US2454530A - Phase adjuster for fixed-branch wave guide - Google Patents

Description

Nov. 23, 1948 J. W.'TILEY 2,454,530 7 PHASE ADJUSTER FOR FIXED-BRANCH WAVE GUIDE Filed Oct. 15, 1944 Patented Nov. 23, 1948 UNI-TED STATES PATENT OFFICE John W. Tiley, Philadelphia, Pa, assigno'r to Phileo Corporation, a corporation of Pennsyl- Vania Application October 13, 1944, serial No. 558,494

3 Claims. (o1. 17s- 44) This invention relates to an electrical apparatus and particularly to an apparatus for changing the phase or electrical length between two points in a wave guide or coaxial cable. In the use of wave guides and coaxial lines, it is frequently necessary to effect a junction at a point on the line having a certain phase relationship and, in many instances, it is desirable to vary the phase without changing the physical connection on the line. Thus in tuning sections of transmission lines, stubs at pre-determined electrical points on the line are frequently-necessary so that matching will result. In other instances, it may be desirable to stretch the line. By virtue of the invention herein, it is possible to control the phase accurately at any desired point along a line and to do this in a manner which is simple.

The invention utilizes the fact that the velocity of propagation and wave length of high frequency energy through a dielectric material is dependent upon the nature of the material particularly the dielectric constant. Thus the veloc ity of propagation in air is substantially different from that in solid dielectric material such as polystyrene or other similar materials. As a rule, the apparent velocity is less in such materials, the decrease being sufiiciently great so that the wave length in a dielectric material is sub stantially different from that in air. The invention broadly consists in the use of a movable dielectric material through which the electric fields in a wave guide or coaxial cable are propagated. Means are provided for effecting gradual transition of the dielectric medium through which propagation is effected so that reflections will not occur.

Since propagation through a solid dielectric material is at a difierent velocity than through air, the mere disposition of such material in a wave guide or coaxial line itself introduces a phase displacement along the physical length of the line. By providing for adjustment of such solid dielectric material along the line, a delicate phase control at a particular point on the line may be effected.

For a fuller description of the invention, reference will now be made to the drawings Wherein Figure 1 is a perspective view of the invention as applied to a wave guide. Figure 2 is a sectional elevation of the same structure.

Figure 3 is a perspective view of the invention as applied to a coaxial cable.

Figure 4- is a sectional elevation of the invention shown in Figure 3.

Referring now to Figures 1 and '2, a rectangular wave guide in is shown made of any suitable material such as copper. The '0. sides H and I2 and the 6 sides l3 and I4 may have the usual proportions determined by cut on frequency and width of the frequency band to be transmitted. The simple TEOI mode of transmission willbe assumed. While the invention may be applied to other kinds of guide; e. g. circular and to other modes of transmission, both analysis and phase control become quite complex. At a certain point on one of the b sides such as side [4, a wave guide branch section may be connected in series in a manner well known in the art. This section may have a and b sides 2! and 22 with their corresponding mates. In order to provide suitable matching, a diaphragm 25 with a window 25 may be provided. The location of the diaphragm and size of window 26 will all be determined by the frequency and the type of matching to be obtained. If desired, the branch guide may be taken from-the a side of the main guidein which case the branch is in 's'hunt. For the purposes of this invention, the branch may be connected in either fashion.

It is clear that wall M of the wave guide is broken away at 21 to accommodate the branch wave guide. At this point, it may be desirable to control the phase of the energy. To accomplish this, wave guide I0 is provided with an elongated block 39 of dielectric material such as polystyrene or any other material having the desired properties. Block 30 is preferably large enough to fit snugly withinwave guide l0 and is prov-ided with tapering ends 3| and 32. The taper is normal to the a side. The length of the taper is preferably of the order of at least a quarter wave length as measured in block 30 and serves to provide a short transition section from one dielectric, namely air, to another dielectric, namely block 30-. Thus reflections are minimized. The taper need not necessarily be straight and in fact may be in a different general plane. Matching dielectrics to avoid reflection is well known in the art. The length of block 30 including ends 3I' and 32 is preferably at least one wave length long althcughit may be shorter.

Translation of block 30 longitudinally of wave guide 10 may be effected by a suitable thin handle 33 projecting through a slot 3! along the cen ter of one of the b sides of the wave guide preferably side l3. Handle 33 is preferably of the same material as dielectric 30. The actual knob on top of handle 33 may be of any desired Inaterial. In order to prevent radiation through 3 slot 34, blocks 35 and 36 may be provided lengthwise of slot 34 outside of the guide. These blocks have opposing faces 31 and 38 provided with channels 39 and 40 cut therein. In accordance with well-known practice, the dimensions from slot 34 to the bottom of channels 39 and 40 are about a quarter wave in length. By virtue of this construction, a choking action will result and tend to effectively seal slot 34 against leakage of energy.

The total amount of phase displacement obtainable with the construction such as shown in Figures 1 and 2 depends upon the length of dielectric block 30 and the decrease in velocity with respect to air. Thus if the velocity in air is more than in dielectric block 3|], then it will take about 10 wave lengths of material of which block 30 is made to provide complete 360 degree phase displacement. In practice, however, such a large phase displacement is not necessary. The amount of phase displacement required will depeend upon demands of the system and may vary within wide limits.

It is clear that as block 30 is moved along Wave guide l0 that the phase of energy along opening 21 will vary. Thus the phase of energy going down branch guide may be adjusted to any desired value. The amount of phase displacement per wave length of dielectric material Will be the angular difference in wave length between air and dielectric material. Thus as an example if the wavelength in air is 10 cm. and the wave length in dielectric block is 9 cm. then movement of block 30 for a distance of 9 cm. will cause a phase displacement of 36 degrees.

Referring now to Figures 3 and 4, the invention is shown as applied to a coaxial cable. In this construction, the outer conductor and inner conductor 45 have their diameters related in the usual manner well known in the art to provide a characteristic impedance of a desired value. Branching off from the cable is a section consisting of an outer conductor 48 and inner conductor 49. In both cables, the inner conductors may be supported in spaced relationship to the outer conductor in any desired manner such as by a system of insulating beading or by metal stubs both well known in the art. Inner conductor 49 of the branch cable has a loop going to outer conductor 48 for picking up energy. In order to vary the phase of energy picked up by loop 50, a block of dielectric material 52 is disposed Within outer conductor 45 of the main cable. Block 52 has tapered ends 53 and 54 preferably a quarter wave length at least as measured in the dielectric material. The length of the block itself is preferably at least one wave length including the tapered parts and may be longer if desired. Block 52 is slidable along conductor 46 and may be adjusted by means of a handle 55 of the same dielectric material passing from block 52 through slot 55. Slot 56 may, if desired, be provided with choking flanges such as are shown in the construction of Figure l to prevent leakage of energy.

In order to provide clearance for loop 50, a suitable slot in insulating material 52 may be provided.

The phase relationship between points 60 and GI in the Wave guide, these being on opposite sides of dielectric block 30, are fixed irrespective of movement of block 35, assuming block 30 does not reach to these points. Intermediate point 62, however, will have its phase varied by movement of block 30. The same is true of the coaxial cable construction. It is understood that within the wave guide or coaxial cable, the normal dielectric through which propagation takes place need not necessarily be air at atmospheric pressure. Thus the air may be at high or low pressure or other gases or liquids may be used. It is only necessary that the normal dielectric be a fluid through which a movable dielectric may be translated.

The dielectric may be a composite structure and fashioned in any desired manner. So long as the dielectric corresponding to block 30 is in the form where it may be translated, the desired effect may be obtained.

In selecting the material of which the dielectric is made, it may be found advantageous to select a material having a dielectric constant which is not too high. The effect of filling a wave guide with a material having a higher dielectric constant than air is similar to retaining air and increasing the guide width, that is the b side, as faras cut off frequency is concerned. Where a wave guide is operated well within the band of frequencies for which it is designed for normal propagation, an increase in the dielectric constant within the guide may not necessarily have any serious effects. However, if the increase is too great or if the frequency within the wave guide is near the cut off, the change in dielectric constant may be enough to change the mode of transmission or result in cut off.

What is claimed is:

1. In a device of the character described, a hollow main conducting conduit having an input and an output for transmission of high frequency electric energy, a branch conduit coupled to said main conduit for diverting at least part of the electric energy transmitted, a solid dielectric member extending along said main conduit and filling substantially the entire cross-section thereof, said solid dielectric member being disposed in said main conduit at the junction with said branch conduit, said solid dielectric member having a length of at least a substantial portion of one wave length and means for adjusting said solid dielectric member along said main conduit to vary its position with respect to the branch conduit whereby the phase of the electric field diverted into said branch conduit may be varied while maintaining the over-all phase relationship between input and output constant.

2. The structure of claim 1 wherein said solid dielectric member has tapered end portions to prevent substantial reflection and wherein each tapered portion has a length substantially of the order of one-quarter of a wave length.

3. In a device of the character described, a main coaxial cable comprising an outer conductor and inner conductor with a fiuid'dielectric therebetween, a branch coaxial cable coupled to said main coaxial cable, said branch coaxial cable having the outer conductor metallically joined to the outer conductor of said main coaxial cable, said branch coaxial cable having an inner conductor terminating in a pick-up loop coupled to the fluid dielectric within said main coaxial cable, a solid dielectric member disposed within said main coaxial cable and filling substantially all of the space taken up by the fluid dielectric in said main coaxial cable, said solid dielectric member having tapered ends and extending for a substantial portion of the wave length of transmitted energy and being disposed at the junction with said branch coaxial cable, and means for adjusting the position of said solid dielectric member in said main coaxial cable with respect to said branch coaxial cable whereby the phase of electric energy diverted to said branch coaxial cable may be Varied.

JOHN W. TILEY.

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

UNITED STATES PATENTS Name Date Bowen Sept. 13, 1938 Number OTHER REFERENCES Practical Analysis of Ultra High Frequency,

by Meagher and Markley, published by R. C. A.

1 Service Co., August 1943.

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