Calibration of a phase shifter of a microwave module for domestic microwave cooking appliances

Abstract

The invention relates to a method (S41 - S48) for calibrating a phase shifter of a microwave module intended for installation in a household cooking appliance, wherein the method comprises at least the following steps: (i) providing a microwave module to be calibrated with respect to its phase shift and a microwave module already calibrated with respect to its phase shift, the microwave outputs of which are connected to respective inputs of a combiner; (ii) specifying a common target amplitude and a common target frequency for both microwave modules as well as a target phase shift at the calibrated microwave module and a target phase shift at the microwave module to be calibrated; (iii) generating, by means of both microwave modules, a respective microwave signal with the respectively specified target values; (iv) measuring a signal present at the output of the combiner;(v) storing the values of at least the target phase shift and the target frequency specified for the microwave module to be calibrated and / or values derived therefrom, as well as the associated measured value, as data entries of a phase calibration data set; (vi) varying the target phase shift on the microwave module to be calibrated within a third phase group of different target phase shifts, and...;

Description

[0001] The invention relates to a method for calibrating a phase shifter of a microwave module intended for installation in a household cooking appliance. The invention further relates to a calibration setup for implementing this method. The invention also relates to a household microwave cooking appliance in which at least one microwave module calibrated according to the present method is installed.

[0002] DE 10 2019 128 204 B4 discloses a method for calibrating a microwave module for a cooking appliance, wherein the microwave module has a microwave output and a control loop, the method comprising the following steps: generating electromagnetic radiation by the microwave module, wherein the generated electromagnetic radiation is defined by an electromagnetic wave comprising an amplitude and a phase, emitting 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 regulating the amplitude and / or phase of the generated electromagnetic radiation by means of a control and / or evaluation unit external to the microwave module, which is connected to the control loop in a signal-transmitting manner,so that the electromagnetic radiation generated by the microwave module is stable in terms of amplitude and phase.

[0003] EP 3 000 283 B1 discloses an apparatus for processing an object in a cavity by radio frequency radiation emitted by one or more radiating elements configured to emit the RF radiation in response to RF energy applied thereto, the apparatus comprising: an RF energy supply component configured to supply RF energy for application to one or more radiating elements; a memory storing a set of coefficients;and a processor configured to receive feedback in response to the emission of RF radiation by one or more of the radiating elements and to control the application of RF energy to one or more of the radiating elements based on the feedback and the set of coefficients, wherein the set of coefficients is associated with the RF energy delivery component and includes error correction coefficients configured to correct systematic errors in the operation of the RF energy delivery component.;

[0004] WO 2015 / 099651 A1 discloses a method for calibrating a device configured to generate at least one radio frequency (RF) feed in an enclosed cavity. The method comprises: selecting at least one subset of frequencies within a bandwidth of the at least one RF feed; setting an input power for the at least one RF feed for each of the at least one subset of frequencies; operating the at least one RF feed with the input power at each of the subset frequencies; sampling output power data at the at least one RF feed; interpolating the sampled output power data across the bandwidth of the at least one RF feed; and storing the output power data and the interpolated output power across the bandwidth of the at least one RF feed in a lookup table.

[0005] WO 2016 / 144872 A1 discloses a method for calibrating a set of devices, each device comprising an amplifying component and a measuring component that outputs a digital signal indicative of the radio frequency power sensed at the amplifying component, comprising: selecting a frequency from a set of frequencies; selecting a phase value from a set of phase values; selecting a power level from a set of power levels; setting a subset of the set of devices to output a signal of the selected frequency, the selected phase value, and the selected power level; measuring a forward power level and a reverse power level; processing the measurements of the forward and reverse power levels to calibrate the digital signal output from the measuring component of each set of devices; and storing the calibrated digital signal output in non-volatile memory.

[0006] DE 10 2019 128204 B4 discloses a method for calibrating a microwave module for a cooking appliance, wherein the microwave module has a microwave output and a control loop, comprising the following steps: - generating electromagnetic radiation by the microwave module, wherein the generated electromagnetic radiation is defined by an electromagnetic wave comprising an amplitude and a phase, - emitting 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 - regulating the amplitude and / or phase of the generated electromagnetic radiation by means of a control and / or evaluation unit external to the microwave module, which is connected to the control loop for signal transmission,so that the electromagnetic radiation generated by the microwave module is stable in terms of amplitude and phase. Furthermore, a calibration system, a microwave module, and a cooking appliance are described.

[0007] An oven according to EP 3 549 396 B1 comprises a cooking chamber configured to receive a food product and an RF heating system configured to inject RF energy into the cooking chamber using solid-state electronic components. The solid-state electronic components include power amplifier electronics configured to inject a signal into the cooking chamber via a coupling assembly operatively connected to the cooking chamber via a waveguide assembly. An isolation assembly is provided between the coupling assembly and the power amplifier electronics. The power amplifier electronics are controlled based at least in part on an efficiency parameter determined from a forward power value and a reverse power value, each measured after the isolation assembly.

[0008] An oven according to EP 3 593 592 B1 comprises a cooking chamber configured to receive a load and an RF heating system configured to inject RF energy into the cooking chamber using solid-state electronic components. The solid-state electronic components include power amplifier electronics configured to inject a signal into the cooking chamber via an antenna assembly. The power amplifier electronics comprise at least a first power amplifier and a second power amplifier operatively connected to the cooking chamber via a first antenna and a second antenna of the antenna assembly, respectively. The first and second antennas are operatively connected to the respective first and second power amplifiers via a first coupling structure and a second coupling structure, respectively.A directional coupler is provided at a connection section defined for at least one of the first and second coupling structures. The directional coupler is configured to provide a forward wave parameter and a reflected wave parameter to a measurement assembly configured to calculate modified S-parameters at the connection section.

[0009] A microwave generation system according to US 2019 / 080886 A1 comprises a modular architecture that can be configured to deliver output power from less than 1 kilowatt to over 100 kilowatts. The various power levels are achieved by combining the RF outputs of multiple RF power amplifiers in a single structure. The system can be used on any ISM band. Each system component contains a dedicated embedded microcontroller for powerful, real-time control response. The components are connected to a high-speed digital data bus and are controlled and monitored by a control program running on a host computer.

[0010] It is the Aufgabe The present invention aims to at least partially overcome the disadvantages of the prior art and, in particular, to provide a particularly accurate way of calibrating a microwave module of a household microwave cooking appliance.

[0011] This object is achieved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims.

[0012] The object is achieved by a method for calibrating a phase shifter of a microwave module intended for installation in a household cooking appliance, the method comprising at least the following steps: (i) Providing a microwave module to be calibrated with respect to its phase shift and a microwave module already calibrated with respect to its phase shift, the microwave outputs of which are connected to respective inputs of a combiner; (ii) Specifying a common target amplitude and a common target frequency for both microwave modules, as well as a target phase shift on the calibrated microwave module and a target phase shift on the microwave module to be calibrated; (iii) Generating, by means of both microwave modules, a respective microwave signal with the specified target values; (iv) Measuring a signal present at the output of the combiner; (v) Storing the values ​​of at least the target phase shift and the target frequency specified on the microwave module to be calibrated and / or values ​​derived therefrom, as well as the associated measured value, as data entries of a phase calibration data set;(vi) varying the target phase shift on the microwave module to be calibrated within a third phase group of different target phase shifts and repeating steps (iii) to (v) for several, in particular all, target phase shifts of the third phase group.

[0013] This method offers the advantage that the phase shift of the microwave module to be calibrated can be calibrated using a simple measurement setup based on an already phase-calibrated microwave module. Calibrating the phase shift is particularly advantageous if the microwave module to be calibrated is intended for use in a microwave cooking appliance with multiple microwave modules, where a targeted interference pattern is to be generated in the cooking chamber by setting a phase shift between the microwaves radiated into the cooking chamber.

[0014] The household microwave cooking appliance can be a standalone microwave appliance or a combination microwave appliance, e.g., an oven with a microwave function and, if appropriate, a steam treatment function. The household microwave cooking appliance has at least one microwave module. The microwave signals generated by the at least one microwave module are radiated as microwave radiation via one or more antennas or "ports" into a cooking chamber that can be closed by a microwave-tight door. Typically, during microwave operation of the household microwave cooking appliance, a portion of the radiated microwave radiation is fed back into the at least one antenna.

[0015] The microwave module is, in particular, a separately manufactured and independently manageable unit prior to installation in the household microwave oven. At least one antenna can be connected directly or via a microwave signal line to the microwave output of the built-in microwave module. In the present method, however, the microwave output is connected to the measuring system without an antenna, and the microwave output of the measuring system is also antennaless. Consequently, during the calibration method, no microwave radiation is emitted into the room; instead, only conducted microwave signals are generated. This is advantageously particularly simple to implement, error-resistant, and radiation-safe.

[0016] The fact that a common target amplitude and a common target frequency are specified for both microwave modules means that the microwave signal can be adjusted in terms of frequency and amplitude.

[0017] A further development is that the frequency of the microwave signal can be adjusted using a signal generator (e.g., an oscillator, VCO, PLL, synthesizer, resonant circuit, etc.). The signal generator can be supplied with a clock base by means of a clock generator. The clock generator and / or the signal generator can be part of the microwave module, but do not have to be. Thus, the clock generator and / or the signal generator can be components of a separate signal generation module.

[0018] To suppress unwanted frequencies outside a specific frequency band, for example, a bandpass filter can be connected downstream of the signal generator. The bandpass filter can be a component of the microwave module or a signal generation module.

[0019] To increase efficiency, a controlled chopper can be connected downstream of the signal generator, especially downstream of the bandpass filter, if present. The chopper can be a component of the microwave module or a signal generation module.

[0020] A first amplifier ("intermediate amplifier") can be connected downstream of the signal generator. The intermediate amplifier can also be connected downstream of the bandpass filter and / or the chopper, if present. The intermediate amplifier can be a component of the microwave module or a signal generation module. The intermediate amplifier can be a power-controlled amplifier. The power-controlled intermediate amplifier can, in particular, amplify the amplitude or power of the incoming microwave signal by a predetermined factor.

[0021] A controlled phase shifter of the microwave module can be connected downstream of the signal generator. The phase shifter can also be connected downstream of the bandpass filter, the chopper, and / or the repeater, if present. The phase shifter is particularly advantageous for microwave modules that are to be installed in groups of at least two microwave modules in a household microwave oven and are intended to generate a targeted interference pattern in the cooking chamber during operation of the microwave oven.

[0022] A controlled attenuator of the microwave module can be connected downstream of the signal generator. The attenuator can also be connected downstream of the bandpass filter, the chopper, the repeater, and / or the phase shifter, if present. The attenuator can, in particular, reduce the amplitude or power of the incoming microwave signal by a predetermined factor.

[0023] At least one second amplifier ("final amplifier") can be connected downstream of the signal generator, the output of which is, in particular, directly connected to the directional coupling device of the microwave module. The final amplifier can be single- or multi-stage. In particular, the final amplifier can have a single- or multi-stage preamplifier and a main amplifier connected downstream of the preamplifier.

[0024] The controlled components of the microwave module such as the signal generator, the chopper (if not part of a signal generation module), the repeater, the phase shifter, the attenuator, etc. can be controlled by a common control device of the microwave module, e.g. by means of a microcontroller, ASICs, FPGAs, etc.

[0025] It is also possible to connect a frequency meter or spectroscope to a measurement output of the directional coupling device of the measuring system for measuring the amplitude in the forward direction in order to assess the quality of the microwave signal, e.g., its bandwidth. A deviation between the target frequency and the actual frequency can also be measured and corrected by calibration.

[0026] In principle, the target frequency, the target phase shift and the target amplitude can also be varied or permuted within their groups, and then the measured values ​​for corresponding triples or "triple pairs" of three simultaneously set target values ​​can be saved in a calibration data set.In general, the order in which the desired parameters are varied is arbitrary: for example, if the values ​​of the desired frequency, the desired phase shift, and the desired amplitude are varied, first a respective value of the desired frequency and the desired phase shift can be fixed and the values ​​of the desired amplitude can be varied, then a value of the desired phase shift can be changed and for the new pair of values ​​of the desired frequency and desired phase shift, the values ​​of the desired amplitude can be run through again until all values ​​of the desired phase shift have been set, and then a new value of the desired frequency is set, etc. However, all values ​​of the desired phase shift can also be run through analogously for a fixed value of the desired amplitude before the desired amplitude is varied, etc.

[0027] A further development is that, linked to the target values, a temperature, in particular the temperature of a power amplifier, in particular the main amplifier, is also measured and stored in the calibration data set. This offers the advantage that, when setting a target power, the decreasing gain of the main amplifier due to heating can be taken into account, and a temperature dependence of the detectors' power measurement can also be corrected. Alternatively or additionally, the temperature measurement can be used to detect possible impending overheating of the power amplifier, in particular the main amplifier.

[0028] One embodiment includes, in step (vi), additionally varying the target frequency within a third frequency group of different target frequencies, and performing steps (iii) to (v) additionally for several, in particular all, target frequencies of the third frequency group. This also allows frequency-dependent correction coefficients to be obtained from the calibration, which increases the correction accuracy.

[0029] In one embodiment, the target phase shift specified in step (ii) on the calibrated microwave module is 0°, and the target phase shift within the third phase group includes at least the target values ​​0° and 180°. This is particularly advantageous because the sum signal should have a maximum amplitude at 0° and a minimum amplitude at 180°. Actual deviations at these points can be particularly easily converted into correction factors.

[0030] It is an embodiment that correction factors for the operation of the microwave module to be calibrated are calculated from the stored data entries of the phase calibration data set, on the basis of which the phase shifts are adapted to the respective associated target phase shifts.

[0031] The correction factors can generally be obtained, for example, by interpolation and, if necessary, extrapolation of the calibration data sets. The entries in the calibration data sets can serve as support points. The interpolation and extrapolation can be carried out using any suitable calculation method, e.g., by fitting to a polynomial function. In the simplest case, for example, a measured value x is measured at detector 14a, e.g., x = 140 W. In reality, however, a power f(x) = 130 W was transmitted, measured with the much more accurate detector 55a-1. If a linear polynomial function is used, the functional relationship between x and f(x) is the equation f(x) = m x + x 0 with m and x0 being the correction factors. With further measurements at other target powers, the correction factors m and x0 can be determined. Typically, however, the actual value is derived from a multidimensional polynomial function of higher order (e.g.,at least quadratic) order, e.g. according to f(x, y, z) = a + bx + cx 2< +dy + ey 2< + fz + gz 2< + ...) with f(x, y, z) the power measured at the detector 55a-1, x the power measured at the detector 14a, y the set value of the desired frequency, z the set value of the desired phase shift and a, b, c, d, e, f and g correction factors.

[0032] In addition, the relationship between component deterioration over time and stress factors such as power, voltage peaks, and temperature can be known from preliminary aging tests. This aging can also be incorporated / considered in the correction factors.

[0033] In particular, correction factors can be calculated for the following measured values: Amplitude or power of the microwave signal in the forward direction measured at a directional coupling device of the microwave module compared to the actual amplitude or power of the microwave signal in the forward direction measured at the directional coupling device of the measuring system, in particular if a substitute load is connected; amplitude or power of the (reflected) microwave signal in the reverse direction measured at the directional coupling device of the microwave module compared to the actual amplitude or power of the microwave signal in the reverse direction measured at the directional coupling device of the measuring system when measuring with a reflective end termination of the measuring system or amplitude or power of the microwave signal in the reverse direction measured at the directional coupling device of the microwave module compared to the values ​​of the amplitude or power corrected with the correction factors for the substitute load.Power of the microwave signal in the forward direction when measured without the (then disconnected) measuring system.

[0034] These correction factors may depend on frequency, amplitude, temperature, phase shift and / or aging.

[0035] A directional coupling device is a measuring device that taps into a passing microwave signal and provides a very small portion of the passing microwave signal as a measurement signal. In particular, measurement signals dependent on the direction of travel of the microwave signal are provided, i.e., a measurement signal that represents a measure of the power / amplitude of a microwave signal traveling in the forward or transmission direction to the microwave output, and a measurement signal that represents a measure of the power / amplitude of a microwave signal traveling in the reverse or reflection direction from the microwave output.

[0036] The directional coupling device can be, for example, a bidirectional, circulatorless directional coupler or a directional coupling system with a circulator.

[0037] The dummy load, e.g., 50 ohms, serves to absorb or dissipate a forward-flowing microwave signal as completely as possible after it has passed through the two directional coupling devices. Ideally, no portion of the microwave signal would be reflected or recirculated in the reverse direction.

[0038] The "reflective termination" can be an open end ("open") in one form, or a defined short circuit ("short") in another. Both termination types produce total internal reflection and differ only in the phase position of the reflected signal. The equivalent load can also be referred to as a "matched termination."

[0039] For some types of phase shifters, an additional correction factor can be calculated: Specified or set target phase or phase shift (e.g. as control value of the phase shifter) to the actually existing phase shift, e.g. determined by means of the above phase calibration method. This correction factor may depend on the amplitude, frequency, temperature and / or aging.

[0040] For some types of signal generators, e.g. VCO and resonant circuit: Preset or set frequency (e.g. as control value of the signal generator) to the actual frequency of the microwave signal in the forward direction measured by the measuring system. This correction factor may depend on the amplitude, frequency, temperature and / or aging.

[0041] Another possible correction factor may include, for example: the set target amplitude (e.g. as control value of the attenuator) to the actual amplitude measured on the measuring system in the transmitting direction. This correction factor may depend on temperature, frequency, phase and / or aging.

[0042] The object is also achieved by a household microwave cooking appliance, comprising a cooking chamber which can be closed in a microwave-tight manner by means of a door and which can be supplied with microwaves, at least one microwave module which is designed to set at least one amplitude and one frequency of a microwave signal emitted at a microwave output to variable target values, and which has a directional coupling device at least for measuring the amplitude of an emitted microwave signal and a reflected microwave signal;a control device configured to adapt at least one microwave parameter, including the amplitude of the microwave signal transmitted to the at least one antenna, to an associated target value based on correction factors calculated according to at least one of the above methods, wherein the calibration data sets are stored in a non-volatile memory of the household microwave cooking appliance and the correction factors are calculable by means of the microwave module itself, in particular by means of its control device.

[0043] The household microwave cooking appliance can be designed analogously to the above calibration procedures, and vice versa, and provides the same advantages.

[0044] In general, the microwave module can comprise all the components necessary to generate a line-based microwave signal, from the clock generator to the power amplifier. However, for a compact and cost-effective design, it can be advantageous if at least some signal generation components are not installed in a microwave module, but are, for example, installed independently or installed in a dedicated signal generation module that can include the clock generator, the signal generator, the bandpass filter, and / or the chopper. The use of a standalone signal generation module can be particularly advantageous if it generates a microwave signal that can be applied to multiple microwave modules—for example, via a splitter.

[0045] The object is further achieved by a calibration setup for carrying out the method for calibrating the phase shift, comprising a calibrated microwave module, at least one microwave module to be calibrated and a measuring system, wherein - the measuring system comprises a combiner whose inputs are connected to the microwave outputs of the microwave modules and whose output is connected to a detector of the measuring system, and wherein - the detector is connected to a data processing device of the measuring system which can be coupled to control units of the microwave modules for controlling them; and wherein at least a frequency and a phase shift, possibly also an amplitude, of the microwave signal generated thereby can be varied at the microwave modules.

[0046] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of embodiments, which are explained in more detail in connection with the drawings. Fig.1 shows a structure of a semiconductor microwave generation system with a microwave module; Fig.2 shows a variant of a directional coupler of the microwave module from Fig.1 ; Fig.3A shows another variant of a directional coupler of the microwave module from Fig.1 ; Fig.3B shows another variant of a directional coupler of the microwave module from Fig.1 ; Fig.4 shows a structure of a semiconductor microwave generation system with two microwave modules; Fig.5 shows another structure of a semiconductor microwave generation system with two microwave modules; Fig.6 shows a calibration structure not belonging to the invention for calibrating the microwave module from Fig.1 ; Fig.7 shows a Fig.6 shown calibration setup feasible first part of a calibration procedure not belonging to the invention; Fig.8 shows a second part of the calibration procedure not belonging to the invention according to a first variant, which is based on the in Fig.7 shown first part, Fig.9 shows a second part of the calibration process not belonging to the invention according to a second variant, which is based on the Fig.7 shown first part; Fig.10 shows an inventive calibration setup for calibrating the microwave module from Fig.1 ; and Fig.11 shows a Fig.10 shown calibration setup feasible inventive calibration procedure.

[0047] Fig.1 shows a structure of a semiconductor microwave generating section 1 for generating microwave radiation.

[0048] At the beginning of the microwave generation path 1, there is a clock generator 2, such as a quartz oscillator or other frequency source, whose clock signal is fed into a controllable signal generator 3. The clock signal is very frequency-stable and can, for example, have a clock frequency in a range between several hundred kHz and several tens of MHz. A bandwidth is typically a few hertz to several tens of hertz.

[0049] Using the clock signal, signal generator 3 generates a working or microwave signal at a desired microwave frequency with comparatively low power. The microwave frequency generated by signal generator 3 can be adjusted by means of a control device, e.g., a microcontroller 4 (frequency-variable signal generator 3). In particular, microwave signals with a frequency in a frequency range between 2.4 GHz and 2.5 GHz can be generated, but are not fundamentally limited thereto. Signal generator 3 can, for example, be an oscillator, VCO, PLL, synthesizer, resonant circuit, etc.

[0050] A bandpass filter 5—which is optional—is connected downstream of the signal generator 3. This has the advantage of suppressing unintentionally generated unwanted frequencies, e.g., outside an ISM band or outside the adjustable frequency range, e.g., outside the 2.4 GHz to 2.5 GHz band.

[0051] The optional bandpass filter 5 is followed by a controllable chopper 6, which is generally optional. The presence of the chopper 6 offers the advantage of enabling partial power generation with very high efficiency. The microwave generation system 1 can be set to a power level at which it operates with the highest possible efficiency. Partial power generation is achieved with the chopper 6 by switching the microwave signal on and off at specific times, e.g., similar to a PWM control. Desired partial power or full power can be specified using the microcontroller 4.

[0052] The optional chopper is followed by an optional amplifier ("intermediate amplifier") 7. Whether and at which point an intermediate amplifier 7 is required depends on the specific implementation of the microwave generation path 1. For example, an intermediate amplifier 7 can be used if the amplitude of the microwave signal is considered too low at this point in the microwave generation path 1. Multiple intermediate amplifiers 7 can also be distributed along the microwave generation path 1.

[0053] The optional intermediate amplifier 7 is followed by a likewise optional phase shifter 8. However, the phase shifter 8 may be required if a desired interference pattern is to be generated in a cooking chamber 23 of the household microwave cooking appliance 24 using at least two microwave generation paths 1. The magnitude of the phase shift of the incoming microwave signal is controlled via the microcontroller 4, e.g., in steps of 1°, 2°, 5°, or 10° within a range between 0° and 180° or 0° and 360°.

[0054] The optional phase shifter 8 is followed by an amplitude controller in the form of an attenuator 9. The attenuator 9 controls the amplitude of the microwave signal entering the preamplifier 10 and reduces this amplitude, in particular, by an amount or factor adjustable by the microcontroller 4. Instead of the attenuator 9, a controllable amplifier, e.g., a VCA, can also be used as the amplitude controller. Furthermore, the amplitude can be adjusted via a suitable intermediate amplifier 7, for which, for example, its gate voltage is controlled.

[0055] The attenuator 9 is followed by a final amplifier 10, 11 in the form of a series circuit, used here as an example, consisting of another amplifier ("preamplifier") 10 and yet another amplifier ("main amplifier") 11. The preamplifier 10 can be constructed in multiple stages. If at least one intermediate amplifier 7 is present, it is located in the microwave generation path 1 between the signal generator 3 and the final amplifier 10, 11.

[0056] A directional coupling device 12 is connected downstream of the main amplifier 11, to whose measuring outputs 13a and 13b respective detectors 14a and 14b, e.g., voltmeters, are connected. The measuring signals from the detectors 14a, 14b and an optional temperature sensor 15, e.g., arranged on the main amplifier 11, are fed to the microcontroller 4 directly or via an analog-to-digital converter (not shown).

[0057] An antenna 16 is connected to the output of the directional coupling device 12, which converts the microwave signal into microwave radiation and radiates it, e.g. directly into a cooking chamber or into a microwave guide.

[0058] In particular, a measurement signal, in particular a voltage signal, is output at the measurement output 13a, which is a measure of the amplitude and thus the power of the microwave signal traveling to the antenna 16 in the forward or transmission direction. A measurement signal, in particular a voltage signal, is output at the measurement output 13b, which is a measure of the power of the reverse microwave signal coupled in via the antenna 16. These powers can be used, for example, for controlling, in particular regulating, the semiconductor microwave generation path 1.

[0059] In general, the components 2 to 15 described above can be arranged arbitrarily in the household microwave cooking appliance. It is particularly advantageous if at least some of these components 2 to 15 are parts of a microwave module 17 that is prefabricated before installation in the household microwave cooking appliance. For example, components 3 to 15 can be parts of the microwave module 17, as indicated by dashed lines, or components 2 to 15 can be parts of the microwave module 17, as indicated by dotted lines. However, other assignments to one or more modules are also possible, as will be described in more detail below. Typically, in the installed state, the antenna 16 is connected to a (microwave) output 18 of the microwave module 17. Furthermore, two or more of the components 2 to 15 can be functionally replaced by a single component.If, for example, a synthesizer is used as signal generator 3, one or more of components 6, 8, and / or 9 can be omitted, since a synthesizer already incorporates their functions. Many synthesizers available on the market can chop (switch on and off in time) and phase shift. Some can also implement fine-tuned amplitude control.

[0060] Fig.2 shows a variant of a directional coupler 12 in the form of a bidirectional directional coupler 12-1 without a circulator. The measurement outputs 13a, 13b represent only a fraction of the amplitude of the working or microwave signal passed through the directional coupler 12-1. Typical coupling values ​​are in the range of -30 dB. By far the largest portion of the microwave signal arriving from the main amplifier 11 leaves the directional coupler 12-1 toward output 18 or antenna 16.

[0061] Fig.3A shows a variant of the directional coupler 12. A directional coupler 12-2 is used, which has a circulator 19 following the main amplifier 11. The circulator 19 protects the main amplifier 11 from excessively high reflected signals from the cooking chamber. The circulator 19 transmits the microwave signal received by the main amplifier 11 through a one-way directional coupler 20 toward the output 18 or the antenna 16. Signals reflected from the cooking chamber, which flow from the antenna 16 toward the circulator 19, are redirected by the circulator 19 through another one-way directional coupler 21 to a terminating resistor 22.

[0062] Fig.3B shows a variant of the directional coupler 12 in the form of a directional coupler 12-3 with circulator 19, in which, compared to the directional coupler 12-2, the circulator 19 and the one-way directional coupler 20 (with the associated components) are arranged in reverse in the signal path.

[0063] Fig.4 shows a structure of a microwave generation line 31 of a household microwave cooking appliance 32 with two microwave modules 17. Their signal generator 3 is fed from the same clock generator 2, which can be a separate component from both microwave modules 17 or can be integrated into one of the microwave modules 17. The microcontrollers 4 are both controlled by a common control unit 33, for example, to set phase shifts on one or both of the microwave modules 17. By phase shifting the microwave signals of the two microwave modules 17, interference patterns can be specifically generated in the cooking chamber 23.

[0064] The microwave generation path 31 can be continued analogously for more than two microwave modules 17.

[0065] Fig.5 shows a further configuration of a semiconductor microwave generation system 41 of a household microwave cooking appliance 42 with two microwave modules 17 with two microwave modules 43, which are fed with microwave signals from a common signal generation module 44. The microwave modules 43 now only comprise components 7 to 15 each, while components 2, 3, 5, 6 are assigned to the signal generation module 44. The microwave modules 43 further comprise a microcontroller 45 for controlling the associated components 7 to 9 and for evaluating the measurement signals from the directional coupling device 12, while the signal generator 3 and the chopper 6 are controlled by a microcontroller 46. The microcontrollers 45 and 46 are in turn under the control of the common control unit 33.

[0066] The output signals of the signal generation module 44 are split by means of a splitter 47 and forwarded to the inputs of the microwave modules 43.

[0067] The microwave generation path 41 can also be continued analogously for more than two microwave modules 43, as indicated by the dashed line extending from the splitter 47.

[0068] Due to component and installation tolerances of components 2 to 15 and 17 to 22, it may happen that the measured values ​​output by detectors 14a, 14b to microcontrollers 4 and 45, respectively, contain errors, so that, for example, instead of a set target power, target frequency, and / or target phase shift, a deviating microwave signal is output to output 18 or antenna 16. To correct this error, one or more components of semiconductor microwave generation system 1, in particular microwave module 17, can be calibrated, which will be explained in more detail below.

[0069] Fig.6 shows a calibration setup for calibrating a microwave module 17, selected here as an example, with its components 2 to 15 by means of a measuring system 51. The microwave module 17 is connected on the input side to a clock generator 2.

[0070] Connected to its microwave output 18 is now not the antenna 16, but a directional coupling device 52 of the measuring system 51. The directional coupling device 52 can be equipped, analogously to the directional coupling device 12-1, as a bidirectional directional coupler without a circulator or, analogously to the directional coupling device 12-2, with a circulator. The directional coupling device 52 has a higher measurement accuracy / lower error tolerance than the directional coupling device 12. Analogously to the directional coupling device 12, the directional coupling device 52 has a microwave output 53, a measurement output 54a for measuring microwaves traveling in the transmission direction to the microwave output 53, and a measurement output 54b for measuring microwaves reflected back from the microwave output 53.A detector 55a-1 for measuring an amplitude of the measurement signal present at the measurement output 54a and optionally a detector 55a-2 for measuring a frequency of the measurement signal present at the measurement output 54a (e.g., a spectroscope) are connected to the measurement output 54a. A detector 55b for measuring an amplitude of the measurement signal present at the measurement output 54b is connected to the measurement output 54b. The detectors 55a-1, 55a-2, and 55b are connected to a data processing device 56, such as a computer of the measurement system 51, which stores their measured values ​​and / or values ​​derived therefrom. In principle, the detector 55a-2 can be dispensed with, and the frequency, with a sufficiently high sampling rate, can also be determined from the amplitude measured values ​​of the detector 55a-1.

[0071] In a further development, the data processing device 56 calculates correction factors from stored values, which are designed to correct systematic errors in the functioning of the microwave module 17, in particular when the microwave module 17 is installed in a household microwave cooking appliance. The correction factors can also be referred to as calibration factors, calibration coefficients, error correction coefficients, etc. For this purpose, the correction factors can be transferred, for example, to a non-volatile memory of the microwave module 17 (e.g., an EEPROM) that can be accessed by the microcontroller 4, 45 or that is integrated into the microcontroller 4, 45. Alternatively, the measurement data are transferred to a non-volatile memory of the microwave module 17 that can be accessed by the microcontroller 4, 45 or that is integrated into the microcontroller 4, 45, and the correction factors are calculated from this basis by the microcontroller 4, 45 itself.

[0072] The microwave output 53 can be provided with various interchangeable attachments, e.g. a dummy load 57, e.g. of 50 ohms, or an attachment ("calibration attachment") 58 which provides a reflective end termination at the microwave output 53, at which microwave signals sent in the transmission direction by the directional coupling device 52 to the microwave output 53 are practically completely reflected back.

[0073] The measurement section of the measuring system 51 and any connecting cables to the detectors 55a-1, 55a-2, and 55b have advantageously been measured using a precise network analyzer or similar device to obtain the actual, generally frequency-dependent correction values ​​of the calibration setup itself. This can also be expressed as the fact that the measuring system itself is already calibrated (pre-calibrated).

[0074] Fig.7 shows one based on the Fig.6 illustrated calibration setup, the first part of a calibration procedure for calibrating at least the power output of the microwave module 17.

[0075] For this purpose, in step S1, the microwave output 18 of the microwave module 17 is connected to the input of the directional coupling device 52 of the measuring system 51. For example, the attachment representing a substitute load 57 is initially connected to the microwave output 53 of the measuring system 51. The data processing device 56 directly controls the individual controllable components 3 and 6-9 of the microwave module 17 via the microcontroller 4. The control of the microcontroller 4 is thus deactivated. Furthermore, an input of the signal generator 3 is connected to an output of a clock generator 2.

[0076] In a step S2, the data processing device 56 sets initial values ​​for a target frequency, target amplitude, and target phase shift. For example: the target frequency can be varied in a range [2.4; 2.5] GHz, e.g. in steps of 0.01 GHz or 10 MHz; e.g. by means of the signal generator 3. The corresponding desired target frequencies or those set from this range form a first frequency group; the target power can be varied in a range [120; 300] W, e.g. in steps of 60 W, for example by means of the attenuator 9. The corresponding desired target powers or those set from this range or, analogously, target amplitudes form a first amplitude group; the target phase shift can be varied in a range [0; 360] °, e.g. in steps of 10 °, namely by means of the phase shifter 8. The corresponding desired target phase shifts or those set from this range form a first phase shift group.

[0077] In the following, it is assumed, for example, that the initial target frequency corresponds to the lowest frequency value from the first amplitude group, the initial target power corresponds to the lowest amplitude value from the first amplitude group and the initial target phase shift corresponds to the value 0°.

[0078] In a step S3, the microwave module 17 is now activated with the specified values ​​for the target frequency, target amplitude, and target phase shift. In this case, the signal generator 3 generates an operating or microwave signal which has the specified nominal target frequency and is subsequently filtered in the bandpass filter 5. The filtered microwave signal is chopped in the chopper 6 and amplified for the first time by the intermediate amplifier 7. The microwave signal is then phase-shifted by the phase shifter 8 by the specified target phase shift, e.g., within a range [0°; 360°]. The microwave signal is then either passed unattenuated through the attenuator 9 or attenuated by the attenuator 9 to a desired amplitude level. The attenuated microwave signal is then amplified first by the preamplifier 10 and then by the main amplifier 11 to the desired target power orTarget amplitude amplified, which should be present at the microwave output 18.

[0079] In a sub-step S3a, the microwave signal output by the main amplifier 11 is passed through the directional coupling device 12. A very small portion of the microwave signal is coupled out as a measurement signal to the measurement output 13a by the directional coupling device 12 and measured in a step S4 by the detector 14a. The measurement signal can be present, for example, as a voltage signal and is representative of the amplitude of the microwave signal output by the main amplifier 11 and thus also of its power. Any conversion from voltage to amplitude or power can be performed, for example, using a data set provided by the manufacturer of the directional coupling device 12. It should be noted that these conversion data may also be subject to tolerances or errors.

[0080] From the microwave output 18, the microwave signal travels in a sub-step S3b through the directional coupling device 52 of the measuring system 51 to the microwave output 52 of the measuring system 53 and is then at least largely absorbed in the equivalent load 57. A small portion of the microwave signal conducted to the equivalent load 53 is coupled out of the directional coupling device 52 to the measuring connection 54a and measured in step S5 at the detector 55a-1 with respect to its amplitude / power and optionally at the detector 55a-2 with respect to its frequency, bandwidth, etc.

[0081] A portion of the microwave signal reflected back from the microwave output 52 is measured in step S4 or step S5 in a fundamentally analogous manner with regard to its amplitude / power at the detector 13b and at the detector 55b.

[0082] Therefore, at least values ​​are available for: target frequency, target amplitude / power, target phase shift, amplitude of the microwave signal in the transmission direction measured at detector 13a, amplitude of the reflected microwave signal measured at detector 13b, amplitude of the microwave signal in the transmission direction measured at detector 55a-1 and amplitude of the reflected microwave signal measured at detector 55b.

[0083] In step S6, the measured values ​​(e.g. voltage values, amplitude, frequency, phase shift) and / or values ​​derived therefrom (e.g. power) are stored together with the specified target values ​​as data entries of a calibration data set.

[0084] The sequence of steps S3 to S6 is then repeated with variation, in particular stepwise incrementation, of the target values ​​until corresponding data entries are available in the calibration data set for all desired permutations of the target values.

[0085] This can be implemented, for example, as shown, by first checking in step S7 whether the highest value of the microwave frequency is set.

[0086] If this is not the case ("N"), the current value is changed to the next higher value in step S8, e.g., increased by one step, and the system branches back to step S3. The variation of the frequency can also be referred to as a "frequency sweep."

[0087] However, if this is the case ("Yes"), the quality of the microwave signal (actual frequency, measured frequency, bandwidth, harmonics, etc.) can optionally be evaluated in step S9 from the measurement signals measured by detector 55a-2. For this purpose, it is advantageous if the amplitude still corresponds to the initial, lowest amplitude, but is generally at least rather low.

[0088] Following step S8 or S9, in step S10, the frequency value is first reset to its lowest value. Then, in step S10, the system checks whether the highest amplitude / power value is set. If this is not the case ("N"), the current amplitude / power value is changed to the next higher value in step S11, e.g., increased by one step, and returns to step S3. The variation of the amplitude can also be referred to as an "amplitude sweep."

[0089] However, if step S10 is answered affirmatively ("Yes"), the amplitude value is first reset to its lowest value in step S12 and then a query is made as to whether the highest phase shift value has been set. If this is not the case ("No"), the current phase shift value is changed to the next higher value in step S13, e.g., increased by one step size, and the system branches back to step S3. The variation of the phase shift can also be referred to as a "phase sweep."

[0090] If step S12 is answered positively, a calibration data set is available containing the measured amplitudes / powers as a function of the varied or "swept" setpoints. Optionally, the temperature T measured by the temperature sensor 15 can also be stored.

[0091] Of course, one or more setpoints can also be decremented starting from a highest value or set in any other order.

[0092] A calibration data set available after step S12 for a microwave output 53 equipped with the dummy load 57 could therefore, for example, look as follows if the target frequency f soll is incremented from 2400 MHz to 2500 MHz in steps of 50 MHz, the target phase shift φ soll is incremented from 0° to 240° in steps of 120°, and the target amplitude / power P soll is decremented from 300 W to 120 W in steps of 60 W: f [MHz] φ soll [°] P soll [W] T [°C] P14a [dBm] P 14b [dBm] P 55a-1 [dBm] P 55b [dBm] 2400 0 300 45 54,5 34,5 54,2 24,2 2450 0 300 48 55,0 35,0 54,7 24,7 2500 0 300 50 54,3 34,3 54,0 24,0 2400 120 300 51 54,0 34,0 53,7 23,7 2450 120 300 52 54,5 34,5 54,2 24,2 2500 120 300 53 53,8 33,8 53,5 23,5 2400 240 300 53 54,2 34,2 53,9 23,9 2450 240 300 54 54,7 34,7 54,4 24,4 2500 240 300 54 54,0 34,0 53,7 23,7 2400 0 240 54 53,8 33,8 53,4 23,4 2450 0 240 55 54,2 34,2 53,8 23,8 2500 0 240 55 53,6 33,6 53,2 23,2 2400 120 240 55 53,4 33,4 53,0 23,0 2450 120 240 55 53,8 33,8 53,4 23,4 2500 120 240 56 53,3 33,3 52,9 22,9 ⋮ 2500 240 120 ... ... ... ... ...

[0093] This data set enables exact detection of the transmitted amplitude of the microwave module 17 by means of the integrated detector 14a.

[0094] In addition to the first part of the calibration procedure, a second part is carried out, which is described in more detail below.

[0095] Fig.8 shows a second part of the calibration procedure according to a first variant, which, as shown, is based on the Fig.7 can follow the first part shown, but can in principle also be carried out before the first part.

[0096] Following the first part, the calibration attachment is now changed in a step S14, namely from the equivalent load 57 to a calibration attachment which acts like a reflective end closure and therefore ideally totally reflects incident waves.

[0097] In a step S15, the data processing device 56 again sets initial values ​​for the target frequency and the target amplitude, in particular analogously to step S2. However, the limits of the adjustable value ranges and / or the step sizes may differ from the case with the substitute load 57. For example, it may be the case that the higher amplitudes set when using the substitute load 57 are so high that they could lead to damage to the main amplifier in the event of backreflection in the event of an open or short-circuited end. Therefore, in the second part of the calibration process, lower target powers are set which are at most as high as the reflected amplitude that the main amplifier 11 can withstand. For example, the target power can only be varied within a range of [120; 180] W, e.g., in steps of 30 W or 60 W. Consequently, the corresponding desired target powers or those set from this range form the target powers.Analogously, target amplitudes define a second amplitude group that differs from the first amplitude group. The second frequency group can also differ from the first frequency group or the second phase group, but this is not required.

[0098] In the following, for the second part, it is assumed, as an example, that the initial target frequency corresponds to the lowest frequency value from the second frequency group and the initial target power corresponds to the highest amplitude value from the second amplitude group.

[0099] Furthermore, in step S15, the phase shift is set, for example, to a fixed value, in particular 0°, and is not further varied in the second part.

[0100] Steps S16 to S23 are carried out analogously to steps S3 to S8 and S10 to S11 (i.e. step S9 of the quality check of the microwave signal is not carried out again), whereby the measured values ​​or values ​​derived therefrom are stored as data entries of a further calibration data set.

[0101] A further calibration data set available after a positive answer to step S22 for a microwave output 53 equipped with the calibration attachment 58 could then, for example, include values ​​of the powers P 14a , P 14b , P 55a-1 and P 55b as well as the temperature T for the target frequency f soll incremented from 2400 MHz to 2500 MHz in steps of 50 MHz and the target amplitude / power P soll decremented from 180 W to 120 W in steps of 30 W. In contrast to the calibration data set created with the equivalent load 57, the amplitude and power values ​​P 14b and P 55b measured at the detectors 14b and 55b for the reflected microwave signal are now significantly higher due to the total internal reflection.

[0102] Subsequently, in a step S24, the microwave module 17 is switched off.

[0103] For the subsequent step S25, there are, among other things, two possibilities: In a first variant, correction coefficients are calculated from the calibration data sets by means of the data processing device 56. These correction coefficients are intended to calibrate the operation of the microwave module 17, in particular based on the measured values ​​output by the detectors 14a and 14b, in order to output microwave signals at the microwave output 18 whose amplitude, frequency, and / or phase correspond as precisely as possible to the set target values. In particular, it is possible to correlate or assign the measured values ​​output by the detectors 14a and 14b with high accuracy to the values ​​of the amplitude / power emitted in the transmission direction and the reflected amplitude / power actually present at the microwave output 18.

[0104] The correction coefficients can be calculated from the entries in the calibration data sets, for example, by a function fit with the entries as reference points, for example, by calculating polynomial functions of any order greater than one, i.e., they can be approximated using linear, quadratic, etc. polynomials. This allows, for example, interpolation to assign correction coefficients to sets of target values ​​that have not been directly set. Furthermore, it is possible to extrapolate the entries in the calibration data sets to sets of correction coefficients that lie outside the range of one or more set target values.For example, it may be the case that the calibration data set for the calibration attachment 58 serving as the reflective end termination lacks some measurement points for the target amplitude that are higher than the maximum target amplitude permitted by the main amplifier 11, but less than or equal to the maximum adjustable target amplitude. The missing measurement points can be extrapolated from the existing measurement points, or the correction coefficients for the missing target amplitude values ​​can be extrapolated from the existing target amplitude values.

[0105] These correction coefficients are then transferred from the data processing device 56 into a non-volatile data memory of the microcontroller 4 or into a non-volatile data memory of the microwave module 17 connected to the microcontroller 4.

[0106] In a second variant, the correction coefficients are transferred as such into the non-volatile data memory by means of the data processing device 56. The microcontroller 4 is configured to calculate correction coefficients from the calibration data sets.

[0107] Subsequently, the measuring system 51 can be separated from the microwave module 17, whereupon the microcontroller 4 operates independently again.

[0108] The microwave module 17 can then be installed in a household microwave oven, or the phase shift can be calibrated in a further calibration setup, as shown in the Figuren 10 and 11 explained in more detail below.

[0109] First, Fig.9 However, a second part of the calibration procedure according to a second variant, which, as shown, is based on the Fig.7 can follow the first part shown or can be carried out before the first part.

[0110] In this variant, following the positive response to step S12 and after the complete variation or "sweeping" of the target values ​​of power, frequency, and phase shift, the directional coupling device 52 is disconnected from the microwave module 17 in a step S26, so that the microwave output 18 itself serves as an open end, causing a total reflection of the (transmitted) microwave signals traveling in the transmission direction to the microwave output 18. The detectors 55a-1, 55a-2, and 55b are therefore not used.

[0111] Subsequently, steps S27 to S35 are executed analogously to steps S15 to S23, thus creating another calibration data set with the entries of the measured values ​​of the powers P 14a and P 14b and, if applicable, the temperature T for the setpoints f soll and P soll. In a further development, the calibration data set from the first part can be applied directly to the measured values ​​of the transmitted power P 14a.

[0112] Following the positive response in step S34 after a complete sweep of the target frequency and the target amplitude, steps S24 and S25 can be carried out analogously to the first variant.

[0113] Fig.10 shows a further calibration setup for calibrating the phase shift of the microwave module 17 by means of a measuring system 61 using an already calibrated microwave module 17 kal . The signal generators 3 of the two microwave modules 17 and 17 kal are connected to the same clock generator 2. The microwave outputs 18 are connected via an optional respective attenuator 62 of the measuring system 61 to respective inputs of a combiner 63 of the measuring system 61, the output of which is connected to a detector 64, e.g., a voltmeter, of the measuring system 61, which in turn is connected to the data processing device 56 of the measuring system 61. Cable lengths should be taken into account in the setup in order to be able to detect and, if necessary, compensate for phase shifts caused by different cable lengths.

[0114] One advantage of using attenuators 62 is that many combiners 63 can only withstand low power levels, so attenuators 62 serve to protect combiner 63. A further advantage is that the two microwave modules 17 and 17 kal can then be operated at high output power. The power level can then be set approximately the same, and the absolute deviations are no longer significant relative to the high level. At low levels (e.g., due to internal pre-attenuation by attenuator 9), a relative amplitude error would be extremely noticeable.

[0115] Here, too, the data processing device 56 controls the microcontrollers 4 of the microwave modules 17 and 17kal in such a way that the data processing device 56 directly controls the individual components of the microwave modules 17 and 17kal. The control function of the microcontrollers 4 is thus deactivated.

[0116] If the phases of the microwave signals emitted at the microwave outputs 18 are in phase (i.e., they have a phase shift of 0° between them), the detector 64 measures a maximum sum signal. If the phases of the microwave signals emitted at the microwave outputs 18 are in phase opposition (i.e., they have a phase shift of 180° between them), the detector 64 measures a minimum sum signal. This is used to determine whether the phase shifter 8 of the microwave module 17 to be calibrated is operating correctly or whether the phase shift at this phase shifter 8 should be corrected or calibrated based on the measured actual phase shift to the target phase shift.

[0117] Fig.11 shows one based on the Fig.10 Calibration procedure that can be carried out using the calibration setup shown.

[0118] In a step S41, for the Fig.10 Using the calibration setup shown, the same target amplitude / target power is set on both microwave modules 17 and 17 kal using the data processing device 56. In particular, the target amplitude can be set to a medium value, such as 100 W.

[0119] Furthermore, the target phase shift of the microwave module 17 kal is set to a specific value from a third phase group of different phase shift values, advantageously to 0°. Since the microwave module 17 kal is already calibrated, it can be assumed that its target phase shift corresponds to its actually set phase shift with high accuracy.

[0120] In step S41, the target phase shift of the microwave module 17 is also set to a specific initial value from the third phase group, advantageously to the same value as the set target phase shift of the calibrated microwave module 17 kal , in particular to 0°.

[0121] In step S42, it is queried whether all values ​​of the target phase shift to be set have already been set once.

[0122] If this is not the case ("N"), in step S43 the sum signal of the two microwave signals of the two operated microwave modules 17 and 17 kal , in particular measured, present at the output of the combiner 63 by means of the detector 64 is transmitted to the data processing device 56 and stored there together with the values ​​of at least the set nominal frequency and the nominal phase shift set on the microwave module 17 as a data entry in a further calibration database.

[0123] In addition, in step S44, the value of the desired phase shift set on the microwave module 17 is changed by a step size, e.g. 30°, 60°, 90° or 180°, e.g. incremented or decremented, and branched back to step S42.

[0124] However, if the query in step S43 is answered positively ("Y"), the desired values ​​of the third phase group have been passed through or swept once, and the process branches to step S45. If the phase shifter 8 of the microwave module 17 is operating correctly, the sum signal is maximum at 0° and minimum (close to zero) at 180°.

[0125] In step S45, the target phase shift of the microwave module 17 is reset to the determined initial value.

[0126] In step S46, a query is made as to whether all values ​​of the target frequency to be set from the third frequency group have already been set once.

[0127] If this is not the case ("N"), the program branches to step S47, where the target frequency on both microwave modules 17 and 17kal is set, in particular incremented or decremented, to an identical new value from the third frequency group. The program then branches back to step S42.

[0128] However, if this is the case ("Y"), the calibration data set is complete, based on which the phase shift of the phase shifter 8 of the microwave module 17 can be corrected. The program then branches to step S48, in which—analogous to steps S24 and S25—in one variant, correction coefficients are calculated from the calibration data set using the data processing device 56. These correction coefficients are intended to calibrate the operation of the microwave module 17 in order to output microwave signals whose phase or phase shift corresponds as closely as possible to the set target values.Here too, in a second variant, the correction coefficients can be transferred from the data processing device 56 into a non-volatile data memory of the microcontroller 4 or into a non-volatile data memory of the microwave module 17 connected to the microcontroller 4, wherein the microcontroller 4 is configured to calculate correction coefficients for the phase shift from the calibration data set.

[0129] Subsequently, the measuring system 61 can be separated from the microwave module 17, whereupon the microcontroller 4 operates independently again.

[0130] Of course, the present invention is not limited to the embodiment shown.

[0131] In general, "a", "an", etc. can be understood as a singular or a plural, in particular in the sense of "at least one" or "one or more", etc., as long as this is not explicitly excluded, e.g. by the expression "exactly one", etc.

[0132] A numerical value may also include the exact number stated as well as a usual tolerance range, as long as this is not explicitly excluded. Bezugszeichenliste

[0133] 1Microwave generation path 2Clock generator 3Signal generator 4Microcontroller 5Bandpass filter 6Chopper 7Repeater 8Phase shifter 9Attenuator 10Preamplifier 11Main amplifier 12Directional coupling device 12-1Bidirectional directional coupler without circulator 12-2Directional coupler with circulator 12-3Directional coupler with circulator 13aMeasurement output for forward power 13bMeasurement output for reverse power 14aForward power detector 14bReverse power detector 15Temperature sensor 16Antenna 17Microwave module 17 cal Precalibrated microwave module 18Microwave output of the microwave module 19Circulator 20One-way directional coupler 21One-way directional coupler 22Termination resistor 23 Cooking chamber 24 Household microwave cooking appliance 31 Microwave generation section 32 Household microwave cooking appliance 33 Control unit 41 Microwave generation section 42 Household microwave cooking appliance 43 Microwave module 44 Signal generation module 45 Microcontroller 46 Microcontroller 47 Splitter51Measuring system 52Directional coupling device 53Microwave output of the measuring system 54aMeasuring output for power in forward direction 54bMeasuring output for power in reverse direction 55a-1Detector for amplitude measurement 55a-2Detector for frequency measurement 55bDetector for amplitude measurement 56Data processing device 57Equivalent load 58Reflecting end termination 61Measuring system 62Attenuator 63Combiner 64Detector S1-S35Process steps S41-S47Process steps

Claims

1. A method (S41-S48) for calibrating a phase shifter (8) of a microwave module (17) intended for installation in a household cooking appliance (42), wherein the method (S41-S48) comprises at least the following steps: (i) providing a microwave module (17) to be calibrated with respect to its phase shift and a microwave module (17) already calibrated with respect to its phase shift kal ), the microwave outputs (18) of which are connected to respective inputs of a combiner (63); (ii) specifying a common target amplitude and a common target frequency for both microwave modules (17, 17 kal ) and a target phase shift on the calibrated microwave module (17 kal ) and a desired phase shift on the microwave module (17) to be calibrated (S41); (iii) generating, by means of both microwave modules (17, 17 kal), a respective microwave signal with the respectively predetermined target values (S43); (iv) measuring a signal (S43) present at the output of the combiner (63); (v) storing the values of at least the target phase shift and the target frequency predetermined for the microwave module to be calibrated and / or values derived therefrom, as well as the associated measured value, as data entries of a phase calibration data set (S43); (vi) varying the target phase shift on the microwave module (17) to be calibrated within a third phase group of different target phase shifts (S44) and each time repeating steps (iii) to (v) for several, in particular all, target phase shifts of the third phase group.

2. Method (S41-S48) according to claim 1, wherein in a step (vi) the target frequency is additionally varied within a third frequency group of different target frequencies (S47) and steps (iii) to (v) are additionally carried out for several, in particular all, target frequencies of the third phase group.

3. Method (S41-S48) according to one of the preceding claims, wherein the measured values in step (ii) on the calibrated microwave module (17 kal ) specified target phase shift is 0° and the target phase shift within the third phase group includes at least the target values 0° and 180°.

4. Method (S41-S48) according to one of the preceding claims, in which correction factors for the operation of the microwave module to be calibrated are calculated (S48) from the stored data entries of the phase calibration data set, on the basis of which correction factors the phase shifts are adapted to the respectively associated desired phase shifts.

5. A household microwave cooking appliance (42), comprising - a cooking chamber (23) that can be closed microwave-tight by means of a door and can be supplied with microwaves, - at least one microwave module (17) that is configured to adjust at least one amplitude and one frequency of a microwave signal emitted at a microwave output (18) to variable setpoints, and that has a directional coupling device (12) at least for measuring the amplitude of an emitted microwave signal and a reflected microwave signal, and - a control device (4) that is configured to adapt at least one microwave parameter, including the amplitude of the microwave signal emitted to at least one antenna (16), to an associated setpoint based on correction factors calculated from the stored values according to the method according to claim 4,- wherein the calibration data sets are stored in a non-volatile memory of the household microwave cooking appliance (42) and the correction factors can be calculated by means of the microwave module (17), in particular by means of its control device (4).

6. Calibration setup for carrying out a method (S41-S48) according to one of claims 1 to 4, comprising a calibrated microwave module (17 kal ), at least one microwave module (17) to be calibrated and a measuring system (61), wherein - the measuring system (61) has a combiner (63) whose inputs are connected to the microwave outputs (18) of the microwave modules (17, 17 kal ) and whose output is connected to a detector (64) of the measuring system (61), - the detector (64) is connected to a data processing device (56) of the measuring system (61), which is connected to control units (4) of the microwave modules (17, 17 kal) for controlling the same; and wherein the microwave modules (17, 17 kal ) at least one frequency and one phase shift of the microwave signal generated thereby are variable.

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