Omnidirectional antenna using dipoles

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

OMNIDIRECTIONAL ANTENNA USING DIPOLES

Filed Feb. 20. 1953

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FIG.I

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INVENTOR

WALTER STOHR

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ATTORNEY

2,880,418

Patented Mar. 31, 1959

United States Patent Office

2,880,418

OMNIDIRECTIONAL ANTENNA USING DIPOLES

Walter Stohr, Berlin-Siemensstadt, Germany, assignor to Siemens &amp; Halske Aktiengesellschaft, Munich, Germany, a corporation of Germany

Application February 20,1953, Serial No. 338,057

Claims priority, application Germany March 3,1952

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 ±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 10/25 and preferably 15/25. The length of the dipoles is about 20 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—Ί and 8—9 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 5 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 10 the input impedance of the dipoles and the wave impedance of the feed lines.

The spacing between the respective arms 14—15 and 16—17 as well as 18—19 and 20—21 which extend from the centers of gravity of the corresponding dipole ele15 ments is reduced, due to the considerable shortening of the dipole elements, thus reducing the concentration resulting 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 ±20% Jm wherein / is the operating frequency and f_m the mean fre30 quency 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 35 in a level disposed underneath. The dipole elements of the different 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 re40 suits 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 ₄j 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 50 very good matching in a broad frequency range will thereby be achieved than was heretofore possible with other types of antennas.

The tower or mast may also be provided with further antennae for other purposes and/or operative wavelength.

If radiation over 360° is not required in preference to radiation in a smaller sector, the dipoles of the nondesired radiation directions may be omitted and such 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.