EP0797267B1 - Radio frequency filter - Google Patents

Radio frequency filter Download PDF

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Publication number
EP0797267B1
EP0797267B1 EP19970301913 EP97301913A EP0797267B1 EP 0797267 B1 EP0797267 B1 EP 0797267B1 EP 19970301913 EP19970301913 EP 19970301913 EP 97301913 A EP97301913 A EP 97301913A EP 0797267 B1 EP0797267 B1 EP 0797267B1
Authority
EP
European Patent Office
Prior art keywords
filter
construction
resonator
resonators
inner conductors
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 - Lifetime
Application number
EP19970301913
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0797267A2 (en
EP0797267A3 (en
Inventor
Jukka Loukkola
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Powerwave Comtek Oy
Original Assignee
Filtronic LK Oy
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 LK Oy filed Critical Filtronic LK Oy
Publication of EP0797267A2 publication Critical patent/EP0797267A2/en
Publication of EP0797267A3 publication Critical patent/EP0797267A3/en
Application granted granted Critical
Publication of EP0797267B1 publication Critical patent/EP0797267B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/205—Comb or interdigital filters; Cascaded coaxial cavities
    • H01P1/2056—Comb filters or interdigital filters with metallised resonator holes in a dielectric block

Definitions

  • the present invention relates to radio frequency filters and an arrangement for adjusting the frequency response of the filter, more particularly to filters having a resonator construction.
  • Ceramic filters are very popular in radio techniques. One of their advantages is their simple construction. Due to their compact construction they are stable; the frequency characteristics of the ceramic filters are not significantly influenced by the vibration and the temperature variations of the device. Due to their simple construction, they are, in addition, suitable for serial production.
  • the known basic construction of a ceramic filter consists, as shown in figure 1, of a dielectric element with two holes, the inner surfaces of which are metal plated.
  • the other surfaces of the element, except for the so called open upper surface, are totally metal plated, and the metal plating of the lower surface is connected with the metal plating of the holes.
  • the metal plated holes being short circuited at their lower ends, form a resonator construction supplied capacitively through the metal plated areas formed on the upper surface of the part.
  • the frequency characteristics of the construction are primarily a function of the hole size, the distance between the holes and the capacity coupling determined by the patterning of the upper surface.
  • the construction forms a quarter-wave resonator.
  • half-wave resonators can be implemented with the same kind of a construction, whereby the both ends of the resonator holes are short circuited.
  • the electric field strength is at its maximum when the magnetic field is at its minimum, whereas at the short-circuited end of the hole, the electric field strength is at its minimum (nearly zero), and the magnetic field is at its maximum.
  • the surface currents appearing in the plating are at their maximum at the short-circuited end of the construction.
  • JP 03 293802 is known a dielectric resonator filter, in which the short-circuit conductor does not cover all the bottom surface of the dielectric block round resonator holes. The purpose is to adjust couplings between resonators so that mass productivity is improved. Conductive short-circuit material is primarily absent between resonator holes.
  • An object of the invention is to realize in a new manner a filter with an arrangement for adjusting it's frequency response.
  • a filter according to the invention is characterized by that which is specified in the independent claim 1.
  • a preferred embodiment of the invention provides a small sized and more versatile resonator filter construction compared with prior art.
  • An embodiment of the invention may also provide a construction, the characteristics of which can easily be changed, even in serial production.
  • An embodiment of the invention may further provide a simple resonator construction adjustable after the production, for the tuning of which no movable parts are required.
  • Implementation of the invention may be achieved by changing the flow of the surface currents of the short-circuited end of the construction, e.g. by forming patterns on the area between the short-circuited ends of the resonators.
  • the inner conductors of the filter may be short circuited only at their one end in order to form a quarter-wave resonator construction.
  • the inner conductors may be short circuited at their both ends in order to form a half-wave resonator construction.
  • the control means of electric currents may be for each resonator respectively formed only to one of the two means short circuiting the ends of the resonator, or formed to both of the means short circuiting the ends of the resonator.
  • the input and output signal of the filter may be galvanically coupled with some of the control means of electric currents in order to arrange an inductive input/output to the filter.
  • the filter may have a basic construction of a ceramic filter. Accordingly, the control means of electric currents may be on the surface of a dielectric element forming the filter, or may be on a separate plate forming a galvanic contact between the resonator holes and a side surface of the dielectric element.
  • the resonators of the filter may be formed according to a stripline resonator construction, and/or a helical resonator construction, and/or a coaxial resonator construction.
  • inventions of the invention are based on the realisation that a change caused to the surface current causes a change to the inductive characteristics of the construction and vice versa. Accordingly, through the patterning of the bottom plating of the filter construction, it is possible to affect the flow of the surface currents characteristic of different wave forms determining, among other things, the effective serial inductance against the ground coupled to the resonator. This serial inductance adjusts the resonance frequency of the resonator and the coupling between the resonators. Through the patterning of the plating it is also possible to affect the amount of the serial inductance between the inner conductors of the resonators, which primarily adjustes the coupling between the resonators.
  • the bottom or the lower surface of the filter construction refers to that surface of a frame element having a form of a substantially rectangular prism, which corresponds to the short-circuited end of a quarter-wave resonator, and the upper surface refers to the surface that corresponds to the open end of a quarter-wave resonator, and that the invention is not limited to a certain position of use or viewing direction of the filter.
  • an area that is only partly plated with electrically conducting material will be formed to the short-circuited end of the filter.
  • the surface currents of the filter are influenced and, through that, the couplings between the resonators and the characteristic frequencies of the resonators are influenced.
  • electrically conducting material attached to the construction by other means than plating can be used.
  • Figure 3 shows one method in accordance with the present invention, for forming pattems on the lower surface of the filter construction.
  • the inner conductors of the resonators have galvanic couplings through the strip areas A1 and A2 to the ground potential of the end surfaces of the filter construction.
  • the strip area A12 couples the areas A1 and A2 with each other.
  • Coils L1 and L2 illustrate the effective inductance between the central conductor of the resonator and the ground potential of the construction, caused by the strip portions A1 and A2.
  • Coil L12 illustrates the inductance of the strip portion A12 between the inner conductors.
  • the lower surface is firstly either totally or partly plated with an electrically conducting plating.
  • the plating is then removed or added according to need.
  • conducting material can be added to the strip areas A1 and A2 of the pattern formed according to figure 3, whereby the effective serial inductance against the ground coupled to the resonator will decrease.
  • Figure 5 shows the influence of narrowing the strip area A12, in other words, of increasing the inductance of the coil L12 described by the equivalent circuit, on the frequency response (insertion loss) of the filter.
  • the solid curve describes the response of the starting situation of the filter illustrated in figure 3, and the broken line curve describes the situation after the area A12 has been narrowed.
  • the narrowing decreases the inductive total coupling, the capacity coupling staying almost constant.
  • the narrowing of the area A12 has a clear influence on the coupling between the resonators.
  • Figure 6 illustrates the influence of the widening of the strip areas A1 and A2, in other words, of decreasing the inductance of coils L1 and L2 shown in the equivalent circuit, on the frequency response of the filter.
  • the solid curve describes the response of the starting situation of the filter shown in figure 3, and the broken line curve describes the situation after widening the areas A1 and A2.
  • the widening of said areas decreases the inductive total coupling between the resonators.
  • the widening of the portions A1 and A2 moves the resonator frequencies upwards.
  • the strip areas causing the desired electric characteristics can be made by removing certain plating areas from the surface that has first been totally plated. Another alternative is to make a ready patterned plating having already the characteristics with influence on the surface currents. If additional adjustment is desired,. the plating can be removed from certain points or added to desired points of the plating of the lower surface.
  • the input and output couplings to the resonators are implemented as capacitive couplings.
  • One advantage of a construction in accordance with the invention is that the input and output couplings can be easily implemented also inductively by connecting the input and output signals directly with a galvanic contact to strip areas of the bottom.
  • the dielectric filter in accordance with the present invention can consist of one dielectric element, whereby the patterning in accordance with the invention is totally on the surface of the element.
  • the dielectric filter in accordance with the present invention can also be a combination of a dielectric element and a plate patterned with conducting material, whereby the patternings of the element and the plate are electrically connected with each other and the patterning in accordance with the invention can either partly or totally be also on the surface of the plate.
  • the invention is also applicable to filters implemented with other resonator constructions, like stripline, helical or coaxial resonator constructions, in other words, with constructions, at least one end of which is short circuited, whereby surface currents are generated to the short-circuited end to be influenced in accordance with the present invention.
  • the invention is applicable to serial production and facilitates the serial production of the resonator filters, because it is possible by means of the invention to produce a basic model that can be adjusted afterwards for various purposes. Additionally, the invention allows a stable tuning: no separate tuning means that could move due to vibration, impacts etc. are used for the tuning.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
EP19970301913 1996-03-22 1997-03-21 Radio frequency filter Expired - Lifetime EP0797267B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI961329 1996-03-22
FI961329A FI102433B (sv) 1996-03-22 1996-03-22 Radiofrekvensfilter och metod för justering filterns frekvensfunktion

Publications (3)

Publication Number Publication Date
EP0797267A2 EP0797267A2 (en) 1997-09-24
EP0797267A3 EP0797267A3 (en) 1998-07-15
EP0797267B1 true EP0797267B1 (en) 2003-09-24

Family

ID=8545717

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19970301913 Expired - Lifetime EP0797267B1 (en) 1996-03-22 1997-03-21 Radio frequency filter

Country Status (6)

Country Link
EP (1) EP0797267B1 (sv)
JP (1) JPH1013107A (sv)
AU (1) AU1640697A (sv)
CA (1) CA2200636A1 (sv)
DE (1) DE69725038T2 (sv)
FI (1) FI102433B (sv)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3317404B1 (ja) 2001-07-25 2002-08-26 ティーディーケイ株式会社 誘電体装置

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2109641B (en) * 1981-10-02 1985-08-14 Murata Manufacturing Co Distributed constant type filter
JPH03293802A (ja) * 1990-04-11 1991-12-25 Murata Mfg Co Ltd 誘電体フィルタ
EP0552761B1 (en) * 1992-01-23 1999-07-07 Murata Manufacturing Co., Ltd. Dielectric filter and manufacturing method thereof
KR0147726B1 (ko) * 1994-06-16 1998-08-17 무라따 야스따까 유전체 필터

Also Published As

Publication number Publication date
CA2200636A1 (en) 1997-09-22
FI961329A (sv) 1997-09-23
EP0797267A2 (en) 1997-09-24
DE69725038D1 (de) 2003-10-30
FI102433B1 (sv) 1998-11-30
EP0797267A3 (en) 1998-07-15
FI102433B (sv) 1998-11-30
DE69725038T2 (de) 2004-06-09
FI961329A0 (sv) 1996-03-22
AU1640697A (en) 1997-09-25
JPH1013107A (ja) 1998-01-16

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