Patent Application
20060033663
The invention relates generally to mobile platform communication systems. More specifically, the invention relates to combined optical and electromagnetic antenna systems that utilize a common aperture to transmit and receive both optical and electromagnetic signals.
Broadband communication access, on which our society and economy is growing increasingly dependent, is becoming more readily available to users on board mobile platforms such as aircraft, buses, ships, trains and automobiles. Typically, mobile platform communications systems that provide such access utilize electromagnetic communication signals, also generally referred to in the art as radio frequency (RF) signals, to communicate with a remote, typically ground based, system. To increase available bandwidth, some known mobile platform communication systems have implemented optical, i.e. laser, communication systems in addition to the electromagnetic systems.
Generally, known communication systems for mobile platforms that provide both optical/laser and electromagnetic modes of communication require separate optical and electromagnetic apertures. Thus, such systems generally include at least one optical terminal and at least one separate electromagnetic antenna mounted on the mobile platform. However, separate optical and electromagnetic apertures/antennas add additional equipment costs, add significant weight and occupy valuable space which may not be available on a given mobile platform.
Commonly, combined communication systems utilize satellite dishes, phased arrays and telescopes to provide for the communication of both optical and electromagnetic signals. For example, at least one known system includes a small planar electronically scanned electromagnetic phased array antenna and at least one separate optical phased array (OPA) terminal. However, the phased array antenna and the OPA must be implemented separately and care must be taken to implement both systems such that each performs to expectation at the expense of increased physical space consumption. Additionally, when separate optical and electromagnetic systems, specifically the optical terminals and electromagnetic antennas, are mounted on the mobile platform in close proximity, alignment and calibration become difficult to optimize. Therefore, set-up of such systems can be very time consuming and performance often inhibited.
Therefore, it would be desirable to add additional communications bandwidth by adding optical communications to a mobile platform communications system while minimizing the footprint of the exterior communications equipment, e.g. antenna and related electronics, on the mobile platform.
In one preferred implementation of the present invention an antenna system for communicating electromagnetic and optical signals using a common aperture is provided. The system includes at least one optical phased array terminal integrated with an optically transparent electromagnetic antenna such that the optically transparent electromagnetic antenna and the optical phased array terminal share a common aperture. The optically transparent electromagnetic antenna includes a substrate fabricated of a substantially non-conductive material that is substantially optically transparent to optical signals having a wavelength within a specific portion of the optical spectrum. An antenna element layer, including an array of electromagnetic antenna elements electrically connected by transmission lines and a plurality of phase shifters electrically connected to the electromagnetic antenna elements is disposed onto the substrate. The antenna elements and the transmission lines are fabricated of a conductive material that is deposited such that they are substantially optically transparent to optical signals having a wavelength within the specific portion of the optical spectrum. The phase shifters are fabricated of a semiconductor material that may or may not be transparent to optical signals.
The optically transparent electromagnetic antenna further includes various other layers. For example the optically transparent electromagnetic antenna may also include a ground plane layer and additionally layers for data, clock and a power distribution. Each of the layers is independently fabricated of a conductive material that is optically transparent to optical signals having a wavelength within the specific portion of the optical spectrum.
The features, functions, and advantages of the present invention can be achieved independently in various embodiments or may be combined in yet other embodiments.
The present invention will become more fully understood from the detailed description and accompanying drawings, wherein;
Corresponding reference numerals indicate corresponding parts throughout the several views of drawings.
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application or uses. Additionally, the advantages provided by the preferred embodiments, as described below, are exemplary in nature and not all preferred embodiments provide the same advantages or the same degree of advantages.
Electromagnetic antennas, such as the optically transparent electromagnetic antenna 26, are often generally referred to in the art as radio frequency (RF) antennas. The optically transparent electromagnetic antenna 26 is not restricted to use with RF signals, but is adapted for transmission and/or receipt of electromagnetic signals of other wavelengths, for example microwave signals. Generally, the optically transparent electromagnetic antenna 26 could transmit and/or receive signals having wavelengths between 2 GHz and 120 GHz. Thus, for convenience and clarity, the optically transparent electromagnetic antenna 26 will be referred to herein as the OT antenna 26. In a preferred embodiment, the OT antenna 26 is an optically transparent planar electronically scanned phased array antenna. For additional convenience and clarity, the optically phased array terminal(s) 30 will be referred to herein as the OPA terminal(s) 30.
The antennal element layer 42 includes a plurality of antenna elements 46 arranged and electrically connected by transmission lines 50 to form an array. The antenna elements 46 are polarized antenna elements. Particularly the antenna elements 46 can be left-hand, right-hand or linearly polarized. The transmission lines 50 are preferably fabricated to match the impedances of the antenna elements 46 to an array input impedance, e.g. 50 ohms. Additionally, in a preferred implementation, the antenna element layer 42 includes phase shifters 54, for example, microwave monolithic integrated circuit (MMIC) phase shifters, electrically connected to each antennal element 46 to provide electronic scanning for the OT antenna 26. In a preferred embodiment, the phase shifters 54 provide up to plus or minus fifty degrees of scan performance. The antenna layer 42, e.g. antenna elements 46 and the transmission lines 50 are fabricated of an optically transparent electrically conductive material deposited on the optically transparent substrate 38. For example, the antenna elements 46 and the transmission lines 50 can be fabricated from Indium Tin Oxide, gold arranged in a grid, or any other material that has good electrical conductive properties such as high conductive loss resistivity and can be deposited onto the substrate 38. The phase shifters 54 can be fabricated using standard semiconductors, e.g. silicon germanium or gallium arsenide, and mounted on the substrate 38 by non-conducting epoxy glue. As shown in
In a preferred implementation, the antenna elements 46 are gold deposited onto the substrate 38 in a rectilinear grid or mesh using lithography. That is, the antenna elements 46 are not solid, but form a screen-like element. Although, the rectilinear grid of the antenna elements 46 is not shown in
As illustrated in
Further yet, the OT antenna 26 illustrated in
Between each of the layers 42, 58, 66, 70 and 74 is a dichroic layer 78 fabricated from an optically transparent dichroic material, for example a polyimide, a vapor deposited silica spacer, an optically transparent epoxy, Mylar™ film, glass or quartz. The dichroic material is optically transparent to optical signals having a wavelength within the same portion of the optical spectrum as the antenna element layer 42, the ground plane layer 58, the data layer 66, the clock layer 70, the power layer 74 and the substrate 38. The thicknesses of the dichroic layers 78 are variable based on processing and design requirements of the OT antenna 26
As described above, the OT antenna 26 and the OPA terminal(s) 30 share a common aperture 36. Specifically, optical signals to and from the OPA terminal(s) 30 pass through the same aperture 36 as electromagnetic signals to and from the OT antenna 26. Therefore, optical signals to and from the OPA terminal(s) 30 must also pass through the OT antenna 26. The optically transparent material(s) used to fabricate the various components and layers of the OT antenna 26 allow the optical signals to pass through the OT antenna 26 with minimal loss. Electromagnetic signals are transmitted or received by energizing the various components and layers of the OT antenna 26, described above, without interference from the OT terminal(s) 30. In a preferred embodiment, a separate transmit antenna assembly 14 and a separate receive antenna assembly 14 are employed by the mobile platform communication system. In this embodiment, the transmit antenna assembly 14 is described above with reference to
In an alternate preferred embodiment, a single antenna assembly 14 is utilized for both transmitting and receiving optical and electromagnetic signals. In this embodiment, the single antenna assembly 14 would include the LNA components, a transmit/receive switch and the second power layer, as described above.
The present invention provides an optically transparent electromagnetic antenna 26 integrated with, e.g. placed over, an array 34 of optical phased array terminals 30. Thus, a completely integrated electromagnetic/optical phased array antenna is provided that requires minimal space to install and utilizes a common aperture.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
