EP0318478B1 - Multiple resonator component-mountable filter - Google Patents
Multiple resonator component-mountable filter Download PDFInfo
- Publication number
- EP0318478B1 EP0318478B1 EP87903794A EP87903794A EP0318478B1 EP 0318478 B1 EP0318478 B1 EP 0318478B1 EP 87903794 A EP87903794 A EP 87903794A EP 87903794 A EP87903794 A EP 87903794A EP 0318478 B1 EP0318478 B1 EP 0318478B1
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- EP
- European Patent Office
- Prior art keywords
- filter
- resonator
- dielectric
- resonators
- conductive material
- 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
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- 230000008878 coupling Effects 0.000 claims abstract description 42
- 238000010168 coupling process Methods 0.000 claims abstract description 42
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- 239000004020 conductor Substances 0.000 claims abstract description 24
- 239000003989 dielectric material Substances 0.000 claims description 20
- 239000000758 substrate Substances 0.000 abstract description 9
- 238000007747 plating Methods 0.000 description 25
- 230000005540 biological transmission Effects 0.000 description 21
- 238000001465 metallisation Methods 0.000 description 18
- 239000000919 ceramic Substances 0.000 description 10
- 239000003990 capacitor Substances 0.000 description 7
- 238000010586 diagram Methods 0.000 description 5
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 3
- MCMNRKCIXSYSNV-UHFFFAOYSA-N ZrO2 Inorganic materials O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 3
- QVQLCTNNEUAWMS-UHFFFAOYSA-N barium oxide Chemical compound [Ba]=O QVQLCTNNEUAWMS-UHFFFAOYSA-N 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 230000001939 inductive effect Effects 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910010293 ceramic material Inorganic materials 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000003780 insertion Methods 0.000 description 2
- 230000037431 insertion Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 239000011324 bead Substances 0.000 description 1
- 230000001413 cellular effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 238000009966 trimming Methods 0.000 description 1
Images
Classifications
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- 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
-
- 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
- H01P1/213—Frequency-selective devices, e.g. filters combining or separating two or more different frequencies
- H01P1/2136—Frequency-selective devices, e.g. filters combining or separating two or more different frequencies using comb or interdigital filters; using cascaded coaxial cavities
Definitions
- the present invention is related generally to radio frequency (RF) filters, and more particularly to a dielectric band pass filter having an improved capacitive inter-resonator coupling via metalization and an improved mounting apparatus, producing a filter that is particularly well adapted for use in mobile and portable radio transmitting and receiving devices.
- RF radio frequency
- Japanese patent application JP 60-254802 describes a distributed constant type filter having electrodes connected electrically to internal conductors of resonance units formed in an open end surface of a dielectric block, whereby the resonance units are coupled mutually through electrostatic capacity.
- a dielectric filter for passing a band of radio frequencies and rejecting other bands of frequencies, having a volume of dielectric material having first, second, and side surfaces, said second and side surfaces being substantially covered with a conductive material; a plurality of holes extending through said dielectric material from said first surface to said second surface, the surface of at least two of said holes being substantially covered with a conductive material which is electrically common at said second surface, thereby forming at least two resonators; characterised by: first electrode means disposed on said first surface, connected to said conductive material of said side surface, and extending partially between a first surface hole of a first resonator of said at least two resonators and a first surface hole of a second resonator of said at least two resonators, whereby coupling between said first resonator and said second resonator may be limited.
- the present invention advantageously provides a dielectric filter having an improved capacitive coupling. Furthermore, the present invention enables the dielectric filter to have its filter characteristics modified by changing metalization coupling resonators therein. In addition, the present invention allows the coupling of such filters in a configuration that enables their performance as a radio transceiver duplexer.
- a further benefit derived through the implementation of the invention is that the dielectric filter may be mounted and connected to a printed circuit board or other substrate element in a manner similar to other electrical components.
- Figure 1 is a perspective view of a conventional dielectric filter illustrating the orientation of the resonator elements and the input/output coupling.
- Figures 2, 3 and 4 are sectional views of Figure 1 illustrating metalization patterns which may be employed in the resonator holes.
- Figure 5 is a bottom perspective view of a dielectric block filter and mounting bracket employing the present invention.
- Figure 6 is a sectional view illustrating an input or output terminal employed in the present invention.
- Figure 7 is a dimensional diagram of the mounting bracket employed in the present invention.
- Figure 8 is a dimensional view of a printed circuit board mounted duplexer employing component-mountable filters.
- Figure 9 is a schematic diagram of a component-mountable filter.
- Figure 10 is a schematic diagram of the duplexer of Figure 8.
- Figure 11 is a schematic diagram of a printed circuit mounted duplexer employing component-mountable filters in a diversity receive antenna configuration.
- Figure 12A, 12B, 12C, 12D, and 12E illustrate metalization patterns which may be employed in the present invention.
- Filter 100 includes a block 105 which is comprised of a dielectric material that is selectively plated with a conductive material.
- Filter 100 is generally constructed of a suitable dielectric material such as a ceramic material which has low loss, a high dielectric constant, and a low temperature coefficient of the dielectric constant.
- filter 100 is comprised of a ceramic compound including barium oxide, titanium oxide and ziconium oxide, the electrical characteristics of which are similar to those described in more detail in an article by G.H. Jonker and W. Kwestroo, entitled “The Ternery Systems BaO-TiO2-ZrO2", Published in the Journal of the American Ceramic Society, Volume 41, no. 10 at pages 390-394, October, 1958.
- the compound in table VI having the composition 18.5 mole percent BaO, 77.0 mole percent TiO2 and 4.5 mole percent ZrO2 and having a dielectric constant of approximately 40 is well suited for use in the ceramic of the present invention.
- a dielectric filter such as that of block 105 of Filter 100 is generally covered or plated, with the exception of areas 107, with an electrically conductive material such as copper or silver.
- a filter such as block 105 includes a multitude of holes 109 which each extend from the top surface to the bottom surface thereof and are likewise plated with an electrically conductive material. The plating of the holes 109 is electrically common with the conductive plating covering the block 105 at one end of the holes 109 and isolated from the plating covering the block 105 at the opposite end of the holes 109. Further, the plating of holes 109 at the isolated end may extend onto the top surface of block 105.
- each of the plated holes 109 is essentially a foreshortened coaxial resonator comprised of a short coaxial transmission line having a length selected for desired filter response characteristics.
- the block 105 is shown in Fig. 1 with six plated holes, any number of plated holes may be utilized depending upon the filter response characteristics desired).
- Conductive plating 204 on dielectric material 202 extends through hole 201 to the top surface with the exception of a circular portion 240 around hole 201.
- Other conductive plating arrangements may also be utilized, two of which are illustrated in Figures 3 and 4.
- conductive plating 304 on dielectric material 302 extends through hole 301 to the bottom surface with the exception of portion 340.
- the plating arrangement in Fig. 3 is substantially identical to that in Fig. 2, the difference being that unplated portion 340 is on the bottom surface instead of on the top surface.
- conductive plating 404 on dielectric material 402 extends partially through hole 401 leaving part of hole 401 unplated.
- the plating arrangement in Fig. 4 can also be reversed as in Fig. 3 so that the unplated portion 440 is on the bottom surface.
- Coupling between the plated hole resonators is accomplished through the dielectric material and may be varied by varying the width of the dielectric material and the distance between adjacent coaxial resonators.
- the width of the dielectric material between adjacent holes 109 can be adjusted in any suitable regular or irregular manner, such as, for example, by the use of slots, cylindrical holes, square or rectangular holes, or irregularly shaped holes.
- RF signals are capacitively coupled to and from the dielectric filter 100 by means of input and output electrodes 111 and 113, respectively, which, in turn, are coupled to input and output connectors 101 and 103, respectively.
- the resonant frequency of the coaxial resonators provided by plated holes 109 is determined primarily by the depth of the hole, thickness of the dielectric block in the direction of the hole, and the amount of plating removed from the top of the filter near the hole.
- Tuning of filter 100 may be accomplished by the removal of additional ground plating or resonator plating extending upon the top surface of the block 105 near the top of each plated hole.
- the removal of plating for tuning the filter can easily be automated, and can be accomplished by means of a laser, sandblast trimmer, or other suitable trimming devices while monitoring the return loss angle of the filter.
- a dielectric filter employing the present invention is shown in a exploded perspective view.
- a block of dielectric material 501 is placed in a carrying bracket 503 which performs the multiple functions of providing a rigid mounting platform such that dielectric block 501 may be inserted into a printed circuit board or other substrate, providing simplified input and output connections via feed through terminals 505 and 507, and providing positive ground contact between the conductive outer surface of dielectric block 501 and bracket 503 via contacts 509, 510, 511, 512, and other contacts not shown.
- Contacts 509 and 510 additionally provide a dielectric block 501 locating function within the bracket 503.
- Mounting bracket 503 further provides mounting tabs 515-525 to locate and support the bracket and filter on a mounting substrate and provide positive ground contact for radio frequency signals from the mounting bracket 503 to the receiving mounting substrate.
- a mounting bracket for a dielectric filter has been disclosed in U.S. Patent Application No. 656,121, "Single-Block Dual-Passband Ceramic Filter", filed in behalf of Gayrusch on September 27, 1984 and assigned to the assignee of the present invention. This previously disclosed bracket, however, does not provide the simplified mounting of the bracket of the present invention.
- the dielectric filter 501 consists of a ceramic material and utilizes seven internally plated holes as foreshortened resonators to produce a band pass filter for operation in radio bands reserved for cellular mobile telephone.
- the conductive plating covering the ceramic block 501 extends conformally on all surfaces except that on which the resonator plating is wrapped from the holes onto the outer surface.
- holes 529-535 have corresponding plating 537-543 metallized on the outer surface of block 501. These areas 537-543 are electrically separate from the ground plating but provide capacitive coupling to the ground plating.
- an input plated area 547 and an output plated area 549 provide capacitive coupling between the input terminal 505 and the coaxial resonator formed from the internally plated hole 529 and its externally plated area 537 while plated area 549 provides capacitive coupling between the output terminal 507 and the output resonator formed from plated hole 535 and external plated area 543.
- Ground stripes 553-558 are plated between the coaxial resonator plated holes in order that inter-resonator coupling is adjusted.
- Ceramic block 501 is inserted into bracket 503 with the externally plated resonator areas 537-543 oriented downward into the bracket 503 such that additional shielding is afforded by the bracket 503.
- Input mounting pin 505 is connected to plated area 547 and output terminal 507 is connected to plated area 549 as shown in Fig. 6.
- the center conductor 605 is brought into contact with plated area 547 by the dimensions of the bracket 503 and the block 501.
- the center conductor 605 is soldered or otherwise conductively bonded at one end to area 547 to provide a reliable RF connection to plated area 547.
- the other end of the center conductor 605 may then be easily soldered or plugged into a substrate which holds the mounting bracket 503.
- a similar construction is employed for output terminal 507 and its associated plated area 549.
- a detail of the mounting bracket 503 is shown in Fig. 7.
- the spacing of the mounting tabs 515-525 is shown in detail for the preferred embodiment. These spacings are important at the frequencies of operation of this filter in order to maintain maximum ultimate attenuation.
- Low ground path inductance in the mounting bracket is realized by placing mounting tabs 517 and 519 close to the input and output ports (505 and 507 of Fig. 5 respectively) and the remainder of the tabs above the side and bottom of the bracket 503.
- Connection between the dielectric block 501 and bracket 503 is assured near the input and output terminals by contacts similar to contacts 511 and 512 located close to the terminals. All contacts, 509, 510, 511, and 512 (and the equivalent contacts on the opposite side of the brackets not shown), may be soldered or otherwise bonded to the dielectric block 501 such that electrical connection may be permanently assured.
- the position of the tabs 518, 520, and 521 are asymmetrical.
- the input/output terminals 505 and 507 are offset from the centerline of the bracket 503. This asymmetry enables a "keying" of the bracket 503 so that a filter can be inserted in a printed circuit board or other substrate in only one orientation.
- a dielectric filter block such as block 501 is mounted in bracket 503 and becomes a unitized circuit component which may be inserted into a printed circuit board or substrate 801.
- Appropriate holes 803 and 805 are located on the printed circuit board 801 to accept the input and output terminals 505 and 507 (not shown in Fig.8), respectively.
- appropriately located slots 815-825 are located in the printed circuit board 801 to accept the corresponding tabs of the bracket 503.
- the filter 501 and bracket 503 may be mounted on a circuit board 801 like any other component and circuit runners may extend from the input hole 803 and the output hole 805 such that the filter may be electrically connected to other circuitry with a minimum of effort.
- the circuit board runners, 807 and 809 may be constructed as stripline or microstrip transmission lines to yield improved duplexer performance.
- FIG. 9 there is illustrated an equivalent circuit diagram for the dielectric filter 501 utilized as a band pass filter.
- An input signal from a signal source may be applied via terminal 505 to input electrode 547 in Fig. 5, which corresponds to the common junction of capacitors 924 and 944 in Fig. 9.
- Capacitor 944 is the capacitance between electrode 547 and the surrounding ground plating
- capacitor 924 is the capacitance between electrode 547 and the coaxial resonator provided by plated hole 529 in Fig. 5.
- the coaxial resonators provided by plated 529-535 in Fig. 5 correspond to shorted transmission lines 929-935 in Fig. 9.
- Capacitor 925 represents the capacitance between the resonator provided by plated hole 535 and electrode 549 in Fig. 5
- capacitor 945 represents the capacitance between electrode 549 and the surrounding ground plating.
- An output signal is provided at the junction of capacitors 925 and 945, and coupled to output terminal 547 for utilization by external circuitry.
- a multi-band filter comprised of two intercoupled dielectric band pass filters 1004 and 1012 and employing the present invention.
- Two or more of the inventive band pass filters may be intercoupled on a printed circuit board or substrate to provide apparatus that combines and/or frequency sorts two RF signals into and/or from a composite RF signal.
- the present invention is employed in the arrangement of Fig. 10 which couples a transmit signal from an RF transmitter 1002 to an antenna 1008 and a receive signal from antenna 1008 to an RF receiver 1014.
- the arrangement in Fig. 10 can be advantageously utilized in mobile, portable, and fixed station radios as an antenna duplexer.
- the transmit signal from RF transmitter 1002 is coupled to filter 1004 by a transmission line 1005, realized by the plated runner 807 of Fig. 8 on the printed circuit board in the preferred embodiment, and the filtered transmit signal is coupled via circuit board runner transmission line 1006 (runner 809 of Fig. 8) to antenna 1008.
- Filter 1004 is a ceramic band pass filter of the present invention, such as the filter illustrated in Figs. 5 and 8.
- the pass band of filter 1004 is centered about the frequency of the transmit signal from RF transmitter 1002, while at the same time greatly attenuating the frequency of the received signal.
- the length of transmission line 1006 is selected to maximize its impedance at the frequency of the received signal.
- a received signal from antenna 1008 in Fig. 10 is coupled by transmission line 1010, also realized as a printed circuit board runner, to filter 1012 and thence via circuit board runner transmission line 1013 to RF receiver 1014.
- Filter 1012 which also may be one of the inventive band pass filters illustrated in Figs. 5 and 8, has a pass band centered about the frequency of the receive signal, while at the same time greatly attenuating the transmit signal.
- the length of transmission line 1010 is selected to maximize its impedance at the transmit signal frequency for further attenuating the transmit signal.
- the dielectric band pass filters 1004 and 1012 utilize a dielectric of ceramic and are constructed in accordance with the present invention as shown in Fig. 5.
- the filters 1004 and 1012 each have a length of 7.6 cm and a width of 1.14 cm.
- the height is a primary determinant of the frequency of operation and, in the preferred embodiment, is 1.24 cm in the transmit filter 1004 and 1.12 cm in the receive filter 1012.
- Filter 1004 has an insertion loss of 2.5 dB and attenuate receive signals by at least 50 dB.
- Filter 1012 has an insertion loss of 3.0 dB and attenuates receive signals by at least 60 dB.
- An alternative interconnection of the circuit board monostable dielectric block filters is shown in Fig. 11.
- the antenna receiving the best signal may be switchably coupled to the receiver and provide the well-known antenna diversity function.
- the separate transmit and receive filters 1004 and 1012 may be coupled by 180° reflection coefficient transmission lines 1107 and 1109 in a fashion to provide a diversity receive function.
- the filter operational characteristics may be determined by the metallization pattern employed on the surface of the dielectric block which is not fully metallized.
- Dielectric filters such as described herein are instrinsically coupled by inductance. That is, the magnetic fields in the dielectric material govern the coupling.
- the inductance may be changed, and even overcome, by introducing capacitive between the resonators. Referring again to Fig. 5, it can be seen that a seven pole configuration is realized by serially coupling the resonators created by the metallized holes 529-535 and surface plating 539-543. As shown, the capacitive coupling between the resonators is restricted by the grounded strip electrodes 554-557.
- a controlled capacitive coupling may be achieved by providing incomplete strip electrodes running on the surface of the dielectric block between two resonators.
- incomplete strip electrodes 553 and 558 between input resonator and output resonator and the other resonators, provide a controlled capacitive coupling to enable combined inductive and capacitive coupling between adjacent resonators.
- the use of inductive or capacitive coupling provides steeper filter attenuation skirts on either the high side of the filter passband or the low side of the filter passband, respectively.
- the dielectric filter blocks are combined as a duplexer filter as shown diagrammatically in Fig. 10, it is advantageous to employ a filter having a step attenuation skirt above the passband as the filter passing the lower frequencies. Also it is advantageous to employ a filter having a steep attenuation skirt below the passband as the filter passing the higher frequencies. In this way, additional protection of transmit and receive paths from each other can be realized without additional filter resonator elements.
- An advantage of the dielectric filter blocks of the present invention is that the number and spacing of resonators used in the transmitter filter 1004 (of Fig. 10) may be equal to the number and spacing of the resonators in the receive filter 1012.
- the type of coupling is determined by the metalization pattern employed.
- the transmit filter 1004 utilizes inductive coupling between resonators as illustrated in the metalization pattern of Fig. 12A.
- the capacitive coupling between the middle resonators is reduced by the complete strip electrodes while the input and output resonators utilize more capacitance in the incomplete strip electrodes in their coupling to the middle resonators.
- the receive filter 1012 utilizes capacitive coupling between resonators as illustrated in the metalization pattern of Fig. 12B. Capacitive coupling is enabled by the unblocked metalized resonators. (Capacitive coupling may be enhanced by metalization islands such as shown in Fig. 12C).
- a novel feature of the present invention creates the ability of the coupling to be changed by changing the metalization. Additionally, the mode of resonator operation may be changed from band pass to band stop by utilizing one or more resonators as a transmission zero rather than as a transmission pole. Transmission zero realization by metalization change only is shown in Fig. 12D.
- the output electrode 1203 is coupled to the first transmission pole resonator 1205 by metalization runner 1207. Coupling is also realized from output electrode 1203 to transmission zero resonator 1209. In the embodiment shown, the transmission zero is tuned to the low side of the passband to realize additional rejection on the low side of the passband.
- a filter utilizing metalization such as that shown in Fig. 12D would be suitable for use in a duplexer such as described above.
- Additional zeros may be created by proper coupling to other resonators. Such coupling is shown in the metalization of Fig. 12E.
- a printed circuit board mountable, multiple resonator dielectric filter has been shown and described.
- This filter utilizes metalized hole resonators having coupling characteristics determined by the metalization pattern on one surface of the dielectric block.
- the dielectric block is metalized with a conductive material on all but one surface from which the hole resonators extend into the dielectric block. Electrode metalization around the holes provides capacitive coupling to this conductive material and from one resonator to an adjacent resonator. Capacitive coupling between the resonators is controlled by an electrode at least partially between two adjacent hole resonators to adjust the capacitive coupling between the resonators. Input and output coupling is accomplished via terminals asymmetrically arranged in a mounting bracket.
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Abstract
Description
- The present invention is related generally to radio frequency (RF) filters, and more particularly to a dielectric band pass filter having an improved capacitive inter-resonator coupling via metalization and an improved mounting apparatus, producing a filter that is particularly well adapted for use in mobile and portable radio transmitting and receiving devices.
- Conventional dielectric filters such as those shown in UK Patent Application GB 2163066A or in UK Patent Application GB 2165098A offer advantages in physical and electrical performance which make them ideally suited for use in mobile and portable radio transceivers. Connecting the filter input and output terminals to utilization means external to the filter, however, has been a problem. Typically, coaxial or other forms of transmission line are manually soldered to the input and output terminations and then each manually connected to the utilization means. When such filters are used as antenna combining duplexers for a transceiver, two dielectric blocks are used and the number of connections doubles. Additionally, the critical nature of the connecting transmission line length becomes subject to human error.
- Japanese patent application JP 60-254802 describes a distributed constant type filter having electrodes connected electrically to internal conductors of resonance units formed in an open end surface of a dielectric block, whereby the resonance units are coupled mutually through electrostatic capacity.
- In accordance with the present invention, there is provided a dielectric filter for passing a band of radio frequencies and rejecting other bands of frequencies, having a volume of dielectric material having first, second, and side surfaces, said second and side surfaces being substantially covered with a conductive material; a plurality of holes extending through said dielectric material from said first surface to said second surface, the surface of at least two of said holes being substantially covered with a conductive material which is electrically common at said second surface, thereby forming at least two resonators; characterised by: first electrode means disposed on said first surface, connected to said conductive material of said side surface, and extending partially between a first surface hole of a first resonator of said at least two resonators and a first surface hole of a second resonator of said at least two resonators, whereby coupling between said first resonator and said second resonator may be limited.
- Therefore, the present invention advantageously provides a dielectric filter having an improved capacitive coupling. Furthermore, the present invention enables the dielectric filter to have its filter characteristics modified by changing metalization coupling resonators therein. In addition, the present invention allows the coupling of such filters in a configuration that enables their performance as a radio transceiver duplexer. A further benefit derived through the implementation of the invention is that the dielectric filter may be mounted and connected to a printed circuit board or other substrate element in a manner similar to other electrical components.
- An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings.
- Figure 1 is a perspective view of a conventional dielectric filter illustrating the orientation of the resonator elements and the input/output coupling.
- Figures 2, 3 and 4 are sectional views of Figure 1 illustrating metalization patterns which may be employed in the resonator holes.
- Figure 5 is a bottom perspective view of a dielectric block filter and mounting bracket employing the present invention.
- Figure 6 is a sectional view illustrating an input or output terminal employed in the present invention.
- Figure 7 is a dimensional diagram of the mounting bracket employed in the present invention.
- Figure 8 is a dimensional view of a printed circuit board mounted duplexer employing component-mountable filters.
- Figure 9 is a schematic diagram of a component-mountable filter.
- Figure 10 is a schematic diagram of the duplexer of Figure 8.
- Figure 11 is a schematic diagram of a printed circuit mounted duplexer employing component-mountable filters in a diversity receive antenna configuration.
- Figure 12A, 12B, 12C, 12D, and 12E illustrate metalization patterns which may be employed in the present invention.
- In Figure 1, there is illustrated a dielectrically loaded
band pass filter 100 employing aconventional input connector 101 and aconventional output connector 103. Such a filter is more fully described in U.S. Patent No. 4,431,977 "Ceramic Band Pass Filter" and assigned to the assignee of the present invention and incorporated by reference herein.Filter 100 includes ablock 105 which is comprised of a dielectric material that is selectively plated with a conductive material.Filter 100 is generally constructed of a suitable dielectric material such as a ceramic material which has low loss, a high dielectric constant, and a low temperature coefficient of the dielectric constant. In the preferred embodiment,filter 100 is comprised of a ceramic compound including barium oxide, titanium oxide and ziconium oxide, the electrical characteristics of which are similar to those described in more detail in an article by G.H. Jonker and W. Kwestroo, entitled "The Ternery Systems BaO-TiO₂-ZrO₂", Published in the Journal of the American Ceramic Society, Volume 41, no. 10 at pages 390-394, October, 1958. Of the ceramic compounds described in this article, the compound in table VI having the composition 18.5 mole percent BaO, 77.0 mole percent TiO₂ and 4.5 mole percent ZrO₂ and having a dielectric constant of approximately 40 is well suited for use in the ceramic of the present invention. - A dielectric filter such as that of
block 105 ofFilter 100 is generally covered or plated, with the exception ofareas 107, with an electrically conductive material such as copper or silver. A filter such asblock 105 includes a multitude ofholes 109 which each extend from the top surface to the bottom surface thereof and are likewise plated with an electrically conductive material. The plating of theholes 109 is electrically common with the conductive plating covering theblock 105 at one end of theholes 109 and isolated from the plating covering theblock 105 at the opposite end of theholes 109. Further, the plating ofholes 109 at the isolated end may extend onto the top surface ofblock 105. Thus, each of the platedholes 109 is essentially a foreshortened coaxial resonator comprised of a short coaxial transmission line having a length selected for desired filter response characteristics. (Although theblock 105 is shown in Fig. 1 with six plated holes, any number of plated holes may be utilized depending upon the filter response characteristics desired). - The plating of
holes 109 in thefilter block 105 is illustrated more clearly by the cross-section through anyhole 109.Conductive plating 204 ondielectric material 202 extends throughhole 201 to the top surface with the exception of acircular portion 240 aroundhole 201. Other conductive plating arrangements may also be utilized, two of which are illustrated in Figures 3 and 4. In Fig. 3,conductive plating 304 ondielectric material 302 extends throughhole 301 to the bottom surface with the exception ofportion 340. The plating arrangement in Fig. 3 is substantially identical to that in Fig. 2, the difference being thatunplated portion 340 is on the bottom surface instead of on the top surface. in Fig. 4,conductive plating 404 ondielectric material 402 extends partially throughhole 401 leaving part ofhole 401 unplated. The plating arrangement in Fig. 4 can also be reversed as in Fig. 3 so that theunplated portion 440 is on the bottom surface. - Coupling between the plated hole resonators is accomplished through the dielectric material and may be varied by varying the width of the dielectric material and the distance between adjacent coaxial resonators. The width of the dielectric material between
adjacent holes 109 can be adjusted in any suitable regular or irregular manner, such as, for example, by the use of slots, cylindrical holes, square or rectangular holes, or irregularly shaped holes. - As shown in Fig. 1, RF signals are capacitively coupled to and from the
dielectric filter 100 by means of input andoutput electrodes 111 and 113, respectively, which, in turn, are coupled to input andoutput connectors - The resonant frequency of the coaxial resonators provided by
plated holes 109 is determined primarily by the depth of the hole, thickness of the dielectric block in the direction of the hole, and the amount of plating removed from the top of the filter near the hole. Tuning offilter 100 may be accomplished by the removal of additional ground plating or resonator plating extending upon the top surface of theblock 105 near the top of each plated hole. The removal of plating for tuning the filter can easily be automated, and can be accomplished by means of a laser, sandblast trimmer, or other suitable trimming devices while monitoring the return loss angle of the filter. - Referring now to Fig. 5, a dielectric filter employing the present invention is shown in a exploded perspective view. A block of
dielectric material 501 is placed in acarrying bracket 503 which performs the multiple functions of providing a rigid mounting platform such thatdielectric block 501 may be inserted into a printed circuit board or other substrate, providing simplified input and output connections via feed throughterminals dielectric block 501 andbracket 503 viacontacts Contacts dielectric block 501 locating function within thebracket 503.Mounting bracket 503 further provides mounting tabs 515-525 to locate and support the bracket and filter on a mounting substrate and provide positive ground contact for radio frequency signals from themounting bracket 503 to the receiving mounting substrate. A mounting bracket for a dielectric filter has been disclosed in U.S. Patent Application No. 656,121, "Single-Block Dual-Passband Ceramic Filter", filed in behalf of Kommrusch on September 27, 1984 and assigned to the assignee of the present invention. This previously disclosed bracket, however, does not provide the simplified mounting of the bracket of the present invention. - In one preferred embodiment the
dielectric filter 501 consists of a ceramic material and utilizes seven internally plated holes as foreshortened resonators to produce a band pass filter for operation in radio bands reserved for cellular mobile telephone. In this embodiment the conductive plating covering theceramic block 501 extends conformally on all surfaces except that on which the resonator plating is wrapped from the holes onto the outer surface. Thus, holes 529-535 have corresponding plating 537-543 metallized on the outer surface ofblock 501. These areas 537-543 are electrically separate from the ground plating but provide capacitive coupling to the ground plating. Additionally, an input platedarea 547 and an output platedarea 549 provide capacitive coupling between theinput terminal 505 and the coaxial resonator formed from the internally platedhole 529 and its externally platedarea 537 while platedarea 549 provides capacitive coupling between theoutput terminal 507 and the output resonator formed from platedhole 535 and external platedarea 543. Ground stripes 553-558 are plated between the coaxial resonator plated holes in order that inter-resonator coupling is adjusted. -
Ceramic block 501 is inserted intobracket 503 with the externally plated resonator areas 537-543 oriented downward into thebracket 503 such that additional shielding is afforded by thebracket 503. Input mountingpin 505 is connected to platedarea 547 andoutput terminal 507 is connected to platedarea 549 as shown in Fig. 6.Input terminal 505, which may be a low shunt capacity feed through such as a 100B0047 terminal manufactured by Airpax Electronics Inc., consists of asolderable eyelet 601 and insulatingglass bead 603 supporting acenter conductor 605. Theeyelet 601 is conductively bonded tobracket 503 to provide a secure mounting for theinput connector 505. Thecenter conductor 605 is brought into contact with platedarea 547 by the dimensions of thebracket 503 and theblock 501. Thecenter conductor 605 is soldered or otherwise conductively bonded at one end toarea 547 to provide a reliable RF connection to platedarea 547. The other end of thecenter conductor 605 may then be easily soldered or plugged into a substrate which holds the mountingbracket 503. A similar construction is employed foroutput terminal 507 and its associated platedarea 549. - A detail of the mounting
bracket 503 is shown in Fig. 7. The spacing of the mounting tabs 515-525 is shown in detail for the preferred embodiment. These spacings are important at the frequencies of operation of this filter in order to maintain maximum ultimate attenuation. Low ground path inductance in the mounting bracket is realized by placing mountingtabs bracket 503. Connection between thedielectric block 501 andbracket 503 is assured near the input and output terminals by contacts similar tocontacts dielectric block 501 such that electrical connection may be permanently assured. - It can be readily ascertained that the position of the
tabs output terminals bracket 503. This asymmetry enables a "keying" of thebracket 503 so that a filter can be inserted in a printed circuit board or other substrate in only one orientation. - One unique aspect of the present invention is shown in Fig. 8. A dielectric filter block such as
block 501 is mounted inbracket 503 and becomes a unitized circuit component which may be inserted into a printed circuit board orsubstrate 801.Appropriate holes circuit board 801 to accept the input andoutput terminals 505 and 507 (not shown in Fig.8), respectively. Further, appropriately located slots 815-825 are located in the printedcircuit board 801 to accept the corresponding tabs of thebracket 503. Thus thefilter 501 andbracket 503 may be mounted on acircuit board 801 like any other component and circuit runners may extend from theinput hole 803 and theoutput hole 805 such that the filter may be electrically connected to other circuitry with a minimum of effort. The circuit board runners, 807 and 809, may be constructed as stripline or microstrip transmission lines to yield improved duplexer performance. - Referring to Fig. 9, there is illustrated an equivalent circuit diagram for the
dielectric filter 501 utilized as a band pass filter. An input signal from a signal source may be applied viaterminal 505 to inputelectrode 547 in Fig. 5, which corresponds to the common junction ofcapacitors Capacitor 944 is the capacitance betweenelectrode 547 and the surrounding ground plating, andcapacitor 924 is the capacitance betweenelectrode 547 and the coaxial resonator provided by platedhole 529 in Fig. 5. The coaxial resonators provided by plated 529-535 in Fig. 5 correspond to shorted transmission lines 929-935 in Fig. 9. Capacitors 937-943 in Fig. 9 represent the capacitance between the coaxial resonators provided by the extended plating 537-543 of the plated holes in Fig. 5 and the surrounding ground plating on the top surface.Capacitor 925 represents the capacitance between the resonator provided by platedhole 535 andelectrode 549 in Fig. 5, andcapacitor 945 represents the capacitance betweenelectrode 549 and the surrounding ground plating. An output signal is provided at the junction ofcapacitors output terminal 547 for utilization by external circuitry. - Referring now to Fig. 10, there is illustrated a multi-band filter comprised of two intercoupled dielectric
band pass filters RF transmitter 1002 to anantenna 1008 and a receive signal fromantenna 1008 to anRF receiver 1014. The arrangement in Fig. 10 can be advantageously utilized in mobile, portable, and fixed station radios as an antenna duplexer. The transmit signal fromRF transmitter 1002 is coupled to filter 1004 by atransmission line 1005, realized by the platedrunner 807 of Fig. 8 on the printed circuit board in the preferred embodiment, and the filtered transmit signal is coupled via circuit board runner transmission line 1006 (runner 809 of Fig. 8) toantenna 1008.Filter 1004 is a ceramic band pass filter of the present invention, such as the filter illustrated in Figs. 5 and 8. The pass band offilter 1004 is centered about the frequency of the transmit signal fromRF transmitter 1002, while at the same time greatly attenuating the frequency of the received signal. In addition, the length oftransmission line 1006 is selected to maximize its impedance at the frequency of the received signal. - A received signal from
antenna 1008 in Fig. 10 is coupled bytransmission line 1010, also realized as a printed circuit board runner, to filter 1012 and thence via circuit boardrunner transmission line 1013 toRF receiver 1014.Filter 1012, which also may be one of the inventive band pass filters illustrated in Figs. 5 and 8, has a pass band centered about the frequency of the receive signal, while at the same time greatly attenuating the transmit signal. Similarly, the length oftransmission line 1010 is selected to maximize its impedance at the transmit signal frequency for further attenuating the transmit signal. - In the embodiment of the RF signal duplexing apparatus of Fig 10, transmit signals having a frequency range from 825 MHz to 851 MHz and receive signals having a frequency range from 870MHz to 896MHz are coupled to the antenna of a mobile radio. The dielectric
band pass filters filters filter 1004 and 1.12 cm in the receivefilter 1012.Filter 1004 has an insertion loss of 2.5 dB and attenuate receive signals by at least 50 dB.Filter 1012 has an insertion loss of 3.0 dB and attenuates receive signals by at least 60 dB. An alternative interconnection of the circuit board monostable dielectric block filters is shown in Fig. 11. - It is sometimes desirable to utilize two switchable antennas for a receiver so that the antenna receiving the best signal may be switchably coupled to the receiver and provide the well-known antenna diversity function. By not providing a transmission line coupling directly between
transmission lines 1006 and 1010 (at point A) but by inserting anantenna switch 1101 selecting a shared transmit/receiveantenna 1103 and a receiveonly antenna 1105 between the antennas, the separate transmit and receivefilters coefficient transmission lines - The filter operational characteristics may be determined by the metallization pattern employed on the surface of the dielectric block which is not fully metallized. Dielectric filters such as described herein are instrinsically coupled by inductance. That is, the magnetic fields in the dielectric material govern the coupling. The inductance may be changed, and even overcome, by introducing capacitive between the resonators. Referring again to Fig. 5, it can be seen that a seven pole configuration is realized by serially coupling the resonators created by the metallized holes 529-535 and surface plating 539-543. As shown, the capacitive coupling between the resonators is restricted by the grounded strip electrodes 554-557. Capacitive coupling by metalization gaps or additional metalization islands has been shown in the aforementioned U.S. Patent Application No. 656,121 by Kommrusch filed September 27, 1984. According to one novel aspect of the present invention, a controlled capacitive coupling may be achieved by providing incomplete strip electrodes running on the surface of the dielectric block between two resonators. In the preferred embodiment,
incomplete strip electrodes - When the dielectric filter blocks are combined as a duplexer filter as shown diagrammatically in Fig. 10, it is advantageous to employ a filter having a step attenuation skirt above the passband as the filter passing the lower frequencies. Also it is advantageous to employ a filter having a steep attenuation skirt below the passband as the filter passing the higher frequencies. In this way, additional protection of transmit and receive paths from each other can be realized without additional filter resonator elements.
- An advantage of the dielectric filter blocks of the present invention is that the number and spacing of resonators used in the transmitter filter 1004 (of Fig. 10) may be equal to the number and spacing of the resonators in the receive
filter 1012. The type of coupling is determined by the metalization pattern employed. The transmitfilter 1004 utilizes inductive coupling between resonators as illustrated in the metalization pattern of Fig. 12A. The capacitive coupling between the middle resonators is reduced by the complete strip electrodes while the input and output resonators utilize more capacitance in the incomplete strip electrodes in their coupling to the middle resonators. The receivefilter 1012 utilizes capacitive coupling between resonators as illustrated in the metalization pattern of Fig. 12B. Capacitive coupling is enabled by the unblocked metalized resonators. (Capacitive coupling may be enhanced by metalization islands such as shown in Fig. 12C). - A novel feature of the present invention creates the ability of the coupling to be changed by changing the metalization. Additionally, the mode of resonator operation may be changed from band pass to band stop by utilizing one or more resonators as a transmission zero rather than as a transmission pole. Transmission zero realization by metalization change only is shown in Fig. 12D. The
output electrode 1203 is coupled to the firsttransmission pole resonator 1205 bymetalization runner 1207. Coupling is also realized fromoutput electrode 1203 to transmission zeroresonator 1209. In the embodiment shown, the transmission zero is tuned to the low side of the passband to realize additional rejection on the low side of the passband. A filter utilizing metalization such as that shown in Fig. 12D would be suitable for use in a duplexer such as described above. - Additional zeros may be created by proper coupling to other resonators. Such coupling is shown in the metalization of Fig. 12E.
- In summary, then, a printed circuit board mountable, multiple resonator dielectric filter has been shown and described. This filter utilizes metalized hole resonators having coupling characteristics determined by the metalization pattern on one surface of the dielectric block. The dielectric block is metalized with a conductive material on all but one surface from which the hole resonators extend into the dielectric block. Electrode metalization around the holes provides capacitive coupling to this conductive material and from one resonator to an adjacent resonator. Capacitive coupling between the resonators is controlled by an electrode at least partially between two adjacent hole resonators to adjust the capacitive coupling between the resonators. Input and output coupling is accomplished via terminals asymmetrically arranged in a mounting bracket. Mounting tabs on the bracket opposite a recessed area holding the dielectric block secure the filter to the circuit board and provide ground connection for the filter. Use of two filters on a printed circuit board with copper runners forming transmission lines of appropriate electrical length creates a duplexer for transceiver applications.
Claims (7)
- A dielectric filter for passing a band of radio frequencies and rejecting other bands of frequencies, having a volume of dielectric material (501) having first, second, and side surfaces, said second and side surfaces being substantially covered with a conductive material; a plurality of holes (529-535) extending through said dielectric material (501) from said first surface to said second surface, the surface of at least two of said holes being substantially covered with a conductive material which is electrically common at said second surface, thereby forming at least two resonators; characterized by:
first electrode means (553) disposed on said first surface, connected to said conductive material of said side surface, and extending partially between a first surface hole of a first resonator (529) of said at least two resonators and a first surface hole of a second resonator (530) of said at least two resonators, whereby coupling between said first resonator (529) and said second resonator (530) may be limited. - A dielectric filter in accordance with claim 1, wherein said first electrode means (553) further comprises two strips of conductive material disposed essentially perpendicular to a line drawn between said first surface hole of said first resonator (529) and said first surface hole of said second resonator (530), said two conductive strips having a first end and a second end, a gap between said first end of each said conductive strip, and said second end of each said conductive strip connected to said conductive material of said side surface.
- A dielectric filter in accordance with claim 1 or 2, comprising first and second capacitive means (937, 938) each including a second electrode means (537,538) coupled to and essentially surrounding said first surface holes of said first and second of said at least two resonators (529, 530) for capacitively coupling said first resonator (529) to said second resonator (530) and capacitively coupling said first and second resonators (529, 530) to the conductive material on the side surfaces of said volume of dielectric material.
- A dielectric filter in accordance with claim 1, 2 or 3, further comprising a third electrode (547) disposed on said first surface of said volume of dielectric material near, and coupled to, said first resonator (529) and wherein said third electrode includes a conductive material portion of said first surface of said volume of dielectric material.
- A dielectric filter in accordance with any preceding claim, further comprising a third resonator (535) formed from a third hole of said plurality of holes, the surface of said third hole being substantially covered with a conductive material which is electrically common at said second surface.
- A dielectric filter in accordance with claim 5, further comprising a third capacitive means including a second electrode means (543) coupled to and essentially surrounding said first surface hole of said third resonator (535) for capacitively coupling said third resonator (535) to the conductive material on the side surfaces of said volume of dielectric material.
- A dielectric filter in accordance with claim 6, further comprising a fourth electrode (549) disposed on said first surface of said volume of dielectric material near, and coupled to, said third resonator and wherein said fourth electrode (549) includes a conductive material portion of said first surface of said volume of dielectric material.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/890,686 US4692726A (en) | 1986-07-25 | 1986-07-25 | Multiple resonator dielectric filter |
US06/890,682 US4716391A (en) | 1986-07-25 | 1986-07-25 | Multiple resonator component-mountable filter |
US890682 | 1986-07-25 | ||
US890686 | 1986-07-25 | ||
PCT/US1987/001210 WO1988001104A1 (en) | 1986-07-25 | 1987-05-27 | Multiple resonator component-mountable filter |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0318478A1 EP0318478A1 (en) | 1989-06-07 |
EP0318478A4 EP0318478A4 (en) | 1989-11-20 |
EP0318478B1 true EP0318478B1 (en) | 1995-02-15 |
Family
ID=27128957
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP87903794A Expired - Lifetime EP0318478B1 (en) | 1986-07-25 | 1987-05-27 | Multiple resonator component-mountable filter |
Country Status (10)
Country | Link |
---|---|
EP (1) | EP0318478B1 (en) |
JP (1) | JP2764903B2 (en) |
CN (1) | CN1011102B (en) |
AT (1) | ATE118653T1 (en) |
CA (1) | CA1277729C (en) |
DE (1) | DE3751062T2 (en) |
DK (1) | DK64488A (en) |
FI (1) | FI890243A (en) |
NO (1) | NO173413C (en) |
WO (1) | WO1988001104A1 (en) |
Families Citing this family (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DK87157C (en) * | 1955-11-16 | 1959-04-13 | Kristian Jacobsen | Hinge. |
FR2610662B1 (en) * | 1986-12-27 | 1990-07-06 | Scharwaechter Gmbh Co Kg | REMOVABLE DOOR HINGE |
US5103197A (en) * | 1989-06-09 | 1992-04-07 | Lk-Products Oy | Ceramic band-pass filter |
JPH0338101A (en) * | 1989-07-04 | 1991-02-19 | Murata Mfg Co Ltd | High frequency coaxial resonator |
GB2236432B (en) * | 1989-09-30 | 1994-06-29 | Kyocera Corp | Dielectric filter |
US5045824A (en) * | 1990-09-04 | 1991-09-03 | Motorola, Inc. | Dielectric filter construction |
GB2263363B (en) * | 1992-01-07 | 1996-05-08 | Marconi Gec Ltd | Electrical filter |
US5405107A (en) * | 1992-09-10 | 1995-04-11 | Bruno; Joseph W. | Radar transmitting structures |
JPH0670301U (en) * | 1993-03-15 | 1994-09-30 | 日本電業工作株式会社 | Bandpass filter |
JP3158963B2 (en) * | 1995-05-31 | 2001-04-23 | 株式会社村田製作所 | Antenna duplexer |
US6472952B1 (en) | 1998-11-10 | 2002-10-29 | Matsushita Electric Industrial Co., Ltd. | Antenna duplexer circuit with a phase shifter on the receive side |
JP5906886B2 (en) * | 2012-03-29 | 2016-04-20 | 宇部興産株式会社 | Dielectric resonant component |
DE102014007927A1 (en) * | 2014-05-27 | 2015-12-03 | Kathrein-Werke Kg | High frequency-tight housing, in particular high-frequency-proof filter housing |
JP6942271B2 (en) * | 2018-01-31 | 2021-09-29 | ケーエムダブリュ・インコーポレーテッド | Cavity filter |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4431977A (en) * | 1982-02-16 | 1984-02-14 | Motorola, Inc. | Ceramic bandpass filter |
JPS59114902A (en) * | 1982-12-21 | 1984-07-03 | Fujitsu Ltd | Dielectric filter |
JPS60114004A (en) * | 1983-11-25 | 1985-06-20 | Murata Mfg Co Ltd | Dielectric coaxial resonator |
JPS60152102A (en) * | 1984-01-19 | 1985-08-10 | Murata Mfg Co Ltd | Distributed constant type filter |
JPS60254802A (en) * | 1984-05-30 | 1985-12-16 | Murata Mfg Co Ltd | Distributed constant type filter |
JPS6152003A (en) * | 1984-08-21 | 1986-03-14 | Murata Mfg Co Ltd | Dielectric filter |
GB2165098B (en) * | 1984-09-27 | 1988-05-25 | Motorola Inc | Radio frequency filters |
JPH0624282B2 (en) * | 1986-07-16 | 1994-03-30 | 株式会社村田製作所 | Filter device |
-
1987
- 1987-05-27 JP JP62503469A patent/JP2764903B2/en not_active Expired - Lifetime
- 1987-05-27 EP EP87903794A patent/EP0318478B1/en not_active Expired - Lifetime
- 1987-05-27 AT AT87903794T patent/ATE118653T1/en not_active IP Right Cessation
- 1987-05-27 WO PCT/US1987/001210 patent/WO1988001104A1/en active IP Right Grant
- 1987-05-27 DE DE3751062T patent/DE3751062T2/en not_active Expired - Lifetime
- 1987-06-05 CA CA000538924A patent/CA1277729C/en not_active Expired - Lifetime
- 1987-07-24 CN CN87105317A patent/CN1011102B/en not_active Expired
-
1988
- 1988-02-09 DK DK064488A patent/DK64488A/en unknown
- 1988-03-23 NO NO881269A patent/NO173413C/en unknown
-
1989
- 1989-01-17 FI FI890243A patent/FI890243A/en not_active IP Right Cessation
Also Published As
Publication number | Publication date |
---|---|
JPH01503428A (en) | 1989-11-16 |
JP2764903B2 (en) | 1998-06-11 |
WO1988001104A1 (en) | 1988-02-11 |
NO173413C (en) | 1993-12-08 |
EP0318478A1 (en) | 1989-06-07 |
CA1277729C (en) | 1990-12-11 |
DE3751062T2 (en) | 1996-01-18 |
DE3751062D1 (en) | 1995-03-23 |
CN87105317A (en) | 1988-04-27 |
FI890243A0 (en) | 1989-01-17 |
ATE118653T1 (en) | 1995-03-15 |
DK64488D0 (en) | 1988-02-09 |
DK64488A (en) | 1988-02-11 |
NO173413B (en) | 1993-08-30 |
EP0318478A4 (en) | 1989-11-20 |
NO881269D0 (en) | 1988-03-23 |
NO881269L (en) | 1988-03-23 |
CN1011102B (en) | 1991-01-02 |
FI890243A (en) | 1989-01-17 |
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