US3787787A - Circular waveguide mode filter - Google Patents

Circular waveguide mode filter Download PDF

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Publication number
US3787787A
US3787787A US00272037A US3787787DA US3787787A US 3787787 A US3787787 A US 3787787A US 00272037 A US00272037 A US 00272037A US 3787787D A US3787787D A US 3787787DA US 3787787 A US3787787 A US 3787787A
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Prior art keywords
waveguide
circular waveguide
mode
semicircular
mode filter
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Expired - Lifetime
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US00272037A
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English (en)
Inventor
S Shimada
K Hashimoto
K Kondoh
M Koyama
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NTT Inc
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Nippon Telegraph and Telephone Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/16—Auxiliary devices for mode selection, e.g. mode suppression or mode promotion; for mode conversion
    • H01P1/163—Auxiliary devices for mode selection, e.g. mode suppression or mode promotion; for mode conversion specifically adapted for selection or promotion of the TE01 circular-electric mode

Definitions

  • ABSTRACT A circular waveguide mode filter is provided which comprises a circular waveguide consisting of an upper 10 Claims, 19 Drawing Figures PMEMEMNZZ'QM Y 3.787.787"
  • the present invention relates to generally a filter used in TE mode transmission lines composed of circular waveguides and more particularly a circular capable of giving high attenuation to the undesired higher modes such as the circular TE mode without affecting the propagation of the desired circular TE mode.
  • Circular waveguides used in the millimeter wave communication systems generally have an inner diameter considerably greater than the wavelength of the desired TE mode in order to reduce the attenuation due to the wall heat loss of said mode.
  • the circular waveguide for a millimeter wave communication system whose frequency range is from 40 to 80 GHz or from 40 to l20 GHz has an inner diameter from 40 to 60 mm. Therefore, a considerable number of modes can be propagated through the circular waveguide.
  • the undesired modes other than the circularly symmetric modes such as TE TE and TE may be sufficiently suppressed, so that the circular waveguide line must be generally provided with mode filters'for attenuating the undesired TE modes (n E 2).
  • the undesired modes TE are generated in the corner waveguides which may be regarded as a sort of mirror capable of bending the microwaves at sharp angles at bends. ln inter-city or interoffice trunk lines which have a considerable number of bends, the corner waveguides are used so that the degradation of the transmission characteristic occurs due to the conversion and reconversion of the TB. signal mode and the undesired TE (n y; 2) modes. Therefore, mode filters must be provided capable of absorbing the undesired modes generated in the corner waveguides.
  • the present invention is mainly directed to the absorption and attenuation of the TE mode, but it should be understood that the present invention may be also applied to the absorption and atteniiation of other undesired modes.
  • the undesired TE mode may be absorbed by the lossy material.
  • the attenuation of the undesired TE mode higher than 2 dB/m attained by the resonant slot type mode filter is in the relatively narrow frequency band of 5 Gl-lz at 50 Gl-lz.
  • the resonant slot type mode filter is not adapted for use in the broad band.
  • the higher the frequency the lower becomes the attenuation of the undesired TE mode.
  • a circular waveguide mode filter of the type comprising a pair of upper and lower semicircular waveguide sections having different radii.
  • the underlyin'gprinciple of the circular waveguide mode filter is based on the fact that the phase velocities of the semicircular modes propagating through the semicircular waveguide sections having different radii are different from each other.
  • the undesired TE mode maybe attenuated without the desired TE mode being adversely affected.
  • the phase'difference between the pair of semicircular waveguide sections is an integer integral of 2w, (that is 2mr'where n 0, l, 2, 3 so that the electric fields of the TE.
  • the modes may be directed in the same directions at the outlet of the each semicircular waveguide.
  • the specific phase relations described above are not maintained when the frequency varies sothat the insertion loss of the TB mode is increased.
  • the prior art circular waveguide mode filter is not effective over a broad band.
  • the attenuation of the undesired TE mode is dependent solely upon the mode conversion at the output of the waveguide so that the multiple reflections in the semicircular waveguide sections occur.
  • the TE mode absorption effect is reduced and the reflection characteristic of the desired TE, mode is adversely affected.
  • the mode conversion At the outlet of the waveguide, the mode conversion generates diverse modes some of which cannot be effectively absorbed by the helix waveguide. Therefore, the reconversion into the TE mode will occur at .the imperfect portions of the helix waveguide.
  • One of the objects of the present invention is therefore to provide an improved circular waveguide mode filter with a broad band width.
  • Another object of the present invention is to provide an improved circular waveguide mode filter which is shorter in over-all length, simple in construction and reliable and dependable in operation and not so severe in manufacturing and laying tolerances or errors as compared with the prior art mode filters.
  • a circular waveguide mode filter comprises a pair of semi-circular waveguide sections having different radii, and a dielectric disposed in the semicircular waveguide section having a smaller radius at such a position where said dielectric will not adversely affect the TE mode propagating through said semicircular waveguide section with a smaller radius.
  • phase velocity of the TE mode propagating through the semicircularwaveguide section with a smaller radius becomes different from that of the TE mode propagating through the other semicircular waveguide section with a greater radius so that the field intensity of the TE mode propagating through the semicircular waveguide section with a smaller radius is directed at the outlet of the mode filter in the direction opposite to that of the field intensity of the TE mode propagating through the other semicircular waveguide section with a greater radius.
  • the apparatus radius of the semicircular waveguide section with a smaller radius becomes equal to that of the other semicircular waveguide section with a greater radius because of the dielectric or magnetic material disposed in the semicircular waveguide section with a small diameter so that the TE modes propagating through the both waveguide sections become equal in phase velocity.
  • the circular TE mode is derived from the outlet of the circular waveguide mode filter whereas the undesired circular TE mode is absorbed by the mode filter.
  • FIG. Us a perspective view partly in section of a circular waveguide mode filter in accordance with the present invention.
  • FIG. 2 is a cross sectional view thereof
  • FIGS. 3a through 3d illustrate the electric and magnetic' field distributions of the circular TE and TE modes used for explanation of the underlying principle of the present invention
  • FIGS. 4(a) and 4(b) are curves ilustrating the insertion loss of the TE mode and attenuation loss of the TE moade respectively of a circular waveguide without the dielectric of FIG. 1;
  • FIGS. 4(c) and 4(d) are curves corresponding to FIGS. 4(a) and 4(b) respectively when a dielectric is employed, as shown in FIG. 1.
  • FIGS. 5a and 5b illustrate the advantages of the circular waveguide mode filter in accordance with the present invention over the prior art wave coupling type mode filter
  • FIGS. 6(a) and 6(b) are cross sectional views of a second and a third embodiments of the present invention of the type utilizing the dielectric materials;
  • FIGS. 7(a) and 7(b) are cross sectional views of a fourth and fifth embodiments of the present invention of the type utilizing the magnetic materials;
  • FIG. 8 is a longitudinal sectional view of a modification of the embodiment shown in FIG. 1;
  • FIGS. 9(a) and 9(b) are top views of modifications of a thin metallic slab or sheet partition wall having resistor elements or films.
  • a circular waveguide mode filter generally designated by l in accordance with the present invention generally comprises an upper and lower semicircular waveguide sections 10 and 20 partitioned from each other by a thin metallic slab 2.
  • the middle waveguide section 13 of the upper semicircular waveguide section 10 has a radius smaller than that of the lower semicircular waveguide section 20, and a semicylindrical dielectric 3 having a radius smaller than that of the middle waveguide section 13 is disposed inside the section 13 coaxially thereof. More particularly, as shown in FIG.
  • the radius R of the lower waveguide section 20 is greater than the radius R of the middle waveguide section 13, and the semi-cylindrical dielectric 3 has a radius equal to 0.5462R'.
  • the middle waveguide section 13 has both of its ends joined to the semicircular waveguide sections 11 and 15 on the sides of the input and output respectively, through tapered semicircular waveguide sections 12 and 14, respectively.
  • the radial field distributions of the transverse electric field components E and the longitudinal magnetic field components Hz of the TE and TE modes are shown in FIG. 3. That is, the electric field distributions of the TE and TE modes are shown in FIGS. 3(a) and 3( b), respectively, whereas the magnetic field distributions are shown in FIGS. 3(c) and 3(d), respectively.
  • the electric field component E of the TE mode becomes zero at a point spaced apart by 0.5462R from the center. Therefore when the dielectric 3 is disposed as shown in FIG.
  • the TE semicircular waveguide propagating through the section 10 is not substantially affected by the dielectric 3 except that its phase velocity is changed because the radius of the middle waveguide section 13 is smaller.
  • the apparent radius of the section 10 becomes greater because of the influence from the dielectric 3.
  • phase velocities of TE modes propagating through the semicircular waveguide sections 10 and 20 are different from each other because of the difference in radius of the upper and lower semicircular waveguide sections 10 and 20. Therefore, it becomes possible to reverse the directions of the TE modes propagating through the waveguide sections 10 and 20 at the outlets thereof if the lengths thereof are suitably selected. Furthermore, for the TE modes the apparent radius of the upper semicircular waveguide 10 may become equal to the radius of the lower semicircular waveguide section 20 when the radii of the upper and lower semicircular waveguide sections 10 and 20 and the dielectric material 3 are suitably selected. As a result, there will be difference in phase velocity between the TF modes propagating through the upper and lower semicircular waveguide sections 10 and 20. That is, the directions of the electric fields of the TE., modes at the outlets of the semicircular waveguide sections 10 and 20 become equal. In this case, the TE modes propagating through the upper and lower semicircular waveguide sections 10 and 20 have no phase difference.
  • the circular waveguide shown in FIG. 1 comprising the input and output waveguide sections 11 and 15, 100 mm in length, the tapered waveguide sections 12 and I4, 75 mm in length and the middle section 13, 300 mm in length and having the overall length of 650 mm was used.
  • the radius R of the upper semicircularwaveguide section 10 was 23.0 mm whereas the radius R of the lower semicircular waveguide section 20 was 25.5 mm.
  • the semi-cylindrical dielectric 13 with a dielectric constant of 1.03 and a length of 100 mm and a thickness of 2.0 mm was disposed in the semicircular waveguide section 10 at a distance of 0.5462R' from the center thereof.
  • FIGS. 4(a) and 4(b) show the insertion loss characteristic of the TE mode and attenuation loss characteristic of the TE mode when the dielectric 3 was not used.
  • the loss of the TE mode signal is relatively higher, about 2 dB at a low frequency, and therefore is not satisfactory in practice.
  • the better TE mode characteristic corresponding to the theoretical value may be obtained.
  • FIGS. 4(c) and 4(d) show the corresponding characteristics when the dielectric 3 was inserted.
  • the experimental values are indicated by the solid lines whereas the theoretical values, by the broken lines. From FIG.
  • the improvement over the loss characteristic of the TE mode can be attained by the insertion of the dielectric 3 into the semicircular waveguide section 10 with the smaller radius of the circular waveguide l.
  • the reason is that, as described above, the apparent radius of the upper semicircular waveguide section 10 for the TE mode becomes equal to the radius of the lower semicircular waveguide section 20.
  • the effect of the dielectric 3 upon the TE mode is almost negligible, and the ab sorption loss becomes greater because of the difference in radius between the upper and lower semicircular waveguide sections 10 and 2.
  • FIG. 5(a) shows the relation between the radius and length of the filter; and FIG. 5(b), the relation betwen the dimensional error in radius of the filter and the maximum attenuation of the TE mode.
  • the mode filter in accordance with the present invention is designated by the solide lines, where as the prior art mode filter, by the broken lines. It is readily seen that the overall length of the mode filter in accordance with the present invention is shorter than that of the prior art mode filter and that the dimensional errors or tolerances required for the mode filter in accordance with the present invention are not so severe as those required for the prior art mode filter.
  • the circularwaveguide comprises the upper and lower semicircular waveguide sections 10 and partitioned from each other by the metallic slab or sheet 2 as in the case of the first embodiment, but instead of the semi-cylindrical dielectric 3, dielectric rods 3 and 3' are disposedin the upper semicircular waveguide section 10 with a smaller radius at a distance equal 0.54-62R respectively on both sides of the center of the section 10.
  • the mode of operation of the second embodiment is substantially similarto that of the first embodiment.
  • the effects of the dielectric rods 3 and 3' upon the TE mode propagating through the semicircular waveguide section 10 are almost negligible, but the phase velocity is changed as the radius of the upper semicircular waveguide section 10 is smaller.
  • the apparent radius of the upper semicircular waveguide section 10 becomes greater because of the presence of the dielectric rods 3 and 3 so that the phase velocity of the TE mode propagating through the upper semicircular waveguide section 10 equals that of the TE mode propagating through the lower semicircular waveguide section 20.
  • the upper, and lower semicircular waveguide sections 10 and 20 have the same radius, and semicircular dielectric 3 is disposed within the upper semicircular wave- 1 guide section 10 at a distance equal to 0.5462R from the center thereof as in the case of the first embodiment, whereas a semi-cylindrical dielectric 4 is disposed upon the inner wall of the lower semicircular waveguide section 20.
  • the apparent radius for the TE mode of the lower semicircular waveguide section 20 which has the same radius with that of the upper semicircular waveguide section 10 is made greater by disposing the semi-cylindrical dielectric 4 within the lower section 20 so that the phase velocities of the TE modes propagating through the waveguide sections 10 and 20 may be different from each other.
  • the apparent radius becomes greater, but the apparent radius for the TE mode propagating through the upper semicircular waveguide section 10 becomes greater because of the presence of the dielectric 3.
  • FIG. 7(a) The fourth and fifth embodiments of the present invention employing magnetic material are shown in FIG. 7.
  • the fourth embodiment shown in FIG. 7(a) is substantially similar in construction to the first embodiment described with reference to FIGS. 1 and 2 except that a semi-cylindrical magnetic material 5 is disposed within the upper semicircular waveguide section 10 with a radius smaller than that of the lower semicircular magnetic material 6 is disposed to contact the inner wall of the lower semicircular waveguide section 20 having the radius equal to that of the upper waveguide section 10.
  • the mode filter for the circular waveguide in accordance with the present invention described so far has various advantages hitherto unattained by the prior art mode filters, but the problem of the reflected waves in the filter is left unsolved.
  • the present invention can also solve this problem as will become more apparent from the following embodiments to be described in conjunction with FIGS. 8 and 9.
  • FIG. 8 is a longitudinal sectional view of the waveguide shown in FIG. 1.
  • the circular waveguide generally designated by l is divided into the upper and lower semicircular waveguide sections 10 and 20 by the metallic slab 2, and the semi-cylindrical dielectric 3 is disposed within the middle section 13 with a radius smaller than the upper waveguide section 11 or 15.
  • resistor elements or films 2 and 2" are disposed upon the partition wall 2 in the inlet and outlet waveguide sections 11 and 15 in opposed relation with the inner walls thereof.
  • the TE modes which propagate throughthe upper and lower semicircular waveguide sections 10 and and which are out of phase at the outlets of the waveguide sections 10 and 20, may be absorbed by the resistor element or film 2" so that the problem of the reflected waves may be overcomed.
  • the resistor film 2' at the inlet can absorb the still remaining reflected waves of the TE, and TE modes which are out of phase in the upper and lower semicircular waveguide sections 10 and 20. Thus, multireflection can be prevented.
  • the resistor elements 2 and 2" are disposed at right angles to the directions of the electric field intensities of the TE modes which are in phase in the upper and lower semicircular waveguide sections 10 and 20 so that they are almost not affected when the thickness of the resistor films or elements 2' and 2" is made sufficiently smaller relative to the wavelength.
  • the two resistor films or elements 2' and 2" have been described as being disposed at the inlet and outlet of the waveguide respectively, it is sufficient in practice to place only the resistor element or film 2" at the outlet of the waveguide.
  • the upper and lower semicircular TE modes opposite in phase are subjected to asymmetrical mode transformation at the output section of the metallic partiation plate.
  • FIG. 9(a) shows a rectangular thin metallic slab 2 having the rectangular resistor plates or films 2' and 2".
  • FIG. 9(b) shows the modification of the thin metallic partition slab 2 having the tapered or pentagonal resistor films or elements 2' and 2" which are more effective in absorbing the reflected waves than the rectangular resistor elements shown in FIG. 9(a).
  • helical waveguides or ring mode filters may be utilized in order to absorb the undesired modes generated by the imperfections of the waveguides.
  • helix waveguides may be utilized instead of the semicircular waveguide sections.
  • the waveguide in accordance with the present invention may be so designed as to absorb other higher circular modes.
  • a circular waveguide mode filter of the type with low transmission losses for the desired TE, mode and with high attenuation for the undesired TE modes (where n a 2) comprising a circular waveguide comprising a pair of semicircular waveguide sections having different radii, and a dielectric so disposed in one of said pair of semicircular waveguide sections with a smaller radius that the propagation of said undesired TE modes may not be adversely affected by said dielectric.
  • a circular waveguide mode filter as set forth in claim 2 comprising a thin metallic slab positioned to partition said pair of circular waveguide sections, and a resistive material in contact with said thin metallic slab.
  • a circular waveguide mode filter as set forth in claim 4 comprising a thin metallic slab positioned to partition said pair of circular waveguide sections, and a resistive material in contact with said thin metallic slab.
  • a circular waveguide mode filter as set forth in claim 4 comprising a thin metallic slab positioned to partition said pair of circular waveguide sections, and a resistive material in contact with said thin metallic slab.
  • a circular waveguide mode filter as set forth in claim 1, comprising a thin metallic slab positioned to partition said pair of circular waveguide sections, and a resistive material in contact with said thin metallic slab.
  • a circular waveguide mode filter as set forth in claim 8, comprising a thin metallic slab positioned to partition said pair of circular waveguide sections, and a resistive material in contact with said thin metallic slab.

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US00272037A 1971-07-19 1972-07-14 Circular waveguide mode filter Expired - Lifetime US3787787A (en)

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JP46053688A JPS5141502B1 (OSRAM) 1971-07-19 1971-07-19

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US (1) US3787787A (OSRAM)
JP (1) JPS5141502B1 (OSRAM)
DE (1) DE2235346C3 (OSRAM)
FR (1) FR2146375B1 (OSRAM)
GB (1) GB1395638A (OSRAM)
SU (1) SU459000A3 (OSRAM)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4145673A (en) * 1977-07-19 1979-03-20 Societe Anonyme Dite Compagnie Industrielle Des Telecommunications Cit-Alcatel Multiplexer for millimetric waves
US4222018A (en) * 1977-07-07 1980-09-09 The Marconi Company Limited Mode filters
US4608713A (en) * 1983-01-20 1986-08-26 Matsushita Electric Industrial Co., Ltd. Frequency converter
US9531048B2 (en) 2013-03-13 2016-12-27 Space Systems/Loral, Llc Mode filter
US9559397B2 (en) * 2014-04-09 2017-01-31 The Boeing Company Circular dielectric polarizer having a dielectric slab sandwiched by dielectric core portions having air cutouts therein
CN119447758A (zh) * 2024-08-23 2025-02-14 西安空间无线电技术研究所 一种金属圆波导到太赫兹介质圆波导间的能量耦合装置

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2360185A1 (fr) * 1976-07-27 1978-02-24 Cit Alcatel Procede de fabrication d'un filtre passe-haut pour ondes millimetriques et filtre obtenu par ce procede
JPS5374496A (en) * 1976-12-15 1978-07-01 Fuji Electric Co Ltd Paper leaf examining apparatus
JPS5949274U (ja) * 1983-08-18 1984-04-02 富士電機株式会社 紙葉片

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2129669A (en) * 1937-03-30 1938-09-13 Bell Telephone Labor Inc Guided wave transmission
US2762982A (en) * 1951-05-17 1956-09-11 Bell Telephone Labor Inc Mode conversion in wave guides
US2951219A (en) * 1958-12-29 1960-08-30 Bell Telephone Labor Inc Mode selective devices for circular electric wave transmissions
US3321720A (en) * 1961-11-09 1967-05-23 Shimada Sadakuni Circular waveguide teon mode filter

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2129669A (en) * 1937-03-30 1938-09-13 Bell Telephone Labor Inc Guided wave transmission
US2762982A (en) * 1951-05-17 1956-09-11 Bell Telephone Labor Inc Mode conversion in wave guides
US2951219A (en) * 1958-12-29 1960-08-30 Bell Telephone Labor Inc Mode selective devices for circular electric wave transmissions
US3321720A (en) * 1961-11-09 1967-05-23 Shimada Sadakuni Circular waveguide teon mode filter

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4222018A (en) * 1977-07-07 1980-09-09 The Marconi Company Limited Mode filters
US4145673A (en) * 1977-07-19 1979-03-20 Societe Anonyme Dite Compagnie Industrielle Des Telecommunications Cit-Alcatel Multiplexer for millimetric waves
US4608713A (en) * 1983-01-20 1986-08-26 Matsushita Electric Industrial Co., Ltd. Frequency converter
US9531048B2 (en) 2013-03-13 2016-12-27 Space Systems/Loral, Llc Mode filter
US9559397B2 (en) * 2014-04-09 2017-01-31 The Boeing Company Circular dielectric polarizer having a dielectric slab sandwiched by dielectric core portions having air cutouts therein
CN119447758A (zh) * 2024-08-23 2025-02-14 西安空间无线电技术研究所 一种金属圆波导到太赫兹介质圆波导间的能量耦合装置

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SU459000A3 (ru) 1975-01-30
FR2146375A1 (OSRAM) 1973-03-02
FR2146375B1 (OSRAM) 1977-04-01
DE2235346C3 (de) 1980-10-09
JPS5141502B1 (OSRAM) 1976-11-10
DE2235346A1 (de) 1973-01-25
GB1395638A (en) 1975-05-29
DE2235346B2 (OSRAM) 1980-02-21

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