The present invention relates generally to phased array systems and more particularly to a conformal tile module for phased array systems.
Early implementations of phased array systems were based on passive arrays that included a centralized transmitter and receiver module and a phase shifter at each array element. The passive corporate feed networks for such radar systems introduced high losses. Ferrite phase shifters were typically employed due to their low loss; however, ferrite phase shifters are generally large and heavy devices. Active array systems were developed due in part to advances in microwave integrated circuits and have improved radar sensitivity due to lower radio frequency (RF) losses than passive arrays. Each element of an active array system includes a transmitter and receiver module (i.e., “T/R module”) having a phase shifter and amplifiers. Advantageously, active arrays can continue to operate with only gradual degradation as the number of failed array elements increases.
Mission performance requirements for phased array systems have become more demanding. For example, phased array systems providing a surveillance function are often limited to a single mode of operation or surveillance task. Redundant systems may be required to accommodate simultaneous modes of operations. Moreover, the weight and size of a phased array system are important factors for airborne and spaceborne implementations. Lower cost is desired to accelerate development of more sophisticated systems, including systems with greater numbers of T/R modules than current phased array systems.
A phased array system having a digital channel for each array element provides the most operational flexibility. Multiple beams can be formed simultaneously over a defined angle space and full adaptive control is possible; however, significant digital processing capability is required. Furthermore, fitting all of the components, including receivers and analog to digital converters, in a small volume near each element provides a significant challenge. The DC power requirements, thermal management, and cost of components are additional barriers to implementation of such systems.
Phased array systems employing digital subarrays represent a compromise between single agile beam systems with analog beamformers and all-digital systems employing digital beamformers. The density of digital channels used with digital subarrays is significantly less than the number of array elements. As a result, digital processing requirements are reduced. However, the system size and the cost and complexity of the subarray networks make them unsuitable for many applications. In addition, modification or replacement of a portion of the array elements is difficult and can require significant down time.
In one aspect, the invention features a tile module for a phased array system. The tile module includes a plurality of array elements, a plurality of controller modules and a two-dimensional network module. The array elements are configured as a two-dimensional array and each array element is adapted for receiving an RF signal. Each controller module is in communication with a respective one of the array elements and provides a phase shift and an attenuation. The two-dimensional network module includes a portion of an overlapped subarray manifold and is in communication with the array elements. The two-dimensional network module provides a weighted combination of received RF signals from the array elements of the tile module and array elements in other tile modules disposed in a same subarray of the phased array system.
In another aspect, the invention features a tile module for a phased array system. The tile module includes a plurality of array elements, a plurality of controller modules, a plurality of one-dimensional network modules and an orthogonal one-dimensional network module. The array elements are configured as a two-dimensional array and each array element is adapted for receiving an RF signal. Each controller module is in communication with a respective one of the array elements and provides a phase shift and an attenuation. Each one-dimensional network module is in communication with a respective subset of the array elements and generates a first weighted combination of the RF signals received by the respective subset of the array elements. The orthogonal one-dimensional network module is in communication with the one-dimensional network modules and generates an orthogonal weighted combination in response to the first weighted combinations of the RF signals received from the one-dimensional network modules.
In still another aspect, the invention features a tile module for a phased array system. The tile module includes a plurality of array elements, a plurality of controller modules and a two-dimensional network module. The array elements are configured as a two dimensional array and each array element is adapted for transmitting an RF signal. Each controller module is in communication with a respective one of the array elements and provides a phase shift and an attenuation. The two-dimensional network module includes a portion of an overlapped subarray manifold and is in communication with the array elements. The two-dimensional network module provides to each array element a weighted combination of transmit RF signals applied to the tile module and other tile modules disposed in a same subarray of the phased array system.
In yet another aspect, the invention features a tile module for a phased array system. The tile module includes a plurality of array elements, a plurality of controller modules, a one-dimensional network module and a plurality of orthogonal network modules. The array elements are configured as a two dimensional array and are each adapted for transmitting an RF signal. Each controller module is in communication with a respective one of the array elements and provides a phase shift and an attenuation. The one-dimensional network module has an input terminal to receive a transmit RF signal and generates a first plurality of weighted transmit RF signals. Each orthogonal network module is in communication with the one-dimensional network module and a subset of the array elements. Each orthogonal network module generates weighted combinations of weighted transmit RF signals and each of the weighted combinations is provided to a respective one of the array elements.
The above and further advantages of this invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in the various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
In brief overview, the present invention relates to a tile module for a phased array system such as a phased array radar system or a phased array communications system. The tile module includes array elements configured in a two-dimensional array which is part of a larger subarray in the phased array system. A control module communicates with each array element to control a phase shift and an attenuation. A two-dimensional overlapped subarray manifold provides a weighted combination of RF signals received by the array elements of the tile module and array elements of other tile modules disposed in the same subarray of the phased array system. Advantageously, tile modules can be fabricated in large quantities, can be tested and calibrated independently, and can easily be installed or replaced in the phased array system.
The active array system 10 operates with a single agile beam 34 for transmit and receive functions. Consequently, a single system 10 generally cannot be tasked for missions requiring multiple beams.
The tile modules 78 are structurally identical to each other and each includes a portion of the analog overlapped subarray network 54 for each of nine subarrays 70 in which it is a member. For example, the tile module 78E at the center of the subarray 70A shown in
The tile module 78 at the center of a subarray 70, i.e., the tile module 78 centered about the phase center 74 of the subarray 70, provides an RF signal which is a weighted analog combination of the RF signals received by the array elements 14 in the subarray 70 as described in more detail below. Each tile module 78 includes a two-dimensional network module which receives RF signals from the array elements 14 in a subarray 70. A two-dimensional subarray manifold associated with the subarray 70 includes analog circuitry distributed in a center tile module and eight surrounding (i.e., adjacent) tile modules. The analog circuitry combines predefined “weights” of the RF signals from the array elements 14 as a single output signal.
Although not shown, the weighting and combining process is implemented in two dimensions. More specifically, the twelve weighted combinations that are generated for the first dimension are weighted according to another set of predetermined coefficients and combined to generate the subarray output signal. Generally, the predetermined coefficients are the same for both dimensions.
Referring to
The weighted combination of RF signals from the first combiner 110A is provided through path 114 to a respective row network module of one of two neighboring tile modules (not shown) in the same subarray that correspond to the same rows of the aperture. Similarly, the weighted combination of RF signals from the third combiner 110C is provided through path 118 to a respective row network module in the other neighboring tile module in the same rows of the aperture. Each of the two neighboring tile modules provides a weighted combination of RF signals from its respective row network module through path 122 or 126. A 3:1 combiner 130 generates a row weighted output signal by combining the weighted combinations received from respective row network modules of the two neighboring tiles with the weighted combination received from combiner 110B.
The effective weighting for each RF signal path from an array element 14 through the 1:3 combiner 130 is determined by the product of the predetermined coefficients of the 1:3 divider 106, 4:1 combiner 110 and 3:1 combiner 130 in the path. For example, the coefficient C6 is determined by the product of coefficients A2, W6 and A2. To achieve a weighting that result in a 180° phase shift, preferably each of two of the predetermined coefficients for an RF path introduces a 90° phase shift as it is generally more difficult to achieve a weighting of 180° with a single divider 106 or combiner 110, 130 over the full bandwidth.
The row weighted output signal is provided to one of four 1:3 dividers 134 (only one divider 134A is identified) in a column network module 138. Each of the three other 1:3 dividers 134 receives a weighted combination from a respective one of the other row network modules 102B, 102C and 102D in the tile module 78. The divided RF signals are weighted according to one of three predetermined coefficients A1, A2 and A3 and distributed to three 4:1 combiners 140A to 140C (generally 140) in a manner similar to that described for the row 1 network module 102A. Each of the two neighboring tile modules in the same subarray that are aligned in the same columns of the aperture receives a weighted combination of RF signals from the respective one of the first and third combiners 140A and 140C through path 142 or 146, respectively. Each of the two neighboring tile modules provides a weighted combination of RF signals from their column network modules through path 150 or 154. A 1:3 combiner 158 generates a manifold output signal at terminal 162 by combining the weighted combinations received from the two neighboring tiles with the weighted combination from combiner 140B.
Each tile module 78 includes all of the required overlapped subarray components. Consequently, the backplane is simplified to a set of passive electrical interconnects. The RF signals, digital control signals, and DC voltage are supplied to or from the tile module 78 via push-on electrical connectors 166 and 170. Heat generated in the tile module 78 is extracted through a set of thermal vias 178 which also serve as accurate mounting posts.
Although the illustrated tile module 78 includes a 4×4 arrangement of 16 array elements 14, it should be recognized that other numbers of array elements 14 are contemplated by the invention. Moreover, although the subarrays disclosed above are defined by a 3×3 configuration of tile modules 78, it should be recognized that a subarray can include other numbers and configurations of tile modules with the appropriate analog circuit modification to the row network modules and column network modules.
In the illustrated embodiment, the 16 array elements 14 of the tile module 78 are arranged in a 4×4 configuration along one surface. The tile module 78 also includes a two-dimensional network layer 182, an RF multi-chip module (MCM) housing 186 having 16 RF MCMs 190, RF electrical connectors 166 and DC electrical connectors 170. The two-dimensional network layer 182 includes a multi-layer dielectric board. The multi-layer board includes in-layer and between layer RF signal paths to enable combining and splitting of RF signals and to receive and distribute RF signals from other tile modules in the same subarray. The multi-layer board is also used for DC digital signal distribution for phase shifting and attenuation control and includes a power distribution network for RF MCMs 190. The RF MCM housing 186 has 16 cavities fabricated in a layer of Silicon-Aluminum (Si—Al) alloy. The alloy enables efficient heat transfer from the RF MCMs 190 and limits thermal stresses in the tile module 78. More specifically, the alloy is selected for its coefficient of thermal expansion (CTE), high thermal conductivity, low density, low resistivity, ease of fabrication and plateablity with high specific stiffness. Other alloys, composites, and metals with similar material properties can be used.
In some embodiments, the tile module 78 includes array elements 14 having two or more phase shifters to enable operation with two or more beam clusters. Each phase shifter controls the phase for a particular operating frequency band. In one example, an array element 14 has one phase shifter for a first operating frequency band (e.g., 8.5 GHz to 9.0 GHz) and a second phase shifter for a second operating frequency band (e.g., 9.5 GHz to 10.5 GHz). An RF signal resulting from a combination of the RF signals in each operating frequency band is provided by each array element 14 and processed (i.e., weighted and combined) by the subarray manifolds defined in the network layer 182. In contrast to the active array system 50 of
The RF MCM housing 186 is attached to the network layer 182 using a compression interface comprising a gold elastomer 206 material and the standoffs for the thermal vias 178. The standoffs are secured to the RF MCM housing 186 by screws. The gold elastomer 206 couples the RF ground between the RF MCM housing 186 and RF MCMs 190 to the network layer 182 and provides the RF ground through the RF and digital connectors 166 and 170 to the active array system.
The illustrated embodiment of the tile module 78 is described in reference to manufacture from specific materials and components. It should be realized that there are a variety of other materials having satisfactory electrical and mechanical properties that can be utilized for manufacturing the tile module 78.
Although the embodiments described above relate primarily to a receive-only phased array system, the invention contemplates the extension of this architecture to transmit functionality and a combination of transmit and receive functionality. In one approach, the overlapped subarray manifold is used for both transmit and receive signal distribution between the array elements and the subarray input/output ports. In another approach, a separate manifold is employed to distribute the transmit signals to the array elements. The former approach has the advantage of using a single overlapped subarray manifold for both transmit and receive functions; however, transmit amplifiers at each array element are required to operate in a linear mode because the overlapped subarray manifold generates a small but significant non-uniform amplitude distribution across the array. In the latter approach, the transmit signals are uniformly distributed across the array, and the transmit amplifiers can thus operate in a highly efficient saturation mode.
While the invention has been shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.
This invention was made with United States government support under Contract No. F19628-00-C-0002 awarded by the United States Air Force. The government may have certain rights in the invention.