JP4704384B2 - Spectrum analyzer - Google Patents

Description

  The present invention relates to a spectrum analyzer (sometimes referred to as a signal analysis device or a reception device) capable of correcting a frequency response characteristic of a level (power magnitude or amplitude), and in particular, a level of frequency over a measurement frequency band. The present invention relates to a technique for correcting fluctuations due to aging of response characteristics, environmental temperature, and the like.

  Conventionally, a spectrum analyzer is configured as shown in FIG. In FIG. 3, it can be roughly divided into a receiving unit 3, an intermediate processing unit 5, and a calibration unit including a fixed oscillation unit 20 and a correction unit 21. In FIG. 3, the reception unit 3 receives a reception signal at the input terminal 1 and converts the reception signal into an appropriate operation level by the ATT 3a (variable attenuator), and the reception signal at the appropriate level. Are mixed with the frequency from the local oscillator 3c and converted into an intermediate frequency (fm) signal. The intermediate processing unit 5 receives the output from the mixing unit 3b, sorts and extracts only the desired intermediate frequency signal component from the other components, and switches the intermediate frequency signal to the required frequency component by switching the bandwidth of the tuning filter. RBW (Resolution Band Width) for selection, LOG converter for linear logarithm conversion of the output of the RBW, detector for detecting the output of the LOG converter, VBW (video filter for controlling the video band of the output of the detector) ) Etc. Specifically, the intermediate processing unit 5 is configured by a DSP including a processor that performs high-speed processing by converting digital data after the frequency of the intermediate frequency signal is further lowered. Then, by sweeping the frequency of the local oscillator, the received signal is selected and measured (analyzed), and the measurement result is displayed on the coordinates with the horizontal axis representing the frequency and the vertical axis representing the level.

  If a spectrum analyzer having a measurement band of several GHz is configured with such a configuration, the spectrum analyzer itself (in particular, the receiving system 100 including the receiving unit 3) has level frequency response characteristics. Spectrum analyzer level frequency response characteristics (also referred to as level-to-frequency characteristics, hereinafter simply referred to as “frequency response characteristics”) are used to receive signals of the same level by changing the frequency within the measurement frequency band. When a level measured at a certain reception frequency (for example, a level of 50 MHz) is used as a reference, it means a deviation of a level measured at another reception frequency with respect to the reference level.

  Therefore, conventionally, when the frequency response characteristic is measured at the time of shipment, a correction value for correcting the frequency response characteristic is stored in advance in the correction unit 21, and when the measurement is actually executed on the user side, The correction means 21 is corrected with the correction value, and the corrected reception level is output or displayed. In preparation for the case where the measurement level fluctuates due to aging, ambient environmental temperature, or the like, level calibration means (fixed oscillation unit 20 and correction means 21 in FIG. 3) are provided. In FIG. 3, it has a fixed oscillation unit 20 that outputs a reference signal (for example, 0 dBm at 50 MHz) having a single frequency and a stable frequency and level. The reference signal is input and actually received, and the correction unit 21 adjusts the internal measurement value so that the measurement value detected and output from the intermediate processing unit 5 is 0 dBm, and stores the adjustment value. Therefore, when the signal under measurement is received and measured after the calibration by the level calibration means, the correction means 21 reduces the level fluctuation by the adjustment value, and further corrects the frequency response characteristic as described above. Can be output. However, in such a method, the adjustment value adjusted so as to eliminate the fluctuation at 50 MHz by the level calibration means is uniformly applied to all the reception frequencies.

  In general, according to the product catalog, even in the case of a broadband spectrum analyzer, even if it is corrected by such a conventional technique, the uncertainty due to the frequency response characteristic is almost within ± 1.5 dB.

  Other examples in which frequency response characteristics are calibrated in a spectrum analyzer are shown in Patent Document 1 and Patent Document 2. Patent Document 1 is to prevent the influence of frequency response characteristics in a narrow range within a bandpass filter (corresponding to RBW in FIG. 3) for extracting an intermediate frequency signal. It corrects the measurement signal. This correction method does not improve the frequency response characteristics over the measurable frequency range.

  The technique of Patent Document 2 is a technique in which a value measured by a spectrum analyzer is precisely calibrated externally when the spectrum analyzer is used for a specific application such as a mobile terminal test. Also in this case, the calibration means as shown in FIG. 3 was provided, but this is insufficient, so this is an example in which calibration is performed externally.

JP 2005-3623 A JP 2003-32199 A

  In recent years, the spectrum analyzer has been required to have higher accuracy in the accuracy of the level of the frequency component analyzed by itself.

  In the above prior art, when the frequency response characteristics fluctuate due to aging, ambient environmental temperature, etc., the calibration method that applies the same value calibrated at a single frequency of 50 MHz to each frequency, Insufficient correction.

  An object of the present invention is to provide a technique capable of correcting at each frequency even if the frequency response characteristic fluctuates due to secular change, ambient environmental temperature, or the like.

  In order to achieve the above object and allow the user to sequentially calibrate the frequency response, the main configuration is as follows (1) to (4). (1) With a simple configuration, the frequency is stable over the measurement band, and synchronized with the frequency sweep of the spectrum analyzer (the signal from the fixed oscillation unit 20 described in the prior art is swept by the spectrum analyzer. As a calibration signal source that can be received. (2) Furthermore, the level of the calibration signal is stabilized by ALC (automatic level control) that is resistant to secular change or temperature environment over the measurement band. (3) When this calibration signal is input to the spectrum analyzer at different times, the fluctuation value of the frequency response characteristic after a predetermined time or after aging (or after the environmental temperature changes) is obtained, and this fluctuation at each frequency is obtained. The calibration was such that the measured value could be corrected based on the value. (4) The frequency response characteristic of the spectrum analyzer alone and the frequency response characteristic of the spectrum analyzer based on the calibration signal in (2) above (including the frequency response characteristic of the calibration signal itself) are unique. Since there is no significant correlation, for example, a correction value (first correction value) based on the frequency response characteristic of the spectrum analyzer alone at the time of shipment and the initial frequency response of the spectrum analyzer based on the calibration signal (2) under the same environmental conditions The characteristic (first characteristic value) is acquired, that is, the two are correlated and stored with respect to the environmental change element, and then the calibration signal is again used when the environmental condition changes or time passes. Obtain the frequency response (second characteristic value) of the spectrum analyzer according to, and use these values to determine the correction value during use. The value measured by receiving a signal to be measured has a configuration to correct in the correction value. By doing this, the fluctuation (the first characteristic value−the second characteristic value) during this period cancels the frequency response characteristic of the calibration signal itself, and can be regarded as the fluctuation of the first correction value.

As a specific configuration, the invention described in claim 1 mixes the input signal from the receiving end with the output of the frequency-swept local oscillator (3c), converts it to an intermediate frequency signal, and detects the intermediate frequency signal. And a reception system (100) that outputs the measurement value as a measurement value, the spectrum analyzer including a fixed oscillator (9) that generates a signal having the same frequency as the frequency of the intermediate frequency signal, The output signal obtained by mixing the output of the local oscillator with the output level stabilized (200), and the output signal from the output means is applied in advance to the receiving end. The first characteristic value including the frequency response characteristic of the level obtained by the output of the receiving system is stored, and an output signal from the output means is applied to the receiving end during subsequent use to Gain in output Storing the second characteristic value including the levels of the frequency response characteristic, based on the difference between the characteristic values of the characteristic value and the second first, obtained by inputting a signal to be measured on the receiving end And a correction means (6) for correcting the measured value.
According to a second aspect of the present invention, in the first aspect of the invention, the correction unit is obtained based on a known calibration signal input to the receiving end together with the first characteristic value. In addition, a first correction value for correcting the frequency response characteristic of the level of the receiving system is stored, and the first correction value, the first characteristic value, and the second characteristic are used in use. The measurement value obtained by inputting the signal under measurement is corrected based on a difference from the value.
According to a third aspect of the present invention, in the second aspect of the present invention, the correction unit stores the first correction value and the first characteristic value in a read-only manner, and the second characteristic value is stored. Is stored in a rewritable manner each time it is used, and at the time of use, an operation of [first correction value + first characteristic value−rewritten latest second characteristic value] is performed for each corresponding frequency. Then, a correction value during use is obtained, and the measurement value obtained by inputting a signal under measurement to the receiving end is corrected by the correction value during use .
The invention according to claim 4 mixes the input signal from the receiving end with the output of the frequency-swept local oscillator (3c) to convert it to an intermediate frequency signal, and detects the intermediate frequency signal and outputs it as a measurement value. And a fixed oscillator (9) that generates a signal having the same frequency as the frequency of the intermediate frequency signal. The output of the fixed oscillator and the output of the local oscillator An output means (200) for stabilizing the output level of the output signal obtained by mixing, and a signal under measurement input in the measurement mode, and an output of the output means in the calibration mode are input to the receiving end. And a first correction value for correcting a frequency response characteristic of the level of the reception system, which is obtained in advance based on a known calibration signal input in the measurement mode. In the calibration mode, the first characteristic value including the frequency response characteristic of the level obtained by the output of the receiving system by the output signal from the output means is stored, and the calibration mode is set in the subsequent use. Each time, the second characteristic value including the latest level frequency response characteristic obtained from the output of the receiving system by the output signal from the output means is stored, and the first correction value and the first correction value are stored. Correction means (6) for correcting the measurement value obtained by inputting the signal under measurement in the measurement mode based on the difference between the characteristic value and the second characteristic value.

According to the first to fourth aspects of the present invention, the output means and the correction means measure the fluctuation value of the frequency response characteristic at different times, and the measured received signal is corrected based on the fluctuation value at that frequency. Thus, uncertainty is reduced.

According to the second, third, and fourth aspects of the present invention, it is possible to perform correction by taking into account fluctuations during use to the correction value based on the frequency response characteristic of the spectrum analyzer stored in advance.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a functional configuration of the present invention. FIG. 2 shows various correction values (characteristic values) for correcting the frequency response characteristics.

  The functional configuration of this embodiment will be described with reference to FIG. In FIG. 1, a receiving system 100 including a receiving unit 3 and an intermediate processing unit 5 has the same configuration as that in FIG. In FIG. 1, configurations denoted by the same reference numerals as those in FIG. 3 have the same functions.

  The functions on the operation route as the original spectrum analyzer will be briefly described (some explanations overlap with the background explanation).

[overall structure]
The operation unit 14 can select and set one of a measurement mode (measurement mode) for measuring the signal under measurement and a calibration mode (CAL mode) for acquiring correction data for correcting the measurement value. ing. In addition, the operation unit 14 can set measurement conditions such as a measurement frequency range (sweep frequency range) as described later.

  The control unit 13 controls the switch 2, the reception unit 3, the intermediate processing unit 5, the correction unit 6, and the signal processing unit 7 according to the setting from the operation unit 14.

  In the measurement mode, the control unit 13 connects the input terminal 1 for inputting the signal under measurement and the reception terminal 2a of the reception unit 3, and uses the sweep frequency range and sweep time of the local oscillator 3c as an instruction from the operation unit 14. Set based on. Also, the RBW and VBW of the intermediate processing unit 5 can be controlled by setting from the operation unit 14. The correction means 6 corrects the measured value of the output of the receiving system (measured level value) based on the data stored in the first storage unit 6a and the second storage unit 6b (details will be described later). The signal processing means 7 uses the sweep frequency when the control unit 13 controls the local oscillator 3c as the horizontal axis (which also corresponds to the sweep time), and the vertical axis as the level based on the set value of the ATT 3a. The corrected measurement value received from the correction unit 6 is displayed on the display unit 8 on the coordinate as the axis.

  In the calibration mode, the control unit 13 connects the output of the output unit 200 and the receiving end 2a of the receiving unit 3, and the entire range in which the sweep frequency range of the local oscillator 3c can be measured (the frequency response characteristic is not necessarily flat). The measurement conditions such as ATT3a, RBW, and VBW are measured as constant values (constant conditions regardless of the setting of the operation unit 14). The correction means 6 acquires and stores a correction value (characteristic value) of the frequency response characteristic based on the output of the receiving system 100 (details will be described later). The display means 8 is notified via the signal processing means 7 that it is “in calibration mode”. In the calibration mode, in order to acquire a correction value (characteristic value), the frequency of the local oscillator 3c may be swept at a frequency step Δf to be acquired (details will be described later).

"Configuration of output means 200"
Next, the output means 200 that outputs a calibration signal used in the calibration mode will be described. As the output means 200, the calibration mode is a period during which the user cannot measure, so that a correction value (characteristic value) is acquired in a short time, the calibration signal is a frequency that is accurately received, and a temperature change or the like. It is desired to output a stable level. Therefore, in FIG. 1, the frequency can be tracked to the frequency of the local oscillator 3c and output so that the correction value (characteristic value) can be obtained by one sweep, and the level can be stabilized and output by the ALC loop. . For this reason, a correction value can be acquired in a short time.

  In FIG. 1, the fixed oscillation unit 9 is a signal source that stably outputs the same frequency as the intermediate frequency fm received by the intermediate processing unit 5. As the signal source, when the frequency is low, the output of the crystal oscillator may be directly used. However, when the frequency is high, for example, a low-frequency crystal oscillator that oscillates at a frequency fm / N (N is an integer) and a VCO (Voltage controlled oscillator), frequency divider that divides the output frequency f0 into 1 / N, the output of the frequency divider (frequency f0 / N) and the output of the low-frequency crystal oscillator (frequency fm / N) A PLL circuit including a phase detector that detects the phase difference and controls the VCO so that the phase difference is eliminated may be provided, and the frequency f0 = fm may be output from the VCO by the control of the PLL circuit.

The second mixing unit 11 mixes the signal received from the fixed oscillating unit 9 via the variable ATT 10 and the output from the local oscillator 3c, and has a calibration signal having a frequency fl-fm. Is output. If the frequency fl of the local oscillator 3c is variable from frequencies fs to ft, the frequency of the calibration signal is [fs to ft−fm]. In the calibration mode, this calibration signal is passed through the switch 2. Then, the signals are mixed by the receiving unit 3, and the intermediate processing unit 5 selects [fs−ft−fm] − [fs−ft] = fm as a frequency component signal.

  The detector 12 detects the level (power) of the calibration signal output from the output means 200, converts it to the magnitude of the DC voltage, and outputs it. The fluctuation of the level detection sensitivity by the detector 12 with respect to the environmental change becomes a fluctuation of the level of the calibration signal directly when the ALC is configured. Therefore, the fluctuation is stable against a temperature change or the like in a desired frequency band. Things are desired. Specifically, when detecting using a diode, a direct current bias is applied to the diode to detect a calibration signal in the linear region of the diode. In addition, there are other methods such as detecting the level by heat / electric conversion. In any case, the detection unit 12 only needs to detect only the reference level for obtaining the correction value (characteristic value) in the calibration mode (for example, the level of the calibration signal is a reference level, for example, 0 dBm). If it is, it is sufficient that the level in the vicinity of 0 dBm can be detected linearly), the dynamic range to be operated can be narrowed, and stable level detection is possible. For example, if the upper limit of the measurement frequency range is 6 GHz and the reference level is 0 dBm, it is desirable to detect up to 6 GHz with an uncertainty within ± 0.1 dB in the temperature range of 0 ° C. to 50 ° C.

  The amplifier 15 compares the DC voltage output from the detector 12 with a preset reference voltage Er, and performs negative feedback control on the attenuation amount of the variable ATT 10 so that these values match. The reference voltage Er is set to a voltage value corresponding to 0 dBm if the level of the calibration signal is the above-described standard level, for example, 0 dBm.

  The variable ATT 10 is an attenuator that can vary the amount of attenuation, but may be an amplifier that can vary the gain. The dynamic range of the variable ATT 10 cancels out the level within the change range of the frequency response characteristic of the calibration signal output from the second mixing unit 11 and the change range of the frequency response characteristic changing at a desired temperature. This is the level range required for As an attenuator capable of changing the amount of attenuation, an element or a circuit whose impedance is changed by direct current control, such as a pin diode, is used.

[Acquisition of correction value (characteristic value) and calibration mode]
The correction value (characteristic value) is acquired at the following two times (a) and (b).
(A) Acquire in advance regardless of the measurement time. This time is at the time of factory shipment or calibration by a service person. The two correction values (characteristic values) to be acquired are the following (a-1) and (a-2).
(a-1) Acquisition of a correction value for correcting frequency response characteristics in a spectrum analyzer.
In this case, the control unit 13 sets the switch 2 to the Meas side (measurement mode side), sets the correction unit 6 to the correction data acquisition state, and sets the measurement condition to be the same as the calibration mode. Since this is difficult to set on the user side, it is usually appropriate to perform it at the time of shipment or calibration by a service person. However, in this case, the measurement may be performed while sweeping the frequency of the local oscillator 3c, or the frequency changed by the predetermined frequency step Δf may be set and received at the input terminal 1 from the operation unit 14 as described below. good.
Then, a calibration signal having a correct level and a frequency varied by a predetermined frequency step Δf is input to the input terminal 1. The reason why the frequency is varied at the predetermined frequency step Δf is that if the measurable frequency range is, for example, 6 GHz, the amount of correction values and the amount of work to be acquired become enormous if the frequency is reduced, for example, Δf = 5 MHz. It is practical to make corrections in steps or 10 MHz steps and interpolate between them. In order to set the calibration signal to the correct level, every time the frequency of the calibration signal is changed, the calibration signal is input to a highly calibrated power meter, and the power meter indicates a predetermined reference level, for example, 0 dBm. This can be achieved by adjusting the level of the calibration signal so that

  The correction means 6 receives the calibration signal input in this way, acquires a value measured for each frequency step, and acquires a frequency response characteristic. For example, when a calibration signal of 50 MHz and 0 dBm is received, the output of the receiving system 100 (output of the intermediate processing unit 5) is adjusted and fixed so that it becomes 0 dBm, and then the frequency is changed one after another to change the signal of 0 dBm. 0 dBm is subtracted from the output of the receiving system 100 when the signal is input, that is, the value of the difference from 0 dBm is stored corresponding to the frequency. Then, for example, frequency response characteristics such as 0 dB for 50 MHz, +0.02 dB for 55 MHz, +0.03 dB for 60 MHz,..., -0.2 dB for 6 GHz are obtained. This is directly stored as a first correction value in the first storage unit 6a in correspondence with the frequency at that time. The format for storing is shown in FIG. When the frequency response characteristic is used as a correction value as it is, the correction means 6 corrects by subtracting the first correction value from the output of the receiving system 100 during measurement in the measurement mode. On the other hand, when the first correction value is obtained by inverting the sign of the frequency response characteristic, the first correction value is added to the output of the receiving system 100 for correction when measuring in the measurement mode.

(A-2) Acquisition of first characteristic value by calibration signal from output means 200 Set the calibration mode at the same time if possible under the same measurement conditions and environmental conditions as when the first correction value was acquired. Then, the calibration signal from the output means 200 is input to the receiving end 2a, and the first characteristic value is acquired. That is, at this time, the frequency of the local oscillator 3c may be swept in steps of the frequency step Δf. The correcting means 6 stores the output of the receiving system 100 at each frequency varied at the frequency step Δf at this time as a first characteristic value. As shown in FIG. 2, it is convenient to store the first correction values in association with each other.

  The first correction value and the first characteristic value stored in the first storage unit 6a are read-only when used by the user and are not rewritten by the user's operation. This is because the first correction value and the first characteristic value are values that serve as a reference when the correction value is subsequently obtained.

  The first correction value and the first characteristic value stored in this way are data correlated in the same environment or the like. That is, even if the environment changes and the frequency response characteristic of the receiving system 100 changes, it can be considered that the effect of the change on the first correction value is the same as the effect on the first characteristic value.

(B) Acquisition of the second characteristic value by the calibration signal from the output means 200 during use When the user sets the calibration mode using the operation unit 14 during use, the output means 200 can be used under the above-described constant measurement conditions. The calibration signal is received. The correcting means 6 stores the output of the receiving system 100 at each frequency varied at the frequency step Δf at this time in the second storage unit 6b as the second characteristic value (see FIG. 2). The second characteristic value includes a level fluctuation depending on the secular change of the spectrum analyzer or the environmental change after the first characteristic value is acquired. As the second characteristic value stored in the second storage unit 6b, a new second characteristic value is acquired every time the user sets the calibration mode, thereby updating and storing it as the latest second characteristic value. Is done.

(C) Correction Value (Characteristic Value) Based on the above configuration, [first characteristic value−second characteristic value] corresponds to the fluctuation of the spectrum analyzer characteristic, and the first characteristic value and the first characteristic value Since the correction values in (1) have a one-to-one correlation with fluctuations due to environmental changes or the like, the fluctuations can be regarded as fluctuations in the first correction value. Therefore, [first correction value + first characteristic value−second characteristic value] is a correction value in use (that is, when the second characteristic value is acquired), that is, a correction value in use.

  Note that the first characteristic value and the second measured value are frequency response characteristics (relative values) when the level output by each receiving system 100 is acquired. 2 characteristic value] only needs to be a frequency response characteristic. Therefore, each of the first characteristic value and the second measurement value is obtained as an absolute value, and the frequency response characteristic of a predetermined reference frequency is set to 0 dB. When the first correction value is obtained, the first characteristic is measured when “the absolute value output from the receiving system 100 is measured at 0 dBm at the reference frequency”. The level of the calibration signal of the output means 200 when acquiring the value is adjusted so that the above-mentioned “the absolute value output from the receiving system 100 when the correction value is acquired is 0 dBm at the reference frequency”. If so, the first characteristic value and Measurement of 2 may be an absolute value of the level at which each reception system 100 outputs. That is, in this case, not only the variation of the frequency response characteristic but also the variation of the absolute value is corrected.

“Measurement of measured signal; measurement mode”
A user inputs a signal to be measured to the input terminal 1 to set the measurement mode, and sets the measurement frequency range (sweep frequency range), ATT3a, RBW, VBW, and the like to desired values for measurement. The correction unit 6 receives the measurement frequency information (corresponding to the information of the sweep frequency) from the control unit 13, and receives the first correction value and the first frequency at the current frequency from the first storage unit 6a and the second storage unit 6b. The characteristic value and the second characteristic value are read out, and based on them, [first characteristic−second characteristic value] = use correction value is obtained, and the obtained use correction value is used at the frequency. The measured value is corrected and displayed as a correct measured value on the display means 8 via the signal processing means 7. However, when the measured frequency of the signal under measurement is between the above-mentioned frequency steps Δf, the correcting means 6 determines the upper and lower frequencies sandwiching the frequency of the signal under measurement from the first storage unit 6a and the second storage unit 6b. The first correction value, the first characteristic value, and the second characteristic value in the step are read out, the proportional interpolation calculation is performed, and the first correction value, the first characteristic value, and the The correction value in use is obtained from the characteristic value of 2 by the same calculation as described above, and the measured value is corrected. Although not shown, the correction unit 6 is provided with a third storage unit, and the above calculation is performed when the second characteristic value is acquired, and the obtained correction value during use is stored in the third storage unit. The measurement value may be corrected by reading the correction value in use when measuring the signal under measurement.

  From the above configuration, the frequency response characteristic and its variation can be corrected over a substantially measurable frequency range. Therefore, it is possible to perform measurement with reduced frequency response uncertainty in a desired frequency band.

It is a figure which shows the function structure in embodiment of this invention. It is a figure which shows the format in which a correction | amendment means memorize | stores a correction value (characteristic value). It is a figure for demonstrating a prior art.

Explanation of symbols

1 input terminal, 2 switch, 3 receiving unit, 3a ATT, 3b first mixing unit,
3c local oscillator, 5 intermediate processing unit, 6 correction means, 6a first storage unit,
6b 2nd memory | storage part, 7 signal processing means, 8 display means, 9 fixed oscillation part,
10 variable ATT, 11 second mixing section, 12 detection section, 13 control section,
14 operation units, 15 amplification units, 20 fixed oscillation units, 21 correction means,
100 receiving system, 200 output means

Claims (4)

A receiving system (100) for mixing an input signal from a receiving end with an output of a frequency-swept local oscillator (3c) to convert it to an intermediate frequency signal, detecting the intermediate frequency signal and outputting it as a measurement value is provided. A spectrum analyzer,
It has a fixed oscillator (9) that generates a signal having the same frequency as that of the intermediate frequency signal, and the level of the output signal obtained by mixing the output of the fixed oscillator and the output of the local oscillator is stabilized. An output means (200) for outputting after conversion to
In advance, the first characteristic value including the frequency response characteristic of the level obtained by applying the output signal from the output means to the receiving end and obtained by the output of the receiving system is stored. A second characteristic value including a frequency response characteristic of a level obtained by applying an output signal from the output means to the receiving end and obtained by the output of the receiving system is stored, and the first characteristic value and the second characteristic value are stored. A spectrum analyzer comprising correction means (6) for correcting the measured value obtained by inputting a signal under measurement to the receiving end based on a difference from a characteristic value . The correction means corrects a frequency response characteristic of the reception system level obtained in advance based on a known calibration signal input to the receiving end together with the first characteristic value. Is obtained by inputting the signal under measurement based on the first correction value and the difference between the first characteristic value and the second characteristic value in use. The spectrum analyzer according to claim 1, wherein the measured value is corrected. The correction means stores the first correction value and the first characteristic value in a read-only manner, stores the second characteristic value in a rewritable manner at each use, and responds at the time of use. For each frequency, the calculation of [first correction value + first characteristic value−rewritten latest second characteristic value] is performed to obtain a correction value in use, and the signal under measurement is input to the receiving end. The spectrum analyzer according to claim 2, wherein the measured value obtained by correction is corrected by the correction value during use . A receiving system (100) for mixing an input signal from a receiving end with an output of a frequency-swept local oscillator (3c) to convert it to an intermediate frequency signal, detecting the intermediate frequency signal and outputting it as a measurement value is provided. A spectrum analyzer,
It has a fixed oscillator (9) that generates a signal having the same frequency as the intermediate frequency signal, and stabilizes the level of the output signal obtained by mixing the output of the fixed oscillator and the output of the local oscillator. Output means (200) for outputting
A switching means (2) for inputting the signal under measurement input in the measurement mode and the output of the output means to the receiving end in the calibration mode;
A first correction value for correcting the frequency response characteristic of the reception system level obtained in advance based on a known calibration signal input in the measurement mode, and from the output means in the calibration mode. And the first characteristic value including the frequency response characteristic of the level obtained at the output of the receiving system by the output signal of the output signal, and at the time of subsequent use, from the output means each time the calibration mode is set Storing a second characteristic value including a frequency response characteristic of the latest level obtained by an output of the reception system by an output signal; the first correction value; and the first characteristic value and the second characteristic value. And a correction means (6) for correcting the measurement value obtained by inputting the signal under measurement in the measurement mode based on the difference between the spectrum analyzer and the spectrum analyzer.

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