US3098230A - Telescoping submarine antenna with capacitive coupling - Google Patents

Description

July 16, 1963 R. s. NICKERSON ETAL 3,098,230

TELESCOPING SUBMARINE ANTENNA WITH CAPACITIVE COUPLING Filed May 22, 1961 5 j g I 20 j 25 24 g 22 as arm m l2 34" I2 RICHARD s. NICKER N PAUL A. CRANDEL E BY ATTORNEYS 3,098,230 Patented July 16, 1963 ice 3,098,230 TELESCOPING SUBMARINE ANTENNA WITH CAPACITIVE COUPLING Richard G. Nickerson, Sudbury, and Paul A. Crandell, Bedford, Mass., assignors to Electronautics Corporalion, Maynard, Mass, a corporation of Massachusetts Filed May 22, 1961, Ser. No. 111,781 2 Claims. (Cl. 343-709) This invention relates in general to antenna systems and in particular to an antenna system for operation under water.

Antenna systems for submarines present some serious problems to the designer. In a typical installation where a retractable antenna is used, it is necessary, of course, that the coupling of the antenna to the radio apparatus be made in such a manner that the antenna is not grounded to the hull of the ship. Obviously, in an environment of sea water, shorting of the antenna to the hull through the Water is difiicult to avoid.

The most commonly used system at present is probably that in which a cable extends from the radio apparatus to a metal ring which is, in turn, in contact with the base of the antenna. The coupling unit by which contact is made is usually enclosed in a housing through which the antenna passes. It is attempted to prevent surrounding sea water from entering the enclosure between its inner wall surfaces and the antenna by utilizing O-ring seals. This expedient has not yielded satisfactory results, primarily because the operating conditions impose severe mechanical stresses and hydrostatic pressures against the antenna and the enclosure. Seepage of sea Water into the protected contact area causes grounding of the metal rings and disabling of the radio apparatus.

Shot-ting of the antenna itself has been avoided by covering the antenna with a suitable plastic, but moisture leaks such as those described above in the coupling area nullify any advantages derived from the use of the plastic covering of the antenna per se. Of course, the fact that the an tenna must be retractable simply magnifies the problem of protection from shorting in the coupling area.

It is, therefore, the primary object of the present invention to couple an antenna to radio apparatus without shorting due to moisture seepage.

It is another object of the present invention to improve radio operation in submersible vehicles.

It is still another object of the present invention to provide an antenna system suitable for use on a submarine.

The foregoing and other objects are attained in the present invention by coupling the antenna to the radio apparatus in such a manner that no portion of the RF signal circuit is exposed to contact with surrounding sea water. The coupler between the radio apparatus and the antenna is made up of a pair of coaxial metal elements which are separated by suitable dielectrics to form a capacitive connection between the radio apparatus and the antenna. In the coupler, one of the metallic elements is preferably in rounded by the plastic insulating material of the antenna. The second metallic sleeve and its plastic covering are of proper dimensions to fit within the first metallic sleeve and its plastic covering. The dimensions and the spacing of the sleeves are such that the coupler adds very little to the impedance seen by the transmitter of the radio apparatus, and the impedance is of such a value that it can be easily compensated for by tuners presently in use. Power loss of only a negligible amount is encountered in the coupler.

Inasmuch as the inside diameter of the coupler housing and the outside diameter of the antenna mast are so close, with proper lubrication between the two, no objectionable seepage takes place even though the antenna is retractable. In addition, roller assemblies may be provided to maintain the antenna concentric under varying wind and water loading and to facilitate raising and lowering of the antenna. For a better understanding of the present invention, reference should be made to the following specification of a preferred embodiment thereof, which should be read in conjunction with the appended drawing, the single FIGURE of which is a sectional view, partially cut away, of the antenna, coupling unit and the hull of the submarine.

In the drawing there may be seen a portion of the submarine hull 12 to which a plastic housing 14 is joined by a series of studs, of which the stud 16 is typical. Usually, the housing is generally cylindrical and three or more bolts may be used to hold it in place on the hull.

The lower end of the housing 14 is fitted closely and may be sealed into an opening which is provided in the hull 12. A cable 18 running from the radio apparatus (not shown) is suitably sealed in place in the housing 14 with its central conductor 20 in contact with a conduction member 22. The conduction member 22 is threaded into the housing 14 with a suitable sealing ring 23 disposed in the housing and contacted by a cap 24 on the conduction member. The conduction member 22 may be threaded at its end and screwed into a collar 26 brazed or otherwise suitably fastened to a metallic sleeve 28. The metallic sleeve 28 is embedded in the plastic of the housing 14 and is concentric with a large opening formed vertically through the housing 14. The thickness of the plastic disposed internally of and lining the metallic sleeve 28 may be of the order of 0.010" to 0.125", and preferably 0.025" to 0.050.

Below the ring 32 comes into contact with the stop ring 30 and ther upward motion of the antenna mast 34 is thus vented.

Within the projected area of the metal sleeve 28 is a second metal sleeve 36, smaller than and concentric with the sleeve 28. The sleeve 36 is embedded within the body of the antenna mast 34 and is covered by a layer of plastic which may be of the order of 0.010" to 0.125", and preferably 0.025 to 0.050, in thickness. The metal sleeve 36 is formed into a ring of greater thickness adjacent its upper end, and to that end there may be soldered or otherwise firmly mechanically and electrically connected a mesh screen 38. The screen 38 serves as the active conductive element running the length of the antenna mast, and it is also embedded within the plastic of the body of the antenna mast.

The electrical operation of the antenna system is quite efiicient by comparison to known submarine systems. The same limitations which occur because of the shortfurpre-

cant degradation of electrical performance. In presently used submarine antenna systems, the real part of the lmpedance seen by the system at the input coupler is:

where 8" being the length of the antenna and r its radius. By this method, Z is computed to be equal to 318 ohms for a -foot antenna with a 25-foot radius.

Calculated values of the impedance, (R+ 'Xa), at the antenna input over a range of frequencies from 2 to 3. megacycles indicate that a large mis-match to the 50- ohm transmitter impedance is presented over much of the operating range of the system. The mis-match is compensated for by means of an RF tuner which places a variable inductance in series with the antenna. It should be noted, however, that the tuner compensates only for the imaginary component of the impedance and some loss results from the resistance rnis-match.

The effect of the coupler of the present invention may be computed for comparison with the input impedances calculated above. If a pair of concentric conducting cylinders of infinite length, having an inner radius a and an outer radius b respectively, are considered, it may be considered that the electrical displacement is radially outward from the axis. In these conditions, from Gausses Electrical Flux Theorem, it may be postulated that:

f,e1 J-TzdS=21rreE=q where q is the total charge, E is the electrical field and r" is the radius of the cylinder, wherein a r b. The electrical field is literally the divergence of the potcntial; therefore,

The potential between the cylinders is:

and, therefore, the capacitance per unit length of a cylindrical capacitor is:

7 .354 10210 D/d where e is a dielectric constant of 4.5, D is 6.313 and d is 6.187". These dimensional values of inner and outer capacitor plates are based upon an antenna mast diameter of 6.250" which allows for a thickness of dielectric between the plates of .125". Great accuracy may be obtained by calculating the effect of the air gap and the lubricant that would be present in the antenna coupling of the invention. Obviously, the over-all capacitance of the condenser is determined by the series combination of the capacitances of the three dielectric layers of the gap, the plastic material and the lubricant. If the gap between cylinders is reduced to a minimum, its effect becomes negligible and may be ignored. In any event, a total capacitance of 1600 et. for a coaxial coupler of the type shown having a length of 6" has been computed. The capacitance of the antenna is, of course, in series with the capacitance of the coupling device, and the additional impedance which it contributes is not only insignificant, but within the range of compensation by the tuners conventionally used.

The voltage gradient in the coupler capacitor is as follows:

AE 5450( SP peak volts where S is the voltage standing wave ratio, P is the power in kilowatts and d is the radius of the inner plate in thousandths of an inch or mils. The gradient reaches a value of 1.2 peak volts per thousandth of an inch of thickness, assuming a voltage standing wave ratio of 4 to 1, an input of 1 kilowatt into the coaxial coupler, and a characteristic impedance 2,, of the coupler of about .65 ohms. The breakdown voltage in the plastic insulating material is about 62 volts per thousandth of an inch of thickness which insures a margin of safety of approximately to 1. Capacitors of this type or of even smaller diameters have been found to operate safely up to 10,000 volts without breakdown.

At the highest frequency of operation, the dissipation factor of the dielectric may cause a power loss of as much as 2 percent. Such a loss is not significant when considered with all other system losses.

Although the housing of the coupler as a preferred embodiment of the invention has been made up of glassfabric resin laminates as has the plastic body of the antenna mast itself, other materials may be successfully used. A typical glass fabric suitable for the purposes of the invention may be glass-fabric having a Garan or Volan finish, and any one of several weaves may be used such as 181, 18ll50, 164l50, 121 or even woven roving. The resin may be epoxy, polyester, phenolic or silicone. Other resins may also be used, but ease of fabrication suggests the foregoing materials as being preferred. Obviously, such materials as Teflon, polyethylene, modified polystyrenes and polyurethanes may also be used in conjunction with suitable catalysts known in the art.

The metal from which the coupler sleeves and the mesh element of the antenna are made may be any low resistance conductive material. Copper, brass, aluminum, steel and various alloys are satisfactory. The sleeves are embedded between layers of the glass-resin fabric, and the only critical structure requirements are in maintaining the proper spacing between the capacitor plates formed by the sleeves. In other words, the thickness of the material surrounding the antenna mast sleeve and of that lining the housing sleeve must be carefully maintained. It is also desirable that the metal be carefully cleaned before it is embedded in the surrounding plastic in order that suitable adhesion may take place.

Although what has been described constitutes a preferred embodiment of the invention, other suitable structures within the scope of the invention will suggest themselves to those skilled in the art upon a reading of the foregoing specification. By way of example, rather than limitation, a flat strip of metal might be wound in the form of a helix within the plastic section of the base of the antenna mast. A second helix might be contra-Wound within the coupler housing, the end of the second helix being directly connected to the end of the cable from the radio apparatus. In this alternative, as in the preferred embodiment described above, no contact is possible between the active elements and the surrounding sea water by reason of their embodiment in the plastic insulating material. This and other alternative structures wherein the active coupler elements are completely prevented from contact with a potentially shorting environment are believed to be within the spirit and scope of the present invention, which should be limited only as necessitated by the breadth of the following claims.

What is claimed is:

1. An antenna system for a submarine in which at least a portion of said system is normally submerged comprising an insulating housing, a cable fixed in said housing, a first conductive sleeve connected to said cable for RF energy transfer therebetween, said first conductive sleeve being embedded in said housing, said housing having an opening formed therethrough concentric with said first conductive sleeve, and an antenna mast movable in said opening, said antenna mast being formed of insulating material, an antenna element and a second conductive sleeve embedded in said insulating material, said second conductive sleeve being electrically connected to said antenna element, a capacitive coupler of energy between said cable and said antenna element being formed by said first and second conductive sleeves.

2. An antenna system for a submarine having a hull which is normally at least partly submerged in sea water comprising an insulated housing attached to said hull, said hull and said insulating housing having similar openings formed therein and defining a substantially continuous passage therethrough, a cable for carrying RF energy sealed into said housing, a first conductive sleeve embeddeed in said housing and connected to said cable for RF energy transfer therebetween, said first conductive sleeve surrounding said opening in said housing, an antenna mast formed of insulating material and mounted for recipro cal axial movement in said passage, an antenna element and a second conductive sleeve embedded in the insulating material of said antenna mast, said antenna element and said second conductive slceve being elcctricaily connected together, said first and second conductive sleeves being closely spaced but insulated from one another whereby RF energy may be coupled capacitively therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 1,715,952 Rostron June 4, 1929 2,300,847 Russel Nov. 3, 1942 2,668,187 Von Wald Feb. 2, 1954 2,681,4l2 Webster June 15, 1954 FOREIGN PATENTS 524,652 Great Britain Aug. 12, 1940

Claims (1)

1. 2. AN ANTENNA SYSTEM FOR A SUBMARINE HAVING A HULL WHICH IS NORMALLY AT LEAST PARTLY SUBMERGED IN SEA WATER COMPRISING AN INSULATED HOUSING ATTACHED TO SAID HULL, SAID HULL AND SAID INSULATING HOUSING HAVING SIMILAR OPENINGS FORMED THEREIN AND DEFINING A SUBSTANTIALLY CONTINUOUS PASSAGE THERETHROUGH, A CABLE FOR CARRYING RF ENERGY SEALED INTO SAID HOUSING, A FIRST CONDUCTIVE SLEEVE EMBEDDED IN SAID HOUSING AND CONNECTED TO SAID CABLE FOR RF ENERGY TRANSFER THEREBETWEEN, SAID FIRST CONDUCTIVE SLEEVE SURROUNDING SAID OPENING IN SAID HOUSING, AN ANTENNA MAST FORMED OF INSULATING MATERIAL AND MOUNTED FOR RECIPROCAL AXIAL MOVEMENT IN SAID PASSAGE, AN ANTENNA ELEMENT AND A SECOND CONDUCTIVE SLEEVE EMBEDDED IN THE INSULATING MATERIAL OF SAID ANTENNA MAST, SAID ANTENNA ELEMENT AND SAID SECOND CONDUCTIVE SLEEVE BEING ELECTRICALLY CONNECTED TOGETHER, SAID FIRST AND SECOND CONDUCTIVE SLEEVES BEING CLOSELY SPACED BUT INSULATED FROM ONE ANOTHER WHEREBY RF ENERGY MAY BE COUPLED CAPACITIVELY THEREBETWEEN.

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