US3371293A - Non-reciprocal strip transmission line phase shifter - Google Patents

Description

Feb. 27, 1968 R. R. JONES ETAL 3,371,293

NON-RECIPROCAL STRIP TRANSMISSION LINE PHASE SHIFTER Filed Aug. 24, 1965 4 Sheets-Sheet 1 QN moheifiaum OEPUNJEO music- 325: GET-2&2

INVENTORS Raymond R. Jones and Lawrence R. Whicker WITNESSES B TOEiEY Feb. 27, 1968 I R. R. JONES ETAL 3,371,293

NON-RECIPROCAL STRIP TRANSMISSION LINE PHASE SHIFTER Filed Aug. 24, 1965 4 Sheets-Sheet 2 FIG. 2 A'rcHme CONDUCTOR V SQUARE LOOP FERRITE p6\ '36 /27 FIG. 3

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DIFFERENTIAL PHASE SHIFT (DEG/INCH) (O I I l I I l l l l l l O 5.0 5.I 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0

FREQUENCY (G C) woo FIG. 4

FREQUENCY (GC) FIGURE OF MERIT (LN/DB) Feb. 27, 1968 R. R. JONES ETAL 3,3 93

NON-RECIPROCAL STRIP TRANSMISSIONLINE PHASE SHIFTER 4 Sheets-Sheet 5 Filed Aug. 24, 1965 SQUARE LOOP FERRIIE mELEc'rRK':

FIG. 6 4 50 HING l 'c UCTORS l I DIELECTRIC 6 5 r 5 1 A 5 m m I Y 2n l 2 C M E 5 m E w E R F 5 5 4 O O O O O O O O O 8 7 6 5 4 3 2 l iuztmmumoue .Eim umqzm 4 .zumum. .=o

Feb. 27, 1968 R. R. JONES ETAL Filed Aug. 24, 1965 LATCHING CONDUCTOR NON-RECIPROCAL STRIP TRANSMISSIONLINE PHASE SHIF'TER 4 Sheets-Sheet 4 2 26 26 20 2L A2 I I I FIG. 8

SQUARE LOOP/ I I /FERRITES a \-MATCHING 6 I TRANSFORMER M asMATCHING TRANSFORMER 26 4 I LATCHING cououcron FIG."

United Sttes Patent 3,371,293 NQN-RECEPROtIAL STRIP TRANSMESSEGN LINE PHASE SlallFlER Raymond E. Jones, Baltimore, and Lawrence R.

Whiclrcr, Severna Park, Md, assignors to Westinghouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Aug. 24, 1965, Ser. No. 482,074 1 Claim. (til. 333-24.]L)

ABSTRACT OF DISCLQSURE A strip transmission line phase shifter containing therein at least one ferrite, each ferrite being of a closed loop geometry. One wall of each ferrite is positioned immediately adjacent the center strip conductor and provides dielectric loading to distort the uniform transverse field for obtaining the planes of circular polarization. In such a manner the dielectric properties as well as the magnetic properties of the ferrite are used.

The present invention relates generally to microwave phase shifters and more particularly relates to a nonreciprocal strip transmission line phase shifter.

Electronically controlled phase shifters capable of being switched in sub-microsecond intervals are highly desirable, for example, in the field of phased antenna arrays. However, the large number of necessary phase shifters presents a matrix which adds considerable size and Weight to a radar system. Strip transmission line components are attractively compact but their utilization for phase shifting has required large solenoids or magnets external to the strip line to xagnetize ferrite slugs located within the line.

It is well known that circularly polarized magnetic fields are a necessary requirement for the operation of nonreciprocal strip transmission lines. A dielectric material is generally disposed within the transmission line to asymmetrically load the line to distort the uniform transverse electric field. The distortion occurs in the form of a density gradient in the transverse electric field, which gives rise to a longitudinal magnetic field component. When a transversely magnetized ferrite is placed in this region of circular RF magnetic field, non-reciprocal phase shift is obtained.

Briefly, the present invention disposes a plurality of ferrite elements between the ground planes, of a strip transmission line structure. Each ferrite element provides dielectric loading and is positioned to asymmetrically load the line to produce the necessary longitudinal magnetic field component for circular polarization. The elements are chosen to be of diiferent lengths. Each is provided with a separate .current path extending therethrough for imposing a circular magnetic field to selected elements for causing the elements so energized to assume one of two stable remanent magnetization states. The closed magnetic loop associated with each element is located entirely within the strip line structure. The magnetic loop is disposed transverse to the longitudinal magnetic field component to shift the phase of the energy in accordance with the length of the elements latched.

Accordingly, an object of the present invention is to provide a non-reciprocal strip transmission line phase shifter which has the desired qualities associated with strip transmission linecomponents and exhibits digital phase shift characteristics.

Another object of the present invention is to provide a non-reciprocal strip transmission line phase shifter which is compact and light in weight yet capable of digital phase shifting in sub-microsecond intervals;

Another object of the present invention is to provide a non-reciprocal, digital phase shifter which combines the rapid switching speeds offered by latching devices and the compactness of a strip transmission line structure.

Another object of the present invention is to provide a phase shifter which is much smaller than its waveguide counterpart, and is better suited for integration into a compact matrix which may contain many identical phase shifters.

Another object of the present invention is to provide strip transmission line phase shifters which are of compact geometry, provide good figures of merit, and require low driving power.

Further objects and advantages of the present invention will be readily apparent from the following detailed description taken in conjunction with the drawing, in which:

FIGURE 1 is a perspective view, partly in section, of a preferred embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the line indicated by the arrows Il-ll of the illustrative embodiment shown in FIG. 1;

FIGS. 3 and 4 are graphical representations of characteristic curves showing the operation of the illustrative embodiment of FIG. 1;

FIG. 5 is a partial cross-sectional view of an alternate embodiment of the present invention;

FIG. 6 is a partial sectional view of another alternate embodiment of the present invention;

FIG. 7 is a graphical representation of characteristic operating curves for the illustrative embodiment shown in FIG. 6;

FIGS. 8, 9 and 10 are top, side and end views of still another illustrative embodiment of the present invention; and

FIG. 11 is a partial cross-sectional view of yet another illustrative embodiment of the present invention.

A five bit strip transmission line phase shifter illustrated in FIG. 1, includingground planes 2 and 4 with acenter strip conductor 6 longitudinally disposed thereinbetween and terminated at one end at an input connection 8 and at the opposite end anoutput connection 10. Ferrite elements l2, l4, 16, 18 and 2d of different lengths are longitudinally disposed adjacent an edge of thecenter strip conductor 6. Quarter wave dielectric matchingtransformers 22 are used at the ends of the ferrite structure.Dielectric separators 24. having the same permittivity as the ferrite elements are used to isolate the various ferrite bits. A latching conductor 25 (FIG. 2) extends longitudinally through the ferrite elements, with-latching control wires 26 connected to the latching conductor 25 through thedielectric separators 24. Abrace 27 supports eachcontrol wire 26 entering eachseparator 24;. When desired, separate latching conductors may be provided through each element. Selected ferrite elements are magnetized in a predetermined direction as determined by signal current pulses passing through the ferrite element when their respectivelatching control wires 26 are energized.

it is well known that circularly polarized magnetic fields are a necessary requirement for the operation of non-reciprocal waveguide devices. However, no component of circular polarization exists in a strip transmission line for the dominant TEM mode. The TEM mode is unsuitable for non-reciprocal phase shift unless the mode can be distorted to create the required circular polarization. In accordance with the present invention theferrite elements 12 through 2%, of a chosen dielectric constant, asymmetrically load the transmission line to distort the uniform transverse electric field. This distortion occurs in the form of a density gradient in the transverse electric field, which gives rise to a longitudinal magnetic field component near the air-dielectric interface. At the same time, the ferrite elements when latched to a remanent state provide a magnetization component transverse or perpendicular to the longitudinal component in the region of the circular RF magnetic field to obtain non-reciprocal phase shift of the microwave energy traveling through the strip transmission line.

Specifically referring to FIG. 2, theferrite element 12 includes atop wall 30, a bottom wall 32 andside walls 34 and 36 disposed to form a longitudinal bore oraperture 38 through which the latching conductor 25 is threaded. Theferrite element 12 is positioned with itsside walls 34 adjacent one edge of thecenter conductor 6 by means of foam supports 40. The necessary transverse magnetic field for non-reciprocal phase shift is provided by theside wall 34 when theferrite element 12. is latched or switched to a predetermined state of remanent magnetization. Theopposite wall 36,top wall 30 and bottom wall 32 complete the magnetic path and provide the necessary dielectric loading to obtain the E field gradient atthe interface between thewall 34 and free space.

Each ferrite element is chosen to have a square loop magnetization curve in which the remanent magnetization M is almost equal to the saturation magnetization M Theside wall 34 of the ferrite element selected to provide transverse magnetic field is magnetized in a chosen direction by passing a current therethrough by means of the latching conductor 25. For example, a positive current pulse through that portion of the latching conductor 25 associated with the selected ferrite element will provide a magnetic field in a circumferential direction to saturate the ferrite element in, say, the plus direction, M The ferrite element will retain the larger part of its magnetization when the current pulse is removed and assume a positive or first state of remanent magnetization M The selected ferrite element is then set to be latched at its positive remanent magnetization point, +M However, if a negative current pulse is applied, the magnetization will be reversed and the material will remain set at a negative or second state of r-emanent magnetization, -M',.

Theside wall 34 adjacent the edge of thecenter conductor 6 will strongly interact with the microwave energy and differentially shift the phase thereof when the direction of the magnetic field in theside wall 34 is changed. The distance across the ferrite element to theother side wall 36 is made sufiiciently large so that the microwave energy interaction with theopposite side wall 36 is insignificant in the phase shifting of the microwave energy. The ferrite elements are of varying length to shift the phase of the microwave energy in different discrete steps, the amount of ferrite material, when magnetized, determining the number of degrees phase shift that will occur.

Measured phase shift and merit data for the illustrative embodiment shown in FIG. 2 is illustrated in FIGS. 3 and 4. The operating curve A resulted from the use of ferrite material having a 47TM5 of 1700 gauss for the latchingelements 12 through 20. The characteristic curve B resulted from the use of yttrium iron garnet with a 471-M of 1600 gauss for the latchingelements 12 through 20. It is seen that in excess of 100 degrees of phase shift per inch is obtained from both materials. This is considerably more than has been obtained for waveguide configurations. A figure of merit, which is defined as degrees of phase shift for db of loss, is shown by the characteristic curve C and is in excess of 400 for both materials across a 5% frequency band.

When desired, additionaldielectric material 42 in FIG. 5 may be disposed between thecenter conductor 6 and the ground planes 2 and 4 to further asymmetrically load the strip line and provide the desired electric field density gradient. The addition of such additional dielectric material however, has been found not to improve the performance significantly.

The alternate embodiment of FIG. 6 utilizes stackedferrite elements 50 and 52 disposed between thecenter conductor 6 and theground plane 2 andground plane 4, respectively. The side wall of interest is magnetized in the same direction for interaction with the circular magnetization. Separate latchingconductors 54 and 56 are simultaneously energized by a proper pulsing circuit to shift the phase of the microwave energy. When desired, additional dielectric loading may be provided by the insertion ofdielectric material 58 extending longitudinally within the aperture of each of the latchingelements 50 and 52. With the arrangement of FIG. 6, considerably less phase shift will be obtained; and the obtained differential phase shift is highly dependent on the dielectric loading within theelements 50 and 52. Plots of phase shift using dielectric materials of various constants are shown in FIG. 7. Although considerably less phase shift is obtained for a given volume'of ferrite material, the geometry shown in FIG. 6 is useful for high power application where reduced interaction with the microwave energy is required.

FIGS. 8, 9 and 10 illustrate an alternate configuration wherein the ferrite elements are alternately disposed on opposite edges of thecenter strip conductor 6. In such a manner the ferrite elements can be stacked to provide a more compact latching ferrite strip line phase shifter.

A printed circuit strip transmission line phase shifter is illustrated in FIG. 11 wherein thecenter conductor 60 is printed on clad low dielectricconstant material 62 disposed between ground planes 64 and 66. Sufficient dielectric is removed to allow for the inclusion of theferrite latching element 68 and its associated latchingconductor 70 and latching controlledwires 72.

Hence, it is readily apparent that the present invention combines ferrite latching elements and the strip transmission line to obtain the desirable characteristics of both. The configuration of ferrite latching elements and their disposition within the strip transmission line about the center strip conductor satisfies the circular field requirements for non-reciprocal action and at the same time maintain a closed path geometry for the magnetic circuit.

The latching elements have been referred to as ferrite elements but it is to be understood that the latching elements may be of any suitable material such as, for example, spinel-type materials and garnet-type ferrites which contain rare earths. It is to be understood that all suitable materials including ferri-magnetic or gyromagnetic materials may be utilized to provide the latching function necessary for providing the transverse magnetic field while being capable of switching in submicrosecond intervals.

Experimental verification of differential phase shift has been obtained at C-band frequencies. The phase shift was measured at 112 and the insertion loss at .25 dbs, respectively. This yields a figure of merit of approximately 450 per db, at 5650 megacycles.

While the present invention has been described with a degree of particularity for the purposes of illustration, it is to be understood that all modifications, alterations and substitutions within the spirit and scope of the present invention are herein meant to be included.

We claim as our invention:

1. A multiple bit latching ferrite-strip line phase shifter comprising, in combination; a center strip conductor longitudinally disposed between ground planes; a plurality of ferrite elements each of different length and each having an aperture extending therethrough; said ferrite elements disposed end to end longitudinally adjacent an edge of said center strip conductor; a wall portion of each said ferrite element abutting the edge of said center strip conductor; said ferrite elements having a dielectric constant substantially greater than air; signal means threaded through the aperture of each said ferrite element for individually latching its respective 5 6 adjacent wall in a predetermined state of remanent mag- References Cited netization; the remaining portion of said ferrite ele- UNITED STATES PATENTS ment providing a closed magnetic loop with said wall portion located entirely within the space between the ground $6,23

planes; said ferrite elements longitudinally disposed along 5 said center strip conductor being alternately disposed HERMAN KARL SAALBACH, 'y Examlneron opposite edges of said center strip conductor. P. L. GENSLER, Assistant Examiner.

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