Patent Description:
In IEEE <NUM>. 11ad currently studied as an international standard for increasing the speed of a wireless local area network (LAN), a carrier frequency is about <NUM> and radio waves of millimeter waves are expected to be used. Here, radio waves (electromagnetic waves) of frequencies of <NUM> to <NUM> are called millimeter waves, radio waves of frequencies of <NUM> to <NUM> are called centimeter waves, and both are included in micro-waves indicating radio waves of frequencies of <NUM> to <NUM> THz.

Furthermore, in IEEE <NUM>. 11ad, a modulation band is <NUM> per channel, which is expected to be about <NUM> to <NUM> times the conventional band. To develop devices suitable for such standards, evaluation of characteristics of devices is performed through the following technique. That is, a measuring device corresponding to a conventional frequency band (e.g., a centimeter-wave band) and frequency converters are combined to evaluate characteristics of devices. Here, the frequency converters are apparatuses that down-convert a millimeter-wave signal to centimeter waves or up-convert a centimeter-wave signal to millimeter waves, for example.

European patent application no. <CIT> describes a circuit for reducing adjacent-channel interference by pre-linearizing and pre-distorting an input signal to be transmitted via a power amplifier having a non-linear transmission characteristic and a limited dynamic range. The circuit has a pre-linearization signal generation unit for producing a pre-linearization signal reflecting a signal portion of said input signal exceeding the dynamic range of said power amplifier. An element for expanding said pre-linearization signal along the time axis to produce an expanded pre-linearization signal reflecting an expanded version of said signal portion of said input signal exceeding said limitation, and an element for combining said expanded pre-linearization signal and said input signal, such that said expanded version of said signal portion of said input signal exceeding said limitation is subtracted from said input signal, to produce a pre-linearized signal, are provided.

United Kingdom patent application no. <CIT> describes a method of scanning a shoe and a respective apparatus. The method comprises sending electromagnetic radiation in the millimetre-microwave regime to the shoe and detecting the reflected signal coming from different surfaces within it with one or more receivers. The analysis of the reflective surfaces along with the reflected signals indicates the composition of the shoe and may identify concealed objects or determine the cushioning ability. The data may be compared to that of a reference shoe, which may or may not have a hidden object. The positions of the reflecting surfaces within the shoe may be determined by sending the signal in time pulses and recording the time of arrival, or sending a range of frequencies and transforming the received spectrum to a time series with an inverse Fourier or chirp transform.

An article entitled "<NPL> et al describes a new range of waveguide harmonic mixers, covering from <NUM> to <NUM>. The article describes redesign and fabrication of extremely low parasitic anti-parallel mixer diodes by two independent, competing groups: RAL and ACST. These diodes can also be used to make excellent sub-harmonic mixers (2nd harmonic of the LO) with high sensitivity. Use of a wideband stripline filter is also described, using a "photonic band gap" structure and an unconventional waveguide transition for the RF signal coupling. Documents <CIT>, <CIT>, <CIT>, <CIT> and the <NPL> disclose further relevant examples of frequency converters.

In evaluation of a device corresponding to millimeter waves as described above, the following problems occur when a frequency converter is used. That is, a frequency converter that inputs or outputs a modulation signal such that the band for the above-mentioned one channel becomes <NUM> is considerably expensive. In addition, the setup for measurement is complicated, device connection errors easily occur, and adjustment takes a long time. A configuration of a mixer included in the frequency converter is considered as one cause of such problems.

<FIG> shows an example of a configuration of a mixer included in a frequency converter used at millimeter waves. In general, it is difficult to manufacture a frequency converter which has a flat frequency characteristic and handles ultra-wideband modulation signals in millimeter waves. In addition, it is difficult to directly generate a millimeter-wave signal from centimeter waves and to directly convert millimeter waves to a centimeter-wave signal while maintaining a flat frequency characteristic. Accordingly, a double super-heterodyne frequency converter <NUM> as shown in <FIG> is generally employed. The frequency converter <NUM> shown in <FIG> includes two mixers <NUM> and <NUM> which receive two different frequencies fLO1 and fLO2 as local oscillation signals. In a case where the frequency converter <NUM> is used as an up-converter, a modulation signal having a frequency fIF1 is input to the mixer <NUM> and converted into a signal having an intermediate frequency fTF2 corresponding to the value of the sum of the frequency fIF1 and the frequency fLO1. Further, a signal having the frequency fIF2 is input to the mixer <NUM> and converted into a radio-frequency signal having a frequency fRF corresponding to the value of the sum of the frequency fIF2 and the frequency fLO2. On the other hand, in a case where the frequency converter <NUM> is used as a down-converter, a radio-frequency signal having a frequency fRF is input to the mixer <NUM> and converted into a signal having an intermediate frequency fIF2 corresponding to the difference value between the frequency fRF and the frequency fLO2. In addition, a signal having a frequency fIF2 is input to the mixer <NUM> and converted into a modulation signal having a frequency fIF1 corresponding to the value of the difference between the frequency fIF2 and the frequency fLO1.

The double super-heterodyne frequency converter <NUM> shown in <FIG> includes two mixers. Accordingly, it is required that the frequency converter <NUM> have two types of local oscillation signals. Furthermore, interconnection between the mixers is required. Such configuration may cause an increase in costs, a complicated measurement setup, an increase in a likelihood of device connection error, and longer adjustment time.

Accordingly, there is a demand for a frequency converter having a simplified configuration, a measuring system, and a measuring method.

The present application can provide a frequency converter, a measuring system, and a measuring method.

Embodiments of the present application will be described below with reference to the drawings. First, a basic configuration of a harmonic mixer included in a frequency converter will be described with reference to <FIG> as an embodiment of the present application. <FIG> is a diagram showing a configuration example of a harmonic mixer <NUM> included in a frequency converter as an embodiment of the present application. Further, an embodiment of the present application relates to a harmonic mixer serving as a frequency converter having a flat frequency characteristic for measurement of modulation signals of an ultra-wideband corresponding to millimeter waves, for example, signals of frequency bands corresponding to the IEEE <NUM>. 11ad standard. Furthermore, the present embodiment relates to a measuring system capable of easily measuring modulation signals of an ultra-wideband corresponding to millimeter waves using a general-purpose digital oscilloscope by using the harmonic mixer so as to be in compliant with the IEEE <NUM>. 11ad standard.

The harmonic mixer <NUM> shown in <FIG> is a mixer including a circuit therein, which distorts an input local oscillation signal to generate harmonics thereof. The harmonic mixer <NUM> receives a local oscillation signal having a frequency fLO1, distorts the local oscillation signal therein to generate harmonics having frequencies n× fLO1, which are n times the frequency of the local oscillation signal, and mixes the harmonics having the frequencies n× fLO1 with an input signal having a frequency fRF (in the case of a down-converter) or an input signal having a frequency fIF1 (in the case of an up-converter).

In a case where the harmonic mixer <NUM> is used as a down-converter, a local oscillation signal is appropriately selected to obtain an output signal having an appropriate intermediate frequency fIF1, in which harmonics n×fLO1 of a certain local oscillation signal fLO1 have been mixed with an input frequency fRF. This relationship is represented by the following equation, where n is an integer equal to or greater than <NUM>, which is called a harmonic number, and indicates a harmonic order. Meanwhile, in the conventional mixer as described above with reference to <FIG>, n=<NUM> is satisfied because frequency conversion is performed without using harmonics.

On the other hand, in a case where the harmonic mixer <NUM> is used as an up-converter, a local oscillation signal is appropriately selected to obtain an output signal having an appropriate output frequency fRF, in which harmonics n×fLO1 of a certain local oscillation signal have been mixed with an input frequency fIF1. This relationship is represented by the following equation.

Next, a configuration example of a frequency converter <NUM> will be described with reference to <FIG> as an embodiment of the present application. The frequency converter <NUM> shown in <FIG> is configured as an up-converter. The frequency converter <NUM> shown in <FIG> includes a harmonic mixer <NUM>, a high pass filter <NUM>, a power amplifier (PA) <NUM>, an isolator <NUM>, and a multiplier <NUM>.

The multiplier <NUM> has a multiplication number of k=<NUM>, for example, receives a local oscillation signal having a frequency fLO1, and doubles the frequency (i.e., multiplies the frequency by k) to generate a radio-frequency signal having a frequency <NUM>× fLO1 (i.e., k× fLO1) and outputs the radio-frequency signal as an output signal. In order to double the frequency fLO1 of the local oscillation signal, for example, in the present embodiment, an active doubler (an active multiplier that doubles the frequency of an input signal and outputs the signal) is used. In a conventional multiplier, the power of an output local oscillation signal which has been multiplied varies according to a multiplied frequency. Consequently, as will be described below, in a case where frequency characteristics (S-parameters) of the amplitude and phase of the harmonic mixer <NUM> are measured and an output signal output from the frequency converter <NUM> is corrected, the signal level of the local oscillation signal output from the multiplier <NUM> is unstable and thus it may not be possible to correct the output signal output from the frequency converter <NUM> with high accuracy and obtain a correct measurement result. Accordingly, in the present embodiment, to make a signal level which has been multiplied constant such that a local oscillation signal with a constant power is output in a predetermined frequency band, an amplification function of automatic gain control (AGC) or a power saturation function is added, and a multiplied local oscillation signal is output to the harmonic mixer <NUM> with a constant power without changing a signal level at any frequency in a predetermined frequency band.

A power level when the local oscillation signal is supplied to the harmonic mixer <NUM> is stabilized in a wide frequency band by using the aforementioned multiplier <NUM> and modulation accuracy and signal level reproducibility in the harmonic mixer <NUM> are improved. Accordingly, when the frequency characteristics (S-parameters) of the amplitude and phase of the frequency converter <NUM> are determined in advance and a signal output from the frequency converter <NUM> is corrected according to the frequency characteristics, the signal level of a local oscillation signal output from the multiplier <NUM> is constant regardless of the frequency thereof, and thus it is possible to correct the signal output from the frequency converter <NUM> with high accuracy at any frequency in a predetermined frequency band and to obtain a correct measurement result. Here, the multiplier <NUM> can arbitrarily change a multiplication number since the multiplication number is changed in combination with the harmonic number of the harmonic mixer <NUM>.

The harmonic mixer <NUM> has a harmonic number of n=<NUM>, receives a modulation signal having a frequency fIF1 as an input signal and receives the radio-frequency signal having the frequency <NUM>×fLO1 output from the multiplier <NUM>. The harmonic mixer <NUM> generates a harmonic signal having a frequency (<NUM>×<NUM>×fLO1=<NUM>×fLO1) twice the input radio-frequency signal having the frequency (<NUM>×fLO1) therein and mixes the harmonic signal with the input signal having the frequency fIF1. The harmonic mixer <NUM> generates and outputs a radio-frequency signal having a frequency fIF1+<NUM>×fLO1 by mixing the harmonic signal having the frequency <NUM>×fLO1 with the input signal having the frequency fIF1. The output of the harmonic mixer <NUM> is input to the high pass filter <NUM>. The high pass filter <NUM> attenuates a low frequency component of the input signal and outputs a resultant signal. The signal output from the high pass filter <NUM> is amplified in the power amplifier <NUM> and input to the isolator <NUM>. The isolator <NUM> is a device that passes a radio-frequency power only in one direction and suppresses input of a reflected wave to the output of the power amplifier <NUM>. In addition, an output signal having a frequency fRF=fIF1+<NUM>×fLO1 is output from the isolator <NUM>. Meanwhile, although both the multiplication number k and the harmonic number n are set to <NUM> in the example shown in <FIG>, the present invention is not limited thereto and may set the numbers to any values.

Here, if fRF= <NUM>, fLO1 = <NUM>, the multiplication number k = <NUM>, and the harmonic number n = <NUM>, the frequency fRF of the output signal becomes fRF = fIF1+k× n×fLO1 = <NUM>+<NUM>×<NUM>×<NUM> = <NUM>. In this case, the frequency converter <NUM> up-converts the frequency fIF1 = <NUM> of the input signal to the frequency fRF = <NUM>.

Meanwhile, the configuration of the frequency converter <NUM> in a case where the frequency converter is configured as an up-converter is not limited to the configuration shown in <FIG> but may be appropriately changed. For example, it may be possible to change the high pass filter <NUM> to a band pass filter, appropriately add (insert) a low pass filter or a band pass filter to (into) each component, or omit the power amplifier <NUM> or the isolator <NUM>. In addition, it may be possible to use an attenuator (high frequency attenuator) instead of the isolator <NUM>. Furthermore, it may be possible to reduce the harmonic number n of the harmonic mixer <NUM> depending on the multiplication number k because the multiplier <NUM> is installed in the aforementioned configuration. Here, the multiplier <NUM> may be omitted.

Next, a configuration example of the frequency converter <NUM> will be described with reference to <FIG> as an embodiment of the present application. The frequency converter <NUM> shown in <FIG> is configured as a down-converter. The frequency converter <NUM> shown in <FIG> includes an isolator <NUM>, a low noise amplifier (LNA) <NUM>, a harmonic mixer <NUM>, a low pass filter <NUM>, a multiplier <NUM>, an attenuator (ATT) <NUM>, and a pre-amplifier <NUM>.

The isolator <NUM> receives a radio-frequency signal having a frequency fRF as an input signal and inputs the output to the low noise amplifier <NUM>. The isolator <NUM> suppresses generation of a reflected wave of the input signal. The low noise amplifier <NUM> amplifies the input signal and outputs the amplified signal to the harmonic mixer <NUM>. The multiplier <NUM> has a multiplication number k=<NUM>, receives a local oscillation signal having a frequency fLO1, doubles the frequency to generate a radio-frequency signal having a frequency <NUM>×fLO1, and outputs the radio-frequency signal. The harmonic mixer <NUM> has a harmonic number n = <NUM>, receives a radio-frequency signal having a frequency fRF output from the low noise amplifier <NUM>, and receives the radio-frequency signal having the frequency <NUM>×fLO1 output from the multiplier <NUM>. The harmonic mixer <NUM> generates a radio-frequency signal having a frequency (<NUM>×<NUM>×fLO1=<NUM>×fLO1) which is twice the input radio-frequency signal having the frequency (<NUM>×fLO1) therein and mixes the harmonic signal with the input signal having the frequency fRF. The harmonic mixer <NUM> generates and outputs a harmonic signal having a frequency fRF-<NUM>×fLO1 by mixing the generated harmonic signal having the frequency <NUM>×fLO1 with the input signal having the frequency fRF. The output of the harmonic mixer <NUM> is input to the low pass filter <NUM>. The low pass filter <NUM> attenuates a high frequency component of the input signal. In this case, the radio-frequency signal (modulation signal) having the frequency fIF1 = fRF-<NUM>×fLO1 is output from the low pass filter <NUM>. Meanwhile, although both the multiplication number k and the harmonic number n are set to <NUM> in the example shown in <FIG>, the present invention is not limited thereto and may set the numbers to any values.

Here, if fRF = <NUM>, fLO1 = <NUM>, k = <NUM>, and n = <NUM>, for example, the frequency fIF1 = fRF-k× n×fLO1 = <NUM>-<NUM>×<NUM>× <NUM> = <NUM> of the output signal is satisfied. In this case, the frequency converter <NUM> down-converts the frequency fRF= <NUM> of the input signal to the frequency fIF1 = <NUM>.

Meanwhile, the configuration of the frequency converter <NUM> in a case where the frequency converter is configured as a down-converter is not limited to the configuration shown in <FIG> but may be appropriately changed. For example, it may be possible to change the low pass filter <NUM> to a band pass filter, appropriately add (insert) a high pass filter or a band pass filter to (into) each component, or omit the low noise amplifier <NUM> or the isolator <NUM>. In addition, it may be possible to use an attenuator instead of the isolator <NUM>. Furthermore, it may be possible to reduce the harmonic number n of the harmonic mixer <NUM> depending on the value of the multiplication number k because the multiplier <NUM> is installed in the aforementioned configuration. Here, the multiplier <NUM> may be omitted.

The attenuator <NUM> attenuates the signal level of a signal reflected from an input terminal of the pre-amplifier <NUM> and suppresses an influence on the output signal at an output terminal of the harmonic mixer <NUM> due to the signal reflected from the pre-amplifier <NUM>. The attenuator <NUM> is interposed between the low pass filter <NUM> and the pre-amplifier <NUM>.

The pre-amplifier <NUM> amplifies the signal level of the output signal from the low pass filter <NUM> and outputs the amplified signal to a digital oscilloscope (a digital oscilloscope <NUM> which will be described below) at the subsequent stage. Accordingly, even in a case where the input sensitivity of the digital oscilloscope that measures the output signal from the frequency converter <NUM> is low, the output signal from the frequency converter <NUM> can be amplified to any signal level. Therefore, it is possible to appropriately adjust the signal level of the output signal from the frequency converter <NUM> in accordance with the dynamic range of the digital oscilloscope that measures the output signal.

Furthermore, since the signal level of the output signal output from the frequency converter <NUM> is adjusted to the sensitivity of the digital oscilloscope <NUM>, in a case where an amplifier is interposed between the frequency converter <NUM> and the oscilloscope <NUM>, a correct measurement result of the output signal cannot be obtained because the characteristics of the amplifier are unknown. However, when the pre-amplifier <NUM> that adjusts the signal level of an output signal is installed in advance in the frequency converter <NUM> as in the present embodiment, the frequency characteristics of the pre-amplifier <NUM> can also be included in the frequency characteristics of the frequency converter <NUM>, and thus it is possible to easily configure a measuring system capable of measuring an output signal with high accuracy in accordance with the input sensitivity of the digital oscilloscope.

Like the multiplier <NUM>, the multiplier <NUM> doubles the frequency fLO1 of the local oscillation signal, for example, in the present embodiment, and thus an active doubler is used. In a conventional multiplier, the power of an output local oscillation signal which has been multiplied varies according to a multiplied frequency. Consequently, as will be described below, in a case where frequency characteristics (S-parameters) of the amplitude and phase of the frequency converter <NUM> are measured and an output signal output from the frequency converter <NUM> is corrected, the signal level of the local oscillation signal output from the multiplier <NUM> is unstable and thus it may not be possible to correct the output signal output from the frequency converter <NUM> with high accuracy and obtain a correct measurement result. Accordingly, in the present embodiment, to make a signal level which has been multiplied constant such that a local oscillation signal with a constant power is output in a predetermined frequency band, an amplification function of automatic gain control (AGC) is added to an output unit, and a multiplied local oscillation signal is output to the harmonic mixer <NUM> with a constant power without changing the signal level at any frequency in a predetermined frequency band.

A power level when the local oscillation signal is supplied to the harmonic mixer <NUM> is stabilized in a wide frequency band by using the aforementioned multiplier <NUM> so that both of a modulation accuracy and signal level reproducibility in the harmonic mixer <NUM> are improved. Accordingly, when the frequency characteristics (S-parameters) of the amplitude and phase of the frequency converter <NUM> are determined in advance in order that a signal output from the frequency converter <NUM> is corrected according to the frequency characteristics, the signal level of a local oscillation signal output from the multiplier <NUM> is constant regardless of the frequency thereof, and thus it is possible to correct the signal output from the frequency converter <NUM> with high accuracy at any frequency in a predetermined frequency band and to obtain a correct measurement result. Here, the multiplier <NUM> can arbitrarily change a multiplication number since the multiplication number is changed in combination with the harmonic number of the harmonic mixer <NUM>.

In addition, the harmonic number n of the each of the harmonic mixers <NUM>, <NUM> and <NUM> shown in <FIG> is not limited to <NUM> but may be <NUM>, <NUM> or the like. Further, the value n is not limited to even numbers but may be an odd number. Each of the harmonic mixers <NUM>, <NUM> and <NUM> may be configured such that the value of the harmonic number n is arbitrarily changed in combination with the multiplication number of the multiplier <NUM>.

That is, there are cases in which spurious is generated depending on the type of a used harmonic mixer according to the harmonic number n due to a frequency, a frequency bandwidth, and the like on which frequency conversion is performed, which is caused by the circuit characteristics of the harmonic mixer, or the like. Accordingly, it is necessary to set the harmonic number of the harmonic mixer as a favorable value in accordance with the characteristics of the used harmonic mixer and also taking into account a combination with a multiple of the multiplier <NUM>, as a result of measurement, experiments and the like corresponding to the frequency and frequency band.

Next, the measuring system <NUM> will be described with reference to <FIG> as an embodiment of the present application. <FIG> is a system diagram showing a configuration example of the measuring system <NUM> as an embodiment of the present application. Meanwhile, in <FIG>, the same components as those shown in <FIG> and <FIG> are denoted by the same reference signs. The measuring system <NUM> shown in <FIG> includes a correction data acquisition unit <NUM> and a measuring unit <NUM>.

The measuring unit <NUM> includes a control unit <NUM>, an arbitrary signal generator <NUM>, a frequency converter <NUM>, a frequency converter <NUM>, a digital oscilloscope <NUM>, and a local oscillator <NUM>. In addition, a specimen <NUM> which is a measurement target sample, such as a radio-frequency device, is inserted between the frequency converter <NUM> and the frequency converter <NUM> when measurement is performed. For example, the specimen <NUM> is a device such as an antenna or a low noise amplifier. Among the components, at least the arbitrary signal generator <NUM> and the digital oscilloscope <NUM> are calibrated measuring devices on the market.

For example, the control unit <NUM> is configured using a computer such as a personal computer. The control unit <NUM> includes a pre-distortion processing unit <NUM>, a correction data storage unit <NUM>, an equalization processing unit <NUM>, and an analysis unit <NUM>. Here, the pre-distortion processing unit <NUM>, the equalization processing unit <NUM> and the analysis unit <NUM> are configured as software executed on the computer configuring the control unit <NUM> using hardware resources of the computer. In addition, the correction data storage unit <NUM> is configured as a predetermined storage region in a storage device included in the control unit <NUM>.

The correction data storage unit <NUM> stores data indicating frequency characteristics (i.e., <NUM>-port S-parameters S21 indicating transfer characteristics) of variations in amplitudes and phases between input/output signals of the frequency converter <NUM> and the frequency converter <NUM>, obtained in the correction data acquisition unit <NUM>. Here, it may be possible to record data indicating how to correct waveforms instead of or in addition to recording of the frequency characteristics, for example.

The pre-distortion processing unit <NUM> performs a process for correcting a signal waveform generated by the arbitrary signal generator <NUM> on the basis of the data indicating the frequency characteristics of the amplitudes and phases of the frequency converter <NUM> and the frequency converter <NUM>, which is stored in the correction data storage unit <NUM>. For example, the pre-distortion processing unit <NUM> changes an amplitude value and a phase value of the waveform generated by the arbitrary signal generator <NUM> in response to a frequency on the basis of the data indicating the frequency characteristics of the amplitude and the phase of the frequency converter <NUM> which is an up-converter such that amplitude characteristic variations and phase characteristic variations due to the frequency converter <NUM> are canceled (i.e., such that frequency characteristics become flat). For example, when an amplitude of an output signal of the frequency converter <NUM> is attenuated to a greater degree in a certain frequency band than in other frequency bands, the pre-distortion processing unit <NUM> performs a correction of amplifying the amplitude value in the frequency band such that the attenuation is eliminated. In addition, when the phase of the output signal of the frequency converter <NUM> is delayed by a greater amount in a certain frequency band than in other frequency bands, the pre-distortion processing unit <NUM> performs a correction of advancing the phase in the frequency band to eliminate the delay.

The equalization processing unit <NUM> performs a correction process on measurement data measured and recorded by the digital oscilloscope <NUM> on the basis of the data indicating the frequency characteristics of the amplitudes and the phases of the frequency converter <NUM> and the frequency converter <NUM>, which is stored in the correction data storage unit <NUM>. For example, the equalization processing unit <NUM> changes an amplitude value and a phase value of the measurement data in response to a frequency on the basis of the data indicating the frequency characteristics of the amplitude and the phase of the frequency converter <NUM> which is a down-converter such that amplitude characteristic variations and phase characteristic variations due to the frequency converter <NUM> are eliminated (i.e., such that frequency characteristics become flat). For example, when the amplitude of an output signal of the frequency converter <NUM> is attenuated to a greater degree in a certain frequency band than in other frequency bands, the equalization processing unit <NUM> performs a correction of amplifying the amplitude value in the frequency band such that the attenuation is eliminated. In addition, when the phase of the output signal of the frequency converter <NUM> is delayed by a greater amount in a certain frequency band than in other frequency bands, the equalization processing unit <NUM> performs a correction of advancing the phase in the frequency band to eliminate the delay.

The analysis unit <NUM> performs a process of analyzing a predetermined radio-frequency characteristic of the specimen <NUM> on the basis of the measurement data corrected by the equalization processing unit <NUM>.

The arbitrary signal generator <NUM> generates a waveform having an arbitrary shape on the basis of a predetermined setting manipulation using a manipulator included in the arbitrary signal generator <NUM> or a control signal input from the control unit <NUM> and inputs the waveform to the frequency converter <NUM>. In the following description, the arbitrary signal generator <NUM> outputs a modulation signal having a predetermined bandwidth of an intermediate frequency FIF1.

The frequency converter <NUM> is configured as an up-converter, as shown in <FIG>, receives a signal having the frequency fIF1 output from the arbitrary signal generator <NUM> as an input signal, and receives a signal having a frequency fLO1 output from the local oscillator <NUM> as a local oscillation signal. In addition, the frequency converter <NUM> mixes the input signal having the frequency fIF1 with a harmonic signal k×n times the local oscillation signal having the frequency fLO1 to output a radio-frequency signal having a frequency fRF as an output signal.

The frequency converter <NUM> is configured as a down-converter, as shown in <FIG>, receives the signal having the frequency fRF output from the frequency converter <NUM> as an input signal, for example, via the specimen <NUM>, and receives the signal having the frequency fLO1 output from the local oscillator <NUM> as a local oscillation signal. In addition, the frequency converter <NUM> mixes the input signal having the frequency fRF with a harmonic signal k×n times the local oscillation signal having the frequency fLO1 to output a signal having a frequency fIF1 as an output signal.

The digital oscilloscope <NUM> receives the output signal of the frequency converter <NUM> at predetermined sampling intervals and records the output signal in a predetermined storage device therein.

The local oscillator <NUM> generates the local oscillation signal having the frequency fLO1, distributes the local oscillation signal, for example, using a distributor which is not shown, and inputs the local oscillation signal to the frequency converter <NUM> and the frequency converter <NUM>.

Meanwhile, the correction data acquisition unit <NUM> is a component for acquiring the transfer characteristics (i.e., <NUM>-port S-parameters S21 indicating the transfer characteristics) of the frequency converter <NUM> and the frequency converter <NUM>, described above with reference to <FIG> and <FIG>, in advance prior to measurement of the specimen <NUM>. That is, the correction data acquisition unit <NUM> measures the frequency characteristics of the amplitudes and the phases of the frequency converter <NUM> and the frequency converter <NUM> in advance prior to measurement of the radio-frequency characteristic of the specimen <NUM> by the measuring unit <NUM>.

In the example shown in <FIG>, the correction data acquisition unit <NUM> includes a millimeter-wave vector network analyzer <NUM>. The millimeter-wave vector network analyzer <NUM> is a measuring device that measures a radio-frequency characteristic of a specimen, such as an S-parameter of a millimeter-wave band and is a calibrated apparatus on the market in this case. In the correction data acquisition unit <NUM>, a circuit composed of an isolator <NUM>, the frequency converter <NUM> or <NUM>, and a local oscillator <NUM> is connected to the millimeter-wave vector network analyzer <NUM>. For example, the local oscillator <NUM> generates a local oscillation signal having the same frequency as the local oscillator <NUM> and inputs the local oscillation signal to the frequency converter <NUM> or <NUM> as a local oscillation signal. Here, the local oscillation signal may be provided by the millimeter-wave vector network analyzer <NUM>. The frequency converter <NUM> and the frequency converter <NUM> are alternately connected to the millimeter-wave vector network analyzer <NUM> so that frequency characteristics of variations in the amplitudes and the phases (i.e., transfer characteristics) between input signals and output signals thereof are measured.

The isolator <NUM> is inserted between a signal output terminal of the millimeter-wave vector network analyzer <NUM> and a signal input terminal of the frequency converter <NUM> or <NUM>. The isolator <NUM> suppresses a signal, which has been output from the millimeter-wave vector network analyzer <NUM> and input to the frequency converter <NUM> or <NUM>, from being reflected to the millimeter-wave vector network analyzer <NUM>. Meanwhile, an attenuator may be used instead of the isolator <NUM>. The applicant confirmed that the effect of waveform correction performed by the pre-distortion processing unit <NUM> and the equalization processing unit <NUM> is improved by installing the isolator <NUM> and the like.

Meanwhile, when the frequency characteristics of the frequency converters <NUM> and <NUM> are measured, the frequency sweep range may be set depending on the bandwidths of the radio-frequency signal fRF and the modulation signal input to the specimen <NUM>. For example, if the specimen <NUM> is a device applied to predetermined wireless communication, the range of frequency sweeping can be set to cover a frequency range determined by the carrier frequency of each channel used in the wireless communication and the bandwidth of a modulation signal of each channel.

A result of measurement using the millimeter-wave vector network analyzer <NUM>, that is, the frequency characteristics (i.e., <NUM>-port S-parameters S21 indicating transfer characteristics) of the amplitudes and the phases of the frequency converter <NUM> and the frequency converter <NUM> are read by the control unit <NUM> via a predetermined recording medium or a predetermined communication line and stored in the correction data storage unit <NUM>.

Next, a flow of a process performed when the radio-frequency characteristic of the specimen <NUM> is measured by the measuring system <NUM> will be described with reference to <FIG> and <FIG>.

First, a user acquires frequency characteristics (S-parameter S21) of the amplitude and the phases of the frequency converters <NUM> and <NUM> using the millimeter-wave vector network analyzer <NUM> (step S101). That is, the S-parameters of the frequency converters <NUM> and <NUM> including harmonic mixers are determined in advance using the millimeter-wave vector network analyzer <NUM>. Here, the measurement may be automatically or semi-automatically performed under the control of the control unit <NUM>, for example.

Then, the frequency characteristics (S-parameter S21) of the amplitudes and the phases acquired in step S101 are stored in the correction data storage unit <NUM> according to a predetermined instruction manipulation performed by the user for the control unit <NUM> and the like (step S102).

Subsequently, the pre-distortion processing unit <NUM> sets pre-distortion to be applied to a waveform (regarded as a reference signal) generated in the arbitrary signal generator <NUM> on the basis of the frequency characteristics (S-parameter S21) of the amplitudes and the phases stored in the correction data storage unit <NUM> according to a predetermined instruction manipulation performed by the user for the control unit <NUM> (step S103).

Thereafter, the user connects the frequency converter (up-converter) <NUM> and the frequency converter (down-converter) <NUM> directly (i.e., via a shortest wave guide or the like) and performs a predetermined instruction manipulation directly or via the control unit <NUM> to input a corrected reference signal generated in the arbitrary signal generator <NUM> to the frequency converter (up-converter) <NUM> and to measure and record an output of the frequency converter (down-converter) <NUM> through the digital oscilloscope <NUM> (step S104). The output terminal (formed as an insertion opening of a wave guide, for example) of the frequency converter (up-converter) <NUM> and the input terminal (formed as an insertion opening of the wave guide, for example) of the frequency converter (down-converter) <NUM> become reference surfaces when the radio-frequency characteristic of millimeter-wave bands of the specimen <NUM> is measured. In addition, the left side of the drawing on the basis of the millimeter-wave reference surfaces is a transmitting side (i.e., up-conversion operation) and the right side of the drawing on the basis of the millimeter-wave reference surfaces is a receiving side (i.e., down-conversion operation).

Next, the user inserts the specimen <NUM> between the frequency converter (up-converter) <NUM> and the frequency converter (down-converter) <NUM> and performs a predetermined instruction manipulation directly or via the control unit <NUM> to input the corrected reference signal generated in the arbitrary signal generator <NUM> to the frequency converter (up-converter) <NUM> and to measure and record an output of the frequency converter (down-converter) <NUM> through the digital oscilloscope <NUM> (step S105).

Subsequently, the equalization processing unit <NUM> performs a correction process (i.e., equalization process) on the data recorded in the digital oscilloscope <NUM> on the basis of the frequency characteristics (S-parameter S21) of the amplitudes and the phases stored in the correction data storage unit <NUM> according to a predetermined instruction manipulation performed by the user for the control unit <NUM> (step S106). Here, for example, the correction process is performed on both the measurement value recorded in step S104 and the measurement value recorded in step S105.

Then, the analysis unit <NUM> performs a process of calculating a constellation (modulation accuracy), a spectrum mask, and the like, for example, on the basis of data corrected by the equalization processing unit <NUM> according to a predetermined instruction manipulation performed by the user for the control unit <NUM> (step S107). Here, an analysis result of the radio-frequency characteristic of the specimen <NUM> can be calculated on the basis of variations in values of amplitude and phase variations (or impedances, distortion amounts and various parameters) in the measurement value obtained in step S105 and corrected in step S106 from reference values which are values of amplitude and phase variations (or impedances, distortion amounts and various parameters) in the measurement value obtained in step S104 and corrected in step S106. That is, the measurement value (or a value obtained by correcting the measurement value) of the specimen <NUM> measured in step S105 may be analyzed on the basis of the measurement values (or a value obtained by correcting the measurement value) of the millimeter-wave reference surfaces measured in step S104.

Next, with reference to <FIG>, description will be made to results of confirmation of effects of correction of amplitudes and phases by the pre-distortion processing unit <NUM> for an input signal to the frequency converter <NUM> at the transmitting side and effects of correction of amplitudes and phases by the equalization processing unit <NUM> for an output signal from the frequency converter <NUM> at the receiving side. <FIG> is a result of observation of a spectrum mask in a case where neither the correction by the pre-distortion processing unit <NUM> nor the correction by the equalization processing unit <NUM> was performed. On the other hand, <FIG> is a result of observation of a spectrum mask in a case where both the correction by the pre-distortion processing unit <NUM> and the correction by the equalization processing unit <NUM> were performed. Here, vector correction disclosed in <FIG> and <FIG> means correction of both the amplitude and the phase.

Furthermore, <FIG> is a constellation in a case where neither the correction by the pre-distortion processing unit <NUM> nor the correction by the equalization processing unit <NUM> was performed. On the other hand, <FIG> is a constellation in a case where both the correction by the pre-distortion processing unit <NUM> and the correction by the equalization processing unit <NUM> were performed. An error vector magnitude (EVM) value was <NUM>% in a case where no correction was performed and <NUM>% in a case where correction was performed, and thus improvement of modulation accuracy was confirmed.

As described above, in the embodiments of the present application, the structure of the frequency converter can be simplified because the frequency converter is configured using the harmonic mixer, and manufacturing costs can be reduced and a measurement setup can be facilitated because a modulation signal is measured using the general-purpose digital oscilloscope. In addition, in a case where the harmonic mixer is used, although an output signal may include many image (false image) signals and these image signals may overlap a desired signal which has been frequency-converted, which may cause deterioration of modulation accuracy and the like, deterioration of the modulation accuracy and the like is prevented by correcting waveforms using measurement values of frequency characteristics of amplitudes and phases. Accordingly, even if a frequency converter has frequency characteristics that are not good as a single body, it is possible to easily improve the characteristics through digital correction. That is, in the present embodiment, the frequency characteristics of the frequency converters <NUM> and <NUM> are found in advance through measurement and digital correction is performed on the frequency converters <NUM> and <NUM> when they are used. Accordingly, even if a property of a device as a single body is not good, it is possible to perform measurement with high accuracy by performing correction.

Meanwhile, embodiments of the present application are not limited to the above-described embodiments. For example, the local oscillator <NUM> may be integrated into the frequency converter <NUM> and the frequency converter <NUM>. It is possible to configure the measuring unit <NUM> more easily by incorporating the local oscillator <NUM> into the frequency converter <NUM> and the frequency converter <NUM>. In addition, the frequency converter <NUM>, the frequency converter <NUM>, and the local oscillator <NUM> may be integrated into the arbitrary signal generator <NUM> or the digital oscilloscope <NUM>. Furthermore, preliminary measurement of the frequency characteristics of the amplitudes and the phases of the frequency converter <NUM> and the frequency converter <NUM> may not necessarily be performed whenever the specimen <NUM> is measured, but, for example, may be performed at a specific interval. Accordingly, there is no need to prepare the generally expensive millimeter-wave vector network analyzer for measurement at all times. In addition, data of preliminary measurement can also be prepared in a plurality of measurement environments such as room temperature.

In addition, <FIG> is a diagram showing another example of comparison results of the presence or absence of correction in the present application. The example of <FIG> shows a comparison in a channel of <NUM> and uses <NUM> QAM and a π/<NUM> BPSK signal. In <FIG>, the comparison results were obtained using a configuration in which the frequency converter (down-converter) <NUM> of <FIG> has a harmonic mixer. Here, the frequency converter (up-converter) <NUM> in <FIG> does not have a harmonic mixer. Meanwhile, a channel used in the comparison results of <FIG> is an allocated channel <NUM> of IEEE <NUM>.

In <FIG>, a constellation <NUM> was obtained when <NUM> QAM was used and correction was not performed. EVM was <NUM>%. With respect to this, signal correction was performed using an S-parameter to obtain a constellation <NUM>. In the constellation <NUM>, EVM was <NUM>%, which was a considerable improvement.

In <FIG>, a constellation <NUM> was obtained when a π/<NUM> BPSK signal was used and correction was not performed. EVM was <NUM>%. With respect to this, signal correction was performed using an S-parameter to obtain a constellation <NUM>. In the constellation <NUM>, EVM was <NUM>%, which was a considerable improvement.

As understood from <FIG>, EVM can be considerably improved even in a configuration in which only the frequency converter (down-converter) <NUM> of <FIG> has a harmonic mixer.

<FIG> is a diagram showing still another example of comparison results of the presence or absence of correction in the present application. The example of <FIG> shows a comparison in a channel of <NUM>, which is different from <FIG>, and uses <NUM> QAM and a π/<NUM> BPSK signal. In <FIG>, the comparison results were obtained using a configuration in which the frequency converter (down-converter) <NUM> of <FIG> has a harmonic mixer. Here, the frequency converter (up-converter) <NUM> in <FIG> has no harmonic mixer. Meanwhile, a channel used in the comparison results of <FIG> is an allocated channel <NUM> of IEEE <NUM>.

As understood from <FIG>, EVM can be considerably improved even in a configuration in which only the frequency converter (down-converter) <NUM> of <FIG> has a harmonic mixer. Although different channels were used in <FIG> and <FIG>, the EVM was considerably improved in both cases.

Furthermore, the present application may have several exemplary embodiments in addition to the above-described embodiments. In a first exemplary embodiment, the frequency converter receives a predetermined input signal and a predetermined local oscillation signal and outputs a signal obtained by mixing the input signal with a harmonic signal having a frequency n times the frequency of the local oscillation signal as an output signal, wherein a circuit that mixes the input signal with the harmonic signal is a harmonic mixer that mixes the harmonic signal with the input signal using a nonlinear characteristic of a semiconductor element, and the input signal or the output signal is subjected, before input to the frequency converter or after output from the frequency converter, to correction on the basis of previously measured frequency characteristics of the amplitude and the phase of the frequency converter.

Further, in a second exemplary embodiment, the frequency converter further includes a multiplier that multiplies the frequency of the local oscillation signal by k times and inputs the resultant signal to the harmonic mixer.

Further, in a third exemplary embodiment, with respect to the frequency converter, the measurement is performed by a vector network analyzer, wherein the vector network analyzer generates and outputs the input signal input to the frequency converter and receives and measures the output signal output from the frequency converter to measure the frequency characteristics of the amplitude and the phase of the frequency converter, and the input signal is input to the frequency converter from the vector network analyzer via an isolator or an attenuator.

Further, in a fourth exemplary embodiment, a measuring system includes: the first frequency converter; the second frequency converter; a signal generator that generates the signal having the corrected waveform and outputs the signal to the first frequency converter; a signal measuring device that measures a signal output from the second frequency converter which has received a signal output from the first frequency converter; and a correction processing unit that performs the correction on the measurement result of the signal measuring device.

Further, in a fifth exemplary embodiment, a measuring method includes inserting a specimen between the first frequency converter and the second frequency converter and measuring a radio-frequency characteristic of the specimen using the first frequency converter, the second frequency converter, a signal generator that generates the corrected modulation signal and outputs the modulation signal to the first frequency converter, a signal measuring device that measures a signal output from the second frequency converter that has received a signal output from the first frequency converter, and a correction processing unit that performs the correction on the measurement result of the signal measurement device.

According to the above-described embodiments, a mixer included in a frequency converter can be constituted of a single harmonic mixer. Accordingly, the configuration can be simplified.

Claim 1:
A frequency converter (<NUM>, <NUM>) configured to receive an input signal and a local oscillation signal and output an output signal, the frequency converter (<NUM>, <NUM>) comprising:
a multiplier (<NUM>, <NUM>) configured to multiply the frequency of the local oscillation signal by k times and input the resultant signal to the harmonic mixer (<NUM>, <NUM>); and
a circuit including a harmonic mixer (<NUM>, <NUM>) configured to input the input signal and the multiplied local oscillation signal having a frequency k times a frequency of the local oscillation signal, the harmonic mixer (<NUM>, <NUM>) being configured to mix the input signal with a harmonic signal having a frequency n×k times the frequency of the local oscillation signal using a nonlinear characteristic of a semiconductor element in order to generate the output signal,
wherein the input signal or the output signal is an ultra-wide band signal corresponding to millimeter waves, and
wherein the input signal or the output signal is configured to be corrected, before input to the frequency converter (<NUM>, <NUM>) or after output from the frequency converter (<NUM>, <NUM>), on a basis of frequency characteristics of an amplitude and a phase of the frequency converter (<NUM>, <NUM>) previously obtained by measurement,
wherein
the multiplier includes a variable gain amplifier or a means having a saturation function at an output stage, the variable gain amplifier and the means being configured to output to the harmonic mixer (<NUM>, <NUM>) the resultant signal of the multiplier with a constant power without changing a level of the resultant signal at any frequency in a predetermined frequency band.