US2243136A - Wide band antenna system - Google Patents

Description

y 1941- B. TREVOR 2,243,136

WIDE BAND ANTENNA SYSTEM Filed Feb. 24, 1940 INVENTOR. BERT/2AM TREVOR ATTORNEY.

Patented May 27, 1941 WIDE BAND ANTENNA SYSTEM Bertram Trevor, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 24, 1940, Serial No. 320,607

6 Claims.

The present invention relates to short wave means for coupling said antenna to a single coaxial transmission line. Another object of the present invention is the provision of coupling means, as aforesaid, which is simple in construction and mechanically strong.

Still another object is the provision of coupling means, as aforesaid, which provides a smooth impedance match between the antenna and the transmission line with an absence or" lumped reactances.

still a further object is the provision of a coupling circuit, as aforesaid, which does not restrict the available band width of the antenna with which it is used.

The present invention features a coupling means for coupling a single coaxial transmission line to a balanced wide band double cone antenna of the general type disclosed in U. S. Patem to Philip S. Carter #2,175,252, granted October 10, 1939.

According to the invention, one cone of the antenna is gradually tapered into the center conductor of the transmission line. The other cone is connected to the center conductor through a balanced shielded two-wire transmission line,

having a total conductor length equal to half the length of the operating wave whereby it is energized in phase opposition to the first cone.

Further objects, features and advantages of the present invention will become apparent from the following detailed description which is accompanied by a drawing in which reference characters I and I indicate the upper and lower halves of the cone antenna proper. The relationship of the diameter of the cones at their bases with respect to their length whereby a wide band characteristic is obtained is set out in more detail in the patent previously referred to.

Radio frequency energy for energizing the cone antenna is brought thereto by means of the coaxial transmission line composed of an outer shell conductor 2 and an inner conductor 3. The inner conductor 3 is held coaxial with the outer conductor by means of lower loss insulators 5. The insulators may be maintained in position with respect to the inner conductor by swedged portions I3, I3 on the inner conductor and, if necessary, with reference to the outer shell by means of screws or rivets I2. The inner conductor 3 of the transmission line is connected directly to the apex of the cone I. The junction between conductor 3 and cone I is made as smooth as possible so that sudden changes of impedance between the cone and the conductor are avoided. Cone I is coupled to inner conductor 3 by means of a balanced two-wire line 3. This line is supported at one end by its connection to cones I and I and at its other end by insulator 8. The insulator is arranged to slide in slot It in the inner conductor to maintain the conductors of line 4 taut. The cones I and I of the antenna may conveniently by supported in position by insulating supporting brackets 8 which, in turn, are supported by metallic ring I attached to outer conductor 2. Holes 9 and 9' are cut in the shell 2 in order that the cone tips may protrude to the interior of conductor 2 to their points of connection with conductors 3 and-4.

From the figure it may readily be seen that one-half of cone and antenna I is fed directly by the inner conductor 3 of the coaxial transmission line, while the other half of the antenna is fed through line 4. The total length of the conductor of line 4 from cone I to cone I is adjusted to half the operating wavelength. The two halves of the antenna will then be energized in counter-phase relationship from the single conductor 3.

In order to assure an accurate impedance match between the antenna and the coaxial transmission line, the antenna impedance between the tips of the cones is arranged to be four times the characteristic impedance of the line 3, 2. Furthermore, the characteristic impedance of line 4 considered as a two-wire transmission line is equal that of the antenna. As

' an example, suppose the impedance of line 3, 2

is ohms, then the angle of the cones and I is so adjusted with respect to their length as to give an antenna impedance of 400 ohms. The diameter of the conductors of two-wire transmission line 4 is so chosen with respect to their spacing that the impedance of the line within outer conductor 2 is 400 ohms. This, then, means that each half of the antenna alone has an impedance of 200 ohms with respect to the neutral plane of the antenna, that is, the outer surface of shell conductor 2. Each of these 200 ohm sources is energized in parallel from the 100 ohm line, thus resulting in a matched condition between the line and the antenna.

The impedance of the two-wire line 4 may vary slightly from the theoretically exact value described above, but it is essential that the total length of conductor of line 4 must be approximately a half wavelength so that the currents in cones l and I will be 180 degrees out of phase with each other. It will be noted that for frequencies either side of resonance reactive components will be introduced more rapidly with departure from resonance as the line impedance 4 departs from the theoretically correct value given above.

The foregoing examples are discussed from the viewpoint of a transmitting system but it should be clearly understood that the invention is as useful for receiving antenna construction.

While I have particularly shown and described several modifications of my invention, it is to be particularly understood that my invention is not limited thereto but that modifications may be made within the scope of my invention.

I claim:

1. In combination, an antenna comprising a pair of conical surfaces of revolution, the apices of such surfaces being adjacent, a single coaxial transmission line having an inner conductor and an outer shell, said inner conductor being connected to the apex of one of said surfaces of revolution and a section of two-wire line having a total length equal to half the length of the operating wave connecting the apex of the other of said conical surfaces of revolution to the junction of said imier conductor and the first said apex, the outer shell of said coaxial line extending over said two-wire line and arranged at right angles to the axes of said conical surfaces of revolution whereby a symmetrical structure is attained.

2. In combination, an antenna comprising a pair of conical surfaces of revolution, the apices of said surfaces being adjacent, a single coaxial transmission line having an inner conductor and an outer sheath, said inner conductor being connected to the apex of one of said surfaces of revolution, said conductor being smoothly tapered into said conical surface, the outer shell of said .transmission line extending beyond said connection, a two-wire line within said shell and connected to said apices, the wires of said line being connected together at a distance equal to .a quarter of the length of the operating wave from the point of connection to said apices.

3. In combination, an antenna, comprising a pair of conical surfaces of revolution, the apices of said surfaces being adjacent a single coaxial transmission line having an inner conductor and an outer shell, said inner conductor being connected to the apex of one of said surfaces of revolution, said conductor being smoothly tapered into said conical surface, the outer shell of said transmission line extending beyond said connection, a two-wire line within said shell and connected to said apices, the wires of said line being connected together at a distance equal to a quarter of the length of the operating wave from the point of connection to said apiece and means for supporting said two-wire line within said shell.

4. In combination, an antenna comprising a pair of conical surfaces of revolution, the apices of said surfaces being adjacent, a single coaxial transmission line having an inner conductor and an outer shell, said inner conductor being connected to the apex of one of said surfaces of revolution, said conductor being smoothly tapered into said conical surface, the outer shell of said transmission line extending beyond said connection, a two-wire line within said shell and connected to said apices, the wires of said line being connected together at a distance equal to a quarter of the length of the operating wave from the point of connection to said apices, the impedance of said two-wire line being equal to that of said antenna and equal to four times that of said coaxial line. 4

5. In combination, a balanced antenna comprising a pair of conical surfaces of revolution, said surfaces being coaxially arranged with their apices adjacent, the effective angle of said surfaces being so adjusted that said antenna has substantially a uniform impedance over a wide band of frequencies, a single coaxial transmission line having an inner conductor and an outer shell, said inner conductor being smoothly tapered into one of said conical surfaces, the outer shell of said transmission line extending beyond said connection, a two-wire line within said shell and connected to said apices, the wires of said line being connected together at a distance equal to a quarter of the length of the operating wave from point of connection of said line to said apices, the impedance of said two-wire line being equal to that of said antenna and equal to four times that of said coaxial line.

6. In combination, an antenna comprising a pair of elongated radiating elements in a colinear end to end relationship, a single coaxial transmission line having an inner conductor and an outer shell, said line being arranged at right angles to said elements at their adjacent ends, said inner conductor being connected to an adjacent end of one of said elements and a section of two-wire line having a total conductor length equal to half the length of he operating wave connecting the adjacent end of the other of said elements to the junction of said inner conductor and the first mentioned adjacent end, the outer shell of said coaxial line extending over said twowire line.

BERTRAM TREVOR.

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