DE2047229A1 - Microwave component - Google Patents

Description

THE GENERAL ELECTRIC AND ENGLISH ELECTRIC COMPANIES LIMITED, London, Great Britain

Microwave component

The invention relates to electrical components for operation in the microwave range (UHF and SHF range), i.e. frequencies in the range from 400 MHz to 30 gigahertz, as used, for example, in telecommunications equipment and the Contain components made of dielectric materials, the response of the component from the dielectric constant of the dielectric material depends.

The aim of the invention is to produce improved microwave components of the kind mentioned, which contain components made of dielectric materials of a certain class, both Dielectric constants controlled within a suitable microwave range as well as at the associated frequencies, im have substantial constant temperature coefficients of the dielectric constant as well as low loss coefficients.

The invention relates to a microwave component with a component made of dielectric material, the response of the component depending on the dielectric constant of the material, which is characterized in that the dielectric component consists of a ceramic dielectric material which essentially consists of one or more compounds the

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general formula ABO, is composed, where A barium, strontium or calcium and B zirconium or titanium mean that the composition of the material is such that the atomic ratio of zirconium to titanium is in the range from 80:20 to 100: 0, that at Presence of both barium and titanium, the amount of which is such that barium titanate does not make up more than 10 mole percent of the material, and that the material has dielectric constants in the range of 25 to 75 in the microwave range, a practically constant temperature coefficient of the dielectric constant and a loss tangent. at 20 ^° C. of not more than 0.005.

The temperature coefficient of the dielectric constant! Of the dielectric material is preferably usually in the range of +50 to -100 parts per million per ^0C . In some cases this coefficient may be required to have a certain positive or negative value in order to avoid other characteristics of the Compensate component, for example, the coefficient of thermal expansion of a metal component. In other cases, however, the composition of the material can be so balanced that the value zero or a value almost zero results for the temperature coefficient of the dielectric constant.

The permissible content of barium titanate in the dielectric materials is limited because the values for the dielectric constant and the loss coefficient for barium titanate are considerably higher than the limit values mentioned above and because this substance also has a very variable temperature coefficient of the dielectric constant. The ratio of barium titanate that can be tolerated in any given material depends, of course, on the composition and resulting properties of the other component or components of the material, but in no event should it exceed 10 mole percent of the material.

109825/1793. ·.

The dielectric material preferably consists of a single one Phase, either in the form of a single compound of the class mentioned with the required properties or in the form of a solid solution of two or more such compounds, in the last-mentioned case the proportions of the individual connections are chosen as they are required to produce a dielectric material with a temperature coefficient for the dielectric constant of zero or a desired positive or negative value. Suitable combinations of compounds are, for example, barium zirconate and strontium zirconate, barium zirconate and calcium zirconate, Strontium titanate and strontium zirconate and calcium titanate and calcium zirconate.

Some preferred dielectric materials for use in accordance with the invention are barium strontium zirconates which include the The atomic ratio of barium to strontium is in the range from 40:60 to 80:20, calcium titanate zirconates, in which the The atomic ratio of titanium to zirconium is in the range of 0: 100 to 5:95, and strontium titanate zirconates in which the The atomic ratio of titanium to zirconium is in the range of 2:98 to 8:92. A special material that can be used for some purposes is particularly advantageous because the temperature coefficient of its dielectric constant is close to zero Barium strontium zirconate with a barium to strontium content in an atomic ratio of 56 (barium): 44 (strontium).

While all of the above-mentioned dielectric materials have loss coefficients in the microwave range of not more than 0.005 and in some cases below 0.001, some materials, in particular the mentioned barium strontium zirconates, which in other respects prove to be particularly advantageous for certain areas of application in the microwave range, have loss figures of more than 0.001 im Microwave range.

109825/1783

The microwave losses of some of these materials, especially the barium strontium zirconate and, to a lesser extent, the strontium titanate zirconate, can, however, be significantly reduced without a large or even a change in the dielectric constant or the temperature coefficient of the dielectric constant by adding a small amount of niobium pentoxide to the materials and / or tantalum pentoxide is admixed, suitable amounts of these additives being in the range from 0.1 to 3.0 mol percent of the compound or compounds ABO. The materials that contain such additives all have loss numbers in the microwave range that ^{do not exceed 0.001 at 20 0} C, while at such frequencies they still have dielectric constants in the range from 25 to 75 and practically constant temperature coefficients of the dielectric constant, which in many cases have values in the range of 25 to 75 correspond to the preferred range mentioned above.

It goes without saying that the term "essentially consists from one or more compounds of the general formula ABOy, as mentioned above with regard to the composition of the dielectric Materials used is used in the meaning that the materials either consist entirely of such Compound or consist of such compounds or of such a compound or of such compounds together with a proportion of niobium pentoxide .und or · or Tantalum pentoxide as indicated above exist. Of course, the materials can also contain small amounts of unavoidable Contain impurities.

An example of a component according to the invention is a microwave band filter which has one or more dielectric resonators in the form of rods, cylinders or disks made of dielectric materials, as specified above, instead of a metallic waveguide resonance circuit, as is part of a conventional microwave filter is,

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holds. A metallic resonator is disadvantageous in a microwave component because it has large dimensions that correspond to the length of half a wavelength in air: The replacement of the metallic resonator by a dielectric resonator enables the size of the resonator to be reduced, since the wavelength is the opposite Relation to the square root of the dielectric constant of the dielectric stands in which ceramic dielectric is considerably less than in air. During operation, a ceramic dielectric resonator is usually arranged within a metal screen, whereby a slight increase in the resonance frequency of the dielectric element is achieved. It has already been proposed to use resonators made of titanium dioxide, but this material has a very high temperature coefficient of dielectric constant (approximately -1000 parts per million / ⁰ C), which makes it unsuitable for this application.

The use of dielectric materials, which are composed of zirconates or titanates and zirconates, as indicated above, with the mentioned additions of. Niobium pentoxide and / or tantalum pentoxide may or may not have occurred as resonators in microwave filters according to the invention because of the temperature stability of the dielectric constant and thus the temperature stability of the resonance frequency of these materials. For example, a resonator of the composition (BAQ κκδΓφ ^) ZrO, consists of Bariumstrontiumzirkonat as a ceramic material, a frequency stability of ^10/0 C, ie, a detuning of only about 20 kHz / ° C for a resonance frequency of 2 GHz. Therefore, the use of dielectric resonators according to the invention makes it possible to manufacture filters with bandwidths of only 20 MHz for operation over a temperature range from 0 to 50 ^° C., for example. In addition, a size reduction of at least 2: 1 in all linear dimensions, based on conventional filters with resonance chambers, can be achieved «Examples of special applications

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Forms are a dielectric material with a loss factor of 0.002 and a corresponding figure of merit of 500, which is suitable for use as a resonator in a broadband filter, and a material with a loss figure of 0.0002 and a figure of merit of 5000, which is suitable as a resonator in a Narrow band filter can be used.

Another type of component in which the aforesaid dielectric materials can advantageously be used are the integrated microwave circuits, the dielectric material being used as a substrate which carries the conductor strips which constitute the elements of the circuit. It has already been proposed to use high density alumina for this purpose, however the temperature stability of the dielectric constant of alumina is not as good as it is required for many applications and it would be desirable to use materials which have higher dielectric constants than that of Aluminum oxide (9.5), especially at frequencies in the UHF range below 3 gigahertz, at which the wavelength in aluminum oxide exceeds 10 cm. The dielectric materials used in the present invention are advantageous in this regard because their composition can be selected to have lower temperature coefficients of dielectric constant than alumina and also because they have higher dielectric constants than alumina, thereby enabling the wavelength in the material at a given frequency is only about half compared to that in aluminum oxide.

The dielectric materials used in the inventive apparatus, can be prepared by methods such as are conventionally employed for the production of ceramic dielectric materials of this type, ie by preparing an intimate mixture of powdered starting materials in the suitable geforder-

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20A7229

th composition, pressing the mixture, and heating the compacts to drain the reaction and sinter. The materials can be prepared from mixtures of the necessary previously prepared compounds of the formula ABO ,, as defined above, but the starting mixture preferably contains the corresponding oxides and / or compounds such as carbonates or hydroxides, which decompose to the oxides on heating. In cases in which niobium pentoxide and / or tantalum oxide is to be added to the material, these oxides can initially be added to the material either in the free state or in the form of an alkaline earth metal or tantalate of the general formula MR ₂ Og or M ₂ R ₂ 0 « are introduced, where M is barium strontium or calcium and R is niobium or tantalum.

A preferred method for producing these materials, in which ceramic bodies of a density which is approximately equal to the theoretical density can be obtained and which therefore have an optimal dielectric constant, is that the starting mixture is isostatically to compact bodies of simple shape, such as For example, rods that pre-burn compact bodies at a sufficiently high temperature to achieve partial sintering sufficient to produce a coherent body, crush the pre-fired compact body into powder, compress the powder into 'compact bodies of the shapes corresponding to the parts to be produced and these compression molded bodies are fired at a temperature above the pre-baking temperature and thereby converted into dense, sintered ceramic bodies. When this method is applied, niobium pentoxide and or or tantalum pentoxide can before necessary, either in the form of free oxides or the compounds mentioned above, either incorporated in the starting mixture or the powdered prefired material, which consists only of the desired compound or compounds ABO-j, added to compression molding and sintering.

109825/1783

The niobium pentoxide and / or tantalum pentoxide is on this Way introduced into the dielectric material before or during the final sintering and apparently goes with the existing ABO ^ Material a solid solution. In some cases where niobium and / or tantalum start out in the form of free oxides is introduced, it is possible or it may be expedient to reduce the content of zirconium or titanium in the dielectric Material by an amount that is stoichiometric to that of the imported niobium and / or tantalum is equivalent to reduce so that the niobium and / or tantalum part of the zirconium and / or titanium in the replaced dielectric material.

The following describes a specific process that is used to manufacture some of the dielectric materials mentioned has been described in the form of an example. The materials made were

(A) barium strontium zirconates with barium: strontium atomic ratios of 0.5 ί 0.5 to 0.7: 0.3;

(B) barium calcium zirconates with barium: calcium atomic ratios of 0.3: 0.7 to 0.05 J 0.95;

(C) Calcium zirconate titanates, with atomic ratios of Zirconium: titanium from 0.935: 0.065 to 0.987: 0.013;

(D) calcium circonate CaZrO ,;

(E) Strontium zirconate titanates with atomic ratios of Zirconia: titanium from 0.94: 0.06 to 0.988: 0.012.

In addition, some of these materials were made with the addition of small amounts of niobium pentoxide.

The above materials were prepared from the following starting materials, all in powder form, which were combined in the appropriate proportions to achieve the desired composition; in the

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Production was niobium pentoxide, if at all, all in one added later stage of the procedure:

(A) barium carbonate, strontium carbonate and zirconia j

(B) barium carbonate, calcium carbonate and zirconia;

(C) calcium carbonate, zirconia and titanium dioxide;

(D) calcium carbonate and zirconia;

(E) strontium carbonate, zirconia and titanium dioxide.

In each case, the mixture of powdered starting materials was milled with water in a porcelain ball mill for thirty-six hours, after which the milled mixture was dried and compacted into rods by hydrostatic pressure of 1100 atm (7 tons per square inch) and the rods were left in air for two hours pre-fired at 1250 ^° C. for a long time. The prebaked rods were crushed in a pin mill and the resulting powder was ground with water (or acetone in one case) in a ball mill for twenty-four hours. The powder was then dried, washed with an essential camphor solution and partly pressed into a disk shape under a pressure of 1420 atm and another part was isostatically pressed into rods under a pressure of 1900 atm. The disks or rods were finally ^{fired for two hours at 1450 °} C. in air in order to convert them into dense, sintered ceramic material.

To make similar materials that contain niobium pentoxide, the required amount of powdered niobium pentoxide was added to the pre-fired powder prior to compression molding and sintering added.

The compositions of a number of materials made by the procedure of the Example are shown in the following table along with the values for some of their properties, dei at an audio frequency of 1.6 kHz and in

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Most cases have been determined at a frequency in the microwave range of 5 gigahertz. When it comes to properties These are the dielectric constants and loss figures at both frequencies, the temperature coefficient of the capacitance the audio frequency and the temperature coefficient of the resonance frequency at the frequency in the microwave range.

The temperature coefficient of dielectric constant of the material has not been determined directly, but it can be easily determined in a known manner from the temperature coefficient of the capacitance or the temperature coefficient of the resonance frequency a microwave cavity containing a slice of the material; the last These properties can be measured more conveniently at audio frequency or a frequency in the microwave range. In practice The important temperature coefficient for microwave applications is that of the resonance frequency that can be measured and not so much that of the dielectric constant, which has to be calculated. The resonance frequency is proportional to E *, where E means the dielectric constant, and the temperature coefficient of the resonance frequency is the negative half of the temperature coefficient proportional to the dielectric constant. When the temperature coefficient of the dielectric constant is small, accordingly, that of the resonance frequency is also small, and when the temperature coefficient of the dielectric constant is large, that of the resonance frequency is also large and has the opposite sign.

To carry out the measurements of said characteristics at audio frequency, the main surfaces of sintered discs of the material, which were prepared as described above were polished to provide flat, parallel surfaces, according to which * is applied to these surfaces silver paste and the whole 12 hours at 120 ^° C. and fired at 650 ^° C. for 1 hour. The measurements of the microwave properties became old non-metal! egg slices at one close by

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5 gigahertz frequency, the temperature coefficients for the resonance frequency were determined for disks that had a diameter of 20 mm and were 4 mm thick landed in the TE _Q11 mode in a closely spaced waveguide reflection cavity, which was blocked in the air regions, resonated in the TE _Q11 mode in a closely fitting waveguide reflection cavity cut-off in the air regions.

Used to make some of the materials listed in the table the following minor deviations were made in the manufacturing process described above:

The compositions 3 and 4 had a ZrOg content that was 2.5 mol% lower. During the preparation of the composition, was the prefired powder ground in acetone instead of in water? and in the production of the material 18 the combustion was carried out at 1350 ^° C. instead of at 1250 ^° C.

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TABEL

composition
(AB0 ₃ -connection-
fertilize) Added law
tes
Nb ₂ O ₅
(Mol.96) Properties at a
Frequency of 1.6 kHz Dielectric
citiy con
constant at
20 ⁰ C 10 x Ver
lust number
tangent)
100 ⁰ C Own
Freq at one
frequency of 5 GHz 10 χ loss number
Tangent)
20 ⁰ C ^Ba x ^Sr 1-x ^Zr0 3 1O ^b xTCC *
ie ⁰ C
(± 15) 10 ^b χ
TCF **
at
⁰ C each Dielectric
citiy con
constant at
20 ⁰ C 1 χ = 0.70 - 39.0 5 2 χ = 0.60 - -45 38.2 19th -5.8 3 χ = 0.50 - -22 36.8 11 4th x = 0.55 - +15 37.6 40 -21.9 15th 5 χ = 0.56 +5 38.1 11 34.8 18th 6th χ = 0.56 0.25 0 30.6 <4 -17.6 34.7 4.7 7th χ = 0.56 1.0 -11 30.5 N <4 -14.4 31.3 4.4 8th CaZr _x Ti ₁ ^ O ₃ 0 36.7 20th -23.7 32.3 9 x = 0.935 - -129 34.7 95 4.0 10 χ = 0.96 - -59 32.9 3 +4.7 31.5 2.5 11 χ = 0.987 0.25 -17 Γ 30.6 340 +6.6 30.3 6.1 12th x 3 0.987 1.0
* 4 ** 4 a «* 4- /« YES « +23 32.9
4- 3 -12.0 26.8 6.2. χ «0.987
t 1 * AW11 «SAT * A * 4 * V. 1 · »*» 1 ^ ί "^ A ΦΑ -39 -15.4 26.8

**) Temperature coefficient of the resonance frequency

CO

VO U.N. to CM O to CM σ » T- O* CM VO * Cn is to VO * <Γ CO * O O- τ- CO ■ if to O- 00 CM Ο * • 4 · fO to to CM CM CM to to to to to

to 0- in τ- O <f Ο CM CM Ο tf \ co T- IfS τ- ΙΟ O CM Τ τ- O- CM τ- Ι CM to to Ι Ι to I. Ι to
V I. I. to CM
O- CM to
V to
V CM to
V CM
T- S. T- OV T- O O- T- <f O T- O VO VO fO VO ITV CM to to to to to to to

IO CM T- IO CM ω O Ο Ο CM to IO to cn O ΙΓ \
I. CM IO cn I. IfN
CM O H I. I. I. CM O I. I. 4k
O T- I. O T- T- •H irv irv IfN 1Λ IfN OO irv trv IfN VO GO öS cn cn cn cn cn cn /O IO m * m » O O O O O O O O N U U H H H M. Il ο ö Ö K H N H H K H ΙΟ VO 0- ω cn T- CM T- T- T- T- T- τ- τ- c3 CM CM

It can be seen from the table that the temperature coefficient the capacitance at the audio frequency and the temperature coefficient of the resonance frequency at the microwave frequency with the composition of the material and that values approaching zero can thus be obtained by considering the compositions each class of material is selected in an appropriate manner. Have the temperature coefficients of the calcium circonate titanates proved to be somewhat sensitive to moisture and are therefore not exactly reproducible if the samples are not thoroughly dried and kept dry during the measurement, so that it is possible that some of the samples, at who the measurements were carried out, the results of which are given in in the table are not sufficiently dry. The barium strontium zirconates and strontium zirconate titanates are not sensitive to moisture.

The above table also shows that the addition of niobium pentoxide to the barium strontium zirconates reduces the loss value only slightly reduced in the listening frequency, but a considerable one Reduction of the loss value at the microwave frequency causes and at the same time the dielectric constant slightly reduced, but no pronounced effect on the temperature coefficients of capacitance and resonance frequency owns. However, the addition of niobium pentoxide has little effect on the at either frequency Loss values of calcium circonate titanate, stront-umcirconate titanate or calcium circonate, and these materials have lower microwave loss numbers than barium strontium circonate in the absence of niobium pentoxide.

The dielectric materials, wur- as described in the example above, produced and listed in the table * to, are suitable for use as resonators for ^filtering:> elements, for example in the form of discs. Suitably shaped sheets of material with a thickness of about 1 can also be used as substrates for integrated microwave circuits which are to be operated at frequencies of 1 to 5 gigahertz.

109825M7S3

Of course, a component according to the invention can have more than one dielectric component of the specified type contain. For example, a microwave filter can include a number of dielectric resonators that are longitudinally the axis of a waveguide that is used below its cut-off frequency.

Two special microwave components according to the invention are shown in the drawings and are described below as an example. In the drawings where the same parts in the different figures bear the same reference numerals

1 shows a longitudinal section through a band filter with five dielectric resonators;

FIG. 2 shows a cross section through a filter according to FIG. 1;

Fig. 3 is a section along the line III-III in Fig. 1 of the filters shown in Figures 1 and 2;

Figure 4 is a view of a micro-ribbon line on a dielectric Substrate and

FIG. 5 shows a cross section along the line V-V in FIG. 4 represent.

According to FIGS. 1, 2 and 3, the relationship between which is shown by the lines II and II-II in FIG. 3 and III-III in FIG Frequency of 4 gigahertz is determined and five resonator disks 1 made of a dielectric material of one of the compositions according to the invention, suitably made of one of the materials listed in the table above,

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each disc having a diameter of 20 mm and a thickness of 4 mm and adjusted to resonate _{in the TE 011 mode.} The resonator disks are held in an outer copper housing 2, which is suitably 14 cm long and has a square cross section of 3.5 cm edge length, by means of a tube 3, cylindrical spacers 4 and rings 5, all of which are made of a dielectric material with a low loss coefficient and low dielectric constant, for example the material available under the trade name "Rexolite", held, the tube 3 being closed at both ends by means of copper caps 6. The resonator disks 1 have central bores 7 'into which rods 8 made of the same dielectric material as that of the disks are inserted. In addition, tuning screws 9 are inserted through the housing 2 to act on the rods 8 so that the position of the rods in the bores 7 is adjusted to adjust the resonant frequency of the disks as required.

As shown in Figures 2 and 3, two 50 ohm flanges 10 are of type N, each at one end of the resonator disk group, attached to the housing; Copper coupling strips 11 and 12 are for the input and output of signals, respectively soldered to the central pins 13 of the flanges and extend through openings in the housing 2, and the copper strips are inside the filter cavity by rings 14 of the same electrical material as that mentioned above Parts 3, 4 and 5 supported.

FIGS. 4 and 5 show a filter circuit in the 50 ohm microband 15, which is held on a substrate 16 in the form of a rectangular plate made of a dielectric material with one of the compositions according to the invention. The substrate can be, for example, 15 μm long, 12.5 mm wide and 0.8 mm thick and, as shown in FIG. 5, has

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a continuous metal coating 17 on the face opposite that on which the ribbon line rests is located. Both the line 15 and the coating 17 suitably consist of one layer Chromium covered with a layer of gold; these layers are created on both sides of the dielectric sheet formed by first evaporating chrome and then gold onto the plate surfaces and finally the Brings the gold layer to the desired thickness by electroplating; part of the coating is then covered by a Side of the plate removed by photoetching to give the desired arrangement 15.

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Claims (11)

Claims 1J microwave component with a component made of dielectric material, the response of the component depending on the dielectric constant of the material, characterized in that the dielectric component consists of a ceramic dielectric material which is essentially composed of one or more compounds of the general formula ABO , where A denotes barium, strontium or calcium and B denotes zirconium or titanium, that the composition of the material is such that the atomic ratio of zirconium to titanium is in the range from 80-20 to 100.0, that in the presence of both barium and Titanium, the amount of which is such that barium titanate does not make up more than 10 mol% of the material, and that the material has dielectric constants in the range of 25 to 75 "" in a practically constant temperature at frequencies ia microwave ranges. n the dielectric constant and © in © Verlas tzahi (loss tangent) at 20 ⁰ C vo n. not filter 0.005 2. Component according to claim 1,
characterized in that the component is made of a dielectric material, the composition of which is adjusted such that a temperature coefficient of the dielectric constant of the material »1t a» positive or negative value within the range of +50 to -100 files ^ e million per Degree Celeiius achieved 2. component geaeö claim 2,
characterized in that the component is made of a dielectric material, the addition of which is set such that a temperature coefficient of 4 dielectricity of the material has the value MiU or a value In the IWse is triggered by it. 4. Component according to claim 1, 2 or 3, characterized in that that the component is formed from one of said dielectric materials which consists of a single phase. . 5. Component according to claim 4, characterized in that that the dielectric material consists essentially of a solid solution of barium zirconate and strontium zirconate or of Strontium titanate or of strontium titanate and strontium zirconate or of calcium titanate and calcium zirconate. 6. Component according to claim 5, characterized in that that the dielectric material is essentially a barium strontium zirconate in which the atomic ratio of barium to strontium is in the range from 40:60 to 80:20. 7. Component according to claim 4 or 5, characterized in that that the dielectric material consists practically of a calcium titanate zirconate in which the atomic ratio of titanium to zirconium is in the range from 0: 100 to 5:95. 8. Component according to claim 5, characterized in that that the dielectric material consists essentially of a strontium titanate zirconate in which the atomic ratio of titanium to zirconium is in the range of 2:98 to 8:92. 109825/1793 9. Component according to one of the preceding claims, characterized in that the component is formed from a dielectric material which is composed of one or more of the compounds ABO, together with niobium pentoxide and / or tantalum pentoxide in a combined ratio of 0.1 to 3 _t O mole percent of the compound or compounds ABQ, wherein the composition of the material is chosen such that it does not have at frequencies in the microwave range a loss factor of about 0.001 at 20 ⁰ C. 10. Component according to one of the preceding claims, consisting of a microwave band filter, which has a resonator in the form of a body formed from the ceramic dielectric material of any preceding claim is composed. 11. Component according to one of claims 1 to 9, consisting of an integrated microwave circuit with a substrate which is composed of one of the ceramic dielectric materials mentioned in claims 1 to 9 and which carries conductor strips which form its circuit elements Wa / Rei / Gu 109825/17 93 Blank page