US2630492A - High-frequency phase shifting apparatus - Google Patents

Description

March 3, 1953 R. B. MUCHMORE 2,630,492

HIGH-FREQUENCY PHASE SHIFTING APPARATUS Filed March 22, 1946 INVENTOR ROBERT B. MUCH/MORE Patented Mar. 3, 1953 HIGH-FREQUENCY PHASE SHIFTING APPARATUS Robert B. Muchmore, Hempstead, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application March 22, 1946, Serial No. 656,201

3 Claims.

The present invention relates generally to high frequency energy transmission apparatus and more particularly to such transmission apparatus of the hollow electromagnetic wave energy conducting type including means for producing variations in phase of the high frequency waves propagated therethrough.

Phase-shifting apparatus of various types are known .each of which have been found to possess one or more of the following structural and/or operational defects. Many of the earlier types are characterized by a relatively large insertion loss which seriously reduces the efiiciency of operation. Others have been disclosed in which impedance mismatch resulting from constructional discontinuities tend to impair the effectiveness of the apparatus. Such discontinuities are either inherent static characteristics of the apparatus or result from normal adjustment of the apparatus. Generally, the mismatch resulting from such discontinuities is either too large to be tolerated at any particular adjustment of the phase shifter, or the magnitude of the mismatch varies as the phase shifter is adjusted, thereby introducing even more undesirable variations in the transmission characteristics of the system.

Other defects in prior art types of hollow wave energy conductor phase shifters include (1) the limitation of operability to a relatively small range of phase shift and ,to a relatively narrow band of frequencies; (2) the existence of sliding joints resulting in poor performance due to faulty or intermittent electrical contact; and (3) the existence of uncovered .slots or other openings through which substantial amounts of energy may be lost by radiation.

A further difficulty with some prior known phase-shifting devices resides in the fact that they are generally employed in systems wherein other components are arranged in a fixed spacial relationship. The devices, however, are them selves characterized by variable over-all dimensions varying in length according to the amount of phase shift introduced. Obviously, this feature renders such devices impractical for usein fixed-arrangement-systems. Accordingly, it is desirable to provide a phase shifter having fixed over-all dimensions 50 that variation in the magnitude of the phase shift introduced is completely independent of the dimensions of the phase shif r- It is, therefore, a principal object of the present invention to provide a new and improved phase-shifting apparatus wherein all the abovedescribed defects are substantially eliminated.

Another object of the invention is to provide a wave-guide phase-shifting apparatus having low insertion loss and which is substantially free from uncovered slots or other openings thereby reducing undesired energy losses.

A further object of the present invention resides in the provision of a wave guide phase-shifting apparatus having means for providing smooth impedance transformation between the portion of the wave guide occupied by the phase shifter and the wave guide portions coupled thereto.

Still another object of the present invention is to provide a wave guide phase shifter which is operable over a relatively wide band of frequencies with substantially constant standing wave ratio.

Yet another object is to provide a phase shifter having no sliding joints associated with the electrical components of the apparatus whereby difficulties resulting from faulty and/0r intermittent electrical contact are virtually eliminated.

A further object of the present invention is to provide variable phase-shifting apparatus having fixed over-all dimensions thereby enabling the apparatus to be inserted in a transmission system without disturbing the spacial arrangement of other components of the system.

In accordance with the present invention, there is provided a wave guide phase shifter whereby substantially any desired amount of variation in phase of the transmitted waves is obtainable by means of a slab of low-loss dielectric material variably positioned within the wave guide, and means for transversely moving said slab relative to the longitudinal axis of the wave guide.

A feature of the present invention is to provide such a wave guide phase-shifting apparatus having a dielectric member within the wave guide, said member being transversely movable thereacross for introducing alterations in the phase of the wave energy transmitted therethrough.

Another feature of the invention is to provide, in a wave guide phase shifter of the above-mentioned type, means for providing smooth electrical transition between the portion of the wave guide occupied by the dielectric slab and the unoccupied portions of the wave guide.

The invention in anotherof its aspects relates to novel features of the instrumentalities, described herein for achieving the principal objects of the invention and to novel principles employed in those instrumentalities, whether or not these features and principles are used for the said principal objects or in the same field. A further object of the invention is to provide improved apparatus and instrumentalities embodying novel features and principles, adapted for use in realizing the above objects and also adapted for use in other fields.

Other objects and advantages of the present invention will become apparent from the specification taken in connection with the accompanying drawing, wherein:

Fig. 1 is a perspective view, partially broken away, of the phase-shifting apparatus of the present invention; and

Fig. 2 is a cross-sectional view taken along the line 2-2 of Fig. 1.

Referring now to the drawing, the phase shifter of the present invention, as disclosed in the illustrated embodiment, comprises a rectangular wave guide section II having top and bottom walls IS, IS and side walls 11, I9.

The ends of wave guide section II may be provided with conventional choke-flange coupling terminals 2|, 23 for coupling the phase shifter to a transmission line or other utilization system (not shown). The coupling terminals disclosed form no part of the present invention, and are herein included merely as illustrative as one type of coupling found to be useful. Thus, a full description thereof is not deemed necessary.

- For producing phase shift in the waves propagated between the terminals 2I, 23 of the wave guide, there is provided a transversely movable slab 25 of low loss dielectric material having a relatively high dielectric constant. Polystyrene, having a dielectric constant of approximately 2.45 at an operating wavelength in the neighborhood of 3 centimeters, has been found to be suitable, although any other dielectric material having comparable properties may be employed.

Slab 25 is mounted within the wave guide H with its longitudinal axis parallel to that of wave guide H and the top and bottom edges l2, [4 thereof supported in adjacent spaced relation with respect to the top and bottom walls I 3, of the guide for free transverse movement across the wave guide. Support means comprising a pair of spaced parallel metallic rods 21, 29, are provided, each of which is suitably embedded or otherwise rigidly connected to the slab 25 at regions intermediate the ends of said rods.

The rods 21, 29 are preferably spaced apart a distance electrically equivalent to one-quarter wavelength at a mean operating frequency and at a mean phase position to minimize the effect of reflections therefrom. The oppositely extending ends of rod 21 pass through aligned openings 3|, 33' formed in sidewalls I1 and I9 respectively while the ends of rod 29 pass through similarly aligned openings formed in sidewalls J1 and I9, respectively. Suitable bearings or bushings 35 may be affixed at each of said openings to facilitate sliding movement of the rods therethrough and to provide additional mechanical support therefor.

It will be noted that the openings are almost completely filled by the rods, hence substantially no radiation of energy can take place. Furthermore, since the openings are provided in the side walls l1, I9, interference by the rods 21, 29 to ,the flow of current in the guide is reduced to a minimum, especially for the so-called TEo, 1 mode of transmission generally used with rectangular 1 a calibrated scale 39 and pointer 40 may be attached to the wave guide and the crossbar, respectively, to indicate the instantaneous position of the slab 25 or the amount of phase shift introduced corresponding thereto.

It is to be understood that the mechanical means herein disclosed for producing transverse movement of the slab 25 across the wave guide is illustrative only; other manually or automatically operated means may be provided, if desired.

To provide smooth electrical transition between the portion of the wave guide ll occupied by slab 25 and the unoccupied portions of the wave guide, slab 25 is provided with tapered end portions 4!, 43 which, as shown, are preferably although not necessarily of substantially equal pitches disposed in mutually opposite senses. The tapered portions 4|, 43 are each of axial length at least equal to one-half wavelength in the wave guide at the center frequency of the operating band and serve as impedance transformers to insure that the impedance at each end of the apparatus viewed toward the slab 25, when the far end is properly terminated, is substantially equal to the characteristic impedance of the wave guides, to which the phase-shifting apparatus is coupled.

In the operation of the device, and assuming wave guide II to be excited in its fundamental or TEo, 1 mode characterized by an electric field extending transversely between the top and bottom walls 13, E5 of the wave guide I l with a maximum of electric intensity substantially coinciding with the longitudinal mid-plane thereof, it is seen that, as the slab 25 is moved from the side wall ll toward the axis, the wavelength in the guide, A of the transmitted waves is progressively decreased. The minimum value of Ag occurs when the longitudinal axis of the slab 25 coincides with the axis of the wave guide while the maximum value of \g occurs when the slab is drawn to one side of the wave guide and adjacent wall I! or wall l9. Variations or shifts in the phase of the transmitted waves are produced corresponding to the reduction in k The cross-sectional area and the length of the slab 25 are each preliminarily selected to yield the desired change in k of the transmitted waves for the desired phase shift. In one successfully operating embodiment of the device, a slab of Polystyrene 4.3)\g long was found to be of length sufficient to produce a maximum shift in phase of 360, corresponding to transverse displacement of the slab from one edge of the wave guide to the central position. For greater ranges of phase shift, it is merely necessary to increase the length of the dielectric slab 25 in proportion to the desired range.

It will be apparent to those skilled in the art, that phase shifters of the type hereinabove described may be constructed to operate with energy conducting systems of other cross-sections and/or excited in modes other than the TEo,1 mode. For maximum efficiency of operation, it is merely necessary that a major cross-sectional dimension of the dielectric slab used be disposed substantially parallel to the electric field of the electromagnetic wave being propagated.

It is to be understood that, While the waveguide apparatus described hereinabove is of rectangular cross-section, the invention is not restricted to such wave guides inasmuch as circular, elliptical or other wave guide cross-sections may be employed with substantially the same effect. Also, the expression hollow electromagnetic wave energy conductor is employed herein to embrace wave guides and coaxial transmission lines.

There has thus been described a novel wave guide phase-shifting apparatus wherein substantially any desired amount of phase shift may be obtained by means of a transverse movable slab of dielectric material within the wave guide having cross-sectional area and length corresponding to the range of phase shift desired and also having means at opposite ends thereof for providing smooth electrical transition between the filled and unfilled portions of the guide.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An adjustable phase-shifting apparatus comprising a rectangular wave guide having a longitudinal axis and adapted to propagate electromagnetic wave energy in a direction parallel to said axis, said guide forming a complete enclosure except at its ends and having a relatively wide and a relatively narrow cross-sectional dimension, means for applying high frequency energy to said guide at one of said ends, means for removing said energy from said guide at the other of said ends, and means for varying the phase velocity of travelling waves propagated through said guide, said means comprising a dielectric body having a rectangular cross-section adjustably positioned within said guide, said body also having a relatively wide cross-sectional dimension parallel to said relatively narrow wave guide dimension and a relatively narrow crosssectional dimension parallel to said relatively wide wave guide dimension, impedance matching means in said body providing substantially matched impedance conditions between said wave guide and said body-occupied Wave guide portion, and means effecting translation of said body in a direction parallel to said relativel wide wave guide dimension.

2. A high frequency device for varying the phase velocity of transmitted microwave energy comprising wave guide means dimensioned to conduct high frequency wave energy and having a longitudinal axis, said guide forming a complete enclosure except at its ends, a dielectric body Within and extending along said wave guide means, means for adjustably positioning said body transversely to said axis of said wave guide means, said body having means providing electrically smooth transition between the portion of said wave guide means occupied by said body and the unoccupied portions of said wave guide means, means for applying high frequency energy to one of said ends of said wave guide, and means for removing said energy from the other of said ends.

3. High frequency phase-shifting apparatus comprising a rectangular wave guide having top, bottom and side walls cross-sectionally dimensioned to conduct high frequency energy of a predetermined frequency band, and totally enclosing the top, bottom and sides of said guide, means for supplying high frequency energy to one end of said guide and means for removing said energy from the other end of said guide, a rectangular dielectric slab within said wave guide having a body portion and tapered end portions, said tapered end portions providing smooth impedance transformation between the slab occupied wave guide portion and the unoccupied portion of said wave guide, and means including at least two parallel rods supporting said. slab within said wave guide and maintaining the lateral edges of said slab in adjacent spaced relation to said top and bottom walls respectively and for adjustably positioning said slab relative to said side walls to vary the phase of waves transmitted therethrough, said rods extending transversely of said guide and spaced apart longitudinally of said guide substantially an odd number of quarter wavelengths at the center of said frequency band.

ROBERT E. MUCHMORE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,669 Bowen Sept. 13, 1938 2,197,123 King Apr. 16, 1940 2,425,345 Ring Aug. 12, 1947 2,427,098 Keizer Sept. 9, 1947 2,430,130 Linder Nov. 4, 1947 2,433,368 Johnson Dec. 30, 1947 OTHER REFERENCES Microwave Transmission Design Data, pub. May 1944 by Sperry Gyroscope 00., Brooklyn, N. Y. (pages 159-176).

Practical Analysis of Ultra High Frequency, by Meagher and Markley (page 1'7), published. August 1943 by R. C. A. Service Co., Camden, N. J.

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