Patent Grant
6930653
1. Statement of the Technical Field
The present invention relates to the field of antennas, and more particularly to adjustable reflectors and sub-reflectors using fluidic dielectrics.
2. Description of the Related Art
Typical satellite antenna systems use either parabolic reflectors or shaped reflectors to provide a specific beam coverage, or use a flat reflector system with an array of reflective printed patches or dipoles on the flat surface. These “reflect array” reflectors used in antennas are designed such that the reflective patches or dipoles shape the beam much like a shaped reflector or parabolic reflector would, but are much easier to manufacture and package on a spacecraft.
However, satellites typically are designed to provide a fixed satellite beam coverage for a given signal and may be limited in bandwidth by the structure of the reflectors. For example, Continental United States (CONUS) beams are designed to provide communications services to the entire continental United States. Once the satellite transmission system is designed and launched, changing the beam patterns to improve the operational bandwidth would be difficult.
The need to change the beam pattern provided by the satellite has become more desirable with the advent of direct broadcast satellites that provide communications services to specific areas and possibly on different frequencies ranges. Without the ability to change beam patterns and coverage areas as well as to flexibly use multiple frequency ranges, additional satellites must be launched to provide the services to possible future subscribers, which increases the cost of delivering the services to existing customers.
Some present systems are designed with minimal flexibility in the delivery of communications services. For example, a symmetrical Cassegrain antenna that uses a movable feed horn, defocuses the feed and zooms circular beams over a limited beam aspect ratio of 1:2.5. This scheme has high sidelobe gain and low beam-efficiency due to blockage by the feed horn and the subreflector of the Cassegrain system. Further, this type of system splits or bifurcates the main beam for beam aspect ratios greater than 2.5, resulting in low beam efficiency values. Other systems attempt to alter beam width and gain by using multiple feed horns. In any event, most of these systems will have a main reflected signal that will be interfered with by a sidelobe of the radiator or feed horn.
In another system as shown in
More specifically,
In any event, a programmable array such as the reflector array 206 can be reconfigured on-orbit. Satellites using the reflector array 206 can be designed for use in clear sky conditions, and, when necessary, the beams emanating from the reflector array 206 can be shaped to provide higher gains over geographic regions having rain or other poor transmission conditions, thus providing higher margins during clear sky conditions.
It can be seen, then, that there is a need in the art for an antenna system that can be alternatively reconfigured in-flight without the need for complex systems. It can also be seen that there is a need in the art for a communications system that can be reconfigured in-flight that has high beam-efficiencies and high beam aspect ratios. An alternative arrangement for achieving the advantages of the antenna of FIG. 1 and other advantages as will be further described below utilizes fluidic dielectrics in accordance with the present invention.
Two important characteristics of dielectric materials are permittivity (sometimes called the relative permittivity or εr) and permeability (sometimes referred to as relative permeability or μr) The relative permittivity and permeability determine the propagation velocity of a signal, which is approximately inversely proportional to √{square root over (με)}. The propagation velocity directly effects the electrical length of a transmission line and therefore the amount of delay introduced to signals that traverse the line.
Further, ignoring loss, the characteristic impedance of a transmission line, such as stripline or microstrip, is equal to √{square root over (Ll/Cl)} where Ll is the inductance per unit length and Cl is the capacitance per unit length. The values of Ll and Cl are generally determined by the permittivity and the permeability of the dielectric material(s) used to separate the transmission line structures as well as the physical geometry and spacing of the line structures.
For a given geometry, an increase in dielectric permittivity or permeability necessary for providing increased time delay will generally cause the characteristic impedance of the line to change. However, this is not a problem where only a fixed delay is needed, since the geometry of the transmission line can be readily designed and fabricated to achieve the proper characteristic impedance. Analogously, wave propagation delays and energy beam patterns through dielectric materials in reflector and/or sub-reflector based antenna systems are typically designed accordingly with a fixed dielectric permittivity or permeability. When various time delays are needed for specific energy shaping or beam forming requirements, however, such techniques have traditionally been viewed as impractical because of the obvious difficulties in dynamically varying the permittivity and/or permeability of a dielectric board substrate material. Accordingly, the only practical solution has been to design variable delay lines using conventional fixed length RF transmission lines with delay variability achieved using a series of electronically controlled switches. Such schemes would be impracticable and overly complicated for a reflector or sub-reflector based antenna.
The invention concerns an antenna utilizing a reflector and/or sub-reflector which includes at least one cavity and the presence, absence or mixture of fluidic dielectric in the cavity. A pump or a composition processor, for example, can be used to add, remove, or mix the fluidic dielectric to the cavity in response to a control signal. A propagation delay or beam pattern or gain of a radiated signal through the antenna is selectively varied by manipulating the fluidic dielectric within the cavity.
The fluidic dielectric can be comprised of an industrial solvent. If higher permeability is desired, the industrial solvent can have a suspension of magnetic particles contained therein. The magnetic particles can be formed of a wide variety of materials including those selected from the group consisting of ferrite, metallic salts, and organo-metallic particles.
In accordance with a first embodiment of the present invention, a reflector antenna comprises a reflector unit having a plurality of cavities, at least one fluidic dielectric having a permittivity and a permeability, and at least one composition processor adapted for dynamically changing a composition of the fluidic dielectric to vary at least the permittivity or permeability in any of the plurality of cavities. The antenna further comprises a controller for controlling the composition processor to selectively vary at least one among the permittivity and the permeability in at least one of the plurality of cavities in response to a control signal.
In accordance with a second embodiment of the present invention, a reflector antenna comprises a reflector unit having a plurality cavities, at least one fluidic dielectric having a permittivity and a permeability, and at least one fluidic pump unit for moving at least one fluidic dielectric among at least one of the plurality of cavities and a reservoir for adding and removing the fluid dielectric to at least one of the plurality of cavities in response to a control signal.
In yet another embodiment of the present invention, a method for energy shaping a radio frequency (RF) signal comprises the steps of propagating the RF signal through a reflector antenna and dynamically adding and removing a fluidic dielectric to at least one cavity within the reflector antenna to vary a propagation delay of the RF signal.
Although the antenna of
Referring to
Referring again to
For the purpose of introducing time delay or energy shaping in accordance with the present invention, the exact size, location and geometry of the cavity structure as well as the permittivity and permeability characteristics of the fluidic dielectric can play an important role. The processor and pump or flow control device (102 and 104) can be any suitable arrangement of valves and/or pumps as may be necessary to independently adjust the relative amount of fluidic dielectric contained in the cavities 106. Even a MEMS type pump device (not shown) can be interposed between the cavity and a reservoir for this purpose. However, those skilled in the art will readily appreciate that the invention is not so limited as MEMS type valves and/or larger scale pump and valve devices can also be used as would be recognized by those skilled in the art.
The flow control device can ideally cause the fluidic dielectric to completely or partially fill any or all of the cavities 106 (or cavities 406 and/or 416 in FIG. 4). The flow control device can also cause the fluidic dielectric to be evacuated from the cavity into a reservoir (not shown). According to a preferred embodiment, each flow control device is preferably independently operable by controller 102 so that fluidic dielectric can be added or removed from selected ones of the cavities 106 to produce the required amount of delay indicated by a control signal 105.
Propagation delay of signals in the dielectric lens antenna can be controlled by selectively controlling the presence and removal or mixture of fluidic dielectric from the cavities 106. Since the propagation velocity of a signal is approximately inversely proportional to √{square root over (με)}, the different permittivity and/or permeability of the fluidic dielectric as compared to an empty cavity (or a cavity having a different mixture with different dielectric properties) will cause the propagation velocity (and therefore the amount of delay introduced)) to be different.
According to yet another embodiment of the invention, different ones of the cavities 106 can have different types of fluidic dielectric contained therein so as to produce different amounts of delay for RF signals traversing the antenna 100. For example, larger amounts of delay can be introduced by using fluidic dielectrics with proportionately higher values of permittivity and permeability. Using this technique, coarse and fine adjustments can be effected in the total amount of delay introduced or in the desired energy shaping of the radiated signal.
As previously noted, the invention is not limited to any particular type of structure. The cavities do not necessarily need to be tubes or in concentric arrangements as shown, but can be formed in various arrangements to accomplish the objectives of the present invention.
Composition of the Fluidic Dielectric
The fluidic dielectric can be comprised of any fluid composition having the required characteristics of permittivity and permeability as may be necessary for achieving a selected range of delay. Those skilled in the art will recognize that one or more component parts can be mixed together to produce a desired permeability and permittivity required for a particular time delay or radiated energy shape. In this regard, it will be readily appreciated that fluid miscibility can be a key consideration to ensure proper mixing of the component parts of the fluidic dielectric.
The fluidic dielectric also preferably has a relatively low loss tangent to minimize the amount of RF energy lost in the antenna. Aside from the foregoing constraints, there are relatively few limits on the range of materials that can be used to form the fluidic dielectric. Accordingly, those skilled in the art will recognize that the examples of suitable fluidic dielectrics as shall be disclosed herein are merely by way of example and are not intended to limit in any way the scope of the invention. Also, while component materials can be mixed in order to produce the fluidic dielectric as described herein, it should be noted that the invention is not so limited. Instead, the composition of the fluidic dielectric could be formed in other ways. All such techniques will be understood to be included within the scope of the invention.
Those skilled in the art will recognize that a nominal value of permittivity (εr) for fluids is approximately 2.0. However, the fluidic dielectric used herein can include fluids with higher values of permittivity. For example, the fluidic dielectric material could be selected to have a permittivity values of between 2.0 and about 58, depending upon the amount of delay or energy shape required.
Similarly, the fluidic dielectric can have a wide range of permeability values. High levels of magnetic permeability are commonly observed in magnetic metals such as Fe and Co. For example, solid alloys of these materials can exhibit levels of μr in excess of one thousand. By comparison, the permeability of fluids is nominally about 1.0 and they generally do not exhibit high levels of permeability. However, high permeability can be achieved in a fluid by introducing metal particles/elements to the fluid. For example typical magnetic fluids comprise suspensions of ferro-magnetic particles in a conventional industrial solvent such as water, toluene, mineral oil, silicone, and so on. Other types of magnetic particles include metallic salts, organo-metallic compounds, and other derivatives, although Fe and Co particles are most common. The size of the magnetic particles found in such systems is known to vary to some extent. However, particles sizes in the range of 1 nm to 20 μm are common. The composition of particles can be selected as necessary to achieve the required permeability in the final fluidic dielectric. Magnetic fluid compositions are typically between about 50% to 90% particles by weight. Increasing the number of particles will generally increase the permeability.
Example of materials that could be used to produce fluidic dielectric materials as described herein would include oil (low permittivity, low permeability), a solvent (high permittivity, low permeability) and a magnetic fluid, such as combination of a solvent and a ferrite (high permittivity and high permeability). A hydrocarbon dielectric oil such as Vacuum Pump Oil MSDS-12602 could be used to realize a low permittivity, low permeability fluid, low electrical loss fluid. A low permittivity, high permeability fluid may be realized by mixing same hydrocarbon fluid with magnetic particles such as magnetite manufactured by FerroTec Corporation of Nashua, N.H., or iron-nickel metal powders manufactured by Lord Corporation of Cary, N.C. for use in ferrofluids and magnetoresrictive (MR) fluids. Additional ingredients such as surfactants may be included to promote uniform dispersion of the particle. Fluids containing electrically conductive magnetic particles require a mix ratio low enough to ensure that no electrical path can be created in the mixture. Solvents such as formamide inherently posses a relatively high permittivity. Similar techniques could be used to produce fluidic dielectrics with higher permittivity. For example, fluid permittivity could be increased by adding high permittivity powders such as barium titanate manufactured by Ferro Corporation of Cleveland, Ohio. For broadband applications, the fluids would not have significant resonances over the frequency band of interest.
The antennas of
In either case, once the controller has determined the updated configuration for each of the cavities necessary to implement the time delay, the controller can operate device 104 to implement the required delay. The required configuration can be determined by one of several means. One method would be to calculate the total time delay for each cavity or for all the cavities at once. Given the permittivity and permeability of the fluid dielectrics in the cavities, and any surrounding solid dielectric (108 in
As an alternative to calculating the required configuration for a given delay or energy shape, the controller 102 could also make use of a look-up-table (LUT). The LUT can contain cross-reference information for determining control data for fluidic delay units necessary to achieve various different delay times and energy shapes. For example, a calibration process could be used to identify the specific digital control signal values communicated from controller 102 to the cavities that are necessary to achieve a specific delay value or energy shape. These digital control signal values could then be stored in the LUT. Thereafter, when control signal 105 is updated to a new requested delay time, the controller 102 can immediately obtain the corresponding digital control signal for producing the required delay.
As an alternative, or in addition to the foregoing methods, the controller 102 could make use of an empirical approach that injects a signal at an RF input port and measures the delay to an RF output port. Specifically, the controller 102 could check to see whether the appropriate time delay or energy shape had been achieved. A feedback loop could then be employed to control the flow control devices (104) to produce the desired delay characteristic.
Referring to
The present invention is ideally applicable to any reflector or sub-reflector type antenna. Operationally, the present invention enables a system designer to alter the size of the reflective surface for a given application or frequency range. The present invention adds further flexibility by controlling the reflection off the surface of the reflectors by dynamically changing the size of the surface with the fluidic dielectric. In essence, the reflector size can be made to vary based on the frequency or application as opposed to existing systems that are constructed on the basis of fixed frequencies since feeds are frequency dependent generally. In this manner, sidelobes created by different feed horns can each be independently averted and not reflected as required by manipulating the size of the reflectors or sub-reflectors using the fluidic dielectric. In one embodiment, when the fluidic dielectric is present, the reflector or sub-reflector is effectively extended in size and when the fluidic dielectric is removed the reflector or sub-reflector is effectively reduced in size.
Those skilled in the art will recognize that a wide variety of alternatives could be used to adjust the presence or absence or mixture of the fluid dielectric contained in each of the cavities. Additionally, those skilled in the art should also recognize that a wide variety of configurations in terms of cavities and reflectors or sub-reflectors could also be used with the present invention. The reflector or sub-reflector of the present invention can be assembled in a configuration that resembles a reflector in forms such as parabolic, circular, flat, etc, depending on the desires of the designer for the available or desired beam patterns antenna. Accordingly, the specific implementations described herein are intended to be merely examples and should not be construed as limiting the invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5162972 | Gripshover et al. | Nov 1992 | A |
| 6417818 | Shipley et al. | Jul 2002 | B2 |
| 6429823 | Bains et al. | Aug 2002 | B1 |
| 6456254 | Reineix et al. | Sep 2002 | B1 |
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| 6650304 | Lee et al. | Nov 2003 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20040227691 A1 | Nov 2004 | US |
