US3601720A

US3601720A - Helical waveguide with varied wall impedance zones

Info

Publication number: US3601720A
Application number: US752271A
Authority: US
Inventors: Tsuneo Nakahara; Masao Hoshikawa
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1967-08-16
Filing date: 1968-08-13
Publication date: 1971-08-24
Anticipated expiration: 1988-08-24
Also published as: FR1578428A; GB1235315A; DE1765940A1

Abstract

Manufacturing methods of the helical waveguide that the wall impedance of the wall structure of the waveguide is alternated discontinuously or continuously in the direction of the axis of the helix by means that jacket or tape of insulating or lossy material having diverse dielectric constants, or roving of lossy material is located on the helix of the waveguide to make the wall structure having the alternated wall impedance and their products.

Description

United States Patent I 1 I l l U I l I-IELICAI. WAVEGUIDE WITH VARIED WALL IMPEDANCE ZONES 9 Claims, I2 Drawing Figs.

US. Cl 333/95, 333/83 A, 333/98 M 1m. Cl IIOlp 3 12, HOlp l/l6 Field ofSearch 333 95,9s A, 95 s [56] References Cited UNITED STATES PATENTS 3,158,824 ll/l964 Larsen et a]. 333/95 FOREIGN PATENTS l,036,34l 7/l958 Germany 333/95 1,068,772 I 1/1959 Germany 333/95 Primary Examiner-Herman Karl Saalbach Assistant ExaminerSaxfield Chatmon, Jr. Attorney-Carothers & Carothers ABSTRACT: Manufacturing methods of the helical waveguide that the wall impedance of the wall structure of the waveguide is alternated discontinuously or continuously in the direction of the axis of thehelix by means that jacket or tape of insulating or lossy material having diverse dielectric constants, or roving of lossy material is located on the helix of the waveguide to make the wall structure having the alternated wall impedance and their products.

PATENTED M248?! 3501.720

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HELICAI. WAVEGUIDE WITH VARIED WALL IMPEDANCE ZONES BACKGROUND OF THE INVENTION l. Field ofthe Invention The present invention relates to a device for the longdistance transmission of electromagnetic wave energy, particularly millimeter wave energy.

2. Description of the Prior Art A helical waveguide is known as the best transmission line for the TE wave mode transmission of millimeter wave energy. A helical waveguide of the prior art is shown in FIG. I, which has a construction wherein a thin insulated copper wire I is helically wound to make an inner surface of the waveguide, said helical wire being surrounded by a jacket 2 of a uniform thickness, usually comprising two layers, one of which is an impedance-transforming layer and the other a lossy layer placed thereon, said jacket 2 being further covered by a protective jacket 3 such as an iron pipe. In place of the helically wound wire, conductor rings sufi'lciently thin for the wavelength may be placed side-by-side to form the inner wall of the waveguide. The electric conductivity of the inner surface of such a helical waveguide is anisotropic. That is to say, the resistivity in the circumferential direction of the helix 1 is small, but the resistivity in the axial direction is infinitely large.

A helical waveguide has a property'that a TE mode which has circular electric component, propagates almost without suffering any attenuation, while, on the contrary, the mode waves which have the electric current component in the axial direction are absorbed and greatly attenuated.

For instance, an attenuation of the TE mode is approximately l.3l .4 db./km. as proved by experiment, for a helical waveguide of 5 l-mm. inner diameter at 50 GC.

Generally speaking, if the inner surface of a helical waveguide is perfectly round and geometrically straight in the direction of the axis, spurious modes will not appear due to mode conversion and there takes place only the attenuation of an exponential function of axial distance due to the heat loss, when the TE mode is applied to said helical wire waveguide.

In the instance where the inside of the helical waveguide has some irregularity or deformation, however, the TE mode degenerates into other spurious modes and a mode conversion loss takes place. The modes degenerated from the TE mode are dependent on the irregularity or deformation.

TEon (here n is a positive integer) modes are caused by the variations in the inner diameter of waveguide, while TXin (here X is E or M, n is a positive integer) modes, such as TM TM TE TE are caused by the bending of the axis.

Among these spurious modes, the TE and TE modes deteriorate, particularly the transmission characteristics therein of the TE mode. The T5,, mode couples strongly with the TE mode and is extremely difficult to remove.

It is well known that the jacket 2 shown in FIG. 1 contributes effectively to the absorption of these unwanted modes as much as possible.

The Smith chart of wall admittance of the helical waveguide as shown in FIG. 1 is shown in FIG. 2.

The central point of this chart is normalized by the wall admittance viewed radially from the inside of waveguide, for example 4/{3 Yo(Yo: free space admittance) where the jacket 2 on the helix 1 is made of insulating material having dielectric constant of 4 and the frequency of the transmission wave is 55.5 GC.

On this admittance chart, two groups of lines of equal transmission losses are drawn, one group of solid lines being for the TE mode and the other group of dotted lines for the TE, mode. It is noted from this chart that any one point on this chart which represents a wall admittance of the helical waveguide corresponds to two transmission losses for the TE mode and the-TE mode shown by two groups of lines.

When a wall admittance is determined to give a greater transmission loss for TE the transmission loss for TE, cannot be taken freely.

The thick line 4 in this chart denotes a trajectory of wall admittance which should be selected to take both transmission losses of the TE and TE modes greater values at the same time. It follows from this that the transmission loss of the TE mode is restricted by the transmission loss of the TE mode.

It is necessary to take both transmission losses of the TE, and the TE as great as possible in order to suppress the signal distortion due to the spurious modes.

This is the essential shortcoming of the helical waveguide of the prior art as shown in FIG. I.

BRIEF EXPLANATION OF DRAWINGS FIG. 1 is a cross-sectional view of a helical waveguide of the prior art.

FIG. 2 is a Smith chart of the wall admittance of a helical waveguide showing two groups of lines of equal attenuation constants of the TE and TE modes.

FIGS. 35, and 11- are cross-sectional views in side elevation of the helical waveguides constructed in accordance with the present invention.

FIG. 6b, FIG. 7b FIG. 8, FIG. 9 and FIG. 10 are perceptional views to explain the manufacturing method of the embodiments of the present invention.

FIG. 12 is a graph of the frequency characteristic curves of the attenuation constant of the TE mode wave.

DESCRIPTION OF PREFERRED'EMBODIMENTS The present invention provides a' new improved helical waveguide which is free from the shortcomings of prior art. The undesirable interrelationship between the attenuations of the TE and TE, modes can be broken by the present invention. The present invention provides helicalwaveguides in which the wall impedance is alternated continuously or discontinuously in the direction of the axis of the helix, for example, by means such that jackets of insulating materials having diverse dielectric constants respectively are located alternately on the helix of the waveguide in the axial direction. Referring to FIG. 3, a cross-sectional view of a helical wave guide is shown as an illustrative embodiment of the present in-' vention.

This waveguide comprises an insulated conductive wire 1 "of a relatively fine diameter closely wound in a helix, with two kinds of jackets 5 and 6 of insulating materials having different dielectric constant from each other alternately surrounding the helix 1 and the outer protective jacket 3 further surrounding the jackets 5 and 6.

In the embodiment as shown in FIG. 3, it is made possible by the present invention to design the jackets 5 and 6 to have greater transmission losses for the TE and TE modes than those of a conventional helical waveguide having a uniform wall impedance. For example, when the wall admittance of the jacket 5 is selected to give 10 db./m. and 2 db./m. of the transmission-losses for the TE and TE respectively, those-of the jacket 6are 0.5 db./m. and 20 db./m. for the TE and TE}, respectively, and the lengths in the axial direction of jacket 5 and 6 are taken as 5 cm. and 10 cm. with respect to each other, the transmission losses of this helical waveguide are approximately 7 db./m. for the TE mode and 8 db./m. for TE mode which is enhanced more than 5-6 db./m. as compared to the case where a loss of 2-3 db./m. of the TE could hardly be obtained by the undesirable interrelationship between the losses when the loss of the TB of a helical waveguide having a unifonn wall impedance is selected as 7 db./m. or so.

A practical structure of this'helical waveguide is as follows.

A copper 0.14 mm. diameter wire 1 coated with an enamel layer of 20p thickness; is wound closely in a helix to form a circular inner surface of the waveguide of 5.l-cm. diameter. Jackets 5 and 6 are surrounded on this helix 1 repeatedly in an alternate sequence. Their lengths in the axial direction are 5 cm. and 10 cm. respectively. Jacket 5 is made of an insulating material layer of dielectric constant 4 and a thickness of 12011.,

and the lossy layer has a specific resistance Zfl-cm. of 0.4

mm. thickness placed over the insulating material layer.

db./m. for the TE mode and 20 db./m. for the TE mode.

The apparent transmission losses of the waveguide of such a structure become approximately 7 db./m. for the TE and 8 db./m. for the TE This embodiment of the present invention has a wall structure making use of two kinds of jacket portions, but it is equally applicable to the embodiment of the present invention to make use of three or more kinds of jackets.

It is also applicable to the embodiment of the present invention to form the wall structure making use of tapes of two or more kinds of material having diverse dielectric constants wrapped in parallel over the helix. 4

It is further applicable to the embodiment of the present invention to form the'wall structure making use of an electrically lossy roving wound closely and sparsely over the helix.

An embodiment of the present invention which has the wall structure of three jackets is shown in FIG. 4.

In FIG. 4, 1 denotes a helical wire, 7, 8 and 9 denote three jackets of insulating materials of different dielectric constants from each other having predetermined axial lengths respectively. 3 denotes an outer protective jacket.

Another embodiment of the presentinvention which has the wall structure of wrapped tapes is shown in FIG. 5.

In FIG. 5, 1 denotes a helical wire, 10 and 11 denote the two tapes of insulating materials of different dielectric constants from each other wound over the helix 1, and 3 denotes an outer jacket.

A helical waveguide having the wall structure of jackets or tapesof difi'erent materials has an apparent transmission constant ofan equivalent waveguideffor example, when two kinds of jackets or tapes are used, their wall impedances are Za and lb respectively and their axial lengths are la and lb longer than the wavelength of the transmission wave, the apparent transmission constant is approximately equal to the transmission constant of a waveguide which has a wall impedance represented by following formula The design of a helical waveguide having a'desira'ble transmission constant will be easily performed by means of selecting the insulating materials of the jackets to have the desirable wall impedances and the axial lengths of the jacket.

It is also possible to design a helical waveguide having a broad frequency band, for example, 30-100 GC, in such a manner that the wall structures are designed for several frequencies over a broad frequency band, for example 40, 60 and 80 GC, and these wall structures are located repeatedly and axially.

A brief explanation of a manufacturing method of the helical waveguides of the invention will be taken up in the following discussion. In FIG. 6a, a tape forming the wall structure of the helical waveguide is shown.

This tape has two

different dielectric zones

12 and 13 alternately changed with a pitch distance longer than a number of circumferences or turns of the helix of the waveguide.

This tape is wrapped as shown in FIG. 6b over the helical' wire I forming the inside wall of waveguide of an insulated enameled copper wire being wound closely on a smoothly polished mandrel 14 which will be subsequently removed.

' iron 'pipe are evacuated, this space is filled by the thermosetting epoxide resin and the resin is set by heating.

' Another embodiment of the present invention is shown in FIG. 7. The tape shown in FIG. 7a, which has two different dielectric constant parts 15 and 16, are varied continuously with a pitch distance sufficjently longer than a number of circumferences or turns of the helix of the waveguide and is wrapped helically and closely on the helix 1 formed upon the mandrel 14 to form a wall structure of the waveguide having varying wall admittance zones 15 and 16 as shown in FIG. 7b.

Still another embodiment of the present invention is shown in FIG. 8.

In FIG. 8, a lossy roving 17 is wound in turns closely and I sparsely, alternately, around the helix 1 formed upon mandrel 14 to form the wall structure of the waveguide having varying

wall admittance zones

18 and 19.

Still another embodiment of the present invention is shown in FIG. 9.

In FIG. 9, lossy roving 17 is wound in a direction nearly vertical and in a direction slanting to the vertical direction, repeating these winding alternately over the helix 1 formed on I wrapped in parallel with each other helically and closely ,over

the helix 1 formed on the mandrel 14 to form the wall structure of thewaveguide having different wall admittance zones ductive material or by partially carbonizing a tape of acryl resin fiber. The roving used in the examples of FIG. 8 and 9 is I prepared by making a roving of glass fiber conductive by coat ing it with graphite.

Another embodiment of the present invention is shown in FIG. 11. In FIG. l l,'two kinds of tapes of insulating material of sufficiently broader width than the wavelength and of the The wrapped tape forms the wall structure having the two

zones

12 and 13 of different wall impedance, which is made of several turns of tapes. After wrapping this tape, a glass fiber roving is wrapped spirally many. times on the tape until the different thickness, are wrapped helically in parallel and inclose contact with each other on the helix 1 to form the wall structures having the different impedance-transforming

layers

24 and 25.

A lossy layer 26 is formed upon the layers '24 and 25. Over the lossy layer 26, a glass fiber roving is wrapped many times to get the required thickness of the glass fiber layer 27. An armor 3, for example an iron pipe surrounds the glass fiber layer 27.

FIG. 12 shows the frequency characteristics of the'attenuation constant of the TB mode wave of the helical waveguides as shown in FIG. 11, and of the helical waveguide-having a uniform transforming layer of the prior art.

In FIG. 12, two

solid lines

28 and 29 show the characteristic curves of a prior art helical waveguide and a dotted line 30 'shows that of the helical waveguide as shown in FIG. 11 from the results of experiment.

One of the helical waveguide of the prior art used in this experiment showing the results of curve 28, has an impedancetransforming layer of a uniform thickness of 50p. and consists of insulating material having a dielectric constant 4. Thereupon a lossy layer of 0.4-mm. thickness, made of the acryl resin fiber roving carbonized at the temperature near 800 C. and

Another waveguide of the prior art showing the curve 29, has an impedance-transforming layer of a uniform thickness of a and consists of insulating material having a different dielectric constant, and thereupon the lossy layer of 0.4-mm.- thickness made of the same material as in the former case was applied.

Attenuation constants of this latter helical waveguide are 9 db./m. for the TE mode and 1.5 db./m. for the TE at 50 GC and 4 db./m. for the TE. and l db./m. for the TE at 80 GC.

The waveguide as shown in FIG. 11 showing the curve 30, has two kinds of impedance-transforming layers of the different thicknesses 50 and 15011. of same axial length 7 cm., located alternately, which is made of a same insulating material of the dielectric constant 4 and thereupon a lossy layer of the same material of the specific resistivity 2 Q-cm.

It is noted from FIG. 12 that the attenuation characteristic curve of TE mode in accordance with the present invention lying between the

curves

26 and 27 has good frequency characteristics.

It is possible to easily design helical waveguides having various attenuation characteristic curves lying between the

curves

26 and 27, according to the present invention.

We claim:

1. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, said wall impedance values being substantially uniform over each of said zones, the axial length of each of said zones being large compared to the wavelength to be used.

2. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, said jacket made of a plurality of tubes of insulating material, any two adjacent ones of which have different dielectric constants, the axial length of each of said tubes being sufficiently longer than the wavelength in use, and a lossy layer surrounding said tubes.

3. The helical waveguide of claim 1 wherein said helical conductor wire is insulated.

4. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, the axial length of each of said zones being large compared to the wavelength to be used, said jacket consisting of a helical wound tape having different adjacent electrically dissipative zones therealong.

5. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values,'the axial length of each of said zones being large compared to the wavelength to be used, said jacket consisting of a roving of electrically dissipative material helically and alternately wound densely and sparsely in adjacent longitudinal zones respectively on said helix to alternately provide said zones.

6. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, the axial length of each of said zones being large compared to the wavelength to be used, said jacket consisting of an insulative tape helically wound on said helix and having a plurality of different zones therealong of different dielectric constants, each of said tape zones being sufiiciently long to provide said axially arranged zones.

7. A helical waveguide as claimed in claim 6 wherein said tape zones graduate one into the other without abrupt change.

8. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, said jacket consisting of a plurality of tapes wound helically in parallel over said conductive wire, each tape being made of insulating material having different dielectric constants than another, the width of each of said tapes being sufficiently longer than the wavelength in use, and a lossy jacket surroundingsaid insulating jacket.

A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which is made of a plurality of tubes of insulating material, any two adjacent ones of which have substantially the same dielectric constant and different thicknesses, the axial length of each of said tubes being sufficiently longer than the wavelength in use, and a lossy layer surrounding said tubes.

Claims

5. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, the axial length of each of said zones being large compared to the wavelength to be used, said jacket consisting of a roving of electrically dissipative material helically and alternately wound densely and sparsely in adjacent longitudinal zones respectively on said helix to alternately provide said zones.

6. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, the axial length of each of said zones being large compared to the wavelength to be used, said jacket consisting of an insulative tape helically wound on said helix and having a plurality of different zones therealong of different dielectric constants, each of said tape zones being sufficiently long to provide said axially arranged zones.

8. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which has a plurality of axially arranged zones, any two adjacent ones of which have different wall impedance values, said jacket consisting of a plurality of tapes wound helically in parallel over said conductive wire, each tape being made of insulating material having different dielectric constants than another, the width of each of said tapes being sufficiently longer than the wavelength in use, and a lossy jacket surrounding said insulating jacket.

9. A helical waveguide comprising a conductive wire wound in a substantially helical form, a jacket over said helix which is made of a plurality of tubes of insulating material, any two adjacent ones of which have substantially the same dielectric constant and different thicknesses, the axial length of each of said tubes being sufficiently longer than the wavelength in use, and a lossy layer surrounding said tubes.