US3916355A - Circular TE{HD on {b mode filter - Google Patents

Circular TE{HD on {b mode filter Download PDF

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Publication number
US3916355A
US3916355A US452357A US45235774A US3916355A US 3916355 A US3916355 A US 3916355A US 452357 A US452357 A US 452357A US 45235774 A US45235774 A US 45235774A US 3916355 A US3916355 A US 3916355A
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Prior art keywords
mode
waveguide
helix
circular
mode filter
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Expired - Lifetime
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US452357A
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English (en)
Inventor
Koichi Inada
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Fujikura Ltd
Fujikura Cable Works Ltd
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Fujikura Ltd
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Priority claimed from JP3382473A external-priority patent/JPS5418900B2/ja
Priority claimed from JP4250573A external-priority patent/JPS49130653A/ja
Priority claimed from JP5600373A external-priority patent/JPS5433700B2/ja
Priority claimed from JP6852973A external-priority patent/JPS5421066B2/ja
Application filed by Fujikura Ltd filed Critical Fujikura Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P3/00—Waveguides; Transmission lines of the waveguide type
    • H01P3/12—Hollow waveguides
    • H01P3/13—Hollow waveguides specially adapted for transmission of the TE01 circular-electric mode

Definitions

  • a circular arc polygonal type waveguide provides an excellent TE mode filter.
  • the electromagnetic field of the fundamental TE mode converts easily to that of undesirable higher order TE modes. This conversion is undesirable for the transmission of millimeter-wave energy.
  • the undesirable TE,,, mode is converted purposely to a higher order TE, mode by the present mode filter, the profile of which is slightly deformed from as compared to the perfectly accurate circular one, and said converted TE mode is absorbed in a conventional helix waveguide.
  • the fundamental TE mode is transmitted in a waveguide without distortion.
  • the present invention relates to a mode filter or a suppressor for an undesired modefor a circular waveguide for transmission of millimeter-wave energy, which involves very small loss of the TE mode and very large loss for higher modes.
  • the TE mode is generally utilized for the transmission of millimeter-wave energy with millimeter wavelengths (for instance 40 100 GHz) since the transmission loss of the TE mode is very small in that frequency band.
  • millimeter-wave energy with millimeter wavelengths (for instance 40 100 GHz) since the transmission loss of the TE mode is very small in that frequency band.
  • a circular waveguide with a diameter several times larger than the wavelength of the energy to be transmitted many higher modes other than the TE mode appear, since the TE mode is not a dominant or principle mode for a waveguide of the above size.
  • a slight deformity of the circular waveguide, a corner waveguide at bend portions and/or an elastic or expansion waveguide are triggers for generation of higher TE modes. These undesirable higher TE modes should be absorbed for the TE mode transmission.
  • TE mode filters which absorb these TE, modes have been proposed. Some of them are a distribution coupling type filter, a long slit type filter, a resonant slit type filter and a phase reverse type filter. But these types of prior mode filters have the following disadvantages: (i) Their structures are very complex, requiring high degree of manufacturing accuracy and thus are very expensive: (ii) It is difficult to obtain large inner diameters such as 51 mm and so, tapered waveguides are needed to mate and these tapers may generate other TE modes. (iii) TE mode loss is relatively large. (iv) The structures of the filters are very complicated and different from that of the waveguide line.
  • the object of the present invention is to provide a TE mode filter which overcomes the abovementioned drawbacks.
  • Another object of the present invention is to provide a mode filter of simple structure which is similar to the structure of a circular'or helix waveguide.
  • Still another object of the present invention is to provide a mode filter of short length, with a very wide frequency band.
  • a mode filter comprising a circular waveguide of a predetermined length, the cross-section of said waveguide being almost circular but being slightly deformed by the existence of a plurality of ridges on the periphery of the waveguide, whereby the mode conversion loss in said waveguide from TE, mode (n a 2) to TE mode is much greater than that from 'IE mode to another modes.
  • FIG. I shows a section of a whole transmission line using the mode filter according to the present invention
  • FIG. 2 and FIG. 3 show two cross sections of mode filter according to the present invention
  • FIG. 4 shows a modified cross section of a mode filter according to the present invention
  • FIG. 5 shows another embodiment of a structure of a mode filter according to the present invention
  • FIGS. 6A through 6F show calculated curves of the characteristics of the mode filter of FIG. 5;
  • FIGS. 7A and 78 also show calculated curves of the characteristics of a mode filter according to the present invention.
  • FIG. 8 shows another cross section of a mode filter according to the present invention.
  • FIG. 9 shows a calculated curves for the practical design of the mode filter of FIG. 8;
  • FIG. 10 shows a longitudinal cross section of another embodiment of a mode filter system according to the present invention.
  • FIG. 11 shows calculated curves of the frequency characteristics of a mode filter according to the present invention.
  • FIG. 12 shows a longitudinal cross section of another mode filter system according to the present invention.
  • FIG. 13 shows a cross section of a mode filter system of FIG. 12
  • FIG. 14(A) and FIG. 14(B) indicate electric fields of a mode filter system similar to that of FIG. 12;
  • FIG. 15 shows curves of attenuated characteristics of TE mode by a mode filter system of FIG. 12;
  • FIG. 16 through FIG. 20 show calculated curves for the practical design of a mode filter according to the present invention.
  • FIG. 21 shows an experimental measured curve of a mode filter according to the present invention.
  • FIG. 1 shows a section of a whole transmission line using the mode filter according to the present invention.
  • reference number 10 indicates a mode filter according to the present invention
  • 20 indicates a helix waveguide
  • 30 and 30a indicate ordinary circular waveguides.
  • the TE mode propagates in the waveguide system of FIG. 1 in the direction of the arrow, and in the waveguide 30, some undesirable modes are generated.
  • TE TE and another higher TE, modes are converted in the mode filter 10 into TE (where n 0) modes which are absorbed in the helix waveguide 20. Accordingly, pure TE mode is provided in the succeeding circular waveguide 30a.
  • the main purpose of the present invention is to provide a mode filter 10 as shown in FIG. 1.
  • the first embodiment of the present invention that is, a mode filter with conductive metal walls, is described below with reference to FIGS. 2, 3 and 4.
  • FIG. 2 shows a cross section of a circular waveguide which is almost circular but is deformed by the existence of three mounds or ridges on its inner periphery, and is made of metal with small wall impedance. In that case. an electromagnetic field of TE (where m 1, 2, 3, is generated.
  • the coupling coefficient C1, between TE,,,, and TED, is expressed below.
  • the mode conversion loss for the TE mode is obtained from the formula (3) as follows;
  • optimum value of p which represents the number of mounds or ridges on the periphery of a waveguide, is determined to satisfy the above conditions.
  • the maximum values of formulas (4) and (6) are, mathematically 2.
  • the calculated value of is shown in Table 2, where the frequency fis GHz (wavelength is 3.75 mm), the radius of a waveguide a is 25.5 mm and 8, which is the deformation rate, is 0.1.
  • the attenuation of TE TE TE modes is calculated from the above formula (3), using Tables I and 2.
  • p 2 the attenuation of the TE mode can be more than ten times as large as that of the TE mode, and the attenuation of the TE mode can be more than sixty times as large as that of the TE mode, therefore, a mode filter with two ridges on the periphery of the waveguide (p 2) is very beneficial.
  • p 3 or p 4 the attenuations of TE TE and TE are almost the same, and a mode filter of p 3 is not effective.
  • the attenuations of TE and TE modes are more than 30 and 110 times, respectively, as large as that of the TE mode, and a mode filter ofp is more effective than that ofp 2.
  • the attenuations of the TE and TE modes are more than 100 and times, respectively, as large as that of the T15 mode.
  • p is greater than seven, the difference of attenuation between the TE mode and higher TE, modes is considerably large and a mode filter with p greater than seven is considered effective.
  • the length l of deformed mode filter is determined to obtain the maximum value of l ⁇ (Bll" Bum-il Since the mathematical maximum value of the above formula is 2, the length I should be determined to ensure that the value of that formula is 2.
  • the TE mode is Said length l is obtained by the formula C03 (B1021- @1511) I: l
  • FIG. 3 shows the cross section of a mode filter 10 for the TE mode according to the presnet invention.
  • Said mode filter 10 has five ridges 10a 10e. (p 5 and 8 0.05) and with a length of 840 mm the attenuation for the TE mode in 80 GHz is thirty times as large as that for the fundamental TE mode.
  • FIG. 4 shows a cross-section of a post type mode filter 11, in which there is a plurality of posts l1a- 1 1e inside the wall. The function of these posts 11a lle is the same as the ridges 10a We of FIG. 3.
  • FIG. 5 shows a structure of a helix type mode filter 12 which has an insulated helix wire 12-1, a dielectric 5 layer 12-2 of thickness t covering the outer portion of the wire 12-1 and a shield layer 12-3 shielding the outer portion of the dielectric layer 12-2.
  • the diameters of the conductor and the insulator of the wire 12-1, are d and D, respectively.
  • the important feature of the sec- 10 0nd embodiment of the present mode filter is that the almost circular inner surface of the wire 12-1 is deformed by the existence of some mounds or ridges. Therefore, the cross-section of the inner surface of the present helix type mode filter is similar to that of FIG. 2 or FIG. 3.
  • the wall impedance of the helix type mode filter is designed so that the TE (n 2 2) mode is converted perfectly to the TE,,,, mode but the TE mode propagates without conversion.
  • the characteristic formula or equation for the particular mode in a helix waveguide or a helix mode filter is the one shown below.
  • e and p. represents space dielectric constant and magnetic space permeability, respectively
  • Zz is a wall impedance
  • a is an inner radius 35 of the helix waveguide
  • p is a number of ridges
  • xi is constant
  • a is attenuation constant
  • B is phase constant.
  • FIGS. 6A through 6F show the curves of the relationship between xi and jmeaZz, where the radius a of a helix waveguide is 25.5 mm, and wavelength A is 3.75 mm. Thevalue of xi ob- 0L00374/mm.
  • the TE mode (xi 10.17 in Table I) and TE. mode can degenerate.
  • a helix waveguide with 4 ridges can be the T5 mode filter. That is to say, the loss of the TE mode is much larger than that of the TE mode.
  • the value of xi of the TE, mode is the same as that of the TE mode and is equal to 7.0. Since the value of xi of the TE mode 3.8) is sufficiently different from the value of xi of 'I'E mode 7.0) the mode conversion loss of the TE mode is very small.
  • a mode filter with five ridges is the most preferable for a TE mode filter.
  • a helix waveguide with seven ridges may be a TE mode filter.
  • 'yn represents the propagation constant of TE,,,,
  • FIGS. 7A and 7B shows two examples of the solution of formula (11) and are curves of Cni/8 of the i mode (vertical axis) versus xi.
  • Cni is represented as ICni/Bl along the vertical axis since the value of 8 is constant in this particular case.
  • FIG. 7A shows the value of ICni/vSl between the TE or TE mode, and the i mode when p 5
  • FIG. 7B shows the value of [Cni/8 lbetween TE or TE and the i mode when p 8.
  • the values of radius a and wavelength A are 25.5 mm and 3.75 mm, respectively.
  • the coupling coefficient Cni changes in the direction of the arrow (inductive or capacitive) in FIG. 7A, depending upon changes of the value of xi. For instance, when the wall impedance 22 changes from zero (metal wall) to capacitive impedance in FIG. 6C, the value of xi of the TE mode approaches close to the value of xi of the TE mode (which is 7.016). Then, as in FIG. 7A, the coupling coefficients between TE and TE becomes small.
  • the amplitude a,-(z) of the i mode and the amplitude a (z) of TE mode in this mode filter is obtained from the following equations.
  • the coupling coefficient Cni is large, the length I can be short.
  • a large coupling coefficient Cni requires a large value of 8, and results in an increased attenuation of the TE mode.
  • a mode filter with 1 less than 17/2 l/Cni is possible, in which case, attenuation of TE mode is reduced a little relative to the short length l.
  • the frequency band of the mode filter is 40 80 GHz the length I should be 750 mm.
  • the value of jweaZz holds about 5 in the whole frequency band.
  • a helix type mode filter Some modifications of a helix type mode filter are possible to make by those skilled in the art. For instance, a plurality of conductive paste disposed on the inner surface of a helix waveguide function in the same manner as mounds or ridges of the mode filter of FIG. 5.
  • the helix type mode filter is, of course, used in the waveguide system shown in FIG. 1, together with an ordinary circular metal wall waveguide and an ordinary helix waveguide.
  • the third embodiment of the present invention concerns a dielectric lined type mode filter, the cross section of which is shown in FIG. 8.
  • a dielectric lined type mode filter 12 comprises the deformed metal wall 12-1 and the dielectric layer 12-2 lined on the inner surface of the metal wall 12-1.
  • the structure of dielectric lined type mode filter is the same as that of the metal wall type mode filter in FIGS. 2 and 3 except that the dielectric lined type mode filter has the dielectric layer 12-2.
  • FIG. 9 shows the calculated curves of the relationship between the thickness 1 of the dielectric layer (horizontal axis) and the value of (vertical axis) for the TE mode and TF mode where a, 25.5 mm and e, 2.3. It should be noted from FIG. 7 that the appropriate thickness of the dielectric layer provides the same phase constant of the TE mode as that of the TE mode, and the same phase constant of the TE mode as that of the TE mode.
  • FIG. 10 shows a part of a mode filter system, which comprises a first mode filter F an ordinary helix waveguide A and a second mode filter F
  • a mode filter F, or F and an ordinary helix waveguide A shown in FIG. 8 provides a mode filter system which covers a very wide frequency band. For instance, if the first mode filter F covers a low frequency band, such as 40 60 GHz, and the second mode filter covers a high frequency band, such as 60 80 GHz, then the whole filter system including both filters F and F covers wide frequency band 40 80 GHz.
  • Each component filter F or F can be a helix type mode filter as illustrated by FIG. 5.
  • the typical numerical design of a combination mode filter system shown in FIG. 10 is as follows:
  • Frequency band 40 80 GHz Length of first filter; L 625 mm (Center frequency is 50 GHz) Length of second filter; L 875 mm (Center frequency is GHz) Length of helix waveguide A; 1000 mm Structure of helix wall in FIG. 5
  • Thickness of dielectric layer t 32 0.5 mm
  • the micro-wave energy propagates in the direction of the arrow, and undesirable TE mode included in the low frequency band is converted by the first filter F, to the TF mode, which is absorbed by the helix waveguide A. Further, undesirable TE mode included in the high frequency band is converted by the second filter F to the TE mode, which is absorbed by a succeeding helix waveguide (not shown).
  • a metal wall type mode filter or dielectric lined type mode filter can be used as a component of a combination filter system, instead of the helix type mode filter.
  • FIG. 11 shows the relationship between the length (horizontal axis; cm) and the mode conversion loss of the TE mode (vertical axis; dB), with parameters of some frequencies, where radius a, 25.5 mm, number of ridges p 9, deformation rate 0.06, and the attenuation of TE mode is less than 0.1 dB.
  • the length of that filter is determined to be 12 cm from Point A in FIG. 11, and the loss of the upper limit frequency (90 GHz) is the same as that of the lower limit of frequency (40 GHz).
  • the fourth embodiment described above with reference to FIG. 10 overcomes that disadvantage, but the mode filter in said fourth embodiment is too large in size.
  • the fifth embodiment provides a wide band mode filter of a small size.
  • FIG. 12 and FIG. 13 show the longitudinal view and cross sectional view, respectively, of a filter system of the fifth embodiment, which comprises a first filter F, and second filter F
  • the second filter F is connected to the first filter F, along a common longitudinal axis, however, corresponding points on the periphery of filters F, and F for instance a on F, and a on F in FIG. 13, are separated from each other by angle 6.
  • Said angle 6 is determined as 6 2rr/4p. Accordingly to the structures in FIGS. I2 and 13, since an ordinary helix waveguide between two filters like those of FIG. is unnecessary, the entire length of the filter system is shortened.
  • FIGS. 12 and 13 The operational principle of the filter system in FIGS. 12 and 13 is explained with a simple example (p 32 2), shown in FIGS. 14(A) and 14( B).
  • a simple example p 32 2
  • FIGS. 14(A) and 14( B When the TE mode propagates in a waveguide with two ridges (p 2) shown in FIG. 14(A), said TE,,,, mode is converted to the TE mode, whose field is shown in FIG. 14(A).
  • Thickness of dielectric layer I 0.5 mm
  • the mode filter described in FIG. 8 is also applicable to the filter system of the fifth embodiment.
  • first filter F, and second filter F should be covered by a metallic cover in practical use.
  • FIG. 16 shows the relationship between jm aZz along the horizontal axis and loss factor Afini along the vertical axis on the condition that p 5, a 25.5 mm and 5 0.04. These curves are calculated from formulae (9) (10) and (11).
  • FIG. I7 shows the curves of the frequency in GHz along the horizontal axis versus the value of JweaZ/zon the condition that 11,, 25.5 mm, a 4, t 0.6 mm and d 0.2 mm.
  • the length l of a mode filter is determined to satisfy the formula 2
  • the length I should be designed from FIG. 18 so that the losses at the highest and lowest frequencies are the same.
  • FIG. 19 shows the frequency characteristics of the loss of TE mode with parameters of wall impedance.
  • the horizontal axis shows the frequency in GHz and the vertical axis shows the loss of TE mode in dB.
  • the condition of FIG. 19 is that p 5, 8 0.04
  • FIG. 20 shows the relationship between the frequency in GHz along the horizontal axis and the loss of the fundamental TE mode in dB along the vertical axis on the condition that p 5. 6 0.04 and I 75 cm.
  • the curve of FIG. 20 shows a total conversion loss where TE mode is converted to TE TE TE and

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US452357A 1973-03-24 1974-03-18 Circular TE{HD on {b mode filter Expired - Lifetime US3916355A (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP3382473A JPS5418900B2 (enrdf_load_stackoverflow) 1973-03-24 1973-03-24
JP4250573A JPS49130653A (enrdf_load_stackoverflow) 1973-04-14 1973-04-14
JP5600373A JPS5433700B2 (enrdf_load_stackoverflow) 1973-05-18 1973-05-18
JP6852973A JPS5421066B2 (enrdf_load_stackoverflow) 1973-06-18 1973-06-18

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US (1) US3916355A (enrdf_load_stackoverflow)
CA (1) CA1012620A (enrdf_load_stackoverflow)
DE (1) DE2414237C2 (enrdf_load_stackoverflow)
FR (1) FR2222764B1 (enrdf_load_stackoverflow)
GB (1) GB1469152A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9531048B2 (en) 2013-03-13 2016-12-27 Space Systems/Loral, Llc Mode filter

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3016503A (en) * 1959-12-29 1962-01-09 Bell Telephone Labor Inc Helix wave guide
US3601720A (en) * 1967-08-16 1971-08-24 Sumitomo Electric Industries Helical waveguide with varied wall impedance zones
US3678420A (en) * 1970-10-27 1972-07-18 Bell Telephone Labor Inc Spurious mode suppressing waveguide
US3732511A (en) * 1972-03-15 1973-05-08 Bell Telephone Labor Inc Waveguide mode filter
US3735188A (en) * 1972-07-03 1973-05-22 Litton Systems Inc Traveling wave tube with coax to helix impedance matching sections

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3016503A (en) * 1959-12-29 1962-01-09 Bell Telephone Labor Inc Helix wave guide
US3601720A (en) * 1967-08-16 1971-08-24 Sumitomo Electric Industries Helical waveguide with varied wall impedance zones
US3678420A (en) * 1970-10-27 1972-07-18 Bell Telephone Labor Inc Spurious mode suppressing waveguide
US3732511A (en) * 1972-03-15 1973-05-08 Bell Telephone Labor Inc Waveguide mode filter
US3735188A (en) * 1972-07-03 1973-05-22 Litton Systems Inc Traveling wave tube with coax to helix impedance matching sections

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9531048B2 (en) 2013-03-13 2016-12-27 Space Systems/Loral, Llc Mode filter

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FR2222764B1 (enrdf_load_stackoverflow) 1979-06-22
GB1469152A (en) 1977-03-30
FR2222764A1 (enrdf_load_stackoverflow) 1974-10-18
DE2414237A1 (de) 1974-10-03
DE2414237C2 (de) 1983-02-24
CA1012620A (en) 1977-06-21

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