US3707688A - High frequency gyromagnetic device employing slot transmission line - Google Patents

Abstract

A high frequency gyromagnetic electromagnetic wave transmission device has a symmetric structure including planar high frequency energy conductors defining a wave guiding slot, the conductors being based on a dielectric substrate and covered by a similar superstrate, in which the dielectric strata are formed with gyromagnetic toroids which may be excited to produce static magnetic bias fields for the control of the velocity of propagation of high frequency energy along the transmission device.

Description

United States Patent Robinson et a1.

[i 3,707,688 [4 1 Dec. 26, 1972 [54] HIGH FREQUENCY GYROMAGNETIC DEVICE EMPLOYING SLOT TRANSMISSION LINE [72] Inventors: Gerald H. Robinson, Dunedin; Harry F. Strenglein, Clearwater, both of Fla.

[73] Assignee: Sperry Rand Corporation [22] Filed: March 31, 1971 [21] Appl. No.: 129,749

' [52] US. Cl. ..333/24.1, 333/84 R [51] 'Int. Cl. ..H01p l/32 [58] Field of Search ..333/l.1, 24.1, 24.2, 84 M,

[56] References Cited UNITED STATES PATENTS 3,237,130 2/1966 Cohn ..333/10 3,602,845 8/1971 Agrios ..333/24.1 3,350,663 10/1967 Siekanowicz et al ..333/1.1

11/1966 Neckenburger ..333/24.2 11/1970 Freibergs ..333/31R OTHER PUBLICATIONS Robinson et al., Slot Line Application To Miniature Ferrite Devices, IEEE Trans. on M'IT, Dec. 1969, p. l097-1 101.

Primary Examiner-Paul L. Gensler Attorney-S. C. Yeaton [5 7] ABSTRACT A high frequency gyromagnetic electromagnetic wave transmission device has a symmetric structure including planar high frequency energy conductors defining a wave guiding slot, the conductors being based on a dielectric substrate and covered by a similar superstrate, in which the dielectric strata are formed with gyromagnetic toroids which may be excited to produce static magnetic bias fields for the control of the velocity of propagation of high frequency energy along the transmission device.

1 Claim, 4 Drawing Figures PATENTEI] UECPB I972 33. 707,688

sum 2 0F 2 FERRIMAGNETIC LAYER FIG.4.

I/VI/E/VTORS GERALD H. POBHVSO/V HARRY F. STRENGLEl/V Z1 TTOR/VEY FERRlMAGNETlC LAYER HIGH FREQUENCY GYROMAGNETIC DEVICE EMPLOYING SLOT TRANSMISSION LINE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to gyromagnetic devices of the type for controlling electromagnetic wave transmission of energy bound to high frequency energy transmission lines and more particularly relates to a symmetl ric planar slot wave transmission system including gyromagnetic media for controlling the velocity of propagation of the high frequency electromagnetic energy.

2. Description of the Prior Art The operation of gyromagnetic materials such as are used in high frequency energy transmission devices is based upon an interaction between electron spins aligned by a magnetic bias field and the magnetic field of the propagating electromagnetic wave. The interaction develops when the bias and high frequency magnetic fields have components that are orthogonally oriented. Under these conditions, the magnetic bias field may affect the electromagnetic wave either reciprocally or non-reciprocally, depending on the polarization of the high frequency electromagnetic wave. Non-reciprocity usually requires a circularly polarized wave, although certain devices utilize the principle of Faraday rotation to obtain non-reciprocal operation with linearly polarized waves. Reciprocal operation, however, requires a linearly polarized electromagnetic wave orthogonally oriented with respect to the magnetic bias field.

The operation of gyromagnetic devices also depends on the magnitude of the bias magnetic field. If the magnitude of the bias field is set at a value below the gyromagnetic resonance level, the interaction between the bias and high frequency magnetic field produces a change in the phase velocity of the electromagnetic wave as it propagates through the gyromagnetic material. When the magnitude of the bias fields in increased to the gyromagnetic resonance level, a reciprocal phase shifter functions as an attenuator or as a reciprocal loss device and a non-reciprocal phase shifter functions as an isolator or non-reciprocal attenuator.

Beside the polarization of the high frequency electromagnetic wave and the magnitude of the bias magnetic field, the intrinsic characteristics of the gyromagnetic material are also significant in determining the nature of operation of gyromagnetic circuit component. Materials having a square hysteresis loop magnetization characteristic readily retain their magnetization. Such materials, when constructed in the form of toroids having closed magnetic paths, have been found useful, for example, in digital latching phase shifters. Other materials which do not have square hysteresis loop characteristics are not capable of maintaining their magnetization. These materials are particularly useful, for example, in continuously variable phase shifters and single side band modulators.

Reciprocal latching digital phase shifters utilize toroids made of gyromagnetic material and may operate by switching between two different magnetization states to provide two discrete values of phase shift. These phase shifters are switched by means of current pulses flowing through an electrical conductor threading the toroid aperture. The switching may be between two magnetization states of unequal magnitude or polarity in a single flux path (known as magnitude or collinear switching), or between two remanent magnetization states in different but intersecting flux paths (known as orthogonal or non-collinear switching). The orthogonal switching technique is free of certain limitations inherent in the magnitude switching technique which unduly complicate the driver equipment and restrict the maximum switching rate. For such reasons, orthogonal switching is often used in practice.

Prior art reciprocal latching types of digital phase shifters employing orthogonal switching techniques generally comprise garnet or ferrite toroidal elements with one or more apertures having an axis of symmetry transverse to the direction of the electromagnetic wave propagation and another aperture having a longitudinal axis of symmetry parallel to the direction of the electromagnetic wave propagation. These devices have been used within transmission line systems wherein the center conductor of the transmission line threads the longitudinal aperture. Besides being restricted to such transmission line systems, these prior art configurations provide closed magnetic paths about the longitudinal aperture that seriously impair latching and fast switching capabilities.

Absent in the prior art are phase control or phase shifting devices fully suitable for direct incorporation into high frequency and microwave integrated circuits. Thus, the inexpensive techniques currently used in manufacture of microwave integrated circuits have not been beneficially applied in integrated circuits requiring phase shifters. The prior art has thus not benefitted by the use of planar balanced phase shifter configurations permitting fully efficient interaction between the controlling bias magnetic field and the high frequency propagating wave energy it is to control. Further, prior art devices generally are characterized by lack of symmetry and permit undesired coupling between the conductors for magnetizing the gyromagnetic material and the high frequency fields they are to control.

SUMMARY OF THE INVENTION The present invention relates to gyromagnetic electromagnetic wave propagation control devices of the type for controlling a characteristic of electromagnetic energy transmission in high frequency transmission lines. The wave propagation control device comprises a symmetric structure including planar high frequency energy conductor strips for defining a wave guiding slot. On each side of the plane of the conducting strips is placed a layer of a gyromagnetic substance in the fonn of a garnet or ferrite material. Formed within the gyromagnetic layers are toroidal magnetic circuits which may be excited for producing cooperating static bias magnetic fields. The latter fields are arranged to interact cooperatively with the gyromagnetic material, altering the phase velocity of propagation of electromagnetic energy along the energy transmission device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view partially in cross section of a balanced slot transmission line as employed in the present invention and showing the character of the fields of electromagnetic waves propagated therein.

FIG. 2 is a perspective view of a modified portion of the transmission line of FIG. 1 showing one means for coupling electromagnetic waves thereto.

FIG. 3 is a cross section view of the embodiment of FIG. 4 taken along the lines 3-3 thereof.

FIG. 4 is a perspective view partially in cross section of a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Slot transmission line planar wave guides, as known in the prior art, consist of a slot or extended gap dividing a conductive coating situated on one side of a dielectric or ferrimagnetic substrate into two portions, the other side of the substrate generally being bare. With a substrate of suitably high permittivity, the mode of excitation of the slot transmission line is such that the traveling wave is closely bound to the region immediately adjacent the slot and radiation is minimized. The oscillating electric field extends generally from one edge of the slot to the other; the oscillating magnetic field lies generally in a plane perpendicular to the slot. The dominant propagation mode is generally like the TE, mode of propagation in rectangular wave guide.

Most important, the propagating electromagnetic wave has elliptically polarized high frequency magnetic field regions as are required for use in microwave gyromagnetic or ferrimagnetic devices, as in nonreciprocal microwave devices. The polarized regions are more effectively available than in other types of transmission lines. For example, in the case of microstrip transmission line, the meander line configuration must be used to provide regions of elliptical polarization. However, in that structure, only a small part of the total transmission line exhibits elliptical polarization which therefore interacts inefficiently with the gyromagnetic or ferrimagnetic material. It is observed that characteristic impedance and phase velocity vary rather slowly with frequency in slot line.

While a complete system of slot line microwave components may be constructed as a microwave integrated circuit using only slot transmission line as the interconnecting agency, there are available in the prior art transition elements between slot line and more conventional wave guiding elements, such as broad band transition between slot line and coaxial line. Unlike microstrip, slot line does not require the use of a grounding plane. Furthermore, slot line is also readily constructed by applying thin metal films to one side of a substrate and then using conventional photo-etching procedures to form the slot.

In the present invention, the balanced slot transmission line of FIG. 1 is employed; the planar high frequency energy conducting strips 1, 1a are sandwiched between dielectric layers 2, 2a in a manner such as to leave an empty slot 3, in the geometrical center of the laminated structure. So as to minimize radiation and to confine the propagating energy closely bound to slot 3, the material selected for layers 2, 2a preferably has a high dielectric constant and slot 3 is made relatively narrow. In this manner, the ratio of guided to free-space wave length may be 0.4 or smaller, though other ratios may be used.

For convenience, the character of the traveling electric field E is represented in FIG. 1 at the input plane 4 of the transmission line at an arbitrary time. The electric field E lines form a symmetric pattern about the slot 3, leaving the upper surface of conducting strip 1 at right angles thereto and some passing through dielectric layer 2 to intersect the upper surface of conducting strip la again at right angles to the latter. Other portions of the electric field symmetrically leave and reenter the upper surface of dielectric layer 2 before terminating on strip 1a. The electric field E pattern has mirror image symmetry above and below the plane of conducting strips 1, la.

In a similar manner, the traveling magnetic field H is shown at an arbitrary time and position with respect to the above representation of the electric field E. The magnetic fields form closed loops passing through the slot 3. The fields are symmetrical about the plane of the conducting strips 1, 1a and are normal to this plane where they pass through it.

It will be understood that the balanced slot transmission line may readily be constructed by using any of several techniques already established for the construction of the various types of planar transmission line, including microstrip transmission line. For example, a suitable dielectric substrate layer 2a may have formed on its surface by vacuum or electroless deposition of copper, silver, or gold a conducting thin layer from which slot 3 may be removed by conventional mechanical or etching processes, thus forming appropriately separated conducting strips 1, la. To complete the symmetric layered structure, the second dielectric layer 2 may be placed on top of the upper surfaces of conducting strips 1, la and may be held in place by conventional fasteners or by a suitable adhesive material.

The dielectric material of layers 2, 2a may be any conventional high dielectric constant material such as conventionally used in microwave integrated circuit technology. Dielectric constants on the order of 16 are often employed. Gyromagnetic or ferrimagnetic materials are found particularly suited when the balanced slot transmission line is to be employed in devices such as electronically adjustable phase shifters. Substances such as yttrium gadolinium iron garnet, including aluminum or dysprosium substituted yttrium gadolinium iron garnet, may be employed. Such materials are described by G. R. Harrison and L. R. Hodges in the US. Pat. No. 3,l32,l05 for Temperature Compensated Yttrium Gadolinium Iron Garnets, issued May 5, 1964 and assigned to the Sperry Rand Corporation. Certain other ferrimagnetic materials, such as aluminum or manganese substituted lithium ferrites also have adequate temperature stability, square magnetization loop characteristics, and microwave propagation properties.

As noted previously, large scale microcircuits may be constructed using balanced slot transmission line; furthermore, it may be readily coupled to conventional non-balanced slot line or to other types of planar or other wave guides. FIG. 2, for example, illustrates a transition from a balanced slot line comprising conductive strips 1, la and dielectric sheets 2, 2a to a nonbalanced section of slot line where both strip conductors 1, la are present, but only dielectric layer 2a is present. A conventional matched transition from the non-balanced slot line section to a coaxial line having concentric conductors 7, 7a may then be made, with outer conductor 7 soldered at 8 to conducting strip 1 or affixed thereto by a conducting epoxy cement. Inner conductor 7a is bent downward to provide a conducting region which may be soldered at 8a to conducting strip la. Other types of matched transitions have been described in the literature for coupling non-balanced slot and microstrip transmission lines directly through one layer of dielectric substrate. The transition or coupling junction is formed by having the microstrip line cross above the slot at right angles thereto, the dielectric layer being interposed between the lines. The end of the microstrip line adjacent the coupling junction is open-circuited one quarter of a wave length from the coupling junction and the slot is short-circuited one quarter of a wave length from the coupling junction.

FIGS. 3 and 4 illustrate an embodiment of the invention in the form of a balanced slot transmission line phase shifter. In FIGS. 3 and 4, the wave guiding function of the apparatus associated with slot 13 comprises conducting strips 11, 11a forming a layer separating ferrimagnetic dielectric layers 12, 12a. Elements 1], 11a, 12, 12a, and 13 cooperate in propagating electromagnetic energy in the same manner as the corresponding respective elements 1, la, 2, 2a, and 3 of FIG. 1. However, ferrimagnetic elements 12, 12a are each modified to form magnetic circuit toroids one above the other in a region which performs the phase shifting function. It will be recognized that various means may be employed to inject high frequency energy into and to abstract it from the propagation structure of FIGS. 3 and 4, such as that of the arrangement of FIG. 2.

Since ferrimagnetic layers 12 and 12a are similar, the toroidal structure in the phase shifting region of only one of these elements requires description. As seen in FIG. 3, ferrimagnetic layer 12 is supplied with an interior hollow portion formed therein by any well known technique. For example, while it is preferred to make the magnetic toroid as an integral element, layer 12 may be made in two parts, one being flat and the other having a hollowed-out portion such that when the two parts are fixed together, the hollow region 20 is enclosed by ferrimagnetic material.

As seen in FIGS. 3 and 4, the hollow region 20 is almost completely filled with a sheet composed of nonmagnetic insulator material 21 which may have substantially the same dielectric constant as that of the ferrimagnetic material. The minor portion of hollow region 20 not filled by dielectric sheet 21 accommodates an electrical conductor wire 22 which extends longitudinally along one side of hollow region 20 generally parallel to the direction of electromagnetic energy translation and along substantially all of the toroidal or phase shifting region. Substantially at the ends of the toroidal region, the ends 23 and 24 of wire 22 are bent upwardly and project through holes drilled in the ferrimagneticlayer 12 so that these may be brought outside of the transmission line system for the supply of control signals to wire 22, as will be further described.

In a similar manner, the bottom ferrimagnetic layer 6 12a is provided with an interior hollow region 20a for accommodating a dielectric sheet 21a and a longitudinal wire 22a whose ends 23a, 24a pass through the lower or outer surface of ferrimagnetic layer 12a, where wire ends 23a, 24a are accessible for the supply of control voltages. The number and placement of wires such as wires 22 and 22a may vary from that shown, as may the relative size of the various parts of the phase shifter device. The supply of electrical signals to the wire ends 23, 23a, 24, 24a is such as to cooperate in producing a controllable amplitude static or biasing magnetic field of a particular sense in the ferrimagnetic layers 12, 12a immediately adjacent slot 13, thus controlling the velocity of propagation of energy down the slot transmission line system.

As in conventional high frequency transmission line phase shifters, any of several types of conventional driving circuits, including analogue or digital circuits, may be employed to supply currents to wires 22, 22a, including single bit and multiple bit driver circuits. In the single bit driver combination, for instance, bias magnetic fields in the toroids of ferrimagnetic layers 12, 12a are erased by a relatively massive current impulse before each commanded setting to saturate the ferrimagnetic material fully and to eliminate all memory of its previously held states; it is then set by the driver circuit to a predetermined unsaturated state by a current pulse calibrated according to the commanded phase shift. Other types of drivers do not drive the material into saturation. Since the particular type of driver current source to be employed does not necessarily constitute a part of the present invention, and since conventional driver circuits may satisfactorily be employed, a detailed description of such driver circuits is not required herein.

It is seen that the invention is a novel high frequency phase control or phase shifting device using a balanced slot transmission line loaded symmetrically by ferrimagnetic circuit toroids. The relative phase of high frequency energy may be varied by changing the level or the direction of the magnetization of the toroids. The composite structure may be housed in a suitable enclosure and coupled to a variety of input-output transmission line types. Particularly advantageous is the fact that the structure of the slot line wave propagating and phase shifting system lends itself readily to the use of known techniques now used in the manufacture of microwave integrated circuits. The symmetry of the system desirably improves efficiency and reduces total size. Latching operation is efficient and the conductors for magnetizing the magnetic circuit toroids are isolated from the high frequency fields they are to control. Driver design is simplified and performance improved. Linear characteristics are readily achieved.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departure from the true scope and spirit of the invention in its broader aspects.

We claim:

1. A compact high frequency energy phase shifter comprising:

first and second planar high frequency current conducting means lying in a common plane and having a narrow gap therebetween for propagating traveling high frequency electric fields therein,

first and second gyromagnetic means symmetrically electrical conductor means within said thin substantially rectangular closed cavity means lying therein substantially parallel to the direction of high frequency field propagation within said narrow said electrical conductor means respectively having extension means passing through said fractional part of said respective gyromagnetic means for the purpose of forming respective pairs of electrical terminal means exterior thereof, and

high frequency energy coupler means coupled in high frequency energy exchanging relation to said first and second high frequency current conducting means at least at one end thereof spaced from said fractional part of said gyromagnetic means.

Claims (1)

1. A compact high frequency energy phase shifter comprising: first and second planar high frequency current conducting means lying in a common plane and having a narrow gap therebetween for propagating traveling high frequency electric fields therein, first and second gyromagnetic means symmetrically disposed on opposed sides of said high frequency current conducting means in contiguous relation therewith for substantially covering same while enclosing said narrow gap, each said gyromagnetic means comprising a temperature stable ferrimagnetic material and having thin enclosed substantiallyrectangular closed cavity means lying substantially parallel to and spaced symmetrically from said common plane and being substantially filled with non-magnetic material having a dielectric constant substantially equal to the dielectric constant of said ferrimagnetic material for defining closed magnetic circuit means in a fractional part of said gyromagnetic means, electrical conductor means within said thin substantially rectangular closed cavity means lying therein substantially parallel to the direction of high frequency field propagation within said narrow gap, said electrical conductor means respectively having extension means passing through said fractional part of said respective gyromagnetic means for the purpose of forming respective pairs of electrical terminal means exterior thereof, and high frequency energy coupler means coupled in high frequency energy exchanging relation to said first and second high frequency current conducting means at least at one end thereof spaced from said fractional part of said gyromagnetic means.

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