HK1085572B - Cavity resonator, use of the cavity resonator in a oscillation circuit - Google Patents

Abstract

Cavity resonator (20) with temperature compensation, comprising a pot (21) and a cover (22) which together surround a cavity resonance volume (V). The pot (21) comprises a first material which has a first temperature expansion coefficient (α1), and the cover (22) comprises a second material which has a second temperature expansion coefficient (α2). The second temperature expansion coefficient (α2) is greater than the first temperature expansion coefficient (α1) and in case of an increase in temperature, the pot (21) expands and the cover (22) deforms resulting either individually or together in an increasing of the cavity resonance volume (V). At the same time, the resonance frequency remains essentially constant.

Description

The present invention relates to cavity resonators and their use specifically in oscillator circuits.

Resonators are important components used in a wide variety of applications, for example microwave systems require high-quality resonators used in filters and oscillators, and a choice must be made between cavity and dielectric resonators, where size, weight, cost and other factors may play a role.

Cavity resonators in the various known embodiments are subject to a change in resonance frequency when the temperature changes, which is undesirable for most applications. A temperature change can result from a change in ambient temperature, a temperature change in an integrated oscillator circuit, or losses occurring in the resonant cavity. A temperature change results in a change in the dimensions of the resonator, which results in the mentioned change in resonance frequency.

There are several approaches to reducing the effect of temperature on resonators, for example, it is possible to reduce the change in resonance frequency caused by a temperature change by inserting a dielectric part into the cavity, where the dielectric part must have an appropriate temperature coefficient of dielectric permittivity.

Err1:Expecting ',' delimiter: line 1 column 265 (char 264)If the materials of the cavity 11 and the rod 12 are chosen so that the rod 12 expands less, the so-called capacitive gap (area 13) between the lower end and the lower wall of the cavity 11 will be larger. This change in the capacitive gap (reduction of the capacitive load of the resonator at temperature increase) in the region 13 causes the resonance frequency of the resonator 10 to remain relatively constant in a certain temperature range. Any such cail-vent resonance factor 10 is of relatively poor quality.Especially at high frequencies above 10 GHz, the quality factor Q decreases progressively due to the high field concentration in the capacitive gap and its immediate surroundings.

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US 5 867 077 is specifically a temperature-compensated microwave filter.

Other resonators are made of Invar® or similar materials with a low coefficient of temperature expansion.

The present invention is based on the state of the art mentioned at the outset and the aim is to create a resonator which prevents or reduces a change in the resonance frequency at a temperature change.

It is another task of the invention to provide various applications for such a novel type of resonator with temperature compensation and corresponding oscillator circuits.

The invention provides for a cavity resonator whose volume increases or decreases with increasing temperature, without the resonance frequency changing more; to this end, the cavity resonator comprises a pot and at least one cover made of materials with different temperature expansion coefficients, at least one cover having a greater temperature expansion coefficient than the pot zone. Although both parts of the cavity resonator, the pot and the cover, contribute to an increase in the cavity volume with increasing temperature, the resonance coefficient can be kept constant in the field of choice by selecting a suitable method of separation, since the cover can be kept in a constant shape and thus be used in a suitable area.

To perform the above-mentioned task, a cavity resonator with the characteristics of claim 1 is provided, the use of a cavity resonator with the characteristics of claim 16 and an oscillator circuit with the characteristics of claim 17 are provided.

Other embodiments of the invention of the cavity resonator are given in dependent claims 2 to 15 and further embodiments of the oscillator circuit are given in dependent claims 18 to 19.

The invention is described in detail below, using the illustrations of examples of execution shown below. Fig. 1A, 1A, a schematic cross-sectional representation of a conventional re-entry cavity resonator, where Fig. 1A represents the state at a temperature T and Fig. 1B at a higher temperature T';Fig. 2a schematic view of a cavity resonator in a first embodiment of the invention;Fig. 3A, 3A, a schematic cross-sectional representation of the electric field intensity distribution in a cavity resonator according to the invention, where Fig. 3A represents the cross-sectional state at a temperature T and Fig. 3B at a higher temperature T';Fig. 4A, 4A, a further schematic cross-sectional representation of a conventional cavity resonator, where Fig. 4A, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, and 6F; Fig. 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, and 6F; Fig. 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, and 6F; Fig. 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 5F, 5F, and 6F, 6F, and 6F; Fig. 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, 4F, and 6F, and 6F, and 6F, and 6F are shown in a diagram of a higher temperature in a room with a higher temperature and a higher temperature; Figure

Detailed description:

The following is a description and definition of terms which appear several times in the description and claims.

Err1:Expecting ',' delimiter: line 1 column 210 (char 209)

Unlike the methods known to date, the invention provides a cavity resonator whose volume increases or decreases with increasing temperature, without a greater change in the resonance frequency.

A first embodiment of the invention is shown in Fig. 2. A schematic view of a cavity resonator 20 is shown. The cavity resonator 20 has a cylindrical pot 21 with a bottom 21.1 and a cover 22 that together enclose a cavity resonance volume V. The cavity resonator 20 is characterized by the fact that the pot 21 contains a first (metallic) material that has a first temperature expansion coefficient α1. The cover 22, on the other hand, contains a second (metallic) material that has a second maximum temperature expansion coefficient α2. According to the original invention, the two cavities have a temperature expansion coefficient α22. The first cavity resonance coefficient α2 is described as α21. The temperature expansion coefficient α2 is increased when the temperature of the cavity is greater than α21. The first cavity is described as α21. The expansion coefficient α2 is increased when the temperature of the cavity is greater than α21.

In the example shown, the pot 21 has a cylindrical shape with a radius R and a (resonator) height H. The cover 22 is a dome-shaped element with a height ΔH and a length P. The pot 21 and the cover 22 are rotationally symmetrical around the axis 23.

The resonance frequency fR, TM010 of the TM010 mode in a cavity resonator with a purely cylindrical cavity is independent of the height H of the pot and is given by the following equation: $f_{R,\mathrm{TM}010}=0.38274\cdot \frac{c}{R},$

Err1:Expecting ',' delimiter: line 1 column 1092 (char 1091)

In addition to the increase in volume from V to V', however, there is also a change in geometrical conditions in the area of the cover 22. The effect of the change in volume and geometry on the electrical properties of the resonator 20 is explained below by Figures 3A and 3B. In Fig. 3A, the distribution of the electric field strength E at an initial temperature T is shown. The cover 22 has a length and a height, as in Fig. 2. We and ΔH. Pd increases the temperature from T to T', the situation is as shown in Fig. 3B, where the cover 22 has a slight upward curve.The length P becomes the length P' and the angle of inclination β becomes ß' with P < P', ΔH < ΔH' and β < β. Approaching P, P increases with the material expansion coefficient α2, while ΔH increases much more due to the leverage effect. In Figure 3B, it can be seen that the electric field strength decreases in the area of the further outward curved cover 22.In the example shown in Figures 3A and 3B, the ratio P/R = 1.01 and the ratio shown in Figure 3B P'/R' = 1.02.

To exploit this effect of local field reduction, as described above, the coefficient of temperature expansion α2 of the cover 22 must be greater than the coefficient of temperature expansion α1 of the pot 21. This results in the radius R of the pot 21 increasing from T to T' and the dome-shaped cover 22 curving further outwards.

The invention shows that, by deforming the cover at temperature rise, an additional volume is formed in the various embodiments, which contributes to increasing the overall volume of the cavity.

The principle of the present invention is described below in Figures 4A-4D, the figures and the following description being a highly simplified representation of the actual situation, which assumes that a cavity resonator can be considered as a combination of capacity C and inductance L, as shown in the following equation, where fR is the resonance frequency: $f_R=\frac{1}{2\pi \sqrt{L\cdot C}}\mathrm{.}$

In Fig. 4A, a conventional cavity resonator 30 with a pot 31 is shown, closed in all directions. This cavity resonator 30 has a volume V, a capacity C and an inductance L at temperature T. If the temperature is now increased from T to T', the condition shown in Fig. 4B results. If only the height H of the resonator top 31 were to change, the resonance frequency fR would remain constant due to the characteristics of the TM010 mode, i.e. fR = f'R, as the capacity, i.e. C'C, decreases and the inductance increases, i.e. L'L.L. increases, but the radius of the resonator top also increases.This results in both an increase in inductance, i.e. L' > L, and an increase in capacity, i.e. C' > C. The volume V has increased by the change in height H and radius R to V', the capacity C' has changed, i.e. C' ≠ C, and the inductance has increased, i.e. L' > L, as already mentioned. Since the product of inductance and capacity remains constant in the case of a change in height, but increases in the case of an increase in radius R (L'C' > LC), an undesirable reduction in the resonance frequency fR results. Temperature cannot be achieved on this W.

Figures 4C and 4D show the behaviour of a resonator 40 according to the present invention. The resonator 40 has a cover 42 with a cone-shaped area that curves downwards in the illustrations shown. This cavity resonator 40 has a volume V1, a capacity C1 and an inductance L1 at temperature T. The inductance L1 is approximately the same as the inductance L in Fig. 4A, since the addition of a curved cover does not cause a significant H-field change and no significant inductance change.

If the temperature is now increased from T to T', the condition shown in Fig. 4D is obtained, whereby the dimensional changes of the resonator 40 have been deliberately exaggerated. The volume of V1 has increased to V1', the capacity of C1' has become smaller, i.e. C1' < C1, and the inductance has increased, i.e. L1' > L1.

A cavity resonator according to the invention can be dimensioned as follows: In a first step, the material can be selected and a resonance frequency for R specified. The pot can include, for example, CuW and the cover CuBe. Then the dimensions of the pot (H and R) and the dimensions of the cover (P and ΔH) are determined. Now, with a commercially available simulation program that solves the present intrinsic value problem for Maxwell's differential equations for the given geometry, the resonance frequency fR can be calculated.In the next step, the effect of a temperature change (increase or decrease in temperature) on the shape of the pot and the cover can be determined by means of commercially available simulation programs for this mechanical problem or by experimental means. In addition, the mechanical stresses in the pot and/or the cover can be calculated/simulated. If the mechanical stresses are to be large, the initial stresses (e.g. H, round ΔH) can be modified again to repeat the calculation.This calculation may include specifications for the mechanical tolerances. If the dependence of the resonance frequency fR on the temperature is within a given range, the calculations can be completed, otherwise the starting values (e.g. H, R and ΔH) can be modified again to repeat the calculation.

If the pot geometry and materials are chosen appropriately and the various embodiments of the invention are covered, the result is at least a reduction in the temperature dependence of the resonance frequency fR within a given temperature range (e.g. operating temperature ±50K) or a complete compensation or even reversal of the temperature dependence (overcompensation).

The invention is particularly suitable for use in circuits designed to process high power signals for broadband communications.

A resonator according to the invention may be part of a filter circuit which includes an oscillator with the resonator in the feedback branch.

The circuit may be based on a ceramic substrate, such as a multilayer LTCC (Low Temperature Cofired Ceramics) substrate, as described in the invention. Such a substrate may be mounted on a base plate, which in turn carries the resonator of the invention.

The preferred embodiment of a circuit 50 is one in which the resonator pot 51 is formed in a base plate 53 of the circuit, as shown in Figure 5. The base plate 53 is connected to a substrate 54 and can serve as a heat sink, e.g. as a heat sink for electronic components mounted on the opposite side of substrate 54.At the opposite end of the pot 51 is a cover 52. This cover 52 includes an outer ring-shaped area 52.1 which runs essentially parallel to the conductive surface 57. In the area around the cylinder axis 58, the cover 52.2 is conical arched downwards. There is a coupler hole 55 for coupling an electromagnetic wave and a coupler hole 56 for disconnecting the wave. Alternatively, this coupling could also be done by one and the same coupler hole. Typically, 54 strip conductors are arranged on the substrate 54 to guide the wave 55 back to the coupling point and on the other side to pick up and re-direct 56.The strip conductors are not shown in Figure 5.

Preferably, in a circuit according to the invention, the first material is chosen so that the coefficient of temperature expansion α1 of the base plate matches the coefficient of temperature expansion a3 of the substrate.

Err1:Expecting ',' delimiter: line 1 column 649 (char 648)The phase-out component 67 is also optional. On the output side, an additional amplifier 68 is provided to generate a sufficiently large output signal power. This second amplifier 68 usually relies on a good dissipation of the loss heat, which can be ensured by the present structure (with a solid, well-conductive floor plate 53, Fig. 5). On the output side of the amplifier 68 is the output (OUT) of the oscillator circuit. At this output the circuit 60 is taken power. A small part of the power is directed through the coupler 66 to the resonator 80 . The resonator 80 is therefore in the feedback path of the circuit 60.

To compensate for temperature shifts in oscillation frequency of the oscillator circuit 60 that may be caused by components of the circuit 60, the temperature compensation of the resonator 80 may be designed so that the resonator 80 itself shows under- or over-compensation.

In the preferred embodiment shown in Figure 6, the circuit 60 includes an electrical component 64 to limit the power. This allows a stable vibration state to be achieved. Power can be decoupled from circuit 60 to a suitable location (denoted OUT), with decoupling being capacitive, inductive, or direct. It is important that the overall gain in circuit 60 is sufficient and the phase position is correct for the oscillation to begin and for circuit 60 to vibrate stable.

The resonator 70 has a cylindrical pot 71 and a cover 72 designed to use the temperature compensation of the invention. The walls 71.1 of the pot 71, the base plate 74 (for example in the form of a single-sided metallized ceramic plate) and the cover 72 together enclose a hollow resonant volume. The top 71 comprises a first (metallic or metallized) material having a first volume of a temperature coefficient of α1 which is expressed in the range of 4 ppm/K and 10 ppm/K. The top 72 has a coefficient of 72 ppm/K. The coefficient of 72 ppm/K is expressed in the range of 75 ppm/K and 7 ppm/K. This is due to a second coefficient of 7 ppm/K, which is expressed in the range of 75 ppm/K and 7 ppm/K. The coefficient of 72 ppm/K is expressed in the range of 75 ppm/K. The coefficient of 72 ppm/K is expressed in the second coefficient of 7 ppm/K. This is due to a coefficient of 7 ppm/K, which is expressed in the range of 7 ppm/K and 7 ppm/K. The coefficient of 72 ppm/K is expressed in the first coefficient of 7 ppm/K, which is expressed in the coefficient of 7 ppm/K. This is due to a coefficient of 7 ppm/K.

In the example shown, the height H is typically between 2 mm and 20 mm. In the example shown, the overall height is approximately 4 mm (total height = H + ΔH). The cover 72 may have a 72.1 circular collar to connect the cover 72 to the 71.1 wall of the top 71. For this purpose, the top 71 can have a greater radius in the upper area than in the lower area. A resulting drill flow of 71.2 degrees will result in a 73 S. The conductive conduction of the cover 72 is carried out at a 73 S. The effective conduction of the cover 72 can be carried out at a 72.2 S. This is because the resistance can be introduced in the area of the 72.2 area, where the conduction ratio can be adjusted by an optional change in the axial resistance of the 72.2 area.

The resonator pot can be drilled, milled, turned, cast, deep-drawn or otherwise manufactured according to the invention. Preferably, the inner walls of the pot are further processed to produce a surface with low surface roughness.

A particularly advantageous design is one in which the walls of the pot have a low roughness and are preferably coated with gold and/or silver.

In a particularly advantageous embodiment, special measures are taken to ensure that the cover and the pot are connected by conductors, which may be present on the entire cover or on a substantial part of it, and preferably electrically and mechanically connected to the pot by a soldering or welding connection.

Another embodiment is 1a: instead of a pot with only one lid, a lid (e.g. made of a prismatic or round tube) with lids on both sides is used, in which case both lids can contribute to compensation with the functional principle described.

The invention is considered to be an advantage of the invention that when using the TM010 mode, the height H of the pot can be freely selected. It is not necessary to meet the condition that the height of the resonator corresponds to half the wavelength as in the case of hollow-line resonators. The invention gives an additional degree of freedom in determining the dimensions of the resonator. The (resonator) height H can be chosen so that a large quality factor Q is obtained. According to the invention, for example, a quality factor of 2500 can be achieved (at fR~30 GHz and gold-metallisation on the surface of the pot and cover).

The cover of the invention is preferably dome, dome or cone shaped and forms a cavity when viewed from the direction of the pot.

Err1:Expecting ',' delimiter: line 1 column 148 (char 147)

Depending on the embodiment of the invention, a resonator may be constructed with a temperature-resonance frequency dependence in the range of -10 ppm/K to +10 ppm/K. The resonance frequency-resonance dependence fR may be determined within a specified range according to the application and may be satisfied accordingly by the corresponding design of the resonator.

The compensation effect of the present invention is quantitatively determined by the choice of materials and by the geometry. Preferably, a material with an expansion coefficient α1 between 4 ppm/K and 10 ppm/K is used for the pot (for example, a copper tungsten alloy, CuW, with α1 = 6.1 ppm/K). The cover, on the other hand, includes a material with an expansion coefficient α2 between 10 ppm/K and 20 ppm/K (for example, another copper-ferrous alloy, CuBe, with α2 = 17.0 ppm/K).

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The invention allows the provision of resonators with a high quality factor Q and low losses. Such resonators are particularly well suited for low-noise oscillator circuits. In filter circuits (composed of several resonators), high-quality resonators allow the realization of steep-flanked, i.e., particularly frequency selective, filters and/or filters with particularly low insertion damping in the pass-through frequency range.

It is another advantage of the invention that the same principle of action can be applied to other resonance modes TEm0m in a rectangular cavity or TM0n0 (with m, n > 0 and integer) in a circular cavity. Many of these resonance modes result in more mechanically demanding (e.g. rectangular instead of circular) and more tolerance sensitive structures.

Claims (19)

1. Cavity resonator (20; 40; 80; 70) with temperature compensation, comprising a pot (21; 41; 51; 61; 71) with a floor (21.1; 54, 57; 74) and a cover (22; 42; 52.1, 52.2; 62; 72), with the pot (21; 41; 51; 61; 71) surrounding jointly with the floor (21.1; 54, 57; 74) and the cover (22; 42; 52.1, 52.2; 62; 72) a cavity resonance volume (V), and

   - the cavity resonator (20; 40; 80; 70) having a resonant frequency (f_R) in operation,

   - the pot (21; 41; 51; 61; 71) comprising a first material which has a first temperature expansion coefficient (α1),

   - the cover (22; 42; 52.1, 52.2; 62; 72) comprising a second material having a second temperature expansion coefficient (α2),

   and with the second temperature expansion coefficient (α2) being greater than the first temperature expansion coefficient (α1), and in case of an increase in temperature there being an expansion of the pot (21; 41; 51; 61; 71) and a deformation of the cover (22; 42; 52.1, 52.2; 62; 72) which jointly causes an enlargement of the cavity resonance volume (V), characterized in that the cover is bulged outwardly in such a way that it forms a cavity when viewed from the direction of the pot, and the cover (22; 42; 52.1, 52.2; 62; 72) bulges as a result of the deformation of the cover (22; 42; 52.1, 52.2; 62; 72), thus resulting in an increase in the resonant frequency (f_R), and the diameter of the pot (21; 41; 51; 61; 71) increases by the expansion of the pot (21; 41; 51; 61; 71), thus resulting in a reduction of the resonant frequency (f_R), with the increase of the resonant frequency (f_R) and the reduction of the resonant frequency (f_R) substantially compensate each other in order to ensure in a temperature range that the resonant frequency (f_R) remains substantially stable.
2. Cavity resonator (20; 40; 80; 70) according to claim 1, characterized in that the cavity resonator (20; 40; 80; 70) has a resonant frequency (f_R) in operation and the increase in the cavity resonance volume (V) during a temperature increase occurs in such a way that the resonant frequency (f_R) remains stable within a predetermined margin, or that the resonant frequency (f_R) has a predetermined temperature coefficient which is unequal to zero.
3. Cavity resonator (20; 40; 80; 70) according to claim 2, characterized in that the resonant frequency (f_R) of at least one resonance mode remains stable.
4. Cavity resonator (20; 40; 80; 70) according to claim 1 or 2, characterized in that a local reduction of an electric field strength ( E ) is obtained in the cavity resonance volume by the deformation of the cover (22; 42; 52.1, 52.2; 62; 72).
5. Cavity resonator (20; 40; 80; 70) according to claim 1 or 2, characterized in that a reduction of a capacitive load of the cavity resonator (20; 40; 80; 70) is obtained by the deformation of the cover (22; 42; 52.1, 52.2; 62; 72).
6. Cavity resonator (20; 40; 80; 70) according to claim 1 or 2, characterized in that a cavity resonator (20; 40; 80; 70) is concerned which operates in TM_0N0 resonance mode, with n>0 and integral numbers applying.
7. Cavity resonator (20; 40; 80; 70) according to one of the claims 1 to 5, characterized in that the cover (22; 42; 52.1, 52.2; 62; 72) is shaped in a cupola-like or conical manner and forms a cavity when seen from the direction of the pot (21; 41; 51; 61; 71).
8. Cavity resonator (20; 40; 80; 70) according to claim 1, 2 or 3, characterized in that a cavity resonator (20; 40; 80; 70) is concerned which is suitable for integration in a metallic baseplate of a ceramic substrate (54; 74), preferably the base plate of an LTCC multi-layer ceramics.
9. Cavity resonator (20; 40; 80; 70) according to claim 8, characterized in that the first material is chosen in such a way that the first temperature expansion coefficient (α1) of the baseplate matches the temperature expansion coefficient (α3) of the substrate (54; 74).
10. Cavity resonator (20; 40; 80; 70) according to claim 1, 2 or 3, characterized in that the cavity resonator (20; 40; 80; 70) has a quality factor (Q) which is determined substantially by the resonator height (H) of the pot (21; 41; 51; 61; 71).
11. Cavity resonator (20; 40; 80; 70) according to claim 1, 2 or 3, characterized in that the pot (21; 41; 51; 61; 71) has a copper alloy, preferably a copper and tungsten alloy (CuW), and the cover (22; 42; 52.1, 52.2; 62; 72) has another copper alloy, preferably a copper and beryllium one (CuBe).
12. Cavity resonator (20; 40; 80; 70) according to claim 1, 2 or 3, characterized in that the second temperature expansion coefficient (α2) is larger than the first temperature expansion coefficient (α1) by between 1.1 and 5 times.
13. Cavity resonator (20; 40; 80; 70) according to claim 1, 2 or 3, characterized in that the pot (21; 41; 51; 61; 71) has a low roughness on the inside and is preferably coated with gold and/or silver.
14. Cavity resonator (20; 40; 80; 70) according to claim 1, 2 or 3, characterized in that means (73) for influencing the resonant frequency are provided which preferably partially protrude into the cavity resonance volume and change the effective permittivity there.
15. Cavity resonator (20; 40; 80; 70) according to claim 1, 2 or 3, characterized in that means (55, 56; 65, 66) are provided for injecting and extracting an electromagnetic wave, with preferably a coupling hole for injecting and extracting being provided.
16. Use of a cavity resonator (20; 40; 80; 70) according to one of the claims 1 to 15 in a microwave system (50; 60), with the cavity resonator (20; 40; 80; 70) being part of an oscillator circuit.
17. Oscillator circuit (50; 60), characterized in that a cavity resonator (20; 40; 80; 70) according to one of the claims 1 to 15 is part of the oscillator circuit (50; 60).
18. Oscillator circuit (50; 60) according to claim 17, characterized in that the oscillator circuit (50; 60) is integrated in or on a ceramic substrate (54; 74), preferably an LTCC multi-layer ceramics.
19. Oscillator circuit (50; 60) according to claim 18, characterized in that a part of the oscillator circuit (50; 60) is arranged on one side of the ceramic substrate (54; 74) and the cavity resonator (20; 40; 80; 70) is arranged on another side of the ceramic substrate (54; 74).