US2648768A

US2648768A - Dipole antenna

Info

Publication number: US2648768A
Application number: US67826A
Authority: US
Inventors: Jr Oakley Mcdonald Woodward
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1948-12-29
Filing date: 1948-12-29
Publication date: 1953-08-11
Anticipated expiration: 1970-08-11

Description

g- 1953 0. M 0. WOODWARD, JR 2,648,768

v DIPOLE ANTENNA Filed Dec. 29, 1948 2 Sheets-Sheet l INVENTOR AT ORNEY &

A 1, 1953 o. MOD. WOODWARD, JR 2,648,768

- DIPOLE ANTENNA Filed Dec. 29, 1948 2 Sheets-Sheet 2 (a) zan ze a/y/v POM/? 634/ F250. MC/SEC. v

(f) H/GHER aw/v0 POM E1? 64/ Q: 2*

- F850. Mysfc.

a 7M BY r J ATTORNEY Patented Aug. 11, 1953 UNITED STATES PATENT OFFICE DIPOLE ANTENNA Application December 29, 1948, Serial No. 67,826

8 Claims.

The invention relates to antennas and particularly pertains to improvements in dipole elements of an antenna array.

.An object of the invention is to provide a simple antenna for radiation and/or reception of signals over a wide frequency range in a single direction, or from opposite directions.

A more specific object of the invention is to provide a simple antenna for receiving television or frequency modulated signals in the presently allotted bands lying between 54 and 216 mc./s. from a single direction, or from opposite directions.

Another object of the invention is to provide a dipole antenna having a figureeight characteristic field pattern over a wide range of frequencies.

A further object of the invention is to provide a dipole antenna element having a substantially uniform response over a wide range of frequencies.

Still another object of the invention is to provide dipole elements presenting a substantially constant standing wave ratio over a wide range of frequencies.

A still further object of the invention is to provide an antenna useful over a wide frequency range and having a field pattern independent of the frequency at which it is employed.

Still another and further object of the invention is to provide an antenna in accordance with the above objects and which does not require any adjustment in use.

These and further objects which will appear as the specification progresses are achieved by means of a simple dipole element having arranged thereon modifying elements as hereinafter described.

The invention will be described with reference to the accompanying drawing forming a part of the specification and in which:

Fig. 1 shows a dipole antenna element known to the art;

Fig. 2 is a graphical representation of the field patterns of the dipole shown in Fig. 1;

Fig. 3 shows an embodiment of a dipole antenna according to the invention;

Fig. 4 shows a dipole antenna element according to the preferred embodiment of the invention;

Fig. 5 shows details of a dipole modifying element according to the invention;

Figs. 6, 7, and 8 are graphical representations of the field patterns of the preferred arrangement shown in Fig. 5; and

Fig. 9 is a graphical representation of the power gain of an antenna according to the invention compared to that of a perfectly matched dipole.

Referring to Fig. 1, there is shown a well known simple dipole antenna element comprising collinear conductors I2, l4 arranged to be a half.- wave long at the desired frequency and having means to connect a transmission line It to. the adjacent ends.

As is also well known, an antenna elementof the type shown in Fig. 1 has a figure-eight field pattern in a plane passing through the conductors as shown at a in Fig. 2. For a dipole element electrically a half-wave longat mc./s. the field pattern will appear as shown byline 2| when the element is operatedat an actual frequency of 55- mc./s., and if the actual operating frequency is 88 mc./s., the field pattern will be as shown by brokenline 22.

Thus far it is obvious that the ordinary dipole element may be used successfully over a narrow frequency range with satisfactory results. If, however, operation at frequencies far remote from the frequency at which the dipole is resonant is attempted, quite different results will be obtained. If the operating frequency is far below the resonant frequency of the dipole, insufficient pickup or radiation will be effected because it is practically impossible to match the simple dipole to any practical transmission system or transducer. If the antenna is operated at frequencies higher than the resonant frequency, the element becomes a larger multiple of fractions of the wavelength than at the resonant frequency, which results in field patterns having a more complex lobing, specific examples of which are shown ,at ,b in Fig. 2. For instance, if the 65 mc./s. element is operated at mc./s., each conductor l2, l4 becomesthree-quarters of the wavelength and the field pattern will have a lobe pattern on both sides of the antenna as shown by line 26 (one side only being shown for clarity). At 17 5 mc./s. the pattern will be that shown by line .25 (again one side only being shown), and at 215 mc./s. the pattern will be that of the lemniscate indicated by. broken line 21. (the complete pattern being shown).

While there may be receiving locations at which a compromise antenna installation can be made to provide suitable radiation or reception at certain desired frequencies in the desired directions, it is often necessary, in fringe area receiving locations, for instance, where all of the transmitters are located in more or less the same direction with respect to the receiver, that the directivity of the field pattern be substantially constant regardless of the frequency used, else a complex and costly rotatable antenna arrangement will be required in order to obtain satisfactory results.

According to the invention, the desired bi-directional characteristic is obtained by altering the current distribution along the dipole conductors. One manner by which this may be accomplished is shown in Fig. 3, wherein at a radiator or receptor conductors I2 and I4 have conductive sleeves 32 arranged thereon by means of con-v ductive disc members 34 to interpose series reactance in the dipole elements. have shown this type of antenna to be still rather narrow banded due partially to the low characteristic impedance of practical coaxial sleeve elements. Higher characteristic impedances and. correspondingly increased band widths are obtained by replacing the sleeves 32 with open wire radiating or receiving hairpin loops 36 or 31 illustrated at b and c.

Improved results are obtained, however, with the arrangement shown in Fig. 4 wherein conductors I2 and I4 have additional radiator or receptor conductors 42 arranged thereon at an angle. Details of one practical manner in which these additional elements 42 may be added to conductors I2, I4 are given in Fig. wherein there is provided a collar member 5I having an aperture 52 therein of diameter to fit the dipole element to be modified I2, upon which after adjustment for optimum results, it is rigidly fastened in place by any known means, shown here as setscrew 53. Spokes 54, corresponding to element 42 of Fig. 4, are set into collar 5| at the desired angle, which angle will usually be found to be about 45. Obviously other fastening arrangements such as split collars, etc., can be used with equal success. While the embodiments shown in Fig. 3 have

non-radiating elements

32, 36, and 31 (36 and 31 progressively permitting more radiation), the added elements shown in Figs. 4 and 5 should be considered as part of the radiating or receiving system.

The addition of

element

42 or 54 at most any point along conductors I2, I4 will efiect improvement of the operation of the dipole element, but optimum results were found to be obtained if the center of area of the V thus formed is located somewhere near the midpoint of the conductors Tests, however,

4 in the impedance at lower frequencies will be effected by the addition of this length of transmission line.

Field patterns for the higher frequencies of 175, 195, and 215 mc./s. obtained with the arrangement shown in Fig. 4 are illustrated in Figs. 6, '7, and 8 respectively. By comparing each of these figures with the corresponding pattern shown in Fig. 2, it is obvious that great improvement in the bidirectional characteristic is obtained.

The embodiment shown in Fig. 4 can be employed at many installations with considerable improvement over the ordinary simple dipole antenna, as will be seen by referring to Fig. 9, wherein there is shown a graph of the power gain of a dipole antenna according to the invention such as shown in Fig. 4 as compared to a dipole antenna as shown in Fig. 1 and an ideally matched transmission line at each point of measurement.

While the invention has been described in terms of express embodiments, it is to be understood that obvious applications of the principles of the invention will be suggested to those skilled in the art without departing from the spirit and scope of the invention, particularly in View of the suggested use of adapters shown in Fig. 5.

I claim:

1. In an antenna comprising a radiator or receptor component having at least one elongated element resonant to a given frequency, said component having a bi-directional field pattern at said given frequency and a natural quadri-di- I2, I4 and the angle formed between one leg of the V and the conductor is approximately 45". Dimensions of an optimum system for receiving television and frequency modulation signals between 54 and 216 mc./s. are given in Fig. 4. Because the efiective area of the composite dipole element is broader in the plane of the V, the element tends to present slightly higher gain in the direction normal to the plane of the V.

The addition of the V elements effects very little change in the impedance at low frequency and correspondingly has little effect on the field patterns. The impedance at high frequencies, however, may be considerably different, partially depending on the type of endseal of the transmission line used. This may readily be corrected by interposing an impedance transformer comprising a short length of transmission line 48 between the conductors I2, I4 and transmission line I6 to improve the impedance characteristic at the higher frequencies. The length of this line should be on the order of a quarter wavelength at the higher frequencies but need not be at all exact, for example, about 16 inches long on the order of a quarter-wave at 195 mc./s'. in the embodiment shown in Fig. 4. Little change rectional field pattern at frequencies above said given frequency, an adapter device mounted on said element substantially centrally of the ends thereof to maintain said bi-directional field pattern at said frequencies above said given frequency, said adapter device comprising a pair of elongated radiator or receptor conductors substantially shorter than said element and arranged in the form of a V, the adjacent ends of said conductors being connected to said element to lie in substantially a single plane and to form an angle of substantially 45 between said element and each of said elongated conductors.

2. An antenna having a bi-directional field pattern comprising a pair of arms arranged endto-end in a straight line but spaced from each other at adjacent ends, a feed line coupled to said adjacent ends, a pair of elongated wires arranged in the form of a V connected at the apex of the V to each of said arms at a location intermediate the ends of the arm and appreciably removed from the end of the arm to which the feed line is coupled, said elongated wires each being shorter than the arm to which it is connected, the distance between apices of said V's being approximately one-third the overall length of said antenna arms.

3. An antenna comprising a radiator or receptor component having at least one elongated element resonant to a given frequency, said component having a bi-directional field pattern at said given frequency and a natural poly-directional field pattern at frequencies above said given frequency, a pair of elongated radiator or receptor conductors substantially shorter than said element and arranged in the form of a V on said element substantially centrally of the ends thereof to maintain said bi-directional field pattern at said frequencies above said given frequency, the adjacent ends of said conductors being connected to said element to lie in substantially a single plane and to form angles of substantially 45 between said element and each of said elongated conductors.

4. In an antenna comprising a radiator or receptor component having at least one elongated element resonant to a given frequency, said component having a bi-directional field pattern at said given frequency and a natural poly-directional field pattern at frequencies above said given frequency, a pair of elongated radiator or receptor conductor substantially shorter than said element mounted on said element substantially centrally of the ends thereof to maintain said bi-directional field pattern at said frequencies above said given frequency, said conductors having the adjacent ends thereof connected to said element and being arranged in the form of a V to lie in substantially a single plane at angles of substantially 45 between said element and each of said elongated conductors.

5. An antenna having a bi-directional field pattern comprising a pair of arms arranged endto-end in a straight line but spaced from each other at adjacent ends, means to couple a feed line to said adjacent ends, a pair of elongated wires arranged in the form of a V connected at the apex thereof to each of said arms at a location intermediate the ends of the arm and appreciably removed from the end of the arm to which said feed line coupling means are located, 0

said elongated Wires each being shorter than the arm to which connected, the distance between apices of said Vs being approximately one-third the overall length of said antenna arms.

6. An antenna having a bi-directional field pattern comprising a pair of elongated conductive arms arranged in substantially end-to-end relationship and spaced apart at adjacent ends, means to couple a feed line to said adjacent ends, a pair of elongated conductors arranged in the form of a V connected at the apex thereof to each of said arms at a location intermediate the ends of the arm and appreciably removed from the end of the arm to which said feed line coupling means are located, said elongated conductors each being shorter than the conductive arm to which connected, the distance between apices of said Vs being approximately one-third the overall length of said antenna arms.

7. An antenna having a bi-directional field pattern comprising a pair of elongated conductive arms arranged in substantially end-to-end relationship and spaced apart at adjacent ends,

mean to couple a feed line to said adjacent ends, a pair of elongated conductors arranged in the form of a V connected at the apex thereof to each of said arms at a location intermediate the ends of the arm and appreciably removed from the end of the arm at which said feed line coupling means are located, said elongated conductors each being shorter than the conductive arm to which connected and the distance between apices of said V's being approximately one-third the overall length of said antenna arms, and the length of each of said conductors being substantially one-third the length of each of said conductive arms.

8. An antenna having a bi-directional field pattern comprising a pair of elongated conductive arms arranged in substantially end-to-end relationship and spaced apart at adjacent ends, means to couple a feed line to said adjacent ends, a pair of elongated conductors connected at adjacent ends thereof to each of said arms at a location intermediate the ends of the arm and extending divergently away from the end of the arm at which said feed line coupling means are located, said elongated conductors being substantially one-third the length of each of said conductive arms, and the center of the projection of said conductors on said arms being approximately at the center of said antenna arms.

OAKLEY McDONALD WOODWARD, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,610,704 Paddack Dec. 14, 1926 1,909,615 Gothe May 10, 1933 2,147,806 Alford Feb. 21, 1939 2,155,955 Peterson Apr. 25, 1939 2,201,857 Dome May 21, 1940 2,248,800 Alford July 8, 1941 2,287,220 Alford June 23, 1942 2,323,641 Bailey July 6, 1943 2,380,333 Scheldorf July 10, 1945 2,411,976 Peterson Dec. 3, 1946 2,425,585 Wheeler Aug. 12, 1947 FOREIGN PATENTS Number Country Date 219,185 Great Britain July 24, 1924 OTHER REFERENCES Radio News, page 41, May 1945.