Abstract:
The present invention is a grounded mast clamp current probe apparatus. The apparatus can have a current probe substantially enclosed by at least one housing. The housing forms an electrostatic shield that prevents passage of electricity to or from the current probe. A plurality of grounding elements are connected to the outer surface of the housing and radiate outwardly from the outer circumference of the housing. Each of the grounding elements radiates at a frequency angle θ, the angle formed between a longitudinal axis of the housing and a longitudinal axis of the grounding elements. The bandwidth and resonant frequency of the current probe is dependent on the frequency angle θ.

Description:
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
     This invention is assigned to the United States Government. Licensing inquiries may be directed to Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; telephone (619) 553-5118; email: ssc_pac_t2@navy.mil. Reference Navy Case No. 101613. 
    
    
     BACKGROUND 
     1. Field 
     This invention relates to the field of radio wave antennas, and more specifically, to adaptive technology for grounding and increasing the bandwidth of currently-deployed antenna structures. 
     2. Background 
     Antennas deployed by the U.S. Navy must interface with commercial communications systems. The ability to interface currently deployed military and civilian technology is critical to command control functions. However, a growing number of commercial communications systems utilize bandwidths that existing military antennas cannot match. 
     The Navy&#39;s Space and Naval Warfare Systems Command (SPAWAR) can have developed technology to adapt existing antennas to provide increased bandwidth and a critical communications interface. One exemplary technology developed by SPAWAR is the Mast Clamp Current Probe (MCCP), disclosed in U.S. Pat. No. 8,164,534 issued to Daniel Tam (Tam &#39;534) and U.S. Pat. No. 7,994,992 issued to Daniel Tam et al. (Tam &#39;992), the contents of which are incorporated herein by reference in their entirety. Tam &#39;534 and Tam &#39;992 teach an adaptive device that can be mounted to existing antennas to convert them to multiband capability without the downtime or redeployment costs typically associated with such capability. Tam &#39;534 and Tam &#39;992 teach a method and devices through which probes, transmitting lines, and receiving lines can be operatively coupled with existing antennas to increase the frequency range and the number of transmission and receiving lines to the number necessary to interface with private sector technology. 
     One problem overcome by the MCCP device is that it improves the voltage standing wave ratio (VSWR) along a transmission line leading to the antenna. 
     Bandwidth, associated with the addition of transmission and receiving components, generally results in an increase in the measurable VSWR. However, as bandwidth and corresponding VSWR increase, it is known in the art that large amounts of power can be reflected to the transmission line. Large amounts of reflected power can damage the radio-transmitting systems. Tam &#39;534 and Tam &#39;992 taught a method and apparatus capable of controlling VSWR associated with bandwidth while preventing damage to the radio. 
     It is a problem known in the art that MCCP-enabled systems must be effectively grounded to form a complete circuit for transmission, and in such a manner that the systems are safe for use aboard a ship. Grounding methods and components in the art that alter the structure of the MCCP system also affect the critical frequencies achieved by the MCCP structures. Grounding structures known in the art (referred to as counterpoises) achieve unpredictable results and compromise mission-critical transmissions. 
     It desirable to have an MCCP-enabled system that is capable of being grounded and maintaining accurate, mission-critical transmission. 
     SUMMARY OF THE INVENTION 
     The present invention is a grounded mast clamp current probe apparatus. The apparatus can have a current probe substantially enclosed by at least one housing. This housing forms an electrostatic shield which prevents passage of electricity to or from the current probe. A plurality of grounding elements are connected to the outer surface of the housing and radiate outwardly from the outer circumference of the housing. Each of the grounding elements radiates at a frequency angle θ, the angle formed between a longitudinal axis of the housing and a longitudinal axis of the grounding elements. The bandwidth and resonant frequency of the current probe is dependent on the frequency angle θ. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a side view of an exemplary embodiment of a grounded MCCP system with grounding elements that are strip-shaped. 
         FIG. 2  illustrates a top view of an exemplary embodiment of a grounded MCCP wherein a slit and current probe are visible. 
         FIGS. 3   a  through  3   c  illustrate three alternative embodiments for placement of strip-shaped grounding elements at varying frequency angles  8 . 
         FIG. 4  illustrates an alternative exemplary embodiment of a grounded MCCP system that utilizes electrolytic fluid streams as grounding elements. 
         FIG. 5  illustrates a graph of data for a grounded MCCP system that shows an exemplary relationship of the frequency angles θ of the grounded MCCP to resonant frequency and bandwidth. 
         FIGS. 6   a  and  6   b  illustrate two alternative embodiments of an antenna structure for a grounded MCCP system where antenna length can have been varied. 
         FIG. 7  illustrates a graph of data for a grounded MCCP system which shows an exemplary relationship of the length of the antenna to resonant frequency and bandwidth for a grounded MCCP system. 
         FIG. 8  is a block diagram of steps that can be taken to accomplish the methods of the present invention according to several embodiments. 
     
    
    
     TERM OF ART 
     As used herein, the term “Mast Clamp Current Probe (MCCP)” is defined as an adaptive device for an antenna, taught by U.S. Pat. No. 8,164,534 and U.S. Pat. No. 7,994,992 (both hereinafter incorporated by reference), which operatively couples current probes, transmitting lines, and receiving lines to existing antennas to increase the frequency range and bandwidth. 
     DETAILED DESCRIPTION OF INVENTION 
       FIGS. 1 and 2  illustrate a side view of an exemplary embodiment of a grounded MCCP system with grounding elements that are strip-shaped. As illustrated in  FIGS. 1 and 2 , grounded MCCP system  100  can be composed of an MCCP  10  mounted to an antenna  30 . MCCP  10  is made up of housing  20 , a current probe  23  (seen in  FIG. 2 ), at least one cable  27 , and a plurality of strip-shaped grounding elements  15   a  through  15   d  forming a counterpoise. 
     Housing  20  can form an electrostatic shield, substantially preventing the passage of electricity to or from the current probe  23 . In the exemplary embodiment shown, a weight-bearing support component (not shown) selectively mounts housing  20  to antenna  30 . In other embodiments, housing  20  may be permanently attached to antenna  30 . 
     As illustrated in  FIGS. 1 and 2 , a cable  27  encloses a single frequency transmitting and receiving line pair operatively coupled to the current probe  23 . Alternative embodiments may include more or fewer line pairs and different physical configurations of cable  27 . In other embodiments, cable  27  may be located inside of antenna  30 . 
       FIG. 1  also illustrates strip-shaped grounding elements  15   a  through  15   d , which store current during signal transmission or reception. These elements provide a ground plane for the MCCP without interfering with MCCP transmission or reception, as they are integrally attached to the outside of housing  20  and therefore outside of the electrostatic shield. Strip-shaped grounding elements  15   a  through  15 N can be attached to the outside of housing  20  with conductive tape, solder or conductive adhesives (note that  FIG. 1  only depicts grounding elements  15   a  through  15   d , but the illustration of four grounding elements in the Figures is not intended to be an implied restriction on the present invention according to several embodiments. In another contemplated embodiment, the strip-shaped grounding elements  15   a  through  15   d  are attached by removable screws or bolts to housing  20 . The screws or bolts fit through matching and aligned holes in strip-shaped grounding elements  15   a  through  15   d  and housing  20 . This enables removal of strip-shaped grounding elements  15   a  through  15   d  for transportation or storage when not needed, as well as replacement of damaged strip-shaped grounding elements  15   a  through  15   d  or alteration of the angle of the strip-shaped grounding elements  15   a  through  15   d . Interlocking, mechanical and integrally machined strip-shaped grounding elements  15   a  through  15   d  are also contemplated. 
     While the above exemplary embodiments of  FIG. 1  form the strip-shaped grounding elements  15   a  through  15   d  from brass, materials in other contemplated embodiments may be, but are not limited to, copper, aluminum and other metallic materials. While the above exemplary embodiments utilize four strip-shaped grounding elements  15   a  through  15   d , other contemplated embodiments may use any number from about four to about three hundred. A larger number of strip-shaped grounding elements reduce the size of the space between the strip-shaped grounding elements to closely emulate a ground plane structure. 
     Exemplary embodiments of  FIG. 1  utilize flat, ribbon-like strip-shaped grounding elements  15   a  through  15   d  with a rectangular cross-section. In alternative embodiments, cross section shapes may include, but are not limited to, circular, square, octagon, geometrically-optimized and irregularly-shaped cross-sections. 
     While strip-shaped grounding elements  15   a  through  15   d  of the above embodiment of  FIG. 1  are approximately 1-inch wide, in alternative embodiments, strip-shaped grounding elements  15   a  through  15   d  may have a width w (See  FIG. 2 ) ranging from about 0.25 inches to about 12 inches. In various embodiments, the width of strip-shaped grounding elements  15   a  through  15   d  may be identified as a dependent upon the width of the housing  20 , being at most about one-half of the diameter of housing  20 . Strip-shaped grounding elements  15   a  through  15   d  may have a length dependent upon the frequency intended to be transmitted from antenna  30 . A formula for determining the length of strip-shaped grounding elements  15   a  through  15   d  is:
 
 L   s =( c /(4 f ))−( R   M   +H   M )
 
where L s  is the length of strip-shaped grounding elements  15   a  through  15   d, c  is the speed of light, f is the transmission frequency, R M  is the radius of the MCCP and H M  is the height of the MCCP, the measurement from base to top (See  FIG. 2 ).
 
     As illustrated in  FIG. 1 , antenna  30  is a mast structurally configured to form an antenna. The exemplary antenna illustrated in  FIG. 1  is a traditional, metal, monopole antenna. In alternative embodiments, antenna  30  may be a dipole and grounded metal pole, an electrolytic fluid antenna, or any structure that may be adapted to function as an antenna. Various embodiments of an electrolytic fluid antenna are contemplated in U.S. Pat. No. 7,898,484 issued to Daniel Tam (Tam &#39;484), the contents of which are incorporated herein by reference in their entirety. In various embodiments, antenna  30  can have at minimum a shaft and a frequency range. Each pair of frequency transmitting and receiving lines within cable  27  can have a distinct frequency within the antenna  30  frequency range. 
       FIG. 2  illustrates a top view of an exemplary embodiment of a grounded MCCP wherein a slit and current probe are visible.  FIG. 2  illustrates a housing  20 , current probe  23 , slit  25  and the radial pattern of strip-shaped grounding elements  15   a  through  15   d.    
     The exemplary embodiment shown in  FIG. 2  utilizes a current probe  23  and corresponding housing  20  that are ring-shaped. In the embodiment shown, ring-shaped current probe  23  produces a relatively even magnetic field that is optimized by the lack of corners (angled paths) characteristic of a ring shape. Alternative contemplated embodiments may utilize angled geometric configurations to optimize current flow for mast structures that have angular cross-sections. Alternative embodiments of the current probe may be, but are not limited to, square-shaped and octagon-shaped, or the geometry and dimensions of the current probe can be adapted to conform to the antenna  30 . 
     In the embodiment shown in  FIG. 2 , housing  20  includes slit  23  located on the inner side of housing  20  adjacent to antenna  30  (shown above in  FIG. 1 ). In this embodiment, slit  23  permits passage of induced voltage necessary for antenna  30  transmissions. 
       FIGS. 3   a  through  3   c  illustrate three alternative embodiments for placement of strip-shaped grounding elements at varying frequency angles  8 .  FIGS. 3   a  through  3   c  illustrate the angles formed by the position of strip-shaped grounding elements  15   a  through  15   d  to the longitudinal axis of housing  20 . As shown, the longitudinal axis of housing  20  can be coincident with an axis defined by the antenna when MCCP  10  is installed on antenna  30 . Stated differently, angle θcan be substantially the angle formed between element  15  and antenna  30 . The angle formed by strip-shaped grounding elements  15   a  through  15   d  alters the resonant frequency and bandwidth of MCCP  10 . This angle is known as the frequency angle θ. For clarity, only strip-shaped grounding element  15   a  is labeled; however, all strip-shaped grounding elements  15   a  through  15   d  form the same frequency angle θ with the longitudinal axis of housing  20 . 
       FIG. 3   a  illustrates an exemplary embodiment of a grounded MCCP system  100  in which strip-shaped grounding elements  15   a  through  15   d  are positioned parallel to the ground at a frequency angle θ of 90 degrees. 
       FIG. 3   b  illustrates an exemplary embodiment of a grounded MCCP system  100  in which strip-shaped grounding elements  15   a  through  15   d  are positioned at a frequency angle θ of 45 degrees. 
       FIG. 3   c  illustrates an exemplary embodiment of a grounded MCCP system  100  in which strip-shaped grounding elements  15   a  through  15   d  are positioned perpendicular to the ground at a frequency angle θ of 0 degrees. 
     As illustrated in  FIGS. 3   a  through  3   c , variations in frequency angle θ are possible. In various embodiments, frequency angle θcan be a function of various feature limitations including, but not limited to, the position of MCCP  10  along antenna  30  and the frequency and bandwidth of the desired transmission signal. 
       FIG. 4  illustrates an alternative exemplary embodiment of a grounded MCCP system  100  that utilizes electrolytic fluid streams as grounding elements. In this exemplary embodiment, the grounding elements are four streams  17   a  through  17   d  expelled from nozzles  16   a  through  16   d  connected to housing  20  by manifold  12 . A tube  29  delivers material for streams  17   a  through  17   d  to manifold  12 . 
     As illustrated by  FIG. 4 , streams  17   a  through  17   d  are expelled to create the grounding elements that make up a counterpoise. The nozzles  16  can be formed with apertures (not shown in the Figures) which can be configured to establish streams  17  having a width ranging from about 0.25 inches to about 12 inches, when the embodiment is viewed in top plan. Streams  17   a  through  17   d  can also be composed of an electrolytic fluid such as, but not limited to, seawater or a similar ionic solution. The temperature of the electrolytic fluid can typically range from about 32 degrees F. to about 80 degrees F., with higher temperatures increasing the electrolytic fluid conductance. 
     The exemplary embodiment of  FIG. 4  utilizes nozzles  16   a  through  16   d , which are connected to manifold  12  through a rotating or swiveling joint so that the frequency angle θ may be adjusted. Nozzles  16   a  through  16   d  may have a radiation angle θranging from about 0 degrees to about 90 degrees. In various embodiments, frequency angle θ is a function of various feature limitations including, but not limited to, the position of MCCP  10  along antenna  30  and the frequency and bandwidth of the desired transmission signal. Alternative embodiments can include a rotating or swiveling joint, which can selectively establish nozzles  16  at angle θ, according to the needs of the user. 
     While the exemplary embodiment of  FIG. 4  illustrates four nozzles  16   a  through  16   d , in other contemplated embodiments, any number of nozzles from about four to about three hundred may be used. In various alternative embodiments, an increased number of nozzles may reduce the width of streams  17 , or may reduce the space between fluid streams to closely emulate a ground plane structure. 
     While the above embodiment of  FIG. 4  utilizes approximately 1-inch wide fluid-expelling apertures of nozzles  16   a  through  16   d , in other contemplated embodiments, apertures of the nozzles  16   a  through  16   d  may have a width ranging from about 0.25 inches to about 12 inches. The width of apertures of nozzles  16   a  through  16   d  may also be determined as dependent upon the width of the MCCP  10 , being at most about one-half of the diameter of the MCCP  10 . The length of streams  17   a  through  17   d  expelled from nozzles  16   a  through  16   d  may be dependent upon the frequency intended to be transmitted from antenna  30 . A formula for determining the length of streams  17   a  through  17   d  is:
 
 L   f =(250×√(10/( f (σ)))−( R   M   +H   M )
 
where L f  is the length of streams  17   a  through  17   d, f  is the transmission frequency, a is the fluid electrical conductivity, R M  is the radius of the MCCP and H M  is the height of the MCCP, the measurement from base to top.
 
     In the exemplary embodiment of  FIG. 4 , manifold  12  may be operatively connected to housing  20  by an attachment means selected from a group consisting of conductive tape, soldering, conductive adhesive, screws, bolts, and interlocking, mechanical and integrally-machined components. 
     In the exemplary embodiment of  FIG. 4 , tube  29  is shown to be outside antenna  30 , but may also be located inside antenna  30  in alternate embodiments. 
       FIG. 5  illustrates a graph of data for a grounded MCCP system that shows an exemplary relationship of the frequency angles θ of the grounded MCCP to resonant frequency and bandwidth. The data in  FIG. 5  documents that the addition of grounding elements, which form a counterpoise, changes the transmission capabilities of the MCCP based on the frequency angle θ. The embodiments shown in  FIG. 5  utilize frequency angles θ of 90 degrees (straight), 45 degrees (angled) and 0 degrees (down). As  FIG. 5  illustrates, in the embodiment having a frequency angle θ of 90 degrees an additional resonance frequency occurs near 240 MHz. Thus, in various embodiments the use of a counterpoise made up of grounding elements in an MCCP system can induce a new resonance frequency. 
     As  FIG. 5  also illustrates, utilizing a frequency angle θ of 45 degrees also increases MCCP transmission bandwidth. In various embodiments, introduction of grounding elements may therefore provide an advantage when transmitting distinct from the grounding capability of the structure. 
       FIGS. 6   a  and  6   b  illustrate two alternative embodiments of an antenna structure for a grounded MCCP system where antenna length can be varied. The change in antenna length alters the resonance frequency produced by the addition of grounding elements that form a counterpoise. The antenna length of the embodiment of  FIG. 6   a  is approximately 12 inches, while the antenna length of the embodiment of  FIG. 6   b  can be extended to approximately 41 inches. 
       FIG. 7  illustrates a graph of data for a grounded MCCP system that shows an exemplary relationship of the length of the antenna to resonant frequency and bandwidth for a grounded MCCP system.  FIG. 7  illustrates that a 12-inch antenna with a 29-inch extension produces a resonant frequency of 71 MHz. A 12-inch length produces a resonant frequency of ˜240 MHz as seen above. The data gathered from this extended-antenna exemplary embodiment indicates that extending the antenna length with various counterpoise configurations may induce new resonance frequencies. To accomplish this, an antenna extension can be added or described above, or the MCCP  10  can be selectively mounted on the antenna (using an attachment means which allows for re-positioning, such as screws, for example) according to the resonant frequency desired by the user. Referring now to  FIG. 8 , a block diagram  100  is shown, which can be used to illustrate steps that can be taken to accomplish the methods of the present invention according to several embodiments. As shown, methods  100  can include the initial step  102  of providing a current probe. The current probe  23  can have the geometry and can be made of the materials as described above. The methods  100  can also include the steps  104  of enclosing the current probe within an electrostatic housing  20 , and connecting a plurality of grounding elements  15  to housing  20 , as shown by step  106 . The grounding elements  15  can be oriented at an angle θ as described above, to manipulate the resulting resonant frequency bandwidth according the needs of the user. The electrostatic housing can also be mounted at different locations on antenna  30  to manipulate the resonant frequency. Or, in cases where the MCCP is permanently fixed to the antenna, the antenna can be lengthened with an extension as described above to manipulate the resonant frequency according to the needs of the user. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principal and scope of the invention as expressed in the appended claims.