Abstract:
An antenna and a method of creating multiple polarization states in an antenna comprising providing to the antenna a single power input, dividing the power received from the single power input, and transmitting the divided power to a radiating element via a plurality of transmission lines.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of the following three U.S. patent applications: (1) Ser. No. 11/472,151, entitled “Universal Antenna Polarization Selectivity via Variable Dielectric Control”, to Jeffery A. Dean, et al., filed on Jun. 20, 2006, which claimed priority to U.S. Provisional Patent Application Ser. No. 60/782,363, filed on Mar. 14, 2006; (2) Ser. No. 11/428,802, entitled “Variable Differential Power Division to Improve Reciprocal RF Power Distribution Efficiency”, to William S. McKinley, et al., filed on Jul. 5, 2006, which claimed priority to U.S. Provisional Patent Application Ser. No. 60/696,828, filed on Jul. 5, 2005; and (3) Ser. No. 11/455,731, entitled “Dynamic, Non Frequency Dispersive, RF Power Division by Means of Variable Dielectric Material Properties”, to William S. McKinley, et al., filed on Jun. 20, 2006, which claimed priority to U.S. Provisional Patent Application Ser. No. 60/782,363, filed on Mar. 14, 2006. The specifications and claims of all above-listed applications are incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable. 
     COPYRIGHTED MATERIAL 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention (Technical Field) 
     The present invention relates to methods and apparatuses to control antenna polarization states. 
     2. Description of Related Art 
     Multiple polarization antennas are typically implemented by either mechanical switches, electronic phase shifters, or by having a dedicated feed port for each polarization. Polarization diversity can also be achieved by means of software processing to combine the orthogonal antenna polarization data sample outputs as a post processing event. Mechanical switches degrade over time and have limited high frequency applications, while electronic phase shifters are relatively expensive and many are able only to adjust phase in discrete increments resulting in some degree of polarization degradation. Defining dedicated antenna feed points for each polarization results in the disadvantage of being inefficient since the power available is divided amongst the various polarization assignments. And, because a software solution requires a post processing schedule, the results are not real time while requiring a relatively complex investment in interface technology. The present invention places all of the available power into the desired polarization and eliminates the limitations associated with mechanical switches and discrete electronic phase shifters. Furthermore, by controlling the phase in a fine analog sense, a more pure polarization sense is obtained. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is of an antenna capable of multiple polarization states comprising: a single power input; a radiating element; a power divider receiving power from the single power input; and a plurality of transmission lines extending from the power divider to the radiating element. In the preferred embodiment, the plurality of transmission lines comprises a variable dielectric material, preferably comprising barium-strontium-titanate. The antenna additionally comprises one or more capacitors providing direct current isolation between the paraelectric material and the power output lines, preferably comprising silicon nitride. The substrate preferably comprises quartz, and the transmission lines gold. The paraelectric material is divided in sections equal in number to the number of the plurality of transmission lines, with the antenna preferably additionally comprising a plurality of bias lines providing input to the sections. The number of transmission lines is preferably two. The antenna preferably divides radio frequency power. 
     The invention is also of a method of creating multiple polarization states in an antenna comprising: providing to the antenna a single power input; dividing the power received from the single power input; and transmitting the divided power to a radiating element via a plurality of transmission lines. In the preferred embodiment, the plurality of transmission lines comprises a variable dielectric material, preferably comprising barium-strontium-titanate. The method preferably additionally comprises providing direct current isolation between the paraelectric material and the power output lines via one or more capacitors, most preferably comprising silicon nitride. The substrate preferably comprises quartz, the transmission lines gold. The paraelectric material is divided in sections equal in number to the number of the plurality of transmission lines. The method preferably additionally comprises biasing the sections via a plurality of bias lines. The number of transmission lines is preferably two. The method preferably divides radio frequency power. 
     Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings: 
         FIGS. 1(   a ) and  1 ( b ) are schematic diagrams of prior apparatuses generating one or two polarizations, respectively; and 
         FIG. 2  is a schematic diagram of the present invention for selectively obtaining a desired antenna polarization state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is of an apparatus and method for obtaining multiple antenna polarization states (such as right hand circular, left hand circular, slant linear, and miscellaneous elliptical polarizations) from a single RF (radio frequency) port. By controlling the dynamic dielectric properties of paraelectric materials (such as Barium-Strontium-Titanate (BST)), the relative phases of two transmission lines feeding two orthogonal antenna polarizations can be controlled, generating various user-defined polarizations at the RF feed point. 
     As shown in  FIG. 1(   a ), a typical single-input antenna will have only a single polarization (such as linear or circular) associated with it. To achieve additional polarizations, as shown in  FIG. 1(   b ), two RF antenna inputs are required, with an additional disadvantage that only half the power is available for each polarization since it is split. The present invention provides a single-input device that is capable of generating multiple polarizations without splitting the power between polarizations. 
     The invention preferably comprises a microstrip power dividing TEE, two identical transmission lines formed upon depositions of barium-strontium-titanate (BST) having ends DC isolated by means of silicon-nitride depositions forming microwave capacitors, and an antenna element with two inputs that are used to excite simultaneously orthogonal polarizations. The constituent elements preferably reside on a common monolithic thin film substrate such as quartz, alumina, or sapphire. The two outputs from the microstrip power divider are routed over independent BST depositions and fed into the orthogonal polarization inputs of the antenna. The microstrip metal depositions routed over the BST depositions are DC (direct current) isolated from the surrounding microstrip metal by depositions of an insulating material such as silicon nitride, effectively forming DC blocks. By varying the ground referenced voltage over each BST deposition, the effective dielectric constant along the transmission lines can be varied by means of a molecular paraelectric effect. This phenomenon effectively alters the electrical phase lengths over the fixed physical lengths of the transmission lines as a function of applied voltage. By appropriately altering the relative phases of the two antenna ports in this manner, different polarizations (such as right hand circular, left hand circular, and slant linear) can be readily achieved. 
     As shown in  FIG. 2 , the preferred apparatus  10  of the invention comprises an initial stage comprising a center-fed RF power splitter  32  receiving input from a single RF input  22 , two independent transmission lines  33 , 33 ′ on a variable dielectric (paraelectric) material  35 , 35 ′ (such as BST). The RF power splitter preferably yields equal signal power levels on the two transmission lines. By properly altering the dielectric properties of each paraelectric BST deposition, by means of applied DC voltage via control lines  24 , 26 , the relative phases between the two transmission lines are changed. 
     A dual-input antenna  40  is preferably employed. Each input to the antenna excites a polarization that is nominally orthogonal to the polarization excited by the other input, and is fed by the respective transmission line from the previous stage. One example of an antenna that meets this specification is a dual fed microstrip patch antenna, as shown in  FIG. 2 . Other antenna concepts would employ some form of ortho-mode transducer to achieve the requisite orthogonal RF relationship. 
       FIG. 2  also shows preferred construction materials and layers, including a base substrate  12  (e.g., quartz, alumina, sapphire), lower conductive layer  14  (e.g., gold, silver, copper), variable dielectric (paraelectric) material  16  (e.g., BST), upper conductive layer  18  (e.g., gold), and insulating capacitor material  20  (e.g., silicon nitride caps). U.S. Pat. No. 6,875,369 to Tidrow et al., dated Apr. 5, 2005, discloses examples of variable dielectric/paraelectric materials. In particular, Tidrow discloses such materials derived from BST (Ba 1-x Sr x  TiO 3 ) suited to the present invention. 
     By applying independent voltage levels across each BST transmission line, the effective dielectric constant of each line is changed. This changes the effective phase through each line, which in turn changes the polarization of the antenna. For the simplest case, the phases through each transmission line are identical. This results in an antenna with a slant linear polarization. If the phase of one transmission line is adjusted such that it leads the phase of the other line by 90 degrees, then one sense of circular polarization is achieved. Adjusting the phase of that same line to lag the phase of the second line by 90 degrees results in an antenna with the opposite sense of circular polarization. Therefore, slant linear, right-hand circular, and left-hand circular polarizations can be achieved by merely adjusting the voltage on the BST transmission lines. Some elliptical polarizations can also be generated, however, these are generally less valuable than the primary polarizations. 
     An additional advantage of this approach is that the relative phases of each transmission line may be adjusted in fine increments to cancel out any phase imperfections in the antenna and/or the power divider. This results in better cross-polarization isolation for the system. 
     The present invention exhibits reciprocal functionality and thus may be employed for both transmit and receive configurations. Additionally, all of these components can exist on a common monolithic substrate, such as quartz, thus making manufacturing easier and less costly. 
     The present invention is particularly useful for advanced sensors and radar and active phased arrays, or any other application where multiple antenna polarizations are desirable. 
     Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference.