relative azimuth tbh of said target relative to said moving platform according to the horizontal coordinate system based on said azimuth th and said moving platform bearing data, deriving a virtual angular position xbh of the AZ axis according to said horizontal coordinate system based on said angular position ibd, a roll angle rx which is an inclination angle of said moving platform from the level about said X axis and a pitch angle py detected by said moving platform inclination angle detecting means, generating an AZ axis control error signal indicating an error A xth in said angular position xbh compared to said relative azimuth # tbh or indicating an error A d xtd according to the moving platform coordinate system and corresponding to the error A 8 xth, and tracking said target in azimuth by the beam of said directional antenna by a rotation about said AZ axis in such a direction as to compensate said error a xth or said error A # xtd based on said generated AZ axis control error signal; and X/Y axes control means for generating an X axis control error signal indicating said inclination angle Axievej and a Y axis control error signal indicating an error A 0 y in said angular position y derived based on at least said pitch angle py, stabilizing said directional antenna against an inclination of said moving platform about said X axis by a rotation about said X axis in such a direction as to compensate said inclination #Xlevel based on said generated X axis control error signal, and tracking said target in elevation by said beam and stabilizing said directional antenna against an inclination of said moving platform about said Y axis by a rotation about said Y axis in such a direction as to compensate said error A 0 y based on said generated Y axis control error signal; and wherein: said controller performs X axis null control based on said inclination angle #Xlevel, assumes that said angular position x detected by said mechanical axis angular position detecting means or a value obtained by adding said inclination angle level from the angular position x is equal to said roll angle rx in said X axis null control, and uses this value of roll angle rx to generate said AZ control error signal.
2. 2. A controller as defined in Claim 1, wherein: said moving platform bearing data input by said moving platform bearing input means is data indicating a bearing # xdd of said moving platform in a plane inclined according to the inclination of said moving platform relative to the horizontal plane; and said AZ aids control means derives a roll angle rd and pitch angle pd of said moving platform according to the moving platform coordinate system based on said angular position # xbd, said roll angle rx and said pitch angle Py, converts said moving platform bearing data to said azimuth # zdh based on said roll angle rd and said pitch angle pd, and uses the resultant azimuth # xdh to deduce said relative azimuth #
3. 3. A controller as defined in Claim 1, wherein said target direction input means comprises: target direction searching means for inputting virtual values # tvh and/or tvh as said azimuth # th and/or said elevation E th. while gradually updating said virtual values until the quality in a signal from said target received by said directional antenna exceeds a predetermined level, and steptrack means for inputting said virtual values tvb and/or E tvb as said azimuth # th and/or elevation th. while updating said virtual values # and/or E tvh in incremental angles by trial and error using said virtual values # tvh and/or E tvb when searching by said target direction searching means had be completed as a starting point.
4. 4. A controller as defined in Claim 2, wherein said target direction input means comprises: target direction searching means for inputting virtual values # tvb and/or # tvh as said azimuth # th and/or said elevation E th while gradually updating said virtual values until the quality in a signal from said target received by said directional antenna exceeds a predetermined level, and step track means for inputting said virtual values 9 tvh and/or bb as said azimuth # th and/or elevation th, while updating said virtual values # and/or E tvh in incremental angles by trial and error using said virtual values # tvb and/or E tvb when searching by said target direction searching means had be completed as a starting point.
5. 5.A controller substantially as hereinbefore described with reference to the accorpanying drawings.
6. 6.Antenna apparatus comprising a controller in accordance with any preceding claim.
7. 7.Antenna apparatus substantially as hereinbefore described with reference to the accompanying drawings.
8. 8. A control method for use in conjunction with an antenna mount having an AZ axis, an X axis, and a Y axis, said AZ axis being arranged on a moving platform along the direction which would be coincide with the direction of the vertical when said moving platform is not inclined, said X axis being supported by said AZ axis so that it is horizontal when said moving platform is not inclined, and said Y axis being supported by said X axis so that it is perpendicular to said X axis, said Y axis pivotally supporting a directional antenna, wherein: said control method comprises the steps of: inputting an azimuth th and elevation E tb of a target according to the horizontal coordinate system; inputting inputting moving platform bearing data which represent or can be converted to a bearing d xdh of said moving platform in said horizontal coordinate system; detecting angular positions xbd, X, andy of said AZ, X, and Y axes; detecting an inclination angle Axw from the level about said X axis and a pitch angle py which is an inclination angle of said moving platform from the level in the direction of said X axis, deriving deriving a relative azimuth # tbb of said target relative to said moving platform according to the horizontal coordinate system based on said azimuth # tb and said moving platform bearing data, deriving a virtual angular position # xbh of the AZ axis according to said horizontal coordinate system based on said angular position 9 xbd, a roll angle rx which is an inclination angle of said moving platform from the level about said X axis and a pitch angle py detected by said moving platform inclination angle detecting means, generating an AZ axis control error signal indicating an error A ith in said angular position # ith compared to said relative azimuth # tbb or indicating an error A ita according to the moving platform coordinate system and corresponding to the error A 6 ith ,and tracking said target in azimuth by the beam of said directional antenna by a rotation about said Al, axis in such a direction as to compensate said error A # x or said error A xtd xtd based on said generated AZ axis control error signal; and generating an X axis control error signal indicating said inclination angle #Xlevel and a Y axis control error signal indicating an error # O y in said angular position y derived based on at least said pitch angle py, stabilizing said directional antenna against an inclination of said moving platform about said X axis by a rotation about said X axis in such a direction as to compensate said inclination #Xlevel based on said generated X axis control error signal, and tracking said target in elevation by said beam and stabilizing said directional antenna against an inclination of said moving platform about said Y axis by a rotation about said Y axis in such a direction as to compensate said error A 0 y based on said generated Y axis control error signal; and performing X axis null control based on said inclination angle #Xlevel,assuming that said angular position x detected by said mechanical axis angular position detecting means or a value obtained by adding said inclination angle Axi., from the angular position xis equal to said roll angle rx in said X axis null control. and using this value of roll angle rx to generate said AZ control error signal.