This disclosure relates generally to antennas, and in particular to reconfigurable antennas.
Consumer and commercial demand for connectivity to data and media is increasing. Improving connectivity can be accomplished by decreasing form factor, increasing performance, and/or expanding the use cases of communication platforms. Transmitters and receivers of wireless data platforms present increased challenges when the transmitter and/or the receiver are moving.
Satellite communication is one context where at least one of the transmitter and receiver may be moving. For example, satellite communication delivery to a residential environment may include a fixed satellite dish and a moving satellite. In an example where satellite communication is delivered to a mobile platform (e.g. automobile, aircraft, watercraft) both the satellite and the mobile platform may be moving. Conventional approaches to address these movements include satellite dishes that may be coupled to mechanically steerable gimbals to point the satellite dish in the correct direction to send/receive the satellite data. However, the form factor of satellite dishes and mechanically moving parts limits the use contexts for these prior solutions, among other disadvantages. Other approaches have been attempted to decrease the form factor of antennas in wireless communication systems, but these approaches provide limited performance.
Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
Embodiments of a reconfigurable holographic antenna, a communication system that includes a reconfigurable holographic antenna, and a method of operating a reconfigurable holographic antenna are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Reconfigurable holographic antenna 199 uses meta-material technology to form transmit beams (e.g. signal 155) that are directed toward satellite 101 and to steer received beams (e.g. signal 105) to receivers for decoding. In one embodiment, the antenna systems are analog systems, in contrast to antenna systems that employ digital signal processing to electrically form and steer beams (such as phased array antennas). Reconfigurable holographic antenna 199 may be considered a “surface” antenna that is planar and relatively low profile, especially when compared to conventional satellite dish receivers.
Control module 280 is coupled to metamaterial layer 230 to modulate the array of tunable slots 210 by varying the voltage across the liquid crystal in
Optical holograms generate an “object beam” (often times an image of an object) when they are illuminated with the original “reference beam.” Radio Frequency (“RF”) holography is also possible using analogous techniques where a desired RF beam can be generated when an RF reference beam encounters an RF holographic diffraction pattern. In the case of satellite communications, the reference beam is in the form of a feed wave, such as feed wave 205 (approximately 20 GHz. in some embodiments). To “steer” a feed wave (either for transmitting or receiving purposes), an interference pattern is calculated between the desired RF beam (the object beam) and the feed wave (the reference beam). The interference pattern is driven onto the array of tunable slots 210 as a diffraction pattern so that the feed wave is “steered” into the desired RF beam (having the desired shape and direction). In other words, the feed wave encountering the holographic diffraction pattern “reconstructs” the object beam, which is formed according to design requirements of the communication system.
The holographic diffraction pattern may be recalculated dynamically (i.e. more than once per second) and driven onto the array of tunable slots as the mobile platform and/or the satellites move to keep up with the changing spatial relationship between the satellite(s) and the reconfigurable holographic antenna. Control module 280 may constantly receive location inputs from sensors (e.g. global positioning satellite (“GPS”) units) and/or networks (wired or wireless) so that it can properly calculate the interference pattern based on a spatial relationship between the reconfigurable holographic antenna and the satellite. When a reconfigurable holographic antenna is deployed in a fixed location (e.g. residential context) the holographic diffraction pattern may be calculated less often.
Metamaterial layer 230 also includes gasket layer 232 and patch layer 231. Gasket layer 232 is disposed between patch layer 231 and iris layer 233. Iris layer 233 may be a printed circuit board (“PCB”) that includes a copper layer as metal layer 236. Openings may be etched in the copper layer to form slots 212. Iris layer 233 is conductively coupled to waveguide 240 by conductive bonding layer 234, in
A voltage between patch layer 231 and iris layer 233 can be modulated to tune the liquid crystal within the slots 210. Adjusting the voltage across liquid crystal 213 changes the orientation of liquid crystal 213 within the chamber, which in turn varies the capacitance of slot 210. Accordingly, the reactance of slot 210 can be varied by changing the capacitance. Resonant frequency of slot 210 also changes according to the equation
where ω is the resonant frequency of slot 210 and L and C are the inductance and capacitance of slot 210, respectively. The resonant frequency of slot 210 affects the energy radiated from feed wave 205 propagating through the waveguide. As an example, if feed wave 205 is 20 GHz., the resonant frequency of a slot 210 may be adjusted (by varying the capacitance) to 17 GHz. so that the slot 210 couples substantially no energy from feed wave 205. Or, the resonant frequency of a slot 210 may be adjusted to 20 GHz. so that the slot 210 couples energy from feed wave 205 and radiates that energy into free space. Although the examples given are digital (fully radiating or not radiating at all), full grey scale control of the reactance, and therefore the resonant frequency of slot 210 is possible with voltage variance over an analog range. Hence, the energy radiated from each slot 210 can be finely controlled so that detailed holographic diffraction patterns can be formed by the array of tunable slots.
Sidewalls 243, waveguide floor 245, and ridge 220 may be a contiguous structure. In one embodiment, an extruded metal (e.g. extruded aluminum) forms the contiguous structure. Alternatively, the contiguous structure may be milled/machined from solid metal stock. Other techniques and materials may be utilized to form the contiguous waveguide structure.
Ridge 220 is configured to reduce mutual coupling between proximate (e.g. adjacent) tunable slots 210. Of course, the amount of energy of feed wave 205 that each tunable slot 210 radiates changes in response to the reactance to which the tunable slot is tuned. But, tunable slots are also prone to mutual coupling effects where the reactance from one tunable slot can cause unintended energy radiation (or lack thereof) of a proximate tunable slot 210. This unintended radiation skews the intended holographic pattern that is driven onto the array of tunable slots, which adversely affects the shaping or steering of feed wave 205. However, experimental data and modeling by Applicant indicated that including a ridge (such as ridge 220) into the waveguide (e.g. waveguide 240) reduced mutual coupling effects between proximate tunable slots 210. Thus, configuring the ridge to reduce mutual coupling made the actual steered beam (object beam) closer to the theoretical steered beam that was calculated to be the result of the feed wave encountering the holographic diffraction pattern driven onto the array of tunable slots 210. Applicant's experiments and modeling also suggested that including ridge structures into waveguides that have a metamaterial layer having tunable slots also increased bandwidth of the waveguides, which may allow for dual-band transmitting and receiving functions from a single aperture. Furthermore, using one or more ridges permits operating at a point of much lower dispersion in the propagation constant of the waveguide, thus improving formation in the steered beam. Additionally, ridges more tightly confine or concentrate feed wave 205 around the ridge resulting in less amplitude and phase perturbations that degrade holographic beam formation. As a manufacturing benefit, the more tightly confined feed wave 205 around the ridge reduces susceptibility to loss incurred around the edges of the waveguide. For example, less than ideal ohmic bonding between sidewalls 243 and conductive bonding layer 234 would not lose as much energy with a magnetic field generated by feed wave 205 concentrated around ridge 220. Concentrating/confining feed wave around ridge 220 also allows for more densely spaced waveguide channels, when a plurality of waveguide channels is used in reconfigurable holographic antenna 299. More densely spaced waveguides allow for more compact form factors of the antenna. Ridge 220, in addition to other ridges described in this disclosure may improve their corresponding antennas as described here.
The non-planar configuration of metamaterial layer 330/430 of reconfigurable holographic antennas 399 and 499 may achieve wider scan angles orthogonal to the waveguide channel when compared to the planar nature of metamaterial layer 230. It is appreciated that the angle of the illustrated slopes in
In
One way to fabricate reconfigurable holographic antenna 599A is to start with a double-ridge waveguide (made from extruded metal for example) and cut the top of the double-ridge waveguide off. Conductive material 555 and/or metal material 565 may be cut with the double-ridge waveguide or added to the double-ridge waveguide after it is cut. The double-ridge waveguide may be brazed into conductive material 555 if it is combined with materials 555 and 565 after cutting the top off. Metal material 565 may be metal or a metallized plastic. Dielectric 517 can then be formed or inserted into the waveguide structure. Next, metamaterial layer 530A is conductively bonded to conductive material 555 by way of conductive bonding layer 534. Conductive material 555 may be a conductive adhesive/epoxy or a filler metal that is bonded to conductive bonding layer 534 by a brazing process. Adhesives may also be used to secure metamaterial layer 530A to the double-ridge waveguide that includes double-ridge waveguide 540A, conductive material 555, and metal material 565. In effect, metamaterial layer 530A (and its metal layers(s) 536) replaces the cut off top of the double-ridge waveguide as the top lid of waveguide 540A with the added benefit that metamaterial layer 530A includes tunable slots 510.
To fabricate reconfigurable holographic antenna 599B, the irises/slots 512 of the tunable slots are milled into the top of the contiguous waveguide structure (e.g. extruded aluminum) that includes sidewalls 543, floor 545, and ridges 520 and 521. The slot is then filled with a dielectric (e.g. Rexolite adhesive) to define the floor of the chamber for liquid crystal 513. Spacers 539 can be adhered to the contiguous waveguide structure (illustrated as solid black), conductive material 555, and metal material 565. Then liquid crystal 513 is placed into the chamber and patch layer 531 is laminated to gasket layer 532 to seal liquid crystal 513.
Waveguides 643, 645, and 647 are conductively coupled to metamaterial layer 630 by way of conductive bonding layer 634. Metamaterial layer 630 includes a two-dimensional array of tunable slots 610. The architecture of metamaterial layer 630 is similar to metamaterial layer 230 except that the arrangement of the array of tunable slots is different. The array of tunable slots 610 includes a first, second, third, and fourth sub-array of tunable slots.
The first sub-array includes tunable slots 610A; the second sub-array includes tunable slots 610B; the third sub-array includes tunable slots 610C; and the fourth sub-array includes tunable slots 610D. Tunable slots 610A each include a patch 611A, liquid crystal 613A and an iris 612A defined by metal layer 636; tunable slots 610B each include patch 611B, liquid crystal 613B, and an iris 612B defined by metal layer 636; tunable slots 610C each include patch 611C, liquid crystal 613C, and an iris 612C defined by metal layer 636; and tunable slots 610D each include patch 611D, liquid crystal 613D, and an iris 612D defined by metal layer 636.
The first sub-array of tunable slots is disposed above narrow-wall waveguide 643, the second and third sub-array of tunable slots are disposed above broadwall waveguide 645, and the fourth sub-array of tunable slots is disposed above narrow-wall waveguide 647. In
The first sub-array of tunable slots and the second sub-array of tunable slots are positioned to constructively interfere to generate a first circularly polarized wave in response to the feed wave. The third sub-array of tunable slots and the fourth sub-array of tunable slots are positioned to constructively interfere to generate a second circularly polarized wave in response to the feed wave. The first and second circularly polarized beams can be used to communicate downlink signal 105 and uplink signal 155. Microwave communication inherently includes circularly polarized beams so native generation of circularly polarized beams is beneficial in satellite communication systems. Prior approaches to generate circularly polarized beams include adding an extra layer to the antenna to circularly polarize the linearly polarized beams generated by the antenna elements. Generating circularly polarized beams with reconfigurable holographic antenna 699 natively allows for antennas with reduced thickness as the circular polarizing layer need not be added.
Metamaterial layer 730 includes an array of tunable slots 710 similar to metamaterial layer 630. The array of tunable slots 710 includes a first, second, third, and fourth sub-array 786, 787, 788, and 789, respectively. The first sub-array includes tunable slots 710A; the second sub-array includes tunable slots 710B; the third sub-array includes tunable slots 710C; and the fourth sub-array includes tunable slots 710D.
Ridge 820A is configured to facilitate a first communication signal, in
Ridge 820B is configured to facilitate a second communication signal, in
In one embodiment, ridge 820A and the first array of tunable slots 810A is configured to receive the first communication signal on a first band (e.g. approximately 20 GHz.) and the ridge 820B and the second array of tunable slots 810B is configured to receive the second communication signal on a second band (e.g. approximately 12 GHz.) having a different frequency than the first band. In this embodiment, the first and second communication signals can be received simultaneously by reconfigurable holographic antenna 899.
In another embodiment, ridge 820A and the first array of tunable slots 810A is configured to receive the first communication signal on a first band and ridge 820B and the second array of tunable slots 810B is configured to transmit the second communication signal on the first band (which has the same frequency). In this embodiment, the first communication signal is being received simultaneously with transmitting the second communication signal.
Ridge 820A and ridge 820B may have tapered edges configured to reduce eddy currents induced by the first communication signal and the second communication signal, respectively. Ridge 820A and ridge 820B are disposed lengthwise down double-ridge waveguide 840, in
Reconfigurable holographic antenna 899 may also be configured for dual polarization reception by configuring ridge 820A to receive a right-hand circularly polarized first communication signal and by configuring ridge 820B to receive a left-hand circularly polarized second communication signal. Dual polarization reception is possible in both even-mode and odd-mode. Dual polarization reception is advantageous when the native transmission of the first communication signal and the second communication signal are right-hand circularly polarized and left-hand circularly polarized, respectively.
The waveguide structures described in
The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
This application is a non-provisional application that claims priority to U.S. Provisional Application No. 61/934,608 entitled “Waveguide Feed Structures for Reconfigurable Holographic Metamaterial Surface Antenna,” filed Jan. 31, 2014. Provisional Application No. 61/934,608 is hereby incorporated by reference. This application is related to a non-provisional application entitled, “Waveguide Feed Structures for Reconfigurable Antenna,” filed on the same day.
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