US 2342721 A
Description (OCR text may contain errors)
Feb. 29, 1944. Y BOERNER 2,342,721
PARABOLIC REFLECTOR Filed 0G12. 10, 1941 /n venl'or: I
Patented Feb. ze, 1944 UNITED PARABOLIC REFLECTOR Rudolf Boerner, Berlin, Germany; vested in the Alien Property Custodian Application Qctober 10, 1941, Serial No. 414,479 In Germany January 20, 1940 (Cl. Z50-11) 3 Claims.
This invention relates to the directional transmission of intelligence and is more particularly concerned with arrangements of .the kind having a parabolic reector and a radiator in the focus thereof.l
According to the invention a convex mirror, that may be of parabolic or hyperbolic shape or may be of the globular, cylindrical or any similar type, is disposed in front of the radiator arranged in the focus, as will be understood from the following description and the acccnipanying` drawing,l in which Fig. 1 is a diagrammatic sectional View of a prior arrangement, Fig. lo is a diagrammatic sectional View showing one embodiment of the invention, Fig. 2 is a graph which illustrates radiation conditions, Fig. 3 is a diagrammatic sectional view of an arrangement similar to that shown in Fig. 1b, Fig. 4a is a diagrammatic sectional View illustrating an improvement upon the arrangement shown in Fig. 1b, Fig. 4b` is a diagram of the radiation pattern produced by the arrangement according to Fig. 4a.
In many cases, as when transmitting secret communications, the radiation-collecting effect should as far as possible be small, that is to say, should be quasi optical, in order on the one hand to reduce the listening range and on the other hand to enable the use of small sending power. The customary reflectors, being somewhat large in depth have a great collecting effect. Also, the use of such large reflectors meets with difficulties which for economical reasons make it desirable to restrict the collecting effect.
In prior arrangements the direct radiation in the case of parabolic reiiectors is either collected with the aid of a separate wave channel or is directed against the reflector in order to underso total reflection.
For instance, as shown in Fig. 1a,a sof-called calotte A, formed as a concave mirror of semiglobular or other suitable shape, is arranged to utilize the direct radiation in a manner to light up the reflector B and thereby to prevent the direct rays and the reflected rays from interfering outside the reflector. A calotte so arranged does not improve the directivity rand is suitable only in the case of reflectors having a large focal distance and a small depth. In the case of all the other reflectors the efliciency is impaired in the mid-zone by a so-called shading eifect due to the screening property of the calotte A.
The novel system shown in Fig. 1b has a refleeting calotte formed as a sort of convex opti cal mirror C by which the direct rays from a radiator S, located in the focus of reflector B, are guided in a special manner. In fact, the rays .are reflected by mirror C and then by reflector B so that the rays outgoing from the reflector are not parallel to its axis but converge or run toward it. As a result, the directivity of the radiation characteristic is increased by values up to While the detrimental shading effect of concave mirrors, such as mirror A, Fig. la, is obviated.
Another advantage due to mirror C is that the l secondary maxima arising in the case of higher maxima of reflection are reduced, as can be seen in Fig. 2.
Instead of one radiator S a number of radiators or groups thereof may be provided. For instance, Fig. 3 shows two radiators Sl, S2.. F denotes the focus of reflector B.
As shown in Fig. 4a an additional radiator S may be arranged within mirror C in order to produce an additional directive beam. This is not possible in prior devices.
The latter arrangement is particularly suitable for producing radiation patterns to be followed by ships, the broad directional beam serving to give a presignal.
What is claimed is:
1. A directional wave transmitter comprising a concave parabolic reflector, a source of radio frequency energy located at the reiiector focus, the arrangement being such that Waves radiating from the source will be reflected in parallel beams, a shield located on the reflector axis beyond the focus in position to intercept outwardly directed waves from said source, and means for projecting a substantial portion of said intercepted energy into the axial zone beyond saidv in claim 1, in which the reflector extends axially beyond the mirror surface.
3'. An arrangement according to claim 1, wherein the said convex mirror surface is a parabolic reector.