v Septvlo, 1946.: . |-|_ LANGSTRÓTH ETAL ` SGANNING DEVICE _ Filed April io, _1942 sg- S’j ///////////////L ‘àîl?/ l W 5i y [ml 'e5 83 , 2,407,305. n 2 sheets-¿Sheet i Ã el ' e7. TH _.m.- ATTQRNEY. Sept V10» 1946- H. LANGsTRoTH ET Al. ' 2,407,305 SCANNING DEV_ICE Filed April l0, 1942 l ' Sheets-Sheet 2 I-»u \\\\|\> \ fil“ 77 i y Patented Sept. 10, 1946 2,407,305 UNITED STATES PATENT OFFICE 2,407,305 SCANNIN G DEVICE Hall Langstroth, Hempstead, and Fred C. Wallace, Flushing, N. Y., assignors to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation of New York Application April 10, 1942, Serial No. 438,398 9 Claims. , (Cl. Z50-11) 2 l The present invention relates to scanning de vices for scanning highly directive radiant energy radiation or receptivity patterns over apredeter mined conical solid angle. In many types of devices, such as object de Further objects and advantages of the present ’invention will be apparent from the following specification and drawings. Fig. 1 shows an elevation view partly in sec tion of one embodiment of the present invention. tectors, it is necessary to project or receive a Fig. 2 shows an enlarged detailed vertical sec sharply directional radiant energy radiation or tion view of a portion of Fig. 1. receptivity pattern and to scan this pattern over Fig. 3 is a section view of the device of Fig. 1 a definite portion of a sphere, especially for the taken along they line 3-3 thereof. purpose of obtaining radiant energy reflections 10 Fig. 4 is a View similar to Fig. 1 showing a modi from anyl object which may be in the field of this fication of a .portion of the device of Fig. 1. radiation and for using such reflected radiation Fig. 5 shows a, detail side elevation of Fig. 4 to indicate the presence and/or position of the viewed along the line 5-5. reñecting object. It is also desirable to inter Fig. 6 is an elevation view partly in section rupt this scanning motion when an object has showing a modiûed construction for the device been detected and to produce a conical motion of Figs. 1 and 4. having a very small apex angle, such as of the Fig. 7 is a View similar to Fig. 5 showing a modi order of four degrees, for the purpose of giving ñed construction suitable for use in Figs. 4,/ 5, or 6. a finer and more accurate indication of the posi Fig. 8 is an elevation view partly in section tion of the reflecting object. 20 showing a further modification of the invention. In the present invention a beam of radiant Fig. 9 is a detail view similar to Fig. 8 showing energy,v such as a high frequency radio beam,_is v still another modiñcation. projected from a suitable highly directional radi Referring to Fig. 1 a suitable directional radi ating or receiving arrangement for radiant en ator which is caused to oscillate slowly or “nod” about an axis substantially perpendicular to the ergy, such as a metallic reñector I preferably of direction of the beam. At the same time, this paraboloidal form and containing a suitable an “nod” axis itself is rotated at a fairly high speed tenna arrangement, is supported for rotation about a “spin” axis normal to the “nod” axis so about an axis 3 as by means of suitable brackets that the beam in effect sweeps out a spiral pat 5 fixed to reflector I and pivotally mounted in a tern caused by the widening of the circles pro 30 yoke l, which is integrally formed with or fas duced by the fast spin motion in response to the tened to .a sleeve 9 whose axis II is perpendicular slow nod motion. Accordingly, the present de to axis 3. Axis 3 is termed the “nod” axis, and vice is enabled to scan in a spiral fashion a sub axis II the “spin” axis. Any suitable type of stantially conical portion of the sphere whose motive means, such as an electric motor, is con extent is determined by the angular limits of the 35 nected to drive an input shaft I3, which has nod oscillation. In addition, means are provided bearings mounted in a ñxed casing I5. Fastened for substantially instantly changing this spiral to shaft I3 are two gears I1 and I9 which are thereby rotated at a fixed speed. Gear I‘I en gages a gear 2I fixed to or integrally formed on position and retaining only the spinning motion. 40 sleeve 9, and thereby :causes the reflector I to The apex angle of this conical scanning is ob continuously rotate at a predetermined speed scanning motion of the beam into a small conical scan by interrupting the nod motion near its zero tained by ofi-setting the orientation of the beam from the axis of spin. Y about spin axis I I. Engaging with gear I9, which is also continuously rotated from shaft I3, is a further gear 23 to which is connected a second Accordingly, it is an object of the present in vention to provide an improved apparatus >for 45 sleeve 25 mounted rotatably and concentrically scanning a predetermined portiony of the sphere within sleevevS. Fastened to the end of sleeve 25 by a directional radiation or receptivity pattern. is a suitable cam 2l formed as a ñat disc con It is another object of the present invention taining a groove 29 eccentric to spin axis II and to provide improved devices for scanning a highly of a, .predetermined shape, chosen, as will 'be de directional radiation or receptivity pattern in a 50 scribed, to provide a suitable type of nod motion spiral. for reii‘ector I. It is still another object of the present inven Engaged in groove 29 of cam 21 is a suitable tion to provide improved devices for effecting follower 3l. It is to be understood that follower spiral scanning and for «converting such spiral 3l is actually located in a plane passing through scanning into ñxed conical scanning, spin axis H and Vertical to the plane of the draw ¿407,305 3 move back and forth in a straight line perpen 4 its nod cycle. ing of Fig. l, but is shown as in Fig. 1 for pur poses of clarity. Cam follower 3| is restricted in its motion to translation only and hence, by the motion of cam 21 relative to yoke 1, is caused to One method of performing this operation is shown in Figs. 1 to 3. Mounted on the nod axis 3 and fìXed with respect to reflector | is a suitably shaped cam or L1 dicular to the plane of the figure. Fastenedto :cam follower 3| is a rack 33 which engages with a pinion 35 fixed to a- cross shaft 31 as by a key 39. Key 39 and shaft 31 are locking piece 59 which has its smallest radius, as at point 9|, at the position corresponding to zero nodof reflector l; that is, at the position where the axis of symmetry of reflector | is most nearly coincident with the spin axis ||, differ adapted to move axially with respect to gear 35 10 ing therefrom only by the apex angle defined above. From this point 3| the radius of cam but any rotational movement of gear 35 produces increases smoothly in both directions to a a corresponding rotational movement of shaft 31.V maximum radius at its tips, as at 63.y Also fixed for rotational motion with shaft 31 as by key 39 is a gear 4|, which engages a gear sec tor 43 fixed to reflector | by a suitable bracket 45. Cooperating with cam 59 is a roller detent B5 mounted on a suitable rod 31 which is normally held away from engagement with cam 59 against the force of a spring 99 by means of a latching As described above, yoke 1 and reflector Al are continuously spinning about spin axis l! at a arrangement comprising a latching member 1| predetermined speed. Cam follower 3| and rack and a projection 13 on the end of shaft 31 serv 33 are also thereby spinning at this spin rate. The gear ratio between gears |9 and 23 is chosen 20 ing as a detent. As described above, shaft 31 is axially translatable. ’ ` to be slightly different from that between gears 1n the position shown in Fig. 1, roller 55 is held l1 and 2l, whereby cam 21 is driven at a rate away from cam 59. However, upon translating slightly different from lthe rate of rotation of shaft 31 to the left, its enlarged portion or detent yoke 1 in spin. Th'is difference is the rate of 13 will move away from latch 1|, permitting the nod, and produces translation of cam follower smaller diameter section 15 of shaft 31 to move 3| and rack 33 with respect to yoke 1, and there within a slot 11 of latch 1l and thereby permit by, through gears 35 and 39 and gear sector 43, ting spring 33 to urge roller 35 into engagement produces the nodding motion of reflector | about with cam 59. Spring 99 is chosen of such strength nod axis 3. Since the rate of nod is much slower than the rate of spin it will be clear that the 30 that if reflector | is free to turn roller 65 en gaging cam 59 will cause reflector | to rotate axis of symmetry of reñector | is caused to sweep until roller 35 engages the smallest radius por out a series of widening or narrowing circles, the tion Si of cam 59, and will thereafter hold reflec circles being generated by spinning about spin tor i centralized in this position. Reflector | axis Il and the widening or narrowing being is made free to rotate in response to the action of caused by nodding about nod axis 3. This in cam 59 and roller E5 by motion of key 39 out of effect produces a spiral scanning of the axis of engagement with gear 35 upon axial motion of reflector | over a predetermined solid angle. shaft 31. When this occurs, gear 35 is left free If the system is to act as a radiator, the radiant to rotate upon shaft 31 and can produce no mo energy to be radiated from reflector | is intro tion of shaft 31, gear 4| and gear sector 43 at duced through a suitable wave guide 41. In view tached to reflector |. of the fact that the radiating arrangement is Such axial motion of shaft 31 is provided by spinning rapidly about spin axis || it is neces~ the energization of a suitable solenoid 11 fas sary to provide a suitable rotating joint 49 for tened to the base or housing l5. Upon energiza coupling the stationary portion 41 of the wave guide to the rotating portion 5| carried by yoke 45 tion of solenoid 11 its »magnetic armature plunger 19 is drawn upward against the tension of a 1. Suitable types of rotating joint are shown in spring 8|, thereby rotating arm 83 about a pivot copending application Serial No. 429,494, for Di rective antenna structure, filed February 4, 1942, in the names of R. J. Marshall, W. L. Barrow, and W. W. Mieher. Rotating wave guide 5| is thenbent around in arcs of suitable radius to extend coaxial with nod axis 3, as at 53. Here again, since the reflector | oscillates about nod axis 3 with respect to mounting yoke 1, a further rotating joint indicated at 55 is provided be- .r tween the section 53 carried by the yoke and section 51 of the wave guide carried by the re flector i. - 35 fixed to base l5. The far end of arm 83 carries a roller 81 which normally rolls within a, pair of guides 89 formed on a third sleeve 9| located co-ncentrically and slidably within sleeves 25 and 9. Thereby, energization of solenoid 11 will produce a downward motion of sleeve 9|, which spins at the same rate as yoke 1. Pivoted to the upper end of sleeve 9| is a link arrangement 93 which, upon a downward mo tion of sleeve 9|, produces a leftward motion of shaft 31, as by means of an arm 95 engaging the end 91 of shaft 31. Shaft 31 is thereby moved Wave guide 51 terminates within reflector | in to the left upon energization of solenoid 11, and any suitable well known type of termination, 60 acts bo-th to disengage the nod driving mechanism such as shown in copending application Serial of reflector | and to disengage latch 1|, whereby No. 429,494. Preferably this termination is so the centralizing cam and roller arrangement adjusted that the orientation of the maximum 59-55 is actuated to centralize the reflector | directivity of the radiation pattern of reflector í and maintain it with its axis of symmetry at is at a slight angle to the axis of spin || even in a fixed scanning angle with respect t0 spin axis the position of Zero nod. This angle is chosen to be the apex angle of the conical scanning to be described below. ‘The angle may be formed |I. Thereafter, so long as solenoid 11 is ener gized, reflector | will be rotating only about’its spin axis | l, and the directional beam of radiant by selecting the proper zero nod condition, or 70 energy, which as described above, is off-set from by off-setting the antenna within reflector |. When conical scanning is desired in the ar rangement already set forth it is merely neces sary to interrupt the nodding motion and to fix th'e reflector | at a predetermined position in 75 ` the spin axis | l, will generate a cone. Preferably the off-set angle is chosen substantially equal to the angular width of the directional radiation pattern, so that an accurate determination of the orientation of a distant object may be made. 2,407,305 5 -Upon deenergi'zation of solenoid 11, spring 8| causes plunger 19 to withdraw from soleonoid 11, thereby moving >sleeve r9| upward and releasing arm 95 from the end of shaft 31. A spring 99, having one end ñXed to the spinning mount IUI and the other end rotatably engaging a collar |03 fixed to shaft 31, urges shaft 31 toward the right. In so doing, and before detent 13 on shaft 31 can enter its mating opening 14 in latch 1|, key 39 once more connects gear 35 to gear sector 43 through gear 4|, and starts the reflector nodding about nod axis 3. In so doing cam 59 now drives roller 65 and its rod 61 downward. As rod 61 6 vantage of greater simplicity over that of Fig. 1, since the use of cam 59 and its follower and the translation shaft 31 is eliminated. However, it has the disadvantage that the system must wait until the reflector I has reached its centralized position in its normal course of operation before reflector I may be centralized to perform conical scanning, whereas, in the system of Fig. 1, no matter what the position of reflector I is at the moment solenoid 'I1 Vis energized, the reflector | is immediately disengaged from the nod drive and returned to its centralized position. i Fig. 6 shows a modified form of construction reaches its lowest position, projection 'I3 of shaft which may replace the cam_21 and the nod-actu 31 slips into its mating opening 14 and thereafter 15 ating apparatus in Figs 1 and 4. Here yoke 1 holds roller 65 away from engagement from cam 59 and the system resumes its spiral scanning as described above. As an alternative construction, shaft 31 need ~ not bemade to rotate. Thus, gears 35 and 4| may be coupled by key 39, which thereby rotates with respect to shaft 31. Key 39 is adapted to be dis» is actuated by sleeve 9 in the same manner as in Figs. l and 4. Sleeve 25 actuates a cylindrical cam I2|, which replaces flat cam 21 in Figs. 1 and ll. Cam I2I is provided with a continuous groove |23 whose disposition on the cylindrical surface of cani |2| is so chosen as to provide a desired type of trans lational motion for its follower |25. Since cam I2I rotates relative to yoke 1, being driven at a engaged from gear 35 by actionof a shoulder on shaft 31, when shaft 31 is shifted axially in re~ Sponse to actuation of solenoid 11, as already de 25 different speed therefrom, follower |25 is trans _lationally oscillated in a direction parallel to spin It will be clear that by the apparatus just de axis II. Accordingly, to provide nod motion it is scribed the transition to conical scanning is made merely necessary to couple cam follower |25 to with the greatest accuracy, ksince the position of the reflector I, as by a suitable arm |21 and a the reflector I during conical scanning is de pivotally connected link |29. termined directly with respect to yoke 1, avoid The mechanism for interrupting the nod mo ing any inaccuracies arising from backlash, etc., tion to provide conical scanning in Fig, 6 is il» which would appear yif reflector I were held at lustrated as being the same as in Fig. 4. any other point of i-ts drive. Fig. '1 shows a modification of a portion of Figs. Suitable counterweights may be provided about e, 5, and 6. Thus, in place of member I 95 having both axes 3 and || to provide both static and a notch |91 and cooperating with projection |99 dynamic equilibrium during scanning. in sleeve 9| as shown in Figs. 4, 5, and 6, member scribed. ‘ ì Figs. 4 and 5 show a modiñed arrangement for A converting from spiral scanning to conical scan §95 may be provided in the form of a cam |95’ similar in contour to cam 5-9 shown in Fig. 3, and ning. Here vcam 59, its roller 95, spring 69, latch 40 projection |99 of sleeve 9| may terminate in a 1| and detent 13 on shaft 31 are omitted. In their suitable roller I lû similar to roller 65 in Fig. 3. place a suitable member |95 having a notch | e1 is ‘ rl‘he operation of this modification clearly com fastened to reflector |, notch |91 corresponding bines the desirable features of Figs. 1 and 4. Thus to the zero nod position of reflector I in' which its the complicated latch and detent mechanism of axis of symmetry most nearly coincides with spin .Y Fig. l is eleminated, while retaining the advan axis | I. Formed upon the end of sleeve 9|, which tage of returning the parabola I to its zero nod is now arranged to be drawn upward upon energi position substantially instantaneously. zation of solenoid 11', is a projection |99 prefer Fig. 8 shows a Vfurther modification of' the in ably rounded and adapted to cooperate with a vention including a modified type of nod--pron preferably V-shaped notch |91 in member I 95. 50 ducing and nod~interrupting mechanism. Thus, Therefore, upon energization of solenoid 11', driving shaft f3 rotates gear I9 which engages sleeve '9| moves upward urging projection |09 a further gear »23 connected as by a suitable pin against member |05. Projection |99 therefore slips into notch |91 when reflector | reaches the or key to sleeve 25. Sleeve 25, however, instead of rotating a cam as in Figs. l, 4, and 6, rotates proper position and serves to hold reflector I yin a carrier member I3I carrying floating pinions this position for conical scanning. At the same |33 illustrated in the figure as being two in num time, as projection |99 slips into notch |91, a key ber, but which may comprise any desired num | I I which serves to couple gear 23 to sleeve 25 ber. The pivots I 35 of pinions |33 are mounted during spiral scanning, is slid upward into a suit equidistant from and parallel to the axis of ron able, preferably annular, recess I I3 in sleeve 9 and 60 tation of carrier I 3| , which is chosen as spin axis disengages sleeve 25 from gear 23 whereby the II. At the same time, gear 23 rotates a gear |31 motion of cam 21 and hence of the power drive for suitably fixed thereto. Gear |31 is illustrated as reflector | in nod is removed. Thereafter reflector being an elliptical gear of the well known type | is maintained centralized and conical scanning and engages with a second elliptical gear |39. is performed. If desired, recess IIS could be a 65 As is well known, two elliptical gears pivoted simple» notch matched to key |I| when projec at respective focal points spaced the proper dis tion |99 falls into notch |01. tance apart will continuously mesh with one an Key | || is shown formed integrally with or other and one will provide a varying speed output fixed to the lower part l9|’ of sleeve 9|, which when the other is driven at a constant speed, therefore rotatesat the same rate as sleeve 25 70 which output speed cscillates between two limits and cam 21. Since the upper part 9|” of sleeve respectively above and below the driving speed. 9| must rotate at the same rate as yoke 1, a suit Accordingly, the output speed of shaft | 4| car able rotatable joint 92 is inserted between the two rying elliptical gear |39 will be alternately slower parts of sleeve 9|. and faster than the speed of shaft 25 and carrier The system shown in Figs. 4 and 5 has the ad 75 |3I, Also attached to shaft I4| is a pinion |43 :2,407,305 8 actuates a further gear |82 Aalso fixed to sleeve |41. Gear |82 operates through a suitable train at whose upper end is mounted an internal gear of gears |83 and |84 to actuate member |53 which |49 meshing with pinions |33. is similar in function to member |53 shown in Floatingly mounted and concentric with sleeves Fig. 8. 25 and |41 is a spur gear |5| engaging pinions Member |53 carries bevel gear teeth which en |33. It will be clear that internal gear |59, car gage with bevel gear sector |55 fixed to the pa rier |3| and its pinions |33, and gear l5 |, provide rabola | as in Fig. 8. The gear ratios involved one well known type of differential gear and ac are so selected that bevel gear |53, which is cordingly, the rotation of gear |5| will be pro portional to the difference in speeds of internal 10 driven at a varying rate of speed, has an aver age speed equal to that of spinning yoke 1. Ac gear |f|| and carrier |3|. cordingly, with respect to yoke 1, gear |53 alter As stated above, carrier |3| is rotated at con nately speeds up and slows down, and therefore stant speed while internal gear |159 is rotated atreverses its direction of motion. In this manner a continually varyingspeed. As a result', the out the nod oscillation is produced. ` put gear |5| will also be rotated at a continually The conversion from spiral scanning to conical varying speed which oscillates between two fixed scanning may be produced in any of the man limits. 'I'he various gear ratios are so chosen ners described with respect to the previous fig that the average speed of gear |5| will be the ures. Thus, if desired, a member |6| carrying a same as the speed of yoke 1, which is driven from , projection |55, similar to the arrangement of Fig. shaft I3 by way of gear |1, gear 3|, and sleeve 8 may be provided to halt the nod motion at a 9, as in the other iigures. In this way gear |5| particular point of the nod cycle as discussed alternately speeds up and slows down with re with respect to Fig. 8. At the same time, the spect to yoke "I and accordingly, it periodically nod drive may be interrupted either in the man reverses its direction of rotation with respect to engaging a further gear |45 fixed to a sleeve |41 yoke 1. 25 ner shown in Fig. 8, or by an immobilizing mem Fastened to gear |5| is a beveled gear |53 which' engages with a beveled gear sector |55 suitably fastened to the parabola |. lin this way, parabola | is oscillated back and forth as the yoke 1 ro tates, and there is thus produced the required nod » motion and spin motion. Itis to be understood that the values of the gear ratios are chosen to provide a suitable rate of non-oscillation. To provide a nod interruption, sleeve 9| is ber |15 of differential |13. This may be done in any suitable manner, as by disengaging rack |16 from gear |11, or by declutching the drive shaft |19 of this oscillating motion from its source of power. Alternatively, gear |53 may be simultaneously disengaged from bevel gear |55, as by the re ciprocation of member -|6| and sleeve 9| iixed thereto. It will be clear that many other de again provided controlled in a manner similar vices for producing this result may be readily to that of Fig. 1 by a solenoid 11. The upper end evolved from the above description. . of sleeve 9| carries a projecting collar |51 so that upon energization of solenoid 11 sleeve 5| moves downward and disengages gear |53 from gear As many changes could be made in the above for the nod motion. At the same time, a projection |59 on a flange |5| fastened to the end of sleeve 9| bears down on beveled sector |55 and is adapted to fall into a notch in sector |55 when the proper orienta tion of parabola | is obtained. These members are so arranged that the nod drive continues until intended that all matter contained in the above description or shown in the accompanying draw ings shall be interpreted as illustrative and not construction and many apparently widely differ ent embodiments of this invention could be made sector |55, thereby interrupting the power drive 40 without departing from the scope thereof, it is in a limiting sense. l What is claimed is: l. A scanning device comprising a directive antenna mounted for rotation and oscillation about independent axes, drive means, means driven by said drive means for rotating said ing the power drive and stopping nod. In this 50 antenna including a first sleeve mounted to ro tate about its longitudinal aXis, means driven way, parabola | is locked into the proper posi by said drive means for oscillating said antenna tion for conical scanning, as discussed above. including a second sleeve concentric with said If desired, a suitable cam and roller arrange ñrst sleeve and rotatably movable with respect ment similar to those of Fig. 3 or Fig. ’1 may be thereto, normally ineffective means for holding provided to centraline the parabola I instan said antenna in a fixed position with reference taneously upon energization of solenoid “i1 and to its axis-of oscillation including a third sleeve interruption of the nod power drive. concentric with said ñrst and second sleeves and Fig. 9 shows a further modiñcation similar in reciprocatively movable with respect thereto, many respects to that of Fig. 8. Thus, drive shaft I3 spins yoke 1 by means of gear |1, gear 2|, and 60 means for disabling said oscillating means, means for rendering said holding means effective, and sleeve 9. Gear |9, also driven from drive shaft means for effecting simultaneous operation of I3, actuates a gear 23 floatingly mounted about both said disabling and rendering means. axis || which thereby drives one member |1| of projection |59 falls into its corresponding notch in sector |55, thereby simultaneously interrupt 2. A Vscanning device as claimed in claim l, a suitable differential gear |13 of any well known type. A second member |15 of differential |13 is 65 in which the reciprocatively movable part of said holding means is a detent and the part that adapted to be oscillated as by means of a rack cooperates with the same is a locking piece |15` engaging therewith and oscillated as by mounted to move with movement of the antenna means of a crank drive arrangement |18 whose about its axis of oscillation. actuating shaft |15 is suitably driven. 3. A scanning device as claimed in claim 1, As a result, the third member |8| of differen in which said holding means is a detent and tial |13 is driven at a varying speed due to the the part that cooperates with the same is a lock combined rates of motion of constantly driven ing piece mounted directly on the antenna in a member |1| and oscillated member |15. Output position to move with movement of the same member |5| of differential |13 is coupled to a suitable gear |45 fixed to a sleeve |41 and thereby 75 about its axis of oscillation. ¿407,305 4. A scanning device as claimed in claim 1, in which the axis of rotation of the antenna is vertical and the axis of oscillation of the antenna is horizontal. 5. A scanning device as claimed in claim 1, in which said oscillating means includes a rotat ing cam plate having a translatably mounted follower therefor. 10 input element of the diñerential at a variable speed, disengageable means for controlling the motion of the antenna about its axis of oscilla~ tion from the output element of the differential, normally ineffective means for interrupting mo tion of the antenna about its axis of oscillation, and means for simultaneously rendering said in terrupting means effective and disengaging said 6. A scanning device comprising a directive an disengageable means. tenna mounted for rotation and oscillation about 8. A scanning device comprising a directive an independent axes, a differential having two input tenna mounted to spin about one axis and nod elements and a single output element, means for about another axis, mechanism operable to spin driving one of the input elements at a constant said antenna including a ñrst sleeve, mechanism speed, means for driving the other input element operable to nod said antenna including a second of the diiîerential ata variable speed, and means 15 sleeve concentric to said first sleeve, and mech for controlling the motion of the antenna about anism operable to interrupt the nodding motion its axis of oscillation from the output element of of said antenna including a third sleeve concen the diñerential. tric to said first and second sleeves. '7. A scanning device comprising a directive 9. A scanning device of the character claimed antenna mounted for rotation and oscillation 20 in claim 8, in which said nodding mechanism in about independent axes, a differential having tWo cludes a rotating cam plate and a reciprocating input elements and a single output element, means for driving one of the input elements at a constant speed, means for driving the other cam follower. HALL LANGSTROTH. FRED C. WALLACE.