Abstract:
A high frequency antenna that is particularly suitable for marine  environts. The high frequency antenna has a metallic base flange, a metallic spring assembly for permitting flexibility and shock resistance and a metallic sleeve all maintained at ground potential so that the antenna is immune to being shorted out such as by salt water and preferably comprised of stainless steel. The radiating element of the antenna is formed on a fiberglass rod and is comprised of a flat, ribbon-like conductor or a plurality of wires approximating a ribbon like conductor. The radiating conductor is wound around the fiberglass rod such that the wound or wrapped areas have a width that is substantially equal to the non-wrapped areas on the rod to permit the ribbon-like conductor to radiate from both sides in order to achieve a low profile antenna.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the fields of antennas and antenna mounting fixtures and, more particularly, to the fields of whip antennas for use on armored vehicles, particularly amphibious landing vehicles for the purpose of providing high frequency radio communications. 
     High frequency whip antennas now in use by the United States Marine Corps are prone to physical damage associated with motion. Vibration causes screw fittings to work loose and accelerations cause failures at antenna bases. Collisions with overhead obstructions especially at speeds above 25 miles per hour are known to cause failures of antenna elements. The encounter of heavy brush and tree limbs at speeds less than 5 miles per hour causes failure at antenna bases also. 
     High frequency whip antennas now in use were not designed for amphibious, marine environments. Mechanical connections tend to corrode when exposed to salt water spray. Base insulators short out when surf breaks over the top of amphibious vehicles. Salt water intrudes into antenna bases to short out or corrode electrical components. 
     High frequency whip antennas now in use are often too tall for use on high mobility vehicles. Although antenna height gives better electrical performance, increased height makes the antenna vulnerable to damage and the vehicle vulnerable to detection because of the increased visibility. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the foregoing enumerated problems with prior art whip antennas and mounting fixtures with a novel antenna and mounting fixture that are designed to resist short circuiting by salt water and with a novel antenna and mounting fixture that resist breakage due to accelerations and overhead obstructions. The present invention is a mobile whip antenna primarily intended for use on armored vehicles, particularly amphibious landing vehicles and serves the purpose of providing high frequency radio communications. 
     The present invention, in its preferred embodiment, comprises a 10-foot fiberglass whip antenna that is comprised of a mounting base assembly which has interior compartments filled with potting compound. The antenna and mounting assembly of the present invention are further comprised of a metal interface sleeve connecting the base spring assembly to the fiberglass whip section and having a spiral-wrapped ribbon-like conductor for radiating. 
     The present invention offers several advantages over existing whip antennas and mounting fixtures. Of primary importance, the present invention is shorter and less visible than existing high frequency mobile whip antennas. It is designed so that it can be completely sealed so as to be impervious to penetration by salt water. It is therefore immune to base insulator shorting and therefor avoids the problem of electrical shock hazard to personnel. The specific construction of the present invention prevents personnel riding in, on, or beside the vehicle to which it is mounted from being struck by the antenna when the vehicle, because of its motion over uneven terrain, is made to buck or cork-screw. The present invention provides a higher radiating efficiency than existing whip antennas of the same electrical height. The present invention features a spiral, multiwire or ribbon-like conductor used as the radiating element. This multiwire or ribbon-like conductor is designed such that its pitch, i.e. number of turns per unit length of supporting fiberglass rod, allows both sides of the ribbon-like conductor to be exposed to the radio universe. This effectively doubles the available radiating surface area of the radiating element as compared to a tightly wound helical radiator and thus reduces skin-effect losses. 
     Another feature of the present invention is that solid dielectric materials are utulized to fill voids within the structure. By this technique, RF potentials are not allowed to develop across air gaps thereby allowing higher power levels to be utilized with smaller antenna dimensions. 
     The whip antenna and mounting assembly of the present invention can be manufactured utilizing relatively unmodified fiberglass fishing pole manufacturing technology in its assembly. Consequently, the manufacturing costs involved in producing antennas in accordance with the present invention are substantially reduced. 
     OBJECTS OF THE INVENTION 
     Accordingly, it is the primary object of the present invention to disclose a novel whip antenna for providing high frequency radio communications that is particularly suitable for amphibious landing vehicles. 
     It is another object of the present invention to disclose a novel whip antenna and mounting assembly which has a coaxial base spring break-away which is maintained at ground potential and which is consequently immune to base insulator shorting. 
     It is another object of the present invention to disclose a whip antenna mounting base assembly that is capable of making a water-tight seal while at the same time making an excellent RF connection. 
     It is another object of the present invention to provide a whip antenna that minimizes the possibility of nearby personnel being struck by it when the vehicle upon which it is mounted traverses uneven terrain. 
     It is a concomitant object of the present invention to disclose an antenna that provides a higher radiating efficiency than prior art whip antennas of the same electrical height. 
     It is a still further object of the present invention to disclose a novel whip antenna radiating element comprised of a spiral multiwire or ribbon-like conductor which allows both sides of the conductor to be exposed to the radio universe. 
     It is another object of the present invention to disclose a novel whip antenna and mounting assembly that can be manufactured utilizing existing technology at a relatively low cost. 
     Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the whip antenna and mounting assembly of the present invention. 
     FIG. 2 is a partially cut away, partial cross sectional side view of the base mounting assembly of the present invention. 
     FIG. 3 is a partially cut away, partial cross sectional side view of the sleeve interface assembly of the present invention and including a partially cut away side view illustration of a portion of the fiberglass whip and radiating element winding pattern of the present invention. 
     FIG. 4 is a side view of the whip portion of the present invention with the outer fiberglass sheath removed, illustrating the preferred embodiment of the radiating element winding pattern of the present invention with dimensions illustrated by way of example. 
     FIG. 5 is an isometric view of a portion of an unwound radiating element of the present invention utilizing the disclosed alternative of a ribbon-like conductor radiating element. 
     FIG. 6 is a partial cross-section, partial cut away side view of the coupling section of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1 the high frequency whip antenna and mounting assembly of the present invention will be described in general terms. The high frequency whip antenna mounting assembly 12 of the present invention is illustrated in FIG. 1 as being secured to a mounting surface 14 which may, for instance, be the mounting platform of an armored amphibious vehicle. It should be understood, however, that the antenna and mounting assembly of the present invention may be utilized in a multitude of other environments and mounted on other surfaces depending upon the particular utilization required or desired. The antenna and mounting assembly 12 are secured to the mounting surface 14 by means of base flange member 16 which has male threaded portions 18 and locking hexagonal nut 20 which attaches to threaded portion 18 on the underside of mounting surface 14. The mounting surface 14 is provided with circular opening or clearance hole 22 for receiving the threaded portion 18 of the base flange 16. Base flange 16 and locking nut 20 are preferably made of stainless steel. A locking washer (not shown) may be used between nut 16 and surface 14. Also, a water sealing conductive gasket (not shown) may be used between flange 16 and the top of surface 14 to ensure a watertight seal. 
     The antenna and mounting assembly 12 further include a base spring assembly 26, preferably comprised of stainless steel, that is secured to the base flange member 16 in a manner to be described in greater detail below. Extending from the upper portion of the base spring assembly 26 is an upper nipple 28 having a male threaded exterior portion for engagement with cooperating female threads at the interior upper portion of the base spring assembly 26. The nipple 28 is secured in position by means of hex nut 29. The nipple 28 is coupled at its upper end to metallic sleeve 30. Nipple 28, hex nut 29 and metallic sleeve 30 are preferably comprised of stainless steel. 
     Metallic sleeve 30 holds the bottom end of fiberglass rod 32 illustrated in dotted lines in FIG. 1. The fiberglass rod 32 extends to the top end or tip 34 of the antenna 12 and serves as the support structure for the radiating elements 36 which are wrapped around the fiberglass rod 32. It is noted that the depiction of radiating elements 36 in FIG. 1 is not to scale and is not intended to be an accurate representation of the location and positioning of the radiating elements 36. The particular winding or wrapping technique utilized and the particular placement of the radiating elements 36 will be described in detail below. FIG. 1 is intended to illustrate only that the radiating element 36 are spiral wrapped conductors, the details of the wrapping being illustrated below. Fiberglass jacket 38 covers the radiating elements 36 and provides weatherproofing and damage protection to the antenna structure. Coupling section 39 to be described in greater detail below is a metallic, preferably brass, coupling that serves to join both the upper and lower portions of fiberglass rod 32. 
     Referring now to FIG. 2 the details of the threaded base flange 16, the base spring assembly 26 and a portion of the metallic sleeve assembly 30 will now be described. As seen in FIG. 2 the threaded base flange 16 has a cup-shaped interior cavity 40. A radio frequency (RF) connector 42 such as a model UG-680/U or a UG-58A/u connector is coupled to the base flange member 16 within the interior cavity 40 by mating engagement of exterior male threads 44 on the RF connector 42 with interior female threads 46 on the base flange 16 or by bolting on (not shown). The RF connector 42 also has exterior male threaded portions 48 for engagement with the coupling fitting of a coaxial connector. Inner coaxial conductor 50 is an integral part of the RF connector 42 and extends from the vicinity of the threaded portions 48 through the connector 42 past base flange member 52 and out the top end 54 where it is connected via solder cup 56 to the inner conductor 58 of coaxial cable 60. As can be seen in FIG. 2, the insulator 62 on coaxial cable 60 is stripped away such that the outer braided conductor 64 is partially exposed in the area within cavity 66 of the base flange 16. The outer braided conductor 64 is electrically connected by means of soldering to the exterior metallic housing 68 of the RF connector 42. Insulative coating or spaghetti tubing 65 is used to cover a portion of braided conductor 64 within cavity 66. 
     A lower nipple 70, preferably made of stainless steel, has male threaded portions 72 which provide for mating engagement with female threaded portions 74 at the top end of base flange member 16. The lower nipple 70 has beveled ends 76 and 78 to avoid puncturing the insulator 62 around coaxial cable 60. Coaxial cable 60 extends through the inner passageway 80 of the threaded lower nipple 70. It is noted at this point that interior cavity 66 formed within the base flange member 16 is filled with potting compound 82 such as polyurethane, polystyrene, polyethylene or any other suitable potting compound. This ensures a watertight seal within the cavity 66 of the components contained therein. 
     As can be seen in FIG. 2, the coaxial cable 60 contains a loop 84 which is formed in order to accommodate movement and bending of the whip antenna 12 around the area of the base spring assembly 26. The base spring assembly 26 includes a lower flange member 86 which is in threaded engagement with the upper end of lower nipple 70. The base spring assembly 26 also includes an upper flange member 88 which is in threaded engagement with upper nipple 28 as is illustrated. Further, the base spring assembly 26 includes exterior spring component 92 which is formed around the lower flange member 86 and upper flange member 88 of the base spring assembly 26. 
     Upper nipple 28 has beveled lower end 94 provided in order to prevent puncturing of the insulator 62 of the coaxial cable 60. Surrounding a portion of the upper end of the upper nipple 28 is metallic sleeve member 30 which is in threaded mating engagement with the upper nipple 28 upper end as is illustrated in FIG. 2. As can be seen in FIG. 2, the coaxial cable 60 extends through the interior passageway 98 within the upper nipple 28 and is brought out through the opening in the open end of upper nipple 28. As illustrated in FIG. 2, upper nipple 28 includes a reduced diameter end 100 with beveled ends 102. The reduced diameter end 100 of upper nipple 28 is sufficiently small to be contained within the interior passageway 104 of sleeve member 30. As can also be seen in FIG. 2, the outer metallic, braided conductor 64 of coaxial cable 60 is brought around the exterior portion of reduced diameter end 100 and may be soldered to the exterior portion of reduced diameter end 100 such that it is in electrical contact with the upper nipple 28 and metallic sleeve 30. This braided conductor 64 is held in place by PVC sleeve 106 that surrounds the braided conductor 64 in the vicinity of the reduced diameter end 100 of upper nipple 28. The PVC sleeve 106 is crimped in place by ferrule 108. 
     As also is illustrated in FIG. 2, the insulator 110 around inner conductor 58 and inner conductor 58 are brought out through the top end of reduced diameter end 100 of the upper nipple 28. Also, the fiberglass rod 32 is contained within the interior passageway 104 of the metallic sleeve 30. The fiberglass rod 32 has a hollowed out core section 112 and the insulator 110 and inner conductor 58 of coaxial cable 60 are extended into this hollowed out core 112. As is also illustrated in FIG. 2, the coaxial cable 60 inner conductor 58 is electrically connected by soldering to standard copper wire 114. 
     Referring now to FIG. 3 it can be seen that the hollowed out core 112 of fiberglass rod 32 extends beyond the upper end 116 of sleeve 30 and is brought out to the surface of fiberglass rod 32. It can also be seen that the stranded copper wire 114 extends through the hollowed out core 112 and is also brought out to the surface of fiberglass rod 32. The stranded copper wire is held in place by retaining key 118, is preferably made of fiberglass or phenolic sheet and is cemented in place with epoxy cement. 
     At the area 120 where the hollowed out core 112 is brought to the surface and where the stranded wire 114 is also brought to the surface of the fiberglass rod 32, the stranded copper wire 114 is attached to the radiating element 36 as by soldering. The radiating element 36 is then helically wound around the fiberglass rod 32 from the area 120 to the tip 34 of the fiberglass rod in a manner to be described more particularly below. 
     Referring now to FIG. 6, the coupling section 39 of the present invention will be described. Fiberglass rod 32 is split and the bottom portion 32a is capped with brass ferrule cap 37. Brass cylindrical sleeve 39 is glued to fiberglass rod upper portion 32b and contains fiberglass rod upper portion 32b. Brass sleeve 39 extends over and is secured to ferrule 37. The radiating conductors 36 are then soldered at solder joint 41 to brass ferrule cap 37 at the fiberglass rod lower portion 32a as illustrated. Similarly, the radiating conductors 36 are soldered at solder joint 43 to brass sleeve 39 at the fiberglass rod upper end 32b as illustrated. Thus electrical continuity is maintained by coupling section 39 between the radiators 36 on the fiberglass rod lower portion 32a and the radiators 36 on the fiberglass rod upper portion 32b. 
     The windig pattern of the radiating element 36 of the antenna 12 will now be described. Referring to FIG. 3, the winding pattern is begun by utilizing, in the preferred embodiment, either ten No. 26 strands or twenty No. 30 strands of copper wire (for purposes of simplicity of illustration, it is noted that FIG. 3 does not show all ten or twenty strands). The strands are wound adjacent each other such that they are in electrical contact with each other and are also laid side by side so as to approximate a ribbon conductor. As can be seen in FIG. 3, the width 122 of the ribbon-like conductor made from the numerous strands of copper wire is such that the numerous strands approximate a ribbon-like conductor. Further, it is important in the winding pattern according to the present invention that the width 122 of the plurality of conductors 124 is approximately equal to the spacing 126 between the wraps of the plurality of conductors 124. This feature of applicant&#39;s invention is further emphasized in FIG. 3 by the reference dimension letter d which indicates that the distance along the longitudinal axis of the tapered fiberglass rod 32 is the same for the group of conductors 124 as for the spacing 126 between adjacent groups of conductors 124. In this way it can be appreciated that the plurality of conductors 124 can radiate from both sides, i.e. not only outwardly from the fiberglass rod 32 but also through the fiberglass rod 32 and out the other side. Thus, by way of example, the portion 124b of the plurality of conductors 124 that are on the underside of fiberglass rod 32 as illustrated in FIG. 3 may radiate through fiberglass rod 32 in a direction out of the page. They also will radiate in the direction looking into the page. 
     In order to accomodate the tapered aspect of the fiberglass rod 32, the pitch, i.e. number of turns per unit length, of the windings of the radiating element 36 is varied along the length of the fiberglass rod 32. More particularly, the pitch of the windings is varied in the manner illustrated in FIG. 4 which illustrates schematically the preferred embodiment of the winding pattern of the present invention. As can be seen in FIG. 4, the winding pattern is initiated with seven turns of either ten No. 26 strands or twenty No. 30 strands of copper wire. This winding pattern extends for approximately fourteen inches at which point, point 128 in FIG. 4, the pitch is increased such that there is one turn per inch of fiberglass rod 32 or fourteen turns in the fourteen inch section of fiberglass rod 32 between points 128 and 130. At transition point 130, either five of the No. 26 strands or ten of the No. 30 strands are cut and terminated. The remaining five No. 26 strands or ten No. 30 strands are wrapped fourteen times around a seven inch length of the fiberglass rod 32 to point 132. Between transition points 132 and 134 the remaining plurality 136 are extended linearly up the fiberglass rod. At transition point 134 on fiberglass rod, the remaining strands 136 are again continued in the wrapping pattern at a pitch rate of fourteen turns per seven inches of length. At transition point 138 on fiberglass rod 32, either three of the five No. 26 strands or six of the ten No. 30 strands are terminated and the remaining two No. 26 strands or four No. 30 strands are wrapped at a pitch rate of two hundred turns per fifty-two inch length of fiberglass rod. This wrapping pattern is continued until the tip 34 of the fiberglass rod 32 is reached. 
     Finally, following the wrapping of the fiberglass whip 32 with the radiating conductors as described above, a fiberglass jacket 140 (see FIG. 3) is put in place over the radiating elements. 
     It should be appreciated, that in lieu of using multi-stranded copper wire as the radiating element with the plurality of strands laid side by side so as to approximate a ribbon conductor, it is considered within the scope of the present invention to actually utilize a ribbon-like conductor as is illustrated, in part in FIG. 5. The ribbon conductor 142 would be formed so as to have the same approximate width of the multiwire radiating element conductors 124, 136, etc. illustrated and described with respect to FIGS. 3 and 4. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.