EP3035435A1 - Resonator, Funkfrequenzfilter und Filterverfahren - Google Patents

Resonator, Funkfrequenzfilter und Filterverfahren Download PDF

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Publication number
EP3035435A1
EP3035435A1 EP14290385.5A EP14290385A EP3035435A1 EP 3035435 A1 EP3035435 A1 EP 3035435A1 EP 14290385 A EP14290385 A EP 14290385A EP 3035435 A1 EP3035435 A1 EP 3035435A1
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EP
European Patent Office
Prior art keywords
resonator
resonators
wall
cap
caps
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.)
Withdrawn
Application number
EP14290385.5A
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English (en)
French (fr)
Inventor
Efstratios Doumanis
Florian Pivit
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Alcatel Lucent SAS
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Alcatel Lucent SAS
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Filing date
Publication date
Application filed by Alcatel Lucent SAS filed Critical Alcatel Lucent SAS
Priority to EP14290385.5A priority Critical patent/EP3035435A1/de
Publication of EP3035435A1 publication Critical patent/EP3035435A1/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P7/00—Resonators of the waveguide type
    • H01P7/04—Coaxial resonators
    • 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
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/205—Comb or interdigital filters; Cascaded coaxial cavities
    • H01P1/2053—Comb or interdigital filters; Cascaded coaxial cavities the coaxial cavity resonators being disposed parall to each other

Definitions

  • the present invention relates to filters for telecommunications, in particular to radio-frequency filters.
  • Combline filters also known as coaxial cavity filters, are often used in base stations for cellular wireless telecommunications, in particular in Frequency Division Duplexer (FDD) systems.
  • FDD Frequency Division Duplexer
  • rejection levels required in a modern FDD system require a number of transmission zeros to be realised in a highly asymmetric filter.
  • coaxial cavity filters cross couplings between the cavity resonators that make up the filter are used to produce the transmission zeros.
  • Transmission zeros are required to provide spectrum-efficient filtering by a limited number of resonators having reasonable size and insertion loss. Typically a number of cross-couplings between cavity resonators is required. That number can be less than half the total number of cavity resonators.
  • the known way to provide the coupling is to provide a machined slot between the cavity resonators into which a capacitive probe extends.
  • the probe is made of conductive material and is supported mechanically by a plastic/dielectric material in the machined slot.
  • the probe may overheat, particularly as for electrical reasons the probe is thermally decoupled from any effective heat sink.
  • the probe heats up, in addition-to an overall reduction in the quality factor of the cavity resonator, arcing may even result.
  • a known approach to address overheating and other thermal-tolerance issues is to manufacture the capacitive probes using suitable materials, for example silver plated steel. Each probe is, in practice, individually designed and manufactured to provide the required cross- coupling.
  • An example of the present invention is a resonator comprising a resonant chamber, the resonant chamber comprising a first wall, a second wall opposite the first wall, and side walls; in which the resonant chamber houses a resonator post which is grounded on the first wall so as to extend into the chamber; the resonator post comprising a cap at its end that is away from the first wall, the cap having at least one arm extending in a direction transverse to the longitudinal axis of the resonator post.
  • a coaxial resonator post having an open end, namely an end away from the end grounded on the cavity, where the open end includes a bent out arm or arms.
  • Each arm may be directed towards a side wall of the chamber.
  • the post and one arm when viewed in profile, may be considered as taking the form of greek letter r (capital gamma).
  • the capacitance at the top of the resonator post follows the shape of the cap which has arms, and, in some embodiments, by using a pair of the caps having arms, capacitive coupling between two resonators is increased, (as compared to known resonators having circular caps).
  • This increase in capacitance means that additional parts, such as auxiliary elements, sometimes known as probes or capacitive probes, in the vicinity of where the capacitive coupling takes place are advantageously not required. In consequence, filters are simpler and, due to the absence of probes which might overheat, suitable for high power applications.
  • Some embodiments provided a greater magnitude of capacitive (i.e. negative) coupling as compared to known filters using circular disc caps operating at the same resonant frequency. In consequence capacitive probes are not required.
  • the cap has four arms so as to take a cross-shape.
  • the cap has one, two or three arms.
  • the cap has more than four arms.
  • Examples of the present invention also relates to corresponding radio frequency filters and methods of filtering.
  • a radio frequency filter comprising two of the resonators in which in the wall between the resonant chambers there is an opening for electrical coupling.
  • the opening is a slot proximal to the caps allowing capacitive coupling between the chambers.
  • one of the two resonators comprises arm which is at least substantially aligned with a corresponding arm of the other of the two resonators.
  • the cap of at least one of the two resonators is rotatable around the longitudinal axis of its respective resonator post in order to tune the electrical coupling.
  • the filter further comprises at least one further resonator, for example two further resonators.
  • the resonators take a configuration, which may be considered a folded configuration, in which the further two resonators have respective resonant chambers interconnected by an opening and each resonant chamber of the additional two resonators is connected to a respective one of the first two resonant chambers by a respective opening, the openings being apertures for inductive coupling.
  • the resonators include resonator posts carrying caps; and the caps of the resonators separated by the slot are rotated to be at least substantially aligned and the caps of the resonators separated by apertures are rotated to be misaligned.
  • the caps are cross-shaped caps, and the caps of the resonators separated by apertures are positioned so that the resonators have respective arms at least substantially 45 degrees or 90 degrees out of alignment.
  • the apertures in the walls between resonant chambers are at least substantially the height of the walls between resonant chambers.
  • Another example of the present invention relates to a method of radio frequency filtering comprising passing a signal for filtering through two resonators, each resonator comprising a resonant chamber, each resonant chamber comprising a first wall, a second wall opposite the first wall, and side walls; in which the resonant chamber houses a resonator post which is grounded on the first wall so as to extend into the chamber; the resonator post has a cap at its end that is away from the first wall; the cap comprising at least one arm extending in a direction transverse to the longitudinal axis of the resonator post; and in which in the wall between resonant chambers there is an opening for electrical coupling.
  • Figures 2 and 3 may be considered schematic (not to scale) even though they indicate some distances.
  • Figure 1 is a diagram illustrating the known cavity resonator including the cap in the form of a circular disc. This provide capacitive loading at the top of the resonator post.
  • Figure 1 is in three parts (a) is a cross sectional view from top, (b) is a diagrammatic three dimensional illustration of the cavity resonator, and (c) shows the electric filed magnitude for the cap which is a circular disc (PRIOR ART).
  • the resonator post with circular cap may be usefully replaced by a cap having one or more arms extending out in a direction transverse to the longitudinal axis of the resonator post.
  • This would allow greater capacitive (also known as 'negative') coupling (as compared to using a circular disc cap with the same fundamental operating resonant frequency). This is explained below.
  • a cavity resonator 10 is provided including a cap 12 in the form of a cross to provide capacitive loading at the top of the resonator post 14.
  • the resonator post 14 with cap 12 is grounded on the bottom 16 of the cavity 18 having metallic walls 20 which constitute an enclosure 22.
  • a tuning screw 15 is provided from the top which does not contact the cap 12 but is adjustable in length for frequency tuning.
  • (a) is a cross sectional view from top
  • (b) is a diagrammatic three dimensional illustration of this cavity resonator
  • (c) shows the electric filed magnitude for the cap 12 which is in the form of a cross.
  • Table 1 Resonator dimensions, cross cap Cavity (Width x Width x Length) 40mm x 40mm x 55mm (88 cm 3 )) Post Diameter 11.2 mm Post Length 46.8mm Thickness of capacitive cross shaped cap 3mm r1 2 mm r2 1 mm l1 31.2 mm l2 9.2 mm
  • Table 2 Resonator dimensions, circular disc cap (PRIOR ART) Resonator Circular Disc Cavity (Width x Width x Length) 40mm x40mm x55 mm (88 cm 3 )) Post Diameter 11.2 mm Post Length 46.8 mm Thick of capacitive cap 3mm Disc diameter 28.4 mm
  • Table 3 Performance of the resonators Resonator Cap Shape Electrical Length (372.2 mm) Gap Size/Cavity Length Resonant frequency Q - Factor (Al/Al) Q/Vol (1/cm 3 ) Circular Disc (PRIOR ART) ⁇ 53 deg 5.2/55 (mm) 807.8 MHz 3288 37.36 Cross ⁇ 53 deg 5.2/55 (mm) 808.9 MHz 3280 37.27
  • the Q factor assumes that both the enclosure and resonator post are made of aluminium.
  • the cavity resonator 10 with cross cap 12 has a slightly lower unloaded Quality factor due to what can be considered as a relative redistribution of capacitance, from between the open end of the resonator post 14 and the top lid (not shown in Figure 2 ) towards between the open end of the resonator post 14 and side walls 20.
  • the cavity resonator 10 with cross cap 12 has a Q factor reduced by 0.24% and a Q per unit volume that is only slightly reduced.
  • Table 4 shows performance of a number of the proposed cavity resonators (having various electrical lengths and miniaturization factors) compared with the cavity resonators of known type having circular disc caps and the same respective electrical length.
  • Gap size refers to the distance of the cap to the top lid of the resonator.
  • a tuning screw (4mm diameter, 2mm long, made of aluminium) was present except in the last case (electrical length ⁇ 41.6 deg).
  • a filter was then evaluated consisting of two cavity resonators basically as shown in Figures 2 and 3 but with a slot in the single separating wall between them as shown in Figure 4 .
  • This filter 11 is shown in Figure 5 .
  • each of the cavity resonators 10' includes full walls 20' on three sides and a single separating wall 21 as shown in Figure 4 .
  • the separating wall 21 includes a slot 23 in its upper portion 25.
  • the slot is rectangular having a specified width and length.
  • the separating wall thickness was taken to be 1 mm, slot width 28.4 mm and resonator dimensions as listed in Table 1 above.
  • the slot length varied between 8 and 22 mm.
  • the magnitude of the coupling coefficient (actually being capacitive hence negative) was determined and results are shown graphically in Figure 6.
  • Figure 6 shows a smooth variation in the capacitive (i.e. negative) coupling as a function of slot length.
  • Figure 7 shows a smooth variation in the negative coupling as a function of slot width, and indicates the maximum magnitude of the coupling possible for this filter and slot configuration.
  • This comparative filter having circular disc caps was found to have a maximum magnitude of capacitive coupling of 3.4 x 10 -03 as compared to 7.1 x 10 -03 for the corresponding filter shown in Figure 5 .
  • the corresponding filter shown in Figure 5 had an approximately 108% higher maximum magnitude of capacitive coupling. It follows that the performance of the filter shown in Figure 5 having the cross shaped caps is substantially better for the same inter-resonator distance and slot width (which is 1 mm).
  • the circular disc caps For the filter with circular disc caps to achieve the same magnitude of capacitive coupling as achieved using cross-shaped resonator caps, the circular disc caps would need to be 4 mm in diameter with a 6.8 mm long aluminium probe (not shown) being deployed.
  • a probe is a metal rod extending into the slot from above in order to tune or enhance the capacitive coupling.
  • a further filter 11' consists of four cavity resonators 26 having resonator posts 14' having cross-shaped caps 12' and with large apertures 28 between cavities 18' except between two of the cavities 30,32 where instead there is a separating wall 21' with a slot 23' (as previously shown in Figure 4 ).
  • this filter 11' can be considered as a four resonator post filter, i.e. four pole filter, with resonator posts 14' having cross -shaped caps 12' , the cavity resonators 26 being disposed in a "folded" layout that employs negative cross-coupling (without a capacitive probe) between two of the cavities 30, 32.
  • the coupling paths are as shown in Figure 8 , namely three apertures 28 with probes 29 which provide inductive coupling, and one slot 23' (without a probe) which provides capacitive coupling.
  • the resonator posts are configured such that two of the resonators posts have arms 34 pointing to the slot 23' (for capacitive coupling) and two have arms 33 nearest apertures 28 that are at 45 degrees to the respective aperture (for inductive coupling).
  • the full height apertures 28 between cavity 1 and cavity 2, and between cavity 3 and cavity 4 have a width of 31mm.
  • the full height aperture 28 between cavity 2 and cavity 3 has a width of 25.7mm.
  • All four resonator posts with caps are identical in shape and side.
  • each aperture 28 is full height and has a respective probe 29 extending into the aperture from above.
  • the way to control or increase the magnitude of the negative (i.e. capacitive) coupling is to bring the two resonator posts with caps into closer proximity to each other, or to adapt the cap by appropriate selection of l 1 and l 2 arm dimensions so as to provide increased negative coupling.
  • it is only the position of the resonator post with cap that is changed not the resonator post with cap itself. In the first approach, the positions can be accurately set using a robot in manufacture.
  • This comparative filter is shown in Figure 9 .
  • Figure 9 is a diagrammatic cross sectional view of this filter which is made up of four cavity resonators 26' having resonator posts 14" having circular caps having large apertures between cavities except between two of the cavities where instead there is a separating wall with a slot 23" (slot width 20mm, slot length 15mm).
  • the capacitive probe 31 is a metallic cylindrical rod (4mm diameter, 6 mm long) which lies in the centre of the slot 23" such that the longitudinal axis of the probe is perpendicular to the plane in which the slot lies.
  • the probe 31 is supported in the slot and separated from the enclosure which is metal by a dielectric spacer (not shown).
  • the slot width is 20mm and the slot height is 15mm.
  • each cavity has a width of 40mm, length of 40mm and height of 55 mm.
  • Each resonator post 14" has a diameter of 11.2 mm.
  • the resonator post lengths are as follows: 46.9 mm in cavity 1 and cavity 4 as shown in Figure 9 , 46. 3 mm in cavity 2 and cavity 3 as shown in Figure 9 .
  • Each capacitive cap is a circular disc having a diameter of 28.4mm and a thickness of 3mm.
  • the full height apertures between cavity 1 and cavity 2, and between cavity 3 and cavity 4 each have a width of 29.9mm.
  • the full height aperture between cavity 2 and cavity 3 has a width of 25.3mm.
  • the tuning screws at the apertures between cavities each have a diameter of 4mm and a length of 20mm. For the sake of completeness, we would add that the cavity corners are rounded to a radius of 3mm.
  • Figure 10 shows a graph of S-parameters response of an example filter as shown in Figures 8 having specific dimensions including a slot length of 15mm.
  • the corresponding graph for a corresponding example filter shown in Figure 9 (ALTERNATIVE PROPOSAL) is also shown for comparison.
  • the use of the cross-shaped caps provides greater capacitive coupling for the same fundamental operating resonant frequency so eliminates the need for a capacitive probe.
  • the two types of couplings one being between cross caps and having no probe, the other being between circular caps and having a probe
  • Figure 11 shows a graph of S-parameters response of another example filter as shown in Figures 8 but having a slot length of 20mm instead so as to increase negative coupling (the S-parameters response for the 15mm slot length shown in Figure 10 is also shown using a dashed line in Figure 11 for comparison). This increase in slot length results in the transmission zeros being closer to the passband.
  • this Figure 11 can be considered to show how a performance characteristic of the coupling mechanism varies the magnitude of negative coupling is increased.
  • Figure 12 is a diagrammatic cross sectional view of a filter including two cavity resonators separated by the wall with the slot and where the cross caps are misaligned by a few degrees specifically one is axially rotated by X degrees and the other is axially rotated by X degrees in the opposite direction so that the arms of the caps are 2X degrees out of alignment (from the arms of the crosses being aligned).
  • Figure 12 viewed from above, one resonator post 14" is rotated anticlockwise and the other resonator post 14"' is rotated clockwise.
  • the arms may be out of alignment in practice by accident or intentionally.
  • Each cavity is 40mm in width and 40 in length and has a height of 55.4 mm.
  • the slot has a width of 20mm and a height of 15mm.
  • the full height apertures 28" are 31.4mm wide into which protrudes a tuning screws of 4mm diameter and 20mm length.
  • the cross shaped caps 12" have arms 33' of span ( l 1 as shown in Figure 3 ) of 32.9 mm and width (12 in Figure 3 ) of 9.2 mm. Walls between cavities are 4mm thick.
  • Figure 13 shows graphs of magnitude of (capacitive/negative) coupling coefficient as a function of axial rotation angle X in degrees, for example filters as shown in Figure 12 , one where the slot is 15mm length and the other where the slot is 18mm length.
  • Post-fabrication tuning may involve, for example, removing the lid of the enclosure to reveal the resonator posts with caps, turning a resonator post with cap manually through an angle, such as a small angle of a few degrees for fine-tuning, then reapplying the lid.
  • Figure 15 is a front view of the aperture shown in Figure 14 .
  • the aperture 28' which is of full height has an aperture width of 26.1 mm and includes a probe 29'.
  • the probe 29' is a metallic cylindrical rod which extends into the aperture from above.
  • the probe 29' is separated from the enclosure which is metal by a dielectric spacer (not shown).
  • Figure 14 is a diagrammatic cross sectional view of a filter including two cavity resonators separated by an aperture and where the cross caps are each roughly 45 degrees out of alignment (from the arms of the crosses being aligned). Specifically one is axially rotated by to lie at 45+X degrees and the other is axially rotated to lie by 45+X degrees in the opposite direction so that the arms of the caps are 90+2X degrees out of alignment (from the arms of the crosses being aligned).
  • the full-height aperture 28' between the two resonator posts with caps is 26.1mm wide.
  • the other two 28"' full height apertures are 31.4mm wide.
  • each aperture protrudes a tuning screw of 4mm diameter and 24mm length.
  • the cross shaped caps have arms of span ( l 1 as shown in Figure 3 ) of 31.2 mm and width (12 in Figure 3 ) of 9.2 mm. Walls between cavities are 4mm thick.
  • Figure 16 shows graphs of coupling coefficient as a function of axial rotation angle for two example filters as shown in Figures 14 and 15 , one with a probe length of 20mm and the other with a probe length of 24 mm.
  • a cap with three arms may be in the form of a triangle where an arm can be, for example, a segment of a triangle including an apex.
  • a lobe of an ellipsoid-shaped cap constitutes an arm.
  • arms can lie in a plane perpendicular to the longitudinal axis of the post or lie at some other angle from the perpendicular.
  • the arms could be bent up, for example by say 30 degrees.
  • the cap is produced by being machined, but in other embodiments it is produced by any of die-casting, laser cutting or some other known manufacturing process.
  • the resonator post and cap may be manufactured separately then mechanically and electrically connected, or manufactured as a single piece.
  • program storage devices e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods.
  • the program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media.
  • Some embodiments involve computers programmed to perform said steps of the above-described methods.

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  • Electromagnetism (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
EP14290385.5A 2014-12-16 2014-12-16 Resonator, Funkfrequenzfilter und Filterverfahren Withdrawn EP3035435A1 (de)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021023610A1 (en) * 2019-08-05 2021-02-11 Commscope Italy S.R.L. Resonant cavity filters including coupling tuning by resonator rotation
WO2021037009A1 (zh) * 2019-08-28 2021-03-04 中兴通讯股份有限公司 交叉耦合滤波器
CN113224487A (zh) * 2020-01-21 2021-08-06 深圳市大富科技股份有限公司 5g无线通信基站

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999030383A2 (en) * 1997-12-11 1999-06-17 Lk-Products Oy Resonator structure
WO2000013256A2 (en) * 1998-08-26 2000-03-09 Allgon Ab Coaxial cavity resonator
US6320483B1 (en) * 1997-09-30 2001-11-20 Allgon Ab Multi surface coupled coaxial resonator
US20080157899A1 (en) * 2006-12-27 2008-07-03 Kathrein-Werke Kg High frequency filter with blocking circuit coupling
US20130009728A1 (en) * 2011-07-06 2013-01-10 Jukka Puoskari Adjustable resonator filter and method for adjusting coupling between resonator cavities

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6320483B1 (en) * 1997-09-30 2001-11-20 Allgon Ab Multi surface coupled coaxial resonator
WO1999030383A2 (en) * 1997-12-11 1999-06-17 Lk-Products Oy Resonator structure
WO2000013256A2 (en) * 1998-08-26 2000-03-09 Allgon Ab Coaxial cavity resonator
US20080157899A1 (en) * 2006-12-27 2008-07-03 Kathrein-Werke Kg High frequency filter with blocking circuit coupling
US20130009728A1 (en) * 2011-07-06 2013-01-10 Jukka Puoskari Adjustable resonator filter and method for adjusting coupling between resonator cavities

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2021023610A1 (en) * 2019-08-05 2021-02-11 Commscope Italy S.R.L. Resonant cavity filters including coupling tuning by resonator rotation
US11996599B2 (en) 2019-08-05 2024-05-28 Commscope Italy S.R.L. Resonant cavity filters including coupling tuning by resonator rotation
WO2021037009A1 (zh) * 2019-08-28 2021-03-04 中兴通讯股份有限公司 交叉耦合滤波器
CN113224487A (zh) * 2020-01-21 2021-08-06 深圳市大富科技股份有限公司 5g无线通信基站

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