US2880418A

US2880418A - Omnidirectional antenna using dipoles

Info

Publication number: US2880418A
Application number: US338057A
Authority: US
Inventors: Stohr Walter
Original assignee: Siemens AG
Current assignee: Siemens and Halske AG; Siemens AG
Priority date: 1952-03-03
Filing date: 1953-02-20
Publication date: 1959-03-31
Anticipated expiration: 1976-03-31
Also published as: NL89425C; NL176342B; BE518091A; GB727527A

Description

March 31, 1959 w. STOHR 2,880,418

OMNIDIRECTIONAL ANTENNA USING DIPOLES Filed Feb. 20. 1953 I3 N 2| l6 wrfq 7 I9 24 6 l8 FIG.|

IN VENTOR WALTER sT6HR ATTORNEY United States Patent OMNIDIRECTIONAL ANTENNA USING DIPOLES Walter Stiihr, Berlin-Siemensstadt, Germany, assignor to Siemens & Halske Aktiengesellschaft, Munich, Germany, a corporation of Germany Application February 20, 1953, Serial No. 338,057

Claims priority, application Germany March 3, 1952 2 Claims. (Cl. 343-799) This invention relates to antennae systems and is particularly concerned with an omnidirectional antenna.

In the case of an omnidirectional antenna comprising dipoles with reflectors which radiate in four main directions displaced by 90, there will be observed in its radiation diagram more or less pronounced extended radiations outside of the main radiation directions. The magnitude of such extended radiations depends, in the presence of suitable relationship of the diameter of the mast or tower to wavelength to be radiated, on the concentration characteristics of the individual dipoles. For example, by using half wave dipoles more energy will be radiated at an angle of 45 to the main radiation direction than in the main radiation direction. By using full wave dipoles, the energy radiated at each angle in the intermediate zones between the four main radiation directions will be smaller than in each of the main radiation directions.

In order to keep the extended radiation of the radiation diagram small, that is, in order to radiate at each angle energy of substantially identical magnitude, the antenna would have to be made of dipoles each of which radiates energy at an angle of :45 to its main radiation direction, which is so small that it furnishes together with the energy of the neighboring dipole of the main radiation direction which is displaced by 90 a practically corresponding energy. In an antenna built up of such dipoles, as much energy would be radiated at the angle of 1:45 to the main radiation direction as in the four main directions.

The object of the invention is to provide an omnidirectional antenna comprising identical dipoles disposed in a common plane or level about a carrier, the dipoles being for good impedance matching shorter than full wave, equipped with reflectors, the ratio of length of the dipoles to the diameter thereof being such that the radiation characteristics is broadened so that the energy radiated in the zone between neighboring main radiation directions corresponds substantially to the energy of the main direction.

There are preferably disposed in one level four identical, for example, cylindrical dipoles arranged to define a rectangle. The radiation characteristic is then broadened with such dipoles in such a degree that one fourth of the energy of the main radiation direction is radiated at an angle of -45 to the main radiation direction.

The ratio of length of the dipole to the diameter is suitably /25 and preferably /25. The length of the dipoles is about to 35% shorter than full wave. The width of the radiation will then vary between that of a full wave dipole and that of a half wave dipole.

The invention will now be explained with reference to the accompanying drawings Figs. 1 and 2 showing in schematic plan views two embodiments of omnidirectional antennas with their carriers.

In Fig. 1, there is a carrier or tower 1 provided with four identically constructed cylindrical or rodshaped dipoles having respectively the elements 2-3, 4-5, 6-7

and 89 arranged to define the outline of the four sides of a rectangle. These dipoles are respectively mounted on reflectors indicated at 10, 11,12 and 13, by means of arms 14 to 21 which are disposed in the zero potential points of the individual dipole elements. The reflectors are held by tubular members 22 to 25 containing the respective feed lines for the dipoles. The length of the dipoles is about 20 to 35% shorter than the operative wave-length in order to obtain good matching between the input impedance of the dipoles and the wave impedance of the feed lines.

The spacing between the respective arms 14-15 and 1617 as well as 18-19 and 20-21 which extend from the centers of gravity of the corresponding dipole ele ments is reduced, due to the considerable shortening of the dipole elements, thus reducing the concentration re sulting from the lateral spacing between the two points of the center of gravity of each pair of dipole elements and thereby broadening the radiation diagram.

The broad band characteristic is with the specified ratio of lengths to diameter of the dipoles so favorable that the antenna is especially adapted for television purposes requiring particularly small mismatching in a broad frequency range wherein f is the operating frequency and f the mean frequency of the range.

The example illustrated in Fig. 2 shows an antenna comprising dipole elements disposed in several planes or levels. The elements indicated in full lines lie in an upper level and the elements indicated in dotted lines lie in a level disposed underneath. The dipole elements of the dilferent levels are angularly displaced by about 22 so that the maxima of the radiation diagram of one level appears in the minima range of the radiation diagram of the other level. This angularly displaced array results in further equalization of the radiated energy.

The anenna may be analogously provided with similarly angular displaced dipole elements in several additional levels. Several dipoles, preferably four dipoles of the same main radiating direction may then be coupled in a radiation unit for the purpose of matching their input impedance to the wave impedance of the feed line.

If a sturdy and stable tower or mast is used, there is the possibility to dispose dipoles in a great number of superposed levels. Greater vertical concentration with very good matching in a broad frequency range will thereby be achieved than was heretofore possible with dipoles may be employed for reinforcing the radiation in the desired sector.

Changes may be made within the scope and spirit of the appended claims.

I claim:

1. An antenna system comprising a plurality of individual structurally identical dipoles arranged in the general outline of a rectangle lying in a common plane about a suitable carrier and having a reflector for each dipole, each dipole comprising at least two colinear radiators, each dipole being for impedance matching shorter than full wave and the length/diameter ratio of each dipole having a value lying between 10 and 25, whereby the radiation characteristics of said dipoles is broadened so that energy radiated in zones lying between neighboring 3 principal-radiation directions corresponds substantially to 2,310,853 Lindenblad Feb. 9, 1943 the energy radiated in the principal radiation directions. 2,419,552 Himmel et a1. Apr. 29, 1947 2. An antenna system according to claim 1, wherein 2,444,320 Woodward; June 29, 1948 the length/diameterot said dipoles is between the values OTHER REFERENCES Brown: Institute of ;Radio Engineers Proceedings, vol. 33, 1945. PP. 257-262.

Bailey: TV and other Receiving Antennas, 1950, Rider Inc., pp. 500-514.

References Citedinthe file .of this patent UNITED STATES PATENTS 2,134,126 Hooven 1 25, 1938 10 Antennas (Kraus), published by ,McGraw-Hill, 1950 2,163,770 Van Radinger June 27, 1939 (pp. 139, 142) 2,238,904 Llgdenblad 1941 The A.R.R.L. Antenna Book," published by Ameri- ,2,298,'449 gBailey Oct. 13, 1942 can Radio Relay League, 1949, pp. 27, 28.