US3030622A - Dipole antenna provided with gas-tight housing - Google Patents

Description

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April 17, 1962 -r LEITNER ET AL 3,030,622

DIPOLE ANTENNA PROVIDED WITH GAS-TIGHT HOUSING Filed April '7, 1959 INVENTORS P0354 7 73 AF z/owv Dema- United States Patent 3,030,622 DIPOLE ANTENNA PROVIDED WITH GAS-TIGHT HOUSING Robert T. Leitner and John E. Drake, Sherburne, N.Y.,

assignors to Technical Appliance Corporation, Sherburne, N.Y., a corporation of New York Filed Apr. 7, 1959, Ser. No. 804,803 3 Claims. (Cl. 343-793) This invention relates to antennas and more especially it relates to antennas of the dipole kind.

A principal object of the invention is to provide an improved dipole antenna which is capable of use under widely varying atmospheric conditions with a high degree of stability in electrical characteristics.

Another object is to provide a dipole antenna which is provided with a pressurized assembly.

A feature of the invention relates to a pressurized dipole antenna wherein the transmission line to the arms of the dipole is constituted of a tubular outer conductor and a concentric inner conductor, the outer conductor adjacent the point of attachment to the dipole arms be ing provided with a slotted section which provides a balun coupling between the dipole proper and the transmission line.

Another feature relates to the novel organization, arrangement and relative location and interconnection of parts which constitute an improved dipole antenna.

In the drawing, which shows one typical example,

FIG. 1 is a vertical elevational view, partly sectional, of a dipole antenna embodying the invention;

FIGS. 2, 3 and 4 respectively are sections along the lines 2-2, 33, and 4-4 of FIG. 1.

Referring more particularly to FIG. 1, the numeral represents a rigid metal mounting plate which supports the antenna assembly. That assembly consists, in general, of a dipole with the dipole arms 11, 12 fastened to a tubular upright 13 which constitutes the outer conductor of a transmission line. The center conductor 14 of that line is in the form of a solid metal rod which is held concentrically within but insulated from the member 13 by a series of insulator washers 15, 16, 17 of a suitable insulation such for example as Teflon. Preferably the member 13, as Well as the dipole arms 11 and 12, are of a light weight tubular metal stock such as aluminum. The member 13 adjacent its lower end is aluminum brazed to a pair of spaced aluminum flanges 18, 19.

The upper end of member 13 is provided with a pair of oppositely disposed longitudinal slots 20, 21. Each of these slots has a length which is approximately equal to a quarter wavelength at the mid-point frequency for which the antenna is designed. At high frequencies these slotted upper end portions of member 13 constitute a short circuited quarter Wavelength transmission line which, by reason of the connection thereto of the dipole arms, provides a balun coupling between the balanced portion of the system, represented by the symmetrical dipole arms, and the unbalanced transmission line 13, 14. The two dipole arms are attached on opposite sides of the open end of the slot. Since the slot is a quarter wavelength long, effectively there is across the dipole terminals a transmission line stub which is shorted at the far end and is resonant by virtue of its length, and it presents to the dipole an infinite or very high impedance. Furthermore, each dipole terminal is now balanced with respect to ground, thus providing a balanced (dipole terminals) to unbalanced (coaxial line) transformation. Energy is fed to the dipole by connecting the center conductor of the coax to one dipole terminal and the outer conductor to the other.

The tubular transmission line conductor 13 is connected to the concentric transmission line conductor 14, for direct current, by means of a bolt or screw 22 closely adjacent the point of connection of the dipole arms to the member 13. Welded or brazed to the extreme upper end of the member 13 in alignment and diametrically opposite to the slots 20, 21 are metal bosses 23, 24, into which are screwed the plugs 25, 26 that are rigidly united respectively to the dipole arms 11 and 12.

We have found that more stable and reliable results are obtained from the antenna by providing a pressurized T-shaped housing consisting of the vertical tubular portion 27 and the horizontal tubular portion 28. The vertical portion 27 at its lower end is welded around its periphery to the upper face of the mounting plate 10, as indicated by the numeral 29, thus forming a sealed joint between the members 10 and 27. The flange 18 of the dipole assembly is fastened against the under face of member 10 by a series of bolts 30, and in order to provide a gas-tight seal, the face of flange 18 is provided with an annular groove 31 in which is mounted the pressure deformable sealing ring 32 so that when the members 10 and 18 are bolted together, a gas-tight joint is provided. In order to maintain the elements 13 concentric within the member 27, a plurality of insulator washers 33, 34, 35 may be provided. These washers may be of the same material as the above described washers 15, 16 and 17. In order to maintain the housing formed of the members 27, 28 gas-tight, annular insulator bushings 36, 37 are provided between the dipole arms 11, 12 and the inner surface of the member 28. Each of these bushings has on its outer peripheral surface a groove 38 in which is seated a pressure deformable sealing ring 39 for example of neoprene. Likewise, the inner peripheral surface of each of the bushings is provided with a groove 40 in which is seated a pressure deformable sealing ring 41. The bushings 36, 37 can be fastened in place by suitable screws 42.

Therefore, gas under pressure, for example five pounds per square inch, is in the complete cavity enclosed by 0 rings 32, 39 and 41 as in the interior of the transmission line which connects to the dipole at flange 19. This is the feed point and critical areas of the dipole Where moisture and other foreign matters might collect and make the antenna inoperative or reduce its efliciency especially when it is subjected to high power as in a transmitting antenna. For this same reason, it is also common to pressurize the transmission line. It is impractical to preclude all moisture by sealing alone but by introduc ing a dry gas it is impossible for any moisture to accumulate. It is unnecessary to have the exterior conductor of a coax line pressurized since there are no voltages or currents exterior to a line of this type. It is unnecessary to pressurize the extreme ends of the dipole since they are far removed (physically) from ground and foreign matter or moisture will not adversely afiect them.

It will be clear from the foregoing that the dipole antenna provides its own inherent balun coupling by means of the slots 20, 21 and the antenna proper is enclosed within a sealed housing constituted of the members 27 and 28. It will be understood, of cause, that the dipole arms 11 and 12 extend outwardly beyond the ends of the member 29 to any desired extent determined by the frequency at which the antenna is intended to be operated. For example, each dipole element is a quarter wavelength and about two-thirds of this length is exposed from outside the sleeve 28. The foregoing described assembly can be coupled to any well known hollow concentric transmission line of the pressurized gas filled kind, and for that purpose the flange 19 may carry a locating pin 43 whereby the flange 19 can be located gas-tight coupled to a corresponding sealed flange on the end of any well known gas filled concentric transmission line (not shown). As is well known, such a line contains a suitable gas, for example nitrogen under a predetermined pressure, and this gas, by reason of the tubular member 13 and the upper open end thereof and the slots 20, 21, fills the entire T-shaped housing comprised of the members 27, 28 and respective ends of which are sealed as above described. We have found that this manner of assembling within a pressurized housing improves the operation and stability of the antenna particularly at very high frequencies of the order of 50 megacycles and up.

When the dipole is used in an array with others of the same kind, the screw 22 establishes a polarity of the dipole and it is physically impossible to see to which dipole arm the screw is associated after the unit is assembled The pin insures that all units are assembled consistently the same and provides an outward identifying mark to be used at installation to insure that the units will be arrayed with the same phase polarity.

Various changes and modifications may be made in the disclosed embodiment without departing from the spirit and scope of the invention.

What is claimed is:

1. A dipole antenna comprising a T-shaped tubular metal housing having a tubular horizontal metal portion joined to a tubular vertical portion to form a structurally rigid T-shaped hollow tubular unit, a dipole having a pair of dipole arms joined to a tubular metal member, said arms extending interiorly through the horizontal portion of said housing but circumferentially spaced there-' from and said tubular metal member extending through the vertical portion of said housing, the ends of said housing being gas-tight sealed, said housing having a filling of an inert gas under pressure and means including a hollow concentric transmission line sealed through the lower end of the vertical portion of the T-shaped housing to maintain the same pressure in the transmission line and in the said housing.

seal in a gas-tight manner said tubular vertical metal memher through the lower end of the vertical portion of said T-shaped housing.

3. In combination a T-shaped tubular metal housing arranged to receive a gas under pressure, insulator sealing rings closing off the ends of the cross top portion of said housing, sealing means closing off the open end of the leg of the T-shaped housing, a transmission line extending through the last mentioned sealed end of said housing, said transmission line comprising a tubular metal member and a concentric conductor, and a pair of dipole arms having their inner spaced ends connected to the upper, end of said tubular metal member and extending outwardly beyond the sealed ends of said cross top portion of said housing, said tubular member being sealed in a gastight manner to the lower end of the vertical portion of said housing whereby the same gas pressure is automatically maintained within said transmission line and Within said housing.

References Cited in the file of this patent UNITED STATES PATENTS 1,388,336 Hanson Aug. 23, 1921 1,747,983 McCarthy Feb. 18, 1930 2,454,907 Brown Nov. 30, 1948 2,462,881 Marchetti Mar. 1, 1949 2,627,026 Kandonian et al. Jan. 27, 1953 2,823,381 Martin et a1. Feb. 11, 1958

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