ACTIVE ANTENNA COMMUNICATION SYSTEM

Abstract: This disclosure provides a communication system using a high-altitude aircraft traveling at relatively slow speeds, which can remain airborne for long periods of time. The communication system uses the airplane as a long term high altitude platform that relays signals between one or more ground-stations and/or satellites, aircraft, and the like. The ground-stations have narrow-beam antennas that are aimable, permitting the aircraft to maintain a larger station than would otherwise be possible using the narrow-beam antennas. The ground-stations adjust their aim based on information either gained by tracking the aircraft's signal, or transmitted by the aircraft to the ground-station.

Description: ACTIVE ANTENNA COMMUNICATION SYSTEM The present application claims priority from a U.S. provisional patent application, Serial No. 60/197,799, filed April 14, 2000, which is incorporated herein by reference for all purposes. The present invention relates to wireless communication systems, and more particularly, to a wireless communication system using an aircraft with one or more ground-based stations. BACKGROUND OF THE INVENTION The need for high-bandwidth, last-mile connectivity to voice and data- stream end-users has been rapidly increasing for quite some time. This need for increased communication capacity exists both in urban locations that have a substantial communications infrastructure, and in lesser-developed areas that lack such infrastructures. Communications signals can be delivered to end-users through a number of different types of communication systems. A wired, terrestrial system typically provides high speed communication for a large bandwidth signal. However, the infrastructure for such a system is expensive and time consuming to build, maintain and upgrade, and it does not, by itself, support mobile communications. A wireless system that uses transmission towers provides reasonably high speed communication for a substantially more limited bandwidth per the ground area served. Geostationary Earth Orbit (GEO) satellites (at an altitude of about 36,000 kilometers) can also provide wireless communications to end-users, but are limited by bandwidth efficiency because of their extremely high altitude. Even narrow-beam antennas mounted at such distances encompass large land areas. Therefore, GEO satellites are limited in their ability to serve high-bandwidth communication needs in most areas, and particularly for densely populated areas. Furthermore, GEO satellites must be in equatorial orbits, which limits their practical use to equatorial land regions. Medium and low Earth orbit (MEO and LEO) satellite systems (at altitudes of 10,000 kilometers and 700-1500 kilometers, respectively) are complex in nature because end-user's are required to have equipment to track the satellites' relative movement across the sky. Non-geostationary satellites require complex, continuously adjusting, directional antennas that are able to gimbal through large angles. These antennas are needed both in the air and on the ground, typically with the ground antennas having secondary antenna systems adapted to switching communications signals from one passing satellite to the next. Of course, none of the above satellites are easily retrieved, e.g., for servicing. Aircraft are used in a wide variety of applications, including travel, transportation, fire fighting, surveillance and combat. Aircraft can be used to relay communication signals. Ground-stations for such a purpose would typically require either low-bandwidth, omnidirectional antennas or large gimbal-angle capabilities (similar to ground-stations for MEO or LEO satellites) because such aircraft would travel substantial distances even if circling. Unfortunately, normal gimbaled ground-stations are expensive devices that are susceptible to damage and wear-and-tear. Using wide-angle or omnidirectional antennas can avoid the use of gimbals. However, the larger broadcast angles require additional power and, more important, limit the reuse of frequencies by nearby ground-stations and/or nearby aircraft. Thus, the system-wide bandwidth is limited by the use of wide angle or omni-directional antennas. An exception to the above-stated requirement for the antennas to have either wide broadcast angles or large-angle gimbals is where the aircraft is capable of station-keeping in a small station in the sky for a long period of time, i.e., act as a long-duration, suborbital high-altitude platform. Such an aircraft is described in U.S. Patent No. 5,810,284. This aircraft design is embodied by the well-known Pathfinder, Centurion and Helios aircraft. These aircraft are capable of maintaining position at stratospheric altitudes for long periods of time, allowing ground-stations to use fixed, narrow- beam antennas (e.g., 2° or 3° bandwidth antennas having no steering mechanisms other than simple ones for initially acquiring the target). These narrow-beam antennas allow for frequency reuse between multiple ground-stations and a given aircraft, as well as between one ground-station (or closely adjoining ground- stations) and multiple aircraft. However, such aircraft can expend significant resources (i.e., power) in maintaining the tight station necessary for using such narrow-beam antennas. The power is spent both in tight maneuvering, and in quickly compensating for momentary variations in local flight conditions. It is desirable to develop a communication system that provides for high-bandwidth signals to a large number of low-priced, durable ground-stations. Various embodiments of the present invention can meet some or all of these needs, and provide further, related advantages. SUMMARY OF THE INVENTION In various embodiments, the present invention solves some or all of the needs mentioned above by providing a communication system that provides for the aircraft to have a larger flight station while still having the advantages of using narrow-beam ground-station antennas. The communication relay system of the invention typically includes an aircraft and a plurality of ground stations for which the aircraft relays signals. The aircraft is configured to stationkeep within a designated flight-station, which is only a portion of the aboveground field of vision that can include a plurality of other potential flight-stations. The aircraft includes a communication relay module, which has one or more antennas for communicating with the ground-stations. The ground-stations are located within a coverage area, and each ground-station has at least one antenna configured to communicate, via communication signals, with at least one of the antennas of the communication relay module. A feature of the invention is that the beamwidth of the ground-station antenna is narrow enough such that it is inadequate to illuminate (i.e., transmit to and/or receive from) the entire flight-station at one time. Because the aircraft can move throughout the flight-station, each ground-station antenna is configured to be steerable under the control of an antenna controller, such that the ground-station antenna can maintain communication with the aircraft's communication relay module as the aircraft moves throughout the flight-station. The antenna controller is configured to limit the steering of the antenna such that it avoids directing the antenna at any flight-station other than the designated flight-station. Advantageously, most embodiments having this feature will have lower power usage by the ground-station antenna, and will have less crosstalk from nearby communications using the same frequencies, as compared to having the ground-station antenna have a beamwidth large enough to illuminate the entire flight-station. Furthermore, the aircraft will have to complete fewer maneuvers and expend less energy to maintain station as compared with a flight-station small enough to be fully illuminated by the narrow-beam ground-station antenna. An additional feature of the invention is that aircraft positional information is transmitted from the aircraft to the ground-station and/or received by the ground station using a wide-beam or omnidirectional antenna, thereby allowing the ground station to receive the information without having its antenna properly aimed at the aircraft. Other features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The detailed description of particular preferred embodiments, as set out below to enable one to build and use an embodiment of the invention, are not intended to limit the enumerated claims, but rather, they are intended to serve as particular examples of the claimed invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustrative view of a preferred embodiment of a communication system embodying the invention. FIG. 2A is an elevational view of an aircraft used in the communication system depicted in FIG. 1. FIG. 2B is a plan view of the aircraft depicted in FIG. 2 A. FIG. 3 is another illustrative view of the communication system depicted in FIG. 1. FIG. 4 is an elevational view of a flight-station, over a number of ground-stations, as used in the communication system depicted in FIG. 1. FIG. 5 is a plan view of an array of flight-stations, as used in the communication system depicted in FIG. 1. FIG. 6 is a plan view of an array of ground-level illuminations by overlapping aircraft antenna beams that define cells within a coverage area, as used in the communication system depicted in FIG. 1. FIG. 7 is an elevational view of directional ground antennas targeting an aircraft within a flight-station, as used in the communication system depicted in FIG. 1. FIG. 8A is a schematic view of a first embodiment of a steerable antenna as used in a ground-station of the communication system depicted in FIG. 1. FIG. 8B is a schematic view of a second embodiment of a steerable antenna as used in a ground-station of the communication system depicted in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention summarized above and defined by the enumerated claims may be better understood by referring to the following detailed description, which should be read in conjunction with the accompanying drawings. This detailed description of particular preferred embodiments of a communication system, set out below to enable one to build and use particular implementations of the invention, is not intended to limit the enumerated claims, but rather it is intended to provide particular examples thereof. With reference to FIG. 1, a communication system embodying the invention includes one or more ground-stations 102, one or more aircraft 104 and preferably one or more satellites 106. The ground-stations are located in cells 108 that are targeted by directional antennas of the aircraft. Each airplane is stationkeeping within a limited flight-station at stratospheric altitudes, e.g., between the altitudes of 50,000 feet and 70,000 feet. Preferably each flight-station is set at the same altitude as the other flight-stations. The aircraft uses one-way or two-way communication signals to relay ground-station communications to other ground- stations and/or satellite networks. Airplane The invention preferably includes the use of an airplane as a substantially geostationary platform having moderately tight station-keeping requirements. In accordance with the present invention, the preferred airplane is of a design similar to that of the Pathfinder, Centurion and/or Helios aircraft. While the preferred airplane's design is described below, further details are provided in U.S. Patent No. 5,810,284, which is incorporated herein by reference. Nevertheless, it is to be understood that other aircraft, such as helicopters, balloons, blimps, kites or other types of airplanes are within the scope of the invention. With reference to FIGS. 1, 2A and 2B, the preferred aircraft 104 embodiment is a flying wing airplane, i.e., it has no fuselage or empennage. Instead, it consists of an unswept wing 112, having a substantially consistent airfoil shape and size along the wingspan. Preferably, six, eight or fourteen electric motors 114 are situated at various locations along the wingspan, each motor driving a single propeller 116 to create thrust. Preferably, two, four or five vertical fins 118a - 118d, or pods, extend down from the wing, with landing gear at their lower ends. The preferred airplane 104 is solar-powered, and includes fuel cells to store energy for continuous day and night flight. It is therefore ideally suited to fly continuous, unmanned missions of over a week to ten days, (e.g., 200 hours) and more preferably, of 3000 hours, or longer. Alternatively, it can be designed to derive some or all of its power from hydrogen fuel (such as liquified hydrogen to be used in either a fuel cell or a conventional motor), fossil fuels or other stored fuels, or combinations of fuel sources such as solar power by day and stored non- renewable or partially renewable fuels by night. The aircraft 104 is longitudinally divided into preferably five or six, modular segments sequentially located along the wingspan. These segments range from 39 to 43 feet in length, and have a chord length of approximately eight feet. Thus, the aircraft has length of approximately eight feet, and preferably has a wingspan of approximately 100, 120, 200 or 250 feet. The airplane's wing segments each support their own weight in flight so as to minimize inter-segment loads, and thereby minimize required load-bearing structure. The fins 118a - 118d extend downward from the wing 112 at the connection points between segments, each fin mounting landing gear front and rear wheels. The fins are configured as pods to contain elements of the aircraft, such as electronics, and/or various payloads. One of the pods, a "control pod" is used to cany control electronics, including an autopilot principally embodied as software, to control the motors and elevators. In addition, the pods carry sensors, including global positioning system equipment, as well as communications equipment. The airplane also includes a communication relay module that includes the aircraft's antennas for transmitting to and/or receiving from the ground- stations. The aircraft's antennas have moderate beamwidths, preferably on the order of 10° - 20°. As a result of the above design, the preferred embodiment of the aircraft is light (less than 1 pound per square foot of wing area), travels at relatively slow air speeds (from 13 knots at low altitudes to 100 knots at high altitudes), and needs relatively little electrical power from the arrays of solar cells in order to stay airborne. The relatively slow flight capabilities of the airplane aid the airplane's capability for long-duration flight and tight maneuvering during stationkeeping. Flight-Stations With reference to FIGS. 1 and 3-6, each airplane 104 stationkeeps, i.e., maintains a substantially geostationary position relative to the ground-stations 102. This substantially geostationary position is a flight-station 132 having a center point 134, and an allowed lateral and altitudinal wandering distance. Thus, the fligh-station is typically a cylindrical shaped section of airspace, where the cylinder shape extends longitudinally in a vertical direction. Preferably, the flight-station is at an altitude of around 60,000-70,000 feet, above normal air traffic and atmospheric disturbances (e.g., storms). At this altitude, the maximum strength winds have lower speed than the winds at lower jet-stream regions. Preferably, each aircraft 104 is maintained in a separate flight-station 132 that is separated from the other flight-stations by a separation distance 136. At any given time, each aircraft could be at any location within its flight-station (as depicted in FIG. 5). The separation distance both assures that one airplane does not fly within the beamwidths of another's associated ground antennas, and serves to protect the airplanes from striking each other. Ground- Station With reference to FIGS. 1 and 3, the ground-stations 102 within each cell 108 are terrestrial communication nodes that preferably broadcast signals to, and/or receive signals from, one or more of the aircraft 104. The ground-stations are typically far more numerous than the number of cells (i.e., there are numerous ground-stations in most cells). Ground-based communications equipment is connected to the ground-stations, and typically includes one or more end-user terminals (i.e., communications equipment for one or more end-users). Each ground-station includes one or more narrow-beam antennas that can each broadcast signals to, and/or receive communication signals from, antennas of the communications module on one of the aircraft. The ground-station antennas preferably have a narrow beamwidth, e.g., around of 2°, 2.5°, 3° or 4°, providing for a high potential bandwidth at reasonable power levels. These antennas have a steering mechanism that provides for the aim of the antenna to be tweaked on the order of 3° or 6° from a nominal position, which is on the order of one to three times the beamwidth of the ground- station antenna. The communication system includes one or more controllers to instruct and thereby control the ground-station antennas' steering. A separate controller can be in each ground-station, or a single controller can be located in either the aircraft or a controlling ground-station. The controlling ground-station can be in contact with the aircraft, which relays control information to the other ground-stations, or directly in communication with the regular ground-stations. Furthermore, a controller can be co-located in a number of system components, such as partially in the airplane and partially in each ground-station. A single ground-station can include multiple ground-station antennas that can be aimed at, and access signals from, different aircraft, thus increasing the available bandwidth. Separate controllers can control the different antennas, or a single system controller can control all the ground-station antennas. The ground-station also includes an initial-aim adjustment mechanism. This mechanism will typically be a manually adjusted and locked system that includes some type of signal strength indicator to aid in setting the nominal aim of the antenna to the center point 134 of a flight-station 132. Ground-station Cells The antennas on each airplane 104 are configured and targeted to illuminate an area 142 of the ground that is substantially filled by one cell 108. These preferably hexagonal cells can be of varied sizes, which are preferably commensurate with the beamwidth of the airborne antennas at a distance equal to the cruising altitude of the airplane. The airplane's antennas can be targeted to illuminate overlapping ground areas so as to achieve complete cellular coverage over a coverage area 144. The coverage area might typically have a radius on the order of 10 to 30 miles. The airplane antennas are carried in one or more payload modules on the airplane 104. Using gimbals, the antennas maintain their attitude, and are decoupled from the roll-pitch-yaw and translational motion of the aircraft. Preferably all of the aircraft antennas are mounted on a single, gimbaled platform to limit the number of active gimbals. Thus, each aircraft antenna's aim is maintained on its respective cell 108. Antenna Beam Manipulation With reference to FIG. 7, under the present invention the size of the flight-station 132 is larger than the narrow-beam beams 152 of the ground-stations 102 could cover without moving. By using a slight tweaking (i.e., minimal steering) of the direction of the ground-station antennas, the communication system can enjoy the benefits of having narrow-beam ground antennas (which would otherwise require flight-stations on the order of ±0.5 mi laterally and ±0.1 mi vertically from a central reference point), while the aircraft can enjoy the benefits of having a larger flight area, such as about ±1.5 mi laterally and ±1.0 mi vertically from a central reference point. In particular, the airplane can be operated on average with less power than would be needed to maintain a smaller station, and the airplane can stationkeep in more difficult whether conditions, such as strong winds, high altitude-penetrating thunderstorms, turbulence and vertical air motions. Furthermore, from the reliability standpoint, it will not have to maneuver as often or as violently, and its antenna platform will be more easily stabilized with more limited deflections. In conducting ground-station antenna steering under the invention, the ground-station antenna controller is preferably configured to steer the antenna beam(s) to move throughout an entire flight-station. They are further preferably configured to limit the ground-station antenna beam steering such that the beams avoid crossing into any flight-station other than a particular, designated flight- station. This configuration might occur in control system software or hardware, because the amount of beam-steering that is necessary will depend on the relative . positions of the ground-station and flight-station, and on the size and shape of the flight-station. In particular, wide flight-stations will require higher movement capability from ground-stations directly underneath the flight-station than from ones substantially distanced from the aircraft's location. Similarly, tall flight-stations will require higher movement capability from ground-stations substantially distanced from the aircraft's location than from ones directly underneath the flight- station. These geometric requirements can be readily calculated by the controller. Turning now to FIGS. 8A and 8B, ground-station antennas will typically include a feed horn 202 and a main dish 204. The antennas might also include a secondary reflector 206. The preferred actuators for tweaking the antenna steering are low powered and long lived. Because they do not need to deflect over large angles, they can be simple mechanisms that are lower cost and can have more reliability than large-angle gimbal systems. Among the types of mechanisms that can be used are servomotors, stepper motors, piezoelectric actuators and bimetallic strips. Gimbals can also be used in some embodiments of the invention. The steering of the antennas can be reoriented mechanically in a number of different ways. For example, an entire antenna assembly could be repositioned. More preferably, however, only a portion of the antenna assembly, such as the main dish (see FIG. 8A), the secondary mirror (see FIG. 8B), or the feed horn could be repositioned to a deflected position 208. Repositioning the feed horn or the secondary mirror is preferred, as they are typically smaller devices. If repositioning either the feed horn or the secondary mirror is used, in might be necessary to use a larger main dish than would be needed for a fixed antenna. Other types of antennas are also within the scope of the invention. For example, a phased array could be used, i.e., a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. In such a case, the antenna could be steered electronically. Likewise, an array of narrow-beam antennas targeted in a pattern that covers the entire flight-station could be selectively used by a control system as a single, steerable antenna. Thus, not all embodiments require a physical motion to steer the antenna. Beam-Steering Control System In order for the ground-station antennas to steer such that their beams follow the airplane as it moves throughout the flight-station, the ground-station must gain antenna-steering information (i.e., information about the required vertical and horizontal ground-station antenna orientation manipulations). This information can be developed in a number of different ways, in number of different control system embodiments. Typically, this information will be generated from aircraft-location information, as well as from information on the relative positions of the ground- stations with respect to the flight-station. In a first embodiment of a ground-station antenna-steering control system for the invention, the airplane's location is established by the airplane, such as by using a global positioning system (GPS) reading. The information is then transmitted to each ground-station, either encoded within the carrier signal noπnally transmitted to each cell, or via a separate, narrow channel broadcast using broad beam or omnidirectional antennas to transmit and/or receive the information. The information can be provided in a number of formats. For example, the information can be sent as an absolute geographic position, a relative position of the aircraft with respect to the cell, or a relative position of the airplane with respect to the flight-station. Alternatively, the information can be transformed into antenna steering information for each given cell and/or each group of one or more ground-stations and then transmitted. It is worth noting that the antenna-orientation information and/or the aircraft location information represent a small amount of data requiring a very low data-rate to transmit, and little transmission power. That information needs to reach every ground-station that has an antenna targeting the aircraft. Each ground-station will have to conduct elevation and azimuth angle steering appropriate for its geographical position relative to the aircraft. If one broad-beam antenna on the plane is used to send plane orientation information to reach all users, then either the information should be coded to each ground-station, specifying that antenna's steering requirements, or each ground-station needs to compute its own steering needs based on the airplane's position information. In a second embodiment of a ground-station antenna-steering control system for the invention, each airplane's location can be established by a ground- based central-control station, such as by using radar ranging and direction finding. The information can be telemetered to the plane and relayed to the ground-stations in a manner similar to that discussed above for the first embodiment of a ground- station antenna-steering control system. Likewise, that information can be transmitted to the ground-stations through other means such as available ground communication systems or separate wireless transmissions. Again, the information can be provided in a variety of forms, such as aircraft location information or antenna steering instruction information. In a third embodiment of a ground-station antenna-steering control system for the invention, the airplane's location is established by each ground- station, such as by an autonomous tracking system based on the aircraft's transmission signal strength. In this type of system, the ground-station antenna is periodically steered through small angles and the signal strength is compared at each position. Stronger signals indicate that the antenna is closer to being centered on the aircraft. Of course, once the ground-station is locked onto its respective airplane, it will stay locked onto it without transmissions of information from the airplane. It should be noted that if the third embodiment's antenna loses track of the airplane, such as might occur when the system is powered down, it can conduct a search pattern covering its range of motion, which should cover the entire flight-station. This ability might also be necessary for other embodiments if the antenna-steering information is sent to the ground-station embedded in the normal transmissions of the aircraft, which would be lost when the antenna lost track of the aircraft. The use of omnidirectional antennas by the control system generally eliminates the need for significant or frequent scanning. Other Considerations The principles of small-angle antenna steering for the ground-station antennas can be adapted to a wide range of flight-station sizes, such as ±15 miles laterally and ±5 miles vertically, or ±20 miles laterally and ±3 miles vertically. However, as the stationkeeping loosens, secondary effects become more relevant, such as signal strength variations as distances vary significantly, or interference with other users of the same frequency that were otherwise shielded by strict directionality. Furthermore, the spacing between one flight-station and nearby flight-stations might need to be increased. Small-angle steering could also be used on the airplane antennas as well as the ground-station antennas, adding a fine control onto the large-angle gimbals that stabilize the antennas during flight. In the overall communication system, there may be ground-stations that do not use only small angle adjustments. Such ground-stations would include mobile ground-stations, and ground-stations that are designed to switch communication between different aircraft (e.g., for aircraft command and control). It should be understood that using limited directional adjustments in ground-stations adds price and complexity over fixed ground-stations, but it provides many benefits related to efficiency, energy supply, and maneuvering ability of the stratospheric airplane serving as a relay station. Thus, the total communication system effectiveness, cost, and reliability can be improved under many embodiments of the invention. The resulting system can be used for two-way communications between ground stations and other locations, one-way broadcasts to the ground- stations, or even one-way broadcasts by the ground-stations. Thus, it should be understood that the above descriptions of antennas illuminating cells or flight stations are a reference to the antennas' beam width taken at a distance, and not necessarily to an antenna configured to transmit communications rather than only receive communications. While particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Thus, although the invention has been described in detail with reference only to the preferred embodiments, those having ordinary skill in the art will appreciate that various modifications can be made without departing from the scope of the invention. Accordingly, the invention is not intended to be limited by the above discussion, and is defined with reference to the following claims.

Claims: I Claim: 1. A communication relay system, comprising: an aircraft configured to stationkeep within one designated flight-station out of a plurality of potential flight-stations, the aircraft including a communication relay module, the communication relay module including one or more antennas; a plurality ground-stations to be located in a coverage area, each ground- station including an antenna configured to communicate via communication signals with at least one of the antennas of the communication relay module, the ground- station antenna having a beamwidth inadequate to illuminate the entire flight-station at one time; and an antenna controller, wherein each ground-station antenna is configured to be steerable under the control of the antenna controller such that the ground-station antenna can maintain communication with the communication relay module when the aircraft moves throughout the designated flight-station, and wherein the antenna controller is configured to limit the steering of the antenna such that it avoids directing an antenna at any flight-station other than the designated flight-station. 2. The communication relay system of claim 1, wherein the antenna controller is configured such that aircraft-location information is transmitted to each ground- station, and each ground-station calculates antenna-steering information from the aircraft-location information. 3. The communication relay system of claim 2, wherein the antenna controller is configured such that the aircraft-location information is developed from sensors aboard the aircraft. 4. The communication relay system of claim 2, wherein the antenna controller is configured such that the aircraft-location information is developed from sensors located on the ground. 5. The communication relay system of claim 1, wherein the antenna controller is configured such that antenna-steering information is transmitted to each ground- station. 6. The communication relay system of claim 1, wherein the antenna controller is configured such that antenna controller's information is transmitted to each ground-station embedded in the communication signals from the communications relay module to the ground-station antenna. 7. The communication relay system of claim 1, wherein the antenna controller is configured such that antenna controller's information is received by each ground- station via an omnidirectional antenna. 8. The communication relay system of claim 1, wherein the antenna controller is configured such that antenna controller's information is transmitted to each ground-station from a ground-based location. 9. The communication relay system of claim 1, the plurality of ground-stations further including a tracking system configured to detect information on the location of the aircraft relative to the ground-stations; wherein the antenna controller is configured to use the information on the location of the aircraft to generate antenna-steering instructions for steering the ground-station antennas. 10. The communication relay system of claim 1, wherein each ground-station of the plurality of ground-stations includes a tracking system configured to detect information on the location of the aircraft relative to the ground-station; wherein the antenna controller is configured to use the information on the location of the aircraft to generate antenna-steering instructions for steering the ground-station antennas. 11. The communication relay system of claim 10, wherein tracking system of each ground-station is configured to use the signal strength of the signal received by the ground-station antenna to detect information on the location of the aircraft, and wherein the antenna controller is further configured to generate antenna-steering instructions for steering the antenna in a search pattern if the ground-station antenna has lost communication with the communication relay module while the aircraft is located in the designated station. 12. The communication relay system of claim 1, wherein the aircraft is a device selected from the group of a blimp, an airplane and a kite. 13. The communication relay system of claim 1, wherein the designated station extends no more than approximately one and one-half miles laterally and no more than approximately one mile vertically from a reference position. 14. The communication relay system of claim 1, wherein the designated station extends no more than twenty miles laterally and no more than three miles vertically from a reference position. 15. The communication relay system of claim 1, wherein the antenna controller and the ground-station antennas are configured such that the ground-station antennas are steerable over no more than approximately six degrees. 16. The communication relay system of claim 1, wherein the antenna controller and the ground-station antennas are configured such that the ground-station antennas are steerable over no more than approximately three degrees. 17. The communication relay system of claim 1, wherein each ground-station antenna includes a main dish and a feed horn, and wherein each ground-station antenna is steerable by displacing the main dish relative to the feed horn. 18. The communication relay system of claim 1 , wherein each ground-station antenna includes a main dish and a feed horn, and wherein each ground- station antenna is steerable by displacing the feed horn relative to the main dish. 19. The communication relay system of claim 1 , wherein each ground-station antenna includes a main dish, a secondary reflector and a feed horn, and wherein each ground-station antenna is steerable by displacing the secondary reflector relative to at least one of the main dish and the feed horn. 20. A communication relay system, comprising: an aircraft configured to stationkeep within one designated flight-station out of a plurality of potential flight-stations, the aircraft including a communication relay module, the communication relay module including one or more antennas; a plurality ground-stations to be located in a coverage area, each ground- station including an antenna configured to communicate via communication signals with at least one of the antennas of the communication relay module, the ground- station antenna having a beamwidth inadequate to illuminate the entire flight-station at one time; and a means for controlling the ground-station antennas, wherein each ground- station antenna is configured to be steerable under the control of the means for controlling such that the ground-station antenna can maintain communication with the communication relay module when the aircraft moves throughout the designated flight-station, and wherein the means for controlling is configured to limit the steering of ground-station antennas such that it avoids directing an antenna at any flight-station other than the designated flight-station. 21. A method of relaying communications, comprising: providing an aircraft configured to stationkeep within one designated flight- station out of a plurality of potential flight-stations, the aircraft including a communication relay module, the communication relay module including one or more antennas; providing a plurality ground-stations to a coverage area, each ground-station including an antenna configured to communicate via communication signals with at least one of the antennas of the communication relay module, the ground-station antenna having a beamwidth inadequate to illuminate the entire flight-station at one time; and controlling the steering of the ground-station antennas such that they maintain communication with the communication relay module as the aircraft moves throughout the designated flight-station, and such that they avoid pointing at any flight-station other than the designated flight-station.

Inventors: MACCREADY PAUL B, MACCREADY, PAUL, B.
Applicants: AEROVIRONMENT INC, MACCREADY PAUL B, AEROVIRONMENT INC., MACCREADY, PAUL, B.
Application year: 2001
Main classification: H01Q3
IPC codes: H01Q1, H01Q3, H04B7