US2272608A - Antenna matching structure - Google Patents

Description

Feb. 10, 1942.- R. B; HOFFMAN 2,272,608

ANTENNA MATCHING STRUCTURE Filed Dec. 19, 1939 2 Sheets-Sheet l FIGJIQ, a new.

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INVENTOR' Ross 3. WF'FMA ATTORNEY Feb. 10, 1942. R. B. HOFFMAN ANTENNA MATCHING STRUCTURE Filed Dec. 19, 1939 2 Sheets-Sheet 2 a T w a 7 a 4 f i- 1 J 1 m .m Y H I| H l hl l l l. Wm llll II T fl m- II I. ll llk will m a m I IHH 0/ 1 HH h l lnflul h l ul hwl W "H O. J M fi Z 3 a A 1 J 5 2 r Y Z w Y m R B F 6 Patented Feb. 10, 1942 UNITED STATES PATENT OFFICE ANTENNA MATCHING STRUCTURE Ross Barnum Hoffman, Chicago, 111., assignor. to International Telephone Development Co. Inc., New York, N. Y., a corporation of Delaware Application December 19, 1939, Serial No. 309,926 Claims. (Cl. 178-44) symmetrical circuits.' A particular example of this type of connection is the matching of a coaxial transmission line to a dipole antenna. Lumped inductances do not'lend themselves to good mechanical arrangement when used at the end of 1 a transmission line to couple the line to a .bal-

' cult to a symmetrical circuit; Figs. 2 and 2a illustrate front and side viewsof an embodiment of my invention.

2a, shows antenna tubes 5 and [3 supported and clamped to the housing 6 by means of bushings I, insulators 8 and clamp nuts 9. An input oroutputcoaxial line I!) is joined to the housing by means of a clamp nut II. The central conductor 23 of this coaxial line is shown connected vto the antenna tube l3 by means of a strap H,

but the straps may be connected to either of the antenna tubes 5 or I3.

The inductance Ll illustrated in Fig. 1 is formed by a transmission line type of inductance,

comprising the antenna tube [3, a tube [4 and a shorting plug IS in Figs. 2- and 2a. The inductance L2 is formed by the antenna tube 5, a tube 14 and a shorting plug IS. A condenser plate I! supported by insulating posts l8 and bar [9, and connected to the tube M by a tube or strap 20, forms the condenser C of that figure.

The condenser plate is made adjustable with re- Figs. 3a, 3b and 3c are'furtherembodiments of my invention. I

In Figs. 1a, 1b, 1c and 1d an'unsymmetrical input such as a coaxial transmission line is connected to the points I and 2. Inductances L com-- bined with the condensers C serve to properly couple this unsymmetrical input to any symmetrical circuit such as a dipole antenna which may be connected to the points 3 and 4. In the preferred form the impedances of the inductances of Fig. 1a should be equal ,and the impedance of the condenser .equal to one-half the magnitude of either of the impedances of the inductances; in the network of Fig. 1b,

outlined in Figs. 3a, 3b and 30 which illustrate spect to the grounded housing 6 by mean of a screw 2| and lock nut 22.

In the preferred form, the length of the tube 14 in the antenna tube should be somewhat shorter than A wave length at the frequency at which the antenna is transmitting or receiving. The length of the tube, however, is not very critical and the shorting plugs may be made adjustable or an approximate length may be determined by computation. When for a given set of conditions the length of the tubeis known as by computation, the shorting plugs I5 and I6 may be permanently or solidly fastened to the tube M. The final adjustments of the circuit as represented by the tube l4 and the antenna tubes and the condenser'll maybe adjusted by means of the screw 2| and the'associated lock nut 22 controlling the condenser plate. The condenser allows adjustment of the matching circuit over a convenient working range.

Structures similar to the above in design may be made to form any of the network shown in Figs. la-ld. Examples of these structures are networks 1b, 1c and 1d respectively. Mechanical detail has not been shown in these figures since the electrical connections and relative positions of the parts are clearly shown, and the antenna tube 5, and the remaining connections are unchanged. In Fig. 3b one of the inductances is eliminated, and a condenser similar to the condenser of Fig. 2 is added, the connections being as shown. In Fig. 30 one of the inductances is eliminated, and the original condenser has both of its plates ungrounded and connected to the antenna tube l3 and outer conducto'r N. The center conductor I! of the remaining transmission line type of inductances 2d and i4 is connected to ground. A special condenser is added for coupling the antenna tube 5 to the system, and this condenser comprises two conducting discs 25 and an insulator 26. The discs 25 may be made adjustable with respect to each other by making the insulator 26 of shim type discs or by threading the tube 5 and its supporting insulator. In some cases the discs 25 may not be included if the capacity between tube 5 and tube 24 is suificiently large.

It is further possible in the above constructions to include the transmission line type of inductor as part of the center conductor 23 of the coaxial line. In this form the center conductor would be tubular near its termination at the housing and a conductor with a plug, similar to the conductor 14 and plug l5 of the other constructions, could be inserted therein.

While I have described particular embodiments of my invention for purposes of illustration, it will be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

What I claim is:

1. A structure adapted to connect a symmetrical circuit to an asymmetrical circuit, comprising a first tubular conductor and a second tubular conductor, a third conductor having portions thereof contained within said tubular conductors forming substantially equal inductances, a fourth conductor and a fifth conductor, a condenser having substantially one-half the impedance of either inductance, connected between said third conductor and said fifth conductor, and means for connecting said fourth conductor to one of said first and second conductors.

2. A structure adapted to connect a symmetrical circuit to an asymmetrical circuit, comprising a first tubular conductor and a second tubular conductor, a third conductor within said first conductor forming an inductance, a fourth conductor within said second conductor forming an aevaeoe inductance having substantially one-half the impcdance of said first inductance, a fifth conductor connected to said third conductor, 'a sixth conductor connected to said fourth conductor, and a condenser having an impedance substantially equal to the impedance of said first inductance connected between said second and third conductors.

3. A structure adapted to connect a symmetrical circuit to an asymmetrical circuit, comprising a first conductor and a second tubular conductor, a third conductor within said second conductor forming an inductance, a condenser having an impedance substantially equal to that of the inductance connected between said first and third conductors, a fourth conductor connected to said third conductor, a fifth conductor, and a condenser having an impedance substantially one-half that of said inductance connected between said second and fifth conductor.

4. A structure adapted to connect a symmetrical circuit, comprising first and second conductors to an asymmetrical circuit comprising third and fourth conductors, said structure comprising a conductive housing, means for clamping said fourth conductor to said housing, insulators clamped to said housing for insulating said first and second conductors therefrom, means for clamping said first and second conductors to said insulators, a fifth conductor having portions thereof within said first and second conductors and electrically connected thereto, a condenser plate in capacity relation with said housing mounted on an adjusting screw and connected to said fifth conductor, and means for connecting said third conductor to a conductor of said symmetrical circuit.

5. A structure adapted to connect a two-conductor coaxial line to a dipole antenna having tubular conductors, comprising a conductive housing, means for clamping the outer conductor of said line to said housing, means for clamping said tubular conductors to said housing at substantially right angles to said line and in axial alignment, a fifth conductor having portions thereof within said tubular conductors and connected at its ends thereto, an adjustable condenser plate in capacity relation with said housing and connected to said fifth conductor, and means for connecting the inner conductor of said line to one of said tubular conductors.

ROSS BARNUM HOFFMAN.

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