Patent Publication Number: US-5155493-A

Title: Tape type microstrip patch antenna

Description:
RIGHTS OF THE GOVERNMENT 
     The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a tape type microstrip patch antenna. 
     Conventionally, microstrip patch antennas are fabricated from printed circuit board materials which consist of a uniform thickness of TEFLON® fiberglass, or a similar type dielectric layer, which has copper layers laminated on both top and bottom surfaces. The appropriate pattern for the patch is then photlithographically defined on the top surface of the copper and the unwanted copper is chemically etched away leaving the desired patch. The bottom copper layer forms the ground plane for the antenna. Due to the nature of the materials and fabrication process, these antennas do not lend themselves to low cost mass production, and do not afford the possibility of quick and simple conformal mounting on differing types of non-planar surfaces, such as aircraft, projectiles, etc. These etched antennas are subject to failure of the dielectric due to flexing. 
     United States patents of interest include U.S. Pat. No. 4,414,550, to Tresselt which relates to a low profile circular array antenna and related microstrip elements. This patent describes an embodiment wherein copper foil tape is soldered to plates of copper cladding on a standard TEFLON® fiberglass stripline board in construction of antenna elements comprised of two patch dipoles. Johnson et al patent No. 4,835,541 relates to a conformal mobile vehicle antenna which involves the use of strips of conductive aluminum tape to establish conductive bonding between other components. Curtice patent No. 3,996,529 is of general interest in that it relates to a varacter tuning apparatus for a microstrip transmission line device which incorporates an insulating material of self adhesive TEFLON® tape. 
     SUMMARY OF THE INVENTION 
     An objective of the invention is to provide an antenna which is simple and easily adaptable to various mounting conditions. 
     The invention is directed to a tape-based microstrip patch antenna wherein single or multiple layers of electrically insulating tape have adhesive applied to one surface for the dielectric of the patch antenna. Electrically conductive foil tape with adhesive applied to one surface is used to create the radiating element and the ground plane. The antenna structure can then be mounted to the desired surface by means of structural tape adhesives. The resultant sandwich structure forms a highly flexible, low profile, low cost, rugged conformal antenna for radiating radio frequency energy. Modification and control of the electrical and performance characteristics of the antenna is provided for as more particularly described in the detailed description herein. 
     The invention comprises a device and related fabrication techniques which bring together a combination of technologies not previously applied to the fabrication and design of microstrip patch antennas. 
     Features 
     Antenna can be fabricated in bulk rolls (peel and stick) at low cost. 
     Antennas are highly flexible and can be made very thin thus will conform to the surface on which it is applied 
     Design allows for great flexibility in the manufacturing process. 
     Dielectric structure can be non-uniform in thickness and inhomogeneous in composition. 
     Eliminates present technology reliance on laminating process for fabrication. 
     Use of structural adhesives provides an extremely strong bond to the underlying structure but can easily be removed by application of proper solvent. 
     Non-homogeneous dielectric thickness can be achieved easily. 
     Shaped dielectric and ground plane (including non-continuous) can be fabricated easily. 
     Antenna thickness can be changed by adding or removing layers of the dielectric tape thus allowing the adjustment of the antenna characteristics even and at the time of application. 
     Multiple frequency resonances may be possible with certain inhomogeneous tape configurations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a diagram showing a tape type microstrip patch antenna mounted on a cylindrical surface; 
     FIG. 1a is a cross section view of the antenna of FIG. 1; 
     FIG. 1b is a cross section view corresponding to that of FIG. 1a, with a tape radome added; 
     FIGS. 2 and 2a are top and cross section views respectively of a microstrip patch antenna with a diode for controlling the characteristics; 
     FIGS. 3-6 are cross section views, and FIG. 7 is an exploded view, showing modifications of the thickness and dielectric constant for the insulating layer to provide different radiating characteristics; and 
     FIG. 8 is a top view of an embodiment of the patch antenna with an optically controlled diode and an embedded optical waveguide; and 
     FIGS. 8a and 8b are cross section views taken respectively along lines 8a--8a and 8b--8b of FIG. 8. 
    
    
     DETAILED DESCRIPTION 
     The invention is disclosed in a report AFATL-TR-89-27 by M. Thursby et al titled &#34;Subminiature Telemetry Antenna Study&#34;, available as of Nov. 2, 1989 from the Defense Technical Information Center (DTIC) as AD-B137 538. A copy of this report is attached hereto as an appendix, and is hereby incorporated by reference. 
     The tape-based microstrip patch antenna incorporates single or multiple layers of electrically insulating tape with the adhesive applied to one surface for the dielectric of the patch antenna. Electrically conductive foil tape with adhesive applied to one surface is used to create the radiating element and the ground plane. The antenna structure can then be mounted to the desired surface by means of structural tape adhesives. The resultant sandwich structure forms a highly flexible, low profile, low cost, rugged conformal antenna for radiating radio frequency energy. It can be easily produced at low cost and is quick and simple to install and remove. 
     FIG. 1 shows a cylindrical surface 10 on which a tape-based microstrip patch antenna 12 is mounted. This embodiment shows a strip line type feed 20. FIG. 1a is a cross section view of the antenna 12 of FIG. 1, showing electrically conductive foil tape 14 applied to the surface 10 as a ground plane, electrically insulating tape 16 applied over the ground plane for the dielectric, and electrically conductive foil tape 18 applied over the tape 16 as the radiating element. FIG. 1b shows the same antenna with insulating tape 22 added over the entire structure as a radome. 
     The fabrication of a patch antenna, with a coaxial feed as shown at point 220 in FIGS. 2 and 2a, (without the diode 232) may comprise the following steps: 
     1. A bare copper substrate 214 is used for the ground plane in the tape antenna structure. 
     2. A hole to pass the feed structure through the ground plane is punched in a position that will allow the patch to be placed approximately in the center of the ground plane. 
     3. The ground plane is cleaned to provide a good soldering surface and improve adhesion of the tape elements to the surface. 
     4. A ring is tinned around the hole. 
     5. After an interface connector is tinned the two are soldered together with the center conductor of the SMA connection centered in the feed hole. 
     6. PTFE dielectric tape 216 is applied to the ground plane in a manner that will allow the patch to be placed on top of the stacked layer of dielectric. 
     7. The active radiating element 218 is placed on top of the dielectric and the feed point 220 is soldered to the active element. 
     8. The entire antenna is covered with a radome (as shown in FIG. 1b) to protect the surface element and provide an integrated antenna structure. 
     Modification and control of the electrical and performance characteristics of the antenna can be incorporated into the tape dielectric layer by embedding electrically or optically controlled devices (e.g. PIN diodes) into the antenna substructure at the time of the tape application thus reducing the number of steps required in the fabrication process of such controlled structures. Optical waveguide structures such as optical fibers or polymer planar waveguides can also be integrated into the structure at the same time the dielectric materials are being laid down. This will allow the use of guided optical waves to control the electrical devices to alter the antenna characteristics. 
     FIGS. 2 and 2a show an optically controlled diode 232 having its cathode connected to the radiating element at point 230 and its anode connected to the ground plane 214. An optical waveguide structure (not shown) may be integrated into the patch antenna to illuminate the diode 232. 
     FIGS. 8, 8a and 8b are views of an embodiment similar to that of FIG. 2, showing how a fiberoptical glass fiber 800 may be embedded in the dielectric. FIG. 8 is a top view showing the orientation of the fiber 800. FIG. 8a is a cross section view of the antenna, to show a cross section of the glass fiber 800, embedded between layers of the dielectric 816. FIG. 8b is a cross section view along the length of the glass fiber 800, showing the fiber 800 coupled to an optically controlled diode 832. Like in FIG. 2, the antenna comprises a ground plane 814, a dielectric layer 816, and a patch element 818. A feed point 820 corresponds to feed point 220 of FIG. 2. The diode 832 has a lead connected to the radiating element 818 at point 830, and a lead connected to the ground plane at point 834. In FIGS. 8a and 8b, the dielectric 816 is shown as comprising four layers 816a, 816b, 816c and 816d. The glass fiber 800 is shown embedded between layers 816b and 816c. 
     The fact that the tape antenna is fabricated with multiple thin layers of tape dielectric allows one to construct a series of layers that are not necessarily uniform in thickness or dielectric constant, and can vary in direction and spatial position. FIGS. 3-7 are schematic representations of this characteristic. This feature allows one to easily produce steps and graded thickness characteristics within the antenna dielectric structure, thereby providing for the possibility that modes other than the conventional modes of resonance might be set up within the antenna and alter the frequency, bandwidth, and spatial field pattern of operation. This provides for adaptive control of antennas that is not available with conventionally fabricated antennas. 
     FIG. 3 shows the patch antenna in which the dielectric layer is of uniform thickness and homogeneous in the dielectric constant ε. FIGS. 4 and 5 show patch antennas in which the dielectric layer is of non-uniform thickness but homogeneous in the dielectric constant ε. FIG. 4 shows a continuously variable thickness, and FIG. 5 shows a case with stepped thickness with layers of insulating tape, being thinner in the center. There are several possible variations of non-uniform thickness, such as thin at one end, and increasing in thickness toward the other end. Also the feed point be at various places with respect to the thick and thin areas. 
     FIGS. 6 and 7 show patch antennas in which the dielectric layer is of uniform thickness but non-homogeneous in the dielectric constant. FIG. 6 shows the insulating layer having three strips of tape with respective dielectric constants of ε 1 , ε 2  and ε 3 . FIG. 7 is an exploded view of a patch antenna, in which the insulating layer has a shaped dielectric ε 1 , and a portion in the center having a dielectric constant ε 2 . 
     The dielectric layer and active element are made of a tape material and therefore can be shaped to conform to the surface of the device on which they are being applied. Thus these devices provide a natural technique for constructing conformal antenna structures. 
     One application of the antenna structure described above is to the telemetry of data from various flying vehicles such as aircraft, missiles, and projectiles. The new technology involved makes realizable and practical the concept of adaptive peel-and-stick antenna systems. That is, a subminiature patch microstrip antenna can be dispensed from a roll of generic patch antenna devices and attached to a desired surface by exposing the adhesive underside of the antenna through removal of a covering release sheet. 
     The invention provides a structure for a telemetry antenna that is easily attached to a munition just prior to testing. The antenna is simple and easily adaptable to various mounting conditions. The potential for use of munitions of sizes from that of a baseball to the size of a large space vehicle requires that the antenna be able to withstand severe environmental conditions including temperature, wind forces, and potentially, plasma effects. 
     It is understood that certain modifications to the invention as described may be made, as might occur to one with skill in the field of the invention, within the scope of the appended claims. Therefore, all embodiments contemplated hereunder which achieve the objects of the present invention have not been shown in complete detail. Other embodiments may be developed without departing from the scope of the appended claims.