US 2595271 A
Description (OCR text may contain errors)
May 6, 1952 M. KLINE ANTENNA LOBE SHIFTING DEVICE W 2 SHEETS-SHEET 1 Filed Dec. 20, 1945 INVENTOR.
MORRIS KLINE y 1952 M. KLlNE 2,595,271
ANTENNA LOBE SHIFTING DEVICE Filed Dec. 20, 1945 2 SHEETS--SHEET 2 I N VEN TOR.
MORRIS KLINE A rhe-f Patented May 6, 1952 UNITED STATES PATENT OFFICE ANTENNA LOBE SHIFTING DEVICE Morris Kline, Little Silver, N. J. Application December .20, 1943, Serial No. 514,941 7 Claims. (01. 250'33.65)
(Granted under the act of March 3, 1883, as amended April30, 1928; 370 0. G. 757) The-invention described herein may be manu factured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.
This invention relates to directional antennae, and more particularly to a method of and means for wobbling the directivity thereof.
In directional radio systems for locating objects such as radiosonde balloon transmitters, it is important to cause the direction of maximum antenna response to be shifted so as to scan a solid angle or cone of space. By this process, which is known as lobe shifting," the position of an object anywhere in the space scanned can be completely defined in terms of its azimuthal and elevational coordinates. 1
One method of object locating by means of directional antenna systems is referred to as double tracking. In this method two highly directional antennae are commonly employed with the lobes equally shifted from a common axis or center line so as to give a cross-over point or overlapping where the signal strengths or responses. of the two antennae are of equal intensity. If this method is employed in a receiving system for example, the apparatus is said to be on target when the energy received by each antenna is equal. It is not necessary, however, to employ two separate antennae, but different sections of a common array may be dephased so that the system possesses divergent andpartially overlapping directivity patterns symmetrically disposed about the so-called axis of the system. The axis of the system is defined as the direction in which the maximum antenna sensitivity is obtained when the elements thereof are in cophasal relation or when no lobe shifting has been effected.
While the usual lobe shifting methods, such as that described above, employ electrical means for effecting the shift without movement of the radiating system itself, it is possible to obtain lobe shifting by mechanical means, the latter method being utilized in this invention. One prior art method of conical scanning or lobe shifting by mechanical means consists in placing some obstacle in the path of radiation, such as a disc, and rotating the radiating element which has been eccentrically displaced from the axis of the system. Another means which is equivalent utilize" a stationary radiating element with a reflector such as a paraboloid rotating eccentrically about the radiator. The latter two means are generally employed in the radio spectrum lying between frequencies of the order of 400 to 3000 mc./sec., and although'the apparatus involved is I physically small in size, there' exists the major disadvantage that for double tracking there is a mechanical problem of rapidly rotating the transmission line and radiating element or paraboloidal reflector.
In order to avoid the disadvantages of the prior art methods described above which include serious balancing problems and the difiicult problem of feeding energy to or from the radiating element, the inventor has discovered a new and improved mechanical method of achieving mechanical Wobbling of directivityor lobe shifting.
It is the principal object of my invention to generally improve the art of directional antenna systems which employ mechanical means for lobe shifting, conical scanning, or double tracking." It is another object to effect conical scanning by manipulating in the path of radiation an obstacle or reflector, which is auxiliary to a main reflector, and which may assume various geometrical forms.
Another disadvantage of prior art means for Wobbling the directivity of an antenna by mechanical means, where the radiating element is rotated, is that the plane of polarization is constantly changing. While this may not be a disadvantage in certain radio locating applications, it cannot be tolerated in the tracking and locating of meteorological balloon transmitters because only oneplane of polarization, usually vertical, is employed. It is therefore a further ob ject of this invention to utilize a single dipole ele-' ment for double tracking in azimuth and elevation without changing the plane of polarization.
It is still a further object of this invention to combine the reflecting characteristics of both a paraboloid and hemisphere to effect antenna lobe shifting by manipulating the hemisphere around a dipole radiating element located at the focus of the paraboloid.
Accordingly, there is provided a small auxiliary rotating reflector which is used in conjunction with a dipole radiating element and paraboloidal reflector in the preferred embodiment, the latter two elements being fixed in stationary relationship with respect to each other. The auxiliary rotating reflector may be of an infinite number of different geometrical forms, however a hemisphere is used in the preferred embodiment.
Fora better understanding of t i invention, together with other and further objects, reference is had to the following description taken in con- 3 nection with the accompanying drawings in which:
Figure 1 is a sectional view of a radiating element located at the focus of a paraboloidal reflector and an auxiliary hemispherical reflector placed with its center at the dipole;
Figure 2 is similar to Figure l, but shows the direction of lobe shift when the hemisphere is rotated about its center;
Figure 3 is a sectional view of a radiating element located at the focus of a paraboloidal refiector and an auxiliary hemispherical reflector showing the direction of lobe shift when the hemisphere is rotated about a point between the dipole and the deepest point of the hemisphere;
Figure 4 is a modification of this invention cmploying a rotating disc rather than the auxiliary hemispherical reflector of Figures 1 to 3.
Figure dis a side elevation showing the principal embodiment of this invent-ion, along with associated and cooperating apparatus.
Reference is now .made to Figure l, which shows a dipole and paraboloidal antenna system commonly used in microwave work. For purposes of illustration, it will be assumed hereinafter that the antenna system is to be used for transmission of radiation, although the same analysis will apply to reception. Dipole 2! is located at the focus of paraboloid 23 and is supported and fed by coaxial transmission line 25. Also shown is a small auxiliary reflector 2? char acteristic of this invention. Were the latter not employed, some of the radiation would not be directed or acted upon by the paraboloid and would travel in undesired directions. The hemisphere 21 increases the efficiency of this system considerably because if the hemisphere is placed with its center at the dipole as shown, it will receive half of the radiation. emitted by the dipole and redirect it to the parabcloid so that the paraboloid can act upon it in the same manner as it does upon the radiation received directly from the dipole.
The element 21 need not necessarily be a hemisphere, but can be any section of a sphere not quite a hemisphere. The paraboloid itself can be made of wooden ribs covered with wire mesh. This structure is preferable from the viewpoint ofcost and ease of construction; further, the use of wire mesh lowers the wind resistance of the structure. Copper wire mesh has'been found to allow practically no back radiation.
A consideration of Figure 1 will show that, when the center of the hemisphere is at the dipole, the radiation strikes the hemisphere normally and is reflected back along a radius to the focus. Hence all of the energy appears to originate from the dipole located at the focus of the paraboloid. By making theradius of the hemiall the radiation striking the hemisphere will be reflected in phase with the radiation going directly from the dipole to paraboloid. To make more clear the manner of effecting a lobe shift, reference is now made to Figure 2.
In Figure 2, the same elements are shown as in Figure 1. However, the hemisphere has been rotated about its center at the dipole as shown. As is described in connection with Figure l, the radiation reflected from the hemisphere is directed back along its radii to the paraboloid through the dipole. Because the hemisphere has been rotated or displaced as shown in Figure 2, more radiation of the proper phase is sent to one side of the paraboloid than to the other side. Thus the sphere an integral number of half wavelengths,
resultant field strength in space is reinforced on one side of the axis and the lobe is shifted to that side in the direction shown by the arrow.
The several influences affecting the optimum size of the hemisphere include the considerations that it can be made too large so as to trap radiation which in the interest of best gain should be allowed to pass. However, thissame factor can be utilized in making the hemispher block more radiation on one side than it does on the other. Of course, blocking cannot be carried too far without bringing down the gain. A properly chosen hemisphere will almost double the power gain of the paraboloid and dipole element used above. Using a hemisphere 10 inches in diameter with. a 5 foot paraboloid at 1200 -mc./sec., a consistent lobe shift of 3 on each side of the axis has been obtained with a minimum of secondary lobes. The hemisphere can be made of copper or can be plastic which is plated with copper.
When the hemisphere is rotated within limits about a point between the dipole and the deepest point in the hemisphere (the center of the hemisphere being initially in the dipole), the lobe is shifted in a direction opposite to that which would be expected from the discussion in connection with Figure '2. Figure 3 shows the direction of shift when the hemisphere is rotated about somepoint A which lies between the dipole and the deepest part of the hemisphere. When the hemisphere is rotated to the position shown, the direction of lobe shift is indicated by the arrow. There are several factors which explain this somewhat surprising result. Firstly, there is'less blocking on one side and more on the other side as compared with the condition where the hemisphere is rotated about its center at the dipole. Secondly, the new position of the hemisphere destroys the phase relationships which would be operative with the center of the hemisphere at the dipole. In this condition, all radiation does not appear to originate at the dipole, but at some image point to one side of the dipole, so when the paraboloid acts upon this radiation, the lobe shift is as shown by the arrow. When the hemisphere is rotated to the other side of the axis of the paraboloid, the lobe is shifted oppositely.
Although the use of the hemisphere is preierable from the above considerations, operation is not limited to the use of this element. In certain applications, other surfaces generated by conic sections, such as hyperboloids, may be of particular value. Also a parasitic dipole element can be employed although this does not effect equal azimuthal and elevational lobe shifts. One modification is'shown in Figure 4. Here, lobe shift is effected by the use of a rotating disc, the plane of which is set at an angle other than to the axis of the paraboloid. The disc might be considered to be the limiting case of a hemisphere which is infinitely shallow. In this modification, the disc 21 is mounted upon a rotating shaft 29. When the disc is in the instantaneous position as shown, the lobe shift will be in the direction of the arrow. While this arrangement can be used for obtaining satisfactory lobe shifts, it does not permit the high over-all antenna system gain characteristic of the preferred embodiment as shown in Figures 1 and 2. Reference is now made to Figure 5, which shows the preferred embodiment of this inven' tion along with other associated and cooperating apparatus for effecting the wobbling of antenna directivity. This figure is similar to Figure 2 with the hemisphere rotated to one side of the axis of the paraboloid. From a consideration of Figure 2-, it is obvious that if the hemisphere were maintained in this position relative to. the axis, and at the same time-were rotated about the axis, the lobe as indicated by the arrow would be caused to scan a solid angle or cone in space. A shaft 29 upon which the hemisphere is mounted is coincident with the axis of the paraboloid. A suitable electric motor 3| provides torque for rotating the shaft and hemisphere. The motor may be mounted upon a plate 33 which is supported by. rods 35 attached to said plate at one extremity and to the paraboloid at the other extremity.
In order to provide proper balance of the radiating elements of the dipole to ground, it is necessary to employ a A; wave choke 31. The position of this element is rather critical and must be determined experimentally in order to obtain equal azimuth and elevation lobes. The coaxial line 25 which supports and'feeds the di pole is coupled to the transmitting or receiving means, whichever is employed, at the extremity of the line opposite the dipole.
The presence of the hemisphere will make several alterations in the radiating system that must be recognized. The presence of a hemisphere does not alter the reactance of the dipole, but almost doubles its radiation resistance. The paraboloid itself has a negligible influence on the'impedance of the dipole. As the addition of an auxiliary reflector, such as the hemisphere, in
ly' located at the focus of the paraboloid and the 1 optimum feed-point must be determined experimentally."
It is to be understood that the invention is in 6 ter and the deepest point of'said hemisphere, said point of displacement being located at'intersection of the axes of said hemisphere and paraboloid; and means for rotating said hemisphere about the axis of said paraboloid to effect a wobbling of the direction of maximum response of said paraboloidal reflector and antenna.
3. In a radio direction finding system for microwave operation, a reflector, said reflector having the form of a paraboloid; a dipole antenna element, said dipole being located in proximity to the focus of said paraboloid; an auxiliary reflector having dimensions that are small relative to the dimensions of said reflector, said auxiliary reflector having the form of any warped concave surface with an axis of directivity, said warped surface being positioned sothat its axis of directivity intersects the axis of said paraboloid at an acute angle and said concave surface facing said paraboloid, and means for rotating said warped surface about the axis of said paraboloid to effect a wobbling of the direction of maximum response of said reflector and antenna.
4. In a radio direction finding system for microwave operation, a reflector, said reflector having the form of a paraboloid; a dipole antenna element, said dipole being located in proxno way limited to the use of hemispheres or discs, Y.
but that an inflnite number of various geometrically-shaped auxiliary reflectors, manipulated in an infinite number of ways, may be employed. to eflect lobeshifting or conical scanning. The
broad aim of this invention is to effect lobe shifting by mutating some obstacle or reflector in the pathof the radiation from a dipole, said reflector being auxiliary to a main reflector such as a paraboloid which is in preferred fixed relationship 1 to the dipole. My invention, therefore, is not to be restricted except insofar as it is necessitated element, said dipole being located in proximity to the focus of said paraboloid, an auxiliary reflector, said auxiliary reflector having substantially.
the form of a hemisphere with its center at the center of said dipole, and the plane of the aperture of said hemisphere being at an angle of other than 90 with respect to the axis of said paraboloid; and means for rotating said hemisphere about the axis of said paraboloid to effect a wobbling of the direction of maximum response of said paraboloidal reflector and antenna.
2. In a radio direction finding system for 1nicrowave operation, a reflector, said reflector having the form of a paraboloid; a. dipole antenna element, said dipole being located in proximity to th focus of said paraboloid; an auxiliary reflector, said auxiliary reflector having substantially the form of a hemisphere, the axis of said hemisphere being displaced from the axis of said paraboloid about a point located between the cenimity to the focus of said paraboloid; an auxiliary reflector having dimensions that are small relative to the dimensions of said reflector, said auxiliary reflector being mounted on the opposite side of said antenna element from said paraboloid with its center on the axis of said paraboloid and adjacent the focus thereof, said auxiliary reflector having the form of any concave surface generated by revolution of a curve, said concave surface facing said paraboloid, the axis of said surface of revolution intersecting the axis of said paraboloid at an acute angle such that substantially all the energy impinging on the auxiliary reflector is reflected back to said paraboloid; and means for rotating said surface of revolution about the axis of said paraboloid to eifect a wobbling of the direction of maximum response of said paraboloidal reflector and antenna.
5. In a radio direction finding system for microwave operation, an antenna array compris-r ing a parabolic reflector,"a dipole antenna element and a parasitic reflector having dimensions which are small relative to said parabolic reflector, said dipole being positioned in proximity to the focus of said parabolic reflector, said parasitic reflector having substantially the form of a hemisphere, said parasitic reflector having its opening toward said parabolic reflector, and being positioned so that theaxis of the parabolic reflector intersects the axis of said parasitic reflector at an angle, and means to rotate said parasitic reflector about the point of intersection of said axes, whereby the direction of maximum radiation of said antenna array is wobbled.
6. An antenna lobe shifting device comprising a radiating element, a directive reflector, an auxiliary reflector mounted on the opposite side of said radiating element from said directive reflector, said auxiliary reflector having substantially the form of a hemisphere with the plane of the opening thereof at anangle other than with respect to the axis of directivity of said directive reflector, and means for rotating said auxiliary reflector about the axis of directivity of said directive reflector.
7. An antenna lobe shifting device comprising a radiating element, a directive reflector, an auxiliary reflector having substantially theform of -a-h,emisphere mounted partially about said radiating element on the opposite side from said direotive reflector with the plane of the opening thereof at an angle other than 90 with respect to the axis of directivity'of said directive reflector, and means for rotating said auxiliary reflector about the axis of directivity of said directive refiector.
MORRIS REFERENCES CITED The following references are of record in the .file of this patent:
' 8 UNITED STATES PATENTS Number Name Date ClaVier we-" Oct. 24, 1933 Clavier at al. p, June 9, 1936 Runge June 8, 1937 Scharlau P May 3, 1938 Sullinger et a1. Dec.2 3, 1941 Feldman Apr.'29, 1947 Becker Oct, 26, 1948 Marshall v Nov. 28, 1950