Patent Application
20090184881
1. Technical Field
This disclosure relates to antenna system. Particularly, this disclosure relates to phased array antenna systems.
2. Description of the Related Art
An essential component of any wireless communications system is the antenna that transmits and/or receives the electromagnetic signals. One conventional antenna structure, often employed in communications satellites, includes a reflector that has received or transmitted signals “reflected” off it and focused to be collected in one or more feed horns. The reflector and feed horn configuration is typically manipulated to direct or “point” the coverage area of such an antenna. Newer antenna systems may employ phased arrays where an array of discrete antenna elements are used in combination to transmit or receive the desired electromagnetic signal. Such phased array systems can dispense with much of the pointing manipulation typically required with conventional reflectors because the output of the discrete antenna elements of the phased array, through the signal processing, create interference patterns of RF energy that create the desired coverage area and coverage signal strength.
A conventional design approach in developing a phased array antenna (or even a conventional reflector) divides the electrical signal design from the structural design. Thus, the signal design will involve developing the combination of radiating elements, waveguides, and filters in order to achieve the desired coverage and signal strength. Separately, the structural design will be developed to derive the structural configuration for the antenna to support the arrangement of electrical components. This approach can yield results that are less than optimal.
Thus, conventional antenna designs utilize separate structural members to support the antenna. Such conventioanl antenna designs also use individually fabricated feed horns or antenna elements. In conventional antennas, the structural members must be separately fabricated and assembled. This adds extra weight, volume, and fabrication cost. Weight and volume are particularly significant constraints in the design of antenna on spacecraft. For example, lower mass and volume antennas can allow the spacecraft to launch on smaller, less-costly launch vehicles. In addition, the installation of individual horns or antenna elements adds complexity to the dimensional stack up and flow time assembly. Some antenna designs have been developed to alleviate some of these problems.
U.S. Pat. No. 7,046,209, issued May 16, 2006 to McCarville et al. discloses an antenna aperture having electromagnetic radiating elements embedded in structural wall portions of a honeycomb-like core. Independent wall sections each having a plurality electromagnetic radiating elements are formed into the honeycomb-like core. Feed portions of each radiating element form teeth that are copper plated before being assembled onto a back skin panel. Each of the teeth are then generally machined flush with a surface of the back skin to present electrical contact pads which enable electrical coupling to each of the radiating elements by an external antenna electronics board.
However, there is still a need in the art for apparatuses and methods for antenna systems that are structurally efficient, with reduced mass and/or volume. In addition, there is a need for such apparatuses and methods to deliver high performance spacecraft antenna on less expensive launch vehicles. There is also a need for such apparatuses and methods to provide phased array antenna that are cheaper, lighter and more powerful than convention antenna systems. There is particularly a need for such methods and apparatuses in spacecraft applications. These and other needs are met by the present disclosure as detailed hereafter.
A structural phased array antenna and method for manufacturing are disclosed. An integrated structural antenna aperture can be used to reduce net weight, cost, and volume where an array of antenna elements are incorporated into a structural member, e.g. in a spacecraft. A structural material layer, such as a structural foam, may be used with an array of individual antenna element cavities machined into the layer. The antenna element cavities are lined with a conductive material, such as plated aluminum. Facesheets may be bonded to the front and/or backside of the structural material layer in order to increase strength using an RF transparent material. The array of antenna elements may be coupled to filters at the back side of structural material layer.
Embodiments of the disclosure allow for less backup structure to support the phased array. In addition, fabrication of the multiple antenna elements in the structural material layer may be machined as a group, rather than individually. This can accelerate overall production of the antenna.
Embodiments of the disclosure can provide large cost savings over the existing antenna solutions by reducing the overall mass and volume of a spacecraft. This can allow the spacecraft to be launched on a smaller, less-costly launch vehicles. Thus, the overall savings can be significant. Embodiments of the disclosure can enable the design, manufacturing, and testing of phased array antennas, particularly space-based antenna, that are cheaper, lighter, and more powerful than current antennas.
A typical embodiment of the disclosure comprises a phased array antenna including a supporting material layer having an array of antenna element cavities, each antenna element cavity of the array of antenna element cavities having an aperture open to a front side of the supporting material layer and an interface open to a back side of the supporting material layer, and a conductive layer lining each antenna element cavity of the array of antenna element cavities. The supporting material layer may comprise a structural foam, such as polymethacrylimide. In some embodiments of the disclosure, the conductive layer may comprise plated aluminum.
The phased array antenna may be employed such that the supporting material layer comprises a support in an underlying structure for the phased array antenna. In one example, the support in the underlying structure for the phased array antenna may be disposed on a spacecraft. The structural efficiency of the phased array yields a lower overall mass, an important consideration in spacecraft design.
In further embodiments of the disclosure, one or more facesheets may be affixed to at least one of the front side and the back side of the supporting material layer to provide additional structural support. Typically, the one or more facesheets comprise a substantially RF transparent material.
In some embodiments of the disclosure, the phased array antenna may also include an array of antenna element filters, each filter of the array of antenna element filters coupled to the interface of each antenna element cavity of the array of antenna element cavities.
In a similar manner, a typical method of manufacturing a phased array antenna comprises the steps of machining an array of antenna element cavities in a supporting material layer, each antenna element cavity of the array of antenna element cavities having an aperture open to a front side of the supporting material layer and an interface open to a back side of the supporting material layer, and lining each antenna element cavity of the array of antenna element cavities with a conductive layer lining. In some embodiments of the disclosure, lining each antenna element cavity of the array of antenna element cavities of the array with the conductive layer lining comprises plating the conductive layer onto a mandrel matching each antenna element cavity, bonding the conductive layer into each antenna element cavity using the mandrel, and removing the mandrel leaving the conductive layer bonded into each antenna element cavity. Method embodiments of the disclosure may be further modified consistent with the apparatus and system embodiments described herein.
In addition, a phased array antenna embodiment may include a material layer means for supporting a structure, the material layer having an array of antenna element cavities, each antenna element cavity of the array of antenna element cavities having an aperture open to a front side of the material layer and an interface open to a back side of the material layer, and a conductive layer lining each antenna element cavity of the array of antenna element cavities. The apparatus embodiments of the disclosure may be further modified consistent with the method and system embodiments described herein.
Referring now to the drawings in which like reference numbers represent corresponding parts throughout:
1. Overview
As previously mentioned, embodiments of the disclosure are directed to structural phased array antennas and methods for their manufacturing. An array of antenna elements can be incorporated into a structural member of a spacecraft where a structural material layer, such as a structural foam, has an array of individual antenna element cavities machined into the layer. The antenna element cavities are lined with a conductive material, such as plated aluminum. Facesheets may also be bonded to the front and/or backside of the structural material layer in order to increase strength and/or stiffness using an RF transparent material. The array of antenna elements may be coupled to filters at the back side of structural material layer that lead to the remainder of the communications signal electronics.
Embodiments of the disclosure allow for less backup structure to support the phased array, thus reducing the weight, cost, and volume. Embodiments of the disclosure afford a unique integrated solution for the aperture antenna elements (feed horns) and structure. This can yield a net lower cost and weight. Additional benefit can be derived from the ability to fabricate the aperture antenna elements together rather than individually as with conventional antennas. Thus, the multiple antenna elements in the structural material layer may be machined as a group, rather than individually produced in the traditional manner. This can further accelerate overall production of the antenna.
Embodiments of the disclosure can provide a significant cost savings over the existing antenna solutions by reducing the overall mass and volume of a spacecraft. This can allow the spacecraft to be launched on smaller, less-costly launch vehicles. Thus, the overall savings can be significant. Embodiments of the disclosure can enable the design, manufacturing, and testing of phased array antennas, particularly space-based antenna, that are cheaper, lighter, and more powerful than current antennas.
2. Structural Phased Array Antenna
Finally, one or more facesheets 114A, 114B may be affixed to one or both of the front and back side of the supporting material layer 104 in order provide additional structural support. The facesheets 114A, 114B should be constructed from an RF transparent material so they do not interfere with the function of the antenna elements 102 in the operating antenna 100. The facesheets are optional, but may be highly desirable in most applications. In use the interface 110 of each antenna element 102 will be coupled to the antenna electronics (e.g. a waveguide or filter). This may be accomplished through a bolted interface (using metal or non-metallic bolts) or possibly by bonding. Accordingly, any facesheet 114B on the back side of the supporting material layer 104 should have cutouts that minimally allow connection to the conductive layer 112 at the interface 110 of each antenna element 102. In addition, to achieve acceptable passive intermodulation (PIM) characteristics, no metal (conductive) materials should be employed for components (e.g., the front side facesheet 114A) disposed above the aperture plane of the antenna elements, i.e., the plane at the front side of the supporting material layer 104.
Various materials may be used in the construction of the structural phased array antenna 100. For space applications, material properties should meet higher standards than terrestrial applications. For example, materials must exhibit limited outgassing (e.g., <1% total mass loss and <0.1% volatile condensable material). Similarly, the materials should be qualified for a wide temperature range (e.g., −15° C. to +120° C.) for space applications. The supporting material layer 104 should be a non-conductive material to eliminate interference with operation of the antenna elements 102. (Conductive materials may be used for the supporting material layer 104, but this will require isolation from the antenna elements, complicating the detailed design.) Structural foams, such as polymethacrylimide, are well suited for use as the supporting material layer 104. The material of the supporting material layer 104 may comprise a homogenous layer (e.g. such as with a structural foam) or a heterogenous layer (e.g., utilizing a combination of materials). The conductive layer 112 lining each of the antenna elements 102 may be a plated metal, such as aluminum, copper, nickel, or gold. Thus, the conductive layer 112 may be extremely thin, e.g. on the order of 1 mil thickness. The minimal thickness coupled with aluminum lining produces a very light weight configuration. The facesheets 114A, 114B may be constructed using Cyanate-Ester Astro-Quartz or fiberglass. Both front and back facesheets can employ similar coefficient of thermal expansion properties to reduce warping of the antenna.
Although most phased array antennas are developed using identical antenna elements, it should be noted that the size and separation of the antenna elements 104 are determined from the combination of structural requirements (strength, stiffness, etc.) and electrical requirements (frequency, power, pointing range, etc.) in the overall design of the antenna 100, as will be understood by those skilled in the art. It should also be noted that although the antenna elements 102 are shown as being identical, this is not required; varying sizes of individual antenna elements and sub-arrays of elements may be employed in accordance with the principles described herein as will be understood by those skilled in the art. In addition, although the exemplary structural phased array antenna 100 is described as a receive antenna, embodiments of the disclosure are not limited to receive antennas. The principles described herein are also directly applicable to transmit antenna, as will be understood by those skilled in the art.
The structural material layer may be made from a structural foam known as ROHACELL® HF, manufactured by Degussa, that is used in antennas, radomes and X-ray tables. This is a polymethacrylimide (PMI) closed-cell rigid foam plastic that does not contain any chlorofluorocarbons (CFCs). The structural foam has a density of approximatley 2.0 lb/ft3, a compressive strength of approximatley 58 psi, a tensile strength of approximatley 145 psi, and meets outgassing requirements described above. In addition, the foam has a survival temperature in excess of 160° C.
The satellite 400 is only an example; those skilled in the art will appreciate embodiments of the disclosure may be applied to any spacecraft. In addition, it should be noted that structural phased array antennas in accordance with the disclosure are not limited to satellite applications, but may be employed with any other type of spacecraft or even terrestrial applications. However, the structural efficiency afforded by embodiments of the disclosure make them particularly useful in satellites because limited mass and volume are always critical constraints in any space-borne system.
As shown above, a phased array antenna in accordance with the disclosure is integrated into a supporting framework. Conventional antennas typically use parasitic weight to provide the backbone of the supporting structure. Embodiments of the disclosure, on the other hand, can reduce the parasitic weight because they provide an integrated structural, load-bearing member. Thus, embodiments of the disclosure enable net cost, weight, and volume savings while still providing equal RF performance of existing antenna solutions.
Embodiments of the disclosure surpass existing solutions because they allow the antenna to be a self-supporting structure. This can reduce or eliminate any parasitic weight as compared with the structural members of existing solutions. This can also improve the installation time and the required envelope due dimensional stack up associated with installing individual feed horns in a conventional antenna.
3. Method of Manufacturing a Structural Phased Array Antenna
Embodiments of the disclosure also encompass a method of manufacturing a structural phased array antenna consistent with the foregoing apparatus and process descriptions.
In addition to the integrated structural phased array, embodiments of the disclosure also provide for ease of installation with the collective fabrication of a “sub-array”. In an effort to further reduce weight and assembly time, embodiments of the disclosure may also include the fabrication of a “sub-array” of antenna elements (which are then integrated into a larger array), as opposed to the fabrication and installation of individual horns as with conventional antennas.
This concludes the description including the preferred embodiments of the present disclosure. The foregoing description including the preferred embodiment of the disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit embodiments of the disclosure to the precise forms disclosed. Many modifications and variations are possible within the scope of the foregoing teachings. Additional variations of the present embodiments of the disclosure may be devised without departing from the inventive concept as set forth in the following claims.
