US3553733A

US3553733A - Transverse electromagnetic devices for ferrite loaded planar circuits

Info

Publication number: US3553733A
Application number: US802353A
Authority: US
Inventors: Daniel C Buck
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1969-02-26
Filing date: 1969-02-26
Publication date: 1971-01-05
Anticipated expiration: 1988-01-05

Abstract

DESCRIBED IS AN INTERGITITAL WAVE CIRCUIT DEPOSITED ON A FERRITE FILM AND HAVING A DIRECT CURRENT MAGNETIC FIELD APPLIED IN THE PLANE OF THE INTERDIGITAL CIRCUIT TO PROVIDE A MICROWAVE DEVICE EMPLOYING GYROMAGNETIC MEDIA FOR PHASE SHIFT, FREQUENCY TRANSLATION, CIRCULATION AND THE LIKE.

Description

' Filed Feb. 26, 1969 Jan. 5,1971 c, BUCK 3,553,733

' TRANSVERSE ELECTROMAGNETIC DEVICES FOR FERRITE LOADED PLANAR CIRCUITS 2 Sheets-Sheet 1 PHASE SHIFT Fig. 2

INVENTOR,

DANIEL C. BUCK ATTORNEY Jan- 5, 1971 D. c. BUCK 3,553,733

TRANSVERSE ELECTROMAGNETIC DEVICES FOR FERRITE LOADED PLANAR CIRCUITS Filed Feb. 26, 1969 2 Sheets-Sheet 2 INVENTOR.

DANIEL C. BUCK Fig.5

Arromvzr United States Patent US. Cl. 343854 8 Claims ABSTRACT OF THE DISCLOSURE Described is an interdigital wave circuit deposited on a ferrite film and having a direct current magnetic field applied in the plane of the interdigital circuit to provide a microwave device employing gyromagnetic media for phase shift, frequency translation, circulation and the like.

Ferrite phase shifters are now well known and usually comprise a slab or rod of ferrite material disposed in a wave guide, together with an external permanent magnet or electromagnet which produces lines of flux which pass through the walls of the wave guide and the ferrite body itself. By varying the strength of the magnetic field, the phase shift caused by the ferrite slab can be varied.

Wave guide systems and conventional ferrite phase shifters, however, are somewhat bulky, particularly in applications such as electronically scanned fixed antenna systems employing a plurality of radiating elements whose phases are electronically varied. 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 movement of the antenna itself. Due to the spacing between and weigh too much in the case of airborne antennas.

In an effort to reduce the size of Wave transmission lines, microstrip planar devices have been developed which comprise an insulating dielectric slab sandwiched between a metallic strip conductor and a ground plate. Efforts have been made to provide microstrip ferrite phase shifters for such devices wherein a ferrite film is deposited on a substrate, and the substrate with the ferrite film positioned between the upper and lower conductors of the microstrip planar transmission line. Unfortunately, mechanically deposited ferrite films are most easily deposited on ceramic substrates. This is a disadvantage in microstrip planar miniaturized devices since the ceramic substrate occupies most of the space between the ground plane and the periodic wave circuit. This reduces the available phase shift substantially in proportion to the amount of dielectric in the microstrip circuit.

SUMMARY OF THE INVENTION As an overall object, the present invention seeks to provide a planar transverse electromagnetic circuit which can be used for both reciprocal and non-reciprocal devices and which has the property of having both conductors in a common plane. In this manner, the device becomes extremely compact.

Another object of the invention is to provide a planar interdigital wave circuit on a ferrite film, deposited on an insulating substrate, and having a direct current magnetic field applied in a direction substantially parallel to that of the digits.

In accordance with the invention, a phase shift device for electromagnetic wave energy is provided comprising a ferrite film deposited on an insulating substrate, strip conductors deposited on the ferrite film and forming an interdigital circuit, and means for inducing lines of magnetic flux in the ferrite film to thereby vary the phase of microwave energy passing through the interdigital circuit.

Preferably, the insulating substrate comprises a ceramic, while the electrical conductors are deposited on the ferrite in a photoresist etching technique similar to that used in the manufacture of printed circuits. Each interdigital circuit comprises a pair of parallel conductors having conductors at right angles thereto which project into the space between the parallel conductors alternately from one parallel conductor and then the other to provide a serpentine path for wave energy passing through the device. By applying a magnetic field t0 the ferrite film along the length of the interdigital circuit, and by varying the magnitude of this magnetic field, variable phase shift of microwave energy passing through the device can be achieved.

In one embodiment of the invention shown herein, interdigital lines formed on a ferrite film are fed in balanced pairs from coaxial lines. Each interdigital line can then be used as an array type phase shifter element; and each coaxial line can drive two antenna elements and, therefore, act as a two-fold power splitter.

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 an isometric view of the phase shifting device of the invention;

FIG. 2 is a graph of insertion phase versus frequency for the circuit of FIG. 1;

FIGS. 3 and 4 illustrate a typical application of the phase shift circuit of the invention;

FIG. 5 shows the manner in which wave energy passes through the circuit of FIG. 3; and

FIG. 6 is an illustration of a plurality of phase shifters in a stacked array.

With reference'now to the drawings, and particularly to FIG. 1, the phase shift device shown comprises a sub strate 10, preferably formed from ceramic material and having a film or layer of ferrite material 12 deposited thereon. The film 12 is formed by depositing a mixture of nitrates of iron and other metals, such as magnesium or magnesium ferrites, in an alcohol solution on the substrate 10. The deposit is then air dried at several hundred degrees centigrade to boil out the organics. It is then fired in a carefully controlled, moderately oxidizing atmosphere to a temperature above about 900 C., and then cooled in an inert atmosphere. After the ferrite film- 12 is formed on the substrate 10, an interdigital circuit can be formed on the ferrite film by conventional photoresist etch techniques wherein the entire film 12 is covered with a copper film and then all but the desired circuit configuration etched away.

The interdigital circuit shown in FIG. 1 includes side strips or

conductors

14 and 16 extending along the length of ferrite strip 12. Projecting outwardly into the space between the

conductors

14 and 16 are strips 18-26 of c'onducting material. The

strips

18, 22 and 26, for example, are connected to the side strip 16 but not to the strip 14. Alternate ones of the

strips

20 and 24, in turn, are connected to the side strip 14 but not the strip 16. In this manner, a serpentine path for wave energy is provided wherein the electric vectors are parallel to the ferrite strip 12 while the magnetic vectors are at right angles to the strip. In this manner, a magnetic field applied parallel to the ferrite strip 12 (i.e., along the digits formed by strips 1826) can be used to effect a shift in the insertion phase of an electromagnetic wave passing through the interdigital circuit.

The dispersion properties of the circuit shown in FIG. 1 can be derived from its Brillouin diagram shown in FIG. 2 which plots frequency versus phase shift per section or digit, P, of the interdigital line. Analysis shows that in the frequency range near w the magnetic field of the applied electromagnetic wave is linearly polarized in the XY plane. Thus, an applied direct current field in the Z direction will cause phase shift. For frequencies near W the magnetic field will have a large circularly polarized component in the YZ plane. This requires that the direct current field be in the X direction. Thus, one can build either reciprocal or non-reciprocal devices based on the interdigital line. As will be understood, there are upper and lower limiting frequencies for an interdigital circuit of given dimensions. Above or below these limits, the circuit itself will radiate energy.

One such device is shown in FIGS. 3 and 4 where eight dipole antennas or radiating elements 28 are fed by four

coaxial transmission lines

30, 32, 34 and 36. Each coaxial transmission line comprises an inner center conductor 38 surrounded by an outer metallic cylindrical shell 40.

At the terminating ends of the coaxial transmission lines 3036 is a ferrite film 42 formed on a ceramic substrate 44 in the same manner as described in connection with FIG. 1. Taking the coaxial transmission line 36, for example, its center conductor 38 is connected to a longitudinal strip conductor 46, while the outer metallic shell 40 is connected to

longitudinal conducting strips

48 and 50 at points spaced 180 apart. With this arrangement, two interdigital circuits are formed, one between the

conductors

46 and 50 and the other between

conductors

46 and 48; the power from the coaxial line 36 being split between the two interdigital circuits. Furthermore, by providing a toroid 52 for each interdigital circuit shown in FIG. 4 and by energizing an electromagnetic coil 54 surrounding the toroid, a magnetic field will be generated in the ferrite in the area of a specific interdigital circuit (i.e., that between strip conductors 46 and 50) to vary the phase of the wave energy passing through that particular interdigital circuit. In this manner, it will be readily appreciated that the direction of propagation of the wave front from the radiating elements 28 can be made to scan to the left or right electronically.

The operation of the device of FIGS. 3 and 4 can perhaps best be understood by reference to FIG. 5. Within the coaxial transmission line, the electric vectors of the electromagnetic wave energy are radial; while the magnetic vectors, H, extend circumferentially around the center conductor 38. The wave fronts of the energy passing through the two interdigital circuits are indicated by the reference numerals and 22. The electric vector E are now parallel to the ferrite film while the magnetic vectors are, of course, at right angles thereto. Note that the two wave fronts are 180 out of phase with respect to each other. By applying an external magnetic field, H or H along the length of the ferrite strip, the phase of the electromagnetic wave energy can also be made to vary.

Instead of using an external magnetic field as illustrated in FIG. 4, for example, it is also possible in accordance with the invention to utilize a film of latchable ferrite material and to pass conductors through holes in the film. By reversing the flow of current through the conductors, various phase shift effects can be obtained.

Furthermore, it is possible to stack a plurality of interdigital circuits as shown, for example, in FIG. 6 where two

phase shifters

60 and 62 are stacked one above the other. Each phase shifter is connected to a plurality of 4

dipole antennas

64 or 66 and fed from coaxial transmission lines 68 or 70. The magnetic flux producing devices are, of course, not shown in FIG. 6.

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.

I claim as my invention:

1. A planar circuit transverse electromagnetic ferrite device for electromagnetic wave transmission systems, comprising a ferrite film deposited on a substrate, electrical strip conductors disposed on said ferrite film and forming an interdigital circuit, means for feeding wave energy to one end of said interdigital circuit, and means for inducing lines of magnetic flux in said ferrite film to thereby vary the characteristics of wave energy pushing through the interdigital circuit.

2. The ferrite device of claim 1 wherein said substrate comprises a ceramic material.

3. The ferrite device of claim 1 wherein said magnetic lines of flux are induced in said film in a direction extending along the digits of said interdigital circuit.

4. The ferrite device of claim 1 wherein said interdigital circuit comprises a pair of parallel conductors deposited along the length of said ferrite film together with stub conductors at right angles to said parallel conductors, said stub conductors being connected alternately to one and then the other of said parallel conductors to provide a serpentine path for wave energy passing through the interdigital circuit.

5. The ferrite device of claim 4 wherein at least two interdigital circuits are deposited on said ferrite film with a common center conductor forming one of the two parallel conductors for each interdigital circuit.

6. The ferrite device of claim 5 wherein the means for feeding wave energy to one end of each of the two interdigital circuits comprises a coaxial transmission line having its center conductor connected to said common center conductor and its surrounding shell connected to the remaining two parallel conductors at points spaced about apart around said outer shell.

7. The ferrite device of claim 6 wherein the ends of said parallel conductors opposite said coaxial transmission line are connected to dipole antennas.

8. The device of claim 7 wherein there are two substrates stacked one above the other, each of said substrates having ferrite films and interdigital circuits deposited thereon, dipole antennas connected to one end of each of the conductors of the stacked interdigital circuits, and coaxial transmission lines connected to opposite ends of the parallel conductors of the stacked interdigital circuits.

References Cited UNITED STATES PATENTS 3,418,605 12/1968 Hair et al 333-24.1 3,448,409 6/1969 Moose et al 333-84X 3,448,410 6/1969 Parks 33331 ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner U.S. Cl. X.R. 33324.l, 31, 73