US2716221A

US2716221A - Rotatable dielectric slab phase-shifter for waveguide

Info

Publication number: US2716221A
Application number: US186623A
Authority: US
Inventors: Philip J Allen
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-09-25
Filing date: 1950-09-25
Publication date: 1955-08-23
Anticipated expiration: 1972-08-23

Description

Aug. 23, 1955 P. J. ALLEN 2,716,221

ROTATABLE DIELECTRIC SLAB PHASE-SHIFTER FDR WAVEGUIDE Filed Sept. 25/1950 I MOTOR %:+a-=r: ""A

INVENTOR PHILIP J. ALLEN United States Patent ROTATABL-E DIELECTRIC SLAB PHASE-SHIF'IER FOR WAVEGUIDE Philip J. Allen, Washington, D. C. Application September 25, 1950, Serial No. 186,623

4 Claims. (Cl. 333-31) (Granted under Title 35, U. S. Code (1952), see. 266) This invention relates to phase shifting apparatus for use .in high frequency transmission systems utilizing hollow waveguides as the transmission means.

More particularly, the present invention relates to phase shifting apparatus for use in hollow waveguides where the degree of phase shift may be simply and quickly varied.

It is known in the prior art that varying the dielectric constant of the medium in which an electromagnetic wave is travelling will vary the velocity of propagation of the wave travelling therein. This change in velocity causes a change in phase of the wave.

Hollow waveguides are utilized as a conduit for electromagnetic energy and placing a piece of low-loss dielectric material Within a waveguide will shift the phase of the waves travelling therein for the reasons just described.

The present invention utilizes a low-loss dielectric material to vary the phase shift of the electromagnetic waves within a hollow waveguide in a novel and expeditious way.

The degree to which the phaseof the energy within a hollow waveguide is shifted by a dielectric material placed therein has been found to depend upon the volume of material within the waveguide cavity, the dielectric constantof the material, and the electric field intensity in the vicinity thereof. Thus, if a given amount of dielectric material is to be placed in a waveguide, inserting it in the vicinity of maximum electric field intensity will cause a maximum apparent phase shift to occur within the waveguide. Conversely, placing a given amount of dielectric material in the portions of the cavity having the least electric field intensity will cause a minimum amount of phase shift.

Accordingly, the present invention utilizes one or more dielectric membersrotatably mounted within the confines of'a hollow waveguide so that the members are positioned in-areas of varying electric field intensity as the members are rotated. Each member rotates about an axis which runs generally parallel to the length of the waveguide.

In one embodiment, the axis of rotation passes through each member. The distance from the axis of rotation to theouter surfaces of the members is varied about the axis so that rotating the members varies the relative position between the non-uniform electric field and the dielectric member thereby varying the phase shift.

In another embodimentthe members are made of material of varying dielectric constant so that rotating the member will cause a variation in phase shift due to the change in relative position between the electric field and the non-uniform dielectric 'member.

'In a third embodiment of the present invention, the axis of rotation is located outside of the dielectric member so that rotation of said member about the axis places the member in electric fields of varying intensity.

:2 energy fed to the antenna elements. By driving the dielectric plate at a high rate of speed, the phase shift of the waveguide energy is quickly varied with ease and simplicity. This was not readily possible with the cumbersome prior art phase shifting devices.

Accordingly one object of the present invention is to provide a novel and simple phase shifting device for use in hollow waveguide systems.

Another object of the present invention is to provide a novel and simple phase shifting device for use in hollow waveguide systems for quickly and continuously varying the phase shift of the energy within the waveguide.

These and other objects of the present invention will become apparent from the specification and drawings wherein:

Figure l is a cross-sectional view of a hollow waveguide showing the phase shifting device forming one embodiment of the present invention located therein.

Figure 2 is a cross-sectional view of Figure 1 along section line 22.

Figure 3 is a cross-sectional view of the phase shifting apparatus within a hollow waveguide showing the dielectric members in a different position from that of Figure 1.

Figure 4 is a View taken along section line 4-4 of Figure 2 including lines representing the electric field intensity across the waveguide cavity.

Figure 5 shows the curves of phaseshift versus degrees of plate rotation for 'two relative positions of the dielectric plates shown in Figures 1-4.

Figure 6 is a second embodiment of the present invention where the dielectric constant of the --dielectric member is varied.

Figure 7 is a third embodiment of the present invention.

Referring now to the drawings Figures 1 "to 4, Where like reference characters denote identical elements, the cavity of a hollow waveguide 1 contains two

dielectric members

2 and 3. A low-loss dielectric material such as polystyrene is preferred for the dielectric members. The 'members 23 are mounted on a shaft 4 so as to be rotatable together about an axis AA'which runs lengthwise of the waveguide (i. e. generally parallel "to the waveguide axis). The cross-sectional area of the members 23 in a plane perpendicular to the axis of rotation AA is made oblong in shape for reasons which will be "hereinafter explained in more detail.

To simplify the drawings, the bearings for shaft-4 have been omitted.

The electric field lines within a rectangular waveguide run parallel to the short dimension of the rectangular waveguide 1 for the TE 1,0 mode as shown in Figure 4 (the density of lines represent the density of the electric field). When dielectric member 3 is in the horizontal position shown by the solid lines in Figure 4, minimum phase shift occurs because the average electric field intensity in the space occupied by member 3 is a minimum. When member 3 has the vertical position shown by the dotted lines in Figure 4, since all of the dielectric material is in the region of greatest intensity, maximum phase shift will result. If member 3 is rotated as by motor 5 which imparts motion thereto through its shaft 4, then member 3 will cause a periodic variation inyphase shift resembling curve b in Figure 5. As there shown, one revolution there causes two cycles of phase shift variation.

If the cross section of the homogeneous dielectric member 3 were circular rather than rectangular, and the axis of rotation was located at the center thereof, then rotation of the member would cause no variation in phase shift since the average field intensity in the space occupied by member 3 remains constant.

From what has been said, it is apparent that a rectangular cross section is not necessary to the operation of the embodiment of Figures 1-4. However, it is imsections 88'.

3 portant that the distance from the axis of rotation to the surface of the dielectric member vary about the axis as measured in a plane perpendicular to the axis.

The cross section is made oblong in shape to obtain large phase shift variations in the embodiment just described.

From Figure 5, it can be seen that the phase shift variation follows the general outlines of a sinusoidal wave when the homogeneous rectangular shaped dielectric member was used.

For best results with this embodiment, the axis of rotation of the dielectric member 3 should be in the vicinity, of maximum electric field intensity and in the center section C-C of the wave guide as shown in Figure 4.

Two dielectric members 23 which are rotatable together are provided in order that the amplitude of the phase shift variation may be simply and conveniently controlled. Each dielectric member 2,.3, causes a phase shift variation and the net effect of the two members is the sum of the individual eifects of the dielectric members. That is, the dielectric members are serially mounted with respect to the electromagnetic energy being propagated in' the waveguide and hence as in the common series relationship the net efiect is the sum of the individual effects.

When members 23 are placed at right angles to each other, on shaft 4, the variation'in average electric field intensity in the space occupied by dielectric member 23 throughout a given revolution is substantially zero so that there is little or no variation in phase shift with the rotation of the dielectric members as shown by curve a in Figure 5.

As members 23 are gradually brought into coincidence (i. e. as angle 0 approaches zero), the amplitude variation of the phase shift curve increases. Curve b in Figure 5 represents the phase shift variation when the dielectric members have the position shown in Figure 3,

Motor shaft 4 may be made of a metallic material without appreciably affecting the field intensity or the losses in the waveguide as long as the cross section of shaft 4 is small relative to that of the waveguide 1.

Shaft 4 extends through openings in dielectric members 23 and thereby causes simultaneous rotation of the dielectric members. The closeness of the fit between one of the dielectric members and shaft 4 is made such that the latter member may be initially positioned rela tive to the shaft 4 in order to vary the relative angle 9 between the dielectric members, but the fit is sufficiently close that the member will not slip as the shaft 4 is rotated.

Other suitable coupling means may of course be utilized.

In Figure 6 is shown another embodiment of the present invention, wherein the dielectric member is nonhomogeneous and cylindrical in shape rather than being homogeneous and fiat as in the embodiment of Figures li-4. The cylindrical member there shown comprises two arcuate sections 8-8 made of one kind of dielectric material, and a center section 7 made of a dielectric material having a different dielectric constant than the If section 7 has a dielectric constant which is greater than that of section 8-8, and the center section'is generally parallel to the electric field lines, maximum phase shift will result. When the center section 7 runs generally perpendicular to the electric field lines, minimum phase shift occurs.

Two angularly disposed similar cylindrical members may be used in the manner described in connection with the embodiment of Figures l4 to provide a control over the amplitude of phase shift variation.

This embodiment has the disadvantage that it causes more impedance mismatch than the embodiment of Figures 1-4 since it displaces a greater cross-sectional area of the waveguide. Also smaller phase shift ampliiii tude variations are obtained with the embodiment of Figure 6. A

Figure 7 is a third embodiment of the present invention wherein the axis of rotation is located along one side of the waveguide cavity and is displaced from the dielectric member.

Radially of the axis of rotation are located dielectric members 2' and 3 which are angularly displaced from each other along the axis as are dielectric members 23 in Figure 2., Members 2 and 3' are shown similar in shape to members 23 but of course may have any suitable shape depending on the phase shift variation desired.

The dielectric members 23' are connected with shaft 4 by dielectric rib members 9'10. As the members are rotated, they are placed in electric field of varying intensity. When the dielectric members are in the center section of the waveguide they produce the greatest phase shift since the intensity of the electric field is there maximum for the TE 1,0 mode.

As the relative position of members 2' and 3' is varied from the right angle relationship shown in Figure 7,

the amplitude of the net phase shift variation increases for reasons apparent from the explanation of the operation of the other embodiments. u

Although the present invention has been only applied to a rectangular waveguide operating in the TE 1,0 mode, it should be understood that the invention herein disclosed is also applicable to waveguides of other modes of electric field distribution.

It should be understood that many modifications may be made of the specific embodiments herein disclosed without deviating from the scope of the present invention.

The invention described herein maybe manufactured and used by or for the Government of the United States I of America for governmental purposes without the payment of any royalties thereon or therefor;

What is claimed is:

l. A phase shifting device for use in hollow waveguide electromagnetic energy transmission systems comprising first and second dielectric members rotatably mounted for rotation together within a hollow waveguide about an axis running within and lengthwise of said waveguide, the distance from said axis to the surface of said members varying about said axis, said members being displaced from each other along said axis and lying serially in the path of the electromagnetic energy being propagated in said waveguide, the angular relation between said members being adjustable whereby the amplitude of the phase shift variation may be readily varied.

' 2. A phase shifting device for use in hollow waveguide electromagnetic energy transmission systems comprising first and second dielectric members, means for rotating said members together within a hollow waveguide through electric fields of varying intensity about an axis located within and lengthwise of said waveguide, said members being displaced from each other along said axis and lying serially in the path of the electromagnetic energy being propagated in said waveguide, the distance from said axis to the surface of said members varying about said axis, the angular relation between said members being adjustable whereby the amplitude of the phase shift variation may be readily varied.

3. A phase shifting device for use in hollow waveguide electromagnetic energy transmission systems comprising first and second dielectric members, means for rotating said members within a hollow waveguide through electric fields of varying intensity about a given axis located within said waveguide in the vicinity of maximum electric field intensity, each of said members being dielectrically unsymmetrical about said axis, said members being displaced from each other along said axis and lying serially in the path of the electromagnetic energy being propagated in said waveguide, the angular relation between said members being adjustable whereby the amplitude of the phase shift variation may be readily varied.

4. A phase shifting apparatus comprising a section of waveguide for the transmission of electromagnetic energy, a pair of dielectric phase shifting members disposed in said section of waveguide, means for rotating said members about an axis located within said waveguide in the region of maximum electric field intensity, said members being longitudinally displaced from each other along said axis and lying serially in the path of the electromagnetic energy being propagated in said waveguide, each of said members being dielectrically unsymmetrical about said axis, and means for changing the relative angular relationship between said members to provide a phase shift variation of variable amplitude.

References Cited in the file of this patent UNITED STATES PATENTS King Apr. 16, 1940 Johnson et al Dec. 30, 1947 Fox Mar. 23, 1948 Revercomb et a1. Oct. 4, 1949 Marshall Jan. 24, 1950 Tyrrell Mar. 27, 1951 White Sept. 11, 1951 Hansen July 8, 1952 FOREIGN PATENTS Great Britain June 28, 1948