Triangular phased array antenna subarray

Antenna subassemblies suitable for use in phased array antennas are disclosed, as are phased array antenna assemblies and aircraft comprising phased array antenna assemblies. In one embodiment, an antenna subarray assembly comprises a thermally conductive foam substrate, a plurality of radiating elements bonded to the foam substrate, and a radome disposed adjacent the radiating elements. The subarray assembly presents a triangular shape when viewed in plan view, and the plurality of radiating elements are arranged in a triangular array on the foam substrate. In some embodiments, a plurality of subarray assemblies may be assembled to form an antenna assembly. In further embodiments an aircraft may be fitted with one or more antenna assemblies. Other embodiments may be described.

BACKGROUND

The subject matter described herein relates to electronic communication and radar systems and to configurations for antenna arrays for use in electronic communication and radar applications.

Aircraft, including spacecraft, commonly incorporate communication systems which utilize an antenna array to communicate with ground-based systems. Phased array antennas find utility in both airborne communication systems and ground-based communication systems. Aircraft, and particularly spacecraft, have limited power sources and therefore must manage power resources. Accordingly, power-efficient phased array antenna systems may find utility.

SUMMARY

In one embodiment, an antenna subarray assembly comprises a thermally conductive foam substrate, a plurality of radiating elements bonded to the foam substrate, and a radome disposed adjacent the radiating elements. The subarray assembly presents a triangular shape when viewed in plan view, and the plurality of radiating elements are arranged in a triangular array on the foam substrate.

In another embodiment, a phased array antenna assembly comprises a plurality of panels, each panel comprising a plurality of antenna subarray assemblies. At least one of the subarray assemblies comprises a thermally conductive foam substrate, a plurality of radiating elements bonded to the foam substrate, and a radome disposed adjacent the radiating elements. The subarray assembly presents a triangular shape when viewed in plan view, and the plurality of radiating elements are arranged in a triangular array on the foam substrate.

In a further embodiment, an aircraft comprises a communication system and a phased array antenna assembly coupled to the communication system and comprising a plurality of panels. Each panel comprising a plurality of antenna subarray assemblies, and at least one of the subarray assemblies comprises a thermally conductive foam substrate, a plurality of radiating elements bonded to the foam substrate, and a radome disposed adjacent the radiating elements. The subarray assembly presents a triangular shape when viewed in plan view, and the plurality of radiating elements are arranged in a triangular array on the foam substrate.

DETAILED DESCRIPTION

Configurations for antenna subassemblies suitable for use in phased array antenna systems, and antenna systems incorporating such subassemblies are described herein. Specific details of certain embodiments are set forth in the following description and the associated figures to provide a thorough understanding of such embodiments. One skilled in the art will understand, however, that alternate embodiments may be practiced without several of the details described in the following description.

The invention may be described herein in terms of functional and/or logical block components and various processing steps. For the sake of brevity, conventional techniques related to inertial measurement sensors, GPS systems, navigation systems, navigation and position signal processing, data transmission, signaling, network control, and other functional aspects of the systems (and the individual operating components of the systems) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical embodiment.

The following description may refer to components or features being “connected” or “coupled” or “bonded” together. As used herein, unless expressly stated otherwise, “connected” means that one component/feature is in direct physically contact with another component/feature. Likewise, unless expressly stated otherwise, “coupled” or “bonded” means that one component/feature is directly or indirectly joined to (or directly or indirectly communicates with) another component/feature, and not necessarily directly physically connected. Thus, although the figures may depict example arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment.

FIG. 1is a schematic exploded, perspective view of an antenna subarray assembly, according to embodiments. In the embodiment depicted inFIG. 1the subarray assembly100is formed in a layered construction and comprises, in order from the bottom up, a heat sink110, a plurality of amplifiers120, a printed wiring board130, a foam layer140, a plurality of radiating elements150, an adhesive layer160, and a radome170.

The radome170may be constructed of any suitable material that is essentially transparent to radio frequency (RF) radiation. For example, the radome170may be constructed of KAPTON®. Alternatively, the radome170may be constructed as a multilayer laminate.

The adhesive layer160may comprise an electrostatically dissipative adhesive to bond the radome170to the foam layer140. The adhesive160extends over and around of the radiating elements150and physically contacts the radiating elements150. The adhesive160allows any electrostatic charge buildup on the radiating elements150to be conducted away from the radiating elements150. It will be appreciated that the electrostatically dissipative adhesive layer160will be coupled to ground when the radiator assembly100is supported on the printed wiring board130shown inFIG. 1. The electrostatically dissipative adhesive160may be formed from an epoxy adhesive, a polyurethane based adhesive or a Cyanate ester adhesive, each doped with a small percentage, for example five percent, of conductive polyaniline salt. The precise amount of doping will be dictated by the needs of a particular application.

The electrostatically dissipative adhesive layer160also helps to form a thermally conductive path to the foam substrate140and eliminates a gap that might otherwise exist between the radome170and the top level of radiating elements150. By eliminating the gap between the inner surface of the radome170and the radiating elements150, a thermal path is formed from the radome170through the layer of radiating elements150.

The radiating elements150are arranged in a triangular array on the foam substrate140. The radiating elements150may be thought of as floating with respect to ground metal patches. While the radiating elements150are shown as having a generally cirular shape inFIG. 1it will be appreciated that the radiating elements150could have been formed to have any other suitable shape, for example that of a square, a hexagon, a pentagon, a rectangle, etc. Also, while only one layer of radiating elements have been shown, it will be appreciated that the assembly100could comprise two or more layers of radiating elements to meet the needs of a specific application. Aspects of the radiating elements150will be discussed in greater detail with reference toFIGS. 2-3, below.

In one embodiment the foam substrate140may be formed from a low RF loss, syntactic foam material which provides a thermal path through the layer of radiating elements150. Thus, no “active” cooling of the radiator assembly10is required. By “active” cooling it is meant a cooling system employing water or some other cooling medium that is flowed through a suitable network or grid of tubes to absorb heat generated by the assembly100and transport the heat to a thermal radiator to be dissipated into space. The use of active cooling significantly increases the cost and complexity, size and weight of a phased array antenna system. Thus, the passive cooling that may be achieved through the use of the syntactic foam substrate140allows the subarray assembly100to be made to smaller dimensions and with less weight, less cost and less manufacturing complexity than previously manufactured phased array radiating assemblies.

In some embodiments the syntactic foam substrate140may be formed as fully-crosslinked, low density, composite foam substrate that exhibits low loss characteristics in the microwave frequency range. The foam substrate140may have a dielectric constant that measures between 1.25 and 1.30 over a frequency range that extends between 10 GHz and 30 GHz and a loss tangent of approximately 0.025 over the same frequency range. Advantageously, the loss tangent is relatively constant over a wide bandwidth and from about 12 GHz to about 33 GHz. The thermal resistance of the foam substrate140is preferably less than about 50.2 degrees C./W. The foam substrate140also preferably has a thermal conductivity of at least about 0.0015 watts per inch per degrees C. (W/inC), or at least about 0.0597 watts per meter per degree Kelvin (W/mK). One particular syntactic foam that is commercially available and suitable for use is DI-STRATE™ foam tile available from Aptek Laboratories, Inc. of Valencia, Calif.

In some embodiments the printed wiring board (PWB)130may be formed from a conventional PWB material, e.g., a Rogers 4003 series dielectric PWB material. A plurality of amplifiers120may be disposed between the PWB130and the heat sink module120. In some embodiments the plurality of amplifiers may be implemented as an array of monolithic microwave integrated circuits (MMICs) which are coupled to a power source and controller by circuit traces in the PWB130.

In some embodiments the heat sink module110may be formed from a phase change material which utilizes heat energy generated by the MMICs to effect a phase change of the material in the heat sink module110. The particular material from which the heat sink module110is formed is not critical. Examples of suitable materials include paraffin and other types of wax which melt at well known temperatures. The particular type of wax or other material used will determine the temperature at which the heat sink will begin to store excess thermal energy.

The various components depicted inFIG. 1may be assembled to form an antenna subarray assembly100substantially in accordance with the description provided in commonly assigned U.S. patent application Ser. No. 12/121,082 to McCarthy, et al., the disclosure of which is incorporated herein by reference in its entirety. Although the thickness of the various layers shown inFIG. 1may vary to meet the needs of a specific application, in one example the syntactic foam substrates140measures between about 0.045 inch-0.055 inch (1.143 mm-1.397 mm) thick. The electrostatically dissipative adhesive layer160may vary in thickness, but in one embodiment measures between about 0.001 inch-0.005 inch (0.0254 mm-0.127 mm) thick. The radome170typically may be between about 0.003 inch-0.005 inch (0.0762 mm-0.127 mm) thick.

FIG. 2is a schematic top, plan view of an antenna subarray assembly100, according to embodiments. Referring toFIG. 2, the subarray assembly100forms a triangle when viewed in a top plan view. The triangle includes a first edge102and a second edge104that are substantially smooth, and a third edge106that presents a sawtooth pattern. In one embodiment the subarray measures 14.072 inches (35.74 cm) in height and 16.256 inches (41.29 cm) in width, such that the surface area of the subassembly is approximately 114.377 square inches (0.0738 square meters). One skilled in the art will recognize that the size of the antenna subarray assembly100may vary depending upon the particular application.

The radiating elements150are arranged in a triangular array on the substrate140. Similarly, the MMICs140are arranged in a triangular array on the heat sink layer110, but are not visible inFIG. 2. In some embodiments the radiating elements measure approximately 0.638 inches (1.62 cm) in diameter. The radiating elements are positioned in horizontal rows such that the centers of adjacent elements within a row are displaced by approximately 1.016 inches (2.58 cm). The rows are displaced by 0.879″ (2.23 cm). In the embodiment depicted inFIG. 1there are 128 radiating elements, which permits the use of a corporate manifold and conventional 3 dB Wilkinson power dividers/combiners to drive the antenna. One skilled in the art will recognize that the particular configuration of the radiating elements on the antenna subarray assembly100may vary depending upon the particular application.

Six triangular subarray assemblies100may be assembled to form a antenna panel200, as indicated inFIGS. 3 and 4. The respective array assemblies may be secured in place by mounting them on a common substrate. As indicated inFIG. 4, the respective assemblies100may be arranged that adjacent subarrays100are 180 degrees out of phase with one another. Since the subarrays are out of phase by 180 degrees, 180 degree hybrid couplers (rat-race couplers) can be used to combine the signals from multiple subarrays. One skilled in the art will recognize that the hexagonal antenna array approximates a circular array. As such, a hexagonal can be used as a feed for a cassegrain dual-reflector antenna where the hexagonal phased array is in front of the focus.

A plurality of antenna panels200may be combined as illustrated inFIG. 5to form an antenna assembly500which may be coupled to a communication system to provide RF communication with remote devices. As illustrated inFIG. 5, an antenna assembly500may comprise full hexagonal panels200and half-hexagonal panels210, which are arranged to form a tightly-packed antenna assembly500. One skilled in the art will recognize that all subassembly panels100are arranged such that they are 180 degrees out of phase with all adjacent subassembly panels100.

Thus, described herein is a construction for a triangular antenna subarray assembly100which may serve as fundamental building block for forming phased array antenna systems, including electronically steerable array antenna (ESA) assemblies. The triangular structure described herein provides numerous advantages over rectangular structures.

From a physical perspective, the use of triangular subassembly100provides a standardized building block from which an antenna panel200and ultimately an antenna assembly500can be formed. The triangular array also provides a space-efficient pattern for antenna elements and can be constructed in relatively large sizes for more efficient manufacture. The design is scalable to accommodate varying sizes of antenna panels200and antenna assemblies500.

From an electrical perspective, the use of triangular subassemblies eliminates or at least reduces several issues associated with rectangular arrays, and particularly with ESA assemblies. Triangular subarray configurations require fewer radiating elements150than rectangular arrays to realize the same grating lobe free electronic scan volume. For example, for a maximum grating lobe free scan angle, θm, of 20 degrees:
1+sin(θm)=1.342  Eq. 1
Thus for a given wavelength, λ, for a square radiating element grid:
λ/dx=λ/dy=1.342 ordx=dy=0.745 λ  Eq. 2
And the area required per radiating element is:
dxdy=(0.745λ)2=0.555λ2Eq. 3
By contrast, for a given wavelength, λ, for a square radiating element grid:
λ/(3dx′)0.5=λ/dy=1.342  Eq. 4
Which resolves to:
dx′=0.430λ, dy=0.745λ  Eq. 5
Since radiating elements are offset in a triangular architecture, the area per element is given by:
2(dx′dy)=2(0.430λ)(0.745λ)=0.641λ2Eq. 6
Thus, for an equivalent scan volume at a 20 degree scan angle, a triangular architecture is approximately 15.5% more efficient than a square architecture.
0.641λ2/0.555λ2=1.155  Eq. 7

In addition, the use of GaN high power amplifiers in transmit mode enables higher power efficiency operation. GaN amplifiers can make use of higher drain voltages (25-50V DC) than traditionally used GaAs devices (3-5V DC). For large arrays this provides a net benefit to overall payload power efficiency due to lower power distribution and conversion losses. GaN devices also have higher allowable channel temperatures than GaAs devices. This allows for simpler thermal control architectures.

In some embodiments an vehicle-based communication system may incorporate one or more antennas constructed according to embodiments described herein. By way of example, referring toFIG. 6, exemplary environment600in which embodiments of an antenna can be implemented. The environment600includes an airborne system602, such as a GPS platform, satellite, aircraft, and/or any other type of GPS enabled device or system. The environment600also includes components604of the airborne system602, mobile ground-based or airborne receiver(s)606, and a ground station608. In this example, the airborne system602is a GPS platform that is depicted as a GPS satellite which includes a wide beam antenna610(also referred to as an “Earth coverage antenna”), and includes a spot beam antenna612(also referred to as a “steerable” spot beam antenna), which may be constructed in accordance with the description provided herein. The wide beam antenna610and the spot beam antenna612each transmit GPS positioning information and navigation messages to the GPS enabled receiver(s)606. The spot beam antenna612provides for the transmission of high intensity spot beams to selected points on the ground without requiring excessive transmitter power.

In this example, the airborne system602includes a telemetry and command antenna614which can be utilized to communicate with the ground station608. In various embodiments, the GPS platform602can be implemented with any number of different sensors to measure and/or determine an attitude of the satellite, where the “attitude” refers generally to an orientation of an airborne system in space according to latitude and longitude coordinates relative to the orbital plane. The GPS platform can be stabilized along three-axes that, in this example, are illustrated as a pitch axis616, a roll axis618, and a yaw axis620.

The airborne system602may includes an antenna positioning system622to position a boresight624of the spot beam antenna612, where the boresight refers generally to the axis of an antenna, or a direction of the highest power density transmitted from an antenna. In this example, the antenna positioning system622includes a gimbals assembly626, a housing assembly628, and roll, pitch, and yaw gyros630which can each drift from an orientation reference due to rate bias, scale factor, and measurement noise. Gyro drift errors of the gyros630can cause enough variance in the antenna positioning system622to cause spot beam antenna pointing error(s) when transmitting GPS signals. A pointing error632results in a spot beam634that is angularly displaced from a commanded spot beam at the antenna boresight624.

The airborne system602may include a calibration control application634(in the components604) to implement embodiments of GPS gyro calibration. The airborne system602also includes various system control component(s)636which can include an attitude control system, system controllers, antenna control modules, navigation signal transmission system(s), sensor receivers and controllers, and any other types of controllers and systems to control the operation of the airborne system602. In addition, the airborne system602, the receiver(s)606, and/or the ground station608may be implemented with any number and combination of differing components as further described below with reference to the exemplary computing-based device600shown inFIG. 6. For example, the receiver606and the ground station608may be implemented as computing-based devices that include any one or combination of the components described with reference to the exemplary computing-based device600.

In this example, the ground station608includes a pointing error estimator638and a gyro calibration application640to implement embodiments of GPS gyro calibration. In an embodiment, the GPS platform602transmits scan signals642to the GPS enabled receiver(s)606via the spot beam antenna612. For example, the scan signals642can be transmitted to the GPS enabled receivers606via the spot beam634which is an inaccurate boresight direction of the spot beam antenna612.

The scan signals642can be transmitted to the GPS enabled receiver(s)606with a known amplitude and in a pattern of a pre-determined scan profile. For example, The GPS platform gimbals assembly626of the antenna positioning system622can slew the spot beam antenna612across one or more of the GPS enabled receivers606in a known, cross scan pattern. The spot beam antenna612can be slewed at a low rate (e.g., 0.1 deg/sec) in azimuth and elevation coordinate frames utilizing a scan pattern that is large enough to produce a noticeable change in signal-to-noise ratio (or carrier to noise) measurements.

The GPS enabled receiver(s)606can receive the scan signals642transmitted via the spot beam antenna612of the GPS platform602and determine signal power measurements for each of the scan signals. In an embodiment, the signal power measurements can be determined as signal-to-noise ratio measurements of the scan signals642. The GPS enabled receiver(s)606can also time-tag, or otherwise indicate a time at which a scan signal is received such that each of the scan signals642can be correlated with antenna position data644to estimate the pointing error632of the spot beam antenna612. The GPS enabled receiver(s)606can then communicate the signal power measurements646to the ground station608.

The GPS platform transmits, or communicates, the antenna position data644for the spot beam antenna to the ground station608where the antenna position data indicates the inaccurate boresight direction634of the spot beam antenna612. Alternatively, the GPS platform602can be commanded to point the boresight direction of the spot beam antenna612at a particular latitude and longitude where a GPS enabled receiver606is located. The accurate latitude and longitude coordinates can also be obtained from the GPS enabled receiver.

The ground station608can receive the signal power measurements646from the GPS enabled receiver(s)606. The pointing error estimator638at the ground station608estimates the pointing error632of the spot beam antenna612based on the signal power measurements646and the antenna position data644received from the GPS platform602. The difference between where a signal-to-noise ratio is measured and where it was expected to be provides an estimate of the antenna pointing error.

The gyro calibration application640at the ground station608can be implemented to determine gyro calibration parameters from the estimated pointing error632. The gyro calibration parameters can include a rate bias and a scale factor communicated to the GPS platform. In an embodiment, antenna pointing error measurements are input to a Kalman filter algorithm to estimate the gyro calibration parameters648to calibrate for the gyro drift errors.

The gyro rate bias and the scale factor parameters can be resolved for all of the gyros630in the three different axes (i.e., pitch axis616, roll axis618, and yaw axis620) by the gyro equation:
ωgyro=(1+SF)ωtrue+bgyro+ηr

where ωgyrois a gyro reading, SF is the gyro scale factor, ωtrueis a true airborne system body rate, bgyrois the gyro rate bias, and ηris the rate noise. Given the ωgyrogyro reading, the gyro rate bias and the scale factor can be estimated. Estimating the gyro calibration parameters utilizing a Kalman filter algorithm is further described in a document “Precision Spacecraft Attitude Estimators Using an Optical Payload Pointing System”, Jonathan A. Tekawy (Journal of Spacecraft and Rockets Vol.35, No.4, July-August 1998, pages 480-486), which is incorporated by reference herein.

The ground station608can communicate or otherwise upload the gyro calibration parameters648to the GPS platform602where the calibration control application634can calibrate the gyros630for the gyro drift errors. The gyro calibration parameters648that are uploaded to the GPS platform can also contain information to correct for the gyro rate output and to provide accurate rate and attitude estimates. With the corrected gyro estimates, the GPS platform602can more accurately point both the GPS Earth coverage antenna610and the spot beam antenna612.

Thus, described herein are constructions for antenna subassemblies, antenna assemblies formed from such subassemblies, and aircraft including antennas formed from such subassemblies. A phased array antenna constructed in accordance with the description provided herein can operate in transmit and receive modes. In some embodiments the radiating elements in the antenna may comprise a low noise amplifier (LNA) formed from Gallium arsenide (GaAs) or Indium phosphide (InP) for receive functionality. The GaN power amplifiers improve power efficiency during the high power mode (transmit) and the antenna uses less power while in receive mode. The same corporate combining network may be used to connect the elements in receive mode and transmit mode and is composed of stripline circuitry in the PWB130.

While the embodiment depicted inFIG. 6illustrates a space-based vehicle, one skilled in the art will recognize that an antenna assembly in accordance with the description provided herein may be implemented on land-based vehicles, water-baesd vehicles, or air-based vehicles. As such, the term “vehicle” should be construed to encompass all such vehicles.

In some embodiments antenna arrays constructed in accordance with the description provided here may be particularly suited for space-based applications due at lest in part to the thermal, electrostatic discharge (ESD), and mass features of the design. However, one skilled in the art will recognize that antenna arrays constructed in accordance with the description provided herein may be used in a wide variety of airborne and terrestrial applications. In addition, antenna arrays constructed in accordance with the description provided herein may be used for in communication systems and radar systems. This provides a particular advantage in radar systems because the same antenna assembly may be used for both transmit and receive modes. For communications system use it provides a compact single antenna solution.