US3007168A

US3007168A - Phase shift scanning antenna

Info

Publication number: US3007168A
Application number: US810136A
Authority: US
Inventors: John A Kuecken
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1959-04-30
Filing date: 1959-04-30
Publication date: 1961-10-31
Anticipated expiration: 1978-10-31

Description

Oct. 31, 1961 J. A. KUECKEN 3,007,168

PHASE SHIFT SCANNING ANTENNA Filed April 30. 1959 2 Sheets-Sheet 1 Ii IO (A I KAN INVENTOR.

JOHN A KUECKEN BY 0/ M M ATT NEYS.

Oct. 31, 1961 J. A. KUECKEN 3,007,168

PHASE SHIFT SCANNING ANTENNA Filed April 30. 1959 2 Sheets-Sheet 2 O-.r........,. INVENTOR.

0 I2 .24 .36 .48 JOHN A. KUECKEN.

PENETRATION (INCHES) a W ATTNEYS.

3,007,168 Patented Oct. 31, 1961 3,007,168 PHASE SHIFT SCANNING ANTENNA John A. Kuecken, Cincinnati, Ohio, assignor to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed Apr. 30, 1959, Ser. No. 810,136 6 Claims. (Cl. 343854) This invention relates to antennas having high-speed, non-linear scans and, more particularly, to antenna arrays provided with mechanical phase shift elements.

In recent years there has been an increasing need for antennas capable of producing high-speed, non-linear scans since this type of antenna performance is required in many applications, such as automatic landing and three-dimensional radar. The trend has been towards one or two-dimensional broadside arrays, many different methods being used to make the beam from such an array squint or scan with the insertion of a progressive phase shift in the array illumination. Similar methods are used for scanning end fire arrays.

Progressive phase shifts in an antenna array have been produced by means of frequency change phase shifters, by means of ferrite element phase shifters, by changing the velocity of propagation, and by means of mechanical phase shifters. In the frequency change type of phase shifter, a progressive phase shift at the various radiators in the array is obtained by altering the excitation frequency of a dispersive network, such as the waveguide. While this system has been effective, it tends to make prodigal use of the frequency spectrum. Ferrite element phase shift mechanisms present difficult problems at this time because of the inherent losses and because of variations in the ferrite materials due to temperature changes. The system of phase shifting by changing the velocity of propagation has been used in several radar applications; however, severe mechanical problems are introduced, and the accuracy of the system leaves much to be desired.

Due to the lack of adequate high dielectric constant materials and the difiiculty involved in obtaining a sufficient phase shift per unit length of waveguide, the mechanical phase shift scanner has not found wide use. However, as a result of the recent improvements in the dielectric materials, and as a result of the advances in the art disclosed herein, mechanical phase shifters are now found to provide the most satisfactory erformance.

It is an object of this invention to provide a light, simple and accurate means for providing a scanning antenna pattern whose scanning action is characterized by low inertia, high speed and non-linearity.

It is another object of this invention to provide an antenna array having self-matching pairs of dielectric plates inserted into the transverse plane of the waveguide for producing a progressive phase shift at the various radiators in the array.

Another object of this invention is to produce a progressive phase shift in an antenna array by means of selfmatching pairs of dielectric plates spaced one-quarter wavelength apart and inserted into the transverse plane of the waveguide.

For further objects and for a more complete understanding of the precise nature of this invention, reference should now be made to the following description and to the accompanying drawings, in which:

FIG. 1 illustrates a cross section of an antenna array constructed in accordance with this invention;

FIG. 2 is a side elevation of the invention, shown partly in section;

FIG. 3 is a perspective view showing the cam-driving mechanism for the phase-shifting elements; and

FIG. 4 is a curve illustrating the phase shift versus dielectric penetration characteristics of a single phase shift element.

The antenna array illustrated in FIGS. 1, 2 and 3 consists of a conventional rectangular waveguide 10 having

walls

11, 12, 13 and 14. A conducting metallic plate 15', which serves as a ground plane for a plurality of conventional radiators 1 6, is secured to the narrow wall 12 of the waveguide 10. The radiators 16 are conventional British type dipoles and are secured on the plate 15 and to the waveguide 10. Although many other forms of radiating elements may be used, the British type of dipole was preferred because of its ability to handle high powers and to produce a clean pattern. Each of the dipoles is illustrated as stacked in the H-plane, but this is only to obtain a higher gain than is produced by an E-plane stacked unit, and E-plane stacked units may be also used.

For feeding each of the radiators 16 from the common waveguide 10, each radiator is excited by means of a magnetic coupling loop 17 extending through the narrow waveguide wall 12, and the waveguide may be end-fed from a source not shown. (In this application the source i located at the left end of the waveguide, as viewed in FIG. 2.) The degree of magnetic coupling may be adjusted during assembly by varying the area within the loop 17.

The waveguide 10 is supported from a box-like structure consisting of

end braces

21 and 22,

lower beams

23 and 24, and

upper beams

25 and 26 to which the waveguide is welded. For producing a phase shift at each dipole radiator 16, phase-shifting elements 31 are pro vided, consisting of self-matching pairs of dielectric plates 31a and 31b arranged for insertion into the transverse plane of the waveguide 10 ahead of the radiator in the path of the wave through the guide. Non-radiating slots 32 in the narrow wall 14 are provided for permitting passage of the pairs of plates. Each of the plates is fabricated of a high dielectric constant material, and for the purpose of providing a self-cancelling action for matching purposes, the plates 31a and 31b in each of the phase-shifting elements 31 are spaced about one-quarter Wavelength apart. Each plate is made of a material having a relatively high dielectric constant; loaded polystyrene materials, such as Stycast K-14, have been used with considerable success.

Each of the phase shift elements 31 is suitably secured to a movable, lightweight platform 33 to which a reciprocating motion is applied for the purpose of inserting and withdrawing the plates into and out from the waveguide. The mounting for each element 31 comp-rises a grooved rectangular block 34 for receiving the plates 31a and 31b, and each of the blocks 34 is removably secured to the platform 33 by any suitable means, such as screws 36. For a purpose hereinafter to be described, the plate 31b is longer than the plate 31a in each pair, and each plate may be provided with saw slots 37, as shown.

The reciprocating motion for the rectangular platform 33 is provided by means of

cams

41 and 42 suitably journaled on a shaft 43 which is driven at a constant speed by any suitable drive mechanism (not shown). The shaft is, in turn, supported within

bearings

44 and 45 in the

end braces

21 and 22. The

earns

41 and 42 are positioned on the shaft 43 to cooperate with

cam followers

46 and 47 suitably secured in appropriately grooved portions of the ends of the platform 33.

The platform 33 is guided during its reciprocating motion by means of rods 51 secured between the beams 23-26 and passing through the appropriately located holes at each corner of the platform. The platform 33 is biased against the cam 41 by means of springs 52 seated between the

beams

25 and 26 and the platform 33. Thus, as the cam 41 is rotated in a counter-clockwise direction, as indicated by the arrow, the cam followers and the platform 33 will move the phase-shifting dielectric plates 31 into and out of the waveguide through the slots 32. Because the dielectric plates and the frame carrying them are small and light, these elements may be reciprocated in other than simple harmonic motion and, in addition, the phase shift exhibited by these elements is a non-linear function of penetration. Both of these factors tend to simplify the problem of obtaining a non-linear scan. FIG. 4 is a curve showing the phase shift versus penetration of a single phase shifter element 31.

In operation it may be observed that with the phaser elements fully withdrawn, the phase velocity within the guide is considerably greater than the propagational velocity in free space. This causes the antenna pattern to lean somewhat away from the normal, back towards the feed end of the array. Conversely, lobes caused by reflections from the elements will lean toward the load end of the array. Insertion of the phaser elements retards the propagational velocity within the guide, thereby causing the antenna radiation pattern (the beam) to swing back toward the load end of the array, through the position where the pattern is normal to the array. In the meantime, any lobes due to the reflections within the antenna will rotate in the opposite direction, both direct and spurious lobes going through the normal condition at some point. It will be recognized that opera tion is most critical in this normal beam position and, in general, it is necessary that reflections be kept very low to permit operation in this condition.

The aciton of the dielectric plates is such as to retard the propagation of the wave through the antenna. How ever, each phasing element gives rise to a certain reflection and, therefore, the plates 31 are run in pairs so spaced that the reflection from the second plate cancels (or is equal in magnitude and opposite in phase to) the reflection from the preceding plate. In practice, slots 37 have been cut in the plates to eliminate unwanted resonances. In addition, slightly diiferent penetrations have been provided for alternate plates in order to obtain a minimum of reflection (V.S.W.R.).

While in the illustrated embodiment the phaser elements are driven in unison to equal depths, it is also possible to employ a separate cam for each phase shift element, thus permitting varying penetrations. It is also possible to use cam-shaped dielectric plates 31 or eccentrics driven directly from a suitably positioned shaft and penetrating the waveguide 10 in a transverse plane. It will be recognized, however, that if the particular antenna application requires a rapid flyback, cam-shaped or eccentric phaser elements will not be practical. In a working embodiment of the invention as illustrated using eight radiators, a phase shift of 100 degrees per inch of penetration was obtained at frequencies in the vicinity of 5,000 me.

It is found in the use of the cam-driven phaser elements as illustrated herein that the spring bounce occurring during flyback does not create a serious problem, particularly because phase shift is very small for small penetrations of the phase shift element and, therefore, the unit is relatively non-critical for the slight fly-back bounce that was noted. It will be recognized that very durable materials, such as tool steel, are required for the cams 41 and 4,2 and for the

cam followers

46 and 47, since these elements will be subject to considerable wear, particularly at the time of flyback.

It will at once be obvious to persons skilled in the art that this invention is subject to many modifications and adaptations. It is intended, therefore, that the invention be limited only by the appended claims as interpreted in the light of the prior art.

What is claimed is:

1. In a broadside antenna array having a plurality of dipole radiators supplied with electromagnetic energy from a rectangular waveguide, apparatus for producing a high-speed, non-linear scan including means for progressively shifting the phase of said electromagnetic energy at each of said radiators, the combination comprising: means mounting said plurality of dipoles along a narrow wall of said rectangular waveguide; pairs of non-radiating transverse slots in said other narrow wall opposite each of said dipoles and slightly ahead of said dipoles in the path of said electromagnetic energy through said waveguide, the slots in each of said pairs being spaced apart approximately one-quarter wavelength; a phase-shifting element for each of said dipoles, said phaseshifting elements each comprising'a pair of high dielectric plates having cross-sectional dimensions approximately equal to said slots; means positioning each of said plates in registry with said slots; and means for inserting and withdrawing said plates into and out of said waveguide through said slots at a predetermined rate whereby the phase of said electromagnetic energy at each of said radiators is altered in a predetermined pattern.

2. The invention as defined in claim 1 wherein said plates are moved into and out from said waveguide by means of a rotating cam.

3. The invention as defined in claim 1 wherein each of said plates is provided with slots for eliminating unwanted resonances.

4. In an antenna array having a plurality of radiators supplied with electromagnetic energy from a rectangular wave guide, apparatus for producing a high-speed, nonlinear scan including means for progressively shifting the phase of said electromagnetic energy at each of said radiators, the combination comprising: means mounting said plurality of radiators along a narrow wall of said rectangular wave guide; pairs of non-radiating slots in saidother narrow wall opposite each of said radiators and slightly ahead of said radiators in the path of said electromagnetic energy through said wave guide, said slots in said pairs being disposed transversely to the. path of said electromagnetic energy approximately one-quarter wavelength apart; a phase-shifting element for each of said radiators, said phase-shifting elements each comprising a pair of high dielectric plates having cross-sectional dimensions corresponding to said slots, said plates being positioned in said slots; and means for reciprocating said plates into and out of said wave guide through said slots at a predetermined rate, whereby the phase of said electromagnetic energy at each of said radiators is altered in a predetermined pattern.

5. The invention as defined in claim 4 wherein each of said plates is provided with a plurality of slots disposed in the direction of motion of said plates into and out of the wave guide, whereby unwanted resonances are eliminated.

6. In an antenna array having a plurality of radiators supplied with electromagnetic energy from a rectangular wave guide, apparatus for producing a high-speed, nonlinear scan including means for progressively shifting the phase of said electromagnetic energy at each of said radiators, the combination comprising: means mounting said plurality of radiators along a narrow wall of said rectangular wave guide; pairs of non-radiating slots in said other narrow wall opposite each of said radiators and slightly ahead of said radiators in the path of said electromagnetic energy through said wave guide, said slots in said pairs being disposed transversely to the path of said electromagnetic energy approximately one-quarter wavelength apart; a phase-shifting element for each of said radiators, said phase-shifting elements each comprising a pair of high dielectric plates having crosssectional dimensions corresponding to said slots, said rocating said plates into and out of said wave guide References Cited in the file of this patent UNITED STATES PATENTS Clapp Oct. 24, 1950 6 Alvarez July 29, 1952 Loveridge Dec. 23, 1952 Ford et al Dec. 4, 1956 Corbell Dec. 25, 1956 Allen et a1. Jan. 22, 1957