US3247474A

US3247474A - Slanted roof type rectangular waveguide having walls constructed to suppress unwanted modes

Info

Publication number: US3247474A
Application number: US320064A
Authority: US
Inventors: Nakahara Tsuneo
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1963-10-30
Filing date: 1963-10-30
Publication date: 1966-04-19
Anticipated expiration: 1983-04-19

Description

April 1966 TSUNEO NAKAHARA SLANTED ROOF TYPE RECTANGULAR WAVEGUIDE HAVING WALLS CONSTRUCTED TO SUPPRESS UNWANTED MODES Filed on. so, 1963 a. L u 4 la. /a.. 56.9. .5 E g. 4

I 2.4 d 2a.- 5.!- 3 a. .54 4 a.

J 4 L0 .3 /a. E195 (d. 35 I 51 6g. 1 5' INVENTOR. 2a.

/ L 3 H15 Arramvev TSUMEOA/AKAHARA United States Patent O 3,247,474 SLANTED ROOF TYPE RECTANGULAR WAVE- GUIDE HAVING WALLS CONSTRUCTED T SUPPRESS UNWANTED MODES Tsuneo Nakahara, Nishinomiya-shi, Japan, assignor to Sumitnmo Electric Industries, Ltd., Osaka, Japan, a company of Japan Filed Oct. 30, 1963, Ser. No. 320,064

7 Claims. '(Cl. 333-73) This invention relates to an improvement on the rectangular waveguide. Its objective is to furnish a rectangular waveguide which will transmit at a low rate of loss only the principal wave that has electric field poralization in the direction of the side walls of the tube. To describe it in further detail the object of this .invention is to transmit at a low rate of loss only the principal wave that has electric field polarization in the direction of the side walls of the tube, solving the degeneration of the wave flowing in the tube of the mode that originally has an equal propagation constant and is in the relation of degeneration.

Other objects and advantages appear hereinafter in the following description and claims.

The accompanying drawings show for the purpose of exemplification without limiting the invention or claims thereto, certain practical embodiments illustrating the principles of this invention wherein:

FIG. 1 is a graphic representation of the dimensional axes of a waveguide.

FIG. 2 is a view of a hollow waveguide of square cross section with all four sides continuous.

FIG. 3 is a view of a hollow waveguide of square cross section with a slit longitudinally in the top of an electr c-conductive side.

FIG. 4 is a view of a hollow waveguide of rectangular cross section the four continuous sides of which have thin layers of loss material and dielectric material on the walls thereof. 7

FIG. 5 is a view of a hollow waveguide of rectangular cross section, three of the walls are continuous andhave their layers of loss material and dielectric material and a slit longitudinally in one electro-conductive side.

FIG. 6 is a view of a hollow waveguide of rectangular cross section, all walls of which are continuous and the upper wall extends outwardly towards a ridge.

FIG. 7 is a view of a hollow waveguide of rectangular cross section, three walls of which are continuous and the upper wall extends outwardly toward a ridge with a slot longitudinally of the ridge.

With a rectangular waveguide which is constituted of an electro-conductive material uniform in all of the directions (X) (Y) (Z), let (a) and (b) represent the transverse dimensions of the waveguide which transmit only the wave of TE mode which is usually the principal and wave and (A) the wave length of the transmitted electromagnetic wave respectively. Then it is necessary that (a) and (b) satisfy the following formulae respectively,

(see FIG. 1). i

Now that hands of exceedingly high frequencies have come to be utilized in recent times, the wave lengths in use are 'becoming shorter and shorter, so that the aforementioned dimensions (a) and (b) of the rectangular waveguide becomes smaller and smaller. This results in an increased transmission loss and lowered power capacity. Consequently, if. a waveguide of a low loss and large capacity is to be obtained also for a band of high frequencies, it is necessary to make both or one of the said dimensions (a) and (b) greater than the aforementioned limits. In the case of such a waveguide, however, the transmission mode is not single, there existing one or more transmission modes of a high order in addition to the TE mode of the principal wave. Even if only the 'I'E mode is excited as is ideal, the transmission energy is converted into high order modes because of the lack of uniformity of the line and its bends, this causing loss, distortion, etc. 'It is therefore necessary to repress the generation high order modes as far as possible. i

As a means to repress the generation of such high order modes, it was proposed'to make a rectangular waveguide whose top and bottom walls are of an electro-conductive material and whose side walls are of poor electro-conductivity in the Z direction and of good electro-conductivity in the X direction, taking advantage of the fact that in the case of TE mode only currents in the X direction flow in the inner surface of the side walls and only currents in the Z direction flow in the center of the inner surface of the top and bottom walls. As a result, it has been shownthat the dimension (a) may be increased to three times the aforementioned limit and the dimension (b) to infinity.

Of TE and TM (m=1, 2, 3 (1:0, 1, 2 however, it is only TE, mode that has the current flowing on the surface of side walls in the-X direction only, and it has been discovered that all the hybrid wave modes (HE modes) having TE, and TM (mn=l, 2, 3 in the relationship of degeneration in the rectangular waveguide mixed belong to this kind of modes. Consequently, the aforementioned waveguide transmits, besides TE mode, I-IE mode at low loss, so that a transmission line desired to trans mit only TE mode at low loss is not obtained.

The rectangular waveguide of this invention is characterized in that it transmits at a low rate of loss only the principal wave that has electric field polarization in the direction of the side walls of the tube, solving the degeneration of the wave flowing in the tube of the mode that originally has an equal propagation constant and is in the relation of degeneration.

The first of the embodiment of this invention is characterized in that the side walls facing each other are made poorly electro-conductive in the axial direction of the tube and electro conduotirve in the direction normal to the axis and athin layer of a dielectric material or magnetic material is provided on the inner surface of each of the said side walls.

A second characteristic of an embodiment is that the side walls facing each other are provided with a thin layer of a dielectric loss material on their inner, surface and a thin layer of a dielectric material or magnetic material is provided further on it. A third characteristic is that one or both of the upper and lower walls facing each other has an inner surface different in efiect from aplane and the side walls facing each other are made poorly electro-condu'ctive in the axial direction of the tube and electro-conductive in the direction normal to the axis.

I will explain the above mentioned characteristics in detail, making reference to the attached drawings. In the figures, the same symbols refer to'the same parts.

FIGURE 2 and FIGURE 3 show embodiments in which the side walls of the waveguide are made poorly electro-conductive in the axial direction of the tube and electro-conductive in the direction normal to the axis and a thin layer of a dielectric material or magnetic material is provided on the inner surface of each of the said side walls.

In FIGURE 2, 1a, 1b are the upper and lower walls made of an electro-conductive material, 2a, 2b are side walls facing each other, made of electro-conductive material 4 and dielectric material 3placed alternately in the axial direction of the tube, so that it is poorly electroconductive in the axial direction of the tube and is electroconductive in the direction normal to the axis. a, 5b are thin layers of a dielectric material or magnetic material provided on the inner surface of the said

side walls

2a, 2b.

In FIGURE 3, the embodiment illustrated in FIGURE 2 is provided in the upper wall In with slits (d) uniform in the longitudinal direction of the tube.

With these embodiments, the degeneration of 'I'F mode and TM mode is solved mainly by the effect of the dielectric material or magnetic material provided on the inner surface of the side walls and HE mode becomes no longer the eigen mode and can no longer be transmitted at low loss. If TE mode whose electric field component is parallel to the wall surface on the side walls is considered, the other modes sustain an exceedingly great loss due to the dielectric material placed alternately with an electro-conductive material to form the side walls, while the loss sustained by TE mode is exceedingly small as compared with other modes. In consequence, it is possible to transmit only TE mode at a low rate of loss by suitably selecting the distance between the side walls facing each other.

FIGURE 4 and FIGURE 5 illustrate embodiments in which the side walls of the rectangular waveguide are facing each other provided with a layer of loss material on the inner surface and a thin layer of a dielectric material or magnetic material is provided further upon it. In the figures, the same symbols as those in FIG- URE 2 represent the same parts. 3a and 3b, and 6a and 6b are the thin layers of a loss material provided on the inner surface of the walls. A

thin layer

4a, 4b, 5a and 5b of a dielectric material or magnetic material is provided further on them. In FIGURE 5, the upper wall 1a is provided with a slit (d) uniform in the longitudinal direction of the tube.

In these embodiments, the degeneration of TE mode and TM mode is solved mainly by the effect of the dielectric material or magnetic material on the inner surface of the side walls, and HE mode becomes no longer the eigen mode and can no longer be transmitted at low loss. If TE mode whose electric field component is parallel to the wall surface on the side walls is considered, the loss sustained by this 'mode from the loss material is exceedingly small as compared with all the other modes. Consequently, it is possible to transmit only TE mode at a low rate of loss by suitably selecting the distance between these side walls facing each other.

FIGURE 6 and FIGURE 7 show embodiments in which one or both of the upper and lower walls are made to have an inner surface different in effect from a plane. In the figures, only the upper wall 1a has outwardly extending slanted planes. As in the embodiment shown in at least FIGURES 2, 3, 6 and 7, the side walls are made poorly electro-conductive in the axial direction of the tube and electro-conductive in the direction normal to the axis, by placing a dielectric material 3 and electro-conductive material 4 alternately. FIG- URE 7 shows the embodiment of FIGURE 6 in which the upper wall 1a is provided with a slit (d) uniform in the longitudinal direction of the tube.

In these embodiments, because one or both of the upper and lower walls have a length dilferent in efiect from that of a plane, the degeneration of TE mode and TM mode is solved and HE mode becomes no longer the eigen mode and can no longer be transmitted at low loss. If TE mode whose electric field component is parallel to the wall surface on the side walls is considered, the other modes sustain a very great loss due to the dielectric material, while the loss sustained by TE mode is exceedingly small as compared with other modes. Consequently, it is possible to transmit only TE mode at a low rate of loss by suitably selecting the distance between the side walls facing each other.

I claim:

1. A rectangular waveguide comprising a tube having upper and lower walls with opposite side walls, at least one of said upper and lower walls facing each other has an inner surface which is different in effect from a plane and the side walls facing each other are made poorly electro-conductive in the axial direction of the tube and electro-conductive in the direction normal to the axis.

2. A rectangular waveguide comprising a tube having upper and lower walls with opposite side walls, at least one of said upper and lower walls facing each other is different in effect from a plane and have a slit uniform in the axial direction of the tube, and the side walls facing each other are made poorly electro-conductive in: the axial direction of the tube and electro-conductive in the direction normal to the axis.

3. A waveguide comprising a tube having a top and a bottom with opposed sides, said top and bottom consisting of an electro-conductive material in slanted planes extending toward an apex that is parallel to the longitudinal axis of the tube, said opposed sides consisting of strip sections alternately in the axial direction of the tube of electr-o-conductive material and of dielectric ma terial to make the whole of each of the opposite sides poorly electro-conductive in the axial direction of the tube but alternately electro-conductive in the direction normal to the axis of the tube, and thin layers of dielectric material aud magnetic material on the inner surfaces of said sides.

4. The waveguide of claim 3 wherein at least one of said top and said bottom of said tube has a slit along the apex in the longitudinal direction of the tube.

5. A waveguide comprising a tube having a top and a bottom with opposed sides, said top and bottom consisting of an electro-conductive material, said opposed sides consisting of strip sections alternately in the axial direction, a plurality of electro-conductive material to make the whole of each of the opposite sides poorly electro-conductive in the axial direction of the tube but alternately electro-conductive in the direction normal to the axis of the tube, thin layers of dielectric material and magnetic material on the inner surfaces of said sides, and slanted planes in at least one of said top and said bottom of said tube extending toward an apex that is parallel to the longitudinal axis of said tube.

6. The waveguide of claim 5 wherein at least one of said top and said bottom of said tube has a slit at the apex of said slanted planes. 1

7. The waveguide of claim 5 wherein at least one of said top and said bottom has a slit in the longitudinal direction of the tube.

FOREIGN PATENTS 1,219,805 12/1959 France.

HERMAN KARL SAALBACH, Primary Examiner.