Lightweight deployable antenna system

A deployable antenna assembly includes a canister providing an elongated chamber and an elongated hollow mast with a mounting member on its upper end. A coaxial cable extends into the hollow mast to provide radio signals to the antenna assembly and four antenna members of resiliently deflectable wire spaced at 90 degrees intervals about the periphery of the mounting plate comprise a generally helical coil and elongate arms extending downwardly along the inner wall of the canister, and each opposed pair comprises a dipoles. A pair of baluns are connected to the coaxial cable and disposed adjacent the mounting member, and a phase shifter are connected between the coaxial cable and one of the baluns. Connectors conductively connect the central conductor of the balun to the coil of one of the antenna members of a dipole, and the conductive shield to the coil of the other antenna member of a dipole. A sealing medium is provided about the baluns, and phase shifter. The coils of the antenna members are flexed when the arms are the downwardly extending position within the canister, and the canister is slidable relative to the mast and antenna members to free the arms therefrom for extension into a horizontal position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Turning first to FIG. 1, therein fragmentarily illustrated is a deployable 
antenna assembly for marine applications which embodies the present 
invention and is comprised of a tubular canister generally designated by 
the numeral 10 with a closed top end wall or cap 28 above which is 
disposed a penetrator generally designated by the numeral 12 and 
illustrated in phantom line. The antenna assembly generally designated by 
the numeral 14 is disposed within the canister 10 and includes an 
elongated cylindrical mast 16 having a top plate 18 extending across its 
upper end upon which is supported the mounting member 20. 
Extending between the cap 24 which bears against the end cap 28, and the 
mounting member 20 are spacers 22, and fasteners 26 maintaining the 
elements in assembly. As seen in FIG. 1, the canister 10 is comprised of 
the cap 24 and the tubular body 30. 
Seated in a coaxial cavity in the cap 24 is a discharge element 32 which is 
actuatable by a signal transmitted thereto through the conductor 34. 
As seen in FIGS. 1 and 2, four antenna elements generally designated by the 
numeral 36 are spaced about the periphery of the mounting member 20 at 
90.degree. intervals, and each comprises a length of resiliently 
deflectable wire formed into a helical coil 38 with a tail 40 extending 
from one end thereof which is bonded to the mounting member by adhesive or 
resin as indicated by the numeral 42. Extending from the opposite end of 
the coil 38 is an elongated arm 44 which, when the antenna elements 36 are 
unrestrained, will extend in a horizontal plane as indioated in FIG. 2. 
In FIG. 1, the arms 44 are deflected downwardly and flex the coil spring 
38, and they resiliently bear against inner wall of the tubular body 30 of 
the canister 10. As best seen in FIG. 2, the mounting member 20 may 
include a cruciform element 21 on its upper surface. 
Turning now to FIG. 4, therein illustrated is a balun generally designated 
by the numeral 46 and utilized in the present invention. It is comprised 
of a conductive core 50, an insulating layer 52 thereabout, a tubular 
copper element 54 functioning as a conductive shield, a length of plastic 
sheath or tubing 56 tightly seated thereabout, and conductive copper tape 
58 wound thereabout over a predetermined length of the balun. As indicated 
by the numeral 60, the copper tape is conductively bonded to the copper 
tubing 54 at a point spaced a distance X from the feed into the balun as 
will be described more fully hereinafter. 
In FIG. 3 there is illustrated a phase shifter 62 utilized in the present 
invention and it conveniently comprises a length of the coaxial cable 
utilized in the balun of FIG. 3 (except that the insulating tubing 56 and 
copper tape 58 are omitted), and it is formed into a U-shaped 
configuration. 
Turning now to FIG. 5, therein illustrated diagrammatically are the 
electrical components of the deployable antenna assembly showing the 
manner in which they are connected to each other. At the lower end of FIG. 
5, there can be seen the fragmentarily illustrated coaxial cable 64 which 
is delivering the radio signal to the antenna assembly. From its 
conductive core 50 extend the leads 66 and 70 respectively to the 
conductive core 50 of the balun 48 and of the phase shifter 62. From the 
conductive shield 54 of the coaxial cable 64 extend the leads 68 and 72 to 
the conductive shield 54 of the balun 48 and of phase shifter 62. In turn, 
the leads 74 and 76 extend from the conductive core 50 and conductive 
shield 54 of the phase shifter 62 to the conductive core and conductive 
shield of the balun 46. 
Extending from the opposite end of the balun 46 are leads 82, 84 which are 
conductively bonded to terminals 85a and 85b on the cruciform element 21 
of the mounting member 20. Leads 78 and 80 from the balun 48 are in turn 
bonded to the terminals 85c and 85d. 
Extending from the terminals 85a and 85b are leads 86 and 88 which extend 
to the coils 38a and 38b of the opposed antenna elements which form a 
dipole. Similarily, leads 90 and 92 extend from the terminals 85c and 85d 
to the coils 38c and 38d of the antenna elements providing the other 
dipole. 
As diagrammatically illustrated in FIGS. 1 and 5, the baluns 46, 48 and 
phase shifter 62 and the connections to the coaxial cable 64 are potted in 
a synthetic resin to provide a water tight seal about them and their 
leads. In addition, as seen in FIG. 1, synthetic resin material is 
deposited about the ends of the leads and the terminals 85 to provide a 
seal thereabout. 
Upon actuation of the discharge element 32 as a result of a signal 
transmitted through the conductor 34, the penetrator 12 and the canister 
10 are pushed upwardly and free from engagement with the antenna assembly 
14. At this point, the arms 44 of the antenna elements 36 spring outwardly 
into a horizontal position as a result of the torsion in the coils 38. 
As previously indicated, the antenna 14 comprises a pair of dipole antennas 
which are oriented 90 degrees apart in a common horizontal plane and each 
of the dipoles is fed with a sleeve type balun to ensure balanced element 
feed point current thereto. The baluns in turn are fed in phase quadrature 
(a relative phase difference of 90.degree. as a result of the phase 
shifter 62) so that the resulting overhead radiation is right hand 
circular polarized (RHCP). As will be appreciated, the phase quadrature 
employed in the present invention results in the dipole antenna being 
nearly omnidirectional with the wave from the back side of the antenna, 
i.e., towards the water or ice, being cross polarized with respect to the 
skyward wave. 
To reduce the size of the antenna elements 36, the arms 44 are less than 
1/4 wave length and are tuned to resonance by using approximately 0.75 
turn of the coil 38 as a series inductor at the feed point. The antenna 
elements are desirably fabricated from phosphor bronze wire to improve 
their corrosion resistance while providing a reasonable compromise among 
modulus, spring retention, conductivity, and the ability to be wet with 
solder. In one embodiment which has been field tested satisfactorily, the 
wire had a thickness of about 0.045 inch diameter. 
To provide good conductivity and resistance to corrosion, the leads from 
the terminals to the coils are desirably provided by silver plated copper 
braid. If so desired, the core and a portion of the conductive shield can 
be used to provide the lead to the terminals from the baluns. 
Sleeve type baluns were chosen for the antenna assembly of the present 
invention because of their low loss and their compatibility with the 
hollow mast structure. The relatively low bandwidth of this type balun 
(approximately 5 MHz) is easily accommodated in a single frequency 
application. 
As indicated, the baluns are each constructed using a semi-rigid coaxial 
cable, preferably about 0.085 inch outside diameter, having a tubular 
copper sleeve as the shield and providing the semi-rigidity. A length of 
this cable is coated with heat shrink tubing and then covered with copper 
tape over a length which is then bonded or soldered to the copper tubular 
sleeve at a point which is a distance of approximately 1/4 of the 
effective wave length away from the feed to the balun. The copper tape and 
the semi-rigid cable sleeve serve as the outer and inner conductor 
respectively of a coaxial sleeve balun. The non-shorted end of the balun 
is trimmed until the antenna feed presents an open circuit to the 
undesirable unbalanced currents; the correct tuning may be verified using 
an impedance analyzer. 
Other types of insulating medium between the copper tape and the copper 
tubing representing the outer conductor or shield of the coaxial cable may 
also be employed. Although the heat shrink tubing is not a perfect 
dielectric, the impedance of the balun to the flow of unbalanced currents, 
which varies from 300-500 ohms, is sufficient. 
As previously indicated, the proper phase relationship between the dipoles 
is maintained by delaying the phase of the one dipole through a quarter 
wave length of semi-rigid coaxial cable similar to that employed for the 
baluns. The loop is formed and retained next to the balun in order to 
minimize the electronic package. 
The antenna feed is conveniently provided by a low loss teflon dielectric 
flexible coaxial cable which has its outer jacket etched prior to potting 
of the baluns and phase shifter to ensure proper adhesion of the epoxy 
potting compound to it as well as to the other components. 
In use of the antenna assembly, it is directed to the surface from an 
underwater vehicle or facility. The penetrator shown in FIG. 1 effects 
penetration through any surface ice, after which the discharge element is 
actuated to propel from the antenna assembly the penetrator and the 
canister. This frees the antenna arms to effect their deployment. A buoy 
(not shown) maintains the antenna mast in an elevated position relative to 
the environment so that the antenna elements are spaced above the water or 
surrounding ice pack. The relatively compact profile of the antenna 
assembly provides reasonable stability, even in high wind speeds of 70 
miles per hour. 
Thus, it can be seen that the antenna assembly of the present invention is 
one which is readily deployable from its storage condition to its 
operative position. The components are relatively simple and economical to 
fabricate and the components, when assembled, are relatively protected 
from the hostile marine environment to enable use for a reasonable working 
period without substantial loss in efficiency.