Patent Application
20060152410
The invention relates generally to controlling a pointing angle of an antenna, such as a phased array antenna. More particularly, the invention relates to a system and method for steering an antenna to maintain communication with a satellite or distant antenna when the geolocation and/or the orientation of the antenna rapidly changes.
Many known antennas, such as phased array antennas (PAA's), use electronic beam steering control for pointing the antennas and communicating with satellites. Such antennas are often mounted on mobile platforms such as ships, trains, buses, and aircraft. Typically, current designs rely on centralized inertial navigation systems (INS) located in a central equipment bay of the mobile platform for positioning and controlling a beam pointing angle of the antenna. For example, antenna receiving units monitor the strength of an electromagnetic signal received from a target satellite and use power tracking to close the steering control loop. Antennas that transmit only typically operate utilizing open loop electronic beam steering to point the antenna based on computations by the INS.
Generally, the update rate for such antenna beam pointing controls is relatively slow, for example below 100 Hz. Due to the inherently long latency of such antenna control systems, communication links with the target satellite can be interrupted by unexpected movement of the mobile platform. Typically, if the mobile platform turns more than 20°/sec in any direction, the communication link will be at least temporarily interrupted. For example, large ships may have antenna equipment mounted on top of tall masts. Relative motions between the ship, the masts and rough sea presents problems for beam pointing using current beam steering systems. As another example, fast moving land vehicles often maneuver in trenched and bumpy terrain. Traversing such terrain could cause an antenna mounted to the top of the vehicle to move and change pointing directions more than 20° in several different directions within a very short period of time. In additions, extremely fast and nimble aircraft, such as the F-18, can make drastic course and orientation adjustments. Current antenna steering system struggle to adjust, i.e. correct, the beam pointing angle of an antenna to continuously maintain a satellite communication link during such drastic and quick movements of the antenna.
Furthermore, the expense and mass of a large, slow responding INS based system hinders its use on private or commercial mobile platforms, e.g. small aircraft, cars or trucks, in which passengers would benefit from a robust communication link for such things as Internet access.
Therefore, it is desirable to implement an antenna steering system and method that will continuously adjust the beam pointing angle of an antenna that is subject to rapid and relatively large movements within a large range of pointing angles. More particularly, such a preferred system and method would maintain an uninterrupted communication link with a satellite regardless of the frequency and magnitude of changes in the geolocation and/or orientation of the antenna.
An antenna steering system in accordance with a preferred embodiment, includes a plurality of gyro sensors fixed in close proximity to an antenna. By being fixed located in close proximity to the antenna, the gyro sensors are oriented to match the antenna's orientation so that the gyro sensors are essentially at and continuously maintain the same position and orientation as the antenna. That is, as the antenna moves due to movement of a platform to which the antenna is mounted, e.g. an aircraft, the gyro sensors continuously maintain essentially the same geolocation and/or orientation as the antenna. The gyro sensors measure angular rotation of the antenna about an X-axis of the antenna, about a Y-axis of the antenna and about a Z-axis of the antenna.
The system additionally includes a beam steering processing unit (BSPU), preferably also in close proximity to the antenna. In a preferred implementation the gyro sensors are included in the BSPU. A beam steering phase controller (BSPhC) included in the BSPU receives positional change signals from the gyro sensors. The positional change signals include the angular rotation measurement data. The BSPhC utilizes the angular rotation measurements to determine a predicted amount of movement, i.e. a change in geolocation and/or orientation, of the antenna within a specified time period. For example, the BSPhC determines a predicted amount of antenna movement for each consecutive 1 ms period. Based on the predicted amount of antenna movement, the BSPhC adjusts a beam pointing angle of the antenna to compensate for the predicted amount of movement.
In another preferred embodiment of the present invention, a method for steering an antenna includes measuring a movement of the antenna away from a pointing direction, i.e. a change in geolocation and/or orientation. Such movement is measured by measuring angular rotation of the antenna utilizing one or more gyro sensors (or their equivalent) that are oriented to match the antenna orientation in 3-dimensional space. Generally three gyro sensors are used with each gyro sensor being arranged to measure angular rotation around one of three mutually orthogonal axes designated as the X-axis, the Y-axis gyro sensor and the Z-axis. In one implementation, the gyro sensors are included in a local navigation system fixedly located in close proximity to the antenna. Therefore, the gyro sensors maintain essentially the same geolocation and orientation as the antenna throughout any movement of the antenna.
In an exemplary embodiment, the method includes predicting the degree of angular rotation of an antenna away from a pointing direction, the angular velocity, and/or the angular acceleration along any one or more axes in a Cartesian 3-dimensional space, and computing control commands to adjust the beam pointing angle of the antenna based upon the predictions. Usually, such correction is accomplished using electronic beam steering commands fed to a controller for a phased array antenna. For example, a predicted amount of angular rotation of the antenna about the X-axis is determined at a specified time, e.g. 1 ms, based on the measurement of angular rotation about the X-axis. Additionally, a predicted amount of angular rotation of the antenna about the Y-axis at the specified time is determined based on the measurement of angular rotation about the Y-axis. And, a predicted amount of angular rotation of the antenna about the Z-axis at the specified time is determined based on the measurement of angular rotation about the Z-axis. The predicted amounts of angular rotations are converted to vector gradients in accordance with the following equations:
dx′=dxα+dxβ+dxγ;
dy′=dyα+dyβ+dyγ; and
dz′=dzα+dzβ+dzγ.
A beam pointing angle of the antenna is adjusted in accordance with the vector gradients.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. Furthermore, the features, functions, and advantages of the present invention can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments.
The present invention will become more fully understood from the detailed description and accompanying drawings, wherein;
Corresponding reference numerals indicate corresponding parts throughout the several views of drawings.
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application or uses. Additionally, the advantages provided by the preferred embodiments, as described below, are exemplary) in nature and not all preferred embodiments provide the same advantages or the same degree of advantages.
Referring to
The gyro sensors 34 continuously communicate positional change signals to a beam steering processing unit (BSPU) 38. The BSPU 38 is any suitable computer-based device including at least one electronic memory, i.e. data storage, device and capable of receiving data and executing various beam steering algorithms and commands in response thereto. The positional change signals provide measurement data indicating a change in the geolocation and/or the orientation of the antenna 18 as a result of movement of the mobile platform 14. Particularly, the positional change signals provide measurement data indicating an amount of angular rotation of the antenna 18 about the X, Y and/or Z axes. Utilizing the positional change signals, a beam steering phase controller (BSPhC) 42; included in the BSPU 38, determines a predicted amount of movement of the antenna 18 within a specified periodic time period, for example every 1 ms. Based on the predicted amount of movement, the BSPhC 42 outputs a signal used to essentially continuously adjust a beam pointing angle of the antenna 18 to compensate for the predicted amounts of movement. Therefore, the antenna 18 continuously maintains an uninterrupted communication link with the satellite 22. The BSPhC 42 can be any controller suitable for retrieving data from look up tables, performing calculations, executing the beam steering algorithms and providing steering control signals to an antenna steering mechanism (not shown). In a preferred implementation the BSPhC 42 electronically steers the beam pointing angle of the antenna 18 in spherical coordinates, but compensates, i.e. corrects, the beam pointing angle for movement of the antenna 18 according to pitch, roll and yaw motions along the X, Y and Z axes.
In a preferred embodiment the BSPU 38 includes a compensation circuit 44 that compensates the positional signals for temperature at the gyro sensors 34 and acceleration of the antenna 18. The compensation circuit 44 can be any circuit suitable to execute a compensation algorithm for adjusting variance in the angular rotation measurements caused by environmental temperature at the gyro sensors 34, for example a field programmable gate array (FPGA). The local navigation system 30 includes a temperature sensor 46 that measures the temperature of the environment to which the gyro sensors 34 are exposed. The BSPhC 42, i.e. the compensation circuit 44, receives temperature readings from the temperature sensor 46 and based on the temperature readings, the compensation circuit 44 compensates angular rotation measurements due to effects the environmental temperature may have on the gyro sensors 34.
Additionally, the compensation circuit 44 adjusts for variances in the angular rotation measurements caused by acceleration and/or deceleration of the mobile platform 14. The local navigation system 30 includes at least one acceleration sensor 50, e.g. an accelerometer(s), that measures acceleration and deceleration of the mobile platform 14. The accelerometer(s) 50 communicate(s) the acceleration/deceleration measurements to the BSPhC 42, i.e. the compensation circuit 44. The compensation circuit 44 utilizes the acceleration/deceleration measurements to compensate the angular rotations for variances caused by effects of the acceleration/deceleration on the gyro sensors 34. To compensate for temperature and acceleration, the compensation circuit 44 executes algorithms derived from specifications of the gyro sensors 34, the acceleration sensor 50, and the temperature sensor 46. Additionally, the compensation circuit 44 utilizes outputs from the accelerometer(s) 50 to remove any accumulated drift or bias of the gyro sensors 34.
Referring now to
dx=sin θ·cos φ,
dy=sin θ·sin φ; and
dz=cos θ.
Referring now to
Once the antenna 18 is pointed at the initial beam pointing angle, future beam pointing angles necessary to continuously maintain an uninterrupted communication link with the satellite 22 are determined completely by the local navigation system 30. Thus, the local navigation system 30 becomes an autonomous steering system for the antenna 18. However, the centralized navigation system 26 can provide periodic updates or a new target position when needed.
After the initial communication link is established, the X-axis gyro sensor 34A measures the angular rotation a of the antenna 18 about the X-axis a predetermined number of times (n) within a first time period (t). For example, the angular rotation α is measured ten times every 1 ms. The measurements of the angular rotation α are communicated from the X-axis sensor to the BSPhC 42. Likewise, the Y-axis and the Z-axis gyro sensors 34A and 34C respectively measure the angular rotations β and γ of the antenna about the Y and Z axes the predetermined number of times n within the first time period t. The measurements of the angular rotations β and γ are communicated from the Y-axis and the Z-axis sensors to the BSPhC 42. Thus, as the mobile platform 14 moves and changes geolocation and/or orientation, the X, Y and Z axis sensors 34A, 34B and 34C measure angular rotation of the antenna 18 about the respective axes due to the movement of the mobile platform 14.
Utilizing the measurements of α, the BSPhC 42 determines an average amount of angular rotation (ΔVα) of the antenna 18 about the X-axis for the first time period t. Utilizing the measurements of β, the BSPhC 42 determines an average amount of angular rotation (ΔVβ) of the antenna 18 about the Y-axis for the first time period t. Utilizing the measurements of γ, the BSPhC 42 determines an average amount of angular rotation (ΔVγ) of the antenna 18 about the Z-axis for the first time period t. In a preferred form, the BSPhC 42 includes three electronic computing devices 62A, 62B and 62C that respectively determine the average amounts of angular rotation ΔVα, ΔVβ and ΔVγ. The electronic computing devices 62A, 62B and 62C can be any suitable electronic computing devices capable of determining the average amounts of angular rotation ΔVα, ΔVβ and ΔVγ, for example, three FPGAs. Alternatively, the electronic computing devices 62A, 62B and 62C can be a single FPGA containing all the digital circuitries needed to determining the average amounts of angular rotation ΔVα, ΔVβ and ΔVγ. Accordingly, the first electronic computing device 62A would determine ΔVα, the second electronic computing device 62B would determine ΔVβ and the third electronic computing device 62C would determine ΔVγ. In a preferred embodiment, the average amounts of angular rotation ΔVα, ΔVβ and ΔVγ are determined in accordance with the following equations:
ΔVα=[(Vα1+Vα2+ . . . Vαn)/n]−Vαnull, wherein Vαnull is the value of the vector V along the X-axis at the initial beam pointing angle;
ΔVβ=[(Vβ1+Vβ2+ . . . Vβn)/n]−Vβnull, wherein Vβnull is the value of the vector V along the Y-axis at the initial beam pointing angle; and
ΔVγ=[(Vγ1+Vγ2+ . . . Vγn)/n]−Vγnull, wherein Vγnull is the value of the vector V along the Z-axis at the initial beam pointing angle.
The BSPhC 42, e.g. the electronic computing device 62A, then determines a predicted amount of angular rotation (α′) of the antenna 18 about the X-axis for a second time period (T), based on the average amount of angular rotation ΔVα. The second time period T is function of the first time period t. In like fashion, the BSPhC 42, e.g. the electronic computing devices 62B and 62C, determines a predicted amount of angular rotation β′ and a predicted amount of angular rotation γ′ of the antenna 18 about the Y and Z axes for the time period T based on the average amounts of angular rotations ΔVβ and ΔVγ. In a preferred embodiment, the predicted amounts of angular rotations α′, β′ and γ′ are determined in accordance with the following equations:
α′=ΔVa*T;
β′=ΔVβ*T; and
γ′=ΔVγ*T.
As described above, the signal polarity averaging and filtering circuit determines the rotational direction positional change signals generated by the gyro sensors 34. Referring to
if the direction of the predicted angular rotation α′ is counter-clockwise, then
dxα=sin(θ+α′)·cos φ=(sin θ+α′ cos θ)·cos φ
dyα=sin(θ+α′)·sin φ=(sin θ+α′ cos θ)·sin φ
dzα=cos(θ+α′)=cos θ−α′ sin θ; and
if the direction of the predicted angular rotation α′ is clockwise, then
dxα=sin(θ+α′)·cos φ=(sin θ+α′ cos θ)·cos φ
dyα=sin(θ+α′)·sin φ=(sin θ+α′ cos θ)·sin φ
dzα=cos(θ+α′)=cos θ−α′ sin θ,
wherein, θ and φ are the spherical coordinates of the vector V at the present beam pointing angle, for example the spherical coordinates of V at the initial beam pointing angle.
Referring now to
if the direction of the predicted angular rotation 13′ is counter-clockwise, then
dxβ=sin(θ+β′)·cos φ=(sin θ+β′ cos θ)·cos φ
dyβ=sin(θ+β′)·sin φ=(sin θ+β′ cos θ)·sin φ
dzβ=cos(θ+β′)=cos θ−β′ sin θ; and
if the direction of the predicted angular rotation β′ is clockwise, then
dxβ=sin(θ+β′)·cos φ=(sin θ+β′ cos θ)·cos φ
dyβ=sin(θ+β′)·sin φ=(sin θ+β′ cos θ)·sin φ
dzγ=cos(θ−β′)=cos θ+β′ sin θ,
wherein, θ and φ are the spherical coordinates of the vector V at the present beam pointing angle, for example the spherical coordinates of V at the initial beam pointing angle.
Referring to
if the direction of the predicted angular rotation γ′ is counter-clockwise, then
dxγ=sin θ·cos(φ+γ′)=sin θ·(cos φ−γ′ sin φ)
dyγ=sin θ·sin(φ+γ′)=sin θ·(sin φ+γ′ cos φ)
dzγ=cos θ; and
if the direction of the predicted angular rotation γ′ is counter-clockwise, then
dxγ=sin θ·cos(φ+γ′)=sin θ·(cos φ−γ′ sin φ)
dyγ=sin θ·sin(φ+γ′)=sin θ·(sin φ+γ′ cos φ)
dzγ=cos θ,
wherein, θ and φ are the spherical coordinates of the vector V at the present beam pointing angle, for example the spherical coordinates of V at the initial beam pointing angle.
Referring now to
dx′=dxα+dxβ+dxγ;
dy′=dyα+dyβ+dyγ; and
dz′=dzα+dzβ+dzγ.
The BSPhC 42 then outputs a signal utilized to steer the antenna 18 to have a new beam pointing angle defined by the predicted phase vector gradients dx′, dy′ and dz′. Therefore, the beam pointing angle is adjusted to compensate for the predicted amount of movement of the antenna to thereby maintain the communication link with the satellite 22, or alternatively a distant antenna. Furthermore, the process of measuring the angular rotations of the antenna 18 about the X, Y and Z axes and compensating the beam pointing angle in response thereto is continuously repeated for each subsequent first time period t so that an essentially continuous communication link with the satellite is maintained.
It should be understood that although the present invention, as described above, is applicable for use with various types of antennas, it is particularly useful for phased array antennas (PAAs). It should further be understood that a PAA includes a plurality of antenna array modules that are each independently steered, i.e. pointed, to have their own beam pointing angles. Therefore, the beam pointing angle of each antenna array module of a PAA would be essentially continuously adjusted based on the predicted phase vector gradients dx′, dy′ and dz′. Accordingly, in a preferred embodiment, the localized navigation system 30 includes an array module phase shift device 66 that includes a module location lookup table 70 and a phase shift calculator 74. In an exemplary embodiment, the module lookup table 70 and the phase shift calculator 74 are FPGAs. The module lookup table 70 stores physical locations, i.e. distances in wavelength, from each array module to a phase center of the antenna 18. The phase shift calculator 74 utilizes the signal output from the BSPhC 42 and the locations stored in the module lookup table 70 to compute a phase delay for each array module based on the module's physical location.
Next, the BSPhC 42 receives from the gyro sensors 34 angular rotation measurements α, β and γ of the antenna 18 about each of the X, Y and Z axes the predetermined number of times n within the first time period (t), as indicated at 108. In a preferred embodiment, once the amounts of angular rotations α, β and γ are determined, the signal polarity averaging and filtering circuit 58 discards any transient noise and determines a rotational direction for each of the angular rotations α, β and γ, as indicated at 110. Based on the angular rotation measurements α, β and γ, the BSPhC 42 determines the average amounts of angular rotation ΔVα, ΔVβ and ΔVγ of the antenna 18 about each of the X, Y and Z axes for the first time period t, as indicated at 112. The BSPhC 42 then determines the predicted amounts of angular rotation α′, β′ and γ′ of the antenna 18 about each of the X, Y and Z axes, at the second time period T, based on the average amounts of angular rotation ΔVα, ΔVβ and ΔVγ, as indicated at 114.
Next, the BSPhC 42 converts the predicted angular rotations α′, β′ and γ′ to radians based on the rotational direction of the predicted angular rotations α′, β′ and γ′, as indicated at 116. Based on the radian conversions, the BSPhC 42 determines the predicted vector gradients dx′, dy′ and dz′ for the beam pointing vector along the X, Y and Z axes, as indicated at 118. The predicted vector gradients dx′, dy′ and dz′ indicate a predicted amount of change in at least one of the geolocation and the orientation of the antenna 18 along the X, Y and Z axes at the second time T. The BSPhC 42 utilizes the predicted vector gradients dx′, dy′ and dz′ to output a signal used to steer the antenna 18 to a corrected beam pointing angle to thereby maintain the communication link with the satellite 22, as indicated at 120. Or, if the antenna 18 is a PAA, the signal output from the BSPhC 42 is passed through the array module phase shift device 66 to output a modulated signal used to point each of the antenna array modules. Thus, the beam pointing angles of each array module is independently corrected based on the predicted vector gradients dx′, dy′ and dz′. It should be understood that the independent corrected beam pointing angles of each antenna array module cumulatively comprise a single beam pointing angle for PAA.
It will be appreciated that the first time period t, if no one or more of the average amounts of angular rotation ΔVα, ΔVβ and ΔVγ are net zero, i.e. there is no net motion of the antenna 18, the associated compensation calculations are skipped for that specific first time period t.
The local navigation system 30 continues to measure the angular rotations α, β and γ and adjust the beam pointing angle every subsequent first time period t, as indicated at 122. Therefore, the local navigation system 30 autonomously steers, either electronically or mechanically, the antenna 18 to continuously maintain an effectively uninterrupted communication signal with the satellite 22, regardless of the frequency and magnitude of movements made by the mobile platform.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
