Patent Description:
An antenna system in a high-altitude platform (HAP), such as a balloon, may provide coverage to a large area on the ground. Interference is of minimal concern when the HAP flies over sparsely populated regions. However, in some situations, the HAP may fly close to country borders or close to terrestrial communication towers. In these situations, it is more likely to encounter interference, and likely reduce the coverage and capacity of the HAP.

<CIT> describes a phased array antenna system with an intermodulation beam nulling device.

<CIT> describes an antenna apparatus for use in a wireless network and method of operating such an antenna apparatus. A wireless network controller provides a configuration of such an antenna apparatus, a method of operating such a wireless network controller, and a resulting wireless network. The antenna apparatus comprises a directional antenna and a uniform circular antenna array. The directional antenna can be rotatably positioned about an axis with respect to a fixed mounting portion of the apparatus in dependence on wireless signals received by the antenna array. The antenna array allows the antenna apparatus to receive wireless signals isotropically and thus to accurately monitor the wireless signal environment in which it finds itself. The antenna apparatus can thus monitor and characterise incoming signals, both from external interference sources and from other network nodes, and the directional antenna can then be positioned in rotation to improve the network throughput.

An antenna system including a detachable nulling subassembly may be provided in the HAP. The detachable notch element subassembly may include a plurality of notch antenna elements that may be individually activated and deactivated through the use of a nulling activation switch. The detachable nulling subassembly may be configured to easily attach and detach (or otherwise engage or disengage) to/from an interface of a primary antenna system, prior to the launch of the HAP for a particular mission.

In particular, the detachable nulling subassembly includes a plurality of nulling antenna elements, which may be configured to modify an antenna pattern footprint (i.e., a beamforming signal) of a primary antenna system of the HAP. The antenna pattern footprint on the ground provided through the use of the primary antenna system may be modified when one or more of the nulling antenna elements are activated or deactivated. For example, at least a portion of the antenna pattern footprint may be reduced in size when a notch element is activated, and expanded or returned to its original footprint when the nulling antenna elements are deactivated.

A balloon-based communication system may have four sectors, where each sector may generally have an unmodified beam pattern that extends <NUM> (or more or less) in a particular geographical direction. The long term evolution (LTE) footprint may be limited to a <NUM> radius, but the splatter (extra energy) may extend out to <NUM>. Activation of the notch subassembly (nulling elements) may reduce this beam pattern with a resultant modified beam pattern that only extends <NUM> (or more or less) in the particular geographical direction. In one aspect, a communication apparatus for a HAP includes a transmitter configured to generate an RF signal, a primary antenna system configured to generate an RF beam based on the RF signal, the primary antenna system including a first plurality of antenna elements, a first power divider, and a nulling activation switch having at least a first contact and a second contact, and a detachable nulling subassembly in communication with the nulling activation switch. The detachable nulling subassembly may be configured to modify the RF beam generated by the primary antenna system by generating nulling signals when the nulling activation switch is controlled to feed the RF signal to an input of the detachable nulling subassembly. The first power divider includes an input in communication with the transmitter, and a plurality of outputs. The input of the first power divider may receive the RF signal from the transmitter, and the plurality of outputs of the first power divider are coupled to respective antenna elements of the primary antenna system. The detachable nulling subassembly includes a second power divider having an input and a plurality of outputs, a plurality of phase shifters, and a plurality of nulling antenna elements. The detachable nulling subassembly is in communication with the nulling activation switch via an interface. The interface may be a wired or wireless interface. The interface may be a wired harness connector. The detachable nulling subassembly is in communication with the second contact of the nulling activation switch. The transmitter is in communication with the first contact of the nulling activation switch. The RF signal is fed to the input of the second power divider when the nulling activation switch is closed such that the first contact is connected to the second contact. Each output of the second power divider feeds the RF signal to a respective processing chain including a phase shifter connected in series with a nulling antenna element. A position of the nulling activation switch may be controlled based on one or more of a location of a high-altitude platform, knowledge of ground terrestrial locations, knowledge of country borders, and knowledge of service regions. A limit may be established as to a total power flux density across borders that should not be exceeded from a sum of all HAP transmissions or a total power flux density to terrestrial towers from the sum of all HAP transmissions.

In another aspect, a method is provided for nulling an RF beam for a HAP. The method includes generating, by a transmitter, an RF signal, generating, by a primary antenna system, an RF beam, determining, by one or more processors, a result indicating whether to modify the beamforming signal, and when the result indicates to modify the beamforming signal, generating, by a detachable nulling subassembly based on the RF signal, nulling signals to modify the beamforming signal generated by the primary antenna system.

<FIG> depicts an example system <NUM> in which a fleet of balloons or other high altitude platforms described above may be used. This example should not be considered as limiting the scope of the disclosure or usefulness of the features described herein. System <NUM> may be considered a balloon network. In this example, balloon network <NUM> includes a plurality of devices, such as balloons 102A-F as well as ground base stations <NUM> and <NUM>. Balloon network <NUM> may also include a plurality of additional devices, such as various devices supporting a telecommunication service (not shown) as discussed in more detail below or other systems that may participate in the network.

The devices in system <NUM> are configured to communicate with one another. As an example, the balloons may include communication links <NUM> and/or <NUM> in order to facilitate intra-balloon communications. By way of example, links <NUM> may employ radio frequency (RF) signals (e.g., millimeter wave transmissions) while links <NUM> employ free-space optical transmission. Alternatively, all links may be RF, optical, or a hybrid that employs both RF and optical transmission. In this way balloons 102A-F may collectively function as a mesh network for data communications. At least some of the balloons may be configured for communications with ground-based stations <NUM> and <NUM> via respective links <NUM> and <NUM>, which may be RF and/or optical links.

In one scenario, a given balloon <NUM> may be configured to transmit an optical signal via an optical link <NUM>. Here, the given balloon <NUM> may use one or more high-power light-emitting diodes (LEDs) to transmit an optical signal. Alternatively, some or all of the balloons <NUM> may include laser systems for free-space optical communications over the optical links <NUM>. Other types of free-space communication are possible. Further, in order to receive an optical signal from another balloon via an optical link <NUM>, the balloon may include one or more optical receivers.

The balloons may also utilize one or more of various RF air-interface protocols for communication with ground-based stations via respective communication links. For instance, some or all of balloons 102A-F may be configured to communicate with ground-based stations <NUM> and <NUM> via RF links <NUM> using various protocols described in IEEE <NUM> (including any of the IEEE <NUM> revisions), cellular protocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/or LTE, <NUM> and/or one or more proprietary protocols developed for long distance communication, among other possibilities. In one example using LTE communication, the base stations may be Evolved Node B (eNodeB) base stations. In another example, they may be base transceiver station (BTS) base stations. These examples are not limiting.

In some examples, the links may not provide a desired link capacity for HAP-to-ground communications. For instance, increased capacity may be desirable to provide backhaul links from a ground-based gateway. Accordingly, an example network may also include balloons, which could provide a high-capacity air-ground link between the various balloons of the network and the ground base stations. For example, in balloon network <NUM>, balloon 102F may be configured to directly communicate with station <NUM>.

Like other balloons in network <NUM>, balloon 102F may be operable for communication (e.g., RF or optical) with one or more other balloons via link(s) <NUM>. Balloon 102F may also be configured for free-space optical communication with ground-based station <NUM> via an optical link <NUM>. Optical link <NUM> may therefore serve as a high-capacity link (as compared to an RF link <NUM>) between the balloon network <NUM> and the ground-based station <NUM>. Balloon 102F may additionally be operable for RF communication with ground-based stations <NUM>. In other cases, balloon 102F may only use an optical link for balloon-to-ground communications.

The balloon 102F may be equipped with a specialized, high bandwidth RF communication system for balloon-to-ground communications, instead of, or in addition to, a free-space optical communication system. The high bandwidth RF communication system may take the form of an ultra-wideband system, which may provide an RF link with substantially the same capacity as one of the optical links <NUM>.

In a further example, some or all of balloons 102A-F could be configured to establish a communication link with space-based satellites and/or other types of HAPs (e.g., drones, airplanes, airships, etc.) in addition to, or as an alternative to, a ground based communication link. In some embodiments, a balloon may communicate with a satellite or a high altitude platform via an optical or RF link. However, other types of communication arrangements are possible.

As noted above, the balloons 102A-F may collectively function as a mesh network. More specifically, since balloons 102A-F may communicate with one another using free-space optical links or RF links, the balloons may collectively function as a free-space optical or RF mesh network. In a mesh-network configuration, each balloon may function as a node of the mesh network, which is operable to receive data directed to it and to route data to other balloons. As such, data may be routed from a source balloon to a destination balloon by determining an appropriate sequence of links between the source balloon and the destination balloon.

The network topology may change as the balloons move relative to one another and/or relative to the ground. Accordingly, the balloon network <NUM> may apply a mesh protocol to update the state of the network as the topology of the network changes. Balloon network <NUM> may also implement station-keeping functions using winds and altitude control or lateral propulsion to help provide a desired network topology. For example, station-keeping may involve some or all of balloons 102A-F maintaining and/or moving into a certain position relative to one or more other balloons in the network (and possibly in a certain position relative to a ground-based station or service area). As part of this process, each balloon may implement station-keeping functions to determine its desired positioning within the desired topology, and if necessary, to determine how to move to and/or maintain the desired position. For instance, the balloons may move in response to riding a wind current, or may move in a circular or other pattern as they station keep over a region of interest.

The desired topology may vary depending upon the particular implementation and whether or not the balloons are continuously moving. In some cases, balloons may implement station-keeping to provide a substantially uniform topology where the balloons function to position themselves at substantially the same distance (or within a certain range of distances) from adjacent balloons in the balloon network <NUM>. Alternatively, the balloon network <NUM> may have a non-uniform topology where balloons are distributed more or less densely in certain areas, for various reasons. As an example, to help meet the higher bandwidth demands, balloons may be clustered more densely over areas with greater demand (such as urban areas) and less densely over areas with lesser demand (such as over large bodies of water). In addition, the topology of an example balloon network may be adaptable allowing balloons to adjust their respective positioning in accordance with a change in the desired topology of the network.

Other than balloons, drones may fly routes in an autonomous manner, carry cameras for aerial photography, and transport goods from one place to another. The terms "unmanned aerial vehicle (UAV)" and "flying robot" are often used as synonyms for a drone. The spectrum of applications is broad, including aerial monitoring of industrial plants and agriculture fields as well as support for first time responders in case of disasters. For some applications, it is beneficial if a team of drones rather than a single drone is employed. Multiple drones can cover a given area faster or take photos from different perspectives at the same time.

The balloons of <FIG> may be high-altitude balloons that are deployed in the stratosphere. As an example, in a high altitude balloon network, the balloons may generally be configured to operate at stratospheric altitudes, e.g., between <NUM>,<NUM> ft and <NUM>,<NUM> ft or more or less, in order to limit the balloons' exposure to high winds and interference with commercial airplane flights. In order for the balloons to provide a reliable mesh network in the stratosphere, where winds may affect the locations of the various balloons in an asymmetrical manner, the balloons may be configured to move latitudinally and/or longitudinally relative to one another by adjusting their respective altitudes, such that the wind carries the respective balloons to the respectively desired locations. Lateral propulsion may also be employed to affect the balloon's path of travel.

In an example configuration, the high altitude balloon platforms include an envelope and a payload, along with various other components. <FIG> is one example of a high-altitude balloon <NUM>, which may represent any of the balloons of <FIG>. shown, the example balloon <NUM> includes an envelope <NUM>, a payload <NUM> and a coupling member (e.g., a down connect) <NUM> therebetween. At least one gore panel forms the envelope, which is configured to maintain pressurized lifting gas therein. For instance, the balloon may be a superpressure balloon. A top plate <NUM> may be disposed along an upper section of the envelope, while a base plate <NUM> may be disposed along a lower section of the envelope opposite the top place. In this example, the coupling member <NUM> connects the payload <NUM> with the base plate <NUM>.

The envelope <NUM> may take various shapes and forms. For instance, the envelope <NUM> may be made of materials such as polyethylene, mylar, FEP, rubber, latex or other thin film materials or composite laminates of those materials with fiber reinforcements imbedded inside or outside. Other materials or combinations thereof or laminations may also be employed to deliver required strength, gas barrier, RF and thermal properties. Furthermore, the shape and size of the envelope <NUM> may vary depending upon the particular implementation. Additionally, the envelope <NUM> may be filled with different types of gases, such as air, helium and/or hydrogen. Other types of gases, and combinations thereof, are possible as well. Shapes may include typical balloon shapes like spheres and "pumpkins", or aerodynamic shapes that are symmetric, provide shaped lift, or are changeable in shape. Lift may come from lift gasses (e.g., helium, hydrogen), electrostatic charging of conductive surfaces, aerodynamic lift (wing shapes), air moving devices (propellers, flapping wings, electrostatic propulsion, etc.) or any hybrid combination of lifting techniques.

According to one example shown in <FIG>, a payload <NUM> of a balloon platform includes a control system <NUM> having one or more processors <NUM> and on-board data storage in the form of memory <NUM>. Memory <NUM> stores information accessible by the processor(s) <NUM>, including instructions that can be executed by the processors. The memory <NUM> also includes data that can be retrieved, manipulated or stored by the processor. The memory can be of any non-transitory type capable of storing information accessible by the processor, such as a hard-drive, memory card (e.g., thumb drive or SD card), ROM, RAM, and other types of write-capable, and read-only memories. The instructions can be any set of instructions to be executed directly, such as machine code, or indirectly, such as scripts, by the processor. In that regard, the terms "instructions," "application," "steps" and "programs" can be used interchangeably herein. The instructions can be stored in object code format for direct processing by the processor, or in any other computing device language including scripts or collections of independent source code modules that are interpreted on demand or compiled in advance. The data can be retrieved, stored or modified by the one or more processors <NUM> in accordance with the instructions.

The one or more processors <NUM> can include any conventional processors, such as a commercially available CPU. Alternatively, each processor can be a dedicated component such as an ASIC, controller, or other hardware-based processor. Although <FIG> functionally illustrates the processor(s) <NUM>, memory <NUM>, and other elements of the control system <NUM> as being within the same block, the system can actually comprise multiple processors, computers, computing devices, and/or memories that may or may not be stored within the same physical housing. For example, the memory can be a hard drive or other storage media located in a housing different from that of the control system <NUM>. Accordingly, references to a processor, computer, computing device, or memory will be understood to include references to a collection of processors, computers, computing devices, or memories that may or may not operate in parallel.

The payload <NUM> may also include various other types of equipment and systems to provide a number of different functions. For example, as shown the payload <NUM> includes one or more communication systems <NUM>, which may transmit signals via RF and/or optical links as discussed above. By way of example only, the communication system <NUM> may provide LTE or other telecommunications services. The communication system(s) <NUM> may include communication components such as one or more transmitters and receivers (or transceivers) and an antenna system having one or more antennas. In accordance with one aspect shown in <FIG>, the communication system <NUM> includes a transmit (Tx)/receive (Rx) RF subassembly <NUM>, a primary antenna system <NUM> and detachable nulling subassemblies <NUM>. The Tx/Rx RF subassembly <NUM> may include one or more receivers <NUM> and one or more transmitters <NUM>, as shown in <FIG>. The one or more processors <NUM> is in communication with the one or more receivers <NUM> and the one or more transmitters <NUM>. The primary antenna system <NUM> may have multiple sectors with different beams providing coverage for a number of ground-based users. For example, the primary antenna system <NUM> may have four sectors. Each sector may reach <NUM> kilometers or more or less from a point on the ground directly below the balloon platform carrying the payload <NUM>. In some implementations, more or less sectors may be covered by the primary antenna system <NUM> or additional sectors may be covered by additional antenna systems on the communication system <NUM>.

The one or more processors <NUM> may control the entire communication system <NUM>. Alternatively, one or more additional processors may be incorporated into one or more of the Tx/Rx RF subassembly <NUM>, the primary antenna system <NUM> and the detachable nulling subassemblies <NUM> to control various features of the communication system <NUM>.

The primary antenna system <NUM> shown in <FIG> may include nulling activation switches <NUM>, each having at least three contacts <NUM><NUM>, <NUM><NUM> and <NUM><NUM>, a power divider <NUM> and a plurality of antenna elements <NUM><NUM>, <NUM><NUM>, <NUM><NUM> and <NUM><NUM>. <FIG> shows the nulling activation switches <NUM> in a nulling bypassed mode, where an RF signal <NUM> generated by the one or more transmitters <NUM> is permitted to travel to an input of the power divider <NUM>, which outputs RF signals to respective ones of the plurality of antenna elements <NUM><NUM>, <NUM><NUM>, <NUM><NUM> and <NUM><NUM> when the nulling activation switches <NUM> connect contacts <NUM><NUM> and <NUM><NUM> together. The detachable nulling subassemblies <NUM> may be attached to the primary antenna system <NUM> via an interface <NUM>, such as a wired or wireless interface.

As shown in <FIG>, a nulling activation switch <NUM><NUM> connects contacts <NUM><NUM> and <NUM><NUM> together, such that the RF signal <NUM> generated by the one or more transmitters <NUM> is permitted to travel to an input of nulling subassemblies <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM><NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM><NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. When the one or more processors <NUM> control the nulling activation switch <NUM><NUM> to contacts <NUM><NUM> and <NUM><NUM> together such that the RF signal <NUM> is permitted to travel to the nulling subassemblies <NUM><NUM> and <NUM><NUM>, the nulling subassemblies <NUM><NUM> and <NUM><NUM> are activated by allowing the RF signal <NUM> to flow through the power dividers <NUM><NUM> and <NUM><NUM> and a plurality of processing chains including the phase shifters <NUM><NUM> - <NUM><NUM>, and the nulling antenna elements <NUM><NUM> - <NUM><NUM>, respectively. In one aspect, the power ratio of the power dividers <NUM> and <NUM> may be dynamically adjusted. Alternatively, the power ratio of the power dividers <NUM> and <NUM> may be selected as a matter of design choice. In other implementations, more or fewer processing chains may be included in the nulling subassemblies <NUM>, and they may be configured such that each one of the processing chains may be individually activated or deactivated, based on which sectors should be nulled. The phase shifters <NUM> are aligned to generate nulling signals output by the nulling antenna elements <NUM>. The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> to feed the primary antenna system <NUM> based on the RF signal <NUM>. The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> to feed the primary antenna system <NUM> based on the RF signal <NUM> Thus, the primary antenna system <NUM> generates a beam based on one or both of RF signals <NUM><NUM> and <NUM><NUM>.

As shown in <FIG>, a nulling activation switch <NUM><NUM> connects contacts <NUM><NUM> and <NUM><NUM> together, such that the RF signal <NUM> generated by the one or more transmitters <NUM> is permitted to travel to an input of nulling subassemblies <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM><NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM><NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. When the one or more processors <NUM> control the nulling activation switch <NUM><NUM> to connect contacts <NUM><NUM> and <NUM><NUM> together such that the RF signal <NUM> is permitted to travel to the nulling subassemblies <NUM> and <NUM><NUM>, the nulling subassemblies <NUM> and <NUM><NUM> are activated by allowing the RF signal <NUM> to flow through the power dividers <NUM><NUM> and <NUM><NUM> and a plurality of processing chains including the phase shifters <NUM><NUM> - <NUM><NUM>, and the nulling antenna elements <NUM><NUM> - <NUM><NUM>, respectively. The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> to feed the primary antenna system <NUM> based on the RF signal <NUM>. The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> to feed the primary antenna system <NUM> based on the RF signal <NUM>. Thus, the primary antenna system <NUM> generates a beam based on one or both of RF signals <NUM><NUM> and <NUM><NUM>.

As shown in <FIG>, a nulling activation switch <NUM><NUM> connects contacts <NUM><NUM> and <NUM><NUM> together, such that the RF signal <NUM> generated by the one or more transmitters <NUM> is permitted to travel to an input of nulling subassemblies <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM><NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. When the one or more processors <NUM> control the nulling activation switch <NUM><NUM> to connect contacts <NUM><NUM> and <NUM><NUM> together such that the RF signal <NUM> is permitted to travel to the nulling subassemblies <NUM><NUM> and <NUM><NUM>, the nulling subassemblies <NUM><NUM> and <NUM><NUM> are activated by allowing the RF signal <NUM> to flow through the power dividers <NUM><NUM> and <NUM><NUM> and a plurality of processing chains including the phase shifters <NUM><NUM> - <NUM><NUM>, and the nulling antenna elements <NUM><NUM> - <NUM><NUM>, respectively The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> to feed the primary antenna system <NUM> based on the RF signal <NUM>. The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> to feed the primary antenna system <NUM> based on the RF signal <NUM>. Thus, the primary antenna system <NUM> generates a beam based on one or both of RF signals <NUM><NUM> and <NUM><NUM>.

As shown in <FIG>, a nulling activation switch <NUM><NUM> connects contacts <NUM><NUM> and <NUM><NUM> together, such that the RF signal <NUM> generated by the one or more transmitters <NUM> is permitted to travel to an input of nulling subassemblies <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM><NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. The detachable nulling subassembly <NUM> shown in <FIG> is for port <NUM> of sector <NUM> and may include a power divider <NUM><NUM>, phase shifters <NUM><NUM> and <NUM><NUM> and nulling antenna elements <NUM><NUM> and <NUM><NUM>. When the one or more processors <NUM> control the nulling activation switch <NUM><NUM> to connect contacts <NUM><NUM> and <NUM><NUM> together such that the RF signal <NUM> is permitted to travel to the nulling subassemblies <NUM><NUM> and <NUM><NUM>, the nulling subassemblies <NUM><NUM> and <NUM> are activated by allowing the RF signal <NUM> to flow through the power dividers <NUM><NUM> and <NUM><NUM> and a plurality of processing chains including the phase shifters <NUM><NUM> - <NUM><NUM>, and the nulling antenna elements <NUM><NUM> - <NUM><NUM>, respectively. The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> outputs to feed the primary antenna system <NUM> based on the RF signal <NUM>. The detachable nulling subassembly <NUM><NUM> outputs RF signal <NUM><NUM> to feed the primary antenna system <NUM> based on the RF signal <NUM>. Thus, the primary antenna system <NUM> generates a beam based on one or both of RF signals <NUM><NUM> and <NUM><NUM>.

Although <FIG> illustrate (for simplification) that detachable nulling subassembly <NUM> associated with two different ports of a sector output the RF signals <NUM>, the configurations of the nulling activation switches may be modified to provide RF signals associated with only one of the ports of a sector, both ports of each of the <NUM> sectors, a particular port of each of the <NUM> sectors, and the like.

Returning to <FIG>, the payload <NUM> is illustrated as also including a power supply <NUM> to supply power to the various components of balloon. The power supply <NUM> could include one or more rechargeable batteries or other energy storage systems like capacitors or regenerative fuel cells. In addition, the balloon <NUM> may include a power generation system <NUM> in addition to or as part of the power supply. The power generation system <NUM> may include solar panels, stored energy (hot air), relative wind power generation, or differential atmospheric charging (not shown), or any combination thereof, and could be used to generate power that charges and/or is distributed by the power supply <NUM>.

The payload <NUM> may additionally include a positioning system <NUM>. The positioning system <NUM> could include, for example, a global positioning system (GPS), an inertial navigation system, and/or a star-tracking system. The positioning system <NUM> may additionally or alternatively include various motion sensors (e.g., accelerometers, magnetometers, gyroscopes, and/or compasses).

Payload <NUM> may include a navigation system <NUM> separate from, or partially or fully incorporated into the control system <NUM>. The navigation system <NUM> may implement station-keeping functions to maintain position within and/or move to a position in accordance with a desired topology or other service requirement. In particular, the navigation system <NUM> may use wind data (e.g., from onboard and/or remote sensors) to determine altitudinal and/or lateral positional adjustments that result in the wind carrying the balloon in a desired direction and/or to a desired location. Lateral positional adjustments may also be handled directly by a lateral positioning system that is separate from the payload. Alternatively, the altitudinal and/or lateral adjustments may be computed by a central control location and transmitted by a ground based, air based, or satellite based system and communicated to the high-altitude balloon. In other embodiments, specific balloons may be configured to compute altitudinal and/or lateral adjustments for other balloons and transmit the adjustment commands to those other balloons.

In order to change lateral positions or velocities, the platform may include a lateral propulsion system. <FIG> illustrates one example configuration <NUM> of a balloon platform with propeller-based lateral propulsion, which may represent any of the balloons of <FIG>. As shown, the example <NUM> includes an envelope <NUM>, a payload <NUM> and a down connect member <NUM> disposed between the envelope <NUM> and the payload <NUM>. Cables or other wiring between the payload <NUM> and the envelope <NUM> may be run within the down connect member <NUM>. One or more solar panel assemblies <NUM> may be coupled to the payload <NUM> or another part of the balloon platform. The payload <NUM> and the solar panel assemblies <NUM> may be configured to rotate about the down connect member <NUM> (e.g., up to <NUM>° rotation), for instance to align the solar panel assemblies <NUM> with the sun to maximize power generation. Example <NUM> also illustrates a lateral propulsion system <NUM>. While this example of the lateral propulsion system <NUM> is one possibility, the location could also be fore and/or aft of the payload section <NUM>, or fore and/or aft of the envelope section <NUM>, or any other location that provides the desired thrust vector.

The navigation system is able to evaluate data obtained from onboard navigation sensors, such as an inertial measurement unit (IMU) and/or differential GPS, received data (e.g., weather information), and/or other sensors such as health and performance sensors (e.g., a force torque sensor) to manage operation of the balloon's systems. When decisions are made to activate the lateral propulsion system, for instance to station keep, the navigation system then leverages received sensor data for position, wind direction, altitude and power availability to properly point the propeller and to provide a specific thrust condition for a specific duration or until a specific condition is reached (e.g., a specific velocity or position is reached, while monitoring and reporting overall system health, temperature, vibration, and other performance parameters).

Further, the one or more receivers <NUM> may be configured to receive signals from a simulation and control system on the ground. For example, a simulation and control system <NUM> may be part of the ground base station <NUM> or the ground base station <NUM> shown in <FIG>, or another type of ground station. Alternatively, the simulation and control system <NUM> may be separate from any node and operate independently. The simulation and control system <NUM> may run simulations based on the location of the HAP, and determine whether nulling should be enabled and, if so, on which sectors. The simulation aims to maximize total number of subscribers or some other parameter to be optimized. For example, the simulation and control system <NUM> may make decisions as to whether to control the nulling activation switch <NUM> to activate the detachable nulling subassemblies <NUM> shown in <FIG>. Such decisions may be based on one or more of a location of the HAP, knowledge of ground terrestrial locations, knowledge of country borders, and knowledge of service regions. Further, various constraints need to be taken into consideration. For example, a limit may need to be established as to a total power flux density across borders that should not be exceeded from all HAP transmissions (i.e., the sum of all HAP transmissions). Further, a limit may need to be established as to a total power flux density to terrestrial towers from all HAP transmissions (i.e., the sum of all HAP transmissions). In addition, it may be necessary to prohibit uplink (UL) interference from exceeding some predetermined threshold. The one or more receivers <NUM> may detect such UL interference, which may be caused by UE transmissions sent to the terrestrial towers, Total power flux density at any and all relevant points on the ground may be constantly monitored based on the sum of all HAP transmissions. When a simulation shows that the signals on the ground exceed a particular threshold, this mechanism can be triggered. In addition, the UL noise level (interference level) can be measured to determine whether to turn on this mechanism based on a dynamic measurement.

As shown in <FIG>, the one or more transmitters <NUM> in the Tx/Rx RF subassembly <NUM> outputs the RF signal <NUM> to an input of the power divider <NUM> and a nulling activation switch <NUM> in the primary antenna system <NUM>. The one or more processors <NUM> output a signal <NUM> to control the nulling activation switch <NUM> to selectively feed the RF signal <NUM> to the detachable nulling subassemblies <NUM> by connecting the contacts <NUM><NUM> and <NUM><NUM> together. Thus, when the RF signal <NUM> is fed to the input of the power dividers <NUM> in the detachable nulling subassemblies <NUM>, the phase shifters <NUM> are aligned to generate nulling signals output by the nulling antenna elements <NUM>. Beams are generally formed by having antenna arrays with multiple elements. The beams are steered or the beam shape is changed by having different gain and phase for each of the elements. We can change the gain or the phase and create beams with more gain, steer the beams in different directions, create nulls in the beams, etc. Phase can be changed by adjusting or selecting specific phase shifters. Alternatively, phase can be changed by changing cable lengths between elements (e.g., changing traces the between elements).

Referring to <FIG>, the one or more receivers <NUM> may detect beams generated by the primary antenna system <NUM> and the detachable nulling subassemblies <NUM>. Based on these beams, the one or more processors <NUM> may communicate with the simulation and control system <NUM> in the ground base station <NUM> shown in <FIG>, so that it may perform analysis and calculations to determine whether the detachable nulling subassemblies <NUM> should be activated and, if so, how nulling activation switches <NUM> should be controlled so that the beam pattern generated by the primary antenna system <NUM> is changed by beams generated by the detachable nulling subassemblies <NUM>.

Multiple elements may be combined to form beams by using appropriate gains and phases for different antenna elements. The final composite beam pattern may depend on one or more of a beam pattern for the individual elements, distance between the individual elements and gain and phase used on the individual elements. The nulling sub-assemblies provide the ability to change the final beam pattern because they provide elements whose gain and phase can be changed as required. This increases the degrees of freedom available and provides a way to create nulling.

The primary antenna system <NUM> generates beams that form a footprint on the ground for providing communication service to a plurality of terrestrial users. The one or more processors <NUM> may be configured to communicate with the simulation and control system <NUM> to monitor and analyze the HAP's position with regard to a country border and/or an object (e.g., a terrestrial tower), as well as establishing various thresholds and standards (e.g., International Telecommunication Union (ITU) standards) that should not be exceeded. The interface <NUM> allows the HAP operator the flexibility to disconnect the detachable nulling subassemblies <NUM> and fly without including it in the payload.

Specific ones or all of the sector processing chains in the detachable nulling subassemblies <NUM> may be deactivated or activated in response to the one or more processors <NUM> detecting the location of the HAP, the location of one or more other HAPs, the location of users, the location of terrestrial towers, LTE simulations, and/or an estimation of power flux density on the ground.

<FIG> shows an example flow diagram in accordance with aspects of the technology. More specifically, <FIG> shows a flow of an example method <NUM> for detecting selective activation of antenna notch elements performed.

At block <NUM> of <FIG>, the transmitter <NUM> generates the RF signal <NUM>.

At block <NUM> of <FIG>, an RF beam is generated based on the RF signal by using the primary antenna system <NUM>.

At block <NUM> of <FIG>, the one or more processors <NUM> determines a result indicating whether to modify the RF beam.

At block <NUM> of <FIG>, when the result indicates to modify the RF beam, a nulling activation switch <NUM> in the primary antenna system <NUM> is closed to feed the RF signal <NUM> to a detachable nulling subassembly <NUM>.

At block <NUM> of <FIG>, the detachable nulling subassembly <NUM> generates nulling signals to modify the RF beam generated by the primary antenna system <NUM> based on the RF signal <NUM>.

Claim 1:
A communication apparatus (<NUM>) for a high-altitude platform, HAP, the communication apparatus comprising:
a transmitter (<NUM>) configured to generate a radio frequency, RF, signal;
a primary antenna system (<NUM>) configured to generate an RF beam based on the RF signal, the primary antenna system including:
a first plurality of antenna elements (<NUM>),
a first power divider (<NUM>) having an input in communication with the transmitter, and a plurality of outputs, and
a nulling activation switch (<NUM>) having a first contact (<NUM><NUM>) a second contact (<NUM><NUM>), and a third contact (<NUM><NUM>) ; and
a detachable nulling subassembly (<NUM>) that is configured to attach to and detach from an interface (<NUM>) of the primary antenna system (<NUM>) and is in communication with the nulling activation switch (<NUM>) via the interface, wherein the detachable nulling subassembly (<NUM>) is configured to modify the RF beam generated by the primary antenna system by generating nulling signals when the nulling activation switch is controlled to feed the RF signal to an input of the detachable nulling subassembly,
wherein
the detachable nulling subassembly (<NUM>) includes:
a second power divider (<NUM>) having an input and a plurality of outputs and configured to receive the RF signal from the second contact (<NUM><NUM>),
a plurality of phase shifters (<NUM>), and
a plurality of nulling antenna elements (<NUM>);
the transmitter (<NUM>) is in communication with the first contact (<NUM><NUM>) of the nulling activation switch (<NUM>);
the RF signal is fed to the input of the second power divider (<NUM>) when the nulling activation switch (<NUM>) is closed such that the first contact (<NUM><NUM>) is connected to the second contact (<NUM><NUM>), and each output of the second power divider (<NUM>) feeds the RF signal to a respective processing chain including one of the plurality of the phase shifters connected in series with one of the plurality of the nulling antenna elements; and
the RF signal is fed to the input of the first power divider (<NUM>) when the nulling activation switch (<NUM>) is closed such that the first contact (<NUM><NUM>) is connected to the third contact (<NUM><NUM>), and each output of the first power divider (<NUM>) feeds the RF signal to a respective one of the first plurality of antenna elements (<NUM>).