Abstract:
A low profile broadband antenna capable of measuring shielding effectiveness (SE) of a shielded boundary above or below ground for permanent installation behind walls, under floors, above ceilings and other areas with limited transverse (as opposed to lateral) available space is provided. A spiral antenna having a wide operating bandwidth is positioned within the interior of an environmentally sealed enclosure. The enclosure likewise has a low profile suited for installation in such locations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable 
   STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
   Not Applicable 
   BACKGROUND 
   1. Technical Field 
   The present invention relates generally to antenna devices. More particularly, the present invention relates to a low profile, broadband, environmentally sealed spiral shaped antenna deployable under buildings and behind building walls. 
   2. Related Art 
   Critical infrastructure and government facilities are protected from High-Altitude Electromagnetic Pulse attacks, where a destructive nuclear device such as an atomic or hydrogen bomb is detonated in the atmosphere. Specifically, the initiated nuclear chain reaction also generates electromagnetic radiation strong enough to disturb or destroy electronic circuits in the vicinity of the explosion through current overloads. Protections typically involve barrier or shield installations on the walls, ceilings, and floors of the building, such as boundary or circumferential Faraday shields. The efficacy of the shield installations, also referred to as shielding effectiveness (SE), must be evaluated periodically to ensure the facility and the critical electronic equipment residing therein is properly protected. Conventional techniques for evaluating shielding effectiveness involve the use of three separate linearly polarized antennas to cover the required frequency range, which is inefficient because of the extra time wasted by changing both antenna type and polarization multiple times in the process of test conduct. Furthermore, these conventional antennas require significant volume to use properly, which is deficient both because of the additional wasted space occupied thereby and because of their inability to be used properly in tight spaces. In particular, such conventional antennas may be as large as 4800 cubic inches. Accordingly, there is a need in the art for improved shielding effectiveness evaluation antennas. Furthermore, there is also a need for permanently deployable low profile antennas. 
   BRIEF SUMMARY 
   According to an embodiment of the present invention, there is disclosed an antenna installation assembly for the evaluation of shielding effectiveness of a boundary (circumferential Faraday shield). The antenna installation assembly may include an enclosure that defines a center region and an outer periphery. The depth dimension of the flat enclosure may be substantially less than its lateral dimensions. Furthermore, there may be a conductive spiral antenna that defines a center origin point positioned within the interior of the enclosure. Along these lines, the center origin point may be generally aligned with the center region of the enclosure. The antenna installation assembly may further include a coaxial cable that is in electrical communication with the spiral antenna, and is attached to the center origin point thereof. The coaxial cable may extend toward the outer periphery of the enclosure. There may also be a cable interface in electrical communication with the coaxial cable and attached to the outer periphery of the enclosure. A shielding effectiveness transmit and receive system may be attachable to a pair of antennas in an assembly via the cable interfaces. The present invention will be best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which: 
       FIG. 1  is a perspective view of the antenna installation assembly without a top member of the enclosure being sealed to a bottom member of the same; 
       FIG. 2  is a perspective view of the antenna installation assembly with the sealed enclosure in which the top member is attached to the bottom member; 
       FIG. 3  is a bottom plan view of the enclosure in accordance with one embodiment of the present invention including a plurality of concentric support ribs and intersecting cross members; and 
       FIG. 4  is a perspective view of a reduced size embodiment of the antenna installation assembly for use with smaller enclosures. 
   

   Common reference numerals are used throughout the drawings and the detailed description to indicate the same elements. 
   DETAILED DESCRIPTION 
   The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiment of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the functions of the invention in connection with the illustrated embodiment. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the invention. It is further understood that the use of relational terms such as first and second, top and bottom, and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities. 
   With reference to  FIG. 1 , there is shown an antenna installation assembly  10  that is contemplated to be deployable at HEMP-protected environments where shielding effectiveness is periodically evaluated. Other uses are also envisioned, including Electromagnetic Interference (EMI) testing and coupling measurements. Such applications require the use of matching antenna assemblies, one for transmit and one for receive. These applications, however, are presented by way of example only and not of limitation, and the antenna installation assembly may be deployed for other applications or purposes. In further detail, it is contemplated that one application of the antenna installation assembly  10  is to be permanently placed under buildings or floors, ceilings and roofs thereof, behind walls, or other like limited spaces. It is understood that the low profile of the antenna installation assembly  10 , described in further detail below, makes shielding effectiveness measurement possible when access to floors, either at the ground level or between levels, walls or ceilings is impossible or restricted due to nearby obstacles. 
   As shown in  FIG. 1 , the antenna installation assembly  10  includes an enclosure  12  that defines a center region  14  and an outer periphery  16 . According to one embodiment of the present invention, the outer periphery  16  is generally defined by edge segments  18 , and has an octagonal outline. It will be appreciated by those having ordinary skill in the art, however, that the outer periphery  16  may be variously shaped, and is not limited to an octagonal outline. 
   The antenna installation assembly  10  also includes a conductive spiral antenna  20  that defines a center origin point  22 . The center origin point is understood to be generally aligned with the center region of the enclosure  12 . In a preferred, though optional embodiment, the spiral antenna  20  is characterized by counter-rotating dual prongs  24   a ,  24   b  that extend from the center origin point  22 . Additionally, in such embodiment, the spiral antenna  20  is contemplated to be constructed from two counter rotating spirals of copper materials. The thickness of the copper plate is understood to be 21.6 mil (16 ounce copper). As will be appreciated by those having ordinary skill in the art, any number of techniques may be used to cut the outline of the spiral antenna  20 , including water jet or wire EDM. 
   It is expressly contemplated that the spiral antenna  20  have a sufficient gain for evaluating shielding effectiveness against signals ranging between 10 kHz to 1 GHz, which is the full frequency band as set forth in MIL-STD-188-125-1. With further particularity, the spiral antenna  20  is understood to be a passive receive or transmit having a maximum transmission power of 100 watts. As shown in  FIG. 4 , the physical dimensions of the spiral antenna  20  may be reduced for installation and use in smaller spaces such as a test enclosure  25 . It is understood, however, that reduction in the size of the spiral antenna  20  limits the operational frequency range, specifically, in the lower frequency regions. 
   With reference to  FIGS. 1 and 2 , the enclosure  12  is defined by a top member  26  mated to a bottom member  28 . It is contemplated that the bottom member  28  has a substantial thickness, with the top member  26  being a lid or cover without a substantial thickness relative to that of the bottom member  28 . In other words, the bottom member  28  primarily defines the depth of the enclosure  12 . Along these lines, the depth dimension of the enclosure  12  is substantially less than the lateral dimensions of the same. More particularly, the enclosure  12  may have lateral dimension of 36 inches by 36 inches, and a depth dimension of 2 inches in accordance with one embodiment of the present invention. As indicated above, the slim depth dimensions permit the placement of the antenna installation  10  in a variety of space-constrained locations. 
   Referring to  FIG. 3 , the bottom member  28  defines one or more concentric support ribs  30 . The support ribs  30  are further reinforced with intersecting cross members  32  that extend from one edge segment  18  to another one opposed thereto. As described above, it is contemplated that the antenna installation assembly  10  be deployed under floors where loads may be placed onto the enclosure  12 . In this regard, it is understood that the concentric support ribs  30  and the cross members  32  further buttress the enclosure  12 , thereby increasing the ability to withstand reasonable center pressure and reducing potentially dangerous flexing of the same. 
   As illustrated in  FIG. 1 , the spiral antenna  20  is mounted to the interior of the enclosure  12 . More specifically, the spiral  20  is glued to the enclosure  12 , though any other suitable attachment modality may be readily substituted without departing from the scope of the present invention. According to one embodiment, the enclosure  12  further includes an antenna support member  34  that is receivable within the bottom member  28 . The antenna support member  34  optionally defines an upper surface  36  having a spiral groove  38  that conforms to the outline of the spiral antenna  20 . It is contemplated that the spiral antenna  20  be placed in the spiral groove  38  in a fitted relationship for improved sealing characteristics. Though described in terms of independent components, the bottom member  28  and the antenna support member  34  may be integrally formed and be of a unitary construction. 
   As shown in  FIG. 2 , the enclosure  12  is defined by the top member  26  being mated to the bottom member  28 . According to an embodiment of the present invention, the enclosure  12  may be environmentally sealed for improved weather resistance. It will be appreciated that the enclosure  12  may be deployed in all types of harsh environments for extended periods of time. Along these lines, the enclosure  12  is constructed of acrylonitrile butadiene styrene (ABS) plastic, though any other suitably durable material may be substituted. Generally, the enclosure  12  may be constructed with a thermoforming process. 
   In order to provide an interface to the spiral antenna  20  through which an external shielding effectiveness test device may be connected, the antenna installation assembly  10  further includes a coaxial cable  26 . The cable  26  is in electrical communication with the spiral antenna  20 , and attached to the center origin point  22  thereof. From the center origin point  22 , the cable  26  extends outwards toward the outer periphery  16  of the enclosure  12 . In further detail, the antenna support member  34  defines a channel  40  extending from the outer periphery  16  to the center region  14 , with the cable  26  being routed therethrough. 
   As shown in  FIG. 1 , the cable  26  is coupled to a cable interface  42 . The cable interface  42  is mounted to one of the edge segments  18  of the enclosure  12  in recessed relation to the outer periphery  16 . This placement relationship is contemplated to provide protection for the cabling of the external shielding effectiveness test device and its associated connectors, as well as for the cable interface  42  itself. In accordance with one embodiment of the present invention, the cable interface  42  is an “N” type female RF connector. 
   The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.