US2438343A - High-frequency radiation system - Google Patents

Description

March 23, 1948. c, MCCLELLAN 2,438,343

HIGH-FREQUENCY RADIATION SYSTEM Filed July 9, 1942 WITNESSES: lNVENTOR I ATTOR EY Patented Mar. 23, 1948 HIGH FREQUENCY RADIATION SYSTEM Cyril. E. McClellan, Catonsville,-Md.,1 assignor to Westinghouse Electric: Corporatiomlast Pittsburgh, Pa., a. corporation'ofz Pennsylvania Application July 9, 1942,""Serial"No. 450,301

. 5 Claims. 1

lviy invention relates to arrangements for pro- 'ducing concentrated beams of electromagnetic radiation and, in particular, to-arrangements in WIllCh a parabolic reflector for electromagnetic waves emanating from a dipole radiator is employed to produce such beams.

One object of my invention is to provide an arrangement of the character described in the preceding paragraph in which the radiationat the central axis of the beam shall be of high intensity.

Another object of my invention: is to provide an arrangement of the character above described in which the beam shall be ofsubstantially cylindrical form.

Still another object of my invention is to provide an arrangement in which interposition f a dielectric in the path-of the beam isiemployed to control the phase and distribution I of the radiation emanating from the reflector.

Another object of my. invention is to'provi'de an arrangement of the above mentioned type in which a plane-polarized beam of radiation may be produced.

Still another object of my inventionis to pro-.

vide an arrangement for producing a circularlypolarized beam of radiation from an arrangement of the type mentioned above.

Other objects of my invention will become-apparent upon reading the following description,-

taken in connection with the drawings, in which:

Figure 1 shows a mid-sectional view of a'modification of my invention adaptedto producea plane-polarized cylindrical beam of radiation from a parabolic reflector powered by a dipole;

Fig. 2 shows a. sectional view along the line IIII in Fig. 1;

Fig. 3 shows a mid-sectional view oi-another modification of my invention;

Fig. 4 shows an elevational View of Fig. 3; and

Fig. 5 shows an arrangement adapted to produce a cylindrical beam of circularly-polarized radiation from a reflector of the type just mentioned.

For many purposes, it is desirable to be able to produce a substantially cylindrical beam of electromagnetic radiation, and in the case of radiation having a wave length'oi the order oi a centimeter or so, it is most convenient to attempt this by employing a reflector in the form of a paraboloid of revolution having a dipole radiator fed from some suitable source of alternating current of a wave length of the order of a centimeter and located at the focus of the paraboloid with its axis coincident with that of the paraboloid.

It can be shown that the intensity of the radiation along the axis of the paraboloid is zero if the mid-point of the dipole is positioned at the focal point of th paraboloid. This is a substan- --point =5 located alongthe axis 2 at a distance which is substantial relative to the aperture of 1 therefiector- I, it will-be evident that the radiatial defect from a practical standpoint in the beam from the reflector, since it isusually-desirable" to' have a 'highintensity along the central axis of the latter.

"In accordance-with the form of my invention shown= inFigure 1, I interpose a slab of'di'elec- I tric materialwhich'covers one half of a circular aperture of the reflector, this half being theone located on one side of the mid point of the dipole, andsymmetrical to the dipole axis. Referring 'in detail'to Fig. l, a" paraboloidal reflector l,-of "which themid -section-is shown and which has an axis 2;has located at'its iocusa radiator- 3 which is positioned with its axis parallel to the-axis? and with its mid-point at the focus of the paraboloid. Positioned in frontrof the aperture of the reflector is a semi-circular slab of dielectric 4, suchior instance as glass, having'a thickness parallel to the axis 2 equal to where k is the -wave length of the radiation 'emananting from: the dipole i-i' and n is the index or refraction of the dielectric. If we considera tion at Smaybe'considered as contributed from a series of small areas positioned uponv the sur- 'face-of the'paraboloidI i. Considering any such small areaas that located: at the point t, it will emit radiation to the point. 5' along the. path I. Now consider a point g on the suriace ofreflector i' whi'ch is exactly homologous tothe point 6' on that halfof the reflector below the-axis 2' in Fig. 1. 'I h'e smalh areas? will emit .to the point 5 alongthe path 9. A momentsconsiderationof the symmetry-of the dipole radiator and the re- "flector l- 'willshow that, as has been previously "explained, the'radiationirom the elemental. area 6 will be exactly degrees; out. or phase with the radiation fromthe elemental area 3, but would otherwise be exactly equal in magnitude to thev latter. "the radiation along the path 1 and along the path 9 would arrive with-equal intensity but 180 "degrees -diiference oi phase at the point-:5; hence If. the. dielectric it were removed,

they would cancel each other. Since the same would be true for any symmetrical pair of points like 6 and 3 on the surface of reflector I, and would likewise be true regardless of the position of the point 5 along the axis 2, the intensity of over the number of wave lengths of that same radiation in free space by an amount equal to (1 -1) (at/x) By making the thickness of the dielectric slab 4 just great enough to increase the number of wave lengths between the point 8 and the point 5 by the value one-half, the phase of the radiation arriving at 5 from the point 8 can be switched from 180 degrees out of phase to coincidence of phase with the radiation arriving from the elementary area 6. That is to say, the thickness of the dielectric slab should be such that (n-l) (ac/A) equals one-half; in other words, the thickness at of the slab 4 should be equal to When this is done, the radiation from all points on the lower half of the reflector I will reinforce, instead of cancelling, the radiation from all points of the upper half of the reflector l incident along the axis 2, and a beam having a high intensity along its central axis will result. This beam will likewise be plane-polarized.

As an alternative form the slab 4 in Fig. 1 may be replaced by a slab positioned inside the reflector at any point where the rays incident upon the lower half, let us say, of the reflector will have to traverse a path through the dielectric of the length Figs. 3 and 4 show one example of such an arrangement.

Another way of obtaining a beam of high intensity along its central axis is shown in Fig, 5. Here the dipole and the reflector are of the same type as above described for Fig. 1, but instead of the semi-circular dielectric slab 4, there is placed in front of the reflector aperture a dielectric formed by cutting a cylinder at one end by a plane normal to its axis and having as its opposite end a right-helicoidal surface of one turn having a pitch equal to twice the value determined above for the thickness of the dielectric slab 4.

When a dielectric of the form just described is.

positioned in front of the reflector, the radiation arriving at any axial point 5 from any given point 8 will traverse a path through the dielectric which is greater by an amount than will the radiation travelling to the point from the symmetrical diametrically-opposite point 6; hence the two quanta of radiation will arrive at the point 5 in phase with each other just as they do in the case of Fig. 1. Thus the radiation at points on the axis 5 will be of high intensity. However, because of the different form of the dielectric, the waves at 5 will be circularly-polarized.

The reason for this circular polarization is believed to be as follows: If any two planes passing through the axis of the reflector at right angles to each other he considered, it will be seen that the thickness of the dielectric in these planes is such that the electromagnetic vibrations in the two planes differ in phase by It is a principle of physics that when any object is subjected to vibrations which are 90 out of phase with each other in two planes perpendicular to each other, a circular movement results. One definition of circularly polarized light is that the particles of the ether or other medium which it is traversing move in circular paths, such as those which have just been shown to be characteristic of the elements of the medium traversed by electromagnetic radiation in the arrangement of Fig. 5.

I claim as my invention:

1. In combination, a paraboloidal reflector, a dipole radiator positioned with its mid-point at the focus of said reflector and parallel to the axis thereof, and a dielectric of uniform thickness normal to the axis of said reflector and covering a portion of the aperture thereof.

2. In combination, a paraboloidal reflector, a dipole radiator positioned with its mid-point at the focus of said reflector and parallel to the axis thereof, and a dielectric of uniform thickness covering a semi-circle constituting half the aperture of said reflector.

3. In combination, a paraboloidal reflector, a dipole radiator positioned with its mid-point at the focus of said reflector and parallel to the axis thereof, and a dielectric of uniform thickness which symmetrically covers one half of the aperture of said reflector,

4. In combination, a paraboloidal reflector, a dipole radiator positioned with its mid-point at the focus of said reflector and parallel to the axis thereof, and a dielectric body disposed about the axis of said reflector in front of the aperture thereof and so distributed in thickness that radiation emanating from said reflector on one side of a plane passing through the reflector axis is changed in phase by electrical degrees relative to radiation emanating from points symmetrically disposed thereto on the other side of said plane.

5. In combination, a paraboloidal reflector, a dipole radiator positioned with its mid-point at the focus of said reflector and parallel to the axis thereof, and a dielectric of uniform thickness which intercepts the path of rays incident upon the part of said reflector on one side of a plane through its axis.'

CYRIL E. McCLELLAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,054,895 Dallenbach Sept. 22, 1936 2,271,300 Lindenblad Jan, 27, 1942 FOREIGN PATENTS Number Country Date 436,355 Great Britain Oct. 9, 1935 678,010 Germany June 24, 1939

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