US2263460A - Antenna structure - Google Patents

Description

Nov. 18, 1941. F. GERTH ETAL v 2,263,460

ANTENNA STRUCTURE Filed Jan. 9, 193e 14H02' @y l Patented Nov. 18, 1941 ANTENNA STRUCTURE Felix Gerth, Berlin-Tempelhof, and Walter Max Hahnemann, Berlin-Marienfelde, Germany, assignors to C. Lorenz Aktiengesellschaft, Berlin- Tempelhof, Germany, a company Application January 9, 1936, Serial No. 58,314 In GermanyJanuary 12, 1935 (Cl. Z50-33) 1 Claim.

In order to prevent disturbing fields from occurring in the operation of antenna structures intended for broadcasting arrangements as provided by the invention have a self-oscillating mast, that extends to the earths surface and is excited at its lower end while operating as a dipole which has capacity surfaces at its upper and lower ends and whose centre of oscillation is a quarter of a wavelength, or nearly so, above the earths surface.

It is well known per se to employ oscillation masts, namely in the form known as Blau-Knoxantennas. Such an antenna consists in an upright mast extending substantially to the earths surface but insulated from the earth and tuned to the operative wavelength while being excited at its lower end. In order to ensure that the current distribution is advantageous as regards the diagram of radiation, the mast height in the case of the Blau-KnoX-antenna is about 0.6 i, if i is the operative wavelength. The method of exciting a mast as a dipole fed at its lower end has the advantage that the mast height may be much less than in other cases. In general a height equal to 0.4 A will be sufficient. This is advantageous not only from an economical point of view but is desirable also for the reason that high masts endanger air trame. The use of self-oscillating masts has the advantage above all that the arrangement is much cheaper than the prior ones, since iron masts are known to be much cheaper than wooden masts and cheaper also than masts comprising wooden and iron members, a construction that might be accomplished by making the lower part of iron and the upper of wood.

The invention is explained hereafter by way of example. Figs. l, 2, 3 and 4 are diagrammatic elevations showing each one embodiment of the invention, Fig. 4 being in the nature of a partial reproduction of Fig. l.

In the arrangement according to Fig. 1 the oscillating mast I is not in itself proof against breaking down and is therefore attached to the ground by span ropes 2, 3, 4 arranged around the mast in the usual manner. The ropes are subdivided at suitable points by insulators I6 in a manner well known per se. The ropes 2, 4 are arranged also to form capacity surfaces at the two ends of the dipole constituted by the mast. To such end they have bronze parts I1 by which they are attached to the mast. These parts I1 are represented by heavy lines. In order to form the desired capacity surfaces the ybronze parts I1 are connected to each other by conduc- 55 tors 5, 6. In the simplest case the rope parts l1 are attached to the mast directly. This mode however has the disadvantage that a subsequent tuning of the mast is not possible. The initial design of the mast should be such that the dimensions of the mast are inherently tuned to the desired wavelength. It is advantageous however to provide for a subsequent slight tuning. This in the case represented is accomplished by the conductors 5, 6 not being conductively connected to the mast directly but through tuning coils 1, 8. The tuning may be effected by varying these coils, but may be performed also by varying the number of bronze parts I1 attached to the mast and thus increasing or decreasing the capacity surface. This mode however has the disadvantage that the radiation diagram will be somewhat unsymmetrical. I8 denotes the transmission line from which the dipole is fed over a coupling device I9.

The mast shown in Fig. 2 is in itself proof against breaking down and is therefore only at its middle attached to the ground by span ropes I0. Ropes II are arranged to form an upper capacity surface, these ropes having bronze parts I'I at the top of the mast. A lower capacity surface is formed of bronze ropes I 2 which are connected with the ropes I0.

Such ropes I2 may be provided also in the case of arrangements of the kind shown in Fig. l, as will appear from Fig. 4, and here present the advantage that the lower capacity surface is more remote from the earth surface, thus causing the current loop to be at a higher level than otherwise.

As shown in Fig. 3, it is possible also to effect the fine tuning by means of a self-induction coil I4 arranged to bridge over an insulation I3 disposed in the middle of the mast I and connected to it electrically so as to prolong the dipole.

It is advantageous to bridge over the joints of the superposed parts of the mast by well conducting means. The simplest mode of performing this consists in stretching wires I5 along the mast and fixing them at a number of points to the longitudinal edges of the mast. Such arrangement is of a special simplicity if the mast is of the same cross-sectional area throughout, because in such case it is sufcient to stretch the wires I5 from one end of the mast to the other end thereof.

What is claimed is:

A broadcast antenna structure comprising a continuous conducting mast extending upward from the surface of the earth to a height of about two-fifths of a Wavelength at the frequency to be radiated, a plurality of tension members having insulated conductive portions for staying said mast, a plurality of said portions of said tension members being disposed to form an extended capacity surface adjacent an upper point of said mast and a further plurality of said portions of said tension members being disposed to form a second capacity surface adjacent an intermediate point of said mast remote from the surface of the earth, means for connecting each of said capacity surfaces to the adjacent point of the mast whereby the portion of the mast between said points constitutes a dipole connected at each end to a capacity surface, means for eX- citing said dipole at its lower end at the frequency to be radiated, the dimensions of said portion and said surfaces having such Values that the natural resonance frequency of said di'- pole and capacity surfaces is inherently approximately equal to the frequency to be radiated, and the heights of said capacity surfaces above the surface of the earth being such that the center of oscillation of said dipole is approx imately a quarter wavelength above the earth at said frequency, whereby the current distribution produces an advantageous radiation pattern with said total mast height of only about two-fifths of a wavelength, and a variable impedance included in at least one of said means for connecting vsaid capacity surfaces to the mast whereby the natural resonance frequency of said 15 dipole may be slightly varied.

FELIX GERTH. WALTER MAX HAHNEMANN.

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