Phased array antenna for space based radar

[0002] This invention is related to the invention shown and described in U.S. Ser. No. 10/157,935 entitled “Microelectromechanical Switch”, filed on May 31, 2002 in the names of L. E. Dickens et al. This application is assigned to the assignee of the subject application and is incorporated herein by reference in its entirety.

[0003] 1. Field of the Invention

[0004] This invention relates generally to phased array antennas and more particularly to the architecture of a phased array antenna comprised of one or more antenna tiles consisting of a plurality of laminated circuit boards including various configurations of printed circuit wiring and components.

[0005] 2. Description of Related Art

[0006] Phased array antennas for radar applications are generally known. More recently, the architecture of a radar antenna, particularly for space based radar applications, has resulted in the design of basic building blocks in the form of “tiles” wherein each tile is formed of a multi-layer printed circuit board structure including antenna elements and its associated RF circuitry encompassed in a laminated assembly, and wherein each antenna tile can operate by itself, as a phased array or as a sub-array of a much larger array antenna.

[0007] Each tile is a highly integrated module that serves as the radiator, the transmit/receive (TR) module, RF and power manifolds and the control circuitry therefor, all of which are combined into a low cost light-weight assembly for implementing an active aperture, electronically, scanned, array (AESA). Such an architecture is particularly adapted for airborne or space applications.

[0008] Accordingly, it is an object of the present invention to provide an improvement in phased array antenna systems. It is a further object of the invention to provide an improvement in antenna tile architecture.

[0009] It is still a further object of the invention to provide an improved architecture of an antenna tile which is particularly adapted for space based radar applications.

[0010] The foregoing and other objects are achieved by a phased array antenna tile which is steered by microelectromechanical system (MEMS) switched time delay units (TDUs) in an array architecture which reduces the number of amplifiers and circulators needed for implementing an active aperture electronically scanned array antenna so as to minimize DC power consumption, cost and mass of the system which makes it particularly adaptable for airborne and spaceborne radar applications.

[0011] In one aspect of the invention, it is directed to a phased array antenna of an active aperture electronically scanned antenna system, comprising: one or more antenna tile structures, each tile of which further comprises a laminated assembly including a plurality of contiguous layers of dielectric material having patterns of metallization formed on one or more surfaces thereof and selectively interconnected by an arrangement of surface conductors and conductive vias for implementing transmission, reception, and control of RF signals between an RF input/output terminal and of an antenna assembly including a plurality of radiator elements wherein said radiator elements comprise elements of a space-fed patch antenna assembly including first and second mutually adjacent arrays of aligned patch radiators located on respective layers of foam material on one side of the antenna tile structure; and, a plurality of MEMS type switched time delay units (TDUS) mounted on the other side of the antenna tile structure, being packaged in groups of four in a Quad TDU package and being coupled between the antenna elements and a signal circulator comprising one circuit element of a transmit/receive (TR) circuit including a transmit signal amplifier and a receive signal low noise amplifier, each of said MEMS type switched time delay units respectively including a set of four identical delay transmission line assemblies having a plurality of different length time delay segments selectively interconnected by a plurality of microelectromechanical switch (MEMS) devices for steering one radiator element.

[0012] Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific example, while disclosing the preferred embodiment of the invention, it is provided by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

[0013] The present invention will become more fully understood when the detailed description provided hereinafter is considered in conjunction with the accompanying drawings which are provided by way of illustration only, and wherein:

[0014] FIG. 1 is an electrical block diagram illustrative of the preferred embodiment of an antenna tile in accordance with the subject invention;

[0015] FIG. 2 is an electrical schematic diagram illustrative of one time delay section of a quad time delay unit (TDU) shown in FIG. 1;

[0016] FIG. 3 is a plan view of an implementation of the time delay section shown in FIG. 2;

[0017] FIG. 4 is a partial vertical cross sectional view of an antenna tile in accordance with the preferred embodiment of the subject invention;

[0018] FIG. 5 is a top plan view illustrative of the physical layout of components located on the top of an antenna tile shown in FIG. 4;

[0019] FIG. 6 is a top plan view of the metallization layer formed on a first surface of the antenna tile shown in FIG. 4;

[0020] FIG. 7 is a top plan view of the printed circuit formed on a second surface of the antenna tile shown in FIG. 4;

[0021] FIG. 8 is a top plan view of the printed circuit formed on a third surface of the antenna tile shown in FIG. 4;

[0022] FIG. 9 is a top plan view of the metallization layer formed on a fourth surface of the antenna tile shown in FIG. 4;

[0023] FIG. 10 is a top plan view of the metallization layer formed on a fifth surface of the antenna tile shown in FIG. 4;

[0024] FIG. 11 is a top plan view of the printed circuit formed on a sixth surface of the antenna tile shown in FIG. 4;

[0025] FIG. 12 is a top plan view of the printed circuit formed on a seventh surface of the antenna tile shown in FIG. 4;

[0026] FIG. 13 is a top plan view of the metallization layer formed on an eighth surface of the antenna tile shown in FIG. 4;

[0027] FIG. 14 is a top plan view illustrative of the patch antenna elements located on a ninth surface of antenna tile shown in FIG. 4;

[0028] FIG. 15 is a top plan view of the patch antenna elements located on a tenth surface of the antenna tile shown in FIG. 4;

[0029] FIG. 16 is a receive far-field azimuth antenna pattern for the antenna tile shown in FIGS. 5-15;

[0030] FIG. 17 is a receive far-field field elevation pattern for the antenna tile shown in FIGS. 5-15; and

[0031] FIG. 18 is a set of transmit far-field azimuth patterns over the entire frequency band of the antenna tile shown in FIGS. 5-15.

[0032] There are several challenges facing the next generation of spaced-based radar, namely: reducing mass, cost and power required by the transmit receive antenna module (TRM) and one comprised of “tiles”, particularly where the larger system antenna is made up of an array of tiles. The size, and thus the antenna directivity can be varied simply by changing the number of tiles used.

[0033] In a conventional active aperture electronically scanned array (AESA) there exists a separate radiator assembly including a phased array of many radiator elements. Individual TR modules feed each radiator. Behind the array of radiator elements are located several manifolds for RF, power and control distribution. In a tile-type configuration, on the other hand, all of these functions are integrated into a composite structure so as to lower its mass and thus the mass of the overall radar system. Where such a system is used for space-based radar, DC power is at a premium, particularly in a satellite system, for example, since it must be generated by on-board solar cells and stored in relatively massive batteries. Increasing the antenna gain or area quickly reduces the transmitted power required and thus the cost and the mass of the radar system becomes critical.

[0034] Accordingly, the present invention is directed to a radar system where the mass is minimized by incorporating the functions of several system blocks into a tile assembly.

[0035] Considering now what is at present considered to be the preferred embodiment of the invention, reference will now be made to the various drawing figures which are intended to illustrate the details of one antenna tile which may be used as a single phased array element or one element of a multi-element two dimensional phased array.

[0036] Referring now to FIG. 1, shown there at is an electrical block diagram of the RF portion of a phased array antenna tile in accordance with the preferred embodiment of the subject invention including, among other things, a plurality of circuit elements consisting of identical MEMS switched time delay units (TDU) 10, packaged in groups of four TDUs to form a Quad TDU 12 for steering a respective radiator element 14 of a sixty four element array. As shown, sixty four TDUs 10₁, 10₂. . . 10₆₄packaged in sixteen Quad TDUs 12₁, 12₂. . . 12₁₅, 12₁₆, are used to feed sixty-four radiators 14₁, 14₂. . . 14₆₄via respective tuned transmission lines 16₁, 16₂. . . 16₆₄. Further as shown in FIG. 1, in addition to four TDUs 10, each Quad TDU package 12 includes three signal splitters 18, 19 and 20 which are interconnected between the four TDUs, for example TDU 10₁. . . 10₄in quad TDU 12₁.

[0037] Each TDU 10 of the sixty four TDUs 10₁. . . 10₆₄are identical and are shown in FIGS. 2 and 3 consisting of four time delay bits λ/2, λ/4, λ/8 and λ/16 respectively implemented with different lengths of microstrip circuit segments 22, 23, 24, and 25. These segments are adapted to be selectively connected between terminals 26 and 27 by pairs of identical MEMS switch devices 28₁, 28₂, 30₁, 30₂, and 32₁, 32₂and 34₁, 34₂, preferably of the type shown and described in the above noted related application Ser. No. 10/157,935 entitled “Microelectromechanical Switch”, L. E. Dickens et al.

[0038] Referring back to FIG. 1, pairs of Quad TDU units 12₁, 12₂. . . 12₁₅, 12₁₆are respectively coupled to eight intermediate RF signal circulators 36₁. . . 36₈via signal splitters 38₁. . . 38₈which form part of eight respective transmit receive (TR) circuits 40₁. . . 40₈, each including respective TR switches 42₁. . . 4₂₈coupled to power amplifiers 44₁. . . 44₈for RF signal transmission and low noise amplifiers (LNA) 46₁. . . 46₈for reception.

[0039] Further, the TR circuits 40₁. . . 40₈are coupled to an intermediate signal circulator 36₉of a TR circuit 40₉which is common to all of the radiators 14₁. . . 14₆₄via a MEMS Quad TDU 12₁₇and four power splitters 48₁. . . 48₄. The Quad TDU 12₁₇is identical in construction to the aforementioned Quad TDUs 12₁. . . 16₁₆and includes four TDUs 10₆₅. . . 10₆₈and three signal splitters 18, 19 and 20.

[0040] The TR circuit 40₉is identical to the TR circuits 40₁. . . 40₈and is shown including a transmit power amplifier 44₉and a switched receive low noise amplifier (LNA) 46₉. The amplifiers 44₉and 46₉are shown coupled to a transmit receive amplifier-attenuator circuit 50 comprised of a variable attenuator 52 switched between a transmit power amplifier 54, and a low noise receive amplifier 56. The attenuator 52 is coupled to a “long” time delay unit (LTDU) 58 which connects to RF signal input/output connector 60. LTDU 58 provides a common steering phase for the sixty four individual radiators 14₁. . . 14₆₄which are further modified by their respective TDUs 10₁. . . 10₆₄.

[0041] The Quad TDUs 12₁. . . 12₁₆significantly reduce the number of amplifiers required in comparison to a conventional active aperture electronically scanned array (AESA) architecture, thus minimizing DC power consumption, cost and mass of the system.

[0042] The circuitry shown in FIG. 1 is implemented by a stacked laminate tile structure 70 as shown in FIG. 4 including seven contiguous layers of dielectric material 72₁, 72₂. . . 72₇and two layers of foam material 76₁and 762. The dielectric layers 72₁, . . . 72₇include eight surface patterns of metallization 74₁, 74₂, . . . 74₈. The foam layers 76₁and 76₂include two mutually aligned sets of sixty four rectangular patch radiators 80₁. . . 80₆₄and 82₁. . . 82₆₄as shown in FIGS. 14 and 15. The details of the metallization patterns are shown in FIGS. 5 through 13.

[0043] FIG. 4 discloses the location of a power connector 60 for the application of a DC supply voltage for the active circuit components as well as the RF input/output connector 62 (FIG. 1). The cross section shown in FIG. 4 also depicts two quad TDU packages 12mand 12nmounted on the upper surface 74₁thereof. FIG. 4 also depicts a pair of metallized vias, 84, 86, which, as will be shown hereinafter, act as outer and inner conductors of, for example, a coaxial RF transmission line 16_ifor coupling RF energy to and from one of the radiators, two of which are shown by reference numerals 14mand 14n, each comprised of respective space fed patch radiators 80m, 82nand 81n, 82n. A second pair of coaxial type conductor vias 88 and 90 are used to couple the RF connector 62 to LTDU 58 (FIG. 1).

[0044] Referring now to FIG. 5, this figure discloses the top surface 74₁of the dielectric layer 72₁. Located thereon are most of the components for implementing the circuit configuration shown in FIG. 1, including, for example, the Quad TDU packages 12₁. . . 12₁₇along with other circuit elements which cannot be located within the tile assembly 10 (FIG. 4). In addition to the components mounted on the top of the tile 10, most of the surface 74₁comprises a ground plane 75 as shown in FIG. 6. It is significant to also note that the top surface 74₁also includes the upper ends of a set of metallized vertical vias 86₁, . . . 86₆₄which implement the inner conductors of tuned RF feed lines 16₁. . . 16₆₄to and from the radiator elements 14₁. . . 14₆₄comprised of the patch radiator elements 80₁. . . 80₆₄and 82₁. . . 82₆₄shown in FIGS. 14 and 15.

[0045] The inner conductors 86₁, 86₂. . . 86₆₃, 86₆₄of the feed lines 16₁. . . 16₆₄are further shown in FIGS. 7 through 12, terminating in FIG. 13. The outer conductors 84₁, 84₂, . . . 84₆₃, 84₆₄of the coaxial RF feed lines are shown, for example, by respective rings of vias which encircle the inner conductor vias 86₁. . . 86₆₄. The rings of encircling vias 84₁. . . 84₆₄also connect to annular of metallization members 87₁. . . 87₆₄in metallization pattern 74₄of FIG. 9, as well as through the patterns of metallization 74₅, 74₆, 74₇, 74₈shown in FIGS. 10-13.

[0046] Additionally shown in FIG. 7 is a relatively wide section of stripline 92 and four outwardly extending arms, 94, 96, 98 and 100, which act as DC power lines for the components used in RF transmission portion of the tile structure 70. The RF input/output connector 62 (FIG. 4) connects to an inner conductor 88 and a circular set of vias 90 of a coaxial feed line on the left side of the surface of metallization 742 shown in FIG. 7. This feed line 91 connects to the elements of the “long” variable time delay line (LTDU) shown by reference numeral 58 of FIG. 1 for imparting a common time delay to the RF signals in and out of antenna tile 70.

[0047] The LTDU 68 consists of five discrete stripline line segments 102₁, 102₂, 102₃, 102₄and 102₅of varying length formed on the left hand side of the lower surface 74₂of the dielectric layer 72₂as shown in FIG. 7. The delay line segments of stripline 102₁. . . 102₅also are surrounded by adjacent walls or fences 104₁, 104₂, 104₃, 104₄, and 104₅of ground vias which connect to respective continuous fence elements 105₁, 105₂, 105₃, 105₄and 105₅as shown in FIG. 8 to achieve required isolation. The five delay line segments 102₁. . . 102₅are, moreover, connected to a set of switch elements 106 shown in FIG. 5 located on the top surface 74₁, of the tile.

[0048] FIG. 8 shows the third pattern of metallization 74₃(FIG. 4). In addition to the fence elements 105₁. . . 105₅for the five delay line segments 102₁, . . . 102₅shown in FIG. 7, there is also shown a central elongated strip of metallization 107 and four outwardly extending arm segments 108, 110, 112 and 114 which acts as shielding between the upper DC power line segments 92, 94, 96, 98 and 100 of FIG. 7 and a set of underlying power line segments 116, 118, 120, 122, and 124 on the next lower surface 74₄(FIG. 9), which are utilized for providing DC power for the receiver portion of the antenna tile structure 70.

[0049] FIG. 8 also shows a plurality of wall or fence vias 125 which are utilized as RF shielding for the various overlying stripline elements shown in FIG. 7 consisting of the power splitters shown in FIG. 1.

[0050] With respect to FIG. 9, the surface 74₄primarily comprises a ground plane 126; however, the sixty-four annular segments of stripline metallization 87₁. . . 87₆₄which contact the upper sets of ring vias 84₁, . . . 84₆₄shown in FIGS. 7 and 8, are also located there at as noted above.

[0051] Referring now to FIG. 10, shown there at is the metallization surface 74₅(FIG. 4). It also acts primarily as a ground plane 130; however, it includes narrow lengths of stripline 131 for distributing DC power to the upper layers of the tile structure 70.

[0052] Continuing down through the remaining layers of metallization 74₆, 76₇and 74₈shown in FIG. 4 and further illustrated in FIGS. 11, 12 and 13, reference is now made to FIG. 11 wherein there is shown the pattern of metallization 74₆located on the underside of dielectric layer 72₅and consisting primarily of sixty-four RF signal isolation rings of metallization 132₁, 132₂, . . . 132₆₄, including outwardly projecting portions 134₁, . . . 134₆₄thereof through which passes the inner conductor vias 86₁, . . . 86₆₄of the RF feed lines 16₁. . . 16₆₄(FIG. 1). Also shown are various stripline elements 133 and 135, which are used to route the control signals and low current bias signals to the components on the surface of the tile.

[0053] The isolation rings 132₁, . . . 132₆₄are in registration with an underlying set of like isolation rings 136₁, . . . 136₆₄and projections 138₁, . . . 138₆₄as shown in FIG. 12, comprising a portion of the metallization surface 74₇(FIG. 4). The isolation ring elements 132 (FIG. 11) and 136 (FIG. 12) act as resonant cavities for respective RF exciter elements 140₁, . . . 140₆₄shown in FIG. 12, including low impedance radiator tuning elements 142₁, . . . 142₆₄and which are connected to the RF inner conductor vias 86₁, . . . 86₆₄passing down through the contiguous layers 72₁, . . . 72₇shown in FIG. 4. Various DC conductor lines of stripline 141 are also shown in FIG. 12.

[0054] Referring now to FIG. 13, shown there at is the layer of metallization 74₈(FIG. 4) which, primarily acts as a ground plane 144 However, sixty-four radiation slots 146₁, 146₂, . . . 146₆₄which transversely underlie the exciter elements 140₁, . . . 140₆₄(FIG. 12) are located in the metallization. The radiating slots 146₁, . . . 146₆₄operate to couple and receive energy from the space fed arrays of mutually aligned rectangular patch radiators 80₁, . . . 80₆₄, 82₁, . . . 82₆₄formed on the outer surfaces of the foam layers 76₁and 76₂as shown in FIGS. 14 and 15 and which implement the radiators 14₁. . . 14₆₄shown in FIG. 1. FIG. 13 also shows the RF feed line inner conductor vias 86₁, 86₂, . . . 86₆₄extending to and terminating in the ground plane surface 144 of the metallization 74₈. This portion of the vias 86₁. . . 86₆₄acts as RF feed line tuning stubs, minimizing RF reflections from the radiator elements 80₁. . . 80₆₄and 82₁. . . 82₆₄of FIGS. 14 and 15.

[0055] FIGS. 16-18 are illustrative of far-field radiation patterns obtained from an antenna tile 70 fabricated in accordance with the drawing figures shown in FIGS. 5-15. FIG. 16, for example, shows a set of theoretical receive far-field azimuth patterns 148 and a set of measured patterns 150 at broadside while FIG. 17 discloses a set of theoretical receive far-field elevation patterns 152 and a set of measured patterns 154 at broadside. FIG. 18 is illustrative of a set of transmit far-field azimuth patterns 156 over the entire frequency band for which the tile is designed and shows that the main beam 158 remains fixed in location as frequency is varied due to the use of true time delay rather than phase shift.

[0056] A fabrication of tile antenna in accordance with the subject invention uses standard printed circuit board techniques and materials. All vias are through drills (as opposed to blind laser drilled vias) which greatly simplifies substrate manufacturing. The RF manifolds are fabricated as unbalanced stripline. The symmetric and binary nature of the tile allows for the use of a corporate manifold which uses equal split Wilkinson power dividers and is very forgiving of manufacturing errors, since all the power divisions are of equal magnitude. Layer sharing is necessary to minimize the tile substrate mass; however, it does force special care to maintain a high level of isolation between the RF and DC circuits. All RF traces are surrounded by walls of ground vias, which are tied together on multiple layers to achieve the required isolation. The logic manifold is located primarily between the radiator feed cavities. Also, special care is required to isolate the clock lines from the RF circuitry. The tile, when fabricated with only through drilled holes, achieves a high tile yield, but this means that all vias that connect to the digital circuits must have shielded stubs that extend to the lowermost ground plane layer.

[0057] The foregoing detailed description merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are thus within its spirit and scope.