EP1265314A1 - Dielektrischer Resonator - Google Patents

Dielektrischer Resonator Download PDF

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Publication number
EP1265314A1
EP1265314A1 EP01810457A EP01810457A EP1265314A1 EP 1265314 A1 EP1265314 A1 EP 1265314A1 EP 01810457 A EP01810457 A EP 01810457A EP 01810457 A EP01810457 A EP 01810457A EP 1265314 A1 EP1265314 A1 EP 1265314A1
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EP
European Patent Office
Prior art keywords
dielectric material
permittivity
resonator
dielectric
transmission line
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.)
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Application number
EP01810457A
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English (en)
French (fr)
Inventor
Jan Hesselbarth
Rüdiger Vahldieck
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.)
Institut fur Feldtheorie und Hochstfrequenztechnik Der Eth Zuerich
Original Assignee
Institut fur Feldtheorie und Hochstfrequenztechnik Der Eth Zuerich
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Application filed by Institut fur Feldtheorie und Hochstfrequenztechnik Der Eth Zuerich filed Critical Institut fur Feldtheorie und Hochstfrequenztechnik Der Eth Zuerich
Priority to EP01810457A priority Critical patent/EP1265314A1/de
Publication of EP1265314A1 publication Critical patent/EP1265314A1/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Withdrawn legal-status Critical Current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
    • 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

Definitions

  • This invention relates to dielectric resonators and more particularly to a dielectric resonator comprising a transmission line and a capacitive element as defined in the independent claim.
  • Resonators are primarily used as frequency selective components in microwave filters, oscillators, and antennas. At low frequencies, so-called lumped element capacitors and inductors form a resonator. They, however, fail to work at intermediate and high frequencies. At high frequencies, cavity resonators are used. Since the frequency of the fundamental mode of a cavity is inversely proportional to the cavity dimension, at intermediate frequencies cavity resonators become too bulky. A possibility to reduce the physical size of cavity resonators is to fill them in a suitable way with a high permittivity dielectric material. A further possibility is to use lumped elements also at intermediate and high frequencies by combining them with transmission line elements, e.g. impedances, conductors and dielectrics, forming so-called semi-lumped resonators.
  • transmission line elements e.g. impedances, conductors and dielectrics
  • Some possibilities to achieve at least some temperature stability of the resonance frequency are for example to use metal alloys of minimized thermal expansion, e.g. INVAR, or the use of temperature-compensated dielectric materials, e.g. Ba 2 Ti 9 O 20 as mentioned in the document US-6'034'015 or many others. It is also possible to combine two dielectrics having large variations of permittivity with temperature, but of opposite sign, e.g. TiO 2 and LiNbO 3 as is disclosed in the document US 3'798'578.
  • Temperature compensated dielectric materials offered by several manufactures suffer from various drawbacks. For example these temperature compensated materials have a decreased electrical performance compared to the uncompensated raw materials, which means higher losses. In addition the technological complexity of the production of these ceramics result in low production yields and very high costs.
  • the frequency compensated resonator should be reduced in size compared to or at least not be considerable bulkier than state of the art dielectrically loaded cavity resonators and transmission line resonators.
  • An idea underlying the invention is to divide the resonator into regions where the magnetic field is dominant (i.e. where the main part of the energy is stored in the magnetic field) and regions where the electric field prevails.
  • the resonance frequency is only weakly dependent on the permittivity, i.e. the frequency dependence on the permittivity there is a higher order effect.
  • a first material with a high permittivity and a high temperature coefficient of the permittivity can be used.
  • a second material with a low temperature coefficient of the permittivity e.g. of the opposing sign than the first material can be used.
  • the composite dielectric resonator according to the invention (a "semi-lumped resonator") therefore comprises a first transmission line, a capacitive element and a second transmission line, as well as at least one port for coupling to external circuits.
  • the first and the second transmission line comprise a first dielectric material
  • the capacitive element comprises a second dielectric material, the second dielectric material having a temperature coefficient of permittivity smaller in magnitude than that of the first dielectric material.
  • the transmission lines are electrically of about equal length as and preferably shorter than a quarter of a wavelength of the basic mode and store mainly magnetic field.
  • the variation of the resonance frequency is mainly due to the temperature dependency of the permittivities of the materials involved.
  • the resonance frequency in addition is also influenced by thermal expansion.
  • permittivity variations and thermal expansion have a similar effect, but the latter is generally smaller than the former. Therefore, in the following description only the permittivity variations are discussed. It, however, goes without saying that the temperature dependence due to thermal expansion is also addressed.
  • the transmission line, the capacitative element and dielectric materials are arranged in a way that the resonator has a stabilized resonance frequency against temperature-induced variations of the permittivity of the involved dielectric materials as well as against thermal expansion of dielectric and metallic parts.
  • the first dielectric material, i.e. the dielectric material of the transmission lines can have a much larger magnitude of temperature dependence of permittivity than the dielectric material on which the capacitive element is based.
  • An advantage of the inventive resonator structure is that the resonator can be made physically small when high permittivity dielectric materials are used.
  • a further reduction in size compared to, e.g. dielectrically loaded, cavity resonators can be achieved by a so called semi-lumped structure containing transmission line elements, and e.g. capacitive and/or inductive elements.
  • the dielectric materials of transmission line elements may have much larger magnitudes of temperature dependencies of permittivity than the dielectric material of which the capacitive element is based on.
  • the first dielectric material has a permittivity value exceeding 30, possibly exceeding 60, e.g. exceeding 80 or amounting to 100 (TiO 2 ).
  • the second dielectric material should preferably have a temperature coefficient of permittivity which is of an opposite sign and 1.5 to 20 times, preferably two to ten times smaller in magnitude than the temperature coefficient of permittivity of the first dielectric material. It may e.g. have an absolute value below 0.00015 K -1 , e.g. of less than 0.0001 K -1 .
  • a third well known criterion for choosing materials is the minimization of losses, e.g. due to scattering at grain boundaries.
  • the product Q*f is a essentially constant where Q is the Quality factor of the material (i.e. the inverse of the loss tangent at a given frequency) and f is the frequency (in GHz).
  • Both involved dielectric materials should preferably have low losses and high Q*f products.
  • dielectric materials of high permittivity exhibit lower Q*f products than low permittivity materials.
  • temperature-compensated high permittivity dielectric materials show even lower Q*f products than uncompensated raw materials.
  • an advantage of the resonator structure presented here is that low-loss raw materials can be used.
  • compensated Ba 2 Ti 9 O 20 exhibits similar Q*f having a permittivity of about 39 only
  • compensated commercial BaSmTiO may have a permittivity of about 87 but Q*f of 4'500 (see J. Deriso, "Ceramic-filled transmission lines for circuit miniaturization", in : Materials and Processes for Wireless Communications, Ceramic Transactions, vol. 53, Amer. Ceram. Soc., 1995, pp. 73-82).
  • Q*f should exceed 30'000 for the first material and 80'000 for the second material.
  • dielectric materials that can be used in the present invention are:
  • a small positive temperature coefficient of the capacitance can e.g. be realized by using a dielectric material having a positive temperature coefficient of permittivity or/and by using e.g. an air filled capacitor which electrodes approaching one another by an appropriate thermal expansion of their respective mechanical holders as is disclosed e.g. in the aforementioned document of S.-W. Chen et. al.
  • FIG. 1 shows a perspective cutaway view of a composite dielectric resonator 100 according to the present invention.
  • the resonator 100 contains an outer metallic conductor 101, an inner metallic conductor 102, and an isolating dielectric 103 of a first dielectric material that form a coaxial line section. This line section is short-circuited at one end by a metallic conductor 104.
  • the resonator contains a second short-circuited coaxial line section made of the outer metallic conductor 101, a second inner metallic conductor 105, a second isolating dielectric 106 also made of the first dielectric material, and a second shorting metallic conductor 107.
  • the inner metallic conductor 102 of one first transmission line is connected to a metallic capacitor electrode 108, whereas the second inner metallic conductor 105 of a second transmission line is connected to a second metallic capacitor electrode 109.
  • the electrodes 108 and 109 are isolated from each other and form a capacitor.
  • the space between these electrodes 108, 109 can be filled with an isolating second dielectric material 110.
  • the capacitor formed by 108, 109, 110 as well as the short sections of 102, 107 are embodied in a third isolating dielectric material 112.
  • the third dielectric material 112 can be air or another material having a permittivity which differs from the permittivity of the isolating materials of 103 and 106. Especially, the third dielectric material may have a low permittivity, the transmission lines being formed between the first and second transmission lines, respectively, and the capacitive element by the outer metallic conductor 101, the inner metallic conductor 105 and this third dielectric material 112 is e.g. electrically short and mainly functions to prevent boundary effects at the capacitor electrodes from influencing the mode properties in the first and the second transmission line. In other words, they avoid unwanted electrical coupling of fields between the short-circuited first and second transmission lines and the capacitive element.
  • the resonator further comprises one or two ports (not shown in the figure) for interacting with external components. These ports e.g. slot feeds placed in the endface metallic conductors 104, 107. Such ports shortly described further below with reference to Figs. 8 and 9.
  • FIG. 2 shows the simplified circuit schematic of the resonator of fig. 1. To be seen is a series connection of a first short-circuited transmission line TL1, a first transmission line TL2, a series capacitor C, a second transmission line TL3, and a second short-circuited transmission line TL4.
  • the short-circuited transmission lines TL1 and TL4 are based on high permittivity dielectric material 103, 106 with temperature variation coefficients ⁇ TL . They are electrically shorter than a quarter of a wavelength and store mainly magnetic field.
  • the transmission lines TL2 and TL3 are based on low permittivity dielectric material 112 and are electrically very short. As mentioned, they avoid unwanted electrical coupling of fields between short-circuited transmission lines TL1 and TL4 and the capacitor C. Since the transmission lines TL2 and TL3 are electrically short, their thermally induced influence on the resonance frequency is small and can be compensated by the interaction between short-circuited transmission lines TL1 and TL4 and the capacitor C as a higher order effect. This effect amounts to about the same magnitude as thermal expansion effects.
  • the capacitor C can be based on a dielectric material 110 and has the temperature variation coefficient ⁇ C of the capacitance, which is due to permittivity variation and thermal expansion of the dielectric material.
  • FIG. 3 shows an even more simplified circuit diagram of the resonator of fig. 1 than the one shown in fig. 2: transmission lines TL2 and TL 3 are neglected.
  • FIG. 4 shows a plot of the compensation formula.
  • a complete temperature compensation requires ⁇ CAP and ⁇ TL having opposite sign, and ⁇ TL shall preferably be two to ten times larger in magnitude than ⁇ CAP .
  • FIG. 5 shows another embodiment of a resonator of the present invention.
  • a portion of the composite dielectric resonator 200 has been cut away in order to illustrate in more detail the internal structure thereof.
  • the resonator 200 contains two coaxial line sections formed by an outer metallic conductor 204, inner conductors 206 and 208, respectively, and a high permittivity first dielectric material 205.
  • the first dielectric material 205 may have a large temperature coefficient of permittivity.
  • a metallic strip 207 connects the inner conductors 206 and 208 of the first and the second coaxial transmission lines.
  • a second dielectric material 202 has an appropriate, but small temperature variation of permittivity and forms a series capacitor between the respective ends of the inner conductors 206, 208 of the coaxial lines.
  • the series capacitor is composed of the metallic electrodes 201, 203, 209, and the dielectric 202. Between the electrodes 203, 209 of the capacitor and the first dielectric material 205 an air gap is formed, air being the third dielectric material.
  • FIG. 6 shows the simplified circuit schematic of the resonator of FIG. 5, showing a ring connection of a transmission line TL1, a transmission line TL2, a series capacitor C, and transmission line TL3.
  • TL1 contains both coaxial transmission lines, i.e. the transmission lines formed by the first inner conductor 206 together with the metallic conductor 204 and the first dielectric material 205 as well as the transmission line formed by the second inner conductor 208 together with the metallic conductor 204 and the first dielectric material 205. These two lines function as one element since they are connected by the metal strip 207.
  • the transmission lines TL2 and TL3 are formed by the air gaps between the electrodes 203 and 209, respectively, of the capacitor and the first dielectric material. They are electrically very short.
  • the transmission line TL1 is based on high permittivity dielectric material of temperature variation coefficient ⁇ TL . It is electrically shorter than a quarter of a wavelength and stores mainly magnetic field.
  • the transmission lines TL2 and TL3 are based on low permittivity dielectric material (air in this example) and electrically short. They avoid unwanted electrical coupling of the fields between transmission line TL1 and the capacitor. Since they are electrically short, their thermally induced influence on the resonance frequency is small and can be compensated by the interaction between transmission line TL1 and the capacitor C as a higher order effect. This effect amounts to about the same value as thermal expansion effects.
  • the capacitor C can be based on a dielectric material and has a temperature variation coefficient of the capacitance ⁇ C , which is due to permittivity variation and thermal expansion.
  • FIG. 7 shows the resonator of fig. 5 with transmission lines TL2 and TL3 neglected.
  • a circuit analysis of the circuit shown in Fig. 7 reveals similar results to the results given above if the electrical length of TL1 (see Fig. 7) is set to 2 ⁇ L :
  • the resonance frequency is independent of temperature in first order, and second order effects are compensated with ⁇ CAP which is again much smaller in magnitude than ⁇ TL and has opposite sign.
  • the resonator can also be laid out to be open at one or two ends instead of short-circuited.
  • the electric field prevails at the open ends of the line.
  • the capacitive element storing energy in the form of electric field then is formed by a open line end instead of a capacitor arranged in the interior of the resonator.
  • FIG. 8 illustrates an example of how to couple a resonator 300, which is similar to the resonator structure 100 of fig. 1, to an external circuit by means of one or more coupling slots (302, 303) and microstrip transmission lines (301, 304).
  • FIG. 9 illustrates an example of how to couple a resonator 400, which is similar to the resonator structure 200 of fig. 5, to an external circuit by means of inductive coupling to a transmission line.
  • This transmission line can be a microstrip line between line ends 401, 402, and coupled line section 403.
  • the resonator arrangement shown in fig. 8 realizes the coupling to external microstrip lines by means of coupling slots.
  • a magnetic current is efficiently excited in the slot direction by both the groundplane current of the microstrip line and the radial currents in the shorting plane of the co-axial transmission line.
  • the resonator arrangement shown in fig. 9 realizes the coupling to an external microstrip line by means of a coupled line section.
  • the magnetic fields caused by the microstrip current induce a current in the nearby, parallel metallic strip 207 (of fig. 5) of the resonator and vice versa.
  • the metallic strip 207 (of fig. 5) exhibits particularly high currents at resonance, thus making the coupling easy and efficient.
  • the resonator according to the invention can have a very good temperature compensation without using much expensive highly temperature compensated dielectric material.
  • Such a resonator can further be combined with traditional ways to compensate such as electronic feedback loops etc.
  • the resonators described here are by no means the only embodiments of the invention and that numerous other embodiments may be envisaged.
  • the transmission lines do not have to be essentially homogeneous as described above but may also be inhomogeneous, i.e. composed of different materials.
  • the resonator does not have to be designed to be cylindrical or rectangular as in the above examples but may have any shape allowing modes to resonate.

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EP01810457A 2001-05-10 2001-05-10 Dielektrischer Resonator Withdrawn EP1265314A1 (de)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110304915A (zh) * 2019-04-25 2019-10-08 武汉理工大学 一种高击穿强度低介电常数的微波介质陶瓷材料及其制备方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4491976A (en) * 1981-10-26 1985-01-01 Hitachi, Ltd. Wide-band tuner having a temperature-compensated microstrip resonator arrangement
US4583064A (en) * 1983-09-02 1986-04-15 Matsushita Electric Industrial Co., Ltd. Strip-line resonator

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4491976A (en) * 1981-10-26 1985-01-01 Hitachi, Ltd. Wide-band tuner having a temperature-compensated microstrip resonator arrangement
US4583064A (en) * 1983-09-02 1986-04-15 Matsushita Electric Industrial Co., Ltd. Strip-line resonator

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110304915A (zh) * 2019-04-25 2019-10-08 武汉理工大学 一种高击穿强度低介电常数的微波介质陶瓷材料及其制备方法

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