US3684983A

US3684983A - High speed circulator switch

Info

Publication number: US3684983A
Application number: US47673A
Authority: US
Inventors: John J Cotter; Charles J Abronson
Original assignee: E&M LAB
Current assignee: E&M LAB
Priority date: 1970-06-19
Filing date: 1970-06-19
Publication date: 1972-08-15
Anticipated expiration: 1989-08-15

Abstract

Substantial improvements in the switching speeds of switchable ferrite devices for microwave transmission are realized by the utilization of a low inductance, low loss waveguide section having a principally non-metallic body and a microwave ferrite element, in conjunction with an electro-magnet that is operated by a switchable driver circuit that alternates between opposite polarities and includes means for storing inductive currents while reversing polarity during the switching interval. Such arrangements provide improvements of as much as several orders of magnitude in the switching times of practical microwave devices.

Description

United States Patent Cotter et al.

[ 51 Aug. 15, 1972 [54] HIGH SPEED CIRCULATOR SWITCH [72] Inventors: John J. Cotter; Charles J. Abronson,

both of Agoura, Calif.

[73] Assignee: E&M Laboratories [51] Int. Cl......H0lp 1/32, l-IO3k 17/64, H03k 17/66 [58] Field of Search .....333/l.l, 24.1, 24.2;307/255, 307/262; 217/1485, 151, DIG. 4, DIG. 6

3,340,484 9/ l 967 Siekanowicz et a1 ..333/24.l X 3,564,298 2/1971 Colino ..307/255 X Primary Examiner-Paul L. Gensler Att0mey-Fraser and Bogucki [57] ABSTRACT Substantial improvements in the switching speeds of switchable ferrite devices for microwave transmission are realized by the utilization of a low inductance, low loss waveguide section having a principally non-metallic body and a microwave ferrite element, in conjunction with an electro-magnet that is operated by a switchable driver circuit that alternates between op- [56] References cued posite polarities and includes means for storing induc- UNITED STATES PATENTS tive currents while reversing polarity during the switching interval. Such arrangements provide im- 3,104,361 9/ 1963 Leetmaa et al. ..333/1.1 movements of as much as Several Orders of magnitude 3301,45 8 8/1963 Chandler et '333/ X in the switching times of practical microwave devices. 3,400,304 9/1968 Ziegler ..307/255 X 3,324,418 6/ 1967 Caswell ..333/1.1 7 Claims, 3 Drawing Figures 52 2 RECTIFIER F 7 50 J 48 I 46 cmcnoa CURRENT POWER mus WA SUPPLY RECTIFIER MEANS 52 PAIENTEDAus 1 5 I972 3. 684 98 3 sum 1 OF 2 FIG.-l

RECTIFIER MEANS 26 3o 34 lav/isfiaRs CHARLES J. ABRONSON BY f JOHN J. coma A rroiaws vs PATENTEDAus 1 51912 SHEET 2 UF 2 FlG.-3

' INVENTORS CHARLES J. ABRONSON JOHN J. COTTER ATTO NEYS HIGH SPEED CIRCULATOR SWITCH Applications related to the present application and concurrently filed therewith are applications entitled High Speed Switching Circuit filed June 19, 1970,

Ser. No. 47,674, and Ferrite Microwave Device filed June 19, 1970, Ser. No. 47,676, both assigned to the assignee of the present application.

BACKGROUND OF THE INVENTION transmission. For faster speed operation and for electronic control, however, switchable ferrite devices have been adopted, and these have typically provided switching speeds in the millisecond range. The term switching is most widely used in terms of switching between opposite polarities of magnetization of the ferrite, so as to provide different directions of circulation in a microwave circulator, or different directions of isolation in an isolator device. The term also encompasses different levels of magnetization, such as may be utilized in digital phase shifter devices.

In the microwave ferrite switchable devices that are currently known for operation at the higher frequencies, such as X-band or K band, switching speeds have typically been limited to the millisecond range. These frequencies, which may be regarded as the middle and higher microwave frequencies, require field strengths of such magnitude that rapid reversal of a driver current for the electromagnet for the microwave ferrite imposes special demands. Circuit losses and transient effects with the heretofore known systems have prohibited the achievement of substantially faster switching times.

In this specific example of a microwave circulator for operation at frequencies greater than 7 gigaHertz, for example, it was sought to achieve microsecond switching times, constituting objectives almost three orders of magnitude more severe than existing ferrite microwave circulators could achieve. It was also required that such results be obtained with comparable insertion loss, VSWR and isolation to existing devices.

SUMMARY OF THE INVENTION Systems in accordance with the invention utilize a novel combination of waveguide construction, magnetic circuit path arrangement and switchable driver circuit in a ferrite microwave device to provide remarkable improvements in switching speeds. In general terms, the waveguide comprises a principally nonmetallic body of low inductance, low loss charachaving plated interior channels defining the waveguides, and incorporates ferrite pole pieces in the magnetic path with internal microwave ferrite elements, and with interposed dielectric discs between the pole piece ferrites and the microwave ferrites, the thin dielectric discs having conductive surfaces forming portions of the waveguide walls. The plated dielectric waveguide body provides the desired low inductance, low loss characteristic, while the pole piece, dielectric disc and microwave ferrite arrangement provides a high parallel Q magnetic circuit. In conjunction with this arrangement a high speed switchable driver circuit is utilized including capacitor means in parallel with the inductive coil for the electromagnet, a substantially constant current power supply, means for switching current from the power supply to the inductive coil with opposite polarities, with the capacitor means being connected to store inductive current during switching, and including rectifier means in series with the inductor for blocking current passage between the inductor and power supply during the switching time interval.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention may be had from the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a combined perspective view, partially broken away, and block diagram of a ferrite microwave device in accordance with the invention;

FIG. 2 is a side sectional view of the arrangement of FIG. 1, showing internal details thereof; and

FIG. 3 is a schematic diagram of the switchable driver circuit shown in block diagram form in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION A specific example of a high speed switchable ferrite microwave device in accordance with the invention is represented by the three port circulator 10 illustrated in FIGS. 1 and 2. A detailed description of the construction of this device is contained in co-pending application Ser. No. 47,676, filed June 19, 1970, to which reference has been previously made. In addition a detailed description of a switchable driver circuit 12 has been provided in the other patent application previously referred to and concurrently filed herewith, Ser. No. 47,674, filed June 19, 1970. Accordingly, for brevity and clarity only the principle coacting elements and relationships of the high speed circulator system will be described in the present application. It is to be noted that the principles and features of the present invention may be utilized in a wide variety of contexts and with other wave transmission devices.

With reference to FIGS. 1 and 2, the three port circulator 10 comprises a non-metallic body that in this instance is defined by a body base element 14 having sides defining portions of sides of an equilateral triangle and three channels of substantially rectangular form extending radially outwardly in a plane normal to a central axis for the circulator 10. The circulator body is completed by a top element 16 that closes off the channels to define a substantially symmetrical three port circulator device. As is well known, the circulator device can be somewhat asymmetrical, having waveguides or wave transmission of 'l configuration, for example, or

may have four or more symmetrically disposed ports. The internal magnetic path including the ferrite structure is disposed along the central axis of the circular and an external C-shaped electromagnet core 20 having an adjacent winding 22 is disposed with its opposite pole tips in magnetic circuit with the internal ferrite structure along the central axis. The winding 22 is here wrapped about the core 20 and energized to provide a selected field strength in the internal ferrite region by current of either polarity provided from the switchable driver circuit 12.

The

body elements

14, 16 of the circulator are principally non-metallic in character, having glass fiber reinforcement within a diallyl iso-phthalate matrix, with the two parts being molded separately, and the mating surfaces and internal walls of the waveguides being machined as necessary. Thus the base element 14 and the top element 16 are essentially dielectric members having very low inductance, and include upper and lower pole piece apertures 24, 26 respectively along the central axis. The internal surfaces of the rectangular waveguides are conductively plated with a relatively thin plate, a 00002-00005 inch layer of gold plating being used in the present example, and extended outwardly to form a small margin about the exterior of the waveguide terminal, on the side face of the circulator 10. For better wear and handling properties, metal flange elements (not shown) may be attached to each of the triangular sides of the circulator 10.

Within the circulator body, upper and lower pole pieces 28, 30 are disposed within the pole piece apertures 24, 26 respectively, the pole pieces here being of the ferrite material for low eddy current and low hysteresis loss characteristics. The internal ferrite structure includes a pair of microwave ferrite elements 32, 34 of generally triangular configuration and separated by an interior dielectric loading element comprising a Teflon member 36. A pair of thin

dielectric discs

38, 40 of circular outline are interposed between each of the pairs of pole pieces 28 or 30 and associated microwave ferrite elements 32 or 34 respectively, with planar areal contact with both. For uniform properties and to minimize resistance and losses, it is preferred to utilize conventional finishing techniques to insure flatness and smoothness of the areal surfaces of the core 20 tips, the pole pieces 28, 30, the

discs

38, 40 and the ferrite elements 32, 34. Adhesives, such as epoxy bonds, are utilized between facing surfaces to unify and rigidify this structure, and the

dielectric discs

38, 40 include thin (approximately 00002-00005 inch) platings of conductive material, specifically silver in this instance, thus defining upper and lower waveguide wall surfaces for the volume in between. It is found advantageous in some instances to utilize a silver epoxy for the bond between the discs and the respective microwave ferrite elements, and in some instances it is preferred to silver plate the microwave ferrite elements on the side facing the waveguide walls.

In the present example, the upper and lower pole pieces 28, 30 protrude inwardly into the waveguide portion, in conjunction with symmetrical transition elements 42, 44 disposed against the upper and lower walls and comprise double step elements having their apices along the center lines of the separate waveguide sections. The transition elements provide a reduced type waveguide section and improve the broad band characteristics of the device. Tuning stops (not shown) may be incorporated in the waveguide or in the transition sections for further improving broad band characteristics. The top and bottom waveguide walls defined by the conductive surfaces of the

dielectric discs

38, 40 in this example lie at an intermediate height on the opposite sides of the microwave ferrite volume, between the reduced height section at the top step of the transition elements 42, 44 and the nominal height of the waveguides themselves. This arrangement provides improved matching but it should be recognized that the transitions may be eliminated or difierent transitions may be utilized, and that if no transitions are utilized the pole pieces 28, 30 may either have some protrusion into the interior of the waveguide or the conductive surfaces on the

discs

38, 40 may be flush with the in terior walls of the waveguide.

As pointed out in greater detail in the previously referred to co-pending application Ser. No. 47,676, filed June 19, 1970, microwave devices such as the circulator 10 according to the invention provide for fast switching times due to low eddy current losses and other desirable characteristics. Thus with presently known microwave devices fabricated, for example, from solid aluminum, the switching time is almost entirely limited by the eddy current losses generated in the aluminum surrounding the magnetic circuit. This may be understood by considering the approximate equivalent electrical circuit which comprises a series inductance and resistance, both in parallel with an equivalent resistance which shunts the coil inductance. The time constant of the circuit approximates L/R where L represents the coil inductance and R represents the shunt resistance. In presently known ferrite devices, R is fairly small and the time constant of the circuit is on the order of several milliseconds, but this is not sufficient for some high speed applications. Since the magnetic field is directly proportional to the current flowing in the inductance coil, the switching time of the magnetic field is proportional to the time required to reverse the direction of current flow in the coil inductance as well as the eddy current losses.

In the switchable driver circuit 12 (FIG. 1) DC signals from a power supply 46 are coupled to a current direction switch 48 which operates under the control command signals to selectively reverse the direction of current through the coupled winding or coil 22 of the electromagnet system. Capacitor means 50 are coupled in parallel with the winding 22, and in series with rectifier means 52 that are also parallel to the inductive coil 22.

The unique co-action between the switchable driver circuit 12 and the circulator 10 components provides characteristics that in the practical example being described enable switching times of 15 microseconds to be realized in standard production units. The magnetic circuit comprises low loss, low inductance elements having high Q at the switching frequency. The waveguide body is also a low inductance, low loss structure and the dielectric discs provide good wave transmission properties due to their conductive surfaces, without introducing high reluctance into the magnetic circuit. In conjunction with these features, the capacitor 50 and rectifier 52 in parallel with the coil 22 provide a drive signal characteristic that compensates for the induction of the coil. When the current direction switch 48 inverts the polarity of the driver signal from the power supply 46, current between the power supply and the coil is blocked by the rectifier means during the switching interval, and the inductive current during the switching interval is also stored in the capacitor means 50.

A specific example of a circuit in accordance with the invention for operation as the switchable driver circuit 12 is shown in schematic form in FIG. 3.

In the particular circuit of FIG. 3, the current direction switch 48 includes four

transistors

56, 58, 60 and 62 interconnected in a bridge circuit 64 to control the direction of current through the electromagnet core winding or coil 22. The capacitor means 50 in the form of capacitor 66 is connected in parallel with the coil 22, and

diodes

68 and 70 comprising the rectifier means 52 are connected in the respective series current paths for blocking reverse current flow out of the bridge circuit during the time that the coil 22 is being switched. The power supply 46 is represented by the terminals +E and

E. Driver transistors

72 and 74 are connected to control the conduction condition of the

transistors

56 and 58 respectively. These in turn are controlled by the condition of an input transistor 76 and corresponding transistor 78 which are responsive to a triggering signal at a terminal 80 applied via input diodes 82. The circuit includes a feedback constant current regulator 84 which comprises a long-tailed pair transistor 86 connected as a differential amplifier stage with current adjustment being possible by virtue of a potentiometer 88 connected across a reference potential derived from a zener diode 90. Whichever one of the

transistors

60 and 62 happens to be conducting for a particular condition of the circuit also serves as a part of the current regulator 84 in controlling the current level. Therefore,

transistors

56, 58, 60 and 62 form a bridge circuit capable of maintaining a constant current as determined by the regulator 84 through the coil 22, with the direction of current flow determined by the trigger signal present at the input terminal 80. The I bridge current path to the terminal E is completed via a diode 92 and resistor 94 from which a potential is applied to one side of the transistor 86. Base bleeder networks for the

transistors

72 and 74 are provided by resistors 96.

In the absence of a positive trigger voltage at the terminal 80, the transistor 76 is cut off so that

transistors

56 and 78 are in saturation;

transistors

58 and 60 are also cut off. In this state,

transistors

62 and 86 and the zener diode 90 (along with the associated resistors) comprise the feedback constant current regulator 84.

When a positive trigger voltage is applied to the input terminal 80,

transistors

56, 62 and 78 are cut off, while

transistors

58 and 76 are in saturation and the current regulator 84 is comprised of

transistors

60, 86 and the zener diode 90.

During the switching interval, immediately after being turned off, the collector voltage of

transistor

60 or 62, as the case may be, rises from zero to a peak value V and falls back to zero as a function of time. Since the peak voltage V should be large in order to accomplish the switching of the circulator coil in as short a time as possible, it is apparent that very high voltage transistors are needed in order to achieve minimum switching time. The maximum collectoremitter voltage that a transistor can withstand depends to a large degree on the manner in which it is turned off, the highest voltage capability being with the baseemitter junction reverse-biased. During the switching time, current reversal takes place in the parallel LC circuit comprising the coil 22 and the capacitor 66 and no collector current flows in either of the

transistors

60, 62. During this time transistor 60 is saturated and transistor 62 is off (or vice versa, depending on the trigger signal applied to the input terminal 80). Under this condition, the emitter voltage of the

transistors

60, 62 is given approximately by the expression where V equals the forward-biased diode drop across the input diodes 82 (approximately 0.7 volts), and the base voltage of the

off transistor

60 or 62 is equal to the collector-emitter saturation voltage of either transistor 76 or 78 (approximately 0.1 to 0.2 volts). The baseemitter junction of the off transistor, 60 or 62, is therefore back-biased by approximately 0.6 to 1 volt which is sufficient to obtain the maximum collector-emitter voltage (V rating of most transistors. The fact that the circuit insures the solid reverse biasing of the off transistor, 60 or 62, in this fashion serves to protect that transistor against the voltage peak developed by the switching coil 22 during the switching interval. Also, the diodes 68 and permit the collectors of the

transistors

60 and 62 to go to a very high voltage without affecting the

transistors

56 and 58.

By virtue of the circuit arrangements in accordance with the invention as hereinabove described, the coil driver stage is enabled to reverse the coil current in an extremely short time interval, thus advantageously realizing the inherent switching capabilities of the ferrite circulator structure, without exceeding the voltage limits of the conventional transistors available for use in the circuit. Moreover, the circuit provides for constant current regulation of the current in the circulator coil during steady state operation with the current level being variable in accordance with the adjustable setting of current level potentiometer 88. During the brief switching interval when the current through the regulator transistor 86 flowing from the bridge circuit 64 is interrupted, the current regulator circuit 84 merely acts to enable the appropriate transistor, 60 or 62, to conduct at the regulated level when current through the bridge 64 is available at the end of the switching interval.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A high speed microwave device comprising:

a hollow dielectric waveguide section having at least one aperture in one of the walls thereof;

ferrite means extending from the hollow interior into the at least one aperture of the waveguide section;

means for magnetizing the ferrite means in a selected direction and including an electrical coil and pole piece means extending from the outside of the waveguide section into the at least one aperture of the waveguide section adjacent the ferrite means;

dielectric means completely disposed within the at least one aperture in the waveguide section so as to lie between and in abutment with the ferrite means and the pole piece means; and

a high speed electronic switchable driver connected to drive the coil with currents of opposite polarities, the circuit including at least one capacitor for temporarily storing energy while switching.

2. A device in accordance with claim 1, wherein said capacitor is coupled in parallel with said coil.

3. A device in accordance with claim 1, further including dielectric load means disposed within the ho]- low interior of said waveguide section adjacent said ferrite means.

4. A device in accordance with claim 1, further including a conductive coating on the interior surfaces of the waveguide section and a conductive coating on a surface of the dielectric means in contact with the ferrite means.

5. A high switching speed microwave circulator comprising:

a dielectric waveguide section having interior surfaces including a pair of broad walls defining a standardized height for the waveguide section, each of the broad walls having an aperture therein along a central axis extending through the waveguide section;

a conductive coating on the interior surfaces of the pair of broad walls into the apertures and into contact with the conductive surfaces of the dielectric elements;

a dielectric load disposed along the central axis and extending between the ferrite elements; and

a high speed electronic switching circuit coupled to the winding and including a power supply arranged to provide relatively constant current through the winding, selectively operable switching means connected between the power supply and the winding for selectively switching the direction of the constant current through the inductive coil, and capacitor means coupled to the winding to absorb inductive current during switching.

6. A circulator in accordance with claim 5, further including a pair of transition elements abutting the interior surfaces of the broad walls within the waveguide section, each of the transition elements having an aperture therein forming a part of the aperture in the adjacent broad wall, and wherein the opposite ends of the a waveguide section including a substantially dielectric, hollow body;

ferrite means extending from the hollow interior into at least one wall of the waveguide section;

a magnetic core having a winding thereon and extending from the outside of the waveguide section into said at least one wall thereof adjacent the ferrite means; and

a switching circuit coupled to said winding and including capacitor means coupled in parallel with the winding for providing resonant energy absorption, a power supply arranged to supply essentially constant, reversible current through the winding, selectively operable switching means coupled between the power supply and the parallel combination of capacitor means and winding for selectively reversing the current applied to the winding by the power supply, and unidirectional current conducting means coupled in series with the winding for blocking the passage of current between the winding and the power supply during the time interval of reversal of current in the winding.

Claims

1. A high speed microwave device comprising: a hollow dielectric waveguide section having at least one aperture in one of the walls thereof; ferrite means extending from the hollow interior into the at least one aperture of the waveguide section; means for magnetizing the ferrite means in a selected direction and including an electrical coil and pole piece means extending from the outside of the waveguide section into the at least one aperture of the waveguide section adjacent the ferrite means; dielectric means completely disposed within the at least one aperture in the waveguide section so as to lie between and in abutment with the ferrite means and the pole piece means; and a high speed electronic switchable driver connected to drive the coil with currents of opposite polarities, the circuit including at least one capacitor for temporarily storing energy while switching.

3. A device in accordance with claim 1, further including dielectric load means disposed within the hollow interior of said waveguide section adjacent said ferrite means.

5. A high switching speed microwave circulator comprising: a dielectric waveguide section having interior surfaces including a pair of broad walls defining a standardized height for the waveguide section, each of the broad walls having an aperture therein along a central axis extending through the waveguide section; a conductive coating on the interior surfaces of the waveguide section; magnetizing means comprising a winding on a magnetic core, the core being disposed outside the waveguide section and having opposite ends extending into the aperture; a pair of dielectric elements disposed within the apertures and in contact with the magnetic core, each of the dielectric elements having a conductive coating on a surface thereof opposite the core and being disposed along the central axis; a pair of ferrite elements disposed along the central axis and extending from positions intermediate the pair of broad walls into the apertures and into contact with the conductive surfaces of the dielectric elements; a dielectric load disposed along the central axis and extending between the ferrite elements; and a high speed electronic switching circuit coupled to the winding and including a power supply arranged to provide relativeLy constant current through the winding, selectively operable switching means connected between the power supply and the winding for selectively switching the direction of the constant current through the inductive coil, and capacitor means coupled to the winding to absorb inductive current during switching.

6. A circulator in accordance with claim 5, further including a pair of transition elements abutting the interior surfaces of the broad walls within the waveguide section, each of the transition elements having an aperture therein forming a part of the aperture in the adjacent broad wall, and wherein the opposite ends of the magnetic core comprise ferrite pole pieces.

7. A high speed circulator switch comprising: a waveguide section including a substantially dielectric, hollow body; ferrite means extending from the hollow interior into at least one wall of the waveguide section; a magnetic core having a winding thereon and extending from the outside of the waveguide section into said at least one wall thereof adjacent the ferrite means; and a switching circuit coupled to said winding and including capacitor means coupled in parallel with the winding for providing resonant energy absorption, a power supply arranged to supply essentially constant, reversible current through the winding, selectively operable switching means coupled between the power supply and the parallel combination of capacitor means and winding for selectively reversing the current applied to the winding by the power supply, and unidirectional current conducting means coupled in series with the winding for blocking the passage of current between the winding and the power supply during the time interval of reversal of current in the winding.