US2103358A - Method of eliminating reradiation - Google Patents

Description

Dec. 28 1937. GOTHE 2,103,358

- METHOD OF ELIMINATING RERADIATION 7 Filed March 15, 1935 INVENTOR. ALBRECHT GOTHE ATTORNEY.

Patented Dec. 28, 1937 METHOD OF ELHWINATING RERADIATION Albrecht Gothe, Berlin, Germany, assignor t0 Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application March 13, 1935, Serial No. 10,787

, In Germany March 26, 1934 1 6 Claims.

It has been known for a long time that the fieldsyof antennae are distorted by neighboring electrical conductors if radio frequency currents 'of substantial strength are flowing through the latter. Among such conductors may be men- .tioned primarily the masts of antennae consisting of metal and the staying or guy means thereof. If the said conductors happen to be in resonance with the working wave or nearly so, they act as reradiators and areliable to alter considerably the radiation diagram of the antenna. At-' tempts are often made to cure this condition by marked detuning. The guying cables or wires are subdivided by insulators. The masts are insulated or grounded, and by the interposition of impedances between the base of the mast and the ground, they are caused to assume a natural period which is as remote from the working wave as is feasible. It has also been suggested to vary the natural wave or period of metallic conductors by the use of tuned ring coils which are placed around the conductor, or by the parallel connection of capacities to the whole conductors or parts thereof.

As long as the length of the conductors liable to act as reradiators does not exceed one-quarter wave-length, substantially, the elimination of reradiation is comparatively simple. But, the situation is aggravated more if the length of the reradiators is of a magnitude of one or several waves. Conductors which are excited by high harmonics, as is well known, have complex radiation diagrams. The ways and means hereinbefore mentioned tothe end of curing reradiation will then be effective only if very definite presuppositions are fulfilled.

When the width of the reradiators is very small compared with the length thereof and the operating wave, there is but one direction of current which coincides with the longitudinal dimension of the conductor. This condition ceases as soon as the conductor assumes the form of a plane or surface; in other Words, if it has a width that is no longer negligibly small in contrast to the wave length. This will happen, for instance, whenever short waves are transmitted from vessels or the like, such as marine vessels or ships, airplanes, etc. The radio frequency current distribution over such surfaces in the majority of cases is determinable only with difiiculty or not at all; otherwise marked reradiation is observed, which has the result that the antenna radiation varies very markedly in different directions.

According to this invention, the reradiation of such surfaces is to be obviated by interconnect ing points presenting substantial radio frequency potential differences by means of chain conductors or filters. The range of transmission of such filters is so adjusted that the working wave encounters the lowest possible impedance.

One fundamental circuit diagram is illustrated in the drawing. Referring to the same, F represents a surface which is excited by a radio frequency radiator St so that radio frequency voltage differences are set up between the points Pl, P2, P3, P4. By the filter system comprising C and L elements, the said points are connected with one another so that the potential differences are eliminated. The particular connection of the filters in the present instance is immaterial, in fact, it may be established also in a Way other than that shown in the drawing. If the voltage distribution over a surface is not known, then a plurality of chain conductors or filters should be employed, while the connecting points should be chosen not over one-half wave length apart.

Frequently it is not desirable, especially in the case of vehicles or vessels, to cover the face of the surface excited by radio frequencies with chain conductors or filters because they will then offer added resistance to the travel or motion of the vessel; not to mention the fact that they are endangered or subject to damaging. According to this invention, therefore, the filters are disposed upon the other face of the surface in question. However, the connecting points or terminals of the filters should be disposed upon the face turned towards the radio frequency radiator; hence, short connecting leads should be brought through holes in the surface.

If there are several working waves for which reradiation by the surface is to be avoided, then, according to this invention either the ranges of transmission of the filters are chosen adequately wide, if the operating waves are close together, or else several filters for different frequency ranges are installed.

The filters, as well known in the art, are built up of concentrated (lumped) inductances and capacities. From the viewpoint of simplicity of installation in the neighborhood of the electrically conducting surface, it will be found desirable to provide electrical shielding for the filter so that its electrical properties will not be a function of the position of the surface. For the purpose of facilitating installation, it would be advantageous to make the electrical shielding which covers the filter flexible.

It is not necessary that the filter should comprise only concentrated inductances and capacities. Indeed substantial parts thereof could consist also or reside in the leads brought to the adjoining connecting points or terminals. It is likewise feasible to use a cable, whose electrical length is equal to the working wave, as a filter, for between the ends of such a cable there exists no voltage difference,-in other words, it acts like an electric short circuit.

What is claimed is: V V

1. The method of eliminatingreradiation from an electrical conducting surface which is excited by a radio frequency radiator, which comprises short circuiting points on said surface facing said radiator which present between said points substantial radio frequency voltage differences at the frequency of the operating wave of said radiator. q

2. In combination, an antenna adapted to raldiate waves, a conductor in the path of said waves, and a path of low impedance to the energy of the waves radiated by said antenna connecting together points on said conductor which face said antenna and whose spacing does not exceed one-half the length of the desired wave and which have substantial radio frequency potential differences between said points at the frequencies of the waves radiated by said antenna.

3. A system in accordance with claim 2, characterized in this that said low impedance means comprises one or more filters.

4. In combination, an antenna adapted to radiate waves, a conductor physically separated from and substantially parallel to said antenna and located in the path of said waves, and a path of low impedance to the energy of the waves radiated by said antenna connecting together points on the surfaces of said conductor facing said antenna and which have substantial radio frequency potential differences between said points "at the frequencies of the waves radiated by said antenna for eliminating reradiation from said conductor.

5.A system inaccordance with claim 4, characterized in, this that said path comprises one or more filters located on the side of said conductor opposite said surface.

6. In combination, an antenna adapted to radiate waves, a conductor in the path of said waves, said conductor having appreciable length with regard to its thickness, and a path of low impedance to the energy of the waves radiated by said antenna connecting together two points on said conductor which face said antenna and whose spacing does not exceed one-half the length of the desired wave and which points have substantial radio frequency potential differences between them at the frequencies of the waves radiated by said antenna.

ALBRECHT GO'IHE.

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