This application is related to the following application U.S. application Ser. No. 14/544,935, “Substrate-Loaded Frequency-Scaled Ultra-Wide Spectrum Element,” filed Jun. 16, 2015, which is incorporated herein by reference in its entirety.
The present disclosure relates generally to antennas, and more specifically to ultra-wideband, phased array antennas.
There are increasing demands to develop a wideband phased array or electronically scanned array (ESA) that include a wide variety of configurations for various applications, such as satellite communications (SATCOM), radar, remote sensing, direction finding, and other systems. The goal is to provide more flexibility and functionality at reduced cost with consideration to limited space, weight, and power consumption (SWaP) on modern military and commercial platforms. This requires advances in ESA and manufacturing technologies.
A phased array antenna is an array of antenna elements in which the phases of respective signals feeding the antenna elements are set in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions, thus forming a beam. The relative amplitudes of constructive and destructive interference effects among the signals radiated by the individual elements determine the effective radiation pattern of the phased array. The number of antenna elements in a phased array antenna is often dependent on the required gain of a particular application and can range from dozens to tens of thousands or more.
Phased array antennas for ultra-wide bandwidth (more than one octave bandwidth) performance are often large, causing excessive size, weight, and cost for applications requiring many elements. The excessive size of an array may be required to accommodate “electrically large” radiating elements (several wavelengths in length), increasing the total depth of the array. Arrays may also be large due to the nesting of several multi-band elements to enable instantaneous ultra-wide bandwidth performance, which increases the total length and width of the array.
Phased arrays antennas have several primary performance characteristics in addition to the minimization of grating lobes, including bandwidth, scan volume, and polarization. Grating lobes are secondary areas of high transmission/reception sensitivity that appear along with the main beam of the phased array antenna. Grating lobes negatively impact a phased array antenna by dividing transmitted/received power into a main beam and false beams, creating ambiguous directional information relative to the main beam and generally limiting the beam steering performance of the antenna. Bandwidth is the frequency range over which an antenna provides useful match and gain. Scan volume refers to the range of angles, beginning at broadside (normal to the array plane) over which phasing of the relative element excitations can steer the beam without generating grating lobes. Polarization refers to the orientation or alignment of the electric field radiated by the array. Polarization may be linear (a fixed orientation), circular (a specific superposition of polarizations), and other states in between.
Phased array antenna design parameters such as antenna element size and spacing affect these performance characteristics, but the optimization of the parameters for the maximization of one characteristic may negatively impact another. For example, maximum scan volume (maximum set of grating lobe-free beam steering angles) may be set by the antenna element spacing relative to the wavelength at the high end of the frequency spectrum. Once cell spacing is determined, a desired minimum frequency can be achieved (maximizing bandwidth) by increasing the antenna element length to allow for impedance matching. However, increased element length may negatively influence polarization and scan volume. The scan volume can be increased through closer spacing of the antenna elements, but closer spacing can increase undesirable coupling between elements, thereby degrading performance. This undesirable coupling can change rapidly as the frequency varies, making it difficult to maintain a wide bandwidth.
Existing wide bandwidth phased array antenna elements are often large and require contiguous electrical and mechanical connections between adjacent elements (such as the traditional Vivaldi). In the last few years, there have been several new low-profile wideband phased array solutions, but many suffer from significant limitations. For example, planar interleaved spiral arrays are limited to circular polarization. Tightly coupled printed dipoles require superstrate materials to match the array at wide-scan angles, which adds height, weight, and cost. The Balanced Antipodal Vivaldi Antenna (BAVA) uses a mix of metallic posts and printed circuit substrate to operate over wideband frequencies but may not be suitable for high power-application because it is limited by the substrate material power handling capability. Furthermore, the BAVA requires connectors to deliver the signal from the front-end electronics to the aperture.
Existing designs often have not been able to maximize phased array antenna performance characteristics such as bandwidth, scan volume, and polarization without sacrificing size, weight, cost, and/or manufacturability. Accordingly, there is a need for a phased array antenna with wide bandwidth, wide scan volume, and good polarization, in a low cost, lightweight, small footprint (small aperture) design that can be scaled for different applications.
In accordance with some embodiments, a frequency scaled ultra-wide spectrum phased array antenna includes a plurality of unit cells of radiating elements and clustered pillars affixed to a base plate. Each radiating element includes a signal ear and a ground ear. Radiating elements are arranged to be electromagnetically coupled to one or more adjacent radiating elements via the clustered pillars. The unit cells are scalable and may be combined into an array of any dimension to meet desired antenna performance. Embodiments can provide good impedance over ultra-wide bandwidth, wide scan volume, and good polarization, in a low cost, lightweight, small aperture size that is easy to manufacture.
Phased array antennas, according to some embodiments, may reduce the number of antennas which need to be implemented in a given application by providing a single antenna that serves multiple systems. In reducing the number of required antennas, embodiments of the present invention may provide a smaller size, lighter weight, lower cost, reduced aperture alternative to conventional, multiple-antenna systems.
According to certain embodiments, a phased array antenna includes a base plate, a clustered pillar projecting from the base plate, wherein the clustered pillar is electrically connected to the base plate, a first radiating element projecting from the base plate and configured to capacitively couple to the clustered pillar, and a second radiating element projecting from the base and configured to capacitively couple to the clustered pillar.
According to certain embodiments, a phased array antenna is configured to transmit or detect RF signals over a bandwidth ratio of at least 2:1. According to certain embodiments, the antenna is configured to have an average voltage standing wave ratio of less than 5:1. According to certain embodiments, the antenna is configured to have an average voltage standing wave ratio of less than 5:1 over a scan volume of at least 30 degrees from broadside.
According to certain embodiments, an antenna element includes a base plate, a first ground clustered pillar projecting from the base plate, a second ground clustered pillar projecting from the base plate and spaced apart from a first side of the first ground clustered pillar, a first ground member projecting from the base plate between the first ground clustered pillar and the second ground clustered pillar, wherein a distal end of the first ground member is configured to capacitively couple to the second ground clustered pillar, and a first signal member projecting from the base plate between the first ground clustered pillar and the first ground member, wherein the first signal member is electrically insulated from the base plate, the first ground clustered pillar, and the first ground member, and a distal end of the first signal member is configured to capacitively couple to the first ground clustered pillar.
According to some embodiments, an antenna element includes a second ground member projecting from the base plate and spaced apart from the first ground clustered pillar on a second side of the first ground clustered pillar opposite the first side, wherein a distal end of the second ground member is configured to capacitively couple to the first ground clustered pillar.
According to some embodiments, an antenna element includes a second signal member projecting from the base plate and spaced apart from the first ground clustered pillar on a third side of the first ground clustered pillar, wherein the second signal member is electrically insulated from the base plate and the first ground clustered pillar, and a distal end of the second signal member is configured to capacitively couple to the first ground clustered pillar, and a third ground member projecting from the base plate and spaced apart from the first ground clustered pillar on a fourth side of the first ground clustered pillar, opposite the third side of the first ground clustered pillar.
According to some embodiments, an antenna element includes a dielectric material separating at least a portion of the first ground clustered pillar from at least a portion of the first signal member. According to some embodiments the dielectric material is a coating on the first ground clustered pillar. According to some embodiments, the dielectric material is a sleeve covering at least the portion of the first ground clustered pillar.
According to some embodiments, the element is configured to receive RF signals in a frequency range between a first frequency and a second frequency that is higher than the first frequency and the first ground clustered pillar and the second ground clustered pillar are spaced apart at a maximum interval of one-half the wavelength of the second frequency.
According to some embodiments, the element is configured to receive RF signals in a frequency range between a first frequency and a second frequency that is higher than the first frequency and the first signal member projects from the base plate with a maximum height of one-half the wavelength of the second frequency.
According to some embodiments, the first ground clustered pillar comprises a projecting portion that projects from the first side of the first ground clustered pillar; and the first signal member comprises a wrapping portion at the distal end that at least partially wraps around the projecting portion of the first ground clustered pillar.
According to some embodiments, a dielectric plug inserted into the base plate for affixing the first signal member to the base plate. The antenna element of claim 10, wherein the dielectric plug comprises a connector for connecting a signal line to the first signal member.
According to some embodiments, the first ground clustered pillar, the second ground clustered pillar, and the first ground member are electrically connected to the base plate. According to some embodiments, the base plate, the first ground clustered pillar, the second ground clustered pillar, the first ground member, and the first signal member each comprise a conductive material.
According to some embodiments, the distal end of the first ground member and the distal end of the first signal member are substantially symmetrical about a plane disposed midway between the first ground member and the first signal member. According to some embodiments, the distal end of the first ground member and the distal end of the first signal member are substantially asymmetrical about a plane disposed midway between the first ground member and the first signal member.
According to some embodiments, a radiating element for a phased array antenna includes a base portion, a first member projecting from the base portion comprising a first stem and a first impedance matching portion, wherein the first impedance matching portion comprises at least one projecting portion projecting from a first side of the first impedance matching portion, and a second member projecting from the base portion and spaced apart from the first member, the second member comprising a second stem and a second impedance matching portion, wherein the second impedance matching portion comprises at least one other projecting portion projecting toward the first side of the first impedance matching portion.
According to some embodiments, the first member further comprises a first capacitive coupling portion on a second side opposite the first side, the first capacitive coupling portion configured to capacitively couple to a first ground clustered pillar. According to some embodiments, the first impedance matching portion and the second impedance matching portion are substantially symmetrical.
According to some embodiments, the first impedance matching portion comprises a first projecting portion at a distal end of the first member and a second projecting portion spaced between the first projecting portion and the first stem, wherein the first projecting portion projects farther than the second projecting portion. According to some embodiments, the first member is insulated from the second member.
In the following description of the disclosure and embodiments, reference is made to the accompanying drawings in which are shown, by way of illustration, specific embodiments that can be practiced. It is to be understood that other embodiments and examples can be practiced and changes can be made without departing from the scope of the disclosure.
In addition, it is also to be understood that the singular forms “a,” “an,” and “the” used in the following description are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is also to be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It is further to be understood that the terms “includes, “including,” “comprises,” and/or “comprising,” when used herein, specify the presence of stated features, integers, steps, operations, elements, components, and/or units, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, units, and/or groups thereof.
Reference is sometimes made herein to an array antenna having a particular array shape (e.g. a planar array). One of ordinary skill in the art would appreciate that the techniques described herein are applicable to various sizes and shapes of array antennas. It should thus be noted that although the description provided herein describes the concepts in the context of a rectangular array antenna, those of ordinary skill in the art would appreciate that the concepts equally apply to other sizes and shapes of array antennas including, but not limited to, arbitrary shaped planar array antennas as well as cylindrical, conical, spherical and arbitrary shaped conformal array antennas.
Reference is also made herein to the array antenna including radiating elements of a particular size and shape. For example, certain embodiments of radiating element are described having a shape and a size compatible with operation over a particular frequency range (e.g. 2-30 GHz). Those of ordinary skill in the art would recognize that other shapes of antenna elements may also be used and that the size of one or more radiating elements may be selected for operation over any frequency range in the RF frequency range (e.g. any frequency in the range from below 20 MHz to above 50 GHz).
Reference is sometimes made herein to generation of an antenna beam having a particular shape or beam-width. Those of ordinary skill in the art would appreciate that antenna beams having other shapes and widths may also be used and may be provided using known techniques such as by inclusion of amplitude and phase adjustment circuits into appropriate locations in an antenna feed circuit.
Described herein are embodiments of frequency-scaled ultra-wide spectrum phased array antennas. These phased array antennas are formed of repeating cells of frequency-scaled ultra-wide spectrum radiating elements. Phased array antennas according to certain embodiments exhibit very low profile, wide bandwidth, low cross-polarization, and high scan-volume while being low cost, small aperture, modular with built-in RF interconnect, and scalable.
A unit cell of a frequency-scaled ultra-wide spectrum phased array antenna, according to certain embodiments, includes a pattern of radiating elements. According to certain embodiments, the radiating elements are formed of substrate-free, interlacing components that include a pair of metallic ears that form a coplanar transmission line. One of the ears is the ground component of the radiating element and can be terminated to the ground of a coaxial connector used for connecting a feed line or directly to the array's baseplate. The other ear is the signal or active line of the radiating element and can be connected to the center of a coaxial feed line. According to certain embodiments, the edge of the radiating elements (the edge of the ears) are shaped to encapsulate a cross-shape metallic clustered pillar, which controls the capacitive component of the antenna and can allow good impedance matching at the lower-frequency end of the bandwidth, effectively increasing the operational bandwidth. This has the advantage of a phased array antenna in which no wideband impedance matching network or special mitigation to a ground plane is needed. Radiating elements can be for transmit, receive, or both. Phased array antennas can be built as single polarized or dual polarized by implementing the appropriate radiating element pattern, as described below.
As shown in
Symmetric Phased Array
An array of radiating elements 200 according to certain embodiments is illustrated in
In the embodiments of
According to certain embodiments, the edges of the radiating elements (the edge of the ears) are shaped to encapsulate cross-shaped metallic clustered pillar 212 to capacitively couple adjacent radiating elements during operation. This can enhance the capacitive component of the antenna, which allows a good impedance match at the low-frequency end of the bandwidth. Through this coupling of clustered pillar 212, each radiating element in a row or column is electromagnetically coupled to ground and the previous and next radiating element in the row or column.
Capacitive coupling is achieved by maintaining a gap 320 between a radiating element ear and its adjacent clustered pillar, which creates interdigitated capacitance between the two opposing surfaces of gap 320. This capacitance can be used to improve the impedance matching of the antenna. Capacitive coupling can be controlled by changing the overlapped surface area of gap 320 and width of gap 320 (generally, higher capacitance is achieved with larger surface area and less width). According to certain embodiments, signal ears 220 and 216 and ground ears 222 and 218 wrap around the cross shape of clustered pillar 212 in order to maximize the surface area. However, other designs for maximizing the capacitive surface area are also contemplated. For example, a clustered pillar and adjacent ear can form interlacing fingers when viewed from above (e.g., the view of
Interdigitated capacitance enables some coupling between adjacent radiating elements in a row (or column). In other words, the electromagnetic field from a first radiating element communicates from its ground ear across the adjacent gap to the adjacent clustered pillar through the interdigitated capacitance and then across the opposite gap to the adjacent signal ear of the next radiating element. Referring to
It should be understood that the illustrations of unit cell 202 in 2C, 3A, 3B, and 3C truncate ground ears 324 and 326 on the left and bottom side of clustered pillar 212 for illustrative purposes only. One of ordinary skill in the art would understand that the relative orientation of one set of radiating elements to an orthogonal set of radiating elements, as described herein, is readily modified, i.e. a signal ear could be on the left side of clustered pillar 212 with a ground ear being on the right side, and/or a signal ear could be on the bottom side of clustered pillar 212 with a ground ear being on the top side (relative to the view of
According to certain embodiments, base plate 214 is formed from one or more conductive materials, such as metals like aluminum, copper, gold, silver, beryllium copper, brass, and various steel alloys. According to certain embodiments, base plate 214 is formed from a non-conductive material such as various plastics, including Acrylonitrile butadiene styrene (ABS), Nylon, Polyamides (PA), Polybutylene terephthalate (PBT), Polycarbonates (PC), Polyetheretherketone (PEEK), Polyetherketone (PEK), Polyethylene terephthalate (PET), Polyimides, Polyoxymethylene plastic (POM/Acetal), Polyphenylene sulfide (PPS), Polyphenylene oxide (PPO), Polysulphone (PSU), Polytetrafluoroethylene (PTFE/Teflon), or Ultra-high-molecular-weight polyethylene (UHMWPE/UHMW), that is plated or coated with a conductive material such as gold, silver, copper, or nickel. According to certain embodiments, base plate 214 is a solid block of material with holes, slots, or cut-outs to accommodate clustered pillars 212, signal ears 216 and 220, and ground ears 218 and 222 on the top (radiating) side and connectors on the bottom side to connect feed lines. In other embodiments, base plate 214 includes cutouts to reduce weight.
According to certain embodiments, base plate 214 is designed to be modular and includes features in the ends that can mate with adjoining modules. Such interfaces can provide both structural rigidity and cross-interface conductivity. Modules may be various sizes incorporating various numbers of unit cells of radiating elements. According to certain embodiments, a module is a single unit cell. According to certain embodiments, modules are several unit cells (e.g., 2×2, 4×4), dozens of unit cells (e.g., 5×5, 6×8), hundreds of unit cells (e.g., 10×10, 20×20), thousands of unit cells (e.g., 50×50, 100×100), tens of thousands of unit cells (e.g., 200×200, 400×400), or more. According to certain embodiments, a module is rectangular rather than square (i.e., more cells along one axis than along the other).
According to certain embodiments, modules align along the centerline of a radiating element such that a first module ends with a ground clustered pillar and the next module begins with a ground clustered pillar. The base plate of the first module may include partial cutouts along its edge to mate with partial cutouts along the edge of the next module to form a receptacle to receive the radiating elements that fit between the ground clustered pillars along the edges of the two modules. According to certain embodiments, the base plate of a module extends further past the last set of ground clustered pillars along one edge than it does along the opposite edge in order to incorporate a last set of receptacles used to receive the set of radiating elements that form the transition between one module and the next. In these embodiments, the receptacles along the perimeter of the array remain empty. According to certain embodiments, a transition strip is used to join modules, with the transition strip incorporating a receptacle for the transition radiating elements. According to certain embodiments, no radiating elements bridge the transition from one module to the next. Arrays formed of modules according to certain embodiments can include various numbers of modules, such as two, four, eight, ten, fifteen, twenty, fifty, a hundred, or more.
In some embodiments, base plate 214 may be manufactured in various ways including machined, cast, or molded. In some embodiments, holes or cut-outs in base plate 214 may be created by milling, drilling, formed by wire EDM, or formed into the cast or mold used to create base plate 214. Base plate 214 can provide structural support for each radiating element and clustered pillar and provide overall structural support for the array or module. Base plate 214 may be of various thicknesses depending on the design requirements of a particular application. For example, an array or module of thousands of radiating elements may include a base plate that is thicker than the base plate of an array or module of a few hundred elements in order to provide the required structural rigidity for the larger dimensioned array. According to certain embodiments, the base plate is less than 6 inches thick. According to certain embodiments, the base plate is less than 3 inches thick, less than 1 inch thick, less than 0.5 inches thick, less than 0.25 inches thick, or less than 0.1 inches thick. According to certain embodiments, the base plate is between 0.2 and 0.3 inches thick. According to some embodiments, the thickness of the base plate may be scaled with frequency (for example, as a function of the wavelength of the highest designed frequency, λ). For example, the thickness of the base plate may be less than 1.0 λ, 0.5 λ, or less than 0.25 λ. According to some embodiments, the thickness of the base plate is greater than 0.1 λ, greater than 0.25 λ, greater than 0.5 λ, or greater than 1.0 λ.
According to certain embodiments, radiating ears 216, 218, 220 and 222 and clustered pillar 212 may be formed from any one or more materials suitable for use in a radiating antenna. These may include materials that are substantially conductive and that are relatively easily to machine, cast and/or solder or braze. For example, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 may be formed from copper, aluminum, gold, silver, beryllium copper, or brass. In some embodiments, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 may be substantially or completely solid. For example, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 may be formed from a conductive material, for example, substantially solid copper, brass, gold, silver, beryllium copper, or aluminum. In other embodiments, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 are substantially formed from non-conductive material, for example plastics such as ABS, Nylon, PA, PBT, PC, PEEK, PEK, PET, Polyimides, POM, PPS, PPO, PSU, PTFE, or UHMWPE, with their outer surfaces coated or plated with a suitable conductive material, such as copper, gold, silver, or nickel.
In other embodiments, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 may be substantially or completely hollow, or have some combination of solid and hollow portions. For example, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 may include a number of planar sheet cut-outs that are soldered, brazed, welded or otherwise held together to form a hollow three-dimensional structure. According to some embodiments, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 are machined, molded, cast, or formed by wire-EDM. According to some embodiments, one or more radiating ears 216, 218, 220 and 222 and clustered pillar 212 are 3D printed, for example, from a conductive material or from a non-conductive material that is then coated or plated with a conductive material.
Referring now to
Referring to
Referring now to
According to certain embodiments, for example as shown in
According to certain embodiments, connector 530 is a female connector. Base plate 514 may be electrically connected to the outer conductor (shield) of the coaxial cable through the body of coaxial connector 530. According to certain embodiments, ground ear 518 is directly electrically connected to the outer conductor of the coaxial cable through a ground conductor of coaxial connector 530. In other embodiments, ground ear 518 is inserted or formed into a side of plug 528 such that a portion of ground ear 518 is exposed, as depicted in
According to certain embodiments, signal ear 516, ground ear 518, plug 528, and connector 530 are built together as a subassembly that may then be assembled into base plate 514. According to certain embodiments, the center conductor of coaxial connector 530 and signal ear 516 are formed from a single piece of material. According to certain embodiments, connector 530 is embedded within base plate 528 (as shown in FIG. 5C). According to some embodiments, connector 530 protrudes from the bottom of base plate 528, protrudes from a recess in the bottom of base plate 514 or is affixed to the bottom plane of base plate 514. According to some embodiments, connector 530 is an off-the-shelf male or female connector, and according to other embodiments, connector 530 is custom built or modified for fitting into base plate 514. According to certain embodiments, connector 530 is designed to be directly attached to a feed line. According to other embodiments, connector 530 is attached to a feed line through an intermediate manifold that, itself, directly connects to feed lines.
The phased array antenna 200, according to certain embodiments, has a designed operational frequency range, e.g., 1 to 30 GHz, 2 to 30 GHz, 3 to 25 GHz, and 3.5 to 21.5 GHz. According to certain embodiments, the phased array antenna is designed to operate at a frequency of at least 1 GHz, at least 2 GHz, at least 3 GHz, at least 5 GHz, at least 10 GHz, at least 15 GHz, or at least 20 GHz. According to certain embodiments, the phased array antenna is designed to operate at a frequency of less than 50 GHz, less than 40 GHz, less than 30 GHz, less than 25 GHz, less than 22 GHz, less than 20 GHz, or less than 15 GHz. The sizing and positioning of radiating elements can be designed to effectuate these desired frequencies and ranges. For example, the spacing between a portion of a first radiating element and the portion of the next radiating element along the same axis may be equal to or less than about one-half a wavelength, λ, of a desired frequency (e.g., highest design frequency). According to some embodiments, the spacing may be less than 1 λ, less than 0.75 λ, less than 0.66 λ, less than 0.33 λ, or less than 0.25 λ. According to some embodiments, the spacing may be equal to or greater than 0.25 λ, equal to or greater than 0.5 λ, equal to or greater than 0.66 λ, equal to or greater than 0.75 λ, or equal to or greater than 1 λ.
Additionally, the height of radiating element 208 and 210 may be less than about one-half the wavelength of the highest desired frequency. According to some embodiments, the height may be less than 1 λ, less than 0.75 λ, less than 0.66 λ, less than 0.33 λ, or less than 0.25 λ. According to some embodiments, the height may be equal to or greater than 0.25 λ, equal to or greater than 0.5 λ, equal to or greater than 0.66 λ, equal to or greater than 0.75 λ, or equal to or greater than 1 λ. For example, according to certain embodiments where the operational frequency range is 2 GHz to 14 GHz, with the wavelength at the highest frequency, 14 GHz, being about 0.84 inches, the spacing from one radiating element to another radiating element is less than about 0.42 inches. According to certain embodiments, for this same operating range, the height of a radiating element from the base plate is less than about 0.42 inches.
As another example, according to certain embodiments where the operational frequency range is 3.5 GHz to 21.5 GHz, with the wavelength at the highest frequency, 21.5 GHz, being about 0.6 inches, the spacing from one radiating element to another radiating element is less than about 0.3 inches. According to certain embodiments, for this same operating range, the height of a radiating element from the base plate is less than about 0.3 inches. It should be appreciated decreasing the height of the radiating elements can improve the cross-polarization isolation characteristic of the antenna. It should also be appreciated that using a radome (an antenna enclosure designed to be transparent to radio waves in the operational frequency range) can provide environmental protection for the array. The radome may also serve as a wide-angle impedance matching (WAIM) that improves the voltage standing wave ration (VSWR) of the array at wide-scan angles (improves the impedance matching at wide-scan angles).
According to certain embodiments, more spacing between radiating elements eases manufacturability. However, as described above, a maximum spacing can be selected to prevent grating lobes at the desired scan volumes. According to certain embodiments, the selected spacing reduces the manufacturing complexity, sacrificing scan volume, which may be advantageous where scan volume is not critical.
According to certain embodiments, the size of the array is determined by the required antenna gain. For example, for certain application over 40,000 elements are required. For another example, an array of 128 elements may be used for bi-static radar.
Asymmetric Phased Array
According to certain embodiment an asymmetric design is employed to increase the manufacturability of the phased array antenna.
Each radiating element 710 includes a pair of metallic ears (716 and 718) that form a coplanar transmission line. Ground ear 718 is formed into the same block of material as base plate 714 and clustered pillars 712 and 730 and is effectively electrically terminated directly to base plate 714. As in the symmetric design described above, signal ear 716 can be connected to the center of a coaxial feed line. The edge of signal ear 716 is shaped to encapsulate clustered pillar 712, but the edge of ground ear 718 is substantially planar and does not wrap around clustered pillar 712. This enables ground ear 718 to be easily machined into the same base plate material or otherwise easily formed along with base plate 714.
Following is a description of the asymmetric design, according to certain embodiments. Unit cell 702 is shown in
According to certain embodiments, an asymmetric design is employed for a dual-polarized phased array antenna as shown in
According to certain embodiments, base plate 814, the clustered pillars (e.g., 862) and the ground ears (e.g., 864 and 866) are formed from conductive materials, such as a metal like aluminum, copper, gold, silver, beryllium copper, brass, and various steel alloys. According to certain embodiments, base plate 814, the clustered pillars (e.g., 862) and the ground ears (e.g., 864 and 866) are formed from a non-conductive material such as various plastics, including ABS, Nylon, PA, PBT, PC, PEEK, PEK, PET, Polyimides, POM, PPS, PPO, PSU, PTFE, or UHMWPE, that is plated or coated with a conductive material such as gold, silver, copper, or nickel. According to certain embodiments, base plate 814, the clustered pillars (e.g., 862) and the ground ears (e.g., 864 and 866) are a solid block of material with holes, slots, or cut-outs to accommodate the signal ears (e.g., 868 and 870) and connectors on the bottom side to connect feed lines. In other embodiments, base plate 814, the clustered pillars (e.g., 862) and the ground ears (e.g., 864 and 866) include cutouts to reduce weight.
According to certain embodiments, base plate 814, the clustered pillars (e.g., 862) and the ground ears (e.g., 864 and 866) are designed to be modular and base plate 814 includes features in the ends to mate with adjoining modules. Such interfaces may be designed to provide both structural rigidity and good cross-interface conductivity. In some embodiments, base plate 814, the clustered pillars (e.g., 862) and the ground ears (e.g., 864 and 866) can be manufactured in various ways including machined, cast, molded, and/or formed using wire-EDM. In some embodiments, holes or cut-outs in base plate 214 may be created by milling, drilling, wire EDM, or formed into the cast or mold used to create base plate 814, the clustered pillars (e.g., 862) and the ground ears (e.g., 864 and 866). Base plate 814 may be of various thicknesses depending on the design requirements of a particular application. Base plate 814 can provide structural support for each radiating element and clustered pillar as well as provide overall structural support for the array. For example, an array of thousands of radiating elements may have a base plate that is thicker than that of an array of a few hundred elements in order to provide the required structural rigidity for the larger dimensioned array. According to certain embodiments, the base plate is less than 6 inches thick. According to certain embodiments, the base plate is less than 3 inches thick, less than 1 inch thick, less than 0.5 inches thick, less than 0.25 inches thick, or less than 0.1 inches thick. According to certain embodiments, the base plate is between 0.2 and 0.3 inches thick.
Radiating Element
As described above, radiating elements (e.g., 410 of
An important design consideration in phased array antennas is the impedance matching of the radiating element. This impedance matching affects the achievable frequency bandwidth as well as the antenna gain. With poor impedance matching, bandwidth may be reduced and higher losses may occur resulting in reduced antenna gain.
As is known in the art, impedance refers, in the present context, to the ratio of the time-averaged value of voltage and current in a given section of the radiating elements. This ratio, and thus the impedance of each section, depends on the geometrical properties of the radiating element, such as, for example, element width, the spacing between the signal ear the ground ear, and the dielectric properties of the materials employed. If a radiating element is interconnected with a transmission line having different impedance, the difference in impedances (“impedance step” or “impedance mismatch”) causes a partial reflection of a signal traveling through the transmission line and radiating element. The same can occur between the radiating element and free space. “Impedance matching” is a process for reducing or eliminating such partial signal reflections by matching the impedance of a section of the radiating element to the impedance of the adjoining transmission line or free space. As such, impedance matching establishes a condition for maximum power transfer at such junctions. “Impedance transformation” is a process of gradually transforming the impedance of the radiating element from a first matched impedance at one end (e.g., the transmission line connecting end) to a second matched impedance at the opposite end (e.g., the free space end).
According to certain embodiments, transmission feed lines provide the radiating elements of a phased array antenna with excitation signals. The transmission feed lines may be specialized cables designed to carry alternating current of radio frequency. In certain embodiments, the transmission feed lines may each have an impedance of 50 ohms. In certain embodiments, when the transmission feed lines are excited in-phase, the characteristic impedance of the transmission feed lines may also be 50 ohms. As understood by one of ordinary skill in the art, it is desirable to design a radiating element to perform impedance transformation from this 50 ohm impedance into the antenna at the connector, e.g., connector 530 in
According to certain embodiments, instead of designing the phased array antenna for 50 ohm impedance into connector 530, the antenna is designed for another impedance into connector 530, such as 100 ohms, 150 ohms, 200 ohms, or 250 ohms, for example. According to certain embodiments, a radiating element is designed for impedance matching to some other value than free space (377 ohms), for example, when a radome is to be used.
According to certain embodiments, the radiating element is designed to have optimal impedance transfer from transmission feed line to free space. It will be appreciated by those of ordinary skill in the art, that the radiating element can have various shapes to effect the impedance transformation required to provide optimal impedance matching, as described above. The described embodiments can be modified using known methods to match the impedance of the fifty ohm feed to free space.
Referring again to
Referring to
As shown in
In addition to the shape, the thickness of a radiating element ear may also affect the impedance transformation of the radiating element. According to certain embodiments, the thickness is less than 0.5 inches or less than 0.25 inches. According to certain embodiments, the thickness is preferably less than 0.125 inches, less than 0.063, less than 0.032, less than 0.016, or less than 0.008 inches. According to certain embodiments, the thickness is between 0.035 and 0.045 inches. According to certain embodiments, the thickness is greater than 0.03 inches, greater than 0.1 inches, greater than 0.25 inches, greater than 0.5 inches, or greater than 1 inch. According to some embodiments, the thickness may be scaled with frequency (for example, the distance may be a function of the wavelength of the highest designed frequency). For example, according to some embodiments, the thickness can be less than 0.2 λ, less than 0.1 λ, less than 0.05 λ. or less than 0.01 λ. According to some embodiments, the thickness can be greater than 0.005 λ, greater than 0.01 λ, greater than 0.05 λ, or greater than 0.1 λ.
According to other embodiments, a radiating element, ear includes two lobes, four lobes, five lobes, or more. According to certain embodiments, instead of lobes, the radiating element ear includes comb-shaped teeth, saw-tooth shaped lobes, blocky lobes, or a regular wave pattern. According to some embodiments, ears of radiating elements have other shapes, for example they may be splines, or straight lines. Straight line designs may be desirable if the antenna array is designed to operate only at a single frequency, if for example, the frequency spectrum is polluted at other frequencies. As appreciated by one of ordinary skill in the art, various techniques can be used to simulate the impedance transformation of radiating elements in order to tailor the shapes of the inner-facing irregular surfaces to the impedance transformation requirements for a given phased array antenna design.
In addition to impedance matching, the shape of the inner-facing surfaces of the comb portions can affect the operational frequency range. Other design considerations may also affect the frequency range. For example, the shape of the capacitive coupling portion 590 and the manner in which it forms a capacitive interface with the adjoining clustered pillar can affect the frequency range. According to certain embodiments, for example, an antenna array according to certain embodiments, without a clustered pillar may have a lower frequency threshold of 5 GHz and the same array with the clustered pillar may have a lower frequency threshold of 2 GHz.
According to certain embodiments, a radiating element 510 can be designed with certain dimensions to operate in a radio frequency band from 3 to 22 GHz. For example, radiating element 510 may be between 0.5 inches and 0.3 inches tall (preferably between 0.45 inches and 0.35 inches tall) from the top of base plate 514 to the top of radiating element 510. According to some embodiments, the height of the radiating elements may be scaled with frequency (for example, the height may be a function of the wavelength of the highest designed frequency). For example, according to some embodiments, the height can be less than 2.0 λ, less than 1.0 λ, less than 0.75 λ, less than 0.5 λ, or less than 0.25 λ. According to some embodiments, the height can be greater than 0.1 λ, greater than 0.2 λ, greater than 0.5 λ, or greater than 1.0 λ.
Stem portions 570 and 572 may be between than 0.5 inches and 0.1 inches tall and preferably between 0.2 inches and 0.25 inches tall. Stem portions 570 and 572 may be scaled by the radiating element height. For example, the height of the stem portions may be equal to or less than ¾ of the element height, equal to or less than ⅔ the element height, equal to or less than ½ the element height, or equal to or less than ¼ of the element height. According to some embodiments, comb portions 580 constitute the remainder of the element height. According to some embodiments, comb portions 580 may be between 0.1 and 0.3 inches tall and preferably between 0.15 and 0.2 inches tall. According to certain embodiments, the distance from the outer edge of the capacitive coupling portion 590 of signal ear 516 to the outer edge of the capacitive coupling portion 590 of ground ear 518 may be between 0.15 inches and 0.30 inches and preferably between 0.2 and 0.25 inches. According to certain embodiments, these values are scaled up or down for a desired frequency bandwidth. For example, arrays designed for lower frequencies are scaled up (larger dimensions) and arrays designed for higher frequencies are scaled down (smaller dimensions).
Performance
Embodiments of phased array antennas described herein may exhibit superior performance over existing phased array antennas. For example, embodiments may exhibit large bandwidth, high scan volume, low cross polarization, and low average voltage standing wave ratio (VSWR), with small aperture and low cost.
According to certain embodiments, the phased array antenna is able to achieve greater than 5:1 bandwidth ratio, where the bandwidth ratio is the ratio of the frequency to the lowest frequency at which VSWR is less than 3:1 throughout the scan volume. Some embodiment may achieve greater than 6:1 bandwidth ratio or greater than 6.5:1 bandwidth ratio. Certain embodiments may achieve greater than 6.6:1 bandwidth ratio. According to certain embodiments, the phased array antenna is capable of achieving a frequency range from 2 to 30 GHz, where the frequency range is defined as the range of frequencies at which VSWR is less than 3:1 throughout the scan volume. Certain embodiment may achieve 3 to 25 GHz and certain embodiments may achieve 3.5 to 21.2 GHz. Certain embodiment may achieve ranges of, e.g., 1 to 30 GHz, 2 to 30 GHz, 3 to 25 GHz, and 3.5 to 21.5 GHz. According to certain embodiments, the phased array antenna can operate at a frequency of at least 1 GHz, at least 2 GHz, at least 3 GHz, at least 5 GHz, at least 10 GHz, at least 15 GHz, or at least 20 GHz. According to certain embodiments, the phased array antenna is designed to operate at a frequency of less than 50 GHz, less than 40 GHz, less than 30 GHz, less than 25 GHz, less than 22 GHz, less than 20 GHz, or less than 15 GHz. The capacitive coupling of the radiating elements, according to certain embodiments, can result in increased bandwidth because the array is matched at the low-frequency end.
Phased array antennas according to certain embodiments can achieve high scan volume. Reduced radiating element spacing, according to some embodiments (e.g., equal to or less than one-half the wavelength at the highest design frequency), can result in increased scan volume due to the reduction in grating lobes. Certain embodiments can have a scan volume of at least at least 30 degrees from broadside over full azimuth. In other words, the beam can be steered in a range of angles from 0 degrees (broadside) to at least 30 degrees from broadside over the full azimuth (in any direction on a plane parallel to the array plane) without producing grating lobes. Certain embodiments can have a scan volume of at least at least 45 degrees from broadside over full azimuth. Certain embodiments can have a scan volume of at least at least 60 degrees from broadside over full azimuth. According to some embodiments, the scan volume is at least 30 degrees with VSWR of less than 4:1. According to some embodiments, the scan volume is at least 45 degrees with VSWR of less than 3:1.
According to certain embodiments, the phased array antenna has low VSWR characteristics. VSWR measures how well an antenna is impedance matched to the transmission line to which it is connected (for example, using a Vector Network Analyzer, such as the Agilent 8510 VNA, according to known methods). The lower the VSWR, the better the antenna is matched to the transmission line and the more power is delivered to the antenna. Low VSWR is important in maximizing the gain of the antenna array, which can result in fewer required radiating elements, which results in reduced aperture, lower weight, and lower cost. According to certain embodiments, the average VSWR (statistical mean of VSWR values at some frequency) is below 5:1, below 3:1, or below 2.5:1. According to certain embodiments, the average VSWR is below 2.5:1 for plus or minus 45 degrees from broadside over full azimuth. According to certain embodiments, the average VSWR is below 1.8:1 for plus or minus 45 degrees from broadside over full azimuth. According to certain embodiments, the average VSWR is below 1.5:1 for plus or minus 45 degrees from broadside over full azimuth. According to some embodiments, the average VSWR is below 5:1, below 3:1, below 2.5:1, or below 1.5:1 for plus or minus 45 degrees from broadside over full azimuth over a frequency range of, e.g., 1 to 30 GHz, 2 to 30 GHz, 3 to 25 GHz, and 3.5 to 21.5 GHz.
In
Plot 950 is a plot of the s-parameter values for a unit cell of radiating elements with the clustered pillar (e.g., unit cell 202 in
The active VSWR across the operational frequency of a phased array antenna according to certain embodiments is plotted in
In accordance with the foregoing, frequency scaled ultra-wide spectrum phased array antennas can provide wide bandwidth, wide scan volume, and good polarization, in a low loss, lightweight, low profile design that is easy to manufacture. The unit cells may be scalable and may be combined into an array of any dimension to meet desired antenna performance.
Phased array antennas, according to some embodiments, may reduce the number of antennas which need to be implemented a given application by providing a single antenna that serves multiple systems. In reducing the number of required antennas, embodiments of the present invention may provide a smaller size, lighter weight alternative to conventional, multiple-antenna systems resulting in lower cost, less overall weight, and reduce aperture.
The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the techniques and their practical applications. Others skilled in the art are thereby enabled to best utilize the techniques and various embodiments with various modifications as are suited to the particular use contemplated.
Although the disclosure and examples have been fully described with reference to the accompanying figures, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosure and examples as defined by the claims.
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