Patent Publication Number: US-6703981-B2

Title: Antenna(s) and electrochromic surface(s) apparatus and method

Description:
TECHNICAL FIELD 
     This invention relates generally to antennas, and more particularly to radio frequency reflective surfaces as used in conjunction therewith. 
     BACKGROUND 
     Antennas that radiate radio frequency energy are well known in the art. An unadorned antenna will typically radiate such energy in an omnidirectional fashion. It is also known to shape and/or specifically direct or steer the radiated energy towards (or away from) a particular area. For example, metal reflectors can be used to inhibit such energy from moving in a given direction. In addition, multiple antenna arrays can be manipulated, as with some proposed sectored antenna patterns and as implemented through baseband phasing techniques, to steer, at least to some extent, the radiated energy. Some such steering systems operate wholly electrically (as by phase adjustment and/or by switching various antennas in and out of operational modes), some wholly mechanical (as by rotor driven sector antennas), or combinations of both approaches. 
     Though suitable for at least some applications, the above solutions are not suitable for all contexts. Further, some of these techniques (and especially the more flexible approaches) are expensive and/or prone to maintenance problems (mechanically based systems utilizing moving mechanical parts are especially subject to these issues). Also, existing techniques, while potentially applicable for generally or specifically directing or blocking a beam of radio frequency energy in a given direction, are generally not useful for control of other potentially important performance parameters, including gain control and beamwidth control. Some combined solutions in this regard, such as use of omnidirectional antennas combined with multiple PIN diode driven scatterers, can effect beam steering and controllable beamwidth but are relatively expensive and further can cause switching spikes that can detrimentally impact system performance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above needs are at least partially met through provision of the antenna(s) and electrochromic surface(s) method and apparatus described in the following detailed description, particularly when studied in conjunction with the drawings, wherein: 
     FIG. 1 depicts an antenna and electrochromic surface as configured in accordance with an embodiment of the invention; 
     FIG. 2 illustrates potential radio frequency energy behavior as can result in accordance with an embodiment of the invention; 
     FIG. 3 depicts an alternative embodiment of an antenna and electrochromic surfaces as configured in accordance with an embodiment of the invention; 
     FIG. 4 depicts another alternative embodiment of an antenna and electrochromic surfaces as configured in accordance with an embodiment of the invention; 
     FIG. 5 depicts yet another alternative embodiment of an antenna and electrochromic surfaces as configured in accordance with an embodiment of the invention; 
     FIG. 6 depicts a block diagram of a system for effecting use of various configurations as configured in accordance with an embodiment of the invention; 
     FIG. 7 depicts an embodiment of multiple antennas and electrochromic surfaces as configured in accordance with an embodiment of the invention; 
     FIG. 8 depicts another embodiment of multiple antennas and electrochromic surfaces as configured in accordance with an embodiment of the invention; 
     FIG. 9 depicts a parabolic reflector and feedhorn as configured in accordance with an embodiment of the invention; 
     FIG. 10 depicts another embodiment of a feedhorn as configured in accordance with an embodiment of the invention; 
     FIG. 11 depicts a perspective view of illustrative components of a handheld radio as configured in accordance with an embodiment of the invention; 
     FIG. 12 depicts a top plan diagrammatic view of a waveguide as configured in accordance with an embodiment of the invention; and 
     FIG. 13 comprises a side elevational diagramatic view of an electrochromic surface as configured in accordance with an embodiment of the invention. 
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Also, various antenna patterns and/or radio frequency energy emissions and reflections are depicted for purposes of illustration only and are not necessarily meant to accurately depict specific likely angles of reflection or the like. 
     DETAILED DESCRIPTION 
     Generally speaking, pursuant to these various embodiments, one or more antennas is used in conjunction with one or more electrochromic surfaces. Through selective energization, these electrochromic surfaces can be rendered partially or substantially wholly opaque to radio frequencies of interest. These electrochromic surfaces are substantially transparent when in the reduced state with a positive bias applied. They are highly conductive in the oxidized state with a negative bias applied. These surfaces require little current for switching and will remain in the same state for hours when no electric current is applied. 
     In various embodiments, such electrochromic surfaces can be used alone or in conjunction with other such surfaces and/or with other more traditional reflective surfaces to generally or specifically direct a beam of radio frequency towards or away from a desired direction. In addition, multiple phased-controlled antennas can be used with such surfaces to gain yet additional control over the resultant beam of energy. 
     In one embodiment, the electrochromic surface can be comprised of a doped conjugated polymer, such as polyaniline that is doped with camphorsulfonic acid and wherein the polymer further includes a source of cations such as sodium, potassium, or lithium. In another embodiment, the electrochromic surface can be comprised of an oxide of at least one of tungsten, molybdenum, or niobium in conjunction, again, with a source of cations. Depending upon the particular configuration selected and the conductive material used for the electrodes, the electrochromic surface can be partially or wholly transparent to visible light at least part of the time. Such transparency offers the possibility of antenna structures that are potentially more aesthetically appealing for at least some applications. 
     Such electrochromic surfaces can also be used to selectively alter the performance of a parabolic antenna feedhorn. For example, such surfaces can be used to allow control over the effective beam width and/or phase taper of such a feedhorn without any mechanical movement. This can facilitate significant operational flexibility with potentially increased operating reliability at reduced cost. 
     Such electrochromic surfaces can also be used in a waveguide to control ingress and/or egress of radiated energy. Further, such surfaces, being energizable to yield varying levels of transparency and opaqueness at radio frequencies of interest, can be used to allow passage of various levels of energy instead of merely functioning as a prior art shutter in this regard. 
     Electrochromic technology has primarily been used for modulation of visible light (as exemplified by variable tint windows or mirrors for home, office, and vehicular use) and also for control of infrared radiation to control home and space vehicle heating. In a typical application, a layer of electrochromic material is disposed between two planar electrodes and next to a layer that comprises a source of cations. Upon applying an electrical bias between the two electrodes, the cations migrate into or from the electrochromic material. The electronic structure of the material is thereby modified along with its absorption and reflection characteristics. 
     As is known in the art, the electrochromic reaction creates both controllable conductivity and controllable light energy absorption. The oxides of tungsten, molybdemum, or niobium are usually used as the electrochromic material. The movement of lithium, potassium, or sodium ions controls the electronic band gap and hence the absorption of light as well as the electric conductivity within the electrochromic material. The band gap energies control light absorption at optical frequencies as well understood in the art. Electrochromic material will typically tint or clear as ions are shuttled back and forth between an electrochromic layer and an ion-storage layer (somewhat akin to two battery electrodes that are separated by an electrolyte), with only a small voltage being required to inject or eject the ions and electrons. Visible spectrum applications typically use WO 3  (or MoO 3  or Nb 2 O 5 ) as the electrochromic material. It is possible that such material will serve a radio frequency application as well, but not presently certain. 
     Polymer materials that are intrinsically conductive can be switched between an insulating and conductive state through electrochemical oxidation and reduction. Polymer materials are used for printed flexible circuits with transistors. They are used at low frequencies for identification tags and anti-theft stickers. Though normally exploited, if at all, for optical purposes (because such changes are often accompanied by significant change in the optical characteristics of the polymer), such materials will also serve a similar purpose at useful radio frequencies. A preferred embodiment therefore utilizes polyaniline as the electrochromic material. In particular, and with reference to FIG. 13, an active electrode comprising a conductive polymer  133  such as polyaniline (which is a conjugated polymer) that has been doped with camphorsulphonic acid is essentially laminated between opposing glass plates  131  and metallic strips  132  (comprised, in this embodiment of substantially parallel stripes of tin oxide) in conjunction with a solid polymer electrolyte  134  and a passive electrode  135  (in this embodiment, lithium) source of cations. The principle of operation remains essentially the same as above. The mechanism leading to a variation in conductivity involves switching between an oxidized and a reduced state of the conductive polymer film  133  using Li +  cations. A low voltage source  136  coupled to the metallic strips  132  controls these reactions. 
     For applications in the visible spectrum, the cations modify the electronic band gap and therefore the minimum frequency at which light will be absorbed. For radio frequencies, these cations modify the electrical conductivity and therefore the corresponding tendency to transmit or reflect radio frequency radiation. Also, while visible spectrum applications tend towards use of a solid planar ITO layer, radio frequency applications benefit from a geometry that will allow for the transmission of radio frequency energy (for example, by shaping the electrode as stripes of conducting material). The effective degree of opacity and transparency to a given bandwidth of radio frequencies will generally be a function of the polymer type, the dopant, relative thickness of the material, morphology, and conductivity. In a preferred embodiment, an active electrode for an electrochromic surface configured in accordance with the invention is polyaniline conductive polymer film that is capable of reversible electrochemical oxidation/reduction reactions and a passive counter electrode is LiMn 2 O 4  that permits reversible operation by storing and supplying the mobile counter ions. 
     Switching times when using lithium in the polyaniline to cause the polyaniline to become conductive tend to be relatively slow (perhaps on the order of ten minutes) though nevertheless suitable for the purposes set forth below. Faster switching times may result when using tungsten oxide instead of polyaniline though use of such a substance may involve a tradeoff for higher resistive power losses internal to the electrochromic plate. Tungsten oxide is presently used in most commercial optical electrochromic embodiments. 
     An effective electrochromic surface suitable for use at, say, 2 GHz (which frequency has a free space wavelength of 0.150 meters) can have a size that is smaller than an average residential window. This result will benefit applications that can utilize a relatively small reflector surface. For embodiments that require a larger reflective surface, the electrochromic surface can of course be scaled larger. A laminated structure as described above can be fashioned quite thinly. Further, there is no particular reason why the surrounding envelope need be comprised of glass as described. Other rigid materials would serve as well (so long as those materials are substantially transparent to the radio frequencies of interest) or, if desired, nonrigid materials. For example, a thin flexible plastic membrane could be used as a substitute for the glass exterior to provide an electrochromic surface that is, itself, flexible. Such an electrochromic surface could be conformally disposed about a suitable mandrel to thereby provide an electrochromic surface of desired configuration. 
     There are a variety of ways in which such electrochromic surfaces can be used to useful effect with one or more antennas. In general, by placing such a surface  11  near a dipole antenna  10  (as shown in FIG.  1 ), the corresponding radiation pattern for the antenna  10  can be selectively impacted. For example, and with reference to FIG. 2, radio frequency waves  21  as emitted by the antenna  10  away from the electrochromic surface  11  in the first instance will travel unimpeded. And, when the electrochromic surface  11  is powered down to a substantially transparent state, radio frequency waves  22  as emitted by the antenna  10  towards the electrochromic surface  11  will also travel unimpeded through the electrochromic surface  11  and beyond. When, however, the electrochromic surface  11  is powered to cause the electrochromic surface  11  to become at least partially opaque to the radio frequency waves, some of the radio frequency waves  23  will be reflected away from the electrochromic surface  11 . By variable control of the energization of the electrochromic surface  11 , the opacity of the electrochromic surface  11  can be selectively controlled and hence the amount of energy that is passed through the electrochromic surface  11  and that is reflected away therefrom. A simple configuration such as that depicted in FIGS. 1 and 2 can be used, for example, to shield the area behind the electrochromic surface  11  from the energy transmissions of the antenna  10 . 
     Referring now to FIG. 3, two electrochromic surfaces  11 A and  11 B can be used, for example, to form a corner reflector. Such a configuration can be used to both shield the area behind the surfaces  11 A and  11 B and to effectively direct the bulk of the radiated energy  23  in a desired direction. As shown, both surfaces  11 A and  11 B are energized and are therefore presenting an opaque surface to the radio frequency emissions of the antenna  10 . As may be appropriate to a given application, however, only one surface.  11 A or  11 B need be energized, such that energy is reflected from one and not the other at any given time. Further, if desired, the degree of opacity and hence the degree of reflection can be selectively varied as well, such that some energy passes through the surface  11 A and/or  11 B and some energy is diverted away therefrom. 
     FIG. 4 depicts another exemplary embodiment wherein the antenna  10  is effectively surrounded by four electrochromic surfaces  11 A,  11 B,  11 C, and  11 D. As depicted, two of the surfaces  11 B and  11 C are substantially opaque such that energy  23  is reflected away therefrom, and two of the surfaces  11 A and  11 D are substantially transparent such that energy  22  passes therethrough relatively unimpeded. With this configuration, any of the surfaces can be rendered opaque, transparent, or somewhere in between to gain significant control over the emission of radio frequency energy into each of the corresponding quadrants. 
     Referring now to FIG. 5, in yet another embodiment one or more electrochromic surfaces  11 A and  11 B can be used in conjunction with two other reflective surfaces  51  and  52  (wherein the latter reflective surfaces  51  and  52  can be other electrochromic surfaces and/or traditional metal conductors). As configured, the two electrochromic surfaces  11 A and  11 B form inner potential reflective surfaces as compared to the outer reflective surfaces  51  and  52 . When one of the inner surfaces (such as the electrochromic surface  11 B) is transparent, radio waves  53  will pass therethrough and subsequently reflect off the corresponding outer reflective surface  52 . Conversely, when one of the inner surfaces (such as the electrochromic surface  11 A) is opaque, radio waves  23  will be reflected therefrom. This directional and/or shielding control can be used in an appropriate application to particularly direct the radio emissions from the antenna  10  and/or control the beam width of the resultant radiation (additional description regarding beam width control is provided below in conjunction with FIG. 7) 
     The above described embodiments include a single antenna  10 . If desired, additional antennas can be included. In particular, phased antenna arrays are well understood in the art, and two or more phase controlled antennas can be used in conjunction with electrochromic surfaces to gain additional directional control over the resultant radio emissions. For example, and referring now to FIG. 6, two antennas  10 A and  10 B can each be coupled via upband modulators  64  to a processor  62  that includes two digital-to-analog converters used as both modulators and phase shifters as well understood in the art. So configured, relatively high speed beam shaping can be effected with respect to the resultant combined emissions as radiated by the two antennas  10 A and  10 B. In addition, however, this embodiment further includes two electrochromic surfaces  11 A and  11 B disposed proximal to the two antennas  10 A and  10 B. Each of the electrochromic surfaces  11 A and  11 B are operably coupled to and controlled by an electrochromic controller  61 . The latter constitutes a relatively slow speed pattern controller that can significantly contribute to overall shaping of the resultant radio emission beam. In this embodiment, this controller  61  can be simply comprised of the appropriate low voltage sources necessary to energize the electrochromic surfaces  11 A and  11 B and, in this embodiment, is itself coupled to a controller  65  that also couples to and influences the high speed beam shaping processor  62 . So configured, the controller  65  can utilize the electrochromic surfaces  11 A and  11 B via the electrochromic controller  61  to coarsely direct the resultant beam and the processor  62  to phase adjust elements of an incoming information signal  63  as provided to the two antennas  10 A and  10 B such that phase adjusting techniques can be utilized to achieve finer, faster, and independent channel frequency adjustments to the resultant shape of the beam as transmitted by this minimal array. 
     FIG. 7 comprises a combination of the embodiments described above with respect to FIG.  6  and FIG.  5 . In this embodiment, course beam shaping is conducted by controlling the opacity of the inner electrochromic surfaces  11 A and  11 B. With both inner surfaces  11 A and  11 B substantially transparent to the radio frequency energy, a relatively wide-lobed beam  71  will tend to result. Conversely, when both inner surfaces  11 A and  11 B are substantially opaque to the radio frequency energy, a relatively narrower and longer beam (i.e., higher gain)  72  will tend to result. (Other coarsely defined beams can be formed by rendering one, but not both, of the inner surfaces  11 A and  11 B substantially opaque.) In either case, the resultant beam can be further more finely shaped (or moved) by phased array techniques as well understood in the art and as represented in FIG. 7 by reference numeral  73 . 
     Other permutations and combinations are of course possible. For example, with reference to FIG. 8, six electrochromic surfaces  11 A,  11 B,  11 E,  11 F,  11 G, and  11 H can be used with one antenna  10 , two antennas  10 A and  10 B, or more to provide a wide variety of possible reflective surface combinations. Each such combination, of course, has a corresponding beam shape and direction. Such flexibility is presently virtually unheard of, as the cost and maintenance issues likely represented by achieving such capability through mechanical means would be considerable. 
     The embodiments described above comprise monopole and/or dipole antennas used in conjunction with one or more electrochromatic surfaces that are selectively used as reflectors to control directionality and/or beam shape. The present invention finds expression through other embodiments as well, however. For example, and referring now to FIG. 9, an antenna comprising a parabolic reflector  92  and a feedhorn  91  can benefit as well. The feedhorn  91  is comprised of conductive material (or nonconductive material having a conductive surface disposed thereon) and includes an aperture formed from inclined surfaces  93  as well understood in the art. In this embodiment, the feedhorn  91  further includes additional inclined surfaces  94  that are formed using electrochromic surfaces as described above. These electrochromic surfaces  94  are more gently inclined than the other inclined surfaces  93  of the feedhorn  91  but, in this embodiment, extend out to a distance sufficient to ensure an aperture  95  that is substantially equivalent to the original aperture of the feedhorn  91 . With a same sized aperture, the feedhorn  91  will exhibit essentially the same gain regardless of whether the electrochromatic surfaces  94  are render opaque or not. But varying the transparency of the electrochromatic surfaces  94 , however, one can selectively vary the phase taper of the feedhorn  91 . This capability can be used in various applications in various ways as desired. 
     With reference to FIG. 10, and referring now to an alternative embodiment, the electrochromic surfaces  101 , while still inclined less sharply than the original inclined surfaces  93  of the feedhorn  91 , extend only so far as the original aperture boundary  102 . So configured, the resultant aperture that occurs when the electrochromatic surfaces  101  are rendered less transparent will be smaller than the original aperture of the feedhorn  91 . As a result, the gain of the feedhorn  91  will be altered. 
     It would be possible, of course, to combine the above described embodiments to yield a feedhorn having both gain and phase taper that could be selectively varied by appropriate control of the electrochromatic surfaces. Such capabilities are beyond any present commercially feasible suggestions as found in the prior art. 
     Yet another application of these inventive concepts is illustrated in FIG.  11 . FIG. 11 diagramatically depicts a printed wiring board  111  of a device such as a handheld two-way radio communications device (such as a cellular telephone-or a two-way dispatch communications unit) and a monopole antenna  10  as attached thereto. In such a configuration, and as well understood in the art, the printed wiring board  111  will act as an counterpoise to the antenna  10 . When designing and manufacturing a device such as this, it is important that the antenna and counterpoise function at some useful point of equilibrium. Tuning and calibrating such a structure can, under some circumstances, be challenging and/or costly or time consuming. Pursuant to this embodiment, an electrochromic surface  11  is disposed substantially normal to the antenna  10  and the counterpoise/printed wiring board  111  (including, in this embodiment, a hole  112  disposed through the electrochromic surface  11  through which the antenna  10  passes). When transparent to the radiated energy, the electrochromatic surface  11  will not substantially impact performance of the device. By energizing the electrochromatic surface  11  to render it at least partially opaque to relevant frequencies of radiated energy, however, the electrochromatic surface  11  joins with the printed wiring board  111  as an effective counterpoise. If surface  11  and board  111  are electrically connected, they will function as one counterpoise. If surface  11  and board  111  are not electrically connected, board  111  will serve as the only counterpoise and surface  11  will constitute an independent reflector. Having these components electrically connected likely constitutes the simplest embodiment for facilitating entire impedance matching. Not having the electrical connection would, on the other hand, likely significantly complicate associated design considerations. These complications, however, might be offset in a given situation by the potential to achieve other design objectives. For example, a separate plate can offer either shielding, radio frequency re-radiation, or specific absorption rate options. Variable opacity/transparency in turn yields a variable counterpoise. This capability allows for tuning and calibration of the antenna and especially facilitates achieving a good impedance match vis a vis the effective counterpoise. 
     In a commercially feasible embodiment, the electrochromatic surface  11  in the above embodiment could be formed, for example, on an inside surface of the device housing. This could result in both a convenient form factor and further contribute to a reduced cost of implementation. 
     In yet another example of an application of these inventive principles, and referring now to FIG. 12, electrochromatic surfaces  123  can be used within a waveguide  120  to selectively attentuate passage of radiated energy as introduced through a waveguide opening  121  through various horn antennas  122 . In particular, by rendering a given electrochromatic surface  123  as only partially opaque, some energy will be able to pass therethrough. Therefore, instead of merely functioning as an open-or-closed shutter, these surfaces can act as a valve to meter the passage of energy therethrough and to the corresponding horn antenna. And again, as with the embodiments above, these benefits are achieved without moving parts and the wear and tear and maintenance concerns that attend such an approach. 
     In all of the above embodiments, one or more electrochromic surfaces (formed on rigid or flexible carrier surfaces) are used in various ways with one or more radio frequency energy radiating elements and/or guiding elements to lend selective reflectivity to achieve greater resultant control over directionality, gain, phase, and/or shape of the radiated energy. These benefits are achieved with few or no moving parts and with a potential degree of high resolution control previously unattainable at any reasonable cost. Further, this technology holds great promise for high reliablity. 
     Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.