US 2514617 A
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Description (OCR text may contain errors)
July 1 1950 w. J. EALBERSHEIM 2514,61 7
DIRECTIVE SCANNING ANTENNA SYSTEM Filed April 13, 1946 FIG.
BEAM CROSS-SECTION\O FIG. .3
NEEDLE BEAM smuo I IN AL L DIRECTIONS FIG. 5
c. p. smsgw "I RANGE AZ/HUTH 2 Sheets-Sheet 1 FIG. 2
BEAM CROSS SECTION LONG/TUO/NAL SECTION FIG. 6
c. n. SCREEN *2 ELEVATION RANGE INVENTOR W J ALBERSHE/M A77 RNEY y 1950 w. J. ALBERSHEIM 2,514,617
DIRECTIVE SCANNING ANTENNA SYSTEM Filed April 13, 1946 2 Sheets-Sheet 2 FIG. 7
CA 271005 RA) OSC/L LOSCOPE RANGE RANGE lNl/ENTOR W J ALBERSHE/M BY A TTORNEV Patente July it, 195
ll". ANTENNA SYSTEM Walter r. Albersheim, ilnteren, N. 3., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y a corporation of New York Application April 13, 1946, Serial No. states (oi. sis-1o) 3 illaims.
dicular fan beams and to resolve without am-- biguity multiple targets located at equal ranges.
Another object of the invention is to rapidly and precisely determine the location of targets by coupling together a rapid fan beam scanner.
with a. precise needle beam scanner.
Referring to the figures of the drawing:
Figs. 1 and 2 represent cross-sections of the beams shown in Figs. 3 and 4 respectively:
Fig. 3 illustrates a needle beam;
Fig. 4 illustrates a fan beam;
Fig. 5 shows a cathode-ray screen for depicting range vs. azimuth coordinates of targets derived by a radar;
Fig. 6 shows a similar cathode-ray screen depicting elevation vs. range of the said targets;
Fig. 7 shows a double ian beam antenna system; and
Fig. 8 shows a combined fan beam and needle beam antenna system.
A needle beam may be defined ideally as a. beam confined to a straight line. In practice however, a certain spread laterally is experienced, which may be of the order of 1.5 degrees or there abouts, as illustrated in Figs. 1 and 3.
A fan beam may be defined as being sharp in one plane and broad in the other, and having in general the configuration of a fan i. e., a lateral spread of degrees or more in one direction and 1.5 degrees in the other, as illustrated in Figs. 2 and 4.
In certain radar systems, such as ground operated anti-aircraft fire control, a. rapid and precise scan of an extended solid angle is required to search for and follow rapidly moving targets.
Since point-by-point scanning by means of a needl beam as in television would be too slow, it has been suggested that radio fan beams be used for scanning the search area by single sweeps. To efiectivey determine the location of a target, two crossed fan beams mutually perpendicular to each other are utilized. The sweep of one fan beamdetermines the azimuth of the target,-while the sweep of the perpendicular fan gle, lone target within the field of view is come pletely and unambiguously determined by two correlated echo images, for example, spots A and D on two separate cathode-ray tubes (Figs. 5 and 6), one representing range vs. azimuth, the other representing elevation vs. range.
However, when a flight of multiple airplanes appears in view, specific target identification becomes diificult and ambiguous. The cathode-ray screens are then flooded with so many target presentations that correlation between individual azimuths and corresponding elevations is rendered practically impossible.
The resulting uncertainty, in identification can be greatly reduced by selecting one of the possible targets on one of the screens showing range and gating the range. By gating is meant the biasing of the receiving amplifiers to extinction at all times, in a known manner, except for a short time interval corresponding to the twoway travel time of an electromagnetic wave to and from a target within th chosen range.
Referring to Figs. 5 and 6, representing the coordinates appearingon the separate cathoderay screens namely, azimuth vs. range, and range vs. elevation respectively, the faint dots shown therein represent the multiple targets whose apparance on the screens is suppressed by the aforementioned range gating. The two heavy dots shown on each screen, namely (A, B) and (C, D) represent two targets located at equal ranges from the radar equipment. It is obvious that a true correlation between azimuth and elevation for these two target echoes is indetermihate-four combinations AC, AD, BC, BD being possible-two representing the true target coordinates and the other two representing false or pseudo targets. Should the gunner select echo image A in Fig. 5 as a target, he would be at a loss to determine whether to point his sights toward C or D on the elevation scale (Fig. 6).
With n targets at equal range, the ambiguity increases as n and the probability of scoring a hit is reduced by a factor n. s
In accordance with one embodiment of the invention, the ambiguity which arises with respect to multiple targets located at equal ranges, may be fully resolved by slowly rotating one or both of the fan beam antennas around an axis directed at a target. The true target may be distinguished by the invariance of its position on the cathode-ray screens with respect to the rotation, whilst the positions of the pseudo targets move or are displaced in accordance with the rotation.
Another embodiment of the invention contemplates determinate and rapid scanning, by combining the characteristics of fan beam scanning with needle beam scanning, through a linking or coupling together of the corresponding antennas.
Referring to Fig. 7, a pair of perpendicular fan beam antennas 2, 3 are shown, each comprising a rectangular wave guide feed horn and a pillbox shaped reflector with divergent flares 6 at the mouth thereof for matching the pill-box antenna to free space. The rectangular feed may be a bent pipe with a flared mouth (not shown) located at the focus of the paraboloidal-shaped pill-box, whereby a fan-shaped beam may be radiated into space. The pill-boxreflector has the shape of a D, and its details are more fully disclosed in the copending application of W. D. Lewis, Serial No. 574,334, filed January 24, 1945, which corresponds to the British Patent 606,927 accepted August 23, 1948, or in an article entitled Microwave Radar Antennas by E. M. Purcell published in Radio-Electric Engineering, vol. 67, May 1946, pages 3-6.
The antennae 2, 3 shown in Fig. 7 are respectively connected to conventional transceiver equipment well known to the radar art and represented in said figure schematically by the rectangular block designated Radar Circuit. This equipment may take various forms as exemplified for instance by U. S. Patent 2,475,707 issued July 12, 1949 to P. A. Jeanne, by U. S. Patent 2,422,697
issued June 24, 1947 to L. A. Meacham, by U. S.
Patent 2,419,205 issued April 22, 1947 to C. B. H. Feldman, and by U. S. Patent 2,426,182 issued August 26, 1947 to 0. E. De Lange.
These patents illustrate and describe the association and operation of the various essential components of a radar circuit, such as, the magnetron, the pulser, the wave guide plumbing," the TR box, the ranging circuit, the radio receivers and the cathode ray oscilloscopes.
the screen as illustrated in Figs. 5 and 8, an ambiguity in correlating their true elevations and azimuths arise. To resolve this ambiguity, the operator performs the final step of rotating the polar axis 6. If both antennas are centered on the same target, the polar axis will be pointing directly at this target, and will continue to do so regardless of polar rotation. In this case, one of the points C, D remains stationary during the rotation of the polar axis, whereupon the polar rotation is stopped, the elevation of the antenna is locked in by an automatic follower (not shown) and the gun is in proper firing position.
If, on the other hand, the antennas point at pseudo or false targets, rotation of the polar axis 6 has the effect of causing the images C, D to be displaced along a circular arc. This displacement apprises the operator of a false target correlation between an azimuth and elevation image, whereupon he'will readjust his elevation until a target image remains steadily centered and unaf- The two radars may operate on the same frequency or on different frequencies, or if desired, one may employ a common transmitter with the antennae 2, 3 sharing its output on a time division or energy division basis.
The azimuth versus range indications are displayed on a cathode ray oscilloscope connected to antenna 2, while the elevation versus range indications are correspondingly displayed on the cathode ray oscilloscope co, ected to antenna 3 as shown in Fig. 7.
The pill-box antennas are rigidly connected by a rod 4, bent and disposed so that the planar portions of said pill-boxes are mutually perpendicular. By means of this arrangement, a pair of crossed perpendicular fan beams are thereby radiated from the open mouths of the pill-boxes.
A solid angle in space, for example, at least 15 degrees square, may be scanned by the crossed fan beams, by rocking or oscillatingsthe feed horn 2' horizontally and feed horn 3' vertically along a straight line. When each of these scanning fan beams strikes a target, an echo is reflected therefrom which produces a visible signal on a cathode-ray oscilloscope screen, as illustrated in Figs. 5 and 6.
The pair of antennas 2, 3 as a unit may be rotated or swung around through an azimuthal angle by rotating pedestal support I. When the azimuth of a target is found, it may be locked in by an automatic follower (not shown). The elevation angle 0 is adjusted by rotating rod 4 in its bearing at the top of the pedestal.
When multiple targets at equal range appear on fected by polar rotation, indicating correct coordinate association. Thereupon, he will lock in the automatic elevation follower.
In accordance with another embodiment of the invention, it has been determined that rapid, pre cise and unambiguous coordinate determination in'object location with radio beams may be obtained by rigidly coupling together a fan beam scanner and a needle beam scanner. Thus, in the embodiment illustrated in Fig. 8, the centering of the fan beam on the target for determination of one coordinate (azimuth) concomitantly swings the rigidly coupled needle beam to the proper azimuth. The needle beam is then swept vertically to determine the other coordinate, i. e., the elevation.
Referring to Fig. 8, two antennas I and 8 are shown, namely, a fan beam radiator I of the "pill-box type aforementioned, and a needle beam radiator I of the paraboloidal type such as is disclosed in the United States Patent of A. C. Beck, 'No. 2,409,183 issued October 15, 1946. The two antennas are rigidly coupled together by a rod 8, which constitutes an axis for the elevational adjustment of the antennas I, I. The pair of antennas may be rotated as a unit about the azimuthal pedestal axis Hi. The feeds II, I! for the. antennas comprise rectangular pipes or horns.
The system shown in Fig. 8 operates in the following manner: 7
The rotational axes 9, III are set in the approximate direction of the target.
Feed horn II is rapidly oscillated sideways to produce a lateral sweep of the vertical fan beam radiated from the pill-box antenna 1. When this beam strikes a target, it is centered and locked-in by an automatic follower (not shown). The azimuth position of the antenna assembly and gun are thereby fixed.
Then, feed horn I3 is rapidly rocked or oscillated up and down to produce a vertical sweep of the needle beam radiated by antenna II, for
determining the elevational coordinate of the.
. in. The gun is now ready to fire.
Various forms of fan beam radiators may be asiasn utilized, such as eloated cylindrical aboloids, cylindrical lenses or elongated sections of paraboioids of revolution.
Various other forms of needle beam radiators antennas providing crossed fan beams for target whereby unambiguous resolution of multiple targets at equal ranges may be provided.
2. In a radar system, a pair of directive radio antennas each having a plane of principal action, scanning means to sweep the plane of action of each of said antennas about a respective sc axis, support means for said pair of antennas adapted for rotation of said pair jointly about a first rotational axis and independent rotationof said pair jointly about a second rotational ams perpendicular to the first, further support means for one of said antennas adapted for independent rotational adjustment of said one antenna about a third rotational ams perpendicular to the secend, said one antenna being supported with its as each of said antennas about a respective scanning axis, support means for said pair of antennas adapted for rotation of said pair jointly 46 about a first rotational axis and independent ro-,
tation of said pair jointl abo t a tional axis perpendicular to the first, f
rotaarmpport means for one of said antennas adapted for independent rotational adjustment of said one antenna about a third rotational axis perpendicular to the second. said one antenna being supported with its scanning axis perpendicular to said third rotational axis, and the other of said antennas being supported with its scanning axis perpendicular to said second rotational axis, transceiver means coupled to. both of said antennas for supplying radio frequency waves thereto and receiving therefrom echoes returned by distant reflecting objects, individual oscilloscopes for said antennas, circuit means responsive to the echoes received from one of said antennas for indicating on one of said oscilloscopes the range and relative azimuth of the objects from which said last-mentioned echoes are received, and circuit means responsive to the echoes received from the other of saidan for indicating on the other of said oscillosco the range and elevation of the objects from which said last-mentioned echoes are received, whereby with said third rotational axis aligned with one of said objects the ambiguity of the indications in the presence of another object at the same range can be resolved by observing the eflect of said rotational adjustment on the said indications.
WALTERLAIB i i CES 9H The'following references are of record in the file of thlspatent:
UNITED STATES PA I Number I Name Date 2,231,929 Lyman Feb. 18, 1941 2,256,787 Lazar Sept. 23, 1941 2,415,095 Varian et al. Feb. 4, 1947 2,417,248 Godet Mar. 11, 1947 2,421,028 King May 27, 1947 2,422,697 Meacham June 24, 1947 2,28,829 Ferrell July 15, 1947 OTHERREFERENCES The sea-26s Radar, Electronics, September was, pp. loo-10s.