US3323081A - Microwave phase shifter - Google Patents

Description

y 1967 P. c. GOODMAN 3,323,081

MICROWAVE PHASE SHIFTER Filed April 8, 1963 VOLTAGE 36 SOURCE PHASE SHIFT AT ZERO CHANGE IN PHASE SHIFT MAGNET'C F'ELD REMAINS CONSTANT PHASE SHIFT WHEN MAGNETIC FIELD OF PARTICULAR MAGNITUDE IS APPLIED Fig. 4

INVENTOR.

I PAUL C.GO0DMAN BY My FREQUENCY (GIGACYCLES) ATTORNEY I I I I I I I I I I I l I I 52 I I PHASE SHIFT (DEGREES) United States Patent Delaware Filed Apr. 8, 1963, Ser. No. 271,362 1 Claim. (Cl. 33331) This invention relates to an improved microwave phase shifter and more particularly, to an electrically variable ferrite core microwave phase shifter.

In coaxial transmission lines, it is often important to have a phase shifter which, upon a change in its propagation constant, can produce a phase shift change which is substantially the same over a broad frequency range and one in which the propagation constant can be changed easily to vary the amount of phase shift change produced. Another requirement of such phase shifters is that they provide reciprocal operation, that is, they should provide substantially the same phase shift in either direction of wave transmission through the line.

This invention relates to an improved microwave phase shifter which provides the above characteristics. In accordance with the invention, a helical conductor or helix is wound on a cylindrical rod of ferrite material. Preferably, the helical conductor is wound in such a way that the length of the conductor is constant when viewed at any given transverse section of the ferrite rod.

The ferrite rod and the helix wound thereon are axially disposed within an outer conductor. A biasing magnetic field is applied to the rod in a direction transverse to the rod and the magnetic field may be varied to change the propagation constant of the line and the amount of phase shift change produced. The symmetry provided by using a transverse magnetic field makes propagation characteristics of the helix completely reciprocal.

An object of this invention is to provide an improved microwave phase shifter which comprises a rod of ferrite material upon which is wound a helical conductor.

Another object of this invention is to provide a phase shifter of the above character having a transverse magnetic field which may be varied to change the propagation constant of the phase shifter.

Other objects and advantages will become apparent from the following description and from the appended drawings and claims.

In the drawings:

FIGURE 1 is a side view, partly in cross section and partly in schematic form, illustrating a phase shifter comprising an embodiment of this invention.

FIGURE 2 is an enlarged cross sectional view of the left end of the phase shifter shown in FIGURE 1.

FIGURE 3 is a section taken at substantially line 3--3 shown in FIGURE 1.

FIGURE 4 is a graph showing the characteristics of the present phase shifter.

In FIGURE 1 a ferrite rod 10, made of a material such as yttrium iron garnet with gadolinium substituted for part of the yttrium, is axially disposed within an outer conductor 12 made of a conductive material such as brass.

A conductor 14 made of a material such as brass is wound on the rod 10. Between the axial positions 16 and 18, the conductor 14 is a helix 19 and from these positions to the ends of the conductor, the conductor is a continuous tube. Preferably, the helix 19 is wound on the rod such that the length of the helix is constant when viewed at any given transverse section of the rod 10. For example, in the transverse section shown in FIGURE 3, the length of the helix portion 20 is maintained constant throughout the helix 19 between the axial positions 16 and 18 to obtain best results. In one phase shifter that was built, this length was maintained constant at .35 inch, using a ferrite rod having a diameter of .20 inch.

A helical section 22 of larger pitch than the rest of the helix 19 and a helical section 24 of still larger pitch are provided at the opposite ends of the helix to act as two section quarter-wave transformers to match the pres ent phase shifter to the coaxial transmission line into which it is to be inserted.

Annular members 26 (only one shown in FIGURE 2) made of a material such as brass are disposed in contact with the opposite ends of the rod 10 and the tubular portions of the conductor 14 extend over the members 26 in electrical contact therewith. Screwed into the members 26 are pronged center conductors 28 for making contact with the center conductor of the coaxial line in which the present phase shifter will be inserted. Annular spacers 30 made of an insulating material as Teflon are inserted into the opposite ends of the conductor 12 over the conductors 28 to maintain the spacing and axial position of the rod 10 and the conductor 14 within the conductor 12.

A pair of pole pieces 32 and 34 of an electromagnet are positioned on opposite sides of the conductor 12 to apply a biasing magnetic field to the rod 10. This magnetic field is provided in the air gap between the pole pieces and is dis-posed in a direction transverse to the rod 10. Suitable path means of high permeability (not shown) are connected between the pole pieces 32 and 34 externally of the conductor 12 to complete the magnetic circuit. A variable direct voltage source 36 is connected to the input of the electromagnet to obtain a magnetic field of a desired amount and direction. The pole pieces 32 and 34 are spaced a sufiicient distance from the ferrite rod 10 to provide a uniform field for the rod and to provide a large air gap between the pole pieces and the rod.

The phase shifter described above may be inserted into a standard coaxial transmission line with standard coaxial connectors (not shown). When so inserted, the center conductors 28 will make electrical contact with the center conductor of the coaxial line and the outer conductor 12 will make electrical contact with the outer conductor of the coaxial line.

In a phase shifter of the above type that was built and designed for 3.3 gigacycle operation, it was found that the phase shifter operated satisfactorily, providing a phase shift change that remained substantially constant from 3 to 3.6 gigacycles, that is, a range of 20%. This is shown in the graph of FIGURE 4. Line 50 is a plot of the phase shift produced by the phase shifter as a function of frequency when the magnetic field applied thereto is zero. Line 52 is a plot of the phase shift when a magnetic field of particular magnitude is applied in a transverse direction to the ferrite rod. It will be noted that between the lines 50 and 52, the phase shift change or difference remains substantially constant over the range from 3 to 3.6 gigacycles, that is, the phase shift change is substantially independent of frequency in this range. If the magnetic field is increased, this further reduces the propagation constant of the phase shifter and the total phase shift produced is correspondingly reduced. However, the phase shift change with respect to the total phase shift produced at a magnetic field of lower magnitude would remain substantially constant over the range from 3 to 3.6 gigacycles.

Another advantage of the phase shifter is that it has excellent reciprocal operation, that is, it will produce essentially the same amount of phase shift regardless of which direction a Wave is transmitted through the coaxial line. This results because the magnetic field is applied in a transverse direction rather than in a longitudinal direction as is the case in certain presently known phase shifters. Also, hysteresis effects in rod 10 are substantially eliminated because of the transverse field and because of the large air gap provided between the pole pieces 32 and 34 and the rod.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications Which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claim.

Having thus described my invention, I claim:

A microwave phase shifter for a coaxial transmission line comprising a conductive tubular outer member for connecting with the outer conductor of the coaxial line,

a ferrite member disposed axially within the outer member,

a conductive helix Wound on the ferrite member,

means for connecting the 'helix in series with the inner conductor of the coaxial line,

the helix having an increased pitch at both ends to match the phase shifter to the coaxial line,

and means for applying a magnetic field to the ferrite member in a direction transverse to the axis of the member to provide for reciprocal operation of the phase shifter,

the magnetic field being applied in the same direction through the ferrite member,

the magnetic field being variable to control the magnitude of the magnetic field thereby controlling the amount of phase shift produced.

References Cited UNITED STATES PATENTS OTHER REFERENCES Scharfman: Ferrite Phase Shifters, Proc. I.R.E., vol. 44, pp. 1456-1459, October 1956.

ELI LIEBERMAN, Primary Examiner.

C. BARAFF, Assistant Examiner.

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