CA1081808A - Dual mode self-equalized bandpass filters - Google Patents
Dual mode self-equalized bandpass filtersInfo
- Publication number
- CA1081808A CA1081808A CA272,929A CA272929A CA1081808A CA 1081808 A CA1081808 A CA 1081808A CA 272929 A CA272929 A CA 272929A CA 1081808 A CA1081808 A CA 1081808A
- Authority
- CA
- Canada
- Prior art keywords
- cavities
- dual mode
- filter
- mode cavities
- equalized
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
- H01P1/207—Hollow waveguide filters
- H01P1/208—Cascaded cavities; Cascaded resonators inside a hollow waveguide structure
- H01P1/2082—Cascaded cavities; Cascaded resonators inside a hollow waveguide structure with multimode resonators
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- Control Of Motors That Do Not Use Commutators (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
A waveguide self-equalized bandpass filter which com-prises a plurality of axially disposed resonant cavities including at least two dual mode cavities. Cross couplings are provided in the dual mode cavities to create a zero-phase difference in the transmission of transverse electric waves. The cross couplings are disposed along the length of the dual mode cavities and along an axis parallel to the longitudinal axis of the filter to achieve passband equalization. The filter may comprise resonant cavities exclusively made of square or cylindrical dual mode cavities or of two cascaded dual mode cavities and a plurality of single mode cavities, the single mode cavities being then axially mounted and in equal number at each extremity of the dual mode cavities.
A waveguide self-equalized bandpass filter which com-prises a plurality of axially disposed resonant cavities including at least two dual mode cavities. Cross couplings are provided in the dual mode cavities to create a zero-phase difference in the transmission of transverse electric waves. The cross couplings are disposed along the length of the dual mode cavities and along an axis parallel to the longitudinal axis of the filter to achieve passband equalization. The filter may comprise resonant cavities exclusively made of square or cylindrical dual mode cavities or of two cascaded dual mode cavities and a plurality of single mode cavities, the single mode cavities being then axially mounted and in equal number at each extremity of the dual mode cavities.
Description
101~1808 The present invention generally deals with waveguide band- -pass filters, and more particularly concerns waveguide filters able to compensate phase distortion in the passband thereof through the use of dual mode resonant cavities so arranged as to define a substantially flat bandpass characteristic in the transmission band of transverse electric tT-E-) waves.
In order to transmit selectively transverse electric waves, any known microwave bandpass filter with a transfer function different from that of the Butterworth or Chebyshev filters requires additional couplings between its non-ad~acent resona-tors. These additional couplings are called cross couplings and their sign determines the type of the bandpass response. A
negative sign results in optimum amplitude bandpass filters, so-called elliptic filters, whereas a positive sign provides optimum phase filters, so-called linear phase filters. The mechanical structures for the above filters are arranged such that the realization of these couplings possible;
The existing waveguide linear phase filters use a chain of single mode resonators folded at its center and forming a "U"
shape configuration. Such filters can be made out of two rec-tangular waveguide sections having a common narrow wall provi-ded with inductive diaphragms for cross couplings. In these filters, sequential couplings result from the use of inductive irises which separate each cavity alon the length of the wave-guide sections. These filters are characterized by an equi-ripple passband and a monotonic stopband attenuation. They usually provide a linear phase and flat group delay over 60 ~
of their bandwidth, and have their input and output ports not in line. A design of this type of filter is described by J.D.
Rhodes in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-l~, No. ¢, June 1970, pp. 290 - 313, and is also dis-\
818(~8 closed in U.S Patent No. 3,597,709 to J.D. Rhodes issuedAugust 3, 1971. A slightly different linear phase filter structure - la -., . .. , .: .
` ~`." ~08181)8 based upon the U-shaped principle but with its ports in line, is des-cribed in U.S. Patent No. 3,882,434 to R. Levy issued May 6, 1975. me latter filter does not however provide all the passband flatness of the one provided by J.D. Rhodes~ but presents sufficient equalization for most communication s~stems.
A different filter structure capable of cross coupling realization is the dual mode axial configuration. This configu- -ration is currently used for the realization of elliptic function filters which, as mentioned above, require all their cross cou-plings negative. The stopband attenuation of these filters is steepened by the real frequency transmission zeros of the ellip-tic function, but their passband amplitude and group delay charac-teristics are non-optimum. These filters are suitable for use in high capacity communication systems if they are cascaded with separate group delay equalizers. Designs of elliptic filters are described by A.E. Atia and A.E. Williams in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-20, No. 4, April 1972, pp. 258 - 265, and also disclosed in U.S. Patent No. 3,697,898 to B.L. Blachier and A.R. Champeau issued October 10, 1972.
A prime object of the present invention resides in ~providing a waveguide bandpass filter which takes advantage of the simple mechanical configuration of the axial dual ~ode elliptic fil*er for the realization of a low-loss linear phase fil-ter.- The filter of the invention may be called a self-equalized bandpass filter since it does not require additional group delay equalizers. Additional advantages of the dual mode self-equalized filters over the prior U-shaped ones, reside in that the self-equalized filters are of a smaller volume and can use higher order modes in the transmission of TE waves for low loss electrical performance.
The present invention therefore resides in a waveguide self-equalized bandpass filter which comprises two cascaded .
:- .
'', 108~808 .
dual mode resonant cavities, a plurality of single mode resonant cavities and coupling screws. The dual and single mode cavities are axially disposed. The single mode cavities are mounted in equal number at each extremity of the dual mode cavities. One coupling screw is provided in each of thé dual mode cavities.
The coupling screws are disposed along the length of the dual mode cavities and albng an axis parallel to the longitudinal axis of the filter so as to create a zero-phase difference in the transmission of transverse electric waves.
Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings, wherein, Figures la and lb illustrate self-equalized band-pass filters exclusively made up of cascaded square and cylindri-cal dual mode cavities, respectively; and Figures 2a and 2b depict self-equalized filters consisting of a combination of two center dual mode cavities and single mode cavities.
Referring to figures la and lb, there is shown an axial dual mode cavity structure of self-equalized filters. In figure la, the structure consists of cascaded square cavities Al, A2 An~ supporting TElon wave resonant modes, whereas, in figure lb, a TElln filter made up of cylindrical cavities Bl, B2 --Bn~ is illustrated. In both cases, the cavities are inductively coupled through their cross-sections and each cavity has an electrical length equal to n1rwhere n is the third mode index, an integer which corresponds to the number of half period field variAtions along the filter axis; Also, the input port PIN and output port PoUT of each filter are provided with suitably aligned inductive slits.
It is to be noted that the sequential couplings M12, M23, M34, etc., are provided by the long coupling slots or irises in the common walls I mounted between two adjacent G ~ ~ 3 ~
`~ 108~8~8 cavities and by the coupling screws C angularly set with regards :
to the tuning screws T, the latter being 90 apart and in line with the two orthogonal field components of the cavity. As in ; - the Butterworth and Chebyshev filters, each coupling screw C
"., . :
is located at 45 with respect to either one of the tuning screws. / ~:
, .. / .
.
/
- ~ /
/
' /
- 3a -, ~'~ .
~ ~081808 The cross couplings M14, ~36~ M58, etc., are obtained through the short common wall slots. In accordance with the present embodiment, a positive cross coupling sign is achieved when all the screws of the cavities are set in line along the length of the filter, thereby realizing a zero phase difference between the reso-nant cavities. In figures la and lb, the electric field vectors show the two orthogonal TElo and TEll waves, respectively, along with their positive coupling signs indicated by the vector direc-tion. ~hen the number of physical cavities in this filter structure is odd, the input and output ports are rotated 90 with respect to one another; they have otherwise the same polarization.
The location of the tuning screws T and coupling screws C
is at the maximum electric field point along the length of each cavity. For fundamental modes (n = 1), this point is at the center of each cavity. Where n > 1, the length location Ls for any extremi-ty of a cavity is Ls = 2K - 1 x Lj where K is any integer ranging from 1 to n and Lj the length of the cavity under consideration.
The choice of Ls = Lj/2 for n odd, and Ls close to Lj/2 for n even, is preferred.
The low-loss linear phase filters (n ~ 1) require special attention in determining the cavity cross-sectional area and length, in order to avoid the propagation of spurious modes in spurious pass-bands within the operating communications band. Suitable techniques for the elimination ofthose spurious modes are given in Canadian Patent application No. 250,162 filed on April 13, 1976 in the name of S. Kallianteris.
Two dual mode self-equalized filters of the type shown in figures la and lb were experimented and evaluated. Both bandpass filters had 6 poles, used 3 physical cavities and were operated at 30 12 GHz. The first filter was a low-loss and used square TE103 dual mode cavities, while the second one operated in the fundamental TElll modes. Both filters presented a bandwidth of 80 ~z, a return , ~
'oss of 26 dB and had t`~elr bandPàS8~ flatness equal to 60~ of their bandwidth. The measured insertion loss was 0.62 dB for the TE103 filter and 0.9 dB for the TE111 filter, which represents a 30%
improvement over known TElll filters.
Figures 2a and 2b show a further em~odiment of the self-equalized filter wherein a reduced number of cross couplings is used.
In fact, as illustrated, the self-equalized filter employs only one cross coupling and may provide flat bandwidth up to 40%. The filter uses an hybrid combination of two rectangular dual mode TElol cavi-ties Al and A2, or two cylindrical dual modes TElll cavities Bl andB2. In each case, the coupling screws C are aligned along the length of the filter to achieve a positive cross coupling. The filter order is increased by adding equal number of rectangular waveguide single mode cavities R including inductive posts P, axial-ly mounted at each end of the two dual mode cavities. With such arrangement, the mechanical symmetry of the filter is maintained since the cross coupling always lies at the filter center.
The single TE10l/dual TElon mode or single TE10l/dual TEl]
mode cavity combination realizes self-equalized filters with higher unloaded Q's than the fundamental mode ones. Such arrangement elimi-nates the spurious passbands of the TElon and TElln self-equalized bandpass filters.
A six-pole filter consisting of two cylindrical TElll dual mode cavities and two rectangular TElol single mode ones, was experimented and analyzed. The filter operated at 12 GHz and had a bandwidth of 80 MHz, a return loss of 26 dB and 37% of its band-width flat. The center frequency insertion loss of the filter was 0.95 dB.
The self-equalized filters of figures 2a and 2b have been devised to provide sufficient equalization for almost all modern communication systems without increasing significantly their manufacturing costs.
... . . . . ;, . ~ . . . . , - . ..
. . .
--` - . 1081808 It is to be noted that all the self-equalized bandpass filters described present equiripple passband and monot~nic stop-band characteristics.
It is to be understood that modifications may be drawn to the above-described preferred embodiments of the present inven-tion without departing from the ambit thereof which is solely limited by the scope of the claims which follow.
, .
In order to transmit selectively transverse electric waves, any known microwave bandpass filter with a transfer function different from that of the Butterworth or Chebyshev filters requires additional couplings between its non-ad~acent resona-tors. These additional couplings are called cross couplings and their sign determines the type of the bandpass response. A
negative sign results in optimum amplitude bandpass filters, so-called elliptic filters, whereas a positive sign provides optimum phase filters, so-called linear phase filters. The mechanical structures for the above filters are arranged such that the realization of these couplings possible;
The existing waveguide linear phase filters use a chain of single mode resonators folded at its center and forming a "U"
shape configuration. Such filters can be made out of two rec-tangular waveguide sections having a common narrow wall provi-ded with inductive diaphragms for cross couplings. In these filters, sequential couplings result from the use of inductive irises which separate each cavity alon the length of the wave-guide sections. These filters are characterized by an equi-ripple passband and a monotonic stopband attenuation. They usually provide a linear phase and flat group delay over 60 ~
of their bandwidth, and have their input and output ports not in line. A design of this type of filter is described by J.D.
Rhodes in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-l~, No. ¢, June 1970, pp. 290 - 313, and is also dis-\
818(~8 closed in U.S Patent No. 3,597,709 to J.D. Rhodes issuedAugust 3, 1971. A slightly different linear phase filter structure - la -., . .. , .: .
` ~`." ~08181)8 based upon the U-shaped principle but with its ports in line, is des-cribed in U.S. Patent No. 3,882,434 to R. Levy issued May 6, 1975. me latter filter does not however provide all the passband flatness of the one provided by J.D. Rhodes~ but presents sufficient equalization for most communication s~stems.
A different filter structure capable of cross coupling realization is the dual mode axial configuration. This configu- -ration is currently used for the realization of elliptic function filters which, as mentioned above, require all their cross cou-plings negative. The stopband attenuation of these filters is steepened by the real frequency transmission zeros of the ellip-tic function, but their passband amplitude and group delay charac-teristics are non-optimum. These filters are suitable for use in high capacity communication systems if they are cascaded with separate group delay equalizers. Designs of elliptic filters are described by A.E. Atia and A.E. Williams in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-20, No. 4, April 1972, pp. 258 - 265, and also disclosed in U.S. Patent No. 3,697,898 to B.L. Blachier and A.R. Champeau issued October 10, 1972.
A prime object of the present invention resides in ~providing a waveguide bandpass filter which takes advantage of the simple mechanical configuration of the axial dual ~ode elliptic fil*er for the realization of a low-loss linear phase fil-ter.- The filter of the invention may be called a self-equalized bandpass filter since it does not require additional group delay equalizers. Additional advantages of the dual mode self-equalized filters over the prior U-shaped ones, reside in that the self-equalized filters are of a smaller volume and can use higher order modes in the transmission of TE waves for low loss electrical performance.
The present invention therefore resides in a waveguide self-equalized bandpass filter which comprises two cascaded .
:- .
'', 108~808 .
dual mode resonant cavities, a plurality of single mode resonant cavities and coupling screws. The dual and single mode cavities are axially disposed. The single mode cavities are mounted in equal number at each extremity of the dual mode cavities. One coupling screw is provided in each of thé dual mode cavities.
The coupling screws are disposed along the length of the dual mode cavities and albng an axis parallel to the longitudinal axis of the filter so as to create a zero-phase difference in the transmission of transverse electric waves.
Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings, wherein, Figures la and lb illustrate self-equalized band-pass filters exclusively made up of cascaded square and cylindri-cal dual mode cavities, respectively; and Figures 2a and 2b depict self-equalized filters consisting of a combination of two center dual mode cavities and single mode cavities.
Referring to figures la and lb, there is shown an axial dual mode cavity structure of self-equalized filters. In figure la, the structure consists of cascaded square cavities Al, A2 An~ supporting TElon wave resonant modes, whereas, in figure lb, a TElln filter made up of cylindrical cavities Bl, B2 --Bn~ is illustrated. In both cases, the cavities are inductively coupled through their cross-sections and each cavity has an electrical length equal to n1rwhere n is the third mode index, an integer which corresponds to the number of half period field variAtions along the filter axis; Also, the input port PIN and output port PoUT of each filter are provided with suitably aligned inductive slits.
It is to be noted that the sequential couplings M12, M23, M34, etc., are provided by the long coupling slots or irises in the common walls I mounted between two adjacent G ~ ~ 3 ~
`~ 108~8~8 cavities and by the coupling screws C angularly set with regards :
to the tuning screws T, the latter being 90 apart and in line with the two orthogonal field components of the cavity. As in ; - the Butterworth and Chebyshev filters, each coupling screw C
"., . :
is located at 45 with respect to either one of the tuning screws. / ~:
, .. / .
.
/
- ~ /
/
' /
- 3a -, ~'~ .
~ ~081808 The cross couplings M14, ~36~ M58, etc., are obtained through the short common wall slots. In accordance with the present embodiment, a positive cross coupling sign is achieved when all the screws of the cavities are set in line along the length of the filter, thereby realizing a zero phase difference between the reso-nant cavities. In figures la and lb, the electric field vectors show the two orthogonal TElo and TEll waves, respectively, along with their positive coupling signs indicated by the vector direc-tion. ~hen the number of physical cavities in this filter structure is odd, the input and output ports are rotated 90 with respect to one another; they have otherwise the same polarization.
The location of the tuning screws T and coupling screws C
is at the maximum electric field point along the length of each cavity. For fundamental modes (n = 1), this point is at the center of each cavity. Where n > 1, the length location Ls for any extremi-ty of a cavity is Ls = 2K - 1 x Lj where K is any integer ranging from 1 to n and Lj the length of the cavity under consideration.
The choice of Ls = Lj/2 for n odd, and Ls close to Lj/2 for n even, is preferred.
The low-loss linear phase filters (n ~ 1) require special attention in determining the cavity cross-sectional area and length, in order to avoid the propagation of spurious modes in spurious pass-bands within the operating communications band. Suitable techniques for the elimination ofthose spurious modes are given in Canadian Patent application No. 250,162 filed on April 13, 1976 in the name of S. Kallianteris.
Two dual mode self-equalized filters of the type shown in figures la and lb were experimented and evaluated. Both bandpass filters had 6 poles, used 3 physical cavities and were operated at 30 12 GHz. The first filter was a low-loss and used square TE103 dual mode cavities, while the second one operated in the fundamental TElll modes. Both filters presented a bandwidth of 80 ~z, a return , ~
'oss of 26 dB and had t`~elr bandPàS8~ flatness equal to 60~ of their bandwidth. The measured insertion loss was 0.62 dB for the TE103 filter and 0.9 dB for the TE111 filter, which represents a 30%
improvement over known TElll filters.
Figures 2a and 2b show a further em~odiment of the self-equalized filter wherein a reduced number of cross couplings is used.
In fact, as illustrated, the self-equalized filter employs only one cross coupling and may provide flat bandwidth up to 40%. The filter uses an hybrid combination of two rectangular dual mode TElol cavi-ties Al and A2, or two cylindrical dual modes TElll cavities Bl andB2. In each case, the coupling screws C are aligned along the length of the filter to achieve a positive cross coupling. The filter order is increased by adding equal number of rectangular waveguide single mode cavities R including inductive posts P, axial-ly mounted at each end of the two dual mode cavities. With such arrangement, the mechanical symmetry of the filter is maintained since the cross coupling always lies at the filter center.
The single TE10l/dual TElon mode or single TE10l/dual TEl]
mode cavity combination realizes self-equalized filters with higher unloaded Q's than the fundamental mode ones. Such arrangement elimi-nates the spurious passbands of the TElon and TElln self-equalized bandpass filters.
A six-pole filter consisting of two cylindrical TElll dual mode cavities and two rectangular TElol single mode ones, was experimented and analyzed. The filter operated at 12 GHz and had a bandwidth of 80 MHz, a return loss of 26 dB and 37% of its band-width flat. The center frequency insertion loss of the filter was 0.95 dB.
The self-equalized filters of figures 2a and 2b have been devised to provide sufficient equalization for almost all modern communication systems without increasing significantly their manufacturing costs.
... . . . . ;, . ~ . . . . , - . ..
. . .
--` - . 1081808 It is to be noted that all the self-equalized bandpass filters described present equiripple passband and monot~nic stop-band characteristics.
It is to be understood that modifications may be drawn to the above-described preferred embodiments of the present inven-tion without departing from the ambit thereof which is solely limited by the scope of the claims which follow.
, .
Claims (3)
1. A waveguide self-equalized bandpass filter;
comprising two cascaded dual mode resonant cavities, a plurality of single mode resonant cavities and coupling screws, said dual and single mode cavities being axially disposed, said single mode cavities being mounted in equal number at each extremity of said dual mode cavities, one coupling screw being provided in each of said dual mode cavities, said coupling screws being disposed along the length of the dual mode cavities and along an axis parallel to the longitudinal axis of said filter so as to create a zero-phase difference in the transmission of transverse electric waves.
comprising two cascaded dual mode resonant cavities, a plurality of single mode resonant cavities and coupling screws, said dual and single mode cavities being axially disposed, said single mode cavities being mounted in equal number at each extremity of said dual mode cavities, one coupling screw being provided in each of said dual mode cavities, said coupling screws being disposed along the length of the dual mode cavities and along an axis parallel to the longitudinal axis of said filter so as to create a zero-phase difference in the transmission of transverse electric waves.
2. A filter as claimed in claim 1,wherein said dual mode cavities are cylindrical cavities whereas said single mode cavities have a rectangular cross-sectional area.
3. A filter as claimed in claim 1, wherein said dual mode cavities have square cross-sectional area, and said single mode cavities are of a rectangular cross-sectional area.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA272,929A CA1081808A (en) | 1977-03-01 | 1977-03-01 | Dual mode self-equalized bandpass filters |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA272,929A CA1081808A (en) | 1977-03-01 | 1977-03-01 | Dual mode self-equalized bandpass filters |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1081808A true CA1081808A (en) | 1980-07-15 |
Family
ID=4108049
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA272,929A Expired CA1081808A (en) | 1977-03-01 | 1977-03-01 | Dual mode self-equalized bandpass filters |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1081808A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0188367A2 (en) * | 1985-01-14 | 1986-07-23 | Com Dev Ltd. | Triple mode dielectric loaded bandpass filters |
| US4630009A (en) * | 1984-01-24 | 1986-12-16 | Com Dev Ltd. | Cascade waveguide triple-mode filters useable as a group delay equalizer |
| CN110364788A (en) * | 2018-04-11 | 2019-10-22 | 上海华为技术有限公司 | Filter |
-
1977
- 1977-03-01 CA CA272,929A patent/CA1081808A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4630009A (en) * | 1984-01-24 | 1986-12-16 | Com Dev Ltd. | Cascade waveguide triple-mode filters useable as a group delay equalizer |
| EP0188367A2 (en) * | 1985-01-14 | 1986-07-23 | Com Dev Ltd. | Triple mode dielectric loaded bandpass filters |
| EP0188367A3 (en) * | 1985-01-14 | 1988-07-06 | Com Dev Ltd. | Triple mode dielectric loaded bandpass filters |
| CN110364788A (en) * | 2018-04-11 | 2019-10-22 | 上海华为技术有限公司 | Filter |
| US11211677B2 (en) | 2018-04-11 | 2021-12-28 | Huawei Technologies Co., Ltd. | Filtering apparatus |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |