JP2019191344A - Phase characteristic calibrator and phase characteristic calibration method - Google Patents

Abstract

To provide an inexpensive phase characteristic calibrator with which it is possible to calibrate the phase characteristic of a millimeter wave band signal measuring circuit.SOLUTION: The phase characteristic calibrator comprises: a calibration signal generation unit 20 for generating a calibration signal Ecomposed of three or more continuous waves differing in frequency; a local emission light generation unit 10 for generating a local emission light Pin which first light composed of continuous light having three or more waves differing in frequency and second light which is a continuous light different from the first light in frequency are synthesized; an electrooptical frequency conversion unit 30 for frequency converting the calibration signal by an electrooptical crystal using the local emission light and outputting an intermediate frequency signal E; and a calibration processing unit 40 for calibrating the phase characteristic of the measuring circuit on the basis of a phase difference characteristic obtained by applying the calibration signal to the electrooptical frequency conversion unit and a phase difference characteristic obtained by applying the calibration signal to the millimeter wave band signal measuring circuit. The frequency interval of three or more continuous waves of the intermediate frequency signal Eis set to be narrower than the frequency interval of three or more continuous waves of the calibration signal E.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a phase characteristic calibration apparatus and a phase characteristic calibration method.

  In order to improve the transmission speed of wireless communication, a communication system that uses a broadband modulation signal in a millimeter wave band, a submillimeter wave band, or a terahertz wave band, which has a higher carrier frequency than before, has been studied. In the following description, the millimeter wave band, submillimeter wave band, terahertz wave band, and the like are collectively referred to as the millimeter wave band.

  In the multi-level quadrature amplitude modulation method with high frequency utilization efficiency, since a small phase error causes deterioration of transmission characteristics, it is required to accurately measure the phase error of a broadband modulation signal. In general, in a broadband signal measurement circuit used in the millimeter wave band, the phase characteristic of the frequency conversion unit in the measurement circuit cannot be ignored, so it is important to calibrate the phase characteristic of the broadband signal measurement circuit.

  FIG. 10 shows a configuration example 1 of a phase characteristic calibration system as a related technique (see, for example, Non-Patent Document 1). This phase characteristic calibration system 100 calibrates the phase characteristics (phase frequency characteristics) of the millimeter waveband signal measurement unit 150, and includes a short pulse light source 111, an optical variable delay unit 113, a synchronization processing unit 115, A calibration signal generation unit 120, an electro-optic frequency conversion unit 130, and a phase difference calculation unit 140 are provided.

Pulsed light P ₁₀ output at a predetermined repetition frequency by the short pulse light source 111 is transmitted to the optical variable delay unit 113 through the optical splitter 112, it is delayed by the optical variable delay unit 113 electrooptical frequency converter 130 polarization separators 132 are sent. The optical variable delay device 113 changes the optical delay time by mechanically moving the position of the mirror 113a.

On the other hand, in the calibration signal generation unit 120, the intermediate frequency signal generated by the intermediate frequency signal generator 121 and the local wave signal of CW (Continuous Wave) generated by the local wave signal generator 122 are converted into a frequency converter 123. The intermediate frequency signal is frequency-converted (up-converted) into a millimeter wave band, and is output from the horn antenna 124 to the electro-optic crystal 131 as a calibration signal _Er . At this time, the intermediate frequency signal and the local oscillation signal are synchronized with the repetition frequency of the short pulse light source 111 by the synchronization processing unit 115, and thereby, the calibration signal _Er in the millimeter wave band synchronized with the repetition frequency of the short pulse light source 111. Is obtained.

  Specifically, using a phase locked loop (PLL) circuit, a sampling clock that is an integral multiple of the repetition frequency of the short pulse light source 111 is supplied to the D / A converter of the intermediate frequency signal generator 121 and the local oscillation signal The reference frequency of the local signal generator 122 is controlled so that the frequency is an integral multiple of the repetition frequency of the short pulse light source 111. By appropriately setting the period of the digital data given to the D / A converter so that the frequency of the intermediate frequency signal is an integral multiple of the repetition frequency of the short pulse light source 111, the frequency of the calibration signal is the repetition of the short pulse light source 111. The integral multiple of the frequency, that is, the repetition period of the short pulse light source 111 is an integral multiple of the period of the calibration signal.

In the electro-optic frequency converter 130, the electric field of the calibration signal _Er is applied to the electro-optic crystal 131, and the short pulse light P ₁₁ from the optical variable delay device 113 is passed through the polarization separator 132. And the short pulse light reflected at the tip of the electro-optic crystal 131 is input to the light receiver 133 via the polarization separator 132 (see, for example, Non-Patent Document 2). Specifically, when an electric field is applied to the electro-optic crystal 131, the polarization of the reflected light from the electro-optic crystal 131 is changed by the electro-optic effect, and the polarization of the reflected light is changed by the polarization separator 132 and the light receiver 133. Changes are detected.

The electrical signal output from the light receiver 133 is proportional to the electric field applied to the electro-optic crystal 131 and also to the optical power of the reflected light from the electro-optic crystal 131. Therefore, calibration electrical signal proportional to the product of the optical power of the signal E _r of the field and the short pulse light P ₁₁ is output, low speed photodetector 133 for detecting only the low-frequency components, electro-optical frequency conversion unit 130 have the same functions as a mixer for frequency-converting the electric signal E ₁₀ calibration signal E _r of the low frequency in the millimeter wave band (down-conversion).

When sufficiently shorter than the inverse of the maximum frequency of the short pulse light P ₁₁ pulse width calibration signal E _r of the electrical electrical signals E ₁₀ outputted from the optical frequency conversion unit 130, calibration signal E _r short optical pulses P ₁₁ Sampled at a repetition period of For the repetition period of the short-pulse light source 111 is an integer multiple of the period of the calibration signal E _r, it will sample repeatedly particular point repeating waveform of the calibration signal E _r. By varying the delay time of the optical variable delay unit 113, since the time of sampling the calibration signal E _r with pulsed light P ₁₁ is changed, the output from the electro-optical frequency conversion unit 130 while changing the delay time of the optical variable delay unit 113 When the electric signal E ₁₀ to be recorded is recorded, the time waveform of the calibration signal _Er in the millimeter wave band can be measured by the low-speed light receiver 133. A signal processing such as Fourier transform is performed on the time waveform of the calibration signal _{Er in} the phase difference calculation unit 140, whereby the signal is converted into the frequency domain and the phase characteristic is calculated.

The millimeter waveband signal measurement unit 150 includes a local oscillator signal generator 152 that generates a CW local oscillator signal, a frequency converter 151 such as a mixer, an intermediate frequency signal measuring instrument 153 such as an A / D converter, and a phase A correction unit 154, which converts the millimeter wave calibration signal _Er or the signal under measurement into an intermediate frequency signal (down-converted) and converts it into a digital signal. By analyzing this digital signal, a measurement result such as an error vector amplitude (EVM) can be obtained.

The calibration signal _Er generated by the calibration signal generation unit 120 is sent to the millimeter waveband signal measurement unit 150 and input to the frequency converter 151, and the CW generated by the local signal generator 152 is transmitted from the local station. The signal is input to the frequency converter 151. The calibration signal _Er is frequency-converted (down-converted) to an intermediate frequency signal by the frequency converter 151 and then converted to a digital signal by the intermediate frequency signal measuring device 153. The digital signal is subjected to signal processing such as Fourier transform in the phase difference calculation unit 140, so that the digital signal is converted into the frequency domain, and the phase characteristic is calculated.

  The phase characteristic of the calibration signal measured by the electro-optic frequency converter 130 as described above and the phase characteristic of the digital signal output from the intermediate frequency signal measuring device 153 by inputting the calibration signal to the millimeter waveband signal measuring unit 150. Based on the above, the phase characteristic of the millimeter waveband signal measurement unit 150 itself is calculated and set in the phase corrector 154 as a phase correction value. When the signal under measurement is measured by the millimeter waveband signal measuring unit 150, the phase characteristics of the millimeter waveband signal measuring unit 150 are corrected by the phase corrector 154 and output as a measurement result.

Next, a method for calibrating the frequency characteristics of the amplitude and phase of the millimeter waveband signal measurement unit 150 will be described in more detail. The frequency characteristic (complex number including phase) of the calibration signal is X _c (f), the frequency characteristic (complex number including phase) of the millimeter wave band signal measurement unit 150 is G (f), and the calibration signal is the millimeter wave band signal measurement unit 150. Let Y _c (f) be the frequency characteristic (complex number including phase) of the output signal from the intermediate frequency signal measuring device 153 when it is input to. As described above, X _c (f) is obtained from the time waveform of the calibration signal measured by inputting the calibration signal to the electro-optic frequency conversion unit 130, and the calibration signal is input to the millimeter waveband signal measurement unit 150 to be frequency converted. Y _c (f) is obtained from the waveform of the intermediate frequency signal, and G (f) can be obtained from the following equation (1).

ここで、ｆ_ＬＯはミリ波帯信号測定部１５０の局発信号の周波数である。

Here, f _LO is the frequency of the local oscillation signal of the millimeter waveband signal measurement unit 150.

  The frequency characteristic (complex number including phase) of the signal under measurement is X (f), and when the signal under measurement is input to the millimeter waveband signal measurement unit 150, the frequency characteristic (phase Assuming that Y (f) is a complex number (including complex number), X (f) in which the frequency characteristics of the millimeter waveband signal measuring unit 150 are corrected can be obtained as a measurement result by the following equation (2).

  FIG. 11 shows a configuration example 2 of another phase characteristic calibration system as a related technique (see, for example, Non-Patent Document 3). This phase characteristic calibration system 200 uses a two-tone light source 211 instead of the short pulse light source 111 and the optical variable delay device 113 of the above configuration example 1, and the electro-optic frequency converter 230 uses the polarization separator 132. Instead, the configuration is the same as the configuration example 1 of the phase characteristic calibration system 100 described above except that the optical circulator 232 and the like are used and the synchronization processing unit 115 is not connected to the calibration signal generation unit 220.

Next, the principle of frequency conversion in the phase characteristic calibration system 200 will be described.
FIG. 12 is an explanatory diagram showing the operation of the phase characteristic calibration system 200 of FIG. 11 by spectrum. 12A shows the frequency component of the output light (two-tone light P ₂₀ ) output from the two-tone light source 211, and FIG. 12B shows the calibration signal E _r output from the calibration signal generator 220. FIG. 12C shows the frequency component of the optical signal P ₂₁ input from the optical circulator 232 to the optical bandpass filter 233, and FIG. 12D shows the output from the light receiver 234. It shows the frequency components of the electrical signal E _20.

As shown in FIG. 12A, the two-tone light source 211 outputs two lights (two-tone lights P ₂₀ ) having optical frequencies f ₁ and f ₂ with the same polarization, and at this time, the difference between the two optical frequencies. Let f _L = f ₂ −f ₁ . The two-tone light P ₂₀ output from the two-tone light source 211 is input to the electro-optical crystal 231 via the optical circulator 232, and the light reflected by the electro-optical crystal 231 is input to the optical bandpass filter 233 via the optical circulator 232. Entered. On the other hand, as shown in FIG. 12B, the calibration signal generation unit 220 generates a calibration signal _Er that is a multitone signal having a carrier frequency f _c and a frequency interval f _m , and electro-optics via the horn antenna 224. Sent to the crystal 231.

When the electric field of the multitone signal from the calibration signal generator 220 is applied to the electro-optic crystal 231, sidebands are generated in the optical signal P ₂₁ reflected by the electro-optic crystal 231 as shown in FIG. The relationship between the optical frequency difference f _L of the two-tone light P ₂₀ and the carrier frequency f _c of the calibration signal _Er is f _L = f _c + f _IF, and light near the optical frequency f ₂ is extracted by the optical bandpass filter 233. If you enter the light receiver 234, and beat generated between the sideband in the vicinity of the optical and f ₂ of the optical frequency f _2, FIG. 12 (d), the center frequency is the frequency interval f _IF f _m The electrical signal (intermediate frequency signal E ₂₀ ) is obtained.

Here, although ignored beat between sideband frequency interval f _m, it is possible to remove the beat component between sideband easily by the bandpass filter when properly setting the relationship between f _IF and f _m. As described above, the calibration signal E _r of the carrier frequency f _c is a center frequency is frequency-converted into an intermediate frequency signal E ₂₀ of f _IF.

Since the phase relationship between the multitones is maintained in the above frequency conversion, the intermediate frequency f _IF is set to a frequency band in which A / D conversion is possible, and the phase difference calculation unit 240 converts the intermediate frequency signal E ₂₀ into A / D. The phase difference between multitones can be calculated by conversion. Similarly to the configuration example 1 of the related art described above, the phase characteristic measured by inputting the calibration signal to the electro-optic frequency converter 230 and the phase measured by inputting the calibration signal to the millimeter waveband signal measuring unit 250. From the characteristics, a phase correction value is obtained and set in the phase corrector 254 of the millimeter waveband signal measuring unit 250. During measurement, the signal to be measured is input to the millimeter waveband signal measuring section 250 to calibrate the phase characteristics. Measurement results can be obtained.

Yukiyasu Kimura, Yasunori Fuse, Noriaki Machitori, Takashi Mori, "Examination of Phase Calibration Method for Terahertz Wave Downconverter Using Electro-Optical Sampling Method", 2018 IEICE General Conference Proceedings, BCI-1-7, 2018 A. Sasaki and T. Nagatsuma, "Millimeter-Wave Imaging Using an Electrooptic Detector as a Harmonic Mixer", IEEE Journal of Selected Topics in Quantum Electronics, vol. 6, no. 5, pp. 735-740, 2000 S. Hisatake, "Visualization of millimeter and terahertz waves based on photonics", 2016 IEEE International Topical Meeting on Microwave Photonics, pp. 73-74, 2016

  However, in the phase characteristic calibration system of FIG. 10, it is necessary to sweep the optical variable delay device 113 in order to obtain the time waveform of the calibration signal. The optical variable delay device 113 has a mechanical movable part, which has the problems of being affected by mechanical vibration, limited operation speed, and short life. In particular, in order to improve the frequency resolution of the phase calibration, it is necessary to increase the time span of the time waveform, that is, to increase the delay time of the optical variable delay device 113, so that the physical dimensions of the optical variable delay device 113 are increased. There was a problem of getting bigger. Further, in order to increase the conversion efficiency of the electro-optic frequency conversion unit 130, it is necessary to increase the optical power of the short pulse light, but since the pulse is short, the peak power becomes very large, and the pulse waveform is caused by a nonlinear effect such as an optical fiber. Is deformed, and there is a problem that the conversion characteristic of the electro-optic frequency converter 130 changes.

  In the phase characteristic calibration system of FIG. 11, the problem of the optical variable delay device and short pulse light does not occur, but the electro-optic frequency converter 230 down-converts the calibration signal and shifts the frequency as a whole. The frequency interval of the three continuous waves of the calibration signal does not change even after the frequency conversion, and it is necessary to calculate the phase difference between the spectral components having a relatively wide frequency interval. For this reason, there has been a problem that the phase measurement accuracy deteriorates due to the influence of the frequency dependence of the phase of the light receiver 234 and subsequent electrical circuits. In addition, the light receiver 234 having a relatively wide band and the A / D converter in the phase difference calculation unit 240 are required, and the sampling frequency of the A / D conversion becomes high and the amount of data increases. There is a problem that the amount is increased and the apparatus is expensive.

  The present invention has been made to solve the above-described problems, and provides an inexpensive phase characteristic calibration apparatus and phase characteristic calibration method capable of accurately calibrating the phase characteristics of a millimeter waveband signal measurement circuit. For the purpose.

In order to achieve the above object, a phase characteristic calibration apparatus according to claim 1 of the present invention is a phase characteristic calibration apparatus (1) for calibrating the phase characteristic of a measurement circuit (50), and has three or more waves having different frequencies. A generator (20) that generates a calibration signal (E _r ) in which continuous waves are combined, a first light in which three or more continuous lights having different frequencies are combined, and three waves of the first light A generator (10) for generating local light (P _L ) synthesized with second light that is continuous light having a frequency smaller than or greater than any of the above continuous light, and using the local light The frequency conversion unit (30) that outputs the intermediate frequency signal (E _IF ) in which three or more continuous waves in the intermediate frequency band are synthesized by frequency conversion of the calibration signal by the electro-optic effect, and 3 of the calibration signal. Change the frequency of continuous wave above the wave within the specified frequency band And a frequency interval between the first light and the second light according to a frequency value to be changed for each frequency change by the frequency change unit (70), and the intermediate frequency The phase difference between three or more continuous waves of the signal is calculated, the first phase difference characteristic over the entire predetermined frequency band is obtained, and the measurement is performed each time the frequency is changed by the frequency changing unit. The calibration signal is measured using a circuit to calculate a phase difference between three or more continuous waves output from the measurement circuit, and a second phase difference characteristic over the predetermined frequency band is obtained. And a calibration unit (40) that calibrates the phase characteristics of the measurement circuit based on the acquired first and second phase difference characteristics, and has three or more continuous waves of the intermediate frequency signal. In any frequency, the calibration signal is continuous for 3 or more waves. And the frequency interval of three or more continuous waves of the calibration signal is different from the frequency interval of three or more continuous lights of the first light, and the intermediate frequency signal The frequency of the calibration signal and the local light is set so that the frequency interval of the continuous wave of three or more waves is narrower than the frequency interval of the three or more continuous waves of the calibration signal. And

  With this configuration, the phase characteristic calibration apparatus according to claim 1 of the present invention does not use the optical variable delay device having the mechanical movable unit as described in Configuration Example 1 in FIG. The phase characteristic can be calibrated with high frequency resolution without being restricted by the above. In addition, since the short pulse light is not used as in the configuration example 1 of FIG. 10, the short pulse light waveform is not deformed and the conversion characteristics of the electro-optic frequency conversion unit are not changed.

  In addition, the phase characteristic calibrating apparatus according to claim 1 of the present invention is set such that the frequency interval of three or more continuous waves of the intermediate frequency signal is narrower than the frequency interval of three or more continuous waves of the calibration signal. As a result, the band handled by the electric circuit can be narrower than in the prior art, and the phase of the calibration signal can be measured with high accuracy using a low-speed A / D converter with a small amount of calculation. For this reason, an apparatus price can also be reduced.

  In the phase characteristic calibrating apparatus according to claim 2 of the present invention, the generator (10) includes a first CW signal generator (11) for generating a first continuous wave signal, and the first continuous wave signal. An optical comb generator (12) for generating an optical comb having a plurality of optical spectral components at a frequency interval of; an optical splitter (13) for splitting the output light from the optical comb generator into two; A first optical bandpass filter (14) and a second optical bandpass filter (15) for extracting different optical spectral components from one and the other output lights of the optical splitter, respectively, and a second continuous wave signal A second CW signal generator (16) that generates the second continuous wave by applying amplitude modulation or phase modulation to the output light of the second optical bandpass filter with the second continuous wave signal. Generate multiple sidebands at signal frequency intervals Optical modulator (17), and the first optical multiplexer for multiplexing the output light of the optical modulator and the output light of the optical bandpass filter (18), characterized by having a.

  With this configuration, the phase characteristic calibrating device according to claim 2 of the present invention is configured to combine the first light obtained by combining three or more continuous lights having different frequencies and the three or more continuous lights of the first light. It is possible to generate local light in which the second light which is continuous light having a frequency lower than or higher than any frequency is combined. Further, every time the frequency changing unit changes the frequency, the frequency interval between the first light and the second light can be changed continuously and over a wide range according to the value of the changed frequency.

  In the phase characteristic calibrating device according to claim 3 of the present invention, the first CW signal generator, the second CW signal generator, and the generation unit have the first frequency synchronized with a common reference frequency. The continuous wave signal, the second continuous wave signal, and the calibration signal are respectively generated, and the frequency of the three or more continuous waves of the intermediate frequency signal is synchronized with the reference frequency, respectively. To do.

  With this configuration, the phase characteristic calibrating device according to claim 3 of the present invention can obtain three or more continuous waves in the intermediate frequency band without a frequency error, and the calibration unit can obtain a continuous wave of three or more waves in the intermediate frequency band. Can be easily calculated.

According to a fourth aspect of the present invention, there is provided a phase characteristic calibrating apparatus for performing a frequency conversion by amplifying three or more continuous waves of the intermediate frequency signal between the frequency converting unit and the calibrating unit. A second frequency conversion unit (60) that outputs a second intermediate frequency signal (E _IF2 ) in which three or more continuous waves of the band are combined, and the calibration unit, instead of the intermediate frequency signal, A phase difference between three or more continuous waves of the second intermediate frequency signal output from the second frequency conversion unit is calculated, and any frequency of three or more continuous waves of the second intermediate frequency signal is calculated. The intermediate frequency signal is set to be lower than any frequency of three or more continuous waves of the intermediate frequency signal.

  With this configuration, the phase characteristic calibrating device according to claim 4 of the present invention includes the second frequency conversion unit, so that the intermediate frequency band is set to a frequency at which 1 / f noise of the electric circuit is reduced, After sufficiently amplifying with the amplifier of the frequency conversion unit, it can be converted to a sufficiently low second intermediate frequency band. As a result, it is possible to realize an inexpensive apparatus by reducing the band and sampling rate of the A / D converter and the like of the calibration unit while maintaining a high S / N ratio while avoiding 1 / f noise of the electric circuit.

  In the phase characteristic calibrating apparatus according to claim 5 of the present invention, the second frequency converter is an orthogonal frequency converter (60A) that outputs an in-phase component and an orthogonal component of the second intermediate frequency signal. And

  With this configuration, the phase characteristic calibration apparatus according to claim 5 of the present invention can prevent the negative frequency component from being folded back by the second frequency converter.

The phase characteristic calibrating apparatus according to claim 6 of the present invention performs frequency conversion by amplifying three or more continuous waves of the intermediate frequency signal between the frequency conversion unit and the calibration unit to perform frequency conversion. A second frequency conversion unit (60) that outputs a second intermediate frequency signal (E _IF2 ) in which three or more continuous waves of the band are combined, and the calibration unit, instead of the intermediate frequency signal, A phase difference between three or more continuous waves of the second intermediate frequency signal output from the second frequency conversion unit is calculated, and any frequency of three or more continuous waves of the second intermediate frequency signal is calculated. The intermediate frequency signal is set to be lower than any frequency of three or more continuous waves of the intermediate frequency signal.

  With this configuration, the phase characteristic calibrating device according to claim 6 of the present invention is provided with the second frequency converter, so that the intermediate frequency band is set to a frequency at which 1 / f noise of the electric circuit is reduced, After sufficiently amplifying with the amplifier of the frequency conversion unit, it can be converted to a sufficiently low second intermediate frequency band. As a result, it is possible to realize an inexpensive apparatus by reducing the band and sampling rate of the A / D converter and the like of the calibration unit while maintaining a high S / N ratio while avoiding 1 / f noise of the electric circuit.

  In the phase characteristic calibrating apparatus according to claim 7 of the present invention, the second frequency converter is an orthogonal frequency converter (60A) that outputs an in-phase component and an orthogonal component of the second intermediate frequency signal. And

  With this configuration, the phase characteristic calibration apparatus according to claim 7 of the present invention can prevent the negative frequency component from being folded back by the second frequency converter.

  In the phase characteristic calibrating apparatus according to claim 8 of the present invention, the first CW signal generator, the second CW signal generator, and the generation unit have the first frequency synchronized with a common reference frequency. The second continuous wave signal, the second continuous wave signal, and the calibration signal are respectively generated, and the second frequency converter performs frequency conversion based on a local oscillation signal synchronized with the reference frequency, and the second frequency converter The frequency of three or more continuous waves of the intermediate frequency signal is respectively synchronized with the reference frequency.

  With this configuration, the phase characteristic calibrating device according to claim 8 of the present invention can obtain three or more continuous waves in the intermediate frequency band without frequency error, and the calibration unit can obtain a continuous wave of three or more waves in the intermediate frequency band. Can be easily calculated.

A phase characteristic calibration method according to a ninth aspect of the present invention is a phase characteristic calibration method for calibrating the phase characteristic of the measurement circuit (50), wherein a calibration signal (three or more continuous waves having different frequencies are synthesized) The generation step of generating E _r ), the first light obtained by synthesizing the continuous light of three or more waves having different frequencies, and the frequency of the continuous light of three or more waves of the first light is smaller than Or a generation step of generating local light (P _L ) synthesized with the second light which is continuous light having a large frequency, and an intermediate frequency by frequency-converting the calibration signal by the electro-optic effect using the local light. A frequency conversion step for outputting an intermediate frequency signal (E _IF ) in which three or more continuous waves of the band are synthesized, and a frequency change for changing the frequency of the three or more continuous waves of the calibration signal within a predetermined frequency band Steps and said lap Each time the frequency is changed by the number changing step, the frequency interval between the first light and the second light is changed according to the value of the changed frequency, and between the three or more continuous waves of the intermediate frequency signal The first phase difference characteristic over the entire predetermined frequency band is acquired, and the calibration signal is measured using the measurement circuit for each frequency change in the frequency changing step. Calculating a phase difference between three or more continuous waves output from the measurement circuit, obtaining a second phase difference characteristic over the entire predetermined frequency band, and obtaining the obtained first and second A calibration step for calibrating the phase characteristic of the measurement circuit based on the phase difference characteristic of 2, and any frequency of three or more continuous waves of the intermediate frequency signal is equal to or greater than three waves of the calibration signal. Than any frequency of continuous wave And the frequency interval of three or more continuous waves of the calibration signal is different from the frequency interval of three or more continuous lights of the first light, and the intermediate frequency signal of three or more continuous waves is continuous. Each frequency of the calibration signal and the local light is set so that a frequency interval of the waves is narrower than a frequency interval of continuous waves of three or more waves of the calibration signal.

  With this configuration, the phase characteristic calibration method according to claim 9 of the present invention does not use the optical variable delay device having the mechanical movable portion as described in Configuration Example 1 in FIG. The phase characteristic can be calibrated with high frequency resolution without being restricted by the above. In addition, since the short pulse light is not used as in the configuration example 1 of FIG. 10, the short pulse light waveform is not deformed and the conversion characteristics of the electro-optic frequency conversion unit are not changed.

  In addition, the phase characteristic calibration method according to claim 9 of the present invention is set such that the frequency interval of three or more continuous waves of the intermediate frequency signal is narrower than the frequency interval of three or more continuous waves of the calibration signal. Therefore, the band handled by the electric circuit can be made narrower than in the prior art, and the phase of the calibration signal can be measured with high accuracy using a low-speed A / D converter with a small amount of calculation. For this reason, an apparatus price can also be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the inexpensive phase characteristic calibration apparatus and phase characteristic calibration method which can calibrate the phase characteristic of a millimeter wave band signal measuring circuit with sufficient precision can be provided.

It is a block diagram of the phase characteristic calibration apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows the spectrum of each signal of the phase characteristic calibration apparatus of FIG. It is explanatory drawing which shows the spectrum of each signal of the phase characteristic calibration apparatus of FIG. It is a block diagram of an electro-optic frequency converter. It is another block diagram of an electro-optic frequency conversion part. It is a block diagram of the phase characteristic calibration apparatus which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which shows the spectrum of each signal of the phase characteristic calibration apparatus of FIG. It is a block diagram of the phase characteristic calibration apparatus which concerns on the 3rd Embodiment of this invention. It is explanatory drawing which shows the spectrum of each signal of the phase characteristic calibration apparatus of FIG. It is a block diagram of the phase characteristic calibration system which concerns on related technology. It is a block diagram of another phase characteristic calibration system which concerns on related technology. It is explanatory drawing which shows the spectrum of each signal of the phase characteristic calibration system of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a configuration diagram of a phase characteristic calibration apparatus 1 according to the first embodiment of the present invention.
The phase characteristic calibration apparatus 1 calibrates the phase characteristic in a predetermined frequency band of the millimeter waveband signal measurement unit 50 which is a measurement circuit to be calibrated. The phase characteristic calibration apparatus 1 includes a local light generation unit 10, a calibration signal generation unit 20, an electro-optic frequency conversion unit 30, a calibration processing unit 40, and a frequency change unit 70.

[Local light generator]
First, the local light generation unit 10 will be described.
The local light generator 10 includes a first CW signal generator 11, an optical comb generator 12, an optical splitter 13, a first optical bandpass filter (BPF) 14, and a second optical bandpass filter (BPF). ) 15, a second CW signal generator 16, an optical phase modulator 17, and an optical multiplexer 18. The local light generation unit 10 is smaller or larger than any frequency of the first light P ₄ in which continuous light of three or more waves having different frequencies is combined and the continuous light of three or more waves of the first light. the second and the light P ₂ is a continuous light of frequency is adapted to generate a synthesized local light P _L. The local light generating unit 10 corresponds to the generating unit of the present invention.

The first CW signal generator 11 outputs a CW signal (electric signal) E ₁ having a frequency f _L1 .

The optical comb generator 12 receives the CW signal E ₁ having the frequency f _L1 and, as shown in FIG. 2A, the optical comb P ₁ having a large number of optical spectrum components with the frequency interval f _L1 centered on the optical frequency f _0. Is supposed to occur. Specifically, the optical comb generator 12 includes a CW light source having an optical frequency f ₀ , an optical phase modulator to which a CW signal having a frequency f _L1 is input, and a Fabry having a free spectral range that is an integer of f _L1. A combination with a Perot resonator may be used, or a mode-locked laser with a center optical frequency f ₀ that outputs a short pulse light with a repetition frequency f _L1 may be used. In the former case, the spectral width of the optical comb P ₁ can be widened by increasing the finesse of the Fabry-Perot resonator, and in the latter case, by narrowing the pulse width of the short pulse light.

The output side of the optical comb generator 12, by adding an optical pulse compressor, such as a highly nonlinear optical fiber (not shown), it is possible to further widen the spectral width of the optical comb P _1. For example, the optical comb P ₁ having a width of several hundreds GHz to several THz can be generated at intervals of several tens of GHz.

The optical branching device 13 branches the optical comb P ₁ output from the optical comb generator 12 into two and sends them to the first optical bandpass filter 14 and the second optical bandpass filter 15, respectively. .

上記式（３）において、光周波数が高い方をｆ_２としている（ｆ_２＞ｆ_１）。ｎは整数である。 The first optical bandpass filter 14 and the second optical bandpass filter 15 each extract predetermined optical spectrum components different from each other. Assuming that the optical frequencies of the extracted optical spectrum components are f ₁ and f ₂ , the frequency interval is expressed by the following equation (3).

In the above formula (3), the higher optical frequency is defined as f ₂ (f ₂ > f ₁ ). n is an integer.

As will be described in detail later, when obtaining the phase characteristics of the calibration signal in a predetermined frequency band, the frequency interval f ₂ -f ₁ between the two optical spectrum components is changed according to the frequency of the calibration signal. To do. Specifically, an optical spectral component that changes the frequency f _L1 of the CW signal E ₁ generated by the first CW signal generator 11 or is selected by the first optical bandpass filter 14 or the second optical bandpass filter 15. By changing n by changing, the frequency interval f ₂ −f ₁ can be changed. Although the frequency f _L1 of the CW signal E ₁ can be continuously changed, it is difficult to make the wide frequency range variable. If you alter the n by changing the optical spectral components selected by the first optical band-pass filter 14 or the second optical bandpass filter 15 can be varied greatly frequency interval f ₂ -f _1, continuously variable Can not be. Therefore, by combining both, the frequency interval f ₂ −f ₁ can be changed continuously and over a wide range.

Here, the optical spectrum components extracted by the first and second optical bandpass filters 14 and 15 are equally spaced from the center optical frequency f ₀ of the optical comb P ₁ (f ₂ −f ₀ = f ₀ −f ₁ ), That is, two optical spectrum components having substantially the same amplitude may be used. Alternatively, in consideration of the loss of the optical phase modulator 17 described later, an optical spectrum close to the center optical frequency f ₀ so that the amplitude on the second optical bandpass filter 15 side becomes large as shown in FIG. May be extracted (f ₂ −f ₀ <f ₀ −f ₁ ). Further, instead of the optical splitter 13 and the first and second optical bandpass filters 14 and 15, an arrayed waveguide grating (AWG) is used to perform branching and optical spectrum extraction with one device. May be. The optical spectra of the output lights P ₂ and P ₃ from the first and second optical bandpass filters 14 and 15 are as shown in FIG.

The second CW signal generator 16 outputs a CW signal (electric signal) E ₂ having a frequency f _L2 to the optical phase modulator 17.

The optical phase modulator 17 changes the phase of light input to the crystal by applying a voltage to the crystal using, for example, the electro-optic effect of the LiNbO ₃ crystal. By inputting the CW signal E ₂ of the frequency f _L2 to the optical phase modulator 17 applies a phase modulation to the optical spectrum component of the optical frequency f _2, around the optical frequency f ₂ as shown in FIG. 2 (c) generating a sideband of the frequency interval _{f L2.} The optical phase modulator 17 corresponds to the optical modulator of the present invention.

Here, the amplitude of the sideband wave changes depending on the degree of modulation of phase modulation. For example, when the input voltage of the optical phase modulator 17 is a sine wave of 0.913 V _π (peak-to-peak), the optical frequency f ₂ −f _L2, 3 one light spectral component of _{f 2, f} 2 _{+ f L2} is substantially the same amplitude. Here, V _π is a voltage value necessary for changing the phase of light by _π in the optical phase modulator 17.

Further, by inputting to the optical phase modulator 17 by superimposing a sine wave of frequency _{2f L2} in addition to the sine wave of the frequency _{f L2,} the optical frequency _{f 2 -2f L2, f 2 -f} L2, f 2, f The five optical spectrum components of ₂ + f _L2 and f ₂ + 2f _L2 can have substantially the same amplitude.

Further, instead of the optical phase modulator 17, a side band wave having a frequency interval f _L2 may be generated similarly using an optical intensity modulator. For example, linear light modulation is performed by using a region where the input voltage of the Mach-Zehnder light intensity modulator is approximately proportional to the output optical electric field amplitude, or by correcting the nonlinear characteristic of the relationship between the input voltage and the output optical electric field amplitude. be able to.

For example, a DC component and a sine wave of frequency f _L2 are input to the light intensity modulator to generate three optical spectrum components of optical frequencies f ₂ −f _L2 , f ₂ , f ₂ + f _L2 , or A sine wave having a frequency f _L2 and a frequency 2f _L2 is input to the optical intensity modulator, and five optical spectra of optical frequencies f ₂ −2f _{L 2} , f ₂ −f _{L 2} , f ₂ , f ₂ + f _{L 2} , and f ₂ + 2f _{L 2} are input. Various optical spectral components can be generated, such as generating components. When the optical spectrum spread by the optical phase modulator 17 or the optical intensity modulator instead thereof is smaller than the frequency interval of the optical comb P ₁ , the second optical bandpass filter 15 and the optical phase modulator 17 or the optical intensity modulation are used. The order of the vessels may be reversed.

Optical multiplexer 18, the output light P ₂ of the first optical band-pass filter 14, and an output light P ₄ optical phase modulator 17 combined polarization multiplexes, so as to output as a local light P _L It has become. Bureau optical spectrum of the light-emitting P _L is as shown in Figure 2 (d). The output light P ₄ optical phase modulator 17 corresponds to the first light of the present invention, the output light P ₂ of the first optical band-pass filter 14 corresponds to the second light of the present invention.

The local light generator 10 may be inserted with an optical attenuator or an optical amplifier for adjusting the optical power as required. For example, in order to adjust the intensity ratio of the optical spectral components of the optical frequency f ₁ and the optical frequency f ₂ , the variable optical attenuation is applied to at least one of the optical path of the first optical bandpass filter 14 or the optical path of the second optical bandpass filter 15. A vessel may be inserted. Further, in order to increase the optical power of the local light P _L, it may be inserted an optical fiber amplifier after the optical coupler 18.

[Calibration signal generator]
Next, the calibration signal generation unit 20 will be described.
As shown in FIG. 1, the calibration signal generator 20 includes an intermediate frequency signal generator 21, a local oscillator signal generator 22, and a frequency converter 23. The calibration signal generation unit 20 is configured to generate a calibration signal _{Er in} which three or more continuous waves having different frequencies within a predetermined frequency band are synthesized. Specifically, the calibration signal generating unit 20, as shown in FIG. 2 (e), the frequency _{f c -f m, f c,} the electrical signal of a millimeter wave band, including at least three spectral components of f c + _{f m} (Calibration signal E _r ) is output. The calibration signal generation unit 20 corresponds to the generation unit of the present invention.

Intermediate frequency signal generator 21, a D / A converter, which is an intermediate frequency signal E ₃ comprising at least three spectral components of the frequency interval f _m such that the output directly by the D / A converter. Instead of the D / A converter, an oscillator for generating a CW signal at an intermediate frequency, an oscillator for generating a CW signal of a frequency f _m, may generate an intermediate frequency signal E ₃ with a mixer .

Local oscillation signal generator 22 is adapted to generate a local oscillation signal E ₄ of CW. Local oscillation signal generator 22 for generating a local oscillation signal E ₄ in the millimeter wave band may include a frequency multiplier for converting a frequency an integer multiple.

The frequency converter 23 includes a mixer, for example, and uses the local signal E ₄ generated by the local signal generator 22 to frequency-convert (up-convert) the intermediate frequency signal E ₃ , for example, a horn The antenna 24 radiates as a calibration signal _Er . Instead of the horn antenna 24, a waveguide, a coaxial cable, or a coaxial connector may be used to connect to the electro-optic frequency converter 30 or the millimeter waveband signal measuring unit 50. The calibration signal generation unit 20 in FIG. 1 is configured to perform frequency conversion once, but may be configured to perform frequency conversion multiple times.

  The intermediate frequency signal generator 21 and the local signal generator 22 are connected to the first CW signal generator 11 and the second CW signal generator 16 of the local light generation unit 10 using, for example, a reference signal of 10 MHz. Although the frequency is synchronized, it is not always necessary to synchronize the frequency.

  In general, in the measurement of phase characteristics, a wideband signal that covers the frequency band that requires phase characteristic calibration is used as the calibration signal, and the frequency band that requires phase characteristic calibration is divided into a plurality of methods. There is a method in which a narrow band signal is used as a calibration signal and a plurality of measurements are performed to obtain a phase characteristic of a necessary band. In the present embodiment, the latter method is used, and a multitone signal having three or more waves (that is, three or more continuous waves having different frequencies) is used as a calibration signal, and a multitone signal within a predetermined frequency band. The phase characteristic of the frequency band is obtained by detecting the phase difference between the multitones while changing the frequency. However, the present invention is not limited to the latter method, and covers the frequency band that requires phase characteristic calibration by increasing the wave number of the continuous wave of the calibration signal and the wave number of the continuous light of the first light. It is also possible to apply to a method of measuring at a time.

  In general, it is not easy to operate with a relatively high-speed D / A converter or a time origin of an A / D converter fixed, but as will be described in detail later, a multitone signal of three or more waves is used. Thus, the phase characteristics can be obtained even when the time origin is indefinite, that is, the absolute time is unknown, by obtaining the second-order phase difference in the first and second phase difference calculators 41 and 43.

[Electro-optic frequency converter]
Next, the electro-optic frequency converter 30 will be described.
As shown in FIG. 1, the electro-optic frequency converter 30 includes an electro-optic crystal 31, an optical branching unit 32, and a light receiver 33. The electro-optical frequency converter 30, the beat of the local light P _L from the local light generator 10 as a local signal, frequency converted by electro-optical effect calibration signal E _r from the calibration signal generator 20 (down-conversion) 3 or more waves continuous wave intermediate frequency band and outputs the combined intermediate frequency signal E _IF Te. The electro-optic frequency converter 30 corresponds to the frequency converter of the present invention.

Electro-optical frequency conversion unit 30 receives the electric field of the calibration signal E _r is applied with a predetermined orientation of the electro-optic crystal 31, a local light P _L to the electro-optical crystal 31 via the optical branching unit 32, an electro-optical The local light reflected from the tip of the crystal 31 is input to the light receiver 33 via the optical branching section 32.

  FIG. 4 is a configuration diagram illustrating a configuration example of the electro-optic frequency conversion unit 30. The electro-optic frequency converter 30 ′ is a method for detecting a change in the polarization of the reflected light from the electro-optic crystal 31. Specifically, the electro-optic frequency converter 30 includes a polarizing beam splitter (PBS) 32 ′, a half-wave plate (HWP) 35, a quarter-wave plate (QWP) 36, and the electro-optic crystal 31. And a light receiver 33.

Polarization beam splitter 32 ', a local light P _L of the input linearly polarized waves to transmit, the polarization beam splitter 32' is the direction of being set. The half-wave plate 35 and the quarter-wave plate 36 reflect half of the optical power of the reflected light from the electro-optic crystal 31 by the polarization beam splitter 32 ′ when no electric field is applied to the electro-optic crystal 31. The ½ wavelength plate 35 and the ¼ wavelength so that the change in the optical power input to the photoreceiver 33 when the electric field is applied to the electrooptic crystal 31 and the electrooptic crystal 31 is maximized. It is desirable to adjust the direction of the plate 36. In order to increase the reflectance of local light, it is desirable to attach a dielectric reflection film 34 to the tip of the electro-optic crystal 31. With this configuration, an electrical signal in which an amplitude component proportional to the electric field applied to the electro-optic crystal 31 is superimposed on an offset corresponding to ½ of the optical power of the reflected light from the electro-optic crystal 31 is output.

  FIG. 5 shows another configuration example of the electro-optic frequency converter. The electro-optic frequency converter 30A is a system that detects a change in the polarization of reflected light from the electro-optic crystal 31 in a differential manner. Specifically, the electro-optic frequency conversion unit 30A includes a polarization beam splitter (PBS) 32a, a half-wave plate (HWP) 35a, the same as the electro-optic frequency conversion unit 30 ′ configured as shown in FIG. In addition to the four-wave plate (QWP) 36, the electro-optic crystal 31, and the light receiver 33a, a polarizing beam splitter (PBS ') 32b, a half-wave plate (HWP') 35b, and a Faraday rotator (FR) 37, a light receiver 33b, and a differential amplifier 38.

Electro-optical frequency conversion unit 30A is a local light P _L of the input linearly polarized waves to transmit, the direction of the polarization beam splitter 32b is set. The direction of the half-wave plate 35 b is set so as to return the polarization rotation of 45 degrees by the Faraday rotator 37 of the incident light. Of the reflected light from the electro-optic crystal 31, the light transmitted through the polarization beam splitter 32a is rotated by 90 degrees, reflected by the polarization beam splitter 32b, and input to the light receiver 33b.

  With this configuration, the outputs of the light receiver 33a and the light receiver 33b have an amplitude component proportional to the electric field applied to the electro-optic crystal 31 at an offset corresponding to ½ of the optical power of the reflected light from the electro-optic crystal 31. Since they are superimposed in opposite directions, the output from the differential amplifier 38 cancels the offset and becomes zero, and the amplitude component proportional to the electric field is doubled. The differential configuration doubles the signal amplitude while the noise does not double, thus improving the signal-to-noise ratio.

  Further, the electro-optic frequency conversion unit 30 uses the optical circulator and the optical bandpass filter as the light branching unit 32 as described as the electro-optic frequency conversion unit 230 in FIG. A method of detecting waves may be used.

Next, the frequency conversion operation in the electro-optic frequency conversion unit 30 will be described.
3 (a) is an optical spectrum of the optical multiplexer 18 the local light P _L output from is an enlarged view of the horizontal axis in FIG. 2 (d). FIG. 3B is a spectrum of the calibration signal _Er output from the calibration signal generation unit 20, and is an enlarged view of the horizontal axis of FIG. f ₂ −f ₁ and f _c are set to different frequencies. Here, an example of f _c > f ₂ −f ₁ is shown, but the magnitude relationship may be reversed. Usually it is desirable to set the _f 2 -f ₁ to a value close to _{f c,} so that the following equation (4) holds.

Furthermore, the frequency interval f _L2 of the continuous light of three or more waves of the first light and the frequency interval f _m of the continuous wave of three or more waves of the calibration signal _Er are set to different frequencies. Here, f _Although an example of _m > f _L2 is shown, the magnitude relationship may be reversed. Usually, it is desirable to set f _L2 to a value close to f _m so that the following equation (5) is satisfied.

A beat having a frequency of f ₂ −f ₁ = nf _L1 is generated by the optical spectrum component of the local light P _{L at} the frequency f _{1 and} the optical spectrum component of the frequency f ₂ , and the electro-optic frequency converter 30 generates the calibration signal E. spectral components _r of frequency _{f c} is frequency-converted to a frequency _f IF1 _{= f} c _{-nf L1.}

Similarly, a beat having a frequency of f ₂ −f _L2 −f ₁ = nf _L1 −f _L2 is generated by the optical spectral component of the frequency f ₁ of the local light P _L and the optical spectral component of the frequency f ₂ −f _L2. and spectral component of the frequency _f c -f _m calibration signal _{E r} by an electro-optical frequency conversion unit 30, the frequency _{f IF1 -f m1 = f c -f} m - is frequency-converted into _(nf L1 _{-f L2)} . Here, the frequency interval after the frequency conversion becomes _f m1 _{= f} m _{-f L2.}

Similarly, a beat with a frequency of f ₂ + f _L2 −f ₁ = nf _L1 + f _L2 is generated by the optical spectral component of the frequency f ₁ of the local light P _L and the optical spectral component of the frequency f ₂ + f _L2. spectral component of the frequency _f c + _{f m} of the calibration signal _{E r} by the optical frequency conversion unit 30, the frequency _{f IF1 + f m1 = f c} + f m - is frequency-converted into _(nf L1 _{+ f L2).} The following expressions (6) and (7) hold from the relationship between the expressions (4) and (5).

That is, the carrier frequency f _c of the calibration signal E _r of the high frequency (millimeter wave band), and at the same time is converted to an intermediate frequency f _IF1 of the low frequency, wide frequency interval f _m in the calibration signal E _r is an intermediate frequency signal E It is converted into a narrow frequency interval f _m1 in _IF . In other words, any frequency of the three or more continuous waves of the intermediate frequency signal E _IF is set to be lower than any frequency of the three or more continuous waves of the calibration signal _Er , The frequency interval of three or more continuous waves of the frequency signal E _IF is set to be narrower than the frequency interval of three or more continuous waves of the calibration signal _Er .

In this way, by converting the calibration signal _Er in the millimeter wave band to an intermediate frequency capable of A / D conversion, and setting the frequency interval f _m1 in the intermediate frequency signal E _IF sufficiently narrow, an electro-optic frequency converter The change in the phase difference of the three spectral components f _IF1 −f _m1 , f _IF1 , f _IF1 + f _m1 due to the frequency characteristics of the electric circuit after 30 light receivers 33 can be made sufficiently small.

If the intermediate frequency f _IF1 is too low, the signal-to-noise ratio deteriorates due to the 1 / f noise of the electric circuit, and if it is too high, a high-speed photoreceiver or A / D converter is required, so select an appropriate frequency. It is desirable to do.

In addition to the above-described frequency conversion, for example, the frequency of f ₂ + f _L2 −f ₁ = nf _L1 + f _L2 between the optical spectrum component of the frequency f ₁ of the local light P _L and the optical spectrum component of the frequency f ₂ + f _L2 There are various combinations in which the spectral component of the frequency f _c of the calibration signal _Er is frequency-converted to a frequency | f _c − (nf _L1 + f _L2 ) | The spectrum of the output signal is as shown in FIG. From these spectra, the low-pass filter or a band-pass filter (not shown), or _by using a narrow photodetector of bands, so as to extract the spectral components in the vicinity of _{f IF1} including _f IF1 _{-f m1, f IF1,} f IF1 _{+ f m1} It may be. FIG. _3D is an enlarged view of the vicinity of the frequency f _IF1 in FIG. The electro-optic frequency converter 30 outputs an intermediate frequency signal E _IF including at least three spectral components of f _IF1 −f _m1 , f _IF1 , and f _IF1 + fm ₁ .

[Frequency changing section]
The frequency changing unit 70 receives an instruction signal from the calibration processing unit 40 and changes the frequency of three or more continuous waves of the calibration signal _Er within a predetermined frequency band. Further, the frequency changing unit 70 determines the frequency interval between the first light (three or more continuous lights) and the second light according to the frequency value of three or more continuous waves of the calibration signal _{Er to be} changed. Is supposed to change.

[Proofreading section]
Next, the calibration processing unit 40 will be described.
As shown in FIG. 1, the calibration processing unit 40 includes a first phase difference calculator 41, a second phase difference calculator 43, an adder 42, and a phase correction value calculator 44. The calibration processing unit 40 receives the phase difference characteristics of the calibration signal Er acquired by using the electro-optic frequency conversion unit 30 and the calibration signal Er from the millimeter wave band signal measurement unit 50 when the calibration signal Er is input to the millimeter wave band signal measurement unit 50. A phase correction value for calibrating the phase characteristic of the millimeter waveband signal measuring unit 50 is calculated based on the phase difference characteristic of the output signal E ₈ , and the phase correction value held by the phase corrector 55 is calculated. The data is updated. The calibration processing unit 40 corresponds to the calibration unit of the present invention.

The first phase difference calculator 41 changes the frequency interval between the first light and the second light in accordance with the value of the changed frequency every time the frequency changing unit 70 changes the frequency, and the intermediate frequency signal E _IF The phase difference between the three or more continuous waves is calculated, and the first phase difference characteristic over the entire predetermined frequency band is acquired.

Specifically, the first phase difference calculator 41 receives the frequency f _IF1 of the intermediate frequency signal E _IF output from the electro-optic frequency converter 30 when the calibration signal _Er is input to the electro-optic frequency converter 30. Calculate the phase difference between the spectral components of −f _m1 , f _IF1 , f _IF1 + f _m1 . For example, the intermediate frequency signal E _IF is A / D converted at a predetermined sampling frequency, and the obtained digital signal is multiplied by the sine function and cosine function of each frequency f _IF1 −f _m1 , f _IF1 , f _IF1 + f _m1. Integration may be performed for a predetermined number of samples, the phase of each spectral component may be calculated using an arctangent function, and a second-order phase difference may be calculated as described later.

When the calibration signal _Er is input to the millimeter wave band signal measurement unit 50, the second phase difference calculator 43 receives the intermediate frequency signal measurement device of the millimeter wave band signal measurement unit 50 every time the frequency change unit 70 changes the frequency. 53 will calculate the phase difference between the three waves or more continuous wave signal E ₈ output from, so as to obtain a second phase difference characteristics throughout a predetermined frequency band. The processing content of the second phase difference calculator 43 is the same as that of the first phase difference calculator 41, but the second phase difference calculator 43 has an A of the intermediate frequency signal measuring unit 53 of the millimeter waveband signal measuring unit 50. A digital signal obtained by A / D conversion by the / D converter may be used.

Phase difference output from the first phase difference calculator 41 (second difference value), after the phase difference between the local light P _L via the adder 42 as required (second difference value) is added, This is input to the phase correction value calculator 44. Station optical amplitude modulator in place of the optical phase modulator 17 of the light emitting generation portion 10 is used, if it is an ideal amplitude modulation, the phase difference between a local light P _L to become zero, by the adder 42 addition of the phase difference between the local light P _L is not required.

Phase correction value calculator 44, the characteristics of the phase difference obtained by adding the phase difference between the local light P _L as needed to the phase difference calculated by the first phase difference calculator 41, # 2 Based on the phase difference characteristic calculated by the phase difference calculator 43, the phase correction value of the millimeter waveband signal measuring unit 50 is calculated. The calculated phase correction value is sent from the phase correction value calculator 44 to the phase corrector 55 of the millimeter waveband signal measuring unit 50, and is used for phase correction when the measured signal is measured by the millimeter waveband signal measuring unit 50. It is done.

  The calibration processing unit 40 and the frequency changing unit 70 are configured using, for example, a computer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), an input / output interface, an external storage device, and the like. Some or all of the functions (excluding A / D conversion) can be realized by executing various programs stored in the ROM or the like by the CPU.

[Millimeter wave signal measurement unit]
Next, the millimeter wave band signal measuring unit 50 that is the calibration target will be described.

  The millimeter wave band signal measurement unit 50 is a signal analyzer that frequency-converts (down-converts) a high frequency signal in the millimeter wave band and measures its signal characteristics. For example, an error vector amplitude (EVM) is obtained by analyzing a modulation signal. May be displayed. Specifically, the millimeter waveband signal measuring unit 50 includes a local oscillator signal generator 52, a frequency converter 51, an intermediate frequency signal measuring device 53, and a phase corrector 55. The calibration target is not limited to this configuration, and any circuit that handles millimeter-wave band high-frequency signals can be the calibration target.

The local oscillation signal generator 52 generates a local oscillation signal of CW. The frequency converter 51 performs frequency conversion (down-conversion) of the calibration signal _Er received by the horn antenna 56 or the signal under measurement using the local signal and converts it to an intermediate frequency signal. Instead of the horn antenna 56, a calibration signal generator 20 or a signal under measurement may be connected using a waveguide, a coaxial cable, or a coaxial connector. The intermediate frequency signal measuring device 53 includes an A / D converter, and converts the intermediate frequency signal into a digital signal. The digital signal output from the intermediate frequency signal measuring device 53 is selectively sent to the second phase difference calculator 43 or the phase corrector 55 by the changeover switch 54. The phase corrector 55 performs phase correction on the digital signal from the intermediate frequency signal measuring device 53 using the information updated by the phase correction value calculator 44, and outputs the result as a measurement result. When the error signal amplitude (EVM) or the like is displayed by analyzing the modulation signal, the modulation analysis is performed using the output of the phase corrector 55.

  The local oscillation signal generator 52 may include a frequency multiplier that converts the frequency to an integral multiple. In addition, although a configuration in which frequency conversion is performed once is shown here, a configuration in which frequency conversion is performed a plurality of times may be used, and a filter that removes unnecessary frequency components may be included.

[Calibration method]
Next, a method for calibrating the frequency characteristics of the millimeter waveband signal measuring unit 50 will be described.

The frequency characteristic (complex number including phase) of the calibration signal is X _c (f), the frequency characteristic (complex number including phase) of the millimeter wave band signal measurement unit 50 is G (f), and the calibration signal is measured as a millimeter wave band signal. Let Y _c (f) be the frequency characteristic (complex number including phase) of the output signal from the intermediate frequency signal measuring device 53 when it is input to the unit 50. X _c (f) is the measurement of the phase difference of an intermediate frequency signal including spectral components of three or more waves by inputting the calibration signal to the electro-optic frequency converter 30 and the carrier frequency f _c within a predetermined frequency band. It can be obtained by changing and repeating. Y _c (f) inputs a calibration signal to the millimeter waveband signal measurement unit 50 and measures the phase difference of an intermediate frequency signal including three or more spectrum components output from the millimeter waveband signal measurement unit 50. it can be obtained by the repeated while changing the carrier frequency f _c within a predetermined frequency band. G (f) can be obtained from the following equation (8).

ここで、ｆ_ＬＯはミリ波帯信号測定部５０の局発信号の周波数である。

Here, f _LO is the frequency of the local oscillation signal of the millimeter waveband signal measurement unit 50.

  Then, the frequency characteristic (complex number including phase) of the signal under measurement is X (f), and the frequency characteristic of the output signal from the intermediate frequency signal measuring device 53 when the signal under measurement is input to the millimeter waveband signal measuring unit 50 ( Assuming that Y (f) is a complex number including a phase, X (f) in which the frequency characteristic of the millimeter waveband signal measuring unit 50 is corrected can be obtained as a measurement result from the following equation (9).

As described above, it is also possible to simultaneously calibrate the amplitude characteristic and the phase characteristic by obtaining the complex frequency characteristic including the amplitude and the phase.
Hereinafter, a method for calibrating the phase characteristic will be described in detail.

As described above, the first phase difference calculator 41 calculates each phase of the spectrum components of f _IF1 −f _m1 , f _IF1 , and f _IF1 + f _m1 . f _IF1 -f ₁ the phase phi of the spectral components of _{m1, 2} a phase spectral component phi of _{f IF1, f IF1 + f} phases phi ₃ spectral components _m1, when the frequency interval _{f m} of the calibration signals Delta] f, The phase difference Δ ² φ / Δf ² is calculated from the following equations (10), (11), and (12).

The operation of calculating the phase difference Δ ² φ / Δf ^2, repeatedly changing the frequency _{f c} of the calibration signal to the extent necessary to obtain the phase difference as a function of _{f c Δ} ² _φ a _(f c) / _Δf ² . By taking the difference of the second floor of the phase, the phase characteristic can be obtained regardless of the absolute time (that is, even if the time origin is unknown).

Phase difference obtained above is dependent on the phase difference of the optical spectrum component of the local light P _L, when the phase difference of the light spectrum component of the local light P _L is not zero, it is necessary to correct. Specifically, the phase of the optical spectrum component of _f 2 _{-f L2} of the local light _{P L} and phi _L1, the phase of the optical spectrum component of _{f 2} and phi _L2, the phase of the optical spectrum component of f 2 _{+ f L2} When phi _L3, the following equation (13), (14), calculates the phase difference Δ ² φ _L / Δf ² than, local light _{P L} (15). Then, as shown in the following equation (16), the phase difference Δ ² φ _L / Δf ² of the local light P _L is added to the phase difference Δ ² φ (f _c ) / Δf ² of the output signal from the electro-optic frequency converter 30. by, local light P phase difference Δ ² φ _{c (f c)} the phase of the optical spectrum components are corrected for _{L /} delta] f ² can be obtained.

For example, when the optical phase modulator 17 of the local light generation unit 10 is ideal phase modulation, since φ _L1 = π / 2, φ _L2 = 0, φ _L3 = π / 2, Δ ² φ _L / Δf ² = Π / f ² _m . In the case where an optical amplitude modulator is used instead of the optical phase modulator 17 of the local light generation unit 10 and is an ideal amplitude modulation, φ _L1 = 0, φ _L2 = 0, φ _L3 = 0, so Δ a ^{_{2 φ L / Δf 2 = 0}} . This phase difference, because determined by the modulation characteristic of the optical spectrum component of the optical frequency f _2, independent of the normal f ₂ -f 1 ₌ nf _L1, when repeated by changing the frequency f _c of the calibration signal is of a constant value What is necessary is just to perform phase difference correction.

The first CW signal generator 11, the second CW signal generator 16, the calibration signal generator 20 (the intermediate frequency signal generator 21 and the local oscillator signal generator 22), and the first phase difference calculation of the local light generator 10. If the sampling frequency of the A / D conversion of the device 41 is synchronized with a common reference frequency, the result of the A / D conversion by the first phase difference calculator 41 does not include a frequency error, and is accurate. Since the spectral components of the frequencies f _IF1 -f _m1 , f _IF1 , f _IF1 + fm ₁ are obtained, the phase difference can be calculated easily and accurately.

Next, the calibration signal _Er output from the calibration signal generation unit 20 is input to the millimeter waveband signal measurement unit 50.

Specifically, a calibration signal _Er having at least three spectral components of frequencies f _c −f _m ′, f _c , and f _c + f _m ′ is input to the millimeter waveband signal measuring unit 50, and an intermediate frequency signal measuring device is obtained. 53, the phase measurement result of the spectrum component of f _c −f _m ′ is φ ₁ ′, the phase measurement result of the spectrum component of f _c is φ ₂ ′, and the calibration signal output from 53 is f _c + f _m ′ Assuming that the phase measurement result of the spectral component is φ ₃ ′ and Δf ′ is the frequency interval f _m ′ of the calibration signal _Er , the phase difference Δ ² φ ′ / is obtained from the following equations (17), (18), and (19). Δf ′ ² is calculated.

The operation of calculating the phase difference ^{Δ 2 φ '/ Δf' 2} , repeatedly changing the extent necessary frequency _{f c} of the calibration signal _{E r,} the phase difference as a function of _{^{f c Δ 2 φ '(f}} c) / Δf ′ ² is acquired.

The phase correction value θ (f _c ) at the frequency f _c can be obtained using the following equations (20), (21), and (22).

Equation (21), in (22), the sum Σ is the integration of while changing the _{f ci} at Delta] f _c interval from the lowest frequency to the frequency _{f c.}

The phase corrector 55 corrects the phase so that the phase difference of the spectrum component when the calibration signal _Er is input to the millimeter waveband signal measuring unit 50 is equal to the phase difference calculated by the first phase difference calculator 41. To do.

As a phase correction method in the phase corrector 55, a frequency domain correction method or a time domain correction method can be employed. In the frequency domain correction method, the digital signal in the time domain obtained by the intermediate frequency signal measuring device 53 is subjected to discrete Fourier transform to be converted into a frequency domain signal, and the phase is rotated by the phase correction value θ (f _c ). Inverse Fourier transform is performed to convert the signal into a time domain signal. In the time domain correction method, a complex amplitude exp {jθ (f _c )} is obtained from the phase correction value θ (f _c ), converted into an impulse response by discrete inverse Fourier transform, and a finite impulse response having the impulse response as a coefficient. A digital signal from the intermediate frequency signal measuring device 53 is subjected to filter processing by an (FIR) filter.

A spectral interval f _m when measuring the phase difference of the calibration signal E _r in the electro-optical frequency conversion unit 30, the spectral interval f _m when measuring the phase difference of the calibration signal E _r in the millimeter wave band signal measuring unit 50 ' Are preferably set equal, but not necessarily limited thereto. Further, a plurality of f _c when measuring the phase difference between the calibration signal E _r in the electro-optical frequency conversion unit 30, a plurality of f at the time of measuring the phase difference of the calibration signal E _r in the millimeter wave band signal measuring unit 50 _Although it is desirable to set _c equal, it is not necessarily limited thereto, and the frequency of the phase difference information may be adjusted by interpolation processing or the like.

  After the phase correction can be performed as described above, the signal under measurement is input to the millimeter waveband signal measuring unit 50 instead of the calibration signal, and the measurement result with the phase corrected is output. When the signal under measurement is a modulation signal such as QPSK (Quadrature Phase Shift Keying) or QAM (Quadrature Amplitude Modulation), perform modulation analysis of the signal whose phase is corrected, and accurately measure error vector amplitude (EVM), etc. Can do. If necessary, the phase calibration using the calibration signal may be performed again periodically or when the ambient temperature changes greatly.

(Second Embodiment)
Next, a phase characteristic calibration apparatus 1A according to a second embodiment of the present invention will be described.

  The phase characteristic calibration apparatus 1A according to the present embodiment is different from the first embodiment in that a second frequency conversion unit 60 is provided between the electro-optic frequency conversion unit 30 and the first phase difference calculator 41. Yes. Other configurations are the same as those of the first embodiment, and the same reference numerals are given to the same configurations, and detailed description thereof is omitted.

As shown in FIG. 6, the second frequency conversion unit 60 includes an amplifier 61, a CW signal generator 62, a mixer 63, and a low-pass filter (LPF) 64. The second frequency converter 60 is for converting the intermediate frequency signal E _IF a further frequency lower second intermediate frequency signal E _IF2 from the electro-optical frequency conversion unit 30.

Specifically, the amplifier 61 amplifies the intermediate frequency signal E _IF input from the electro-optic frequency converter 30 and outputs the amplified signal to the mixer 63, and the CW signal generator 62 generates the second local oscillation signal of CW. And output to the mixer 63. The mixer 63 performs second frequency conversion (down-conversion) on the intermediate frequency signal E _IF using the second local oscillation signal, and outputs the result to the low-pass filter 64. The low-pass filter 64 extracts a desired spectral component and outputs a second intermediate frequency signal _EIF2 . In order to reduce spurious components generated by harmonics or the like during the second frequency conversion, a band pass filter (not shown) may be inserted before the mixer 63.

FIG. 7A shows the spectrum of the intermediate frequency signal E _IF output from the electro-optic frequency converter 30. As described above, there are three or more spectral components at the frequency interval f _m1 around the frequency f _IF1 . FIG. 7B shows a spectrum of the second local signal output from the CW signal generator 62. FIG. 7C shows the spectrum of the second intermediate frequency signal E _IF2 output from the low-pass filter 64. FIG. When the frequency of the second local oscillation signal from the CW signal generator 62 is f _LO2 , the second intermediate frequency is f _IF2 = f _IF1 −f _LO2 , and the frequency interval of the second intermediate frequency signal E _IF2 is f _m1 . .

As shown in FIG. 7C, when a spectral component having a frequency lower than f _IF1 -f _m1 , for example, when the frequency f _IF1 -2f _m1 is lower than the second local frequency f _LO2 , the second intermediate frequency signal E _IF2 Since the spectrum is folded at a frequency of zero, it is desirable to set f _LO2 so that the folded spectrum does not overlap the three spectral components f _IF2 −f _m1 , f _IF2 , and f _IF2 + f _m1 . Here, an example is shown in which f _LO2 <f _IF1 is set, but conversely, f _LO2 > f _IF1 may be set.

In the second embodiment, the intermediate frequency f _IF1 is set to a frequency where the 1 / f noise of the electric circuit is small and sufficiently amplified by the amplifier 61 of the second frequency converter 60, and then the sufficiently low second intermediate frequency f _{IF2 is set.} Has been converted. Frequency spacing of the intermediate frequency signal _{E IF} as described above is expressed by _f m1 _{= f} m _{-f L2,} sufficiently narrow frequency _{f m1} by setting the frequency _{f L2} of the second CW signal generator 16 appropriately The interval can be set, and the frequencies f _IF2 −f _m1 , f _IF2 and f _IF2 + f _m1 of the three spectral components of the second intermediate frequency signal E _IF2 can be sufficiently lowered. . Therefore, while avoiding the 1 / f noise of the electric circuit and maintaining a high S / N ratio, the band of the A / D converter and the like of the first phase difference calculator 41 and the sampling speed are lowered to realize an inexpensive device. be able to.

(Third embodiment)
Next, a phase characteristic calibration apparatus 1B according to a third embodiment of the present invention will be described.

  The phase characteristic calibration apparatus 1B according to the present embodiment is different from the second embodiment in that the second frequency conversion unit 60A is configured to perform orthogonal frequency conversion. Other configurations are the same as those of the second embodiment. The same components are denoted by the same reference numerals, and detailed description thereof is omitted.

In the second embodiment, the negative frequency component is folded back in the second frequency conversion performed by the second frequency conversion unit 60, and the noise in the negative frequency region is also folded back. Therefore, compared with the case where the second frequency conversion is not performed. The S / N ratio deteriorates by about 3 dB. By placing a filter that cuts off frequency components below f _{LO2 in} the signal path before the second frequency conversion, noise in the negative frequency region after the second frequency conversion can be removed. Phase nonlinearity is large, which causes an error in phase measurement. For this reason, in the third embodiment, the second frequency conversion unit 60A is configured to perform orthogonal frequency conversion so that negative frequency components are not folded back in the second frequency conversion.

  As shown in FIG. 8, the second frequency converter 60A includes an amplifier 61, a CW signal generator 62a, two mixers 63a and 63b, a 90-degree phase shifter 65, and two low-pass filters (LPF). ) 64a and 64b.

Specifically, amplifier 61 amplifies the intermediate frequency signal _{E IF} input from the electro-optical frequency conversion unit 30 two mixers 63a, and outputs the 63 b. The CW signal generator 62a generates a CW second local oscillation signal and outputs it to one mixer 63a and also outputs it to the 90-degree phase shifter 65. The 90-degree phase shifter 65 outputs the second local oscillation signal phase-shifted by 90 degrees to the other mixer 63b. Mixers 63a, 63b performs a second frequency conversion to the intermediate frequency signal _{E IF} (down-converted) using the second local oscillation signal 90 ° phase different from each other, respectively low-pass filters 64a, output 64b To do. The low-pass filters 64a and 64b extract and output a desired spectral component. With this configuration, the input signal to the second frequency conversion unit 60A is subjected to quadrature frequency conversion, and two signals of the in-phase component and the quadrature component are output to the first phase difference calculator 41 as the second intermediate frequency signal _EIF2 .

  Instead of the CW signal generator 62a and the 90-degree phase shifter 65, two D / A converters that generate sine waves having a 90-degree phase difference may be used. In order to reduce spurious components generated by harmonics or the like during the second frequency conversion, bandpass filters (not shown) may be inserted before the mixers 63a and 63b.

FIG. 9A shows the spectrum of the intermediate frequency signal E _IF output from the electro-optic frequency converter 30. As described above, there are three or more spectral components at the frequency interval f _m1 around the frequency f _IF1 . FIG. 9B shows the spectrum of the second local signal output from the CW signal generator 62a. FIG. 9C shows the spectrum of the second intermediate frequency signal E _IF2 output from the low-pass filters 64a and 64b. _Assuming that the frequency of the second local oscillation signal from the CW signal generator 62a is f _LO2 , the second intermediate frequency is f _IF2 = f _IF1 -f _LO2 , and the frequency interval of the second intermediate frequency signal E _IF2 is f _m1 . .

However, since the positive and negative frequency components may not be completely separated due to the balance between the two mixers 63a and 63b or the deviation of the orthogonality, and image components may be generated, | f _IF2 −f _m1 |, | f _IF2 |, It is desirable to set f _LO2 so that | f _IF2 + f _m1 | does not overlap each other. Since the frequency zero is affected by the DC offset, it is desirable to set f _LO2 so that each frequency component of f _IF2 −f _m1 , f _IF2 , and f _IF2 + f _m1 does not become zero. In the present embodiment, f _LO2 <f _IF1 is set, but conversely, f _LO2 > f _IF1 may be set.

In the third embodiment, the intermediate frequency f _IF1 is set to a frequency where the 1 / f noise of the electric circuit is small and sufficiently amplified by the amplifier 61 of the second frequency converter 60A, and then the sufficiently low second intermediate frequency f _{IF2 is set.} Has been converted. As described above, the frequency interval f _m1 of the intermediate frequency signal E _IF can be set sufficiently narrow, and the frequencies f _IF2 −f _m1 and f _{IF2 of the} three spectral components of the second intermediate frequency signal E _IF2 can be set. , F _IF2 + f _m1 can be made sufficiently low. Therefore, it is possible to realize an inexpensive device by reducing the sampling rate of the A / D converter of the first phase difference calculator 41 while maintaining a high S / N ratio while avoiding 1 / f noise of the electric circuit. it can. Since the positive and negative frequency components can be separated by the in-phase component and the quadrature component that have undergone quadrature frequency conversion, the negative frequency component is basically not aliased and can be generated in the second embodiment. The ratio is not deteriorated.

  In the second embodiment and the third embodiment, in order to synchronize with the reference frequency, the first CW signal generator 11 and the second CW signal generator 16 of the local light generator 10 and the calibration are performed. In addition to the A / D conversion sampling frequency of the signal generation unit 20 and the first phase difference calculator 41, CW signal generators 62 and 62a that generate the second local oscillation signals of the second frequency conversion units 60 and 60A are also included. Synchronize with a common reference frequency.

  As described above, the present invention has an effect that the phase characteristics of the millimeter waveband signal measurement circuit can be calibrated with high accuracy, and is useful for all of the phase characteristic calibration apparatus and the phase characteristic calibration method.

1, 1A, 1B Phase characteristic calibration device 10 Local light emission generator (generator)
DESCRIPTION OF SYMBOLS 11 1st CW signal generator 12 Optical comb generator 13 Optical splitter 14 1st optical bandpass filter 15 2nd optical bandpass filter 16 2nd CW signal generator 17 Optical phase modulator 18 Optical multiplexer 20 Calibration Signal generator (generator)
21 Intermediate frequency signal generator 22 Local signal generator 23, 51 Frequency converter 30, 30A Electro-optic frequency converter (frequency converter)
31 Electro-optic crystal 32 Optical branching section 32 ', 32a, 32b Polarizing beam splitter (PBS)
33, 33a, 33b Light receiver 34 Dielectric reflection film 35, 35a, 35b 1/2 wavelength plate (HWP)
36 1/4 wave plate (QWP)
37 Faraday rotator (FR)
38 Differential amplifier 40 Calibration processing section (calibration section)
41 First phase difference calculator 42 Adder 43 Second phase difference calculator 44 Phase correction value calculator 50 Millimeter wave band signal measurement unit (measurement circuit)
52 Local signal generator 53 Intermediate frequency signal measuring instrument 54 Changeover switch 55 Phase corrector 60, 60A Second frequency converter 61 Amplifier 62, 62a CW signal generator 63, 63a, 63b Mixer 64, 64a, 64b Low-pass Filter (LPF)
65 90 degree phase shifter REF Reference signal

Claims (9)

A phase characteristic calibration device (1) for calibrating the phase characteristic of a measurement circuit (50),
A generation unit (20) that generates a calibration signal (E _r ) in which three or more continuous waves of different frequencies are combined;
A second light which is a continuous light having a frequency smaller than or greater than any of the first light in which continuous light of three or more waves having different frequencies is combined and the continuous light of three or more waves of the first light. A generator (10) for generating local light (P _L ) synthesized with the light of
A frequency converter (30) for outputting an intermediate frequency signal (E _IF ) in which the calibration signal is frequency-converted by the electro-optic effect using the local light to synthesize three or more continuous waves in the intermediate frequency band;
A frequency changing unit (70) for changing the frequency of three or more continuous waves of the calibration signal within a predetermined frequency band;
For each frequency change by the frequency changing unit, the frequency interval between the first light and the second light is changed according to the value of the changed frequency, and three or more continuous waves of the intermediate frequency signal The first phase difference characteristic over the entire predetermined frequency band is acquired, and the calibration signal is measured using the measurement circuit for each frequency change by the frequency changing unit. And calculating a phase difference between three or more continuous waves output from the measurement circuit, obtaining a second phase difference characteristic over the entire predetermined frequency band, and obtaining the obtained first and A calibration unit (40) for calibrating the phase characteristic of the measurement circuit based on the second phase difference characteristic;
Any of the three or more continuous waves of the intermediate frequency signal is lower than any of the three or more continuous waves of the calibration signal and is three or more continuous waves of the calibration signal And the frequency interval of three or more continuous lights of the first light are different, and the frequency interval of three or more continuous waves of the intermediate frequency signal is three or more of the calibration signal. The phase characteristic calibration apparatus, wherein the calibration signal and each frequency of the local light are set so as to be narrower than the frequency interval of the continuous wave.   The generator (10) includes a first CW signal generator (11) for generating a first continuous wave signal, and an optical comb having a plurality of optical spectrum components at frequency intervals of the first continuous wave signal. An optical comb generator (12) that generates light, an optical splitter (13) that splits the output light from the optical comb generator into two, and different light from one and the other output light of the optical splitter A first optical bandpass filter (14) and a second optical bandpass filter (15) for extracting spectral components, respectively, a second CW signal generator (16) for generating a second continuous wave signal, Light that generates a plurality of sidebands at frequency intervals of the second continuous wave signal by subjecting the output light of the second optical bandpass filter to amplitude modulation or phase modulation with the second continuous wave signal. A modulator (17) and the first optical bandpass; Optical multiplexer which multiplexes the output light of the output light of filters the light modulator (18), the phase characteristics calibration apparatus according to claim 1, characterized in that it comprises a.   The first CW signal generator, the second CW signal generator, and the generation unit are configured such that the first continuous wave signal, the second continuous wave signal having a frequency synchronized with a common reference frequency, and 3. The phase characteristic calibrating apparatus according to claim 2, wherein each of the calibration signals is generated, and frequencies of three or more continuous waves of the intermediate frequency signal are respectively synchronized with the reference frequency. Between the frequency conversion unit and the calibration unit, a second continuous wave of three or more waves in the second intermediate frequency band is synthesized by performing frequency conversion by amplifying three or more continuous waves of the intermediate frequency signal. A second frequency conversion unit (60) for outputting an intermediate frequency signal (E _IF2 ) is further included, and the calibration unit is configured to output the second intermediate signal output from the second frequency conversion unit instead of the intermediate frequency signal. A phase difference between three or more continuous waves of the frequency signal is calculated, and any frequency of the three or more continuous waves of the second intermediate frequency signal is any of the three or more continuous waves of the intermediate frequency signal. The phase characteristic calibrating apparatus according to claim 1, wherein the phase characteristic calibrating apparatus is set to be lower than the frequency of.   The phase characteristic calibration apparatus according to claim 4, wherein the second frequency conversion unit is a quadrature frequency converter (60A) that outputs an in-phase component and a quadrature component of the second intermediate frequency signal. Between the frequency conversion unit and the calibration unit, a second continuous wave of three or more waves in the second intermediate frequency band is synthesized by performing frequency conversion by amplifying three or more continuous waves of the intermediate frequency signal. A second frequency conversion unit (60) for outputting an intermediate frequency signal (E _IF2 ) is further included, and the calibration unit is configured to output the second intermediate signal output from the second frequency conversion unit instead of the intermediate frequency signal. A phase difference between three or more continuous waves of the frequency signal is calculated, and any frequency of the three or more continuous waves of the second intermediate frequency signal is any of the three or more continuous waves of the intermediate frequency signal. The phase characteristic calibrating apparatus according to claim 2, wherein the phase characteristic calibrating apparatus is set to be lower than the frequency of.   The phase characteristic calibration apparatus according to claim 6, wherein the second frequency conversion unit is a quadrature frequency converter (60A) that outputs an in-phase component and a quadrature component of the second intermediate frequency signal.   The first CW signal generator, the second CW signal generator, and the generation unit are configured such that the first continuous wave signal, the second continuous wave signal having a frequency synchronized with a common reference frequency, and Each of the calibration signals is generated, and the second frequency conversion unit performs frequency conversion based on a local oscillation signal synchronized with the reference frequency, and the frequency of three or more continuous waves of the second intermediate frequency signal is: The phase characteristic calibration apparatus according to claim 6, wherein each of the phase characteristic calibration apparatuses is synchronized with the reference frequency. A phase characteristic calibration method for calibrating the phase characteristic of a measurement circuit (50), comprising:
A generation step of generating a calibration signal (E _r ) in which three or more continuous waves of different frequencies are combined;
A second light which is a continuous light having a frequency smaller than or greater than any of the first light in which continuous light of three or more waves having different frequencies is combined and the continuous light of three or more waves of the first light. Generating step of generating local light (P _L ) synthesized with the light of
A frequency conversion step of frequency-converting the calibration signal by the electro-optic effect using the local light and outputting an intermediate frequency signal (E _IF ) in which three or more continuous waves in the intermediate frequency band are synthesized;
A frequency changing step of changing the frequency of three or more continuous waves of the calibration signal within a predetermined frequency band;
For each frequency change in the frequency changing step, the frequency interval between the first light and the second light is changed according to the value of the changed frequency, and three or more continuous waves of the intermediate frequency signal The first phase difference characteristic over the entire predetermined frequency band is acquired and the calibration signal is measured using the measurement circuit every time the frequency is changed by the frequency changing step. And calculating a phase difference between three or more continuous waves output from the measurement circuit, obtaining a second phase difference characteristic over the entire predetermined frequency band, and obtaining the obtained first and A calibration step of calibrating the phase characteristic of the measurement circuit based on the second phase difference characteristic;
Any of the three or more continuous waves of the intermediate frequency signal is lower than any of the three or more continuous waves of the calibration signal and is three or more continuous waves of the calibration signal And the frequency interval of three or more continuous lights of the first light are different, and the frequency interval of three or more continuous waves of the intermediate frequency signal is three or more of the calibration signal. A phase characteristic calibration method, wherein the calibration signal and each frequency of the local light are set so as to be narrower than a frequency interval of a continuous wave.

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