Patent Publication Number: US-7218281-B2

Title: Artificial impedance structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to U.S. application Ser. No. 11/173,182, titled “Artificial Impedance Structures,” filed on Jul. 1, 2005, which is incorporated herein by reference in its entirety. 
   FIELD OF THE INVENTION 
   The present invention relates to artificial impedance structures. More particularly, the present invention relates to propagating electromagnetic waves around solid objects using artificial impedance structures. 
   BACKGROUND 
   A common problem for antenna designers is creating antennas that are able to radiate energy at angles that are shadowed. For example, in Prior Art, a monopole antenna  10  on a conducting cylinder  20 , as shown in  FIGS. 1   a  and  1   b , does not radiate energy below line  3  because the external surface of the cylinder  20  that is below line  3  is shadowed from the monopole antenna  10 . FIG  1   c  shows the radiation pattern  22  produced by the cylinder  20  in  FIGS. 1   a  and  1   b.    
   PRIOR ART 
   The prior art consists of three main categories: (1) holographic antennas, (2) frequency selective surfaces and other artificial reactance surfaces, and (3) surface guiding by modulated dielectric or impedance layers. 
   Example of prior art directed to artificial antennas includes:
     1. P. Checcacci, V. Russo, A. Scheggi, “Holographic Antennas”, IEEE Transactions on Antennas and Propagation, vol. 18, no. 6, pp. 811–813, November 1970;   2. D. M. Sazonov, “Computer Aided Design of Holographic Antennas”, IEEE International Symposium of the Antennas and Propagation Society 1999, vol. 2, pp. 738–741, July 1999;   3. K. Levis, A. Ittipiboon, A. Petosa, L. Roy, P. Berini, “Ka-Band Dipole Holographic Antennas”, IEE Proceedings of Microwaves, Antennas and Propagation, vol. 148, no. 2, pp. 129–132, April 2001.   

   Example of prior art directed to frequency selective surfaces and other artificial reactance surfaces includes:
     1. R. King, D. Thiel, K. Park, “The Synthesis of Surface Reactance Using an Artificial Dielectric”, IEEE Transactions on Antennas and Propagation, vol. 31, no. 3, pp. 471–476, May, 1983;   2. R. Mittra, C. H. Chan, T. Cwik, “Techniques for Analyzing Frequency Selective Surfaces  13  A Review”, Proceedings of the IEEE, vol. 76, no. 12, pp. 1593–1615, December 1988;   3. D. Sievenpiper, L. Zhang, R. Broas, N. Alexopolous, E. Yablonovitch, “High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band”, IEEE Transactions on Microwave Theory and Techniques, vol. 47, no. 11, pp. 2059–2074, November 1999.   

   Example of prior art directed to surface guiding by modulated dielectric or impedance layers includes:
     1. A. Thomas, F. Zucker, “Radiation from Modulated Surface Wave Structures I”, IRE International Convention Record, vol. 5, pp. 153–160, March 1957;   2. R. Pease, “Radiation from Modulated Surface Wave Structures II”, IRE International Convention Record, vol. 5, pp. 161–165, March 1957;   3. A. Oliner, A. Hessel, “Guided waves on sinusoidally-modulated reactance surfaces”, IEEE Transactions on Antennas and Propagation, vol. 7, no. 5, pp. 201–208, December 1959.   

   Example of prior art directed to this general area also includes:
     1. T. Q. Ho, J. C. Logan, J. W. Rocway “Frequency Selective Surface Integrated Antenna System”, U.S. Pat. No. 5,917,458, Sep. 8, 1995;   2. A. E. Fathy, A. Rosen, H. S. Owen, f. McGinty, D. J. McGee, G. C. Taylor, R. Amantea, P. K. Swain, S. M. Perlow, M. ElSherbiny, “Silicon-Based Reconfigurable Antennas—Concepts, Analysis, Implementation and Feasibility”, IEEE Transactions on Microwave Theory and Techniques, vol. 51, no. 6, pp. 1650–1661, June 2003.   

   
     BRIEF DESCRIPTION OF THE FIGS. 
       FIGS. 1   a  and  1   b  relate to Prior Art and depict a monopole antenna on a conducting cylinder, PRIOR ART; 
       FIG. 1   c  relates to Prior Art and depicts a low gain radiation patter generated by the conducting cylinder in  FIGS. 1   a  and  1   b;    
       FIG. 2  depicts an artificial impedance structure; 
       FIGS. 3   a – 3   b  depict a monopole antenna on a cylinder covered by a artificial impedance structure in accordance with the present disclosure; 
       FIG. 3   c  depicts a high gain radiation patter generated by a cylinder in  FIGS. 3   a  and  3   b  in accordance with the present disclosure; 
       FIG. 4   a  depicts a tail of an airplane covered by an artificial impedance structure in accordance with the present disclosure; 
       FIG. 4   b  depicts an engine of an airplane covered by an artificial impedance structure in accordance with the present disclosure; 
       FIG. 5   a  depicts an offensive device being affected by jamming signals; and 
       FIG. 5   b  depicts an offensive device covered by an artificial impedance structure in accordance with the present disclosure. 
   

   In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of every implementation nor relative dimensions of the depicted elements, and are not drawn to scale. 
   DETAILED DESCRIPTION 
   According to the present disclosure, artificial impedance structures may be placed over different surfaces to provide scattering or guiding properties desired by the antenna designer. 
   The artificial impedance structure may be designed to guide and radiate energy from the electromagnetic waves to produce any arbitrary radiation pattern. See, for example, a related application U.S. application Ser. No. 11/173,182, filed on Jul. 1, 2005, “Artificial Impedance Structures,” which is incorporated herein by reference in its entirety. 
   Referring to  FIG. 2 , an artificial impedance structure  25  can be used to design antennas on curved shapes and to have radiation properties that would ordinarily be impossible. The artificial impedance structure  25  may contain an artificial impedance surface  30  that comprises conductive structures  40  printed on a grounded dielectric layer  35  that is thinner than the wavelength of operation. 
   The artificial impedance structure  25  may be applied to solid objects to guide waves around those objects. Because the methods described here can be used to transform one wave into another through surface wave coupling, by engineering the scattering properties of the surface, the same concept can be used if the source wave is an incoming plane wave or the radiation pattern of a nearby antenna. The artificial impedance structure  25  can be used to fill in nulls that would otherwise be created by the vehicle structure on which the antenna is mounted. The artificial impedance structure  25  can also be used to make better omnidirectional antennas that are not affected by the local environment. In one exemplary embodiment, the artificial impedance structure  25  may, for example, be built as a printed circuit board to be wrapped around an object that may be interfering the performance of an antenna. 
   Referring to  FIGS. 3   a  and  3   b , the artificial impedance structure  25  was placed over a cylinder  60  to enable a monopole antenna  70  disposed on the cylinder  60  to produce a narrow beam on the opposite side of the cylinder  60 , toward a direction that is otherwise shadowed. The monopole antenna  70  generates surface currents  80  that propagate along the artificial impedance structure  25  and around the cylinder  60 . The artificial impedance structure  25  was designed using the interference pattern formed by the surface currents, and a plane wave at 135 degrees on the opposite side of the cylinder  60 . The radiation pattern  24  in  FIG. 3   c  of the artificial impedance structure  25  disposed on the cylinder  60  showed a narrow beam at 135 degrees. 
   The artificial impedance structure may also be used to guide incoming plane waves around a solid object. For example, the artificial impedance structure may make portions of an airplane transparent to radiation for greater radar scan range. Referring to  FIG. 4   a , a tail  91  of an airplane  92  may be covered by an artificial impedance structure  95  to allow the radar  93  to see through the tail  91 . Referring to  FIG. 4   b , an engine  101  of an airplane  102  may be covered by an artificial impedance structure  105  to allow the radar  103  to see through the engine  101 . The waves  94  and  104  do not actually pass through the tail  91  and the engine  101 , respectively, but are guided around the tail  91  and the engine  101  by the artificial impedance structure  95  and  101 , respectively, and re-radiate from the other side. 
   Using the concepts described above, an artificial impedance structure may also be designed and used to suppress certain incoming electromagnetic waves from propagating around a solid object. Referring to  FIG. 5   a , a GPS (global position system) guided offensive device  110  is susceptible to jammer signals  112  coming from the ground because the surface of the offensive device  110  may propagate the jammer signals  112  to the GPS receiver  115 . Referring to  FIG. 5   b , an artificial impedance structure  120  may be placed on the portion of the offensive device  110  surrounding the GPS receiver  115 . The artificial impedance designed to only propagate radiation from above the horizon thus making the device  110  more resistant to jammers. The device  110  may be an offensive device. 
   The foregoing detailed description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the invention to the precise form(s) described, but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. Applicant has made this disclosure with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the invention be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ” and no method or process step herein is to be construed under those provisions unless the step, or steps, are expressly recited using the phrase “step(s) for . . . . ”