US2814781A

US2814781A - Microwave phase shifter

Info

Publication number: US2814781A
Authority: US
Publication date: 1957-11-26
Anticipated expiration: 1974-11-26

Description

Now 26, 1957 J. F. ZALESK! MICROWAVE PHASE SHIFTER Filed June 10, 1952 MICROWAVE PHASE SHIFTER John F. .Zaleski, Valhalla, N. Y., assignor to General Precision Laboratory Incorporated, a corporation of New York Application June 10, 1952, Serial No. 292,682

5 Claims. (Cl. 333-6) This invention relates to microwave phase shifters of the type in which the relative phase of microwave energy in two output channels can be changed from a conditio of like phase to a condition of opposed phase.

s The invention is useful in connection with microwave energy at frequencies suitable for transmission in rectangular hollow guide and employs both rectangular guide and coaxial components.

In one embodiment of the invention a rectangular guide input arm is joined at a right angle to two collinear rectangular guide arms to form a series T. The input arm is provided with a rectangular guide stub having a movable closed end in the form of a piston or plunger, such stub being located adjacent the junction, and the collinear arms are provided with a pointed rod positioned internally thereof and coaxially with the input arm. When microwave energy is applied to the input arm it is transmitted out of the two output arms and the relative phase of the outputs is adjusted by movement of the plunger. When the plunger is in such position that the length of the closed stub is equal to one-half of the microwave length of the energy in the guide, the output phases are opposed, and when the stub length equals one-quarter wavelength of the energy' in the guide the output phases are equal.

Further understanding of this invention may be secured from the detailed description and the drawings in which: I

Figure 1 depicts one embodiment of the invention.

Figures 2, 3 and 4 are field diagrams illustrating the operation of the device. I q

' Referring now to Fig. 1, a rectangular guide arm 11 is secured at a right angle to a second rectangular guide to form a series or E-plane T' having in addition to the arm 11 two

collinear arms

12 and 13. The T is matched by any means for microwave energy application at the arm 11 of which means a number are well known. The junction and impedance discontinuities may, for example, be conveniently matched by employment of a metallic button 14 secured to the continuous broad side of the collinear arms, the axis of the button being coincident with the axis of the series arm. A matching means of this type is fully disclosed in Patent No. 2,689,942, entitled Impedance-Matched T Junction by John F. Zaleski, dated September 21, 1954. When the

output arms

12 and 13 are terminated in their characteristic impedances such a series T is substantially reflectionless, one-half of the energy going out of each of the output arms with the phases of the outputs opposed to each other.

A rectangular guide 16 is secured adjacent the arm 13 and parallel to it, with broad faces contiguous. In fact one metallic plate can well serve as both the top broad side of arm 13 and bottom broad side of guide 16, although in the figure two plates are shown. The guide 16 opens into the input arm 11 at 17, and is closed at the other end by a plunger 18 movable by means of a rod 19. The function of plunger 18 is to short-circuit the guide so that it forms a closed-ended stub.

nited States Pate 0 F Although the plunger is shown as a plain sheet or block, it may of course, be provided with wave traps and/or brush fingers as is well understood in the art. When the distance L between the plunger face and the inner wall of arm 11 at the end 17 of the guide is equal to one-half of the microwave length of the input energy in the guide, low impedance is reflected to the end 17 and the T behaves.- exactly as if the stub were'absent and the walls of the arm 11 were continuous, the output energies being equal in amount and opposite in phase.

A conductive rod or probe 21 is secured in the center of the button 14 perpendicular to the common broad face 22 of the

collinear arms

12 and 13 with the axis of the probe coincident with the axis of arm 11. The free end of the rod is preferably tapered to a pointed end 23 to eliminate the presentation of any material discontinuity to microwave energy entering by arm 11. The pointed end 23 of the rod extends to a point which is approximately in the extended plane of the inner sur-' The combination of the pointed probe 21 with the sur rounding walls of the

collinear arms

12 and 13 behaves like a coaxial line. When microwave energy is applied to the arm 11, and the length L of the short-circuited stub 16 is given any value other than where k is the wavelength of the energy in the guide, the applied energy sets up a field that in part bends into the stub 16. A component of the electric lines thereof is then parallel to the probe 21 and this fieldv sets up the TEM coaxial mode around the probe 21. This effect is greatly intensified when the distance L is made approximately equal to the mode transformation being then made with very little loss of energy.

This mode transforming action is illustrated in Figs; 2, 3 and 4 in which the formationof the electromagnetic field is shown progressively. In Fig. 2, microwave energy is introduced at 26 into the series arm 11. The electrio component of the field'perpendicul'ar to the broad faces of the guide is represented by the lines 27, which bend around the corner 28 and pass along the stub guide 16. In Fig. 3 the stub guide 1.6 is shown with a conductive end 29 representing the piston 18 of Fig. l. The distance L between the end 29 and the corner 28 is approximately an odd integral multiple of one-quarter wavelength of the energy in the guide. The effect of this closed resonant stub is to introduce a discontinuity into the wall of the series arm, preventing passage of the energy into the

collinear arms

12 and 13, and to place a voltage loop in the series arm 11, indicated by the closely-spaced electric component lines 31. In Fig. 4 the rod 21 is shown placed axially in the series arm 11, so that it is in the region of the voltage loop indicated by the lines 31, Fig. 3. In this position the rod 21 is most strongly excited by the field with the formation of a field in the TEM mode around it. This coaxial field around a rod such as rod 21 placed at right angles to the axis of the

collinear arms

12 and 13 has the power to start the TE field in those arms, the fields in the two arms being in phase. This is schematically indicated in Fig. 4 by the

electric component lines

32 and 33.

The junction discontinuity and impedance transformation which would cause reflection back into the input Patented Nov. 26,1957

series arm 11 are easily matched out without additional matching devices by adjusting the length L to a moderate departure from its described nominal value, and by adjusting the exact distance D by which the rod 21 projects above the septum 34 separating the stub 16 from the arm 13.

Thus the effect of introducing the probe or rod 21 into the junction, in conjunction with the provision of the quarter-wave stub 16, is to change the collinear arm output energies from an opposite-phase condition to an inphase condition.

In this action higher modes are generated which, however, are quickly damped out in the

rectangular output arms

12 and 13 if their size is maintained below the higher mode cut-oft size. This or some other type of microwave higher mode filter should be employed to maintain the efficiency of the device.

What is claimed is:

l. A microwave phase shifter comprising, a rectangular wave guide series T having an input arm and two collinear output arms perpendicular thereto, a rectangular wave guide stub adjustable to different lengths secured closely adjacent the junction of said input arm and said collinear arms perpendicularly to one broad side of said input arm and in series therewith, and a conductive rod secured to one interior wall of said two collinear output arms extending into said input arm a distance sufiicient to intercept energy reflected by said wave guide stub and having its axis coincident with the axis of said input arm.

2. A microwave junction comprising, a rectangular wave guide series T having an input arm adapted to receive microwave energy and a pair of collinear output arms perpendicular thereto, a wave guide stub connected in series with said input arm and positioned closely adjacent the junction of said input arm and said collinear arms, said wave guide stub having a length equal to an odd integral multiple of one-quarter of the wavelength of said microwave energy, and a conductive rod secured to one interior wall of said collinear arms with its axis extending coincident with the axis of said input arm, said rod having a length such that the end thereof is positioned to intercept energy reflected by said wave guide stub.

3. A microwave device for shifting the relative phase of two output terminals by 180 degrees comprising, a rectangular guide series T having an input arm and two collinear output arms perpendicular thereto, the crosssectional dimensions of the rectangular guide being suitable for transmission of microwave energy in a wavelength band having a selected central wavelength, a rectangular guide stub having one closed end and having a length adjustable to either of two dimensions equal respectively to one-half and one-quarter of said selected central wavelength, said stub being secured perpendicularly to one broad side of said input arm adjacent to one of said collinear arms with the open end of said stub electrically in series with said input arm, and a conductive rod secured to one interior wall of said two collinear output arms and having its axis coincident with the axis of said input arm, said rod having a length such that the end portion thereof lies opposite the open end of said stub.

4. A microwave device as defined in claim 3 in which the conductive rod projects into said input arm a distance such that its free end lies approximately in plane of the distal wall of said stub and which is tapered from said distal end to a point approximately in a plane with the proximate wall of said stub.

5. A microwave device for shifting the relative phase of two output terminals by degrees comprising, a rectangular guide series T having an input arm and two collinear output arms perpendicular thereto, the crosssectional dimensions of the rectangular guide being suitable for transmission of microwave energy in a wavelength band having a selected central wavelength, a rectangular guide stub having one closed end and having a length adjustable to either of two dimensions approximately equal respectively to an integral multiple of one-half and to an odd integral multiple of one-quarter of said selected central wavelength, said stub being secured perpendicularly to one broad side of said input arm adjacent and parallel to one of said collinear arms with the open end of said stub electrically in series with said input arm, and a conductive rod secured to one interior wall of said two collinear output arms having its axis coincident with the axis of said input arm and having its length equal to approximately twice the narrow guide dimension.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,779 Martin July 11, 1950 2,679,582 Edwards May 25, 1954 2,685,065 Zaleski July 27, 1954 2,686,901 Dicke Aug. 17, 1954 OTHER REFERENCES Ragan, Microwave Transmission Circuits, vol. 9, Radiation Laboratory Series. Published 1948, McGraw-Hill Co., pp. 375-376. (Copy in Div. 69.)

M-arcovitz, Microwave Handbook, vol. 10, M. I. T. Rad. Lab. Series, pub. 1951, McGraw-Hill, page 112. (Copy in Scientific Library.)