US2617029A - Nutating antenna - Google Patents

Description

Nov. 4, 1952 K. L. PLUMMER ET ALk 2,617,029

NUTATING ANTENNA Filed June 29, 1948 3 Sheets-Sheet l INVENTORS. KINSEY L. PLUMMER BY GILBERT wlLKEs ATTORNEY NOV, 4, 1952 K. L. PLUMMER ETAL 2,617,029

NUTATING ANTENNA Filed June 29, 1948 3 Sheets-Sheet 2 FIG. 2

l T L I INVENTORS. NSEY L. PLU ER LBERT WILK BY da@ ATTQRNEY IN VEN TORS.

3 Sheets-Sheet 5 KINSEY L. PLUMMER BY GILBERT WILKES K. L. PLUM'MER ETAL NUTATING ANTENNA IIIIIIHI Hillninm. I

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UNITED STATES PATENT OFFICE 4 Claims".

The present invention relates to a wave guide terminal' producing a narrowv beam of radio-frequency radiation andV to a nutator for said beam.

More specifically it relates to a terminal for a wave guide, which may pass through a parabolic reflector to deliver energy toward the reecting surface' from substantially a point at the focus of said reflector.

An object of the inventionv is to feed the radiant energy to the reflector in such way that after reflection a narrow beam, substantially free" from secondaryv lobes, is produced, and to provide means for causing nutation of said beam, that is, causing its axis to' describe a conical surface;

Another object which maybe attained is a rotating unsymmetric'beam in which a small portionV of the total energy maybe fed unsymmetrically to a side of the main. beam to secure irradiation of a greater volumein space'without:

sacrificing the einciency of the device.`

An important object is to provide such nutation by rotating a very slightly bent or sprung element that nevertheless is nearly perfectly -dynamically balanced, wherein the nutation resultsv from rotation about the axis of said; parabolic reecton and is due solely to variation in the direction of the energy reflection from a relatively small element carriedl at the end of said rotating member,` near the focus of' ther concave reiiect'or.v

Another object is to avoid loss of the energy that travels along the guide to said reflector element and then returns adjacent saidguide, in an out-of-phase relation, by interposlng in its path a dielectric element that restores the proper phase relationship by adding just suflicientfurther retardation to accomplish this object.

Other objects and advantages of the invention in part will be specifically pointed out in the specification and in part will become self-evident as the description of the invention proceeds.

While the invention may be embodied in various forms,l a single apparatus involving what is at present believed to be the most satisfactory form, together with a slightly different modication, are selected as the basis of this specification and the drawings` accompanying the same, solely by way of illustration, and not as a limitation of the invention thereto.

In the drawings:

Fig. 1 is a side elevation, partly in section in a vertical axial. plane, of the essential structures ofthe apparatus;

Fig. 2 is an axial section, on an enlarged scale,

and partly broken away, through the feed mem. ber, showing the dielectric insert as well as the phase-shifting dielectric disk;

Fig. 3 isv a perspective view of the dielectric insert, on a slightly increased scale;

Fig. l is a fragmentary detail section, in the plane indicated by line l--llof Fig. 2; l

Fig. 5 a fragmentary elevation, partly in axialv section, ofY` a slightly modified form of the apparatus; and

Fig. 64 is an exploded view, showing the elements constituting the feed.

Referring first mainly to Figs. 1 to 4 inclusive, and incidentally to Fig. 5 for certain detailsL the apparatus comprises a base l carrying the reflector-support Il, in the form of a spider, to which is secured the reflector I2, as by rive-ts 13 or other suitable fastenings. The supportl ilv` has a central opening lf3l affording a free passage through the support and the rehector.

A tubular wave guide l5 of circular cross sectionpasses through the opening i4 and is coupled electrically with the adapter 16 through the chokes il' and Hi as shown, the latter being of conventional design, namely, annularly grooved collarsof proper dimensions for the wave length in use. It will be understood that the waveguide I5 is mounted for rotation about itsv own axis. while the adapter I6 is stationary and usually has a rectangular shape at its'remote end, merging intor a circular cross section at the choke l1, to aiiord proper matching with the guide l5. The chokes are provided to permit rotation of the'last-named guide'.

Such rotation is produced by any suitable means, such as amotorv 19 having a mounting plate 2'0v secured thereto, whereby it may be fastened to the end' wall 2l by suitable means, such as the soc1` eti1eadscrewsV 22 indicated. A protective housing 23. preferably covers the motor and in turn further auxiliary apparatus 24,

such as a speed measuring device for. the motor,

may be supported by a second plate 25 secured to the other end of the. motor I9, and may be protected by a casing 26'; The saidapparatus 24,. however, do not form a part of the present invention and' hence are not further discussed herein;

The entire assemblage, just described, is supported by the central hubof the spider H, as by a suitable number of socket-head screws 2.8V and 29,v passing through the flange 21V andV threaded into plate 30, or passing through plate 3o and threaded into the spider hub, as may be expedient. The plate 30, of course, has a hole 3| alined with hole I4 of the spider hub, and receives the outer housing of an anti-friction bearing 32, here shown as a ball bearing whose inner member 33 is mounted on a sleeve 34, which in turn ts over the outside of the wave guide I5, but is spaced radially therefrom. A spherical, concave seat 35 is formed at the outer end of sleeve 34 against which fits the convex portion of a bushing 36 which ts on and supports the wave guide I for rotationwith said sleeve. Adjustment is provided by the coacting spherical surfaces, so that proper alinement of the axis of rotation of the wave guide I5 may be obtained, screws 31 serving to make and hold such adjustment.

At the other end of sleeve 34 a second antifrction bearing has its inner member 38 surrounding and supporting said sleeve, the outer member 39 of the bearing being held in a cylindrical flange 40 of plate 2l. A tubular spacer 4I surrounds the intermediate portion of sleeve 34, and abuts the bearing members 38 and 33. A set screw 42 is threaded radially through a flange 43 at the end of the spacer 4I, and serves to secure the spacer to the sleeve 34, to rotate therewith. This fiange 43 in turn is secured to the side face of the web 44 of a gear 45, as by screws 46.

Plate 20 is supported by the housing 41, which is silver-soldered thereto at 48 on the one hand, and to the plate 30 at 49 on the other hand.

The motor I9 has its shaft 50 connected to the shaft 52 of gear 53 by a suitable flexible coupling 5I as shown. Shaft 52 is carried in bearings 54 and 55 mounted respectively in plates 53 and 30. An idler gear 51 connects gears 45 and 53, by meshing with both. Preferably the idler 51 is made of non-metallic material, while the gears 45 and 53 are made of metal, to secure smooth running and minimize wear. The idler 51 may be mounted on anti-friction bearings on a stud 58.

The parts so far described constitute mainly the mechanical portion of the apparatus, that is, its drive means, and admit of considerable variation without affecting the electrical features, which will now be discussed in detail, with reference more particularly to Figs. 2, 3 and 4.

The wave guide I5 has a tapered, substantially frusto-conical intermediate portion 59, and a cylindrical end portion 50, said tapered portion thus constituting a transition zone between two cylindrical tubular portions.

The actual source of radiant energy near the reector focus can be considered as the outer end of the metallic guide I5. To reduce aberrations, this source should be as small as possible, without causing cut-01T. By filling a guide with dielectric material, the dimensions of the guide can be reduced without causing cut-olf. The preferred material is Du Pont Teiion." Polystyrene is also suitable. At the same time this dielectric can be extended to support the radiating element. Guide I5 is therefore tapered down, as already stated, through section 59 to a cylindrical section 60 that firmly frictionally engages the dielectric stem 6I, so as to secure rigid mechanical support of the radiating-surface element 64. Stem 6I is provided with a taper at 62 so that the radiant energy traveling in I5 passes Iwithout reflection into the restricted section iISI) thereof. The length of stem 5I and its taper 62 can be adjusted to match out undesirable redections of the radiating element, as is usual in wave guide practice, to effect impedance matching.

The head of the feed has a substantially spherical convex surface 64, facing the reflector I2. This is advantageous as it is found both by experiment, and by reasoning based on ordinary ray optics, that such a surface is necessary to cause the rays emerging from the wave guide to produce a sharp virtual focus at a point beyond the reflector surface 65. The reflector surface B5 may be plane and normal to the wave guide axis, in which case nutation is obtained not by the properties of the head 6I, but by deflecting the head B3 off center by means of screws 31, as shown in Fig. 5. Reflector surface E5 may be plane and tilted from the normal to the axis of the wave guide portion Eil. This will cause the phase of the spherical wave front emerging from surface 64 to be lagged on one side and advanced on the other, and this type of surface provides nutation upon rotating the head 63 on the center of the reflector I2. Both of these nutations resemble that obtained by ordinary mechanical means, and show the well known nutation side lobe in the main radiation pattern. It is well known that this side lobe can be traced to a defective phase front coming out of the reector I2, that is established as soon as the source or feed of such a reflector is displaced laterally from its focus. Such a defective phase front has received the name coma curve, and knowing the characteristics of this curve for a given installation it is possible to cancel or rectify it by giving surface 65 a proper curvature of opposite sign, as can be predicted by ordinary ray optics. Lobeless nutation is then obtained.

Furthermore, the theory of concave reectors shows that the phase and amplitude distributions over a reflector are approximated by the Fourier transforms of the patterns they set up in space. Knowing the expression representing a given non-symmetrical pattern it is, therefore, possible to compute the reflector distribution and phase functions that they require. These functions in turn permit the determination of the surfaces 64 and 65 necessary to set them up. As an example, the configuration shown in Fig. 3 sets up a pattern in space about twice as heavy on one side as on the other.

A more or less flat surface 65 has the objection that it reflects back, down the wave guide 60, a certain portion of the useful energy. This objection is overcome by the conical indentation 6B, `which deflects the energy from the wave guide 60, into the outer portions of reflecting surface `65 so that no direct reflection occurs down the guide 60 back to the source.

It is evident that a tilted plane surface 65 would not provide a circular symmetric reflector irradiation. However, by displacing the indentation zSI5, the desirable symmetric amplitude distribution can be reestablished, while still maintaining the tilted phase front necessary for nute-` tion.

The diameter of the head 63 has a profound inuence on the characteristics of the radiated pattern. To secure appreciable nutation and shaping of the pattern by means of the head, lt is necessary to assign to it a diameter of the order of, or greater than, a wave length. It then becomes possible for more than one modeof oscillation to exist in it, and the proper focal length of matching stem 5I become critical to small frequency variations. Indentation 66, if deep enough, tends to limit the number of oscillation modes possible, by impeding the group of transverse electric modes, and favoring the transverse GNSQQQ magnetic modes. The latter are desirable. in that they are circularly symmetric, and feeds having either a deep indentation 66, or a relatively small diameter of head 63, show better circular symmetry than other -types of feeds used heretofore, while they are less frequency sensitive than feeds with a larger head |63. In the design of the head 5s the desirability of relative freedom from frequency response must be balanced against the ease of obtaining the desired nutation by means of the shape of head 63.

Surface 65 is silvered or aluminized or made conductive in any other way, to secure good reiiecting properties. A protective metal cap 61 fits over this surface 65, and preferably is in close contact therewith. Cap 61 has a flange 58 which surrounds the head 63, and is secured thereto by crimping or by press-fit. The central pit 55 is occupied by a metal projection E9 of a corresponding shape, on the cap El, and this projection is threaded to receive the screw 10, which serves to hold a dielectric disk 'II to the outer flat surface of the cap.

The small dielectric disk 'II secured to the front of the head assists in preventing the loss of radiation from the head. It is the subject of a copending sole application by Gilbert Wilkes, one of the present joint inventors, Serial Number 15,376, filed March 17, 1948, for Back Radiation Reflectors for Radar Feeds.

A bushing 'I2 is secured to the outer surface of the wave guide I5, as by soldering, brazing or welding T3. This bushing has at one end a radial flange i4 and has a threaded portion l5 upon which may be screwed a disk 'i6 of dielectric material, for example, one of those already mentioned. A cover Il having a flange 'I3 fits into the central opening 'i9 of the reflector I2. This cover has an opening 80 which permits passage of the wave guide I5, but does not touch it, and has mainly the purposes of providing a continuation of the reflector I2 and of preventing the entrance of foreign matter.

While Figs. 5 and 6 illustrate a modified form of the invention, many of the mechanical features are identical with those of Figs. 1 to 4. These mechanical features, such as the gearing, the bearings and the sleeve 34 have already been described. The structures of Fig. 5, with the exception of the dielectric lens carried in the wave guide I5, are in fact entirely identical with those of the preceding figures, but in Fig. 5 the wave guide l5 has been intentionally bent slightly, so that instead of rotating in centered relation to the axis of the two bearings, its outer end now describes a circular orbit about said axis, that is, nutation results.

This permits use of a symmetrically constructed dielectric lens, shown, partly in dotted lines, in Fig. 6. This means that the outer end face of the dielectric lens 6I is a plane surface instead of a doubly-curved surface of the type shown in Fig. 3. Electrically, these two give similar results, the nutation with the Fig. 3 lens being obtained by pure rotation of a non-symmetrical surface while the Fig. 6 form requires actual mechanical nutation of the lens, such as is provided by springing the wave guide i5 slightly out of alinement between its bearings. This is accomplished readily by uneven adjustment of the screws 3l, whereby the bushing 35 has its axis turned to make a slight angle with the axis of the bearings, as indicated in a somewhat exaggerated degree in Fig. 5.

The operation of the nutator is very simple, and

consists merely in rotating the wave guide I5, and the structures carried thereby, about the refiector axis by means of the motor I9, through the gears 53, 5l and 45.

In some installations, the focal distance of the parabolic reflector is limited by mechanical considerations. To irradiate properly such a reflector requires a feed of wide-angle irradiation, which is not readily obtainable with usual feeds. On the contrary, with the present unit, the desired angle of irradiation is readily obtained by adjusting the diameter and shape of the head 63, and the shape and depth of the indentation 66.

A further part of this invention concerns the disk 1S. Some radiant energy travels along the outside of the wave guide I5 and this energy will be out of phase with that traveling at a further distance from the guide, and hence ordinarily either would be wholly lost, or would provide an erratic component of the main radar beam and thus produce lobes. This energy is here likewise reflected toward the reflector, and will strike the central region thereof.

The dielectric disk 'l5 is provided, to shift the phase of this energy, to make it agree with that of the main radar beam. Assuming a electrical lag in the energy in traveling outward along guide I5, and an additional 90 lag in its return, the disk 'i6 should also produce a 90 lag so that in its entire journey out and back adjacent to the wave guide, and twice through said disk, said energy will have fallen behind by 360, that is, it will be in phase again after loss of one full cycle, and hence will be added to the main beam in step therewith.

It will therefore be evident to those skilled in the art that the present invention provides a flexible means for choosing the best reflector irradiation and phase function to nt any given reflector and pattern requirements. This permits generally increasing the gain of radar reflectors from the present value, while retaining at all times the desired substantially fixed polarization of the beam. Where a circularly symmetric reflector is used, nutation is obtained by a simple rotation of the head. With good quality dielectrics, of types now available, heating is negligible at the highest powers obtainable, and arcing does not occur in well-designed units. This is a considerable advantage from a practical standpoint, as available sources of R. F. energy have now exceeded the capacity of the usual metallic feeds in the micro-wave spectrum.

As a result of all the dielectric elements provided, a considerable increase of the useful energy of the beam is obtained, eiiiciencies up to 50% higher than those heretofore customary having been secured with receiving meters matched to the particular antennae used. The beam is also remarkably free from the undesirable side-lobes that formerly consumed useful energy and produced confusion. In general the radar antenna function-s also as a receiver, so that the antenna and receiver are automatically well matched one to the other. With improvements in single way transmission of this order, the actual practical gain or increase in range of a radar set becomes appreciable.

While the form of the invention at present preferred has been disclosed in detail, and several modifications have been described or suggested, it is to be understood that numerous other embodiments are possible. Therefore the present invention is not limited to the specific features amaca@ disclosed, but is defined solely in and by the following claims.

What is claimed is:

1. In a nutator, a concave reflector, a tubular wave guide substantially coaxial therewith, adjustable means for bending a portion of said Wave guide slightly off the axis of the reflector, means for rotating said guide about the axis of the reector, means for introducing signal energy into said wave guide from the convex side of the reflector, and a dielectric plug in the bore of said guide at the concave side of the reflector, said plug and the adjacent portion of the wave guide being oppositely tapered to elect impedancematching to each other, said plug having a head extending radially beyond the bore of the wave guide, said head having a conductive surface at its outer end, to reflect signal energy to the concave face of the reflector.

2. A nutator as dened in claim 1, wherein the said conductive surface has a central projection thereon directed toward the concave reflector to modify the reflective effect of said conductive surface.

3. A nutator as defined in claim 1, wherein said head has a convex face facing the concave face of the concave reilector.

4. A nutator as dened in claim 1, wherein there is additionally provided a dielectric disk surrounding said Wave guide portion and positioned between said concave reflector and said head and relatively closer to said concave reflector than to said head.

KINSEY L. PLUMMER. GILBERT WILKES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,407,267 Ginzton Sept. 10, 1946 2,407,690 Southworth Sept. 17, 1946 2,412,867 Briggs et al. Dec. 17, 1946 2,420,007 Olden May 6, 1947 2,422,184 Cutler June 17, 1947 2,425,336 Mueller Aug. 12, 1947 2,429,601 Biskeborn et al Oct. 28, 1947 2,429,640 Mieher et al. Oct. 28, 1947 2,433,924 Riblet Jan. 6, 1948 2,438,343 McCellan Mar. 23, 1948 2,457,562 Karleen Dec. 28, 1948 2,460,401 Southworth Feb. l, 1949 FOREIGN PATENTS Number Country Date 570,038 Great Britain June 20, 1945 579,763 Great Britain Aug. 15, 1946

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