US3396350A - Waveguide - Google Patents

Description

Aug. 6, 1968 w. KRANK ETAL WAVEGUIDE Filed July 28, 1965 Fig. I

3 Sheets-Sheet 1 PRIOR ART Gexwayd SCVLCRLQ b own/L fittoma s Aug. 6, 1968 w. KRANK ETAL 3,396,350

WAVEGUIDE Filed July 28,. 1965 3 Sheets-Sheet 2 Fig. 4

Fig. 5

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Aug. 6, 1968 w. KRANK ETAL 3,396,350

WAVEGUIDE Filed July 28, 1965 3 Sheets-Sheet 3 Inventors: \OoLfgcm Kmnk United States Patent 3,396,350 WAVEGUIDE Wolfgang Kranlr and Gerhard Schickle, Backnang, Germany, assignors to Telefunken Patentverwertungs- G.m.b.H., Ulm (Danube), Germany Filed July 28, 1965, Ser. No. 475,340 Claims priority, application Germany, Aug. 6, 1964, T 26,745; Nov. 23, 1964, T 27,467; Apr. 15,1965, T 28,397

16 Claims. (Cl. 333-95) ABSTRACT OF THE DISCLOSURE A corrugated elliptical waveguide having a non-circular cross section and provided with at least one recess extending in the longitudinal direction of the corrugated guide and disposed symmetrically with respect to the minor cross-sectional axis of the guide for capacitatively loading the guide without substantially decreasing its mechanical flexibility.

The present invention relates generally to the micro wave art, and, more particularly, to a waveguide for transmitting linearly polarized electromagnetic waves of very high frequency and which can be continuously produced.

Among the various conventional forms of waveguides, one form which is called the ridged waveguide is one in which the required dimensions are substantially reduced compared to those of a corresponding rectangular waveguide, and this is accomplished by the capacity load provided by using a ridge or cross-piece. With the same dimensions, the ridged waveguide has a higher limit frequency and a larger bandwidth.

Such a waveguide is shown schematically in FIGURE .1 as being formed by a rectangular waveguide 1 wherein the crosspiece or web 3 is arranged on one broad side a of the waveguide wall and disposed in the longitudinal direction of the waveguide. The height of the web is always smaller than the short side b of the waveguide and the web is symmetrically arranged in the cross section 2 of the Waveguide. This web can be formed by a corresponding recess in the broad side of the waveguide or by a longitudinal rod disposed interiorly of the waveguide. Consequently, the production of such a waveguide requires a larger expenditure than those which are not loaded.

Also, a waveguide which can be wound on a drum, which is constructed of a corrugated tube, and which has an elliptical cross section is already known.

It is the main object of the present invention to provide a novel loaded waveguide which, for the same electrical characteristics has considerable advantages regarding ease of production as compared to known Waveguides.

Another object of the invention is to provide a device of the character described which is relatively simpler and less expensive in construction.

These objects and others ancillary thereto are accomplished in accordance with preferred embodiments of the invention wherein a waveguide for the transmission of linearly polarized electromagnetic Waves of very high frequency can be continuously produced. The waveguide is formed from a corrugated tube having a non-circular cross section and wherein the cross-section edges are free of abrupt changes of direction. The waveguide tube is welded and has a longitudinal seam. The corrugations are prefer-ably arranged in spiral fashion and at least one recess or indention is provided in the direction of the axis of the waveguide and symmetrically with respect to the minor axis thereof. In addition, the corrugation has a cross section which is approximately sinusoidal, the distance between two successive corrugation ridges is between 0.1.

"ice

and 0.25 of the average free space wavelength of the frequency band to be transmitted, the corrugation depth is 0.2 of the major cross-sectional axis, and the length of that portion of the corrugation profile which extends' interiorly into the waveguide is about 10% to 20% shorter than the length of that portion of the corrugation profile which extends outwardly of the waveguide. 1

Additional objects and advantages of the present in.- vention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic perspective view illustrating a known waveguide arrangement.

FIGURE 2 is a schematic sectional view of a waveguide constructed in accordance with the present invention and having a single recess.

FIGURE 3 is a schematic sectional view similar to FIGURE 2 but of another embodiment having a double recess.

FIGURE 4 is a schematic sectional view of a device similar to FIGURE 2 but which is loaded with a dielectric.

FIGURE 5 is a schematic sectional View similar to FIGURE 3 but which is loaded with two dielectrics.

FIGURE 6 is a schematic partial longitudinal sectional view illustrating the dielectric filling in the corrugation grooves.

FIGURE 7 is a view similar to FIGURE 6 illustrating a strip-like dielectric.

FIGURE 8 is a view similar to FIGURE 6 but wherein the dielectric fills only the bottoms of the grooves.

FIGURE 9 is a schematic elevational view of a section of a waveguide wherein various dimensions are shown for explanatory purposes.

FIGURE 10 is a schematic perspective view of a waveguide arrangement having the shape shown in FIGURE 2 and wherein a sheath is provided, with the protective sheath being broken away for purpose of clarity.

With more particular reference to the drawings, FIG- URE 2 illustrates an arrangement of a waveguide constructed in accordance with the invention and wherein a longitudinally welded corrugated tube 4 is provided. This tube has two cross-sectional axes a and b which are disposed at right angles to each other and are of difierent length. A recess 6 is provided in the longer wall of the waveguide and is arranged to be symmetrical to the minor axis b of the cross section and extends for the entire length of the tube in a direction parallel to its longitudinal axis. Thus, the cross section 5 of the waveguide is loaded by the recess 6.

As shown in FIGURE 3, the desired loading of the waveguide can also be obtained by using two recesses 9 and 10 which preferably are identical and symmetrical to the minor cross-sectional axis and wherein the cross section of the waveguide is approximately rectangular when the recesses are not taken into consideration. The shapes and sizes of the recesses depend upon the individual electrical requirements. However, it must be noted that a deep recess decreases the flexibility of the waveguide. It can be seen that the waveguide tube 7 having the two cross sectional axes a and b is provided with the two recesses 9 and 10 as mentioned above and which constrict the cross section 8 symmetrically with respect to the small axis b.

It should be noted that the present invention is not limited only to the cross-sectional shapes shown in FIG- URES 2 and 3, but can be used for different cross sections. For example, it is possible to provide a square, rectangular, round, or elliptical cross-sectional shape, that is the shape not taking the recesses into consideration,

" since the recess'would clearly modify these cross-sectional w 3, forms. Also, the cross section can be arranged to be asymmetrical with respect to at least one of the cross-sectional axes.

I When the, capacity loading of the waveguide is provided by two symmetrically arranged recesses, then the edges of the cross section can be provided in such a manner that they form a Cassinian curve. Such a curve has the following equation expressed in cartesian coordinates:

with the fixed points F F 030), whereby a is a constant and so that an oval with a recess according to FIGURE 3 is provided.

Depending upon the particular apparatus which need be connected to the end of the waveguide, it might be suitable to increase or reduce the load in the end portion and in the extreme case, it would not be loaded at all in order to provide as simple a transition as possible. This can be taken into consideration at the time that the waveguide is produced by changing the recesses toward the end of the waveguide in a suitable manner.

The waveguide can be wound on a drum and due to the load compared to the so-called ridged waveguide it has a larger bandwidth, or, at the same bandwidth, it has smaller dimensions.

The more the cross section of the waveguide deviates from the circular shape the greater is the disadvantageous recess influence on the flexibility of the waveguide.

As a further feature of the invention, the flexibility of the waveguide can be increased by partially replacing the load provided by the recesses by an additional and dielectric load. This makes it possible to use smaller recesses, which increases the flexibility and thereby the usefulness of such a waveguide. On the other hand, if the bandwidth is more important than the flexibility in a particular situation, then an improvement can also be obtained by the use of an additional load. The load can be provided by means of a continuous dielectric member in the form of a flexible strip disposed parallel to the longitudinal axis of the Waveguide. The dielectric member preferably extends into the grooves of the corrugations of the waveguide profile.

FIGURE 4 illustrates a waveguide tube 11 having a recess 13 so as to modify its cross section 12 as in the manner shown. An additional and dielectric load 14 is arranged within the waveguide so that the load provided by the recess 13 can be smaller.

FIGURE illustrates a waveguide 15 provided with recesses 17 and 18. In addition, two dielectric members 19 and 20 are arranged in the cross section 16 and at the recesses.

As shown in FIGURE 6, the dielectric load 23 can be in the form of a continuous strip or web which fills the corrugation grooves 24 of the waveguide tube 22, and which extends parallel to the longitudinal axis 21 of the waveguide tube.

7 FIGURE 7 illustrates a strip-like dielectrical load 28 arranged parallel to the longitudinal axis 25 of the waveguide tube 26 and which rests on the corrugation ridges 27.

Furthermore, the additional load can, when desired, be disposed at periodic distances in the waveguide tube. As shown in FIGURE 8, dielectric elements 32 are disposed in a row or line which is parallel to the longitudinal axis 29 and extend into the corrugation grooves 31 of the waveguide tube '30. The cross section of the load can be varied and this can be done in a manner which keeps the dielectric losses as low as possible. Therefore, the load in the form of a dielectric member is applied at those places where it is the most effective, that is, if the wave guide tube is provided with a recess, at the same place as the recess, or diametrically opposite the recess. If two recesses are provided in the waveguide, then the dielectric load should be applied on one of these two recesses. Be sides the load being influenced by the position and dimensions thereof, it is also influenced, as is known, by the particular dielectric material which is selected in accordance with when'e is the eflective relative permittivity. p

.The dielectric load may be applied during the manufacturing of the waveguide tube. The tube is normally constructed of a metalband which is bent into a circular cross-sectional shape and then longitudinally welded. The smooth or even tube which is thus produced is then provided with the desired corrugation and reshaped in cable-making machinery to have the predetermined cross section. The dielectric coating or load can be applied, during the continuous manufacturing process, on the band before it is bent and this can be accomplished by gluing or spraying. The use of a foam dielectric such as tetrafluorethylene is preferably because of its flexibility.

In order to reduce interfering reflections of a wave fed into the device on the corrugation profile the corrugation can be approximately sinusoidal. The distance e as shown in FIGURE 9 between two corrugation ridges is between 0.1 and 0.25) where A is the awerage wavelength in free space of the frequency band which is to be transmitted. The depth of the corrugation t is smaller than 0.2 of the length of the major cross-sectional axis which is a in FIGURE 2. The length 0 of the portions 32 of the corrugation which extend downwardly or interiorly toward the waveguide tube is arranged to be 10 to 20% shorter than the length d of the portions 33 of the corrugation which extend outwardly.

When the waveguide tube is provided with spiral type corrugation, the pitch of the corrugations should be between 5 and 15 and 8 has proved to be a preferred value.

When the corrugations are arranged to have a profile of the type described above, a sufiicient flexibility of the waveguide is assured and at the same time the reflection factor is considerably decreased with respect to conventional devices. Thus, there is provided a flexible waveguide which can be quickly assembled and which can be used for the transmission of wide bands. Since the waveguide can be continuously produced and can be wound on a drum, the waveguide is particularly suitable for use as an antenna feeder line and in assembling mobile stations. Attenuation and reflection characteristics are com.- parable to rigid or non-flexible waveguide arrangements.

In order to avoid mechanical damage to the waveguide and at the same time to provide protection against corrosion, a non-abrasive plastic sheath or coating can be provided about the waveguide which can be a polyisobutylene mixture with graphite added. Such an arrangement is shown in FIGURE 10 wherein a protective coating 35 is provided on a corrugated waveguide 34.

In the production of this device, it is preferable to deform a longitudinally welded corrugated tube having a circular cross section in a continuous process in a swageing device until the desired cross section is obtained. Subsequently, the corrugated tube is treated by plastic extruding devices which provide a plastic covering which fills the grooves of the corrugation.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and rangeof equivalents of the appended claims. a

What is claimed is:

1. A continuously produceable waveguide arrangement for the transmission of linearly polarized waves of very high frequency comprising a corrugated tube welded longitudinally and having a non-circular cross section provided with corrugations, and having at least one recess disposed in the longitudinal direction of the corrugated tube and arranged symmetrically with respect to the minor cross-sectional axis, wherein the corrugation has a cross section which is approximately sinusoidal, the distance between two successive corrugation ridges is between 0.1 and 0.25 of the average free space wavelength of the frequency band to be transmitted, the corrugation depth is 0.2 of the major cross-sectional axis, and the length of that portion of the corrugation profile which extends interiorly into the waveguide is about to shorter than the length of that portion of the corrugation profile which extends outwardly of the waveguide.

2. An arrangement as defined in claim 1 wherein the entire waveguide device is symmetrical with respect to the minor axis of the cross section.

3. An arrangement as defined in claim 1 wherein the corrugations are in spiral form.

4. An arrangement as defined in claim 1 wherein two recesses are provided which are opposite each other.

5. An arrangement as defined in claim 4 wherein said recesses are identical.

6. An arrangement as defined in claim 1 further comprising at least one dielectric load which extends parallel to the longitudinal axis of the waveguide.

7. An arrangement as defined in claim 6 wherein said dielectric load is provided by a continuous flexible dielectric member.

8. An arrangement as defined in claim 7 wherein the dielectric load fills the corresponding corrugation grooves of the waveguide profile.

9. An arrangement as defined in claim 7 wherein the dielectric member is in strip form.

10. An arrangement as defined in claim 6 wherein said load is provided by dielectric elements disposed at periodic distances from each other and which are arranged in the corrugation grooves.

11. An arrangement as defined in claim 6 wherein there is a single recess and said dielectric load is disposed symmetrically with respect to the minor crosssectional axis.

12. An arrangement as defined in claim 11, wherein said dielectric load is disposed along said recess.

13. An arrangement as defined in claim 11, wherein said dielectric load is disposed opposite said recess.

14. An arrangement as defined in claim 6 wherein there are two recesses and the dielectric load is provided at least at one of the recesses.

15. A waveguide arrangement for the transmission of linearly polarized waves of high frequency comprising a corrugated tube having a non-circular cross section, the corrugations being approximately sinusoidal and the distance between two successive corrugation ridges being between 0.1 and 0.25 of the average free space wavelength of the frequency band to be transmitted, the corrugation depth being 0.2 of the major cross-sectional axis, and the length of that portion of the profile extending interiorly into the waveguide being about 10 to 20% shorter than the length of that portion of the corrugation profile which extends exteriorly thereof, said arrangement further comprising a non-abrasive plastic covering disposed over said tube.

16. A waveguide arrangement as defined in claim 15 wherein the corrugations are arranged to be in spiral fashion and the pitch of the corrugation is between 5 and 15.

References Cited UNITED STATES PATENTS 1,996,186 4/1935 Aifel 333- 2,563,578 8/1951 Candee 333--95 2,590,511 3/1952 Craig et al. 333-95 2,632,805 3/1953 Vogeley et a1. 33395 2,675,832 4/1954 Hamilton 333-95 3,090,019 5/1963 Johnson et a1. 333-95 3,200,356 8/1965 Shuttloifel et a1. 33395 3,299,374 1/1967 Schickle et a1 33395 FOREIGN PATENTS 877,692 9/ 1942 France.

739,488 11/1955 Great Britain. 1,061,850 7/1959 Germany.

425,104 9/ 1947 Italy.

OTHER REFERENCES New Flexible Heliax Waveguide, Andrew, Bulletin 8529, received February 1964.

HERMAN KARL SAALBACH, Primary Examiner.

L. ALLAHUT, Assistant Examiner.

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