US 2831187 A
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A ril 15, 1958 Filed June 23, 1945 F. HARRIS ET AL 2,831,187
RADIO DIRECTION FINDING SYSTEM 2 Sheets-Sheet 1 I 11:11. IEIEZE I FREDERICK HARRIS MURRAY HOLDMAN JAMES R.ATKINSON 'MACK J. SHEETS A ril 15, 1958 F. HARRIS El AL RADIO DIRECTION FINDING SYSTEM Filed June 23, 1945 2 Sheets-Sheet 2 FREDERICK. HARRIS JAMES R. ATKINSON MURRAY HOLDMAN MACK J. SHEETS QKWp LM WWW United tes Patent 2,831,187 RADIO DIRECTION FINDING SYSTEM Frederick Harris, Washington, D. (1., and James R. Atkinson, Murray Holdman, and Mack J. Sheets, United States Navy Application June 23, 1945, Serial No. 601,291
7 8 Claims. 01. 343-120 (Granted under Title 35, U. S. Code (1952), see. 266) This invention relates to short-wave radio searching and direction-finding systems; in particular it relates to a searching and direction-finding system employing shortwave antennas in conjunction with reflectors.
An object of this invention is to provide a system by which the presence of short-wave radio signals from all azimuths can be detected and the approximate bearings of their sources determined.
Another object of this invention is to provide a shortwave antenna element, suitable for use in a searching and direction-finding system, comprising a dip-ole or other antenna in conjunction with a convex reflecting surface. ,Another object of this invention is to provide a shortwave antenna element, suitable for use in a searching and direction-finding system, possessing directional characteristics such that in at least one plane it can transmit or receive radiant energy, without nulls or discontinuities, over an angular span of more than 180.
The searching and direction-finding system embraced in this invention involves the use of suitable receiverindicator and switching appartus in conjunction with two identical antenna elements, each sensitive over more than 180 of angular span, and so oriented that one antenna element or the other is responsive to signals from all directions. Direction-finding is to be accomplished by rotating the antenna elements together until equal signals are received on the two antenna elements.
An antenna element suitable for employment in such a system is a feature of this invention; it comprises a dipole or other antenna in conjunction with a curved reflector so oriented that waves strike the dipole or other device after reflecting from the convex side of the reflector. In the specific embodiments herein described, the reflecting surfaces are sections of hyperbolic cylinders.
The invention will be further described with reference to the exemplary drawings, of which,
Figure 1 is a block diagram of a searching and direction finding system embodying the principles of the invention;
. Figure 2 is a front-view sketch of an antenna element incorporating the principles of the invention and suitable for use with the system of Figure 1;
Figure 3 is a sketch in cross section of the antenna element shown in Figure 2; V
Figure 4 is a plan view, partly in section, of the antenna element shown in Figure 2;
Figure 5 is a graph in polar coordinates showing the response pattern of the antenna element sketched in Figure 2;
Figure 6 is a plan view sketch showing two antenna elements of the type shown in Figure 2 arranged for use in the system of Figure 1;
Figure 7 is a graph in polar coordinates showing on the same axes the response patterns of the two antenna elements of Figure 6;
Figure 8 is a view in perspective of another antenna element embodying the principles of the invention and suitable for use with the system of Figure 1;
Figure 9 is a front view sketch of the antenna element shown in Figure 8; and
Figure 10 is a sketch in cross-section of the antenna element shown in Figure 8.
Referring to Figure l, the search and direction finding system comprehended by this invention comprises two identical antenna elements 101 mounted rigidly with respect to one another but rotatable relative to the earth by rotating means 105; receiver 103, signal strength indicator 104, and a switching means 102 by which the receiver can be alternately connected to one antenna element and the other.
Detailed descriptions of the characteristics of the antenna elements and the operation of the system are set forth in subsequent paragraphs. The system is sensitive to signals from all azimuths, and will determine without sense ambiguity the bearing of any given signal source.
To be suitable for use in the system embraced in this invention, an antenna element should have a wave response characteristic in the horizontal plane which extends, without nulls or discontinuities, over an angular span of slightly more than In this invention the desired wave response characteristic is produced by placing adjacent to an antenna, such as a dipole, a curved conducting reflector With its convex side facing the antenna. In a specific construction embodying the principles of this invention, best results were obtained with a reflector shaped to form a section of a hyperbolic cylinder, the straight cylindrical axis being oriented vertically, and the horizontal cross section being a rectangular hyperbola terminated at its latus rectum. A front view sketch of an antenna element incorporating such a reflector is shown in Figure 2.
Referring to Figure 2, dipole element 2, approximately a half wavelength long, is supported in front of convex reflector 1 by insulators 3. Figure 3 is a cross section view of the element, wherein the antenna members and the insulating supports therefor are diagrammatically indicated. In Figure 3 transmission line 4 is employed to connect dipole element 2 to the receiver component of the system.
The geometric design of the reflector can best be observed from Figure 4, a diagrammatic plan view of the antenna element. Dipole 2 is parallel to the cylindrical axis of the reflector and is located at the geometric origin of the reflectors hyperbolic cross-section, one-quarter wavelength in front of the hyperbolas apex. The edges of the reflector are coincident with the end points of the hyperbolas latus rectum. The width of the reflector is one-half wavelength, it being a geometric property of the rectangular hyperbola that the length of the latus rectum is twice the distance from the origin to the apex. In the specific construction the apparatus was to be operated over a considerable range of wavelengths; hence the wavelength chosen to govern the reflector design was the geometric mean of the maximum and minimum wavelengths to be covered.
Figure 5 is a graph in polar coordinates showing, for the design wavelength, the wave response pattern of the antenna element in the horizontal plane. In Figure 5, the relative bearing of the wave source is indicated in degrees, zerodegrees being arbitrarily taken as the direction of a straight line in the horizontal plane drawn from the hyperbolic apex through the axis of the dipole. Wave response is shown radially; that is, the response in a given direction is proportional to the length of a straight line drawn in the given direction from the origin to the curve.
The response pattern is quasi-cardioid in shape; in the span of 180 wherein the element would be expected to intercept signals there are no discontinuities or nulls '2 in the response pattern; and the total range of response variation in that span is only about two to one. On the other hand, wave response is substantially zero through most of the back 180 span.
Figure 6 is a simplified plan view showing how two antenna elements of the type described might be oriented for operation in a search and direction finding system. The two reflectors 41 and 31 are mounted back to back; dipoles 42 and 32 are mounted relative to their respective reflectors in the same manner as in Figures 2, 3, and 4. The angular azimuth coordinates on Figure 6 are identical with those on Figure 7, and are included to facilitate cross reference between the two figures.
V Figure 7 is a graph in polar coordinates showing, in the same manner as in Figure 5, the wave response patterns of the two antenna elements in-Figure 6, plotted on the same axes. Curve 141 is the response pattern of the element comprising dipole 42 and reflector 41; curve 131 is the response pattern of the element comprising dipole 32 and reflector 31. In every direction the response from one or the other of the two elements is at least 45% of maximum; hence signals 'within the frequency range of the system can be intercepted and detected regardless of the direction from which they come. The responses of the two elements are substantially different to signals from all directions except the two directions marked 90 and 270 Accordingly the bearing of the source of any received signal can be determined by first noting which element yields the stronger signal, thus eliminating sense ambiguity by placing the source within a definite 180 span; then rotating the elements together until the signals received by the two elements are equal, thereby fixing a definite line of direction to the wave source. 7
. Figure 8 shows, in perspective, another antenna element embodying the principles of the invention and suitable for use in the search and direction-finding system comprehended by the invention. In the embodiment of Figure 8, the reflector 11 is a section of hyperbolic cylinder asin the previously described antenna elements; its curvature is less than that of the reflector of the previously described embodiment, however. In this embodiment, the dipole 13, instead of being oriented vertically, parallel to the cylindrical axis of the reflector, is inclined at an angle of 45 from the vertical. Also, instead of being straight, as in the previous embodiment, the dipole is bent so that its two members form an obtuse angle. The dipole 13, approximately one half wavelength long, is
supported at its midpoint by element 14, which serves as a support and as a line balancing converter. The details of member 14 are more clearly shown in Figure 10, which is described in a subsequent paragraph. The midpoint of dipole 13 is, as in the previous embodiment, placed at the geometric origin of the hyperbola, one quarter wavelength from its apex. The ends of the dipole are supported by insulators 12, and, because the dipole is bent toward the reflector, are less than one-quarter wavelength from the surface of the reflector. As in the previously described antenna element, the geometric mean of the maximum and minimum wavelengths to be received was used as the standard for fixing the dimensions.
By tilting the dipole at a 45 angle in this embodiment, improved Wave response to radio signals of horizontal polarization is obtained. It was discovered that by bending the dipole at its midpoint and mounting it as shown in Figure 8, and by reducing slightly the reflector curvature, the wave response pattern of the antenna element could be made approximately similar to that of the previously described antenna element, as graphically represented in Figure 5.
Figure 9 is a front view sketch partly in section, of the antenna element shown in Figure 8.
Figure 10 is a cross-section drawing of the same element, taken along the line 10-1@ in Figure 9. In this drawing reflector 11, insulators 12, dipole 13 and member 14 are shown in cross-section. Insulators 21, fitted into member 14, support the dipole members at their adjacent ends; the upper dipole member is connected by wire 17 to the outer conductor of coaxial transmission line 20; the lower dipole member is connected by wire 18 to the inner conductor of line 20. The outer conductor of line 20 is electrically connected to the reflector 11 at their junction 19. The outer conductor of line 20 and the inner surface of member 14 form a line balancing converter, approximately one-quarter wavelength long and operative to place the two conductors of line 20 at equal impedance above ground at the points where they are connected to dipole 13. Insulator 15 keeps line 20 properly centered within member 14; insulators 16 keep the inner conductor of line 20 properly centered within the outer conductor of line 20. Transmission line 20 serves as a connecting link between the antenna element and the receiver component of the searching and directionfinding system. 7
It is to be understood that the embodiments of the invention shown and described are exemplary only, and the scope of the invention will 'be determined with reference to the appended claims. 7 I
The word antenna wherever used in this specification and in the claims appended hereto is to be taken as including any means for the interchange of radiant energy with space.
The invention described herein may be manufactured and used by or for the Government of the' United States of America for-governmental purposes without the payment of any royalties thereon or therefor.
What is claimed is:
1. 'An antenna system operative over a broad limited angle comprising an antenna and ahyperbolic waverefiector located with its convex side adjacent the antenna, said wave reflector consisting of a hyperbolic cylindrical reflecting surface.
2. An antenna system operative over a broad limited angle comprising an antenna and an'adjacent wavereflector convex thereto, the wave reflector consisting of a hyperbolic cylinder and the antenna being located on the focal line or the hyperbolic cylinder on the side thereof opposite to the included focus.
3. An antenna system having two'el'eme'nts, each operative over a limited angle of more than and comprising an antenna and an adjacent wave reflector convex thereto, the wave reflector of each of the two elements consisting of a hyperbolic cylindrical" reflecting surface with the elements being complementari-ly oriented for 360 operation. a
4. An antenna system operative over a broad limited angle comprising a wave reflector having a convex'side and a dipole antenna mounted off said corivexside, the dipole members being inclined toward the reflector.
5. An antenna system operative over a broad limited angle comprising a cylindrical wave reflector and a dipole antenna mounted off the convex side of the reflector obliquely to the axis of the cylinder, the dipole members being inclined toward the reflector.
6. An antenna system operative over a broad limited angle comprising a wave reflector shaped to form a section of a hyperbolic cylinder and a dipole antenna mounted off the convex side thereof obliquely to" the cylindrical axis of the reflector, the dipole members being inclinedtoward the reflector.
7. In combination, two antenna systems, each having a reflector consisting of a respective hyperbolic cylindrical reflecting surface, and an antenna element disposed to provide radio wave response in opposingfcardi'oid patterns, and means for comparing the-relative intensity of radio waves intercepted by each 'ant'enna system.
8. In combination, first and second radio energy reflectors, each of said reflectors consisting of'a hyperbolic cylindrical section disposed with convex sides thereof oriented in opposing directions, first and second antenna elements each disposed 011? the convex side of the first and second reflectors respectively, means for rotating the center of directivity of both reflector section-antenna element combinations in synchronism, and means for comparing the relative intensity of radio Waves intercepted by each combination.
References Cited in the file of this patent UNITED STATES PATENTS Gerhard Oct. 18, 1938 Hooven Oct. 25, 1938 6 Gerhard et a1 June 3, 1939 Kohl Aug. 22, 1939 Clavier Sept. 26, 1939 Hefele Aug. 5, 1941 Boerner Feb. 29, 1944 Tolson June 3, 1947 Stearns Sept. 9, 1947 Busignies et a1 Aug. 31, 1948 Agate et a1 Dec. 21, 1948 Busignies May 30, 1950 FOREIGN PATENTS Australia Feb. 16, 1933