Abstract:
Method and apparatus for actuating switches in a reconfigurable antenna array. Micro electro-mechanical system (MEMS) switches span gaps between antenna elements disposed on an antenna substrate. An integrated optic waveguide network which directs optical energy towards the MEMS switches is contained in a superstrate disposed above the antenna elements and substrate. The MEMS switches are formed on a semi-insulating substrate. When illuminated, the resistance of the semi-insulating substrate is lowered so as the reduce the resistance between the control contacts. The antenna array is reconfigured by directing optical energy to the photo-voltaic cells connected to selected MEMS switches to close those MEMS switches, thereby electrically connecting selected antenna elements and by directing optical energy to the semi-insulating substrate of selected MEMS switches to open those MEMS switches, thereby electrically disconnecting selected antenna elements.

Description:
FIELD OF THE INVENTION 
     This invention relates to reconfigurable antenna systems, and more particularly, to an apparatus and method for reconfiguring antenna elements in a reconfigurable antenna array. 
     BACKGROUND OF THE INVENTION 
     Reconfigurable antenna systems have applications in satellite and airborne communication node (ACN) systems where wide bandwidth is important and where the antenna aperture must be continually reconfigured for various functions. These antenna systems may comprise an array of individually reconfigurable antenna elements. An antenna array comprised of reconfigurable dipole elements can be reconfigured by varying the resonant length of one or more of the elements. The ability to dynamically vary the resonant length of a dipole antenna enables the antenna to be operated efficiently within multiple frequency ranges. 
     One means of varying the resonant length of a dipole antenna is to segment the antenna lengthwise on either side of its feed point. The resonant length of the antenna may then be varied by connecting or disconnecting successive pairs of adjacent dipole segments. Connection of a pair of adjacent dipole segments may be effected by coupling each segment to a switch. The adjacent segments are then joined by closing the switch. 
     Previous designs for reconfigurable antennas have been proposed which incorporate photoconductive switches as an integral part of an antenna element in an antenna array. See “Optoelectronically Reconfigurable Monopole Antenna,” J. L. Freeman, B. J. Lamberty, and G. S. Andrews,  Electronics Letters,  Vol. 28, No. 16, Jul. 30, 1992, pp. 1502-1503. Also, the possible use of photovoltaic activated switches in reconfigurable antennas has been explored. See C. K. Sun, R. Nguyen, C. T. Chang, and D. J. Albares, “Photovoltaic-FET For Optoelectronic RF/Microwave Switching,”  IEEE Trans. On Microwave Theory Tech.,  Vol. 44, No. 10, October 1996, pp. 1747-1750. One problem with these designs, however, is that the performance of ultra-broadband systems (i.e., systems having an operating frequency range of approximately 0-40 GHz) utilizing these types of switches suffers in terms of insertion loss and electrical isolation. 
     Radio frequency micro-electromechanical system (RF MEMS) switches have been proven to operate over the 0-40 GHz frequency range. A representative example of this type of switch is disclosed in Yao, U.S. Pat. No. 5,578,976. Previous designs for reconfigurable antennas using RF MEMS switches incorporated metal feed structures to apply an actuation voltage from the edge of a substrate to the RF MEMS switch bias pads. A problem with the use of metal feed structures to apply an actuation voltage to the switches is that, in an antenna array, the number of switches can grow to thousands, requiring a complex network of bias lines routed all around the switches. These bias lines can couple to the antenna radiation field and degrade the radiation pattern of the antenna array. Even when the bias lines are hidden behind a metallic ground plane, radiation pattern and bandwidth degradation can occur unless the feed lines and substrate feed through via conductors are very carefully designed because each element in the antenna array may accommodate tens of switches. This problem is magnified enormously as the number of reconfigurable elements increases. Thus, a need exists for an improved apparatus and method for actuating switches in a reconfigurable antenna array. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a means for actuating RF MEMS switches without the need for metal feed structures coupled to the switches. Further objects and advantages of the invention will become apparent from a consideration of the drawings and following description. 
     The present invention uses a series of MEMS switches to reconfigure an antenna element in a reconfigurable antenna system. The MEMS switches and antenna element are mounted on a semi-insulating substrate. The MEMS switches are actuated by optical energy conveyed to the switches via an optical waveguide network integrated into a superstrate, which is coupled to the substrate. Preferably, the superstrate is radio frequency (RF) transparent. The RF transparent superstrate functions both as a framework for incorporation of the optical waveguide network and as a radome for the reconfigurable antenna system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the present invention showing the substrate, incorporating the reconfigurable antenna array, and the superstrate, incorporating the integrated waveguide network. 
     FIG. 2 shows a representative reconfigurable dipole antenna element of the antenna array of the preferred embodiment of the present invention. 
     FIG. 3 shows a representative type of MEMS switch which may be incorporated into the present invention. 
     FIG. 4 is a plan view of the present invention showing the substrate incorporating the reconfigurable antenna array, and the superstrate incorporating the integrated waveguide network. 
     FIG. 5 shows a representative reconfigurable dipole antenna element of the antenna array of an alternative embodiment of the present invention. 
     FIG. 6 is a plan view of an alternative embodiment of the present invention showing the substrate incorporating the reconfigurable antenna array, and the superstrate incorporating the integrated waveguide network. 
     FIG. 7 is a cross-sectional view of the substrate and the superstrate illustrating the operation of the present invention. 
     FIG. 8 is a schematic representation of a photo-voltaic cell coupled to a representative type of MEMS switch which may be incorporated into the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a reconfigurable antenna array  12  according to an embodiment of the present invention. Reconfigurable antenna array  12  comprises a plurality of reconfigurable dipole antenna elements  38  formed on a surface of substrate  10 , a superstrate  44  coupled to the substrate  10  and incorporating an integrated optic waveguide network  46 , and an optical energy generating means  56  coupled to waveguide network  46  for generating optical energy to be conveyed through waveguide network  46  to effect reconfiguration of antenna elements  38 . Optical energy generating means  56  may comprise a linear or matrix LED array or a laser array. While only two representative antenna elements  38  are illustrated in FIG. 1, it is to be understood that the number of elements actually used in a particular application will depend on the particular requirements of that application. Many applications will require large antenna arrays with hundreds or even thousands of antenna elements. 
     FIG. 2 shows, in greater detail, a representative reconfigurable dipole antenna element  38  of antenna array  12 . Antenna element  38  comprises a twin antenna feed structure  58 , a radiating structure comprising series of adjacent metal strip segments  40  formed on substrate  10  (as shown in FIG. 1) and extending to either side of feed structure  58 , and RF MEMS switches  24  coupled to each successive pair of adjacent metal strip segments  40 . A gap  18  separates adjacent metal strips  40 . Gap  18  is opened and closed by operation of the RF MEMS switches  24 , in a manner to be explained later. The optical elements used to control the RF MEMS switches will also be explained later. 
     FIG. 3 shows one form of an RF MEMS switch which may be incorporated into the present invention. The micro-electromechanical system switch, generally designated  24 , is fabricated using generally known microfabrication techniques, such as masking, etching, deposition, and lift-off. In the preferred embodiment, RF MEMS switches  24  are directly formed on the substrate  10  and monolithically integrated with the metal segments  40 . Alternatively, the RF MEMS switches  24  may be discreetly formed and then bonded to substrate  10 . Referring once more to FIG. 2, one RF MEMS switch  24  is positioned proximate each gap  18  between pairs of adjacent metal strips  40  formed on the substrate  10 . As seen in FIG. 3, the switch  24  comprises a substrate electrostatic plate  20  and an actuating portion  26 . The substrate electrostatic plate  20  (typically connected to ground) is formed on the substrate  10 . The substrate electrostatic plate  20  generally comprises a patch of a metal not easily oxidized, such as gold, for example, deposited on substrate  10 . Actuation of the switch  24  opens and closes the gap  18  between the adjacent metal strips  40 , in a manner to be explained later. 
     The actuating portion  26  of the switch  24  comprises a cantilever anchor  28  affixed to the substrate  10 , and an actuator arm  30  extending from the cantilever anchor  28 . The actuator arm  30  forms a suspended micro-beam attached at one end to the cantilever anchor  28  and extending over and above the substrate electrostatic plate  20  and the gap  18  between adjacent metal strips  40  on the substrate  10 . The cantilever anchor  28  may be formed directly on the substrate  10  by deposition buildup or by etching away surrounding material, for example. Alternatively, the cantilever anchor  28  may be formed with the actuator arm  30  as a discrete component and then affixed to the substrate  10 . The actuator arm  30  may have a bilaminar cantilever (or bimorph) structure. Due to its mechanical properties, the bimorph structure exhibits a very high ratio of displacement to actuation voltage. That is, a relatively large displacement (approximately 300 micrometers) can be produced in the bimorph cantilever in response to a relatively low switching voltage (approximately 20 V). 
     A first layer  36  of the actuator arm structure comprises a semi-insulating or insulating material, such as polycrystalline silicon. A second layer  32  of the actuator arm structure comprises a metal film (typically aluminum or 0. gold) deposited atop first layer  36 . The second layer  32  typically acts as an electrostatic plate during operation of the switch. In the remainder of the description, the terms “second layer” and “arm electrostatic plate” will be used interchangeably. As shown in FIG. 3, the second layer  32  is coupled to and extends from the cantilever anchor  28  toward the position on the actuator arm  30  at which electrical contact  34  is formed. As the height of the cantilever anchor  28  above the substrate  10  can be tightly controlled using known fabrication methods, locating the second layer  32  proximate the cantilever anchor  28  enables a correspondingly high degree of control over the height of the second layer  32  above the substrate  10 . As the switch actuation voltage is dependent upon the distance between the substrate electrostatic plate  20  and the arm electrostatic plate  32 , a high degree of control over the spacing between the electrostatic plates is necessary in order to repeatably achieve a desired actuation voltage. In addition, at least a portion of the second layer  32  comprising the arm electrostatic plate, and a corresponding portion of the actuator arm  30  on which second layer  32  is formed, are positioned above the substrate electrostatic plate  20  to form an electrostatically actuatable structure. An electrical contact  34 , typically comprising a metal that does not oxidize easily, such as gold, platinum, or gold palladium, for example, is formed on the actuator arm  30  and positioned on the arm so as to face the gap  18  formed between adjacent metal strips  40 . 
     As shown in FIG. 2, a photovoltaic (PV) cell  42  is coupled to each RF MEMS switch  24 , each PV cell  42  having a pair of electrical contacts. The PV cell electrical contacts are coupled to the substrate and arm electrostatic plates  20  and  32 , respectively, of the RF MEMS switch. Referring to FIG. 4 in conjunction with FIG. 2, the superstrate  44  incorporates an integrated optic waveguide network  46 . Preferably, the superstrate provides less than 1 dB of loss to radio frequency (RF) signals at the frequencies of interest that are radiated onto the superstrate  44 , effectively making the superstrate  44  transparent to radio frequency signals. When coupled to the substrate  10 , the superstrate  44  forms a microwave transparent radome positioned over the substrate  10  and incorporating the reconfigurable antenna array elements  38 . The superstrate  44  may be formed from any suitable RF transparent semi-insulating material that can support the fabrication of optical waveguide network  46 . An example of suitable radome material is a glass or a polymer. The design and fabrication of optical waveguides is well-known in the art. For example, see “Ion-Exchanged Glass Waveguides: A Review,” by R. V. Ramaswamy and R. Srivastava, Journal of Lightwave Technology., vol. 6, no. 6, June 1988, pp. 984-1001; also, “Integrated Optical Waveguides In Polyimide For Wafer Scale Integration”, by R. Selvaraj, H. T. Lin, and J. F. McDonald, Journal of Lightwave Technology, vol. 6, no. 6, June 1988, pp. 1034-1044. Fabrication of integrated waveguide network  46  generally entails forming a series of relatively high refractive index pathways, or waveguides, within a matrix comprised of a relatively lower refractive index material. The relatively lower refractive index material thus functions as cladding, encasing the relatively high refractive index waveguide. Waveguides  48  and  50  may be expediently fabricated by one of two methods. The first method comprises depositing a metal such as titanium on the surface of the superstrate  44 , delineating the waveguide pattern using standard lithography techniques, then raising the temperature of the superstrate  44  to cause an indiffusion process after which the material on the surface is diffused into the superstrate, causing a local increase in its optical index of refraction to form the waveguiding region. Alternatively, the delineation of the surface of the superstrate  44  is done using photolithographic techniques followed by exposure to a solution which exchanges certain atoms in the superstrate  44  with atoms in the solution, causing the index in the delineated regions to be increased thereby creating the waveguides  48  and  50 . Some combination of the two foregoing techniques may also be used to form the waveguides  48  and  50 . 
     Integrated waveguide network  46  comprises RF MEMS switch waveguides  48  and PV cell waveguides  50 . The PV cell waveguides  50  channel optical energy for the purpose of illuminating PV cells  42 , thus causing a voltage to be generated across the PV cell terminals. The RF MEMS switch waveguides  48  channel optical energy for the direct illumination of the RF MEMS switches  24 . Each RF MEMS switch waveguide  48  terminates at and illuminates an RF MEMS switch  24 . 
     Each waveguide  48 ,  50  is coupled to an optical energy generating means  56 , such as a laser or an LED array. The optical energy generating means shown in FIG. 4 is an LED array. Light may be drawn off from the PV cell waveguide  50  or RF MEMS switch waveguide  48  and directed to a PV cell  42  or RF MEMS switch  24  through the use of such well-known means as a waveguide tap or a grating coupler formed in the superstrate  44 . When the superstrate  44  is coupled to the substrate  10 , one such waveguide tap or grating coupler will be positioned directly above each RF MEMS switch  24  in the antenna array  12  so as to direct light onto the switch  24 . 
     Waveguide taps and grating couplers are well-known in the pertinent art. For example, see Optical Integrated Circuits, by H. Nishihara, M. Haruna, and T. Suhara, McGraw-Hill Book Co., New York, 1989, pp. 62-95. Some examples of waveguide taps known in the art are disclosed in U.S. Pat. Nos. 6,002,822 and 5,596,671. Light traveling through a waveguide is confined within a core optical material that has an refractive index that is higher than the surrounding cladding material. A waveguide tap forces the light, normally confined primarily to the waveguide core, to “leak” out of the core at a desired spatial location. The waveguiding effect is destroyed by mechanically or chemically reducing the index difference between the core and the cladding along a certain distance. Some examples of grating couplers known in the art are disclosed in U.S. Pat. Nos. 5,657,407 and 5,961,924. Another example of a grating coupler is described by S. Ura, T. Suhara, H. Nishihara and J. Koyama, in “An Integrated-Optic Disk Pickup Device”, Journal of Lightwave Technology, LT-4, 913-917 (1986). A grating coupler generally comprises a series of grating teeth disposed on the surface of or within the optical waveguide through which light energy may be radiated out of the waveguide. Grating couplers can be fabricated using conventional electron-beam lithography techniques. 
     The spacing between the superstrate  44  and the substrate  10  must be sufficient to ensure focused optical coupling to a PV cell  42  or RF MEMS switch  24  positioned on the substrate  10 , while allowing adequate space for the mechanical motion of the RF MEMS switch  24 . The exact spacing required will depend on factors such as the configuration of the RF MEMS switches  24  employed and the sizes of the PV cells  42  used. 
     The superstrate  44  can be spaced above the substrate  10  using deposited or etched spacers. For a glass waveguide, and hence a glass superstrate, a dielectric material, such as silicon dioxide, can be deposited on the superstrate to form stand-offs for spacing the superstrate from the substrate. An alternative approach would be to cement glass stand-offs on the superstrate and then polish these down to the thickness needed to achieve a desired spacing between the superstrate and the substrate. For a polymer waveguide, a second layer of a different polymer could be spun onto the superstrate after waveguide formation. This could then be etched away so as to leave stand-offs projecting from the superstrate. 
     Positioning of the superstrate  44  with respect to the substrate  10  is determined by the location of the optical waveguides,  48 ,  50 . Features such as waveguide taps and grating couplers incorporated into to the superstrate  44  are preferably positioned directly over an RF MEMS switch  24  or PV cell  42  so that the light from the waveguide shines on the device  24 ,  42 . To aid in positioning of the superstrate  44  with respect to the substrate  10 , optical lithography may be used to produce alignment markers on the superstrate  44  to be aligned with corresponding markers on the substrate  10 . This positioning can be realized using micrometers or piezoelectric positioning devices of the type used in fiber optic device assembly. 
     For optimum optical coupling, the waveguide taps or grating couplers incorporated into the superstrate  44  and the corresponding PV cells  42  or RF MEMS switches  24  on the substrate  10  should preferably remain aligned within a radius of approximately 20 microns. Misalignment between the waveguide taps (or grating couplers) incorporated into the superstrate  44  and the corresponding PV cells  42  or RF MEMS switches  24  on the substrate  10  may result from initial errors in the placement and coupling of the superstrate  44  to the substrate  10 . Additional possible causes of misalignment are mechanical stresses in the substrate  10  and/or superstrate  44 , and thermal expansion differentials caused by differences between the thermal expansion coefficients of the substrate  10  and superstrate  44 . Existing methods, such as the use of mask aligners, can provide the requisite accuracy in alignment during fabrication. 
     The operation of the preferred embodiment will now be discussed. Actuation of the RF MEMS switches  24  residing in a single antenna element  38  is effected by transmission of optical energy through PV cell waveguide  50 . Light generated by a portion of optical energy generating means  56  (here, an LED array located on the edge of the superstrate  44 ) is coupled to the optical waveguide network  46  using known methods and channeled through PV cell waveguide  50 . Waveguide taps direct light away from the PV cell waveguide  50  and onto the PV cells  42 , illuminating the PV cells  42 . 
     FIG. 8 illustrates schematically a PV cell  42  coupled to an RF MEMS switch  24 . The PV cell  42  is coupled to a substrate plate contact  21  and an arm plate contact  33  through an externally provided resistance  72  having a resistance vale of R Se . The substrate plate contact  21  is electrically connected with the substrate electrostatic plate  20  and the arm plate contact is electrically connected to the arm electrostatic plate  32 . When the PV cell  42  is illuminated, a voltage V app  is induced across the PV cell electrical contacts and, correspondingly, across substrate and arm electrostatic plates  20  and  32  of the RF MEMS switch  24  coupled to that PV cell  42 . The RF MEMS switch is closed by means of this electrostatic attraction between the substrate electrostatic plate  20  located on substrate  10  and the arm electrostatic plate  32  located on actuator arm  30 . 
     With switches  24  in the open state, a gap exists between adjacent metal strips  40  constituting dipole antenna element  38 . When voltage V app  is induced across the electrostatic plates  20  and  32  by illumination of the PV cell  42 , the arm electrostatic plate  32  is attracted electrostatically toward substrate electrostatic plate  20 , forcing actuator arm  30  to deflect toward substrate  10 . Deflection of actuator arm  30  toward first substrate electrostatic plate  20 , in the direction indicated by arrow  11  in FIG. 3, causes the electrical contact  34  to come into contact with adjacent metal strips  40 , thereby bridging gap  18  between the metal strips. The amount of light required to close the RF MEMS switches  24  will depend upon the PV cell design and the required actuation voltage. For example, a 7 V driving voltage from a InGaAs PV cell results from 100 pW of illumination at 1550 nm wavelength. Thus, 10-20 mW of optical energy should easily drive tens of PV cells  42  in a column to provide switch actuation voltages of 20-30 V. As light from a single PV cell waveguide  48  is tapped to engage all of the RF MEMS switches  24  residing in a single antenna element  38 , in the normal operating mode of the first embodiment all of the RF MEMS switches  24  will be closed. 
     Key aspects of the present invention are that substrate electrostatic plate  20  and arm electrostatic plate  32  are insulated from the metal strips  40  constituting antenna element  38 , and that electrostatic plates  20  and  32  are dielectrically isolated, even when the switch is closed. Thus, no steady-state bias current is needed for the switch to operate. Also, since no steady DC current flows from the PV cell  42  (only a transient current that builds up an electric field across the electrostatic plates), the PV cell  42  can be made small. Higher voltages V app  can be obtained by using an array of PV cells  42  connected in series. 
     The opening of the RF MEMS switches  24  in order to reconfigure dipole antenna element  38  will now be discussed. Opening of the RF MEMS switches  24  is effected in the following manner by transmission of optical energy through RF MEMS switch waveguides  48 . 
     When actuation voltage V app  is applied to RF MEMS switch  24 , the voltage appearing across substrate electrostatic plate  20  and arm electrostatic plate  32  is given by the relationship 
     
       
           V   app   R   st /( R   st   +R   se ) 
       
     
     where R St  is the resistance of semi-insulating substrate  10  between substrate electrostatic plate  20  and arm electrostatic plate  32  (represented as the resistor  74  in FIG.  8 ), and R Se  is the externally added series resistance  72  on the order of a megohm (this resistance can be monolithically integrated with the RF switch  24 ). When the RF MEMS switch  24  is not illuminated, R St  is much larger than the series resistance R Se , so that almost the entire voltage produced by illumination of the PV cell  42  appears across the RF MEMS switch electrostatic plates  20  and  32 . 
     However, a semi-insulating substrate, comprised of a substance such as gallium arsenide or polycrystalline silicon, will be photoconductive. Thus, when optical energy from the RF MEMS switch waveguide  48  illuminates the portion of semi-insulating substrate  10  insulating the RF MEMS switch substrate electrostatic plate  20  from the RF MEMS switch arm electrostatic plate  32 , the optical energy h v  transferred to substrate  10  causes a proportion of the outer valence electrons of the substrate&#39;s constituent atoms to break free of their atomic bonds, thus creating free carriers. These free electrons are capable of carrying an electric current. Thus, when the RF MEMS switch  24  is illuminated, R St  is reduced by the photoconducting process and becomes much lower than R Se . Consequently, the voltage drop V app  across the electrostatic plates falls below the level required to close the RF MEMS switch  24 , causing the switch to open, interrupting the connection between adjacent metal strips  40  and changing the resonant length of dipole antenna element  38 . Individual switches  24  can be opened by activating the appropriate LED in the LED array  56 . Light from this LED will then be coupled to the appropriate RF MEMS switch waveguide  48 . 
     FIG. 7 shows a cross section of the antenna array where the switches  24  that are open have light from the RF MEMS switch waveguide  48  shining directly upon them. Since the typical width of an optical waveguide is 6-25 microns, hundreds of optical waveguides per inch could originate from the edge of the superstrate  44 , even when the waveguides are separated by up to 8 times the waveguide width to prevent optical cross-coupling. 
     An alternative embodiment of the reconfigurable dipole antenna element  38  of antenna array  12  is shown in FIG.  5 . The arrangement shown in FIG. 5 is representative for each antenna element  38 . Here, a series of PV cell waveguides form a matrix, with at least a horizontal PV cell waveguide  54  and a vertical PV cell waveguide  52  crossing over each PV cell  42 . A separate RF MEMS switch waveguide  48  extends over the RF MEMS switches as shown in FIG.  5 . The RF MEMS switch and PV cell waveguides  48 ,  52 ,  54  may be illuminated by optical LED matrices  57 ,  59  that are located on the edge or edges of the superstrate  44 , as shown in FIG.  6 . The optical LED matrices may comprise a horizontal LED matrix  59  that provides optical power to and controls the horizontal PV cell waveguides  54  and a vertical LED matrix  57  that provides optical power to and controls the vertical PV cell waveguides  52  and the RF MEMS waveguides  48 . Alternative light sources, such as laser sources, may also be used to supply optical energy to the waveguides  48 ,  52 ,  54 . 
     Operation of the alternative embodiment will now be discussed. Operation of the alternative embodiment can best be understood by reference to FIG.  5 . Initially, all of the RF MEMS switches  24  are open. To activate the switches, each switch is addressed sequentially in a raster scan, the appropriate LED&#39;s being turned on if a particular switch  24  is to be closed. At an individual PV cell  42 , each PV cell waveguide  52 ,  54  positioned over a PV cell  42  is tapped so that a fraction of the light flowing through the waveguide  52 ,  54  is incident upon the PV cell  42 . The waveguide taps and the PV cells  42  are designed such that illumination of a PV cell  42  by light tapped from a single PV cell waveguide  52 ,  54  will not enable the cell  42  to generate a voltage sufficient to close the switch  24 . Thus, the amount of light required to close an RF MEMS switch  24  is such that both of the waveguides  52 ,  54  crossing above a PV cell  42  must be illuminated in order to close the switch  24 . If leakage of the charge from the switch electrostatic plates is small (due to the high resistances of the substrate and PV cell), then the switch  24  will remain closed for a length of time, even if no light flows through PV cell waveguides  52 ,  54 . When the array  12  is to be reconfigured, light is channeled through the RF MEMS waveguide  48 , which lies directly above the RF MEMS switches  24 . Taps in the RF MEMS waveguide  48  direct light from the waveguide  48  onto the RF MEMS switches  24 , illuminating the switches  24 . Leakage paths are thus provided for each switch  24  to discharge, and all switches  24  are opened, and ready for the next raster scan. Although the optical waveguides  48 ,  52 ,  54  cross over each other at 90 degree angles in the drawing figures, no energy is coupled from one guide to the other. 
     Thus, the reader will see that the present invention provides reliable actuation of switches in a reconfigurable antenna without the need for an intricate network of metallic bias lines proximate the antenna elements. 
     Although the present invention has been described with respect to specific embodiments thereof, various changes and modifications can be carried out by those skilled in the art without departing from the scope of the invention. In particular, the substrate, actuator portion of the switch, electrostatic plates, the metal contact formed on the actuator portion of the switch, and the metal segments comprising the antenna element may be fabricated using any of various materials appropriate for a given end use design. The substrate, actuator portion of the switch, electrostatic plates, the metal contact formed on the actuator portion of the switch, and the metal segments comprising the antenna element may also be formed in various geometries. It is intended, therefore, that the present invention encompass such changes and modifications as fall within the scope of the appended claims.