US2963662A

US2963662A - Sampling device for teoi mode in

Info

Publication number: US2963662A
Authority: US
Publication date: 1960-12-06
Anticipated expiration: 1977-12-06

Description

Dec. 6, 1960 L. B. FELSEN ErAL 6 6 SAMPLING DEVICE FOR TE MODE IN CIRCULAR WAVEGUIDES Filed Dec. 20. 1957 INVENTORS LEOPOLD B. FELSEN WALTER KU? KAHN ATI'ORNEY United States Patent SAMPLING DEVICE FOR 'I'E MODE IN CIRCULAR WAVEGUIDES Leopold B. Felsen, Flushing, and Walter Kurt Kahn, Brooklyn, N.Y., assignors to Polytechnic Institute of Brooklyn, Brooklyn, N.Y., a corporation of New York Filed Dec. 20, 1957, Ser. No. 704,039

7 Claims. (Cl. 333-9) This invention is concerned with a slotted-section or wave-sampling device for use in a circular waveguide in which wave energy is transmitted according to the circular TE mode. The slotted-section according to this invention is useful generally for the same purposes as the conventional slotted-section for rectangular waveguides.

Heretofore, when it has been desired to measure energy transmitted along a circular waveguide according to the circular TE mode, a rectangular slotted-section was inserted in the circular guide, the input end of the rectangular section being connected to the circular guide through a tapered guide section which converted the circular TE mode to the rectangular TE mode, and the output end of the rectangular section was connected to the outgoing section of the circular guide through a tapered section which converted the rectangular TE mode back to the circular TE mode. The present invention provides a slotted section which does not employ a rectangular waveguide section and does not re quire conversion from one mode to another.

A preferred embodiment of the invention is illustrated in the accompanying drawing in which Figure 1 is a side view of a circular waveguide section, embodying the invention, and Figures 1a, 1b, 1c, and 1d are sectional views of Figure 1 taken along the transverse planes a to d, respectively. The wall thicknesses are exaggerated in the drawing.

As shown in Figure 1, the slotted-section of this invention is embodied in a section of circular waveguide which is of circular section at both ends and may be provided with conventional coupling flanges for insertion into a transmission line of circular section. The wall of the circular waveguide section is indented or otherwise formed to provide an elongated trough formed lengthwise of the section and having planar sidewalls joined along their inner edges at the axis of the section. Thus, as shown in Figure la, the wall 1 of the waveguide is indented to form a trough 'having flat sidewalls 2 and 3 extending from the center of the circular waveguide outwardly along radial lines at an angle 0. To reduce wave reflection, both ends of the trough are tapered to a fine edge as will be seen from the sectional views shown in Figures lb, 1c and 1d, it being understood that the two ends of the trough are symmetrically formed about the transverse mid-plane of the trough. As shown in the drawing, it is preferred to form the trough with the wall 3 remaining fiat throughout its length while the wall 2 is curved over its end portions so that the angle between the two walls gradually decreases until wall 2 merges with the wall 3 at the ends of the trough.

The wall 3 is provided with a slot 4 formed therein parallel with the axis of the guide section, and a probe 5 extends through this slot and is suitably mounted to be moved lengthwise of the slot. This slot is located at a position where the currents in wall 3 are purely longitudinal. This condition is satisfied if the slot is 2,953,662 Patented Dec. 6, 1960 spaced from the axis of the section by a distance equal to 0.628 of the radius of the circular section.

Any suitable arrangement may be provided for mounting probe 5 to be moved along this length of slot 4. For example, the probe may be supported at the end of a co-axial cable 6 which is supported on a slide 7 mounted to slide on a rail 8 which is arranged parallel with the slot.

The trough formed by the walls 2 and 3 constitutes a cavity within the circular waveguide having the shape of a cylindrical sector which is closed at both ends. The angle 6 of the sector, the angle between the flat portions of walls 2 and 3, should be just sulficient to permit the mounting of the probe for movement within the slot 4. The end tapers for the trough can then be short by comparison with tapers of equal quality for converting from circular TE mode to rectangular TE mode. Roughly, the ratio of taper lengths in the two cases would be 0/ 211-.

With the arrangement described above, the probe 5 extends through the slot in the wall 3 in a direction parallel with the electric field of the wave energy for the circular TE mode, and the probe will respond to wave energy in the same manner as in the case of a slotted-section of rectangular waveguide.

For the purpose of reducing or suppressing spurious modes which might be excited by the probe, a thin radial wall or fin 9 is mounted in the main guide to form a sampling guide between the wall 3 and the fin 9. Thus, the probe 5 extends into a sectoral sampling guide of small angle which is open at both ends to the main guide. Excitation of spurious modes and reflections can occur only where the main guide and sampling guide rejoin and would be due to transmission phase or amplitude diflerences between these two guides. The phase difierences can be compensated, the amplitude differences cannot be compensated, and must be kept small, i.e., the probe must be lightly coupled.

From the foregoing it will be seen that the invention provides a wave-sampling device in which the probe 5 extends through a longitudinal slot formed in a flat plate 3 arranged radially within the circular waveguide section, the probe extending through the slot in a direction parallel with the electric field for the TE mode and the probe being mounted for movement lengthwise of the slot. The radial plate 9 need not be used except where it is desired to prevent spurious modes developed by the probe. The radial wall 2 is provided to shield the probe and its mounting from wave energy transmitted on the opposite side of plate 3 from the plate 9 and thereby prevent wave reflection from the shielded parts. The cavity formed by the walls 2 and 3 may be closed if desired except for a slot through which the co-axial cable 6 would extend.

We claim:

1. A wave sampling device comprising a section of circular waveguide having circular end portions and a central portion having a V-shaped trough-like cavity formed in the wall thereof parallel with the axis of said section, the walls of said cavity being formed throughout the major portion of the length of said trough as flat walls extending in radial planes from the axis of said section to the cylindrical wall thereof, one of said flat walls being provided with a slot formed in the midportion thereof parallel with the axis of said section, a probe located in said cavity and extending through said slot in a direction tangent to the electric field within said section for the TE mode, and means mounting said probe for movement along the length of said slot.

2. A wave sampling device according to claim 1 and including a thin flat metallic vane mounted in said section along a radial plane displaced by an acute angle from said slotted wall to form a sector-shaped sampling guide for wave energy to be sampled by said probe.

3. A wave-sampling device comprising a section of circular waveguide having circular end portions, meansforming a sector-shaped cavity extending longitudinally within the mid-portion of said section and covering a small angular portion of the transverse area of said-section, said'cavity being closed at its ends by tapered end portions to prevent wave reflection within said section, one radial wall of said sector-shaped cavity being a' flat, wall extending from the axis of said section to the cylindrical wall thereof and having a slot formed in the midportion thereof parallel with. the axis of said section, a sampling probe mounted within said cavity and having anend extending through said slot in a directiontangent to the electric field for the T15 mode within said section, and means mounting saidprobe for movement lengthwise oi said slot;

4. A wave-sampling device comprising a section of circular Waveguide having circular end.- portions, means forming a sector-shaped sampling'guide extending longitudinally Within the middleportion of said section and covering a small angular portion of the transverse area of said section, said sampling guide being open at its ends 'to Wave energy transmitted through said section, one of the radial wallsof said sampling guide having;

a slot formed in the mid-portion thereof parallel with the axis of said section, a probe mounted outside of said sampling guide and extending into said slot, means supporting said probe for movement lengthwise of saidslot, and means within said sec-tion for shielding said probe. and its mounting means from wave energy transmitted through said mid-portion on the outside of said sampling guide.

5. A wave-sampling device comprising a section of circular waveguide having circular end portions, a flat Wall extending longitudinally within the: middlev portion of said section and extending inwardly from the outer wall thereof toward the center of said middle prtion, said flat wall having a slot formed in the mid- 7 portion thereof parallel with the axis of said section,

a probe mounted on one side of said flat wall and extending into said slot, means supporting said probe for movement lengthwise of said slot, and means Within said section for shielding said probe and its mounting means from wave energy transmitted through the middle portion of said section on said one side of said flat wall.

6. A wave-sampling device according toclaim 5 and including a second flat wall mounted in said section along a radial plane displaced by anacute angle from said slotted wall to. form a sector-shaped sampling guide for waveenergy to be sampledby said probe.

7. A wave-sampling device comprising a section of circular waveguide having circular end portions, means forming a sector-shaped sampling: guideiextendingrlongitudinally within the middle portion of said section and covering a small angular portion of the transverse area of said section, said sampling, guide being open at its end to wave energy transmitted through said section, one of theradial walls of said sampling guide having a slot formed in the mid-portion thereof parallel with the axis of said section, a probe mounted outsidezofsaid sampling guide Within a sector-shaped cavity extending longitudinally within the mid-portion of said section and covering a small angular portion of the transverse area of said section, said cavity being closed at its ends by tapered end portions to prevent wave reflections at the ends of said cavity section, the slotted radial Wall of said sampling guide benig in common with the sampling guide and thesector-shaped cavity, and means mounting the said probe to extend through the slot into said sampling guide and for movement along the length of said slot.

References Cited in the file of this patent V UNITED STATES PATENTS 2,129,714 Southworth Sept. '13, 1938 2,419,208 Frantz et al. Apr. 22, 1947 2,848,690 Miller Aug. 19, 1958 2,864,063" Felsen et a1. Dec. 9, 1958