Patent Grant
6956526
1. Field of the Invention
The present invention relates to a method and apparatus which allows an installer to quickly and accurately point, and fine tune the pointing of an antenna, without the need of utilizing expensive monitoring equipment.
2. Description of the Related Art
Conventional methods of pointing a satellite antenna dish to optimally transmit and receive signals from a geo-synchronous satellite involve mounting the antenna on the intended platform, pointing the antenna in the general direction of the satellite, monitoring the signal strength of the signal received by the antenna (which is transmitted by the satellite) and varying the direction of the antenna in an effort to maximize the strength of the received signal. The position of the antenna which results in maximum received signal strength is selected as the permanent position. This technique is known, as “peaking” the signal.
In one example of performing this technique, the ground terminal (also referred to as the satellite terminal or “ST”), which is located at a remote location and includes the antenna to be aligned, is provided with the capability of generating a voltage signal having a level indicative of the strength of the signal received by the antenna. Typically, the voltage signal is a DC signal and can be measured utilizing a voltmeter or other signal strength indicator. Accordingly, when utilizing the foregoing alignment technique, the operator monitors the strength of the voltage signal, while adjusting the direction of the antenna and selects the position of the antenna corresponding to the highest obtainable level of the voltage signal as measured by the voltmeter. It is noted that in existing satellite receiver/transmitter systems, the value of the signal strength of the voltage signal rises as the antenna is pointed toward the satellite source and falls as it is moved away from the satellite source. Of course, the opposite is also possible.
While the foregoing method allows for the antenna installer to quickly point the antenna in the general direction of the desired satellite, it does not allow the antenna operator to fine tune the pointing of the antenna. In other words, the antenna installer cannot confirm that the maximum possible signal has been received. Indeed, the antenna installer simply adjusts the antenna position until a predetermined acceptable signal strength is received. However, the installer has no means of confirming whether or not this is the maximum possible signal available. This is due to the fact that the directivity of the antenna is relatively flat in the area defining the peak of the antenna pattern. As such, it is difficult to discern the pointing error (i.e., the shift from actual peak). It is noted that while it would be possible for the installer to confirm receipt of the maximum signal strength if the installer was provided sophisticated signal analysis equipment, such as a spectrum analyzer, it is not possible to do so as the costs of providing such equipment to the operator are prohibitive.
Accordingly, there remains a need for an apparatus that allows an antenna operator to quickly and easily determine whether the antenna has been positioned so as to achieve optimum signal strength of the received signal transmitted by the satellite, without the need for the operator to have access to sophisticated signal analysis equipment. It is further noted that the existing antenna pointing techniques are not likely to achieve the stringent antenna pointing requirements/tolerances (e.g., <0.2 degrees) that can be required for successful operation of broadband, multimedia satellite communication systems with terminals employing a receiving antenna having a reduced diameter (i.e., a small antenna). This is especially true given the fact that typical satellite systems uplink at higher frequencies with narrower beam widths, thus pointing errors measured by the receiver are amplified in the transmit direction.
The present invention relates to the method and apparatus for providing a simple, cost effective method and apparatus for allowing a sole installer to quickly and accurately point an antenna so as to optimally transmit and receive signals from a satellite. More specifically, the present invention allows the operator to quickly identify the position of the antenna necessary for maximizing the strength of the incoming (i.e., received) signal from a satellite.
In an exemplary embodiment, the apparatus in accordance with the present invention comprises an antenna dish; an elevation misalignment member coupled to the antenna dish and operative for varying an elevation angle of the antenna dish. The elevation misalignment member is capable of precisely setting the elevation angle in a first misalignment position and a second misalignment position, where the first misalignment position and the second misalignment position represent the same degree of change of elevation from a set elevation angle, and where the first misalignment position and the second misalignment position are in opposite directions from one another. Similarly, the apparatus also comprises an azimuth misalignment member coupled to the antenna dish and operative for varying an azimuth angle of the antenna dish. The azimuth misalignment member is also capable of precisely setting the azimuth angle in a first misalignment position and a second misalignment position, where the first misalignment position and the second misalignment position represent the same degree of change of azimuth from a set azimuth angle, and where the first misalignment position and the second misalignment position are in opposite directions from one another.
The present invention also relates to a method of pointing an antenna at a transmitter, which is referred to herein as the dither pointing method. In an exemplary embodiment, the method comprises the steps of: (a) varying the azimuth of the antenna dish a predetermined number of degrees in a first direction from a predetermined azimuth angle; (b) measuring a first signal strength of an incoming signal received by the antenna dish; (c) varying the azimuth of the antenna dish the same predetermined number of degrees in a second direction from the predetermined azimuth angle, where the second direction is opposite to the first direction; (d) measuring a second signal strength of the incoming signal received by the antenna dish; and (e) comparing the first signal strength to the second signal strength, and if the first signal strength equals the second signal strength, the current predetermined azimuth angle represents the optimal angle of azimuth for the antenna dish. However, if the first signal strength does not equal the second signal strength, the process further comprises the steps of: (f) adjusting the predetermined azimuth angle, and (g) repeating steps (a)–(e). The same process is then repeated for elevation adjustment. It is noted that while in the preferred embodiment the antenna is adjusted first in azimuth and then in elevation, it is also possible to adjust the antenna first in elevation and then in azimuth.
As described below, the method and apparatus for pointing an antenna in accordance with the present invention provides important advantages over the prior art. Most importantly, the present invention provides a low cost means for allowing a sole operator to quickly and easily fine tune the pointing of an antenna so as to maximize the strength of an incoming signal being transmitted by a satellite.
In addition, the method and apparatus of the present invention does not require the installer to be provided with expensive signal analysis equipment, such as a spectrum analyzer, in order to accurately point the antenna.
Yet another advantage is that because the present invention allows for precise alignment of the antenna and substantially eliminates antenna pointing error, the amount of power necessary for achieving acceptable communications between the satellite and the remote terminal coupled to the antenna is reduced. Among other things, this reduction in the power requirement reduces costs, improves overall G/T (i.e., gain/temperature) performance and advantageously reduces the amount of adjacent satellite interference and co-satellite crosspol interference.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings.
a–3d provide a graphic illustration of the dithering process of the present invention.
a–5c illustrate the process of misaligning the antenna utilizing the dither plates of the present invention.
Referring again to
The antenna assembly 10 further comprises a mounting device or antenna stand 45, which is used to elevate the antenna dish 15, feed horn 25 and low noise block radio frequency detector 30, and microwave amplifier 31 above the ground. As explained in further detail below, the assembly 10 further comprises an elevation movement mechanism 50, which functions to attach the antenna stand 45 to the antenna dish 15, and which provides for movement of the antenna dish 15 in the north/south direction (i.e., elevation). The assembly 10 also comprises an azimuth movement mechanism 51, which also functions to attach the antenna stand 45 to the antenna dish 15 and which provides for movement of the antenna dish in the east/west direction (i.e., azimuth). It is noted that in the preferred embodiment, the elevation movement mechanism 50 moves the antenna dish 15 in a direction which is orthogonal to the direction of movement provided by the azimuth movement mechanism 51. The elements forming both the elevation movement mechanism 50 and the azimuth movement mechanism 51 are described in detail below.
When initially aligning the antenna to the desired satellite, the antenna is first pointed in the general direction of the desired satellite. The directional coordinates (i.e., azimuth and elevation) of the antenna necessary for the antenna to point at the desired satellite are known by the installer, and are utilized to initially point the antenna at the satellite. Once the antenna is positioned to the directional coordinates of the desired satellite, the antenna is quickly swept in the azimuth and elevation directions until the antenna is pointed sufficiently accurately that it can begin receiving a signal from the satellite. As such, at this time the measurement device 40 will output a signal indicating the signal strength of the received signal. Typically, there is a predetermined value of received signal strength that indicates that the antenna dish 15 is pointed in the general vicinity of the location that would provide the maximum signal strength. The installer will adjust the antenna in either elevation and/or azimuth until the received signal strength, as measured by the measurement device, exceeds this predetermined value. This process is generally referred to as coarse pointing of the antenna.
Once the antenna is coarse pointed, as stated above, the antenna dish 15 is able to receive a signal from the transmitting satellite. The next step in the alignment process in accordance with the present invention is to fine tune the pointing direction of the antenna. In other words, position the antenna such that the peak of the antenna's receive signal pattern is pointed at the satellite.
More specifically, referring to
In accordance with the present invention, the process of fine tuning the antenna position comprises misaligning the antenna pointing direction symmetrically about the coarse pointing point in both elevation and azimuth, and recording the output of the measurement device at each misaligned location. It is important that the extent of the misalignment about the coarse pointing position is such that the directivity of the antenna receive pattern has a steep positive or negative slope at the misalignment positions. As graphically illustrated in
Specifically, at the peak position, if the antenna is lowered or raised in elevation by the same amount, the corresponding position on the antenna receive pattern will be the same, and therefore result in the same signal strength measurement. At any other position, if the antenna is lowered or raised in elevation by the same amount, the corresponding resulting positions on the antenna receive pattern will not be the same, and therefore will not result in the same signal strength measurement (see, e.g.,
As is noted above, in accordance with the preferred embodiment of the present invention, the azimuth and elevation adjustment mechanisms 76, 77 and the azimuth and elevation dither plates 72–75 are removable from the antenna so that these alignment tools can be re-utilized to align different antennas. However, it is also possible to practice the method of the present invention utilizing alignment tools which are permanently fixed to the antenna.
A more detailed description of the foregoing alignment process is now provided. First, once the coarse pointing position is determined, the azimuth and elevation adjustment mechanisms 76, 77 and the azimuth and elevation dither plates 72–75 are attached to the antenna if they were not mounted during the coarse pointing process. Further, if the azimuth lock-down bolt 54 was tightened following coarse pointing, it is now loosened for the dither process (i.e., alignment process) so as to allow the antenna to move so as to perform the dither process.
As shown in
When performing the dither process, first, the center opening 82 of the azimuth sliding window plate 72 is centered over the center dither reference line 81 on the azimuth indictor plate 73 (as shown in
If the difference between the signal strength readings taken at the two misalignment positions is below a predetermined threshold, the antenna is considered sufficiently well pointed in the azimuth direction. The antenna is returned to the center reference line and the azimuth lock-down bolts 54 are tightened. It is noted that the predetermined threshold is application specific, and depends on the final pointing accuracy requirement, the antenna radiation pattern, the distance to the misalignment positions, and the effect of atmospheric scintillation on the received signal strength.
If, however, the difference between the signal strength readings taken at the two misalignment positions is greater than the predetermined threshold described above, then the antenna is considered misaligned in the azimuth direction, and further alignment is required. This further alignment process is as follows. First, the average of the signal strength readings taken at the two misalignment positions is computed. Then, the antenna is turned a small amount until the signal strength reported by the measurement device 40 is equal to the computed average. When this small adjustment is made to the antenna, the outer dither window on the azimuth sliding window plate 72 will move slightly off of the outer reference line 82 on the azimuth indicator plate 73. Next, the installer aligns the azimuth indicator plate 73 to the new reference line location (i.e., the position where the measured signal strength substantially equals the previously computed average) by unlocking the azimuth indicator plate 73, moving the plate such that the outer window is centered about the corresponding outer reference line, and locking the azimuth indicator plate 73 back down.
After re-centering the outer window, the installer repeats the foregoing process of moving the antenna to the two misalignment positions, recording the signal strengths at the misalignment positions, comparing the difference to the predetermined threshold, and repeating again if necessary. With each iteration, the difference in the two signal strength readings should decrease until the difference is less than the predetermined threshold, at which point the dither process is complete in the azimuth direction. When the dither process is complete in the azimuth direction, the antenna is returned to the center reference line and the azimuth lock-down bolts are tightened.
This same dither process is then repeated with respect to elevation angle utilizing the elevation sliding window plate 74 and the elevation indicator plate 75, and upon completion, the elevation lock-down bolts are tightened. When the antenna has been pointed in both the azimuth and elevation using the above dither method, and the lock-down bolts have been tightened, the azimuth and elevation movement mechanisms and the azimuth and elevation dither indicator plates may be removed by the installer.
It is noted that the necessary amount of misalignment from the coarse pointing position to practice the present invention varies from application to application, as well as from antenna to antenna. Indeed, one of the primary characteristics necessary for determining the amount of misalignment is the antenna receive pattern 61. As stated above, in the preferred embodiment, the amount of misalignment should be sufficient to position the incoming signal on a steep portion of the antenna pattern 61 or, in other words, away from the substantially flat portion of the pattern 61 located by the peak. At locations away from the peak, minor shifts in angle result in noticeable shifts in received signal strength. As a general rule, the misalignment amount should be sufficient to reach 3 dB down from the peak of the antenna receive pattern 61.
Note that the above process uses a visual indicator to determine the precise amount to misalign the antenna to the misalignment positions. However, clearly other methods can be utilized to determine the accurate misalignment angles. These other methods include mechanical, electrical, or alternative visual methods. In all cases the indicator components must be firmly attached to the moveable antenna and the stationary antenna mount stand 45 (pole). Any undesired movement of the indicator components will cause errors in the final pointing accuracy.
It has been noted that atmospheric scintillation will cause the received signal strength to vary. If the scintillation is strong enough it is possible that the signal strength readings taken at the two misalignment positions will rarely be within the predetermined threshold, even if the antenna is pointed with perfect accuracy at the satellite. It is also possible that with strong scintillation the signal strength readings taken at the two misalignment positions will be within the predetermined threshold, even when the antenna angle has an error greater than the desired pointing accuracy the installer is attempting to achieve. For these reasons, in order to negate the effects of scintillation, it is beneficial to signal process the instantaneous receive signal strength at the antenna prior to displaying it at the measurement device 40. One possible implementation of such signal processing would be the utilization of a low pass filter. In the design of such a low pass filter, there is a tradeoff between the dynamic range of the filtered scintillation (the amount of scintillation the installer will see on the measurement device 40) and the time required for the filtered signal strength to achieve a steady-state when the antenna is moved during the dither pointing process. Ideally, the filter would be designed to smooth the worst-case scintillation enough to ensure with high probability that the antenna is pointed to the desired accuracy when the difference between the signal strength readings taken at the two misalignment positions is less than the predetermined threshold. The time-response of the filter would be set such that when the installer moves the antenna the filtered signal strength achieves its steady-state value quickly enough so that the misalignment pointing process can proceed at an acceptable pace to the installer. Different amounts of filtering could be used during the coarse pointing and the dither pointing time periods. Of course, other signal processing techniques to negate the effects of scintillation can also be utilized, for example, a computer program which operated to average the readings of the output amplitude.
It is further noted that with regard to the misalignment members (i.e., dither plates), while one possible embodiment has been illustrated, the present invention in no manner whatsoever intended to be limited to the disclosed embodiment. Clearly variations and/or modifications of the foregoing design of the misalignment member are possible. Indeed, the important aspects are that the misalignment members allow for precise misalignment (i.e., the same amount of variation) about a given position, and that the precise misalignment is repeatable. In other words, with regard to elevation for example, the misalignment member allows for the antenna dish to be shifted down-ward a predetermined amount from a given elevation angle, and then shifted upward by the same predetermined amount from the same given elevation angle. The same requirements hold for the misalignment member utilized to vary the antenna's azimuth.
As stated above, the method and apparatus for pointing an antenna in accordance with the present invention provides important advantages over the prior art. Most importantly, the present invention provides a low cost means for allowing a sole operator to quickly and easily fine tune the pointing of an antenna so as to maximize the strength of an incoming signal being transmitted by a satellite.
In addition, the method and apparatus of the present invention does not require the installer to be provided with expensive signal analysis equipment, such as a spectrum analyzer, in order to accurately point the antenna.
Yet another advantage is that because the present invention allows for precise alignment of the antenna and substantially eliminates antenna pointing error, the amount of power necessary for achieving acceptable communications between the satellite and the remote terminal coupled to the antenna is reduced. Among other things, this reduction in the power requirement reduces costs, improves overall G/T (i.e., gain/temperature) performance and advantageously reduces the amount of adjacent satellite interference and co-satellite crosspol interference.
Variations of the embodiments of the present invention described above are also possible. For example, if the present invention is being utilized to align an antenna with a geo-synchronous satellite, it is possible to have only a single antenna misalignment member (as opposed to having an azimuth misalignment member and an elevation misalignment member). The sole misalignment member functions to misalign the antenna along the orbital arc of the satellite. More specifically, once the antenna is coarse tuned in the same manner as set forth above, the sole misalignment member would allow the antenna to be misaligned in equal amounts along the orbital arc, and the process detailed above of adjusting the alignment until the measured power level of the received signal was equal in both the first and second misalignment positions would be performed, thereby aligning the antenna to the satellite.
Of course, it should be understood that a wide range of other changes and modifications can be made to the preferred embodiment described above. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it be understood that it is the following claims including all equivalents, which are intended to define the scope of the invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5296862 | Rodeffer et al. | Mar 1994 | A |
| 5515058 | Chaney et al. | May 1996 | A |
| 5561433 | Chaney et al. | Oct 1996 | A |
| 5583514 | Fulop | Dec 1996 | A |
| 5760739 | Pauli | Jun 1998 | A |
| 6697026 | Hemmingsen, II | Feb 2004 | B1 |
| 20020018016 | Radonic | Feb 2002 | A1 |
