Abstract:
The present invention provides a programmable image antenna formed on the face plate of a cathode ray tube (CRT) or on another substrate. The inner CRT face is coated with a silicon semiconductor material replacing conventional phosphors utilized in CRTs for generating visual images. An electron beam impinging upon the silicon-coated CRT face plate creates conductive areas during liberation of minority carriers, in the form of electron-hole pairs. Antenna elements having a virtually unlimited variety of shapes and/or sizes can be formed on the CRT face.

Description:
RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application Serial No. 60/203,752 filed May 12, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to antennas and, more particularly, to antenna elements transiently formed on a substrate by a light or an electron beam. 
     BACKGROUND OF THE INVENTION 
     Modem communications technology demands the use of antennas operable in many frequency bands with varying gains, polarizations and radiation patterns. The use of radios which can operate over a very broad spectrum of frequencies has heretofore necessitated the use of multiple, narrow frequency band antennas. Because real estate (i.e., the space required to physically implement an antenna) may be limited in some applications, such as aircraft, satellites etc., antennas capable of operating in two or more contiguous or separated frequency bands have been developed. The term “antenna” in this description applies to single element antennas as well as antenna arrays which may contain several elements. Antenna elements which operate over a very wide frequency band are well known to those skilled in the antenna art. A spiral antenna is typical of such a wideband antenna element. Such elements may be well suited for a single element application, but they cannot be physically placed in a periodic array configuration without overlapping, whereby the spacing between the centroids of the elements is around λ/2, where λ is the wavelength of the highest intended frequency of operation. 
     In addition, the orientation of conventional antenna elements is predetermined during manufacturing. It is not generally possible to change the orientation of a complex structure such as a spiral antenna from a right-hand circular polarization (RHCP) to a left-hand circular polarization (LHCP) antenna. However, there are some antenna reconfigurations in the prior art used to selectively connect and disconnect antenna components, thereby allowing a physical reconfiguration of the antenna. For example, U.S. Pat. No. 4,728,805 utilizes photonics to combine antenna elements in various forms. The prior art reconfigurable antenna systems suffer from several deficiencies that effect performance and commercialization. For example, if a smoothly curving antenna element, such as a spiral, is required, the edges of the elements remain jagged, affecting the performance of the antenna. 
     Several other methods are also known to those skilled in the art of antenna design. For example, a technique for putting several individual antenna elements, such as patch antenna elements, in a given area is to overlay or stack them so that the surface of the lower elements behaves as the ground plane for the elements above them. Unfortunately, the higher frequency elements cannot be arrayed close enough to prevent grating lobes when the beam is scanned. 
     Still another approach is to stack elements made of silicon or other semiconductor material that can become conductive when illuminated with light or electrons. The material is precut into the shape of the antenna element (i.e., dipole, spiral or other shape). In this approach, the array of higher frequency elements is positioned below the low frequency elements to maintain a nearly λ/4 spacing between the array of elements and the ground plane. When the low frequency elements are in use, the higher frequency elements below them are not illuminated, thereby becoming transparent to RF energy. Similarly, when the high frequency or lower elements are in operation, the lower frequency elements above them are turned off, becoming purely dielectric and transparent. The surface elements, however, never become totally transparent because the semiconductor materials comprise high ∈ x  dielectric substrates that are not matched to the surrounding composite materials and foams and therefore cause reflections. What is desired is to have the radiators all on one plane. 
     In U.S. No. Pat. 4,310,843, an electron beam antenna array is depicted, wherein the antenna elements are individually energized by p-n junction devices that are controlled by electron beams from a cathode ray tube device. Although the p-n junctions are within the enclosed structure, the antenna elements connected to the p-n junctions are external to the structure. 
     Each of the prior art technologies has a limitation in that only preconceived configurations are generally selectable. In other words, even for an antenna system with selectable frequency bands, polarizations, or directional characteristics, only those discrete possibilities designed into the antenna may be selected. The inventive antenna, on the other hand, has no fixed realization, but rather is “drawn or painted” by an electron beam or the like onto the inner surface of the faceplate. This allows for a great range of possible operations, and simple programming changes applied to the inventive antenna can create a multitude of configurations. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a programmable image antenna formed on the face plate of a cathode ray tube. The CRT face is coated with a semiconductor material such as silicon, gallium arsenide, or indium phosphide, instead of the typical phosphors utilized in CRTs for generating a visual image. An electron beam, striking a silicon-coated face plate, creates conductive areas as minority carriers, in the form of electron-hole pairs. The lifetime of the minority carriers may be adjusted by the resistivity of the silicon material. In this manner, antenna elements having a virtually unlimited variety of shapes and/or sizes can be formed on the CRT face. Coupling this technology with MEMS switches or similar technology can produce a reconfigurable antenna system having an unparalleled range of flexibility. RF energy is coupled to the projected elements by means of an RF transmission line and balun connecting directly or capacitively to the computer generated elements or by means of fiber optic lines that connect to optical/RF modulators and demodulators situated behind the screen on which the projected elements are made conductive. In the case of a direct connection, conductive tabs in the form of ohmic contacts are deposited at the feed points in the silicon plate. 
     Behind the silicon coated screen, inside the cathode ray tube, is a planar grid structure that operates both as a control screen grid for the electronic beams and as the ground plane for the RF elements. More than one grid may be utilized, such as in the form of FSS structures that can act as ground planes situated at λ/4 at various frequencies. 
     It is therefore an object of the invention to provide a programmable image antenna system whereby an excitation means such as RF energy or photonics is used to create antenna elements. A further object of the invention is to provide a reconfigurable array antenna system consisting of individually created antenna elements. 
     Unlike prior art inventions that described reconfigurable antenna elements being formed externally to the system, the antenna elements of the present invention are in an enclosed structure. In addition, the present invention designs the antenna elements directly on the semiconductor material. 
     It is an additional object of the invention to provide a reconfigurable array antenna system consisting of individually created antenna elements that may be configured as frequency selective surfaces (FSSs) with multiple ground planes. 
     It is another object of the invention to provide a programmable image antenna system formed on the face of a cathode ray tube (CRT), and wherein the system formed on the face of a CRT can be made selectively absorptive or reflective. 
     An object of the invention is a programmable image antenna, comprising a substrate adapted for forming an antenna element thereupon, wherein the substrate is in an enclosed structure. There is a coating disposed upon a first surface of the substrate, the coating being conductive in response to impingement of an energy beam that comes from an energy beam source. There is also an energy beam deflection mechanism for deflecting the energy beam in response to externally-generated energy beam deflection signals, thus controlling the beam. Finally, there is a conductive area formed in a selected portion of the coating in response to impingement of the energy beam. 
     Another object is the programmable image antenna, wherein the substrate comprises the face plate of a cathode ray tube (CRT) and the coating is disposed on the inside of the CRT face plate. In addition, wherein the coating comprises a semiconductor material adapted to release minority carriers comprising electron-hole pairs when impinged by the electron beam, the material comprising one from the group: silicon, gallium arsenide and indium phosphide. 
     An additional object includes the programmable image antenna, wherein the semiconductor material has a controllable resistivity and the lifetime of the minority carriers is adjusted by controlling the resistivity of the semiconductor material. And, wherein the resistivity is controlled by altering the purity of the semiconductor material. 
     Yet a further object is the programmable image antenna, wherein the energy beam source comprises one or more electron guns within the CRT and the energy beam comprises an electron beam. The electron guns are configured to work cooperatively to form the antenna elements on the face plate. 
     Additionally, an object includes the programmable image antenna, further comprising RF energy coupling means operatively connected to the programmable image antenna and adapted for coupling an RF signal to at least one antenna element formed on the CRT face plate. The RF energy coupling means comprises at least one from the group: transmission line and balun. And, the RF coupling means further comprising direct connection conductive tabs deposited at predetermined points on the CRT face plate, wherein the conductive tabs comprise aluminum contacts and the predetermined points comprise feed points, the contacts being plated at the feed points on the coating on the face plate of the CRT. 
     And a further object is for the programmable image antenna further comprising at least one substantially planar grid structure disposed within the CRT intermediate the electron gun and the face plate. Including at least one of the at least one substantially planar grid structures is configured to serve as a ground plane. Also, the programmable image antenna with at least one planar grid structure disposed approximately in a λ/4 relationship relative to the face plate at a predetermined operating frequency. Finally, the programmable image antenna, wherein the at least one substantially planar grid structures comprises at least two planar grid structures disposed within the CRT intermediate the electron gun and the CRT face plate, the at least two planar grid structures being configured to form a frequency selective surface. 
     Yet an additional object is the programmable image antenna, wherein the antenna elements are formed on the substrate in at least one pattern from the group: right-hand spiral, left-hand spiral, bow-tie, horizontally-polarized dipole, vertically-polarized dipole. 
     An object includes the programmable image antenna wherein the energy beam deflection system comprises a cursor addressable energy beam control system. 
     An object also includes the programmable image antenna, wherein the antenna elements are maintained on the CRT face by substantially continuously refreshing the conductive areas by the energy beam and the energy beam deflection mechanism. 
     An object of the invention is a programmable image antenna, comprising a substrate adapted for forming an antenna element thereupon, wherein the substrate is in an enclosed structure. There is a coating disposed upon a first surface of the substrate, the coating being conductive in response to impingement of an energy beam. There is an energy beam source for generating the energy beams, and an energy beam connection mechanism for delivering the energy beam, whereby a conductive area is formed in a selected portion of the coating in response to impingement of the energy beam. 
     In this embodiment an object is for a programmable image antenna wherein the substrate comprises the face plate of a cathode ray tube (CRT) and the coating is disposed on the inside of the CRT face plate. An object for this embodiment is the programmable image wherein the energy beam source is photonic. In addition, wherein the energy beam connection mechanism is fiber optic. Finally, an object is the programmable image antenna, wherein the coating comprises a photonically activated coating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent detailed description, in which: 
     FIG. 1 is a schematic, cross-sectional view of the programmable image antenna system of the invention implemented with a cathode ray tube; 
     FIG. 2 a  is first front view of the CRT shown in FIG. 1, with a RHCP spiral antenna array pattern generated on the CRT face plate; 
     FIG. 2 b  is second front view of the CRT shown in FIG. 1, with a second antenna pattern similar to FIG. 2 a , except that the spirals generated on the CRT face plate are LHCP; 
     FIG. 3 a  is a front view of the CRT shown in FIG. 1, with a bow tie dipole array pattern; 
     FIG. 3 b  is a front view of the CRT shown in FIG. 1, with a frequency selective surface (FSS) pattern; 
     FIG. 3 c  is a front view of the CRT shown in FIG. 1, with an array of vertically-polarized dipoles; and 
     FIG. 3 d  is a front view of the CRT shown in FIG. 1, with an array of horizontally polarized dipoles. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention features a programmable image antenna formed on the face plate of a cathode ray tube. Referring first to FIG. 1, there is shown a schematic, cross-sectional view of a CRT, generally at reference number  100 . Three electron guns  108   a ,  108   b ,  108   c  are located at the rear of CRT  100 . Three electron beams  112   a ,  112   b ,  112   c , generated by electron guns  108   a ,  108   b ,  108   c , respectively, are steered by deflection mechanisms shown here as a deflection yoke  110 . Any combination of magnetic and/or electrostatic deflection methods well known to those skilled in the CRT art could be used. In particular, electron gun control and the manner of implementation is general knowledge. Electron guns  108   a ,  108   b ,  108   c  each have z axis control capability (i.e., electron beams  112   a ,  112   b ,  112   c  may be turned on and off by electrical signals). The combination of the z-axis control and deflection yoke  110  allows for generation of patterns on CRT  100 . 
     CRT  100  has a face  102  coated with a semiconductor material  104 . Amorphous silicon, gallium arsenide and indium phosphide are among the materials known to be suitable for this application. There may well be other materials suitable for use known to those skilled in the art. Semiconductor material  104  forms a screen on the inside of face  102  and replaces light-generating phosphors typically used for visual image production. The semiconductor materials can be applied as a coating or by using vapor or spray-on deposition techniques, as well as other methods familiar to those skilled in the art. 
     One or more conductive planar grid structures (screens)  106 , constructed in a manner similar to a shadow mask or similar component in a conventional CRT, are placed an appropriate distance behind the face plate  102 , typically a distance having a λ/4 relationship to a frequency being transmitted or received by the antenna. Grids  106  operate both as control screen grids for the electron beams  112   a ,  112   b ,  112   c  and as ground planes for the RF elements. Grids  106  may be implemented as frequency selective surface (FSS) structures that can act as ground planes situated at λ/4 at various frequencies. 
     In this example, the three electron beams  112   a ,  112   b ,  112   c  are used to “paint” the antenna elements on the semiconductor screen  104 . The antenna elements are enclosed within the structure. There is no minimum number of electron guns, and any number that can effectively control the entire surface of the semiconductor material without suffering serious blockage from the grids  106  would be satisfactory. The electron guns  108   a ,  108   b ,  108   c  are positioned in such a way as to assure that all points on the semiconductor screen  104  are accessible to at least one of the electron guns  108   a ,  108   b ,  108   c . When electron beams  112   a ,  112   b ,  112   c  strike semiconductor screen  104  on CRT face  102 , conductive areas, formed as minority carriers (not shown) in the form of electron-hole pairs, are liberated. The lifetime of the minority carriers may be adjusted by selecting the purity of the silicon material of predetermined purity. Lifetimes in the range of approximately 0.01 to 1.0 ms are typical, depending upon the choice of semiconductor material and the amount and manner of doping of the semiconductor 
     RF energy is coupled to the projected elements on screen  104  of CRT  100  by means of RF transmission lines  118  and baluns  116  connecting directly or capacitively to computer generated elements (i.e., conducting regions in the semiconductor material  104 ). Typical conductive patterns are shown in FIGS. 2 a ,  2   b  and  3   a - 3   d  which are drawn by the system. Conductive tabs (not shown) in the form of ohmic contacts are deposited at the feed points in the semiconductor screen  104  under baluns  116 . The process involves doping the silicon and plating aluminum contacts. Persons having skill in semiconductor processes are familiar with depositing ohmic contacts onto silicon. Since oxidation is not a problem inside a low atmosphere CRT, transmission lines  118  could make contact as springs originating from the transmission lines and applying pressure to the ohmic contacts. 
     The RF transmission lines  118  are grouped and folded out of the way of the electron beams and brought to the sides of CRT connectors or capacitive patches  120 . The capacitive patches  120  operate in a manner similar to a cellular antenna connected through the windshield of an automobile: the connection is capacitive and need not penetrate the glass. 
     In alternate embodiments, RF energy could also be coupled by means of modulated light via fiber optic lines (not shown) that connect to optical/RF modulators and demodulators (not shown) disposed behind the screen  104  on which the projected elements are made conductive. 
     Referring now again to FIGS. 2 a  and  2   b , there are shown right-hand and left-hand, circularly polarized spiral antenna patterns, respectively, formed on face plate  102  by electron beams  112   a ,  112   b ,  112   c . Referring now also to FIGS. 3 a ,  3   b ,  3   c  and  3   d , there are shown four additional possible antenna patterns. FIG. 3 a  shows an array of bow-tie elements; FIG. 3 b  a frequency selective surface (FSS) pattern; FIG. 3 c  an array of vertically polarized diodes; and FIG. 3 d  an array of horizontally polarized diodes. 
     As may be seen, a wide variety of antenna element shapes may readily be formed on face plate  102  merely by changing the deflection of electron beams  112   a ,  112   b ,  112   c.    
     One of the many advantages of the inventive programmable antenna is that very smooth antenna curvatures can be achieved, as compared to discrete segments connected together with switches. This allows a high degree of precision in the left-hand and right-hand spiral antenna elements shown in FIGS. 2 a  and  2   b , respectively. There is no limit to the number of different patterns that may be generated, a limitation being only the resolution of the semiconductor material  104  on the face  102  of CRT  100 . 
     In other embodiments, a substrate other than a CRT face may be coated with a photonically responsive material. A laser or other similar energy source could then be used to selectively activate conductive areas on the substrate. In yet other embodiments, some type of bipolar, switchable materials could be employed so that a particular conductive pattern on the substrate could be maintained, absent the constant refreshing of an electron gun, laser, or the like. 
     The inventive technique may be used to change antenna characteristics in different ways. A certain antenna configuration could be created for a long period of time by constantly refreshing the screen. When the use of that first configuration was no longer required, an alternate configuration could be “written” to the screen and maintained until a second task was performed using the antenna. Refreshing the screen by utilizing cursor addressable beam control, as occurs with computer screens, allows the system to handle several elements simultaneously. This represents an improvement in flexibility and speed over the raster scan technique of conventional TV sets that operate at 30 Hz. 
     Another mode of operation is also possible. Because the lifetime of the conductivity of the semiconductor material may be relatively short (i.e., on the order of tenths of milliseconds), the inventive system could be used to switch quickly among several antenna configurations, thereby effectively multiplexing the antenna. 
     Another useful feature of the inventive system is to make the antenna “disappear” (i.e., become reflective or lossy) by continuously refreshing the entire surface area of the CRT or other substrate. This has obvious advantages in applications where the antenna and the aperture could become radar reflective, for example, when not in actual use. 
     The features of the present invention could be utilized to change polarization or directionality of the antenna rapidly. If an array of antenna elements is painted, array steering could also be accomplished. 
     The programmable image concept could also be used to construct a reconfigurable reflective surface behind other antenna elements. 
     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. 
     Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.