DE102019128204A1 - Method for calibrating a microwave module, calibration system, microwave module and cooking device - Google Patents

Abstract

A method for calibrating a microwave module (20) for a cooking appliance, the microwave module (20) having a microwave output (26) and a control loop (38), comprises the following steps: Generating electromagnetic radiation by the microwave module (20), wherein the generated electromagnetic radiation is defined by an electromagnetic wave that comprises an amplitude and a phase, - emission of the generated electromagnetic radiation via the microwave output (26) of the microwave module (20), - measurement of a forward wave of the emitted electromagnetic radiation by means of a to the microwave module (20) external measuring device (60), and regulating the amplitude and / or the phase of the electromagnetic radiation generated by means of a control and / or evaluation unit (62) external to the microwave module (20), which is connected to the control loop (38) for signal transmission is, so that the electromagnetic generated by the microwave module (20) He radiation is stable in terms of amplitude and phase. A calibration system (58), a microwave module (20) and a cooking device are also described.

Description

The invention relates to a method and a calibration system for calibrating a microwave module for a cooking appliance. The invention also relates to a microwave module for a cooking device and a cooking device.

In modern cooking appliances, in addition to conventional cooking methods, for example hot air and / or steam, microwaves are also used in order to cook food that has been placed in a cooking space of the cooking appliance. The microwaves are generated by microwave modules, the energy of the microwaves being absorbed by the food and converted into heat, which means that the food is cooked.

Several microwave modules can be used, with the energy distribution of the microwaves generated by the several microwave modules being able to be controlled by targeted superimposition of the electromagnetic waves emanating from the microwave modules. In modern cooking appliances, semiconductor components are used for this purpose, via which the electromagnetic waves with the desired properties can be generated. The microwave modules are usually synchronized with one another.

The use of semiconductor components in the area of cooking appliances to generate microwaves is generally referred to as “solid-state cooking” (SSC) or “radio frequency solid-state cooking” (RF SSC).

The advantage of the semiconductor components compared to a conventional magnetron is that the power or amplitude and the phase of the generated microwaves can be controlled in a targeted manner, so that a targeted superposition of the electromagnetic waves is possible, i.e. constructive and / or destructive interference in certain areas.

It is therefore necessary that the amplitudes and phases of the microwaves provided by the individual microwave modules can be controlled exactly.

For this purpose, it is known from the prior art that the respective microwave modules have an internal regulation in order to regulate the amplitude and phase of the microwaves generated. For the regulation, the scattering parameters (S-parameters) are typically measured as a characteristic property of the cooking space or the food to be cooked in the cooking space, with the aid of which the energy input of the microwaves can be optimized in order to obtain the desired energy distribution, in particular the desired constructive or destructive one Interference of the individual microwaves.

In addition, information about the food to be cooked can be obtained via the scattering parameters, via which the cooking process can then be optimized or dynamically adapted to (changing) properties of the food. It is therefore necessary that the scattering parameters can be measured precisely in order to implement the control accordingly.

In other words, the accuracy with which the phase and amplitude can be regulated at the output of the microwave module depends essentially on the accuracy of the measurement, the measurement results of which are used for the internal regulation.

To measure the scattering parameters, a directional coupler is usually used in the corresponding microwave module, in particular an integrated directional coupler, so that the amplitude and phase of the power output and the power fed back can be measured separately. The output power is to be understood as the power of the forward electromagnetic waves, i.e. in the effective direction, whereas the power fed back corresponds to the power of the reverse electromagnetic waves that occurs due to the reflection factor at the antenna output, in particular due to the adaptation of the antenna.

The corresponding directional couplers are used to separate the two directions by measurement, but they only have a limited ability to separate the two directions from one another. This level is also referred to as the directivity of the corresponding directional coupler, whereby values of around 20 dB can be achieved with reasonable effort. Such a directivity is only partially sufficient for the application cases.

It is therefore necessary to increase the accuracy of the measurement of the measured values provided for the internal control, so that the accuracy of the internal phase and amplitude control of the microwave module can be improved.

• - Erzeugen von elektromagnetischer Strahlung durch das Mikrowellenmodul, wobei die erzeugte elektromagnetische Strahlung durch eine elektromagnetische Welle definiert ist, die eine Amplitude und eine Phase umfasst,
• - Aussenden der erzeugten elektromagnetischen Strahlung über den Mikrowellenausgang des Mikrowellenmoduls,
• - Messen einer vorwärtslaufenden Welle der ausgesandten elektromagnetischen Strahlung mittels einer zum Mikrowellenmodul externen Messvorrichtung, und
• - Regeln der Amplitude und/oder der Phase der erzeugten elektromagnetischen Strahlung mittels einer zum Mikrowellenmodul externen Steuer- und/oder Auswerteeinheit, die mit dem Regelkreis signalübertragend verbunden ist, sodass die vom Mikrowellenmodul erzeugte elektromagnetische Strahlung hinsichtlich Amplitude und Phase stabil ist.

The object is achieved according to the invention by a method for calibrating a microwave module for a cooking appliance, the microwave module having a microwave output and a control loop. The procedure consists of the following steps:

• Generating electromagnetic radiation by the microwave module, the electromagnetic radiation generated being defined by an electromagnetic wave comprising an amplitude and a phase,
• - Sending the generated electromagnetic radiation via the microwave output of the microwave module,
• Measuring a forward wave of the emitted electromagnetic radiation by means of a measuring device external to the microwave module, and
• - Regulation of the amplitude and / or the phase of the electromagnetic radiation generated by means of a control and / or evaluation unit external to the microwave module, which is connected to the control circuit in a signal-transmitting manner, so that the electromagnetic radiation generated by the microwave module is stable in terms of amplitude and phase.

The basic idea of the invention is that the amplitude and the phase of the electromagnetic radiation emitted by the microwave module, i.e. the microwaves, are kept constant during the calibration process by providing an external control in addition to the internal control loop of the microwave module and intervening accordingly to adjust the amplitude or to stabilize the phase of the electromagnetic radiation generated by the microwave module. This ensures that the microwave module can be calibrated more precisely, so that a more precise measurement of the amplitude for the internal regulation is possible later, which ultimately leads to a more precise internal regulation of the microwave module.

In the calibration process of the microwave module, the external measuring device and the external control and / or evaluation unit are provided, which interact with the microwave module to measure and evaluate the electromagnetic radiation emitted by the microwave module and also to regulate the microwave module in this way using the correspondingly designed external control circuit that the phase and the amplitude of the generated and emitted electromagnetic radiation are constant. In other words, the external regulation stabilizes the phase and the amplitude of the electromagnetic radiation generated and emitted by the microwave module.

The external control adjusts, for example, the power of an amplifier of the microwave module during the calibration process.

One aspect provides that a calibration standard is connected during at least one calibration step. In particular, the calibration standard is connected to an output of the external measuring device, which is connected to the microwave output of the microwave module via its input. The result is a measuring section that is completed by the calibration standard. The calibration standard represents a complex load (impedance) that has an influence on the reflection properties.

Based on the connected calibration standard, different measured values are thus obtained, which can be used to calibrate the microwave module.

In particular, three different calibration standards are connected one after the other, for example in three consecutive calibration steps. The three calibration standards are, for example, an open calibration standard (“Open”), a short-circuit calibration standard (“Short”) and a load calibration standard (“Load”). Accordingly, the calibration process is a so-called OSL calibration process in which three different calibration standards are used.

With the open calibration standard ("Open"), the measuring line is defined as open, that is, connected to "nothing". An open end of the line causes total reflection of the transmitted signal. A more precise open calibration standard ("Open") can be implemented for a small frequency range from a short-circuit calibration standard ("Short") and a piece of line that is 90 ° in length at the calibration frequency.

With the short-circuit calibration standard, the measuring line is connected to the cable shielding (ground) in a defined manner, i.e. short-circuited. A short-circuited line end also causes total reflection of the transmitted signal, but the phase of the signal is rotated by 180 ° compared to the open calibration standard.

With the load calibration standard ("Load"), the measuring line is terminated with a defined line impedance.

In principle, measurements are carried out by the external measuring device during each calibration step, ie with the calibration standard connected in each case, in order to externally regulate or stabilize the microwave module with regard to the phase and amplitude of the transmitted microwaves.

Another aspect provides that amplitude values of a forward wave and a backward wave of the generated electromagnetic radiation are measured by means of an internal directional coupler of the microwave module. In this respect, internal measurements of the amplitude values of the forward and backward traveling electromagnetic waves take place during the calibration process of the microwave module Control of the microwave module can be used. The internal directional coupler of the microwave module is used for these measurements. The internal directional coupler decouples the respective electromagnetic waves separately from one another, whose measured values, i.e. their amplitude values, are used by the internal control circuit of the microwave module in order to ensure the internal regulation.

As explained at the beginning, the directional coupler can be used to ensure the separation of the two directions of the electromagnetic waves, so that the parameters of the output power, i.e. the forward waves, and the power fed back, i.e. the backward waves, can be measured separately via the directional coupler. These measurements are carried out for each calibration standard so that corresponding measured values are available for the forward-running wave and the backward-running wave for each connected calibration standard.

The corresponding measured values for the connected calibration standards, i.e. the measured amplitude values, are recorded and used to calibrate the microwave module. The external control during the respective calibration steps, in which a corresponding calibration standard is connected, ensures that the amplitude and phase are stable during the measurements of the amplitude values of the forward-moving wave and the backward-moving wave.

In particular, the measured amplitude values, that is to say the measured values of the internal directional coupler, are used to determine calibration coefficients for the microwave module, by means of which parasitic effects of the directional coupler of the microwave module are compensated. The parasitic effects of the internal directional coupler limit its directivity, which in turn leads to inaccurate measurements during operation of the microwave module, as a result of which the accuracy of the internal phase or amplitude control is impaired.

Corresponding calibration coefficients can be determined via the measured amplitude values during the calibration process, which eliminate these parasitic effects, whereby the accuracy of the measurement via the internal directional coupler and thus also the accuracy of the internal amplitude or phase control can be increased.

The calibration coefficients can be stored in a memory. This ensures that the microwave module is appropriately calibrated for use, since the microwave module, in particular a controller of the microwave module, can access the stored calibration coefficients during operation of the microwave module. In particular, the measured amplitude values are corrected by means of the calibration coefficients in order to eliminate the parasitic effects.

Internal control via the internal control loop does not take place during the calibration process. In other words, the internal regulation is switched off during the calibration process of the microwave module. This means that the microwaves are stabilized during the measurement of the calibration standards exclusively via the external control.

In addition, the object is achieved according to the invention by a calibration system which comprises a measuring device, a control and / or evaluation unit and a microwave module for a cooking appliance. The microwave module has a microwave output and a control loop. The measuring device is assigned to the microwave output. The control and / or evaluation unit is connected to the measuring device and the microwave module, in particular the control loop. The control and / or evaluation unit is set up to stabilize electromagnetic waves generated by the microwave module with regard to amplitude and / or phase.

The microwave module of the calibration system is accordingly the microwave module to be calibrated. The measuring device and the control and / or evaluation unit are designed separately from the microwave module, so that they are connected to the microwave module for the calibration process, which can be carried out with the calibration system.

The control and / or evaluation unit receives measurement results from the measuring device for the forward wave of the electromagnetic radiation emitted by the microwave module. These measurement results are evaluated by the control and / or evaluation unit, the control and / or evaluation unit activating the control loop of the microwave module.

In this respect, the external regulation of the microwave module is obtained via the measuring device and the control and / or evaluation unit.

The calibration system is accordingly set up to carry out the previously described method for calibrating the microwave module.

One aspect provides that the measuring device comprises a directional measuring coupler which has a measuring output. The measurement output is coupled in particular to the control and / or evaluation unit, so that the measurement output present signals are transmitted to the control and / or evaluation unit, which have been previously decoupled.

The directional measuring coupler has a high level of directivity, which is greater than 35 dB, for example. This ensures that the directional measuring coupler can measure the forward electromagnetic wave of the electromagnetic radiation emitted by the microwave module with corresponding accuracy, in particular can separate it from the reverse electromagnetic wave.

In other words, the measurement output is set up to decouple forward-moving waves. The measurement output of the directional measurement coupler, which is coupled to the control and / or evaluation unit, thus at least partially forwards the electromagnetic signals (microwaves) emitted by the microwave module. The corresponding part (fraction of the transmitted power) that is passed on depends on the coupling factor, which is typically -10 dB. The measurement output of the directional coupler can therefore also be referred to as a “coupled port”.

Another aspect provides that the measurement output is connected to a power sensor for amplitude measurement and / or a phase sensor for phase measurement. The amplitude of the forward-traveling wave of the emitted electromagnetic radiation can be measured via the power sensor, in particular of the decoupled part of the forward-traveling wave. The phase of the forward wave of the emitted electromagnetic radiation can be measured via the phase sensor, in particular of the decoupled part of the forward wave. In this respect, the electromagnetic wave of the transmitted microwaves can be characterized accordingly in order to implement an external control accordingly.

The power sensor and / or the phase sensor are or is connected to the control and / or evaluation unit, so that the amplitude or phase information obtained in this way can be forwarded to the control and / or evaluation unit.

The control and / or evaluation unit can in turn determine the calibration coefficients for the microwave module and / or correction values and transmit them to the microwave module. This can be used for external control.

In principle, the phase sensor can be synchronized with the microwave module. This ensures that the microwave module provides a reference for the phase measurement.

Furthermore, the object is achieved according to the invention by a microwave module for a cooking appliance, the microwave module comprising an amplifier and a microwave output. The microwave module also has a directional coupler assigned to the microwave output and a control loop that includes a controller and a controlled system in which the amplifier is provided. The controller is set up to compensate for parasitic effects of the directional coupler. In this respect, the microwave module is a calibrated microwave module that has been calibrated in accordance with the aforementioned method or with the aforementioned calibration system. This ensures that the parasitic effects of the internal directional coupler of the microwave module can be compensated for. The microwave module has accordingly been stabilized externally during the calibration process, in particular the amplitude and / or the phase of the electromagnetic radiation emitted during the calibration process, as a result of which the calibration of the microwave module has been possible correspondingly more precisely.

One aspect provides that a memory is provided in which calibration coefficients are stored that compensate for the parasitic effects of the directional coupler. The microwave module, in particular the controller, can access the calibration coefficients during operation of the microwave module, which ensures that measurement inaccuracies due to the parasitic effects that cannot be avoided are compensated or eliminated. In particular, the measured values of the internal regulation that are affected by the measurement inaccuracies are processed with the stored calibration coefficients in order to eliminate the measurement inaccuracies that occur due to the parasitic effects.

In principle, the microwave module can have a microwave input and / or an antenna which is connected to the microwave output in a signal-transmitting manner, and / or a circulator which is provided between the amplifier and the directional coupler within the controlled system. For example, microwaves are fed to the microwave module via the microwave input, in particular from a microwave source or a microwave generator, that is to say a semiconductor component. This is particularly important if more than one microwave module should be installed in a cooking appliance.

The antenna is used to transmit the electromagnetic radiation available at the microwave output, in particular into a cooking space of the cooking device, provided the microwave module is built into the cooking device. Using the circulator, it is also possible that backward-running waves do not run in the direction of the amplifier, which could damage it.

In addition, the microwave module can comprise a modulator and a demodulator and / or a digital-to-analog converter and an analog-to-digital converter. The modulator and / or the digital-to-analog converter are or is provided within the controlled system. The electromagnetic signals can be modulated or demodulated accordingly via the modulator and demodulator. The respective converters are used to digitize the analog signals so that their processing is simplified.

In addition, the object is achieved according to the invention by a cooking appliance with a cooking space and at least one microwave module of the aforementioned type, the at least one microwave module being assigned to the cooking space. The calibrated microwave module ensures that an exact measurement at the output of the microwave module and thus an exact internal regulation of the phase or amplitude values of the emitted electromagnetic radiation is possible.

In particular, the cooking appliance has a microwave generator and / or several microwave modules. The microwave generator can be a semiconductor component which provides the at least one microwave module with microwaves that are processed and emitted by the microwave module.

In addition, the plurality of microwave modules can each have a microwave input via which the microwave modules are connected in a signal-transmitting manner to the one microwave generator. In this respect, it is ensured that the microwave modules are provided with synchronized microwaves, since the different microwave modules are supplied with microwaves from the same microwave generator.

The individual activation of the microwave modules, that is to say the setting of the amplitude or phase of the emitted electromagnetic radiation, takes place, for example, via the respective modulator of the microwave module.

The respective modulator can therefore be set up to carry out amplitude and / or phase modulation.

In principle, the multiple microwave modules can also be connected to multiple microwave sources or microwave generators, in particular wherein the multiple microwave sources or microwave generators are synchronized with one another.

• - 1 eine schematische Darstellung eines erfindungsgemäßen Gargeräts,
• - 2 eine Darstellung eines erfindungsgemäßen Mikrowellenmoduls,
• - 3 eine schematische Darstellung der im Richtkoppler laufenden elektromagnetischen Wellen und deren Koppelungen mit den Anschlüssen des Richtkopplers, und
• - 4 eine schematische Darstellung eines erfindungsgemäßen Kalibriersystem, mit dem ein erfindungsgemäßes Verfahren zum Kalibrieren eines Mikrowellenmoduls durchgeführt werden kann.

Further advantages and properties of the invention emerge from the following description and the drawings, to which reference is made. In the drawings show:

• - 1 a schematic representation of a cooking device according to the invention,
• - 2 a representation of a microwave module according to the invention,
• - 3 a schematic representation of the electromagnetic waves running in the directional coupler and their coupling with the connections of the directional coupler, and
• - 4th a schematic representation of a calibration system according to the invention, with which a method according to the invention for calibrating a microwave module can be carried out.

In 1 is a cooking appliance 10 shown that a housing 12th having. The case 12th surrounds a cooking space 14th in which a food to be cooked 16 is arranged, as well as a technical room 18th , in the technical parts or components of the cooking appliance 10 are housed.

The cooking appliance also includes 10 in the embodiment shown, four microwave modules 20th each of the cooking space 14th assigned and in 1 are only shown schematically.

The microwave modules 20th are with a single microwave generator 22nd connected, which is designed for example as a resonance oscillator. In other words, it is the microwave generator 22nd a semiconductor component (SSD technology) that serves as a microwave source.

The microwave modules 20th therefore each have a microwave input 24 via which the respective microwave module 20th with the microwave generator 22nd is coupled so that the multiple microwave modules 20th Receive synchronized electromagnetic signals (microwaves) from the same source.

In addition, the microwave modules include 20th one microwave output each 26th , which in the embodiment shown with an antenna 28 is connected, via which the corresponding microwave module 20th generated electromagnetic radiation into the cooking space 14th can be sent out. The antenna 28 is for this purpose with the microwave output 26th of the respective microwave module 20th connected to transmit signals, so that the generated microwaves from the microwave output 26th to the respective antenna 28 can be transferred.

In 2 is one of the microwave modules 20th shown in more detail.

The microwave module 20th has, as already explained, the microwave input 24 over which the microwave module 20th Microwaves from the microwave generator 22nd receives.

In addition, the microwave module 20th in the embodiment shown, a digital-to-analog converter 30th as well as a modulator 32 on.

About the modulator 32 can be used via the microwave input 24 modulate received microwaves accordingly, as will be explained below. To that extent is the modulator 32 to the microwave input 24 subsequently provided.

The modulator 32 is also with an amplifier 34 connected to transmit the signal, the from the modulator 32 modulated microwaves are received and amplified before they pass through the microwave output 26th with which the amplifier 34 is also connected to transmit signals, and the antenna connected to it 28 be sent out.

Between the amplifier 34 and the microwave output 26th is also a directional coupler 36 provided, which is therefore the microwave output 26th assigned.

Via the directional coupler 36 Forward electromagnetic waves and reverse electromagnetic waves can be decoupled separately from each other in order to use them for an internal control loop 38 of the microwave module 20th to use.

The internal control loop 38 includes, among other things, a regulator 40 as well as a controlled system 42 , which will be discussed below.

The directional coupler 36 is set up to transmit a forward traveling electromagnetic wave that is in 2 is denoted by M3, and a reverse electromagnetic wave to be coupled out, which in 2 is denoted by M4.

It also includes the microwave module 20th a demodulator 44 and an analog-to-digital converter 46 , each between the directional coupler 36 and the controller 40 are arranged so that the directional coupler 36 decoupled electromagnetic waves M3 , M4 can be demodulated and digitized, creating measured values M3 , M4 available to the controller 40 for further processing, in particular for regulation.

Due to the directional coupler 36 decoupled electromagnetic waves or the assigned measured values M3 , M4 can the controller 40 based on the received setpoints “setpoint” for the electromagnetic radiation, determine the corresponding setpoints “control” that are sent to the modulator 32 transmitted to the via the signal input 24 to modulate received microwaves accordingly.

These manipulated values "Stell" are initially from the digital-to-analog converter 30th converted before this to the modulator 32 be transmitted.

In other words, the controlled system extends 42 accordingly from the modulator 32 to the directional coupler 36 .

In addition, the microwave module 20th include a circulator, not shown, between the amplifier 34 and the directional coupler 36 within the controlled system 42 is provided. The circulator ensures that reflected or backward traveling electromagnetic waves do not enter the amplifier 34 be able to walk.

The regulator 40 is in particular part of a micro-controller that also has a memory 48 may include, in which previously determined calibration coefficients are stored, to which the microwave module 20th accesses, especially the controller 40 to avoid parasitic effects of the directional coupler 36 to compensate, provided the microwave module 20th has been calibrated as follows using the 4th will be explained.

The parasitic effects of the directional coupler 36 can be based on the representation of the 3 explain in which the directional coupler 36 as well as the electromagnetic waves processed by it are shown.

The directional coupler 36 has an entrance 50 on that of the amplifier 34 assigned. The entrance 50 is in 3 also shown as connection "1".

In addition, the directional coupler has 36 an exit 52 that the microwave output 26th of the microwave module 20th assigned. The exit 52 is in 3 also shown as connection “2”.

In addition, the directional coupler includes 36 a first decoupling output 54 and a second decoupling output 56 , via which the forward-running waves or backward-running waves can be decoupled accordingly. The first decoupling output 54 is in 3 Shown as connection "3", whereas the second decoupling output 56 in 3 shown as port “4”.

Out 3 it becomes clear that some of the forward waves are at the microwave exit 26th or on the antenna 28 due to the Reflection factor S11 be reflected, what with the adaptation of the microwave module 20th related.

A large part of the backward traveling electromagnetic waves ("rev Pwr") are at the second output 56 on, i.e. connection "4", what about the coupling factor K4 in 3 is shown. However, a small part of the electromagnetic waves traveling backwards is also at the first decoupling output 54 on, i.e. connection "3", what about the coupling factor K3 in 3 is shown. In other words, part of the electromagnetic wave traveling backwards is fed into the first decoupling output 54 , ie the connection "3", where actually only the forward-moving waves should be decoupled.

In an analogous way, it results for the forward traveling electromagnetic waves (“fwd Pwr”) that the majority at the first decoupling output 54 , ie connection "3", and a fraction at the second decoupling output 56 are present, i.e. connection "4". This is due to the coupling factors K1 and K2 in 3 shown.

The parasitic effects of the directional coupler 36 represent the respective fractions at the "wrong" decoupling outputs 54 , 56 are coupled out, which is also referred to as crosstalk compared to the main coupling. The crosstalk can be adjusted accordingly via the coupling factors K2 , K3 describe the forward or reverse electromagnetic waves.

To the parasitic effects of the directional coupler 36 to compensate, the fractions or their coupling factors must therefore K2 , K3 are first determined in order to then be able to determine exactly which power actually represents an outgoing power or a reflected power, with the amplitude values being used in principle instead of the power values, which, however, correlate with one another.

This is done using a calibration process for the microwave module 20th , including a calibration system 58 can be used like this in 4th is shown.

The calibration system 58 includes the microwave module to be calibrated 20th a measuring device 60 , a control and / or evaluation unit 62 as well as a calibration standard set 64 , the three different calibration standards 66 includes, namely an open calibration standard (“Open”), a short-circuit calibration standard (“Short”) and a load calibration standard (“Load”).

The measuring device 60 comprises in the embodiment shown a directional measuring coupler 68 who with his entrance 70 with the microwave output 26th , especially the antenna 28 , is connected to transmit signals.

In addition, the directional coupler has 68 an exit 72 via one of the three calibration standards mentioned above 66 with the directional coupler 68 can be coupled.

In addition, the directional coupler has 68 a measurement output 74 , with the one in the embodiment shown, a power sensor 76 as well as a phase sensor 78 are connected, which in turn with the control and / or evaluation unit 62 are connected to transmit signals, so that the power sensor 76 as well as the phase sensor 78 measured values, ie the amplitude or phase information, to the control and / or evaluation unit 62 can be transmitted.

With the directional coupler 68 it is in particular a directional measuring coupler that is set up via its measuring output 74 Coupling out forward-running waves, i.e. forward-running waves from the microwave module 20th emitted microwaves.

In the embodiment shown, it is the directional measuring coupler 68 a directional coupler with three ports or connections

From the embodiment of the calibration system shown 58 it is also clear that the microwave module 20th with the phase sensor 78 is synchronized. This ensures that the phase information of the microwave module 20th , i.e. the generated microwaves, with the phase sensor 78 are synchronized.

With the calibration system 58 , a method for calibrating the microwave module 20th by following the steps below.

In a first step S1 is electromagnetic radiation through the microwave module 20th generated, wherein the generated electromagnetic radiation is defined by an electromagnetic wave comprising an amplitude and a phase. The amplitude or phase of the electromagnetic wave can be controlled accordingly, in particular via the modulator 32 and / or the amplifier 34 .

In a second step S2 , the generated electromagnetic radiation, i.e. microwaves, is transmitted via the microwave output 26th , especially the antenna 28 , of the microwave module 20th sent out. The emitted microwaves run through the entrance 70 in the directional coupler 68 , to which via the measurement output 74 the corresponding forward Wave of the emitted electromagnetic radiation is decoupled.

In a third step S3 , the forward wave of the emitted electromagnetic radiation becomes the microwave module by means of the 20th external measuring device 60 measured, so the power sensor 76 and the phase sensor 78 that with the measurement output 74 are coupled. About the power sensor 76 becomes the amplitude of the forward wave and across the phase sensor 78 the phase of the forward wave is measured.

In a fourth step S4 the amplitude and the phase of the generated electromagnetic radiation are transmitted to the external control and / or evaluation unit 62 transmitted, which evaluates the corresponding information.

In a fifth step S5 regulates the control and / or evaluation unit 62 the amplitude and / or the phase of the electromagnetic radiation generated by the microwave module 20th so that the microwave module 20th generated electromagnetic radiation is stable in terms of amplitude and phase.

This takes place in each case for the different calibration standards 66 instead of that in corresponding calibration steps with the output 72 of the directional coupler 68 get connected.

In this respect, in all three calibration steps, i.e. the three different calibration standards 66 , the amplitude and the phase of the electromagnetic radiation generated via the measuring device 60 and the control and / or evaluation unit 62 externally regulated or stabilized.

There is therefore a corresponding calibration standard during each calibration step 66 to the exit 72 the external measuring device 60 , especially the directional coupler 68 connected. An OSL calibration procedure is carried out accordingly.

With the calibration standards 66 it is a matter of complex loads (impedances) that can be defined using an absolute value and a phase value. The load calibration standard ("Load") is assumed to be ideal, which among other things has no amount, whereas the open calibration standard ("Open") and the short-circuit calibration standard ("Short") have the same amount, but 180 ° Have phase difference from one another. In other words, the open calibration standard and the short-circuit calibration standard each have a reflection coefficient which is phase-shifted by 180 °, which, from a mathematical point of view, results in an opposite sign.

During the individual calibration steps, the forward-running wave and the backward-running wave are checked by means of the (internal) directional coupler 36 of the microwave module 20th decoupled separately from each other to the associated amplitude values as measured values M3 , M4 which are used for the internal regulation. About the measured amplitude values, i.e. the measured values M3 , M4 , can add calibration coefficients for the microwave module 20th be determined, by means of which the parasitic effects of the directional coupler 36 of the microwave module 20th can be compensated.

$$K2=\frac{M{4}_{load}}{Amp}$$

$$K3=\frac{M{3}_{open}-M{3}_{short}}{Amp\ast \left({\Gamma }_{open}-{\Gamma }_{short}\right)}$$

$$K4=\frac{M{4}_{open}-M{4}_{short}}{Amp\ast \left({\Gamma }_{open}-{\Gamma }_{short}\right)}$$

$$Amp=\sqrt{\frac{P_{cal}}{P_{max}}}$$

For this purpose, the calibration coefficients are derived from the measured values M3 , M4 with the correspondingly connected calibration standards 66 determined as follows: $$K1=\frac{\mathrm{M.}{3}_{lOad}}{\mathrm{A.}mp}$$

$$\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}2=\frac{\mathrm{M.}{\mathrm{4th}}_{lOad}}{\mathrm{A.}mp}$$

$$\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}3=\frac{\mathrm{M.}{3}_{Open}-\mathrm{M.}{3}_{sHOrt}}{\mathrm{A.}mp\ast \left({\Gamma }_{Open}-{\Gamma }_{sHOrt}\right)}$$

$$K\mathrm{4th}=\frac{\mathrm{M.}{\mathrm{4th}}_{Open}-\mathrm{M.}{\mathrm{4th}}_{sHOrt}}{\mathrm{A.}mp\ast \left({\Gamma }_{Open}-{\Gamma }_{sHOrt}\right)}$$

$$\mathrm{A.}mp=\sqrt{\frac{{\mathrm{P.}}_{cal}}{{\mathrm{P.}}_{max}}}$$

M3 _load is the measured value M3 with connected load calibration standard ("Load").

M4 _load is the measured value M4 with connected load calibration standard ("Load").

M3 _open is the measured value M3 with an open calibration standard connected ("Open").

M3 _short is the measured value M3 with connected short-circuit calibration standard ("Short").

Γ _open represents the reflection coefficient of the open calibration standard ("Open").

Γ _short represents the reflection coefficient of the short-circuit calibration standard ("Short").

M4 _open is the measured value M4 with an open calibration standard connected ("Open").

M4 _short is the measured value M4 with connected short-circuit calibration standard ("Short").

Pmax represents the maximum output power or the reference value for Amp = 1.

P _cal represents the power at which the respective measurement was carried out.

$$rwdPwr=\frac{M4\ast K1-M3\ast K2}{K1\ast K4-K2\ast K3}$$

$$S11=\frac{M4\ast K1-M3\ast K2}{M3\ast K4-M4\ast K3}$$

Based on the calibration coefficients mentioned above K1 , K2 , K3 , K4 the amplitude or power of the forward-traveling waves ("fwd Pwr") and the amplitude or power of the backward-traveling waves ("rev Pwr") as well as the reflection factor ("S11"), ie the scattering parameters S11 , of the microwave module 20th determine as follows: $$fwd\mathrm{P.}wr=\frac{\mathrm{M.}3\ast K\mathrm{4th}-\mathrm{M.}\mathrm{4th}\ast K3}{K1\ast K\mathrm{4th}-\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}2\ast \mathrm{<figure-callout\; id="3"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}3}$$

$$rwd\mathrm{P.}wr=\frac{\mathrm{M.}\mathrm{4th}\ast K1-\mathrm{M.}3\ast K2}{K1\ast K\mathrm{4th}-\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}2\ast \mathrm{<figure-callout\; id="3"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}3}$$

$$\mathrm{S.}11=\frac{\mathrm{M.}\mathrm{4th}\ast K1-\mathrm{M.}3\ast \mathrm{<figure-callout\; id="2"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}2}{\mathrm{M.}3\ast K\mathrm{4th}-\mathrm{M.}\mathrm{4th}\ast \mathrm{<figure-callout\; id="3"\; label="K"\; filenames="DE102019128204A1\_0009.png,DE102019128204A1\_0010.png"\; state="\{\{state\}\}">K</figure-callout>}3}$$

It should be noted that all measured variables are complex amplitudes and are calculated vectorially.

During the calibration process, internal control takes place via the internal control circuit 38 not held. In other words, the internal regulation is used in the calibration process of the microwave module 20th switched off. This means that the microwaves stabilize during the measurement of the calibration standards 66 takes place exclusively via the external control, i.e. the external control and / or evaluation unit 62 .

The internal control loop 38 , especially the one in the internal control loop 38 intended modulator 32 , is insofar from the external control and / or evaluation unit 62 controlled or activated.

Basically it is with the calibration procedure as well as the calibration system 58 hence it is possible to eliminate the parasitic effects since the above calibration coefficients can be determined.

On the basis of the calibration coefficients, the actually present forward electromagnetic waves and the backward electromagnetic waves as well as the reflection factor can be determined more precisely, in particular the amplitudes or powers of the waves, since the parasitic coupling can be calculated out. This also means that the scattering parameters (S-parameters) can be measured more precisely.

This is important for the internal regulation of the microwave module, since the internal regulation of the phase and amplitude of the generated electromagnetic waves, i.e. the microwaves, can be carried out more precisely due to the more precise determination of the powers. So it leads to the microwave module 20th can be kept more stable with regard to the internal regulation during operation and controlled more precisely.

This is particularly important if there are several microwave modules 20th can be used at the same time, as clearly shown in the cooking appliance 10 according to 1 is shown.

Claims (12)

A method for calibrating a microwave module (20) for a cooking appliance (10), the microwave module (20) having a microwave output (26) and a control circuit (38), with the following steps: - Generating electromagnetic radiation by the microwave module (20), wherein the electromagnetic radiation generated is defined by an electromagnetic wave which comprises an amplitude and a phase, - Sending the generated electromagnetic radiation via the microwave output (26) of the microwave module (20), - measuring a forward wave of the emitted electromagnetic radiation by means of a measuring device (60) external to the microwave module (20), and - Regulation of the amplitude and / or the phase of the generated electromagnetic radiation by means of a control and / or evaluation unit (62) external to the microwave module (20), which is connected to the control loop (38) for signal transmission, so that the generated by the microwave module (20) electromagnetic radiation is stable in terms of amplitude and phase. Procedure according to Claim 1 , characterized in that a calibration standard (66) is connected during at least one calibration step. Procedure according to Claim 1 or 2 , characterized in that amplitude values of a forward wave and a backward wave of the generated electromagnetic radiation are measured by means of an internal directional coupler (36) of the microwave module (20). Procedure according to Claim 3 , characterized in that the measured amplitude values can be used to determine calibration coefficients for the microwave module (20), by means of which parasitic effects of the directional coupler (36) of the microwave module (20) are compensated. Procedure according to Claim 4 , characterized in that the calibration coefficients are stored in a memory (48). Method according to one of the Claims 3 to 5 , characterized in that the measured amplitude values are fed to a controller (40) of the microwave module (20). Calibration system (58) for calibrating a microwave module (20) for a cooking appliance (10), the calibration system (58) having a measuring device (60), a control and / or evaluation unit (62) and a microwave module (20) for a cooking appliance ( 10) includes, wherein the microwave module (20) has a microwave output (26) and a control circuit (38), wherein the measuring device (60) is assigned to the microwave output (26), the control and / or evaluation unit (62) being connected to the measuring device (60) and the microwave module (20), and wherein the control and / or evaluation unit (62) is set up to stabilize electromagnetic waves generated by the microwave module (20) with regard to amplitude and / or phase. Calibration system (58) Claim 7 , characterized in that the measuring device (60) comprises a directional measuring coupler (68) which has a measuring output (74), in particular wherein the measuring output (74) is set up to couple forward waves. Calibration system (58) Claim 7 or 8th , characterized in that the measurement output (74) is connected to a power sensor (76) for amplitude measurement and / or a phase sensor (78) for phase measurement, in particular wherein the power sensor (76) and / or the phase sensor (78) is connected to the control and / or evaluation unit (62) are or is connected. Microwave module (10) for a cooking appliance (10), the microwave module (20) comprising an amplifier (34) and a microwave output (26), the microwave module (20) having a directional coupler (36) assigned to the microwave output (26) and a control loop (38) which comprises a controller (40) and a controlled system (42) in which the amplifier (34) is provided, and wherein the controller (40) is set up to compensate for parasitic effects of the directional coupler (36). Microwave module (20) Claim 10 , characterized in that a memory (48) is provided in which calibration coefficients are stored which compensate for the parasitic effects of the directional coupler (36). Cooking appliance (10) with a cooking space (14) and at least one microwave module (20) Claim 10 or 11 , wherein the at least one microwave module (20) is assigned to the cooking space (14).

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