Abstract:
A reconfigurable directional antenna for transmission and reception of electromagnetic radiation includes a transmission line aligned with and adjacent to a metal antenna element with an evanescent coupling edge having a selectively variable electromagnetic coupling geometry. The shape and direction of the beam are determined by the selected coupling geometry of the coupling edge, as determined by the pattern of electrical connections selected for physical edge features of the coupling edge. The electrical connections between the edge features are selected by the selective actuation of an array of “on-off” switches that close and open electrical connections between individual edge features. The selection of the “on” or “off” state of the individual switches thus changes the electromagnetic geometry of the coupling edge, and, therefore the direction and shape of the transmitted or received beam. The actuation of the switches may be accomplished under the control of an appropriately-programmed computer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   Not Applicable 
   FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   This invention relates generally to the field of dielectric waveguide antennas. More specifically, it relates to such antennas that transmit or receive electromagnetic radiation (particularly millimeter wavelength radiation) in selectable directions determined by controllably varying the effective electromagnetic coupling geometry of the antenna. 
   Dielectric waveguide antennas are well-known in the art, as exemplified by U.S. Pat. No. 6,750,827; U.S. Pat. No. 6,211,836; U.S. Pat. No. 5,815,124; and U.S. Pat. No. 5,959,589, the disclosures of which are incorporated herein by reference. Such antennas operate by the evanescent coupling of electromagnetic waves out of an elongate (typically rod-like) dielectric waveguide to a rotating cylinder or drum, and then radiating the coupled electromagnetic energy in directions determined by surface features of the drum. By defining rows of features, wherein the features of each row have a different period, and by rotating the drum around an axis that is parallel to that of the waveguide, the radiation can be directed in a plane over an angular range determined by the different periods. This type of antenna requires a motor and a transmission and control mechanism to rotate the drum in a controllable manner, thereby adding to the weight, size, cost and complexity of the antenna system. 
   Other approaches to the problem of directing electromagnetic radiation in selected directions include gimbal-mounted parabolic reflectors, which are relatively massive and slow, and phased array antennas, which are very expensive, as they require a plurality of individual antenna elements, each equipped with a costly phase shifter. 
   There has therefore been a need for a directional beam antenna that can provide effective and precise directional transmission as well as reception, and that is relatively simple to manufacture. Preferably, such an antenna would constitute a monolithic structure for the sake of simplicity and economy of manufacture. 
   SUMMARY OF THE INVENTION 
   Broadly, the present invention is a reconfigurable directional antenna, operable for both transmission and reception of electromagnetic radiation (particularly microwave and millimeter wavelength radiation), that comprises a metal antenna element (an antenna plate or layer) with an evanescent coupling edge having a selectively variable coupling geometry. The coupling edge is placed substantially parallel and closely adjacent to a transmission line, such as a dielectric waveguide. The term “selectively variable coupling geometry” is defined as an edge shape comprising a series or pattern of geometric physical edge features that can be selectively connected electrically to controllably change the effective electromagnetic coupling geometry of the antenna plate or layer. As a result of evanescent coupling between the transmission line and the antenna plate or layer when an electromagnetic signal is transmitted through the transmission line, electromagnetic radiation is transmitted or received by the antenna. The shape and direction of the transmitted or received beam are determined by the selected coupling geometry of the evanescent coupling edge, as determined, in turn, by the pattern of electrical connections that is selected for the edge features of the coupling edge. 
   In the preferred embodiments of the invention, the electrical connections between the plate edge features are selectively varied by the selective actuation of an array of “on-off” switches that close and open electrical connections between individual features of the coupling edge. The selection of the “on” or “off” state of the individual switches thus changes the electromagnetic geometry of the coupling edge of the antenna element, and, therefore the direction and shape of the transmitted or received beam. The configuration and pattern of the particular edge features are determined by computer modeling, depending on the antenna application, and will be a function of such parameters as the operating frequency (wavelength) of the beam radiation, the required beam pattern and direction, transmission (or reception) efficiency, and operating power. The actuation of the switches may be accomplished under the control of an appropriately-programmed computer, in accordance with an algorithm that may be readily derived for any particular application by a programmer of ordinary skill in the art. 
   As will be more readily appreciated from the detailed description that follows, the present invention provides an antenna that can transmit and/or receive electromagnetic radiation in a beam having a shape and direction that can be selected and varied. These operating characteristics are achieved in a monolithic structure that is compact, economical to manufacture, and reliable in operation. 

   
     BREIF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a semi-diagrammatic plan view of a reconfigurable antenna in accordance with a first preferred embodiment of the invention; 
       FIG. 2  is a plan view, similar to that of  FIG. 1 , of a specific variant of the first preferred embodiment of the invention; 
       FIG. 3A  is a plan view, similar to that of  FIG. 1 , of a second preferred embodiment of the invention; 
       FIG. 3B  is an elevational view taken along line  3 B— 3 B of  FIG. 3A ; 
       FIG. 4A  is a plan view, similar to that of  FIG. 1 , of a third preferred embodiment of the invention; 
       FIG. 4B  is an elevational view taken along line  4 B— 4 B of  FIG. 4A ; 
       FIG. 5A  is a plan view, similar to that of  FIG. 1 , of a fourth preferred embodiment of the invention; 
       FIG. 5B  is an elevational view taken along line  5 B— 5 B of  FIG. 5A ; 
       FIG. 6A  is a plan view, similar to that of  FIG. 1 , of a fifth preferred embodiment of the invention; 
       FIG. 6B  is an elevational view taken along line  6 B— 6 B of  FIG. 6A ; 
       FIG. 7A  is a semi-diagrammatic perspective view of a sixth preferred embodiment of the invention; 
       FIG. 7B  is a top plan view of the embodiment of  FIG. 7A ; 
       FIG. 8A  is a semi-diagrammatic perspective view, similar to that of  FIG. 7A , of a variant of the sixth preferred embodiment of the invention; 
       FIG. 8B  is a top plan view of the embodiment of  FIG. 8A ; 
       FIG. 9A  is a semi-diagrammatic perspective view of another variant of the sixth preferred embodiment of the invention; 
       FIG. 9B  is a top plan view of the embodiment of  FIG. 9A ; 
       FIG. 10A  is semi-diagrammatic longitudinal cross-sectional view of a seventh preferred embodiment of the invention; 
       FIG. 10B  is a transverse cross-sectional view taken along line  10 B— 10 B of  FIG. 10A ; 
       FIGS. 11A ,  11 B, and  11 C are semi-diagrammatic views of the metal layers and electrodes of the embodiment of  FIGS. 10A and 10B ; 
       FIGS. 12A ,  12 B, and  12 C are semi-diagrammatic views, similar to those of  FIGS. 11A ,  11 B, and  11 C, respectively, of the metal layers and electrodes of a variant of the embodiment of  FIGS. 10A and 10B ; and 
       FIG. 13  is a semi-schematic view of the switch control system employed in the embodiment of  FIGS. 10A and 10B . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIG. 1 , a reconfigurable antenna  100 , in accordance with a first preferred embodiment of the invention, is shown. The antenna  100  comprises a transmission line  102 , in the form of a narrow, elongate rod, and a metal antenna plate  104 , having an evanescent coupling edge  106  that is aligned generally parallel to the axis of the transmission line  102 . The alignment of the plate  104  and the transmission line  102 , and their proximity to each other, allow the radiation from the transmission line  102  to be evanescently coupled to the antenna plate  104 , as is well-known in the art. 
   While the transmission line  102  is preferably an elongate, rod-shaped dielectric waveguide, other types of transmission lines may be employed. Examples of such other types of transmission lines include slot lines, coplanar lines, rib waveguides, groove waveguides, imaging waveguides, and planar waveguides. 
   The coupling edge  106  of the antenna plate  104  is formed with a series or pattern of geometric figures. As shown in  FIG. 1 , the geometric figures may be a pattern of serrations or convexities  108  separated by complementary concavities or notches  110 . Each adjacent pair of serrations or convexities  108  is selectively connectable by a switch  112 . The switches  112  can be selectively closed to change the electromagnetic coupling geometry of the coupling edge  106  by controllably connecting selected pairs of convexities or serrations  108 . By this mechanism of selectively connecting adjacent pairs of convexities  108 , the coupling edge  106  may be defined as having a selectively variable coupling geometry. 
   The switches  112  may be any kind of micro-miniature switch, known in the art, that can be connected to the edge  106  of the coupling plate  104 . For example, the switches  112  can be semiconductor switches (e.g., PIN diodes, bipolar transistors, MOSFETs, or heterojunction bipolar transistors), MEMS, piezoelectric switches, capacitive switches (such as varactors), lumped IC switches, ferro-electric switches, photoconductive switches, electromagnetic switches, gas plasma switches, and semiconductor plasma switches. The selective actuation of the switches  112  is advantageously controlled by an appropriately-programmed computer (for example, a microcomputer), in accordance with an algorithm that may be readily derived for any particular application by a programmer of ordinary skill in the art. 
     FIG. 2  shows an antenna  100 ′ in accordance with a specific variant of the embodiment of  FIG. 1 , comprising a metal antenna plate  104 ′ having an edge  106 ′ configured as a square wave. Thus, the edge  106 ′ comprises a series of square-shaped serrations or convexities  108 ′ formed by a series of square-cut notches or concavities  110 ′. Each adjacent pair of convexities  108 ′ is connectable by a switch  112 ′. In this variant, the width of any particular notch or concavity is a i , and the width of the adjacent serration or convexity is b i . The variant may be configured so that the concavities and the convexities are of equal widths (a i =b i ), or of unequal widths (a i ≠b i ). Alternatively, the concavities may all be of a first width a, and the convexities may all be of a second width b that is not equal to a. Another possible configuration is one in which the sum of the width of any concavity and the width of the next adjacent convexity is the same for each such paired concavity and convexity (a i +b i =a j +b j ). Alternatively, the sum of the width of any concavity and the width of the next adjacent convexity is different for some or all of such concavity/convexity pairs. For some applications, it may be advantageous for the widths of each concavity and/or convexity to be less than one-half the wavelength of the emitted or received radiation. 
     FIGS. 3A and 3B  illustrate an antenna  200 , in accordance with a second embodiment of the invention, having a transmission line  202 , as described above, and a metal antenna plate  204 , the latter having an evanescent coupling edge  206  comprising a series of alternating convexities or serrations  208  and concavities or notches  210 . As in the previously-described embodiment, each adjacent pair of convexities  208  is selectively connectable by a switch  212 . 
   In the antenna of  FIGS. 3A and 3B , the metal antenna plate  204  is advantageously formed or placed on a substrate  214 . The substrate  214  may be a dielectric material, such as quartz, sapphire, ceramic, a suitable plastic, or a polymeric composite. Alternatively, the substrate  214  may be a semiconductor, such as silicon, gallium arsenide, gallium phosphide, germanium, gallium nitride, indium phosphide, gallium aluminum arsenide, or SOI (silicon-on-insulator). 
     FIGS. 4A and 4B  show an antenna  300  according to a third embodiment of the invention, which, like the previously-described embodiments, includes a transmission line  302  and a metal antenna plate  304 . The antenna plate  304  has an evanescent coupling edge  306 , having convexities  308  separated by concavities  310 . Each adjacent pair of convexities  308  is selectively connectable by a switch  312 , as discussed above. In this embodiment, the metal antenna plate  304  is sandwiched between a substrate  314  and a cover layer  316 . As in the embodiment of  FIGS. 3A and 3B , the substrate  314  may be either a dielectric or a semiconductor material. The cover layer  316  is also of a dielectric or semiconductor material, but not necessarily the same material as that of the substrate  314 . 
   An antenna  400  in accordance with a fourth embodiment of the invention is shown in  FIGS. 5A and 5B . The antenna  400  includes a transmission line  402  and a metal antenna plate  404 . The antenna plate  404  has an evanescent coupling edge  406 , having convexities  408  separated by concavities  410 . Each adjacent pair of convexities  408  is selectively connectable by a switch  412 , as discussed above. In this embodiment, the metal antenna plate  404  is formed on or adhered to the front surface of a dielectric or semiconductor substrate  414 , the rear surface of which is attached to a metal backing plate  416 . A metal face plate  418  is separated by an air gap  420  from the metal coupling plate  404 . 
     FIGS. 6A and 6B  illustrate an antenna  500  in accordance with a fifth embodiment of the invention. The antenna  500  includes a transmission line  502  and a metal antenna plate  504 . The antenna plate  504  has an evanescent coupling edge  506 , having convexities  508  separated by concavities  510 . Each adjacent pair of convexities  508  is selectively connectable by a switch  512 , as discussed above. In this embodiment, the antenna plate  504  is sandwiched between a pair of weakly conductive (semiconductor) or non-conductive (dielectric) plates or layers  514 , and this sandwich structure is then further sandwiched between a metal backing plate  516  and a metal face plate  518 . 
     FIGS. 7A through 9B  illustrate further embodiments of an antenna in accordance with the present invention, in which the electromagnetic beam direction can be varied in two dimensions.  FIGS. 7A and 7B  illustrate an antenna  600  in accordance with a sixth preferred embodiment of the invention. The antenna  600  is a composite antenna comprising a stacked array of substantially planar antenna elements  620 , defining substantially parallel planes, and a transmission line element comprising an array of substantially parallel linear transmission lines  622  that are orthogonal to the planes of the antenna elements  620 . Each of the antenna elements  620  may be formed in accordance with the embodiment of  FIGS. 3A and 3B , the embodiment of  FIGS. 4A and 4B , the embodiment of  FIGS. 5A and 5B , or the embodiment of  FIGS. 6A and 6B , as described above. As illustrated, the antenna elements  620  are formed in accordance with the embodiment of  FIGS. 3A and 3B , so that each antenna element  620  comprises a metal antenna plate  624  attached to a substrate  626 , which may be made of any of the above-mentioned dielectric or semi-conductive materials. Each of the antenna plates  624  includes a coupling edge  628  formed with a pattern of convexities  630 , each adjacent pair of which is selectively connected by a switch  632 . The antenna elements  620  are arranged so that their respective coupling edges  628  are in alignment. Evanescent coupling occurs between the transmission line element and the coupling edge  628  of each antenna element  620 . It may be advantageous to separate each of the antenna elements  620  by a separation plate  634 , which may be made of any suitable metal, such as, for example, aluminum, copper, or gold. 
     FIGS. 8A and 8B  illustrate a composite antenna  600 ′ in accordance with a variant of the embodiment of  FIGS. 7A and 7B , described above. The composite antenna  600 ′ is substantially identical to the composite antenna  600  of  FIGS. 7A and 7B , except that it includes a transmission line element comprising an array of substantially parallel linear transmission lines  622 ′ that are substantially parallel to the planes of the antenna elements  620 .  FIGS. 9A and 9B  illustrate a composite antenna  600 ″ in accordance with another variant of the embodiment of  FIGS. 7A and 7B . This variant employs a transmission line element comprising a planar transmission line  622 ″ that is substantially orthogonal to the planes of the antenna elements  620 . 
     FIGS. 10A through 11C  illustrate an antenna  700  in accordance with a specific seventh embodiment of the invention, comprising a dielectric transmission line  702  that is spaced from and aligned with a multilayer coupling structure  720 , in which a plurality of solid state switches are integrated. Specifically, the coupling structure  720  comprises a metal base layer  722  on which is disposed a semiconductor layer  724 . In a specific example of the invention in accordance with this embodiment, the base layer  722  is a layer of aluminum of 5 mm thickness, and the semiconductor layer  724  is silicon, 0.5 mm thick, with a resistivity of 1 kilohm-cm. The upper surface of the semiconductor layer  724  is doped to provide an array of alternating P-doped switch electrodes  726  and N-doped switch electrodes  728  (as also shown in  FIG. 11C ). A first dielectric insulation layer  730 , preferably of silicon dioxide, is formed on the top surface of the semiconductor layer  724 . The first insulation layer  730  is masked and photo-etched, by conventional methods, to form an array of apertures that expose the electrodes  726 ,  728 . In the specific example of the invention, the first insulation layer  730  is 0.5 micron in thickness. 
   An array of conductive metal contacts  732  ( FIG. 11B ) is provided on top of the first insulation layer  730 . In the specific example referred to above, the metal contacts  732  are formed as a series of parallel strips of gold, of 0.5 micron in thickness. The contacts  732  may be formed by any suitable method, such as screen printing or electro-deposition. Each of the contacts  732  has a first end  734  that extends downward through an aperture in the first insulation layer  730  to establish electrical contact with one of the electrodes  726 ,  728 . A second dielectric insulation layer  736  is formed on top of the first insulation layer  730 , so as to cover the entirety of each of the contacts  732 , except for a second end portion  738  of each of the contacts  732  that is left exposed, as shown in  FIG. 10B . The second insulation layer  736 , like the first insulation layer  730 , is preferably formed of silicon dioxide, with a thickness of 0.5 micron. A switch signal wire  740  is attached, by conventional means, to each of the contacts  732  at the second end portion thereof. The purpose of the switch signal wires  740  is discussed below. 
   A metal antenna layer  742  is advantageously formed on top of the second insulation layer  736 . As best shown in  FIG. 11A , the antenna layer  742  comprises a plurality of parallel fingers  744  joined at one end to a continuous strip  746 , and separated by slots or gaps  748 . The metal antenna layer  742  corresponds to the antenna plate in the previously-described embodiments, with an evanescent coupling edge provided by the fingers  744  and the slots  748 , and with the fingers  744  defining the convexities, and the slots  748  defining the concavities, as discussed above with the previously-described embodiments. Each of the fingers  744  overlies two adjacent contacts  732 , as best shown in  FIG. 10A . The fingers  744  and the slots  748  define a square wave coupling edge with a period, in the specific example discussed above, of 0.7 mm. In the specific example discussed above, the antenna layer  742  is made of gold, with a thickness of 1.0 micron. 
   The antenna  700  may advantageously include a metal cover layer  750  that is separated from the antenna layer  742  by an air gap  752 . In the specific exampled referred to above, the cover layer  750  comprises a sheet of aluminum, of 5 mm thickness, and the air gap  752  is 3 mm across. 
   Referring to  FIG. 13 , a control mechanism is shown for selectively actuating the switches formed by adjacent pairs of the P and N electrodes  726 ,  728 . As mentioned above, each of the contacts  732  is in contact with one of the electrodes  726 ,  728 , and each of the contacts  732 , in turn, is contacted by one of the wires  740 . The wires  740  are connected to an electronic controller  754  that selectively provides individual energizing currents to each P-N pair of the electrodes  726 ,  728 . The energizing currents cause carrier injection into the area in the semiconductor layer  724  between the electrodes in the selected electrode pair or pairs, thereby creating a conductive link between each energized electrode pair, each conductive link, in turn, being capacitively coupled to the overlying fingers  744 . Those links correspond to the closed switches described above in connection with the previously-described embodiments, whereby two adjacent convexities (fingers  744 ) of the coupling edge are electrically connected. The electrode pairs that are not energized remain disconnected, corresponding to open switches. In the example shown in  FIG. 13 , electrodes  1  and  2  are energized by the controller  754 , thereby “closing” the semiconductor switch between them. Likewise, a semiconductor switch is closed between electrodes  5  and  6 , which are also energized by the controller  754 . By closing the semiconductor switches between the P and N electrodes in selected electrode pairs, the configuration of the coupling edge provided by the antenna layer  742  is altered by the above-mentioned capacitively-coupled links. 
   In operation, the transmission line  702  supports an electromagnetic wave propagating along the transmission line  702 . Part of the wave propagates outside of the physical confines of the transmission line  702 , forming an evanescent wave. The evanescent wave interacts with the coupling edge defined by the antenna layer  742 , as discussed above, and is scattered by the coupling edge. This scattered wave is no longer supported by the transmission line  702 ; rather, it propagates in free space. The wave front of the scattered wave depends on the selected configuration of the coupling edge of the antenna layer  742 , which can be selectively varied by the controller  754 , in the manner described above. 
   In the example described above in connection with  FIGS. 10A through 11C , the normative (all switches “off”) configuration of the antenna layer  742  is a periodic structure with a period of 0.7 mm. Numerical simulation indicates that to form a quasi-parallel beam propagating in a direction forming an angle of 80 degrees with the transmission line  702 , every fifth pair of electrodes  726 ,  728  must be energized. If every fourth pair of electrodes  726 ,  728  is energized, the propagated beam will be in a direction forming an angle of 92.5 degrees with the transmission line. 
   A second specific example of an antenna in accordance with the embodiment of  FIGS. 10A and 10B  includes essentially the same structure as the first specific example described above, except for the configurations of the contacts, the antenna layer, and the P and N electrodes, which are shown in  FIGS. 12A ,  12 B, and  12 C. Specifically, in this second example, a plurality of P-electrode pairs  726 ′ alternate with a plurality of N-electrode pairs  728 ′, so that there are two P-electrodes  726 ′ followed by two N-electrodes  728 ′, etc., as shown in  FIG. 12C . A plurality of substantially parallel linear contacts  732 ′ ( FIG. 12B ) is provided on the surface of the first insulation layer  730 , each terminating in a transverse contact head  733  that extends downward into the semiconductor layer  724  to contact a pair of like electrodes (i.e., either a pair of P-electrodes  726 ′ or a pair of N-electrodes  728 ′). The metallic coupling layer  742 ′ includes a plurality of parallel fingers  744 ′, each having a first end connected to a continuous strip  746 ′, and a second end terminating in a transverse edge portion  749  that overlies a corresponding one of the transverse contact heads  733 . The fingers  744 ′ are separated by slots or gaps  748 ′. The fingers  744 ′ and the slots  748 ′ form an evanescent coupling edge, with the fingers  744 ′ defining the convexities, and the slots  748 ′ defining the concavities, as discussed above with the previously-described embodiments. The fingers  744 ′ and the slots  748 ′ define a coupling edge with a period of 0.8 mm (measured between centers of the edge portions  749 ). 
   In this second specific example, the first insulation layer  730  is 0.3 micron thick; the contacts  732 ′ are 1.0 micron thick; and the air gap  752  is 2 mm across. All other dimensions and materials of the various layers in the coupling structure  720  are the same as in the first example described above. 
   In the second specific example, activating every fifth electrode pair will result in a beam propagating in a direction forming an angle of 73 degrees with respect to the transmission line, while activating every fourth electrode pair will produce a beam propagating at an angle of 90 degrees with respect the transmission line.