Patent Application
20160084623
1. Field of the Invention
This invention relates to adaptive electronically steerable arrays (AESAs), and more particularly to an AESA system for a missile interceptor comprising multiple AESA arrays positioned on forward facing surfaces of the interceptor's aerodynamic control surfaces for RF target tracking and communications. Deployment of the AESA arrays on the aerodynamic control surfaces frees up volume, thus increasing design options for an IR seeker.
2. Description of the Related Art
Interceptors may be configured to use the RF band for target engagement (e.g. search, acquisition, targeting or terminal engagement) or for communications with another communication station (e.g. another interceptor, a different airborne platform, or ground or sea based system). Historically, the RF antenna would have been positioned behind the radome and had a fixed beam pattern within a field-of-view (FOV), either forward or side-looking. To increase the field-of-regard (FOR), the RF antenna could be mounted on a mechanical gimbal. In some systems, the RF Seeker was paired with an IR seeker to provide dual-band capability. Both systems are mounted within the radome, one forward-looking and the other side-looking. Incorporation of both systems typically required a larger and non-axisymmetric radome, and typically necessitated mechanical gimbal ling to achieve a desired FOR.
An AESA—active electronically scanned array: is a type of phased array radar whose transmitter and receiver functions are composed of numerous small solid-state transmit/receive modules (TRMs). AESA radars aim their “beam” by emitting separate radio waves from each module that interfere constructively at certain angles in front of the antenna. Advanced AESA radars can improve on the older passive electronically scanned array (PESA) radars by spreading their signal emissions out across a band of frequencies, which makes it very difficult to detect over background noise, allowing ships and aircraft to broadcast powerful radar signals while still remaining stealthy.
More recently, interceptors have replaced fixed RF antennas, and particularly mechanically gimbaled antenna with an AESA for RF target engagement. The AESA may be mounted in a forward-looking boresight configuration or a side-looking configuration within the radome. In a dual-band system, as before the AESA may be paired with a mechanically gimbaled IR seeker. Typically, the IR seeker is mounted in the forward-looking position and the AESA is mounted in a side-looking position behind the non-axisymmetric radome.
The AESA has also been developed for use in RF communications when more than one frequency band is used. US 2012/0200449 discloses an AESA system in which multiple arrays of radiating elements and control circuitry to configure the arrays for multi-band and multi-aperture operations are deployed to maintain data links with communication satellites. The arrays are located circumferentially around the interceptor and the control circuitry is configured to switch between the arrays as the interceptor spins to maintain communications with the satellite.
The following is a summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description and the defining claims that are presented later.
The present invention provides an AESA system for interceptor RF target engagement and communications.
In an embodiment, the AESA system comprises a plurality of arrays, each comprising a plurality of radiating elements, each array configured for placement on a forward-facing surface of a different one of a plurality of aerodynamic control surfaces on the interceptor. A plurality of RF transmissive radome elements, each having an aerodynamic shape complementary to the aerodynamic control surface, are placed over one of the arrays. Control circuitry configures the arrays for RF target engagement and communication.
In different embodiments, the control circuitry may configure the arrays to operate independently. For example, the arrays may scan their individual beam patterns to search for and acquire a target or different arrays may be used for RF target engagement and RF communication, either simultaneously or serially. The control circuitry may configure the arrays to operate in concert to form a single combined beam pattern with enhanced sensitivity. This may, for example, be used for target tracking or for communications. The control circuitry may configure the arrays for multi-band operation.
In different embodiments, additional AESA arrays may be positioned on side-facing or aft-facing surfaces of the aerodynamic control surfaces. The control circuitry may configure these additional arrays for RF communications.
In an embodiment, the AESA system is paired with an IR system for dual-mode operation. The IR system is mounted behind a dome on the nose of the interceptor. Because the AESA system is not co-located with the IR system in the dome, there is considerably more flexibility to design the IR system and the dome. For example, the dome may be axisymmetric and the IR system may not require mechanical gimballing. In some applications, a boresighted strapdown IR seeker may provide a sufficient FOR for the mission. Elimination of the mechanical gimbal saves weight, volume, cost and complexity.
In an embodiment of a dual-mode system, the AESA system may be initially configured to independently scan multiple beam patterns to search for and acquire a target. Once acquired, the AESA system may be configured to provide a single beam pattern with enhanced sensitivity to track the target during mid-course flight. Once the range-to-target has closed, the interceptor can use the boresighted strapdown IR seeker to image the target for terminal operations.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments, taken together with the accompanying drawings, in which:
a and 1b are perspective and side views of an embodiment a dual-mode missile seeker including an RF seeker having AESA arrays positioned on aerodynamic control surfaces and a strapdown IR seeker;
a and 2b are perspective and side views of another embodiment a dual-mode missile seeker including an RF seeker having AESA arrays positioned on aerodynamic control surfaces and a strapdown IR seeker;
a, 3b, 3c and 3d are diagrams of an embodiment of an AESA array geometry, the layout of the radiating elements in a single AESA array, the beam pattern for a single array and the beam pattern of the full array;
The present invention describes an AESA system for RF target engagement and communications for interceptor. The AESA system comprises multiple arrays that are deployed on aerodynamic control surfaces of the interceptor. The arrays may be controlled independently or in concert for RF target engagement or communications. The AESA system may be paired with an IR system for dual-mode operation. Removal of the AESA system from the interceptor radome increases the design options for implementation of the IR system. For example, the dual-mode system may be able to eliminate the mechanical gimbal for the IR seeker and use an axisymmetric dome without sacrificing performance.
The interceptor may be any airborne vehicle that includes aerodynamic control surfaces. These surfaces may provide lift or maneuverability, may be fixed or moveable. For example, the interceptor may be a self-propelled missile, a gun-launched projectile, a unmanned aerial vehicle (UAV), a manned aircraft or a planetary lander (provided the destination planet has an atmosphere). Without loss of generality, the AESA system will be shown in described in the context of a missile interceptor having four fixed dorsal fins positioned every 90 degrees about the circumference of the interceptor. The dorsal fins are modified to incorporate the AESA arrays and radome elements.
Referring now to
AESA system 12 comprises a plurality of arrays 30, each comprising a plurality of radiating elements 32. Each array 30 is placed on a different one of the forward-facing surfaces 26 of the fins 24. As shown, each array 30 is connected to a power source such as the interceptor's power bus or a battery to power the radiating elements. A plurality of RF transmissive radome elements 36 are placed over respective arrays 30. The radome elements 36 are formed of a material such as ceramic or organic composite materials that is transmissive in the RF band and physically durable. Each radome element has an aerodynamic shape complementary to said aerodynamic control surface (fin) to maintain the aerodynamic properties of the control surface (fin). The exact shape of the radome element will depend on the cross-section of the fin. In some cases, the array of radiating elements may be larger than the exposed forward-facing surface 26, in which case, the size and shape of the radome element may be modified.
In this embodiment dorsal fin 24 has a triangular cross-section that defines a triangularly shaped forward-facing surface 26 on which an AESA array 30 is placed. AESA array 30 comprises a triangular arrangement of radiating elements 32 coupled to a power source. Radome element 36 has a solid triangular shape that is complementary to the triangular cross-section of fin 24.
Control circuitry 38 is connected to configure the arrays 30 for RF target engagement. The control circuitry may be integrated with other control circuitry on the interceptor that performs other tasks such as general avionics or guidance.
In different embodiments, the control circuitry 38 may configure the arrays 30 to operate independently. For example, the arrays may scan their individual beam patterns to search for and acquire a target. Or different arrays may be used for RF target engagement and RF communication, either simultaneously or serially. The control circuitry may configure the arrays to operate in concert to form a single combined beam pattern with enhanced sensitivity. This may, for example, be used for target tracking or for communications. The control circuitry may configure the arrays for multi-band operation. This may be done, for example, by configuring each radiating element in an array to operate as a single aperture in a first frequency band and by configuring a subset of the radiating elements in an array to operate as a single aperture in a second frequency band. Multi-band operation may be used for either target tracking or communication.
In this embodiment of interceptor 10, the AESA system 12 is paired with IR system 14 for dual-mode operation. In general, IR system 14 can be any system that can be located in the payload 20 behind forward looking IR dome 22, which is formed of materials that are transmissive in the IR band. The IR system may be fixed or gimbaled, and may be forward or side looking. However, because the AESA system is not co-located with the IR system in the IR dome, there is considerably more flexibility to design the IR system and the IR dome. For example, the IR dome may be axisymmetric and the IR system may not require mechanical gimballing. Elimination of the mechanical gimbal saves weight, volume, cost and complexity. Axisymmetric IR domes are less complicated to fabricate, hence less expensive.
In this embodiment, IR system 14 comprises a boresighted strapdown IR seeker 40 with an axisymmetric (hemispheric) dome 22. The strapdown IR seeker 40 comprises an optical telescope 42 and one or more Focal Plane Arrays (PFAs) 44. The optical telescope focuses an enlarged image onto the one or more FPAs for image digitization. The optical telescope combines a number of optical elements e.g. reflective mirrors and/or optical lenses. The telescope may comprise primary, secondary, and possible tertiary optical elements and beam splitters for multiple color FPA input. Once digitized the on board computer can determine target motion to calculate the proper maneuver commands for ultimate interception. The optical telescope has no moving parts, hence is easier and less expensive to produce with greater reliability.
In this embodiment, the IR seeker is a two-color system. The optical telescope includes a primary mirror 45 and a secondary mirror 46 that focus an enlarged image through a hole 47 in bulkhead 48. A sunshade 49 prevents extraneous light from entering the optical system. A beam splitter (not shown) behind the bulkhead splits the focused light into first and second colors and directs the respective colors to a first FPA 50 and a second FPA (not shown). An Inertial Measurement Unit 52 is also mounted behind the bulkhead.
In an alternate embodiment, additional AESA arrays 60 may be deployed at other locations on the interceptor to increase the FOR for RF target engagement or RF communications. The individual and combined beam patterns for the AESA arrays 30 deployed on the forward surfaces of the fins are limited to project in a generally forward direction from the interceptor. In most scenarios this should be sufficient for RF target engagement. However, this configuration does limit the capability for RF communications to communication stations (other inerceptors, other airborne vehicles for advanced cueing, ground stations) that are in front of the interceptor. Additional AESA arrays 60 could be deployed in a side-looking on side-facing surfaces 62 of the dorsal fins, or on an aft-facing surface 64 of the dorsal fin. The arrays on the aft-facing surfaces would be covered with a radome element 66 similar to the forward-facing arrays. The arrays on the side-facing surfaces would be covered with a flat radome element 68.
Referring now to
Referring now to
In a configuration, the gain response 120 of an individual AESA array 112 has a 1-way 3 dB beamwidth 122 that is asymmetric in Az and El depending on the orientation of the fin. The large gap between the apertures (arrays) creates multiple grating lobes in the response. Concurrent independent operation of the individual arrays can be facilitated by use of mutually orthogonal waveforms and frequency diversity for each array. The control circuitry should control the independent beam patterns to avoid attempting to look through the interceptor body, or to ignore the return should the beam look through the interceptor body.
In this configuration, the gain response 130 of the full AESA array has numerous grating lobes 132 with a 1-way 3 dB beamwidth that is approximately symmetric in AZ and El and considerably narrower than that of a single array. The 1-way gain of the full AESA array is significantly greater than that of a single array. The large central obscuration caused by the missile body creates numerous grating lobes when the four arrays are combined to form a full array. Angles derived from the full array must be disambiguated (i.e. the angle measurement must be attributed to the correct lobe). For disambiguation, it may be sufficient to combine the target state estimates from the independent fin arrays. In fact, the fused target state may be good enough to make forming the full array unnecessary. The control circuitry should control the individual beam patterns to avoid attempting to look through the interceptor body to form a combined beam pattern, or to ignore the individual return should the beam look through the interceptor body as part of the combined return.
Referring now to
Referring now to
While several illustrative embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention as defined in the appended claims.
