US3594812A

US3594812A - Strip line ferrite phase shifter

Info

Publication number: US3594812A
Application number: US842447A
Authority: US
Inventors: Daniel C Buck; Theodore M Nelson; Robert A Moore; Leonard Dubrowsky
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1969-07-17
Filing date: 1969-07-17
Publication date: 1971-07-20
Anticipated expiration: 1988-07-20

Abstract

Described is a small, lightweight ferrite phase shifter, constructed in a strip line wave energy transmission assemblage, which is small enough to fit into a steerable antenna array while at the same time providing good electrical isolation between adjacent phase shifters in the array.

Description

I United States Patent 1 13,594,812

[72] Inventors Daniel C. Buck (SUI Field 0! Search 343/854; Hanover; 333/3l.24 l, 84 Theodore M. Nelson. Cntonsville; Robert A. I Moore, Severna Park, Md.; Leonard Refefellm cued Dubrowsky. East Meadow. N.Y. UNITED STATES PATENTS p 841.447 3,225.318 12/ 1965 Heithaus 333/241 x 1 Flled b 1 3,289.115 1111966 Carr 333/31 July 20, 197 1 Westinghouse Electric Corporation Pittsburgh, Pa.

[45] Patented [73] Assignee {54] STRIP LINE FERRITE PHASE SHIFI'ER I3 Claims,5 Drawing Figs.

[52] U.S.Cl 1 343/854, 333/3l,333/84 [51] lnt.Cl....m H .1 H03h7/36,

Primary Examiner-Herman Karl Saalbach Assistant Examiner-Marvin N ussbaum Attorneys-F. H. Henson and E. P. Klipfel ABSTRACT: Described is a small, lightweight ferrite phase shifter, constructed in a strip line wave energy transmission assemblage, which is small enough to fit into a steerable antenna array while at the same time providing good electrical isolation between adjacent phase shifters in the array.

PATENTED JUL20 15m LEONARD DUBROWSKY wf W W Ar arnev STRIP LINE FERRITE PHASE SHIFTER BACKGROU ND OF TH E INV ENTION The present invention is particularly adapted for use in applications such as fixed antenna systems employing a plurality of radiating elements which are electronically scanned. That is, by varying the phases of the respective signals fed to the individual radiating elements, the composite radiated beam can be caused to scan back and forth without mechanical move ment of the antenna itself.

Such electrically steerable antenna arrays have been made using diode or ferrite phase shifters, but generally have been limited to applications in which the beam is steered in a stepwise or digital manner. In certain types of radar installations, such as pulse doppler radar, however, step scanning imposes severe limitations on performance Accordingly, a means for providing a continuously scanning beam is highly desirable for such applications. Diode phase shifters can be ruled out for continuous scanners, since the diodes are used basically as switches rather than as variable reactances. On the other hand, ferrite phase shifters can be utilized to effect an analog variation in phase shift. Such devices usually comprise a slab of ferrite material disposed in a waveguide, together with an external permanent magnet or electromagnet which produces lines of flux which pass through the walls of the waveguide and the ferrite body itself. By varying the strength of the magnetic field, the phase shift caused by the ferrite slab can be varied.

In order to pack such ferrite phase shifters into a halfwavelength spaced antenna array, for example, each individual phase shifter must be small in cross section. This can be most readily achieved by using a TEM mode wave, in which case both the electric and magnetic vectors are perpendicular to the direction of wave propagation and the device cross section does not enter into the performance via a cutoff frequency. One type of configuration giving a TEM propagation in ferrites is a ferrite loaded coaxial line. This construction has the advantages of a cylindrical coil, minimum volume, and easy shield construction; however the ferrites are extremely expensive to form. That is, the center conductor of the coaxial line must extend through the body of ferrite, but since one cannot readily bore a deep thin hole in ferrite, it must be halved, resulting in wasted material. Furthermore, even if the cylinder is cut in half, cutting slots in the resulting half cylinders to provide a bore for the center conductor is expensive when it is desired to make the phase shifters identical or reproducible.

SUMMARY OF THE INVENTION As one object, the present invention seeks to provide a miniature ferrite phase shifter which is usable for phased antenna array applications and which optimizes the figure of merit for TEM mode propogation, but which does not present the aforesaid difficulties experienced in attempting to form a bore in a ferrite-loaded coaxial line.

More specifically, an object of the invention is to provide a phase shifter of the type described comprising a strip line transmission line interposed between slabs of ferrite and sur rounded by a metallic layer comprising a ground plane. With this configuration, no problems are encountered in attempting to bore holes in ferrite slabs or in cutting slots therein.

Still another object of the invention is to provide a miniaturiled ferrite phase shifter which incorporates, as integral elements, a dipole antenna, a surrounding electromagnetic coil and shield, and a manifold connection for connecting the phase shifter to the end ofa strip line transmission line.

In accordance with the invention, a ferrite phase shifter is provided comprising a strip line conductor sandwiched between a pair of ferrite slabs, together with a layer of metallic material surrounding the ferrite slabs and comprising a ground plane. An electromagnetic coil surrounds the layer of metallic material and is adapted to produce a magnetic field extending along the length of the strip line. Finally, a magnetic shield of magnetically permeable material surrounds the coil and can be connected to the ground plane.

Preferably, the layer of metallic material surrounding the ferrite slabs also acts as a heat sink; while the shield surrounding the coil is provided with tabs at both ends thereof on opposite side walls thereof to intercept all magnetic flux and prevent crom coupling from one phase shifter to the other. With this arrangement, one element of a dipole antenna can be connected to the grounded metallic layer of heat sink surrounding the ferrite slab, while the other element of the dipole antenna can be connected to one end of the strip line conduc' tor, thereby providing an integral package containing both the dipole antenna and the phase shifter.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a partially broken-away elevational view of the ferrite phase shifter of the invention;

FIG. 2 is a top view of the phase shifter shown in FIG. I;

FIG. 3 is an end view of the phase shifter shown in FIG. 1;

FIG. 4 is an isometric view ofa partial section of an antenna array utilizing the phase shifters of the invention; and

FIG. 5 is an illustration of still another embodiment of the invention utilizing permanent magnets in combination with an electromagnetic coil.

With reference now to the drawings, and particularly to FIGS. 1-3, the phase shifter shown includes a central strip line conductor 10 sandwiched between a pair of elongated fe r rite slab I2 and I4 which may typically have a thickness of about one-sixteenth inch each. The central strip line conduc tor may be deposited on one of the two

slabs

12 or 14 by one of several possible means, such as evaporation, electroplating, or by using metal foil. Evaporation techniques are attractive for integrated circuits, where the phase shifters are treated as components in a microwave large scale integrated circuit, comprising, for example, a row of elements with their feed manifold in an antenna array.

The ferrite slabs I2 and M are disposed, throughout most of their length, within a surrounding metal layer comprising a lower generally Ushaped member 16 and an upper cover I8. The surrounding metallic layer comprising members 16 and 1B is formed from electrically conductive material and makes up the outer conductor or ground plane of the TEM line. An alternate method is to electroplate the outside of

members

12 and 14 with a suitable conductor such as copper. As shown, it is connected to

flange members

20 and 22 at opposite ends of the phase shifter assembly, these flange members also being grounded. At the same time, the members 16 and I8 surrounding the

ferrite slabs

12 and 14, together with the

end flanges

20 and 22, act as a heat sink for the heat generated by the ferrite lIl absorbing wave energy passing through the phase shifter. Surrounding the heat sink consisting of elements l6 and 1B, and between the flanged

members

20 and 22, is an electromagnetic coil 24 having leads 26 and 28 adapted for connection to a source of electrical energy, not shown.

Finally, surrounding the coil 24 and supported on the

flanges

20 and 22 is an outer cover or shield 30 formed from magnetically permeable material and which shields adjacent phase shifters 32 one from the other in the antenna array of FIG. 4, for example. In this respect, the center conductor or strip line 10 can be bend downwardly as at 34 to provide one element of a dipole antenna; while a second strip of conductive material 36 can be secured to the upper ferrite slab 12 as well as the flange 20, such that it is grounded. The ends of the ferrite slabs I2 and I4 at the other end of the phase shifter are adapted to receive the opposing

ground plane conductors

38 and 40 of a strip line wave transmission line having a center conductor it which contacts the strip line 10 of the ferrite phase shifter and is disposed between electric slab 42 and 44.

Because of the proximity of the phase shifters in the electronically scanned phased array of FIG. 4, for example, it is essential that each phase shifter be magnetically shielded from its neighbors in order to prevent magnetic interaction and resultant phase error. This, of course, is the purpose of the shield shown in FIGS. 1-3. The shield must also provide room for the input and antenna couplings and, therefore. cannot completely surround the phase shifter in these areas. The design employed in accordance with the present invention and shown in FIGS. 1-3 furnishes both excellent shielding and space for the couplings. As can be seen, the shield completely surrounds the solenoid.

Tabs

46 and 48 at the top and bottom of the shield protrude beyond the ferrite slabs l2 and 14 parallel to and wider than the broadwall of the ferrite. providing a low reluctance path intercepting almost all flux lines at this end of the phase shifter. At the antenna end, tabs of such length would interfere with the radiated signal. Therefore, the

shielding tabs

50 and 52 at the forward end of the phase shifter are not as long as those at the opposite end. Again, such a design provides a low reluctance path for most of the magnetic flux.

A modification which reduces average coil power is shown in FIG. 5 wherein elements which correspond to those shown in FIGS. 1-3 are identified by like reference numerals. The device is as before, but includes a set of

permanent magnets

54 and 56 which provide at opposite ends of the ferrite slabs a bias field of roughly half the maximum field required for maximum phase shift. Since the applied field is proportional to coil current, and coil power is proportional to coil current squared on a time average, a given antenna element sweeping through all coil current levels will experience a 4 to l reduction in lR losses by using the bias magnets.

TEM strip line ferrite phase shifters of the type disclosed herein have been built with excellent results. A 400 phase shift has been obtained with a coil power of only one-fourth watt and an insertion loss under l .34 d. giving a figure of merit of 300. VSWR is under L311.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. A ferrite phase shifter for electromagnetic wave energy comprising a strip line conductor sandwiched between a pair of ferrite slabs, a casing of metallic material surrounding said ferrite slabs and comprising a ground plane, an electromagnetic coil surrounding said casing and adapted to produce a magnetic field extending along the length of said strip line conductor, and a magnetic shield of magnetically permeable material surrounding said coil and connected to said ground plane.

2. The ferrite phase shifter of claim 1 wherein wave energy travels along said strip line conductor in the TEM mode.

3. The ferrite phase shifter of claim 1 wherein said casing of metallic material, said coil and said shield are generally rectangular in cross section.

4. The ferrite phase shifter of claim I wherein said shield is provided with tabs at at least one end thereof extending beyond said ferrite slabs.

5. The ferrite phase shifter of claim 3 wherein said shield is provided with tabs at both ends thereof on opposite sidewalls thereof.

6. The ferrite phase shifter of claim 5 including a dipole antenna at one end of the phase shifter, one element of the dipole antenna being connected to said casing and the other element of the dipole antenna being connected to one end of said strip line conductor at said one end of the phase shifter.

7. The ferrite phase shifter of claim 6 including a strip line transmission line connected to said phase shifter with the center conductor of the transmission line in engagement with the strip line conductor sandwiched between said ferrite slabs.

8. The ferrite phase shifter of claim? wherein the ground planes of said strip line transmission line are in engagement with said casing of metallic material surrounding said ferrite slabs.

9. The ferrite phase shifter of claim 2 including permanent magnets at opposite ends of said ferrite slabs, said coil being interposed between said permanent magnets.

10. The ferrite phase shifter of claim 9 wherein said permanent magnets produce a north pole at one end of said ferrite slabs and a south pole at the other end of the ferrite slabs.

ll. The ferrite phase shifter ofclaim 1 wherein said casing is provided with flanges at opposite ends thereof and said shield is wound around and connected to said flanges, said casing and flanges acting as a heat sink.

12. The ferrite phase shifter of claim 6 wherein said other element of the dipole antenna is integral with said strip line conductor.

13. The ferrite phase shifter of claim 6 wherein said one element of the dipole antenna is integral with said casing and said other element of the dipole antenna is integral with said strip line conductor.

Claims

4. The ferrite phase shifter of claim 1 wherein said shield is provided with tabs at at least one end thereof extending beyond said ferrite slabs.

8. The ferrite phase shifter of claim 7 wherein the ground planes of said strip line transmission line are in engagement with said casing of metallic material surrounding said ferrite slabs.

9. The ferrite phase shifter of claim 1 including permanent magnets at opposite ends of said ferrite slabs, said coil being interposed between said permanent magnets.

11. The ferrite phase shifter of claim 1 wherein said casing is provided with flanges at opposite ends thereof and said shield is wound around and connected to said flanges, said casing and flanges acting as a heat sink.