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WO1993001625A1 - Microwave filter - Google Patents

Microwave filter Download PDF

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Publication number
WO1993001625A1
WO1993001625A1 PCT/GB1992/001275 GB9201275W WO9301625A1 WO 1993001625 A1 WO1993001625 A1 WO 1993001625A1 GB 9201275 W GB9201275 W GB 9201275W WO 9301625 A1 WO9301625 A1 WO 9301625A1
Authority
WO
WIPO (PCT)
Prior art keywords
cavities
microwave filter
wall
filter
lid
Prior art date
Application number
PCT/GB1992/001275
Other languages
French (fr)
Inventor
Philip David Sleigh
Original Assignee
Filtronic Components Limited
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Filtronic Components Limited filed Critical Filtronic Components Limited
Priority to EP92915388A priority Critical patent/EP0593635A1/en
Publication of WO1993001625A1 publication Critical patent/WO1993001625A1/en

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

Definitions

  • This invention relates to a microwave filter fo filtering input signals to within a predetermined frequenc band.
  • microwave filter is the so-calle comb-line filter which comprises a plurality of resonan cavities coupled together in a series, each resonant cavit having a central element or resonator.
  • a filter i normally considered to be a passive linear device.
  • signals having frequencies in the filter's frequenc passband may mix to form inter odulation products (passiv intermodulation products) .
  • Two comb-line filters may be forme together in a single structure, to form a diplexer: one filte acts as a transmission filter and the other as a receiv filter. Depending upon the particular wavebands of the tw filters, the frequency of the intermodulation products of th transmission filter may fall within the waveband of the receiv filter.
  • a microwave filter comprising a body having plurality of resonant cavities formed therein, the cavitie being open to one surface of said body, and a lid disposed ove said surface of the body to close said cavities, the cavitie being arranged in a series with each adjacent pair of cavitie physically separated from one another by a wall and couple together by an aperture in that wall, the wall terminatin short of said lid.
  • the body of the microwave filter is forme of a single piece of material including an upstanding elemen or resonator projecting from the base of each resonant cavity. If it is not possible to form the resonators integrally wit the body (e.g. if it is necessary to use different metals) , then each resonator is fixed in intimate contact with the bas of its resonant cavity. By forming the resonators integral with or in intimate contact with the body component, then imperfections at the junction between different components are avoided or minimised at regions of high current density: accordingly the passive intermodulation product is further reduced.
  • a microwave filter comprising a body having at least one resonant cavity formed therein, with an element or resonator projecting into the cavity and formed integrally with or in intimate contact with said body.
  • At least the internal surfaces of the cavities are formed with a layer of silver which has a thickness of at least three times the maximum skin depth for the frequencies passed by the filter: typically the silver layer is at least 8 microns thick. With such a relatively thick layer of silver, it is ensured that all current is carried within the silver layer.
  • the non-adjacent cavities, at one end of the series of cavities are coupled directly so as to form an attenuation pole at one edge of the filter's passband.
  • a required level of signal rejection adjacent that edge is achieved with a minimum number of resonant cavities in the series, for the required width of the passband: this minimises the bandwidth of the highest Q resonator and therefore the current density and hence the passive intermodulation products.
  • a diplexer may comprise two filters in accordance with the invention, one a transmission filter and the second a receive filter.
  • the diplexer may be used for example in a cellular radio base station, typically with the transmission filter having a passband of 935 to 960 MHz and the receive filter a passband of 890 to 915 MHz.
  • a multiplexer may be provided, comprising any desired number of filters each in accordance with this invention.
  • FIGURE 1 is a block diagram of a diplexer in accordance with the invention.
  • FIGURE 2 is a plan view of the diplexer shown with it lid removed;
  • FIGURE 3 is a cross-section through the diplexer on th line III-III of Figure 2;
  • FIGURE 4 is a cross-section through the diplexer on th line IV-IV of Figure 2.
  • a diplexer whic may be used in cellular radio system, for example.
  • Th diplexer has a common terminal connected by a coaxial cable t a transmit/receive antenna 1, and a receive filter Fl and transmission filter F2 both connected to the common terminal and having respective terminals connected by coaxial cables t receiver and transmitter systems.
  • Receive filter Fl has waveband of 890 to 915 MHz and transmission filter F2 has waveband of 935 to 960 MHz, in the example shown.
  • the diplexer comprises a singl body 10 in which the two filters Fl and F2 are formed.
  • Bod 10 is rectangular in shape in the example shown.
  • Each cavity has a coaxial, cylindrical elemen 30 upstanding from its base to form a resonator for th respective resonant cavity.
  • the common coaxial terminal 31 ha its centre pin connected via conductors 32,33 to the resonator 30 of the first resonant cavities 11,21 of the respectiv filters F1,F2.
  • the resonators of the last resonant cavit 16,26 of the respective filters are connected by conductor 34,35 to the centre pin of coaxial terminals 36,37.
  • each filter adjacent cylindrical resonant cavitie e.g. 12,13 are physically separated by a thin wall 40, but ar inductively coupled together through a rectangular aperture 4 formed in the centre of this wall and extending towards th base of the cavities from the top surface of the body 10.
  • the remaining portions of the wall 40 either side o the coupling aperture or iris 41, terminate short of the to surface of the body 10, as shown in Figures 3 and 4.
  • a portion 42 of the wall 40 remains at the bas of the cavities.
  • the portions of the wall with upper surfaces short of the top surface of the body 10 are indicated by W: each of these lies between the adjacent edge of the iris 41 and a line e.g. L which is tangential to the two adjacent cavities.
  • a flat lid 44 is fixed against the top surface of the body 10 to close the resonant cavities.
  • the resonators 30 are formed integrally with the body 10.
  • the body 10 may be is cast in one-piece from e.g. aluminium. At least the internal surfaces of the resonant cavities are given a relatively thick layer of silver, to a thickness at least 3 times the maximum skin depth for frequencies within the respective waveband (and preferably at least 8 microns) .
  • the fourth to sixth cavities 14 to 16 are arranged in a triangle and cavities 14 and 16 are inductively coupled together by a rectangular aperture or iris 46 formed in the wall which separates them. This coupling provides an attenuation pole at the higher-frequency side of the receive waveband.
  • the fourth to sixth cavities 24 to 26 are also arranged in a triangle: a notch 48 is formed in the top of the wall between cavities 24 and 26, and a member (not shown) fits into this notch, the member having a pin projecting into each cavity to provide capacitive coupling between them. This provides an attenuation pole at the lower-frequency side of the transmission waveband.
  • the diplexer which is shown in the drawings exhibits minimal passive intermodulation products, and hence minimal intermodulation distortion, for the reasons explained above. Whilst the drawings show a diplexer, in general a multiplexer may be provided, having any desired number of filters each in accordance with the inventions and having a common terminal: this is represented in Figure 1 by dotted lines to indicate the additional filters Fn which would then be included.

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Abstract

A microwave filter comprises a body (10) having a plurality of resonant cavities (e.g. 11 to 16) formed therein, the cavities being open to one surface of the body (10), and a lid (44) disposed over that surface of the body to close the cavities. The cavities (e.g. 11 t0 16) are arranged in a series with each pair of adjacent cavities physically separated from one another by a wall (40) and coupled together by an aperture (41) in that wall; the wall (40) terminates short of the lid (44), with the result that the formation of passive intermodulation products is substantially reduced.

Description

This invention relates to a microwave filter fo filtering input signals to within a predetermined frequenc band.
One known type of microwave filter is the so-calle comb-line filter which comprises a plurality of resonan cavities coupled together in a series, each resonant cavit having a central element or resonator. Such a filter i normally considered to be a passive linear device. However, at high power levels, non-linear effects become apparent. A a result, signals having frequencies in the filter's frequenc passband may mix to form inter odulation products (passiv intermodulation products) . Two comb-line filters may be forme together in a single structure, to form a diplexer: one filte acts as a transmission filter and the other as a receiv filter. Depending upon the particular wavebands of the tw filters, the frequency of the intermodulation products of th transmission filter may fall within the waveband of the receiv filter.
According to a first aspect of this invention, there i provided a microwave filter comprising a body having plurality of resonant cavities formed therein, the cavitie being open to one surface of said body, and a lid disposed ove said surface of the body to close said cavities, the cavitie being arranged in a series with each adjacent pair of cavitie physically separated from one another by a wall and couple together by an aperture in that wall, the wall terminatin short of said lid.
We have found that by terminating the separating wall short of the lid, the formation of passive intermodulatio products is substantially reduced. This is due to avoidin contact between two components, the body and the lid, at region of high current density.
Preferably the body of the microwave filter is forme of a single piece of material including an upstanding elemen or resonator projecting from the base of each resonant cavity. If it is not possible to form the resonators integrally wit the body (e.g. if it is necessary to use different metals) , then each resonator is fixed in intimate contact with the bas of its resonant cavity. By forming the resonators integral with or in intimate contact with the body component, then imperfections at the junction between different components are avoided or minimised at regions of high current density: accordingly the passive intermodulation product is further reduced.
According to a second aspect of this invention, there is provided a microwave filter comprising a body having at least one resonant cavity formed therein, with an element or resonator projecting into the cavity and formed integrally with or in intimate contact with said body.
Preferably at least the internal surfaces of the cavities are formed with a layer of silver which has a thickness of at least three times the maximum skin depth for the frequencies passed by the filter: typically the silver layer is at least 8 microns thick. With such a relatively thick layer of silver, it is ensured that all current is carried within the silver layer.
Preferably the non-adjacent cavities, at one end of the series of cavities, are coupled directly so as to form an attenuation pole at one edge of the filter's passband. As a result, a required level of signal rejection adjacent that edge is achieved with a minimum number of resonant cavities in the series, for the required width of the passband: this minimises the bandwidth of the highest Q resonator and therefore the current density and hence the passive intermodulation products.
A diplexer may comprise two filters in accordance with the invention, one a transmission filter and the second a receive filter. The diplexer may be used for example in a cellular radio base station, typically with the transmission filter having a passband of 935 to 960 MHz and the receive filter a passband of 890 to 915 MHz.
In general however, a multiplexer may be provided, comprising any desired number of filters each in accordance with this invention.
An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which:
FIGURE 1 is a block diagram of a diplexer in accordance with the invention;
FIGURE 2 is a plan view of the diplexer shown with it lid removed;
FIGURE 3 is a cross-section through the diplexer on th line III-III of Figure 2; and
FIGURE 4 is a cross-section through the diplexer on th line IV-IV of Figure 2.
Referring to Figure 1, there is shown a diplexer whic may be used in cellular radio system, for example. Th diplexer has a common terminal connected by a coaxial cable t a transmit/receive antenna 1, and a receive filter Fl and transmission filter F2 both connected to the common terminal and having respective terminals connected by coaxial cables t receiver and transmitter systems. Receive filter Fl has waveband of 890 to 915 MHz and transmission filter F2 has waveband of 935 to 960 MHz, in the example shown.
Referring to Figure 2, the diplexer comprises a singl body 10 in which the two filters Fl and F2 are formed. Bod 10 is rectangular in shape in the example shown. Each filte comprises a series of n cylindrical cavities 11 to 16 and 2 to 26 having their axes parallel to each other, the cavitie being open to a top surface of the body 10: in the exampl shown n=6. Each cavity has a coaxial, cylindrical elemen 30 upstanding from its base to form a resonator for th respective resonant cavity. The common coaxial terminal 31 ha its centre pin connected via conductors 32,33 to the resonator 30 of the first resonant cavities 11,21 of the respectiv filters F1,F2. The resonators of the last resonant cavit 16,26 of the respective filters are connected by conductor 34,35 to the centre pin of coaxial terminals 36,37.
In each filter, adjacent cylindrical resonant cavitie e.g. 12,13 are physically separated by a thin wall 40, but ar inductively coupled together through a rectangular aperture 4 formed in the centre of this wall and extending towards th base of the cavities from the top surface of the body 10. However, the remaining portions of the wall 40, either side o the coupling aperture or iris 41, terminate short of the to surface of the body 10, as shown in Figures 3 and 4. It wil be noted that a portion 42 of the wall 40 remains at the bas of the cavities. The portions of the wall with upper surfaces short of the top surface of the body 10 are indicated by W: each of these lies between the adjacent edge of the iris 41 and a line e.g. L which is tangential to the two adjacent cavities. A flat lid 44 is fixed against the top surface of the body 10 to close the resonant cavities. The upper surfaces W of the various walls 40 accordingly stop short of the lid 44. The resonators 30 also stop short of the lid 44, and are formed with a coaxial blind bore 45: tuning screws (not shown)are threaded through the lid and project into the respective bores 45.
It will be noted that the resonators 30 are formed integrally with the body 10. The body 10 may be is cast in one-piece from e.g. aluminium. At least the internal surfaces of the resonant cavities are given a relatively thick layer of silver, to a thickness at least 3 times the maximum skin depth for frequencies within the respective waveband (and preferably at least 8 microns) . In the receive filter Fl, the fourth to sixth cavities 14 to 16 are arranged in a triangle and cavities 14 and 16 are inductively coupled together by a rectangular aperture or iris 46 formed in the wall which separates them. This coupling provides an attenuation pole at the higher-frequency side of the receive waveband. In the transmission filter F2, the fourth to sixth cavities 24 to 26 are also arranged in a triangle: a notch 48 is formed in the top of the wall between cavities 24 and 26, and a member (not shown) fits into this notch, the member having a pin projecting into each cavity to provide capacitive coupling between them. This provides an attenuation pole at the lower-frequency side of the transmission waveband.
The diplexer which is shown in the drawings exhibits minimal passive intermodulation products, and hence minimal intermodulation distortion, for the reasons explained above. Whilst the drawings show a diplexer, in general a multiplexer may be provided, having any desired number of filters each in accordance with the inventions and having a common terminal: this is represented in Figure 1 by dotted lines to indicate the additional filters Fn which would then be included.

Claims

(1) A microwave filter comprising a body (10) having plurality of resonant cavities (e.g. 11 to 16)_ formed therein, the cavities being open to one surface of said body (10) , an a lid (44) disposed over said surface of the body to close sai cavities, the cavities being arranged in a series with eac pair of adjacent cavities physically separated from one anothe by a wall (40) and coupled together by an aperture (41) in tha wall, the wall (40) terminating short of the lid.
(2) A microwave filter as claimed in claim 1, in which two non-adjacent cavities (e.g. 14,16), at one end of the series of cavities, are coupled directly to form an attenuation pole at one edge of the filter's passband.
(3) A microwave filter as claimed in claim 2, in which three cavities (e.g. 14,15,16), at one end of the series of cavities, are arranged in a triangle.
(4) A microwave filter as claimed in claim 3, in which the end and end-but-one cavities (16,14) are inductively coupled by an aperture formed in a wall which separates them.
(5) A microwave filter as claimed in claim 3, in which the end and end-but-one cavities (26,24) are capacitively coupled by a probe device which projects into both of them.
(6) A microwave filter as claimed in any preceding claim, having an upstanding resonator element (30) projecting from the base of each cavity.
(7) A microwave filter as claimed in any preceding claim, in which the internal surfaces of the cavities are formed with a layer of silver or other precious metal.
(8) A microwave filter comprising a body (10) having at least one resonant cavity formed therein, with a resonator element (30) projecting into the cavity and formed integrally with or in intimate contact with said body.
PCT/GB1992/001275 1991-07-11 1992-07-13 Microwave filter WO1993001625A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP92915388A EP0593635A1 (en) 1991-07-11 1992-07-13 Microwave filter

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB919114970A GB9114970D0 (en) 1991-07-11 1991-07-11 Microwave filter
GB9114970.8 1991-07-11

Publications (1)

Publication Number Publication Date
WO1993001625A1 true WO1993001625A1 (en) 1993-01-21

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ID=10698188

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1992/001275 WO1993001625A1 (en) 1991-07-11 1992-07-13 Microwave filter

Country Status (3)

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EP (1) EP0593635A1 (en)
GB (1) GB9114970D0 (en)
WO (1) WO1993001625A1 (en)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0823746A2 (en) 1996-08-05 1998-02-11 ADC Solitra Oy A filter and a method for manufacturing a filter
WO1999027605A3 (en) * 1997-11-21 1999-09-02 Ericsson Telefon Ab L M Waveguide filter
US6255917B1 (en) * 1999-01-12 2001-07-03 Teledyne Technologies Incorporated Filter with stepped impedance resonators and method of making the filter
US6366184B1 (en) 1999-03-03 2002-04-02 Filtronic Lk Oy Resonator filter
KR100445743B1 (en) * 2001-09-04 2004-08-25 한국전자통신연구원 Resonator for Filter and Method for Designing Filter using it and Filter Designed by it
US6876277B2 (en) 2001-12-26 2005-04-05 Dragonwave, Inc. E-plane filter and a method of forming an E-plane filter
WO2015150500A1 (en) * 2014-04-04 2015-10-08 Kathrein-Werke Kg Cover lid, housing for electric or electromagnetic applications and method of assembly of a hf housing
US9202660B2 (en) 2013-03-13 2015-12-01 Teledyne Wireless, Llc Asymmetrical slow wave structures to eliminate backward wave oscillations in wideband traveling wave tubes
EP3203575A1 (en) * 2016-02-05 2017-08-09 Spinner GmbH Filter structures for pim measurements
EP3296433A1 (en) * 2012-03-21 2018-03-21 Intel Corporation Lightweight cavity filter and radio subsystem structures

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6313721B1 (en) * 1999-08-06 2001-11-06 Ube Electronics, Ltd. High performance dielectric ceramic filter using a non-linear array of holes

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Publication number Priority date Publication date Assignee Title
CH397889A (en) * 1962-03-30 1965-08-31 Budavox Budapesti Hiradastechn Microwave band filter with symmetrical attenuation characteristics
US3571768A (en) * 1969-09-25 1971-03-23 Motorola Inc Microwave resonator coupling having two coupling apertures spaced a half wavelength apart
DE2327912A1 (en) * 1973-06-01 1974-12-19 Licentia Gmbh CAPACITIVELY COUPLED CAVITY RESONATOR FILTER
DE2640210A1 (en) * 1976-09-07 1978-03-09 Siemens Ag Electromagnetic wave filter with several resonators - handles very short microwaves with resonators grouped in blocks of three
US4307357A (en) * 1980-03-04 1981-12-22 Tektronix, Inc. Foreshortened coaxial resonators
WO1983002853A1 (en) * 1982-02-16 1983-08-18 Motorola Inc Ceramic bandpass filter
WO1987000350A1 (en) * 1985-07-08 1987-01-15 Ford Aerospace & Communications Corporation Narrow bandpass dielectric resonator filter

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH397889A (en) * 1962-03-30 1965-08-31 Budavox Budapesti Hiradastechn Microwave band filter with symmetrical attenuation characteristics
US3571768A (en) * 1969-09-25 1971-03-23 Motorola Inc Microwave resonator coupling having two coupling apertures spaced a half wavelength apart
DE2327912A1 (en) * 1973-06-01 1974-12-19 Licentia Gmbh CAPACITIVELY COUPLED CAVITY RESONATOR FILTER
DE2640210A1 (en) * 1976-09-07 1978-03-09 Siemens Ag Electromagnetic wave filter with several resonators - handles very short microwaves with resonators grouped in blocks of three
US4307357A (en) * 1980-03-04 1981-12-22 Tektronix, Inc. Foreshortened coaxial resonators
WO1983002853A1 (en) * 1982-02-16 1983-08-18 Motorola Inc Ceramic bandpass filter
WO1987000350A1 (en) * 1985-07-08 1987-01-15 Ford Aerospace & Communications Corporation Narrow bandpass dielectric resonator filter

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 10, no. 285 (E-441)(2341) 27 September 1986 & JP,A,61 105 901 ( SUMITOMO ELECTRIC INDUSTRIES LTD ) 24 May 1986 *

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0823746A2 (en) 1996-08-05 1998-02-11 ADC Solitra Oy A filter and a method for manufacturing a filter
US5990763A (en) * 1996-08-05 1999-11-23 Adc Solitra Oy Filter having part of a resonator and integral shell extruded from one basic block
US6167739B1 (en) 1996-08-05 2001-01-02 Adc Solitra Oy Filter and a method for manufacturing a filter
WO1999027605A3 (en) * 1997-11-21 1999-09-02 Ericsson Telefon Ab L M Waveguide filter
US6181224B1 (en) 1997-11-21 2001-01-30 Telefonaktiebolaget Lm Ericsson (Publ) Waveguide filter with a resonator cavity having inner and outer edges of different lengths
US6255917B1 (en) * 1999-01-12 2001-07-03 Teledyne Technologies Incorporated Filter with stepped impedance resonators and method of making the filter
US6366184B1 (en) 1999-03-03 2002-04-02 Filtronic Lk Oy Resonator filter
KR100445743B1 (en) * 2001-09-04 2004-08-25 한국전자통신연구원 Resonator for Filter and Method for Designing Filter using it and Filter Designed by it
US6876277B2 (en) 2001-12-26 2005-04-05 Dragonwave, Inc. E-plane filter and a method of forming an E-plane filter
EP3296433A1 (en) * 2012-03-21 2018-03-21 Intel Corporation Lightweight cavity filter and radio subsystem structures
US9202660B2 (en) 2013-03-13 2015-12-01 Teledyne Wireless, Llc Asymmetrical slow wave structures to eliminate backward wave oscillations in wideband traveling wave tubes
WO2015150500A1 (en) * 2014-04-04 2015-10-08 Kathrein-Werke Kg Cover lid, housing for electric or electromagnetic applications and method of assembly of a hf housing
EP3203575A1 (en) * 2016-02-05 2017-08-09 Spinner GmbH Filter structures for pim measurements
WO2017134246A1 (en) * 2016-02-05 2017-08-10 Spinner Gmbh Filter structures for pim measurements
CN108886190A (en) * 2016-02-05 2018-11-23 斯宾纳有限公司 Filter construction for PIM measurement
KR20180125958A (en) * 2016-02-05 2018-11-26 스피너 게엠베하 Filter structures for PIM measurements
US20180342779A1 (en) * 2016-02-05 2018-11-29 Spinner Gmbh Filter structures for pim measurements
KR101980791B1 (en) 2016-02-05 2019-05-21 스피너 게엠베하 Filter structures for PIM measurements
US10403949B2 (en) 2016-02-05 2019-09-03 Spinner Gmbh Re-filters for PIM measurements and a test bench utilizing the same
CN108886190B (en) * 2016-02-05 2019-11-05 斯宾纳有限公司 Testboard for the filter of RF signal and for measuring passive intermodulation PIM

Also Published As

Publication number Publication date
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EP0593635A1 (en) 1994-04-27

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