US 2605418 A
Description (OCR text may contain errors)
July 29, 1952 A M. GRASS 2,605,418
SCANNING SYSTEM Filed May 9, 1945 INVENTOR. ALBERT M. GRASS ATTORNEY Patented July 29, 1952 SCANNING SYSTEM Albert M. Grass, Quincy, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 9, 1945, Serial No. 592,797
3 Claims. 1
This invention relates to scanning devices, and particularly to highly directional radio antennas intended to scan a region in space.
The subject matter of the broad claims of this application is disclosed in the application of James E. Shepherd, Serial No. 483,698, filed April 19, 1943 now Patent No. 2,432,101 issued December 9, 1947.
Narrow beams are very much desired in radio object detecting and television equipment, where their high directivity permits a high degree of resolving power. However, when a directional radio antenna emitting an extremely narrow beam is used, it is necessary that the direction in which the beam is pointed be changed constantly in accordance with a plan if a large region in space is to be covered by the beam, since a narrow beam will of itself encompassonly a small region. The process of moving a directional beam about to cover progressively a chosen region in space is known as scanning.
Various methods of scanning are possible. If it is desired to scan a region all around the antenna and of a certain angular height, the antenna may be rotated about a vertical axis through 360 degrees, at an initial angle of elevation, and then elevated by an amount that will raise the beam as desired, and rotated again through 360 degrees, the process being repeated until the upper limit of the region to be scanned is reached, whereupon a similar process of depressing or an instantaneous depression to the starting elevation may be employed. If only a sector of the region around the antenna is to be scanned, the antenna may be interrupted in its rotation when the desired sector has been swept through, elevation then being accomplished as outlined above. In addition, many other methods may be employed to cover sectors or regions of various shapes, all of these usually involving sudden changes in the motion of the antenna, and necessitating complicated and expensive gears, cams, and other parts.
My invention is directed to scanning a region of any chosen horizontal and vertical width about the scanning antenna, without the necessity of sudden changes in the motion of the antenna such as sudden elevation or reversal of direction. An object of my invention is to provide a highly directional radio antenna that can scan a region about it at high speed without having to be suddenly started, stopped, or reversed at any time.
Another object is to provide such an antenna that will scan the region around itself a multiplicity of times during one sweep around the region.
A further object is to provide such an antenna that is inexpensive and easy to construct by eliminating the necessity for quick action starting, stopping, and direction-reversing mechanism.
Other andv further objects will appear during the course of the following description, accompanied by the drawing in which:
Fig. 1 is a side elevation partly in section of an embodiment of my invention having associated therewith a diagrammatic representation of the scan of the radio beam. and
Fig. 2- is a representation of the scanning path traced out by the beam as the spinning antenna is revolved about its sweep axis.
A parabolic reflector l is mounted on a shaft 2, at an angle other than perpendicular thereto, so that its principal axis Y--Y makes an angle A with the axis XX of shaft 2. A dipole radiator 3 is positioned in the focus of reflector I at the end of a coaxial transmission line 4, being coupled to line 4 through suitable coupling means 5. The radiator 3, refiectorl, line 4, andcoupling means 5 together-constitute a directional antenna assembly [5. A housing 6 has within it suitable bearings (not shown) to permit spinning rotation of shaft 2 with respect to housing 6 while at the same time holding shaft 2 firmly positioned otherwise. Also contained in housing 6 is a suitable rotating transmission line joint (not shown) for coaxial line 4. A gear I may be mounted on shaft 2 and driven by a motor 9, through a second gear 8, thus causing shaft 2 to revolve and spin the directive antenna assembly l5 about axis XX. The beam of radiation ID of the antenna i5 is directed along axis Y--Y, as in the conventional parabolic reflector type antenna. The width of beam I0 is normally measured at the half power points I Land is here represented as B. As shaft 2 spins beam I0 is caused to trace out a cone, line Z-Z representing the side of this cone opposite to that represented by line Y--Y, being reached when shaft 2 has rotated through 180 degrees. Angle A is the angle made by lines Z-.Z and XX, and is identical to angle A, being the image of angle A. Thus the cone traced out by beam In as shaft 2 spins on axis X-X is represented in plan by lines Y-Y and Z--Z, and has an angular width equal to 2A. Considering half-power points I I, it is apparent that .the path traced out by beam ID at its half-power points is an annular path l2, which is actually a crosssection at point IQ of the cone traced out by entire beam I0. Path it is shown here turned about degrees with respect to its true position and appears in plan. Path I2 is of a thickness which for small values of angle A is substantially identical to the beam width B of beam in, and is one form of the scanning path of my inventlon. Point I9 is midway between points H, on axis Y--Y., and is herein used as a reference point to aid in tracing themotion of beam I0 during the course of this discussion.
In addition to the spin imparted to it by shaft 2, antenna assembly I5 has a revolutionarymotion about a second axis at right angles to axis X-X, insan to: it fbimotor" 13; through gears l4 and l6,a='shaft* l1, and a yoke l8 attached to housing 6. This second axis, which coincides with the axis of shaft 11, is preferably vertical to impart a horizontal sweep motion to the spinning a antenna and cause antenna Hi to soan'the region around itself, its conical scan zand horizontal sweep motion being combined in the process to enable the antenna l5 tosc'anthoroughly a belt or region of a height equal to 2A, as shown in Fig. 2.
upon rotation of said directive axis about said axis of orientation said beam scans at said halfpovver points an annular area in space of a mean diameter proportional to twice said acute angle,
' I and means for-uniformly rotating said antenna about a second axis which is perpendicular to Conceivably, the second or revolutionary axiscould be disposed otherwise than vertically, and it is not intended that the hereinabove described preferred disposition be regarded as the sole manner-' in which my inventionfmay be practiced or used, but only illustr'ativei: Y
' Fig. '2 represents the path: that will be traced by point [9 as beam 10 moves in-conformity with the spin imparted to antenna [5 by shaft2 and with the revolutionarysweep motion imparted to antenna I5 by shaft I11: For the purposes 'of this discussion only, it will be assumed-that the sweep motion is horizontal; :Asant'er'ma' l5 spins on axis X-X but notabout the'axis of shaft 11, and beam [-0 traces outannular path 12', the point 19 will trace out acircularpath' 23; concentric with path l2- and midway between'the'innerand outer boundaries of path l2. "Asantenna:|5 sweepshorizontally about the axis' of shaft H this circu lar' path of point 'l9' 'wil1' be altered to havef-the formiof what'inight be termed a flattenedrhelix 20'. The horizontal sweep' path 2| followedby said axis of orientation at a rate to move said orientation axis through an azimuthal angle equal to the angular width of said beam at said half-power points during a single rotation of sirable that the corresponding points on adjacent coils of the path 20be'no moretha'n' 10' degrees apart, in order 'to assure complete scanning o'f the region'being scanned. 'Thus, the distance'between adjacent coils of path'20 is-represented' in Fig. 2 as (3. By proper adjustmentof the speeds of motors 9 and I3, andby proper 'choice of gears I, 8, I4, and IB,=this conditionmay be're'alized} It will-be noted that aseach s'ucceeding co'il of path 20 is generated its latter half retraces the regiontraced'by preceding coils. Thu's dur-- ing one horizontal sweep "revolution, antenna 15- scans the region around itself: a multiplicity of times. a F'; .7
It-will be appreciated" that antenna l5 need not be swept through B'GO degrees of path '21 ,ibut' could be made" to oscillate back and :forth "in such." a manner-as "to "cover any 'chosen number of degrees. 'Further, "it is tvithin' the teachings of'this invention that motors'i 9'and l3 may be varied" in speed with;'respctito 'each other to renderathe coils of path" 20"closer to each other or further apart, as 'desiredf The herein'z'a'bove described embodimentof my invention isi11us-' trative only," an'd'not the sole 'manner in" which my invention may; be practiced: I regard the scope of 'my invention to be defined in the appended claims.
1-. Ascanning dev'icefo'r a radio ecliddetection system comprising, a directive antenna having an axis of orientation producing a narrow beam of energy having a beam directiveaxis: disposed at an acute angle-tosaid axisof orientation, means for rotatingsaid antenna about said axis of orientation-thereby to rotate saiddirective said directive axis aboutisaid axis of orientation.
2. A search scanning device for;a radio'echo detection system 1 comprising, 1 a directive parabolic antenna mounted to spin about an orientation axis for producing a'beam of energy of a first predetermined small width angle measured at the half-power points, said antenna being arranged to direct the axis of said beam at a second predetermined angle to said orientation axis greater than one-half said beam width angle, means for rotating the axis of said beam about said orientation axis whereby s-aidbeam scans an annular area at said half-power points in a plane perpendicular. to said orientation axis, and means for simultaneously uniformly rotating said'antenna'about a vertical axis at a 30 rate to "move said orientation axis through an' azimuthal'an'gle equal to said first beam width angle during each rotation of said beam about said orientation axis. i
3.'A search scanning device for a radio echo detection system comprising, directive antenna for producing a beam of "electromagnetic energy of a firstpredete'rmined small width angle measured at the half-power'points, saidantenna being mounted to spin about a substantially horizontal spin axis and positioned to di-' rect said beam at a predetermined acute angle to said spin axis of substantially 'greater'magnitude than one-half said beamwidth" angle, means for rotating said beam about "said spin axis to cause said beam toscanan annular-area atsaid half-power points in a plane perpendicular to said spinaxis and havinga mean diam eter proportional 'totwice said acute angle] and 1, means for simultaneously uniformly rotating said antenna about a vertical axis'at a rate to move said spin axis through an azimutharan'gle equal to said beam width angle duringeach' rotation of said beam about said spin axis.
REFERENCES 0121121 I V w The following referencesare of-record' injthe file of this patent:
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