A method for accurately measuring the carrier frequency of a pulse modulated signal

Abstract

The application provides a kind of accurate measurement of the method for measuring the carrier frequency of pulse modulation signal, it is related to pulse signal frequency measurement technical field.This kind of accurate measurement of the method for measuring the carrier frequency of pulse modulation signal, it includes the following steps: S1.Using the frequency spectrum measurement function of frequency spectrometer to measure the approximate frequency of signal, set this frequency as f0, and estimate the error range of f0 by the signal bandwidth of frequency spectrum measurement, S2.Using the IQ acquisition function of frequency spectrometer, center frequency is set as f0, demodulation bandwidth is set to be greater than the signal bandwidth of frequency spectrum measurement, sampling time is T, based on IQ acquisition, obtain phase-time curve and amplitude-time curve, the time of amplitude greater than a certain threshold amplitude is within pulse, other time is outside pulse, only need to care the phase data within pulse.The method has the advantages of accurate measurement of the carrier frequency of pulse modulation signal, and has the advantages of high frequency test accuracy and consistent frequency measurement accuracy of continuous wave signal.

Description

Technical Field

[0001] This invention relates to the field of pulse signal frequency measurement technology, specifically a method for accurately measuring the carrier frequency of a pulse modulation signal. Background Technology

[0002] Pulse modulated signals are an important type of signal in radar and digital communication systems. With the development of electronic technology, the pulse repetition frequency (PRF) of pulse modulated signals has been continuously increasing, and the pulse width has become smaller and smaller. The pulse width and period change rapidly, making it difficult to perform high-precision carrier frequency measurement.

[0003] There are two main methods for measuring the carrier frequency of a pulse-modulated signal. One method is the spectrum analyzer method, which involves multiple frequency conversions of the signal under test to an intermediate frequency (IF) signal, performing an FFT transform on the IF signal to obtain the spectrum information, and then obtaining the carrier signal frequency based on the spectrum information.

[0004] The main drawbacks of using a spectrum analyzer to measure the carrier frequency of a pulse-modulated signal via FFT are: 1) The FFT spectrum of a periodic pulse signal will have multiple comb-like spectral lines, making it difficult to determine which spectral line represents the true carrier spectrum, especially for pulse signals with irregular pulse widths and periods, making it even more difficult to obtain the carrier frequency from the signal's FFT spectrum. 2) The frequency measurement resolution is determined by the length of the FFT, resulting in a relatively large measurement error.

[0005] The second method is the counter frequency measurement method. The main drawback of using a counter to measure the carrier frequency of a pulse-modulated signal is that the measurement error is relatively large when the pulse width is very narrow.

[0006] Pulse-modulated signals are an important type of signal in radar and digital communication systems. With the development of electronic technology, the pulse repetition frequency (PRF) of pulse-modulated signals has been continuously increasing, while the pulse width has become increasingly smaller. The rapid changes in pulse width and period make high-precision carrier frequency measurement difficult. Carrier frequency is a crucial fundamental radio frequency indicator that requires accurate measurement. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address the shortcomings of existing technologies, this invention provides a method for accurately measuring the carrier frequency of pulse modulation signals. This method solves the problems of insufficient accuracy in traditional pulse modulation signal carrier frequency measurement, the inconvenience of traditional methods for measuring pulse signals with irregular pulse widths and periods, and the inconvenience of traditional methods for measuring pulse signals with high pulse repetition frequencies and narrow pulse widths.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the present invention provides the following technical solution: a method for accurately measuring the carrier frequency of a pulse modulation signal, comprising the following steps:

[0011] S1. Use the spectrum measurement function of the spectrum analyzer to measure the approximate frequency of the signal, let this frequency be f0, and estimate the error range of f0 by measuring the signal bandwidth through the spectrum.

[0012] S2. Use the IQ acquisition function of the spectrum analyzer, set the center frequency to f0, the demodulation bandwidth should be greater than the signal bandwidth of the spectrum measurement, the sampling time is T, and obtain the phase-time curve and amplitude-time curve based on the IQ acquisition. The time when the amplitude is greater than a certain threshold is the pulse, and the other time is the pulse. Only the phase data within the pulse is of concern.

[0013] S3. Select the pulse with the longest duration within the pulse, and calculate the frequency difference using the method of measuring the frequency of continuous waves. Record it as Δf1 as a rough estimate of Δf.

[0014] S4. Use the frequency difference Δf1 to compensate the phase curve φ(t) to obtain a new phase curve φ2(t). The phase curve φ2(t) should be a nearly horizontal straight line within one pulse width, but the value is different for different pulses.

[0015] S5. Using the phase difference and time difference between different pulses, calculate the frequency difference again, denoted as Δf2, as a fine correction to Δf;

[0016] S6. The above steps can be iterated to continuously increase the time difference until the time difference is increased to the maximum. At this time, the measurement accuracy reaches the highest level at the current sampling time setting. The frequency fine correction term Δfn obtained in each iteration should be accumulated.

[0017] Preferably, in step S1, the phase-time curve is acquired based on IQ acquisition, the corrected frequency Δf is obtained from the phase-time curve, and the final measured frequency result is f0+Δf.

[0018] Preferably, in step S2, assuming the signal to be measured is a continuous wave signal, when the spectrum analyzer performs IQ acquisition, the center frequency is set to f0, and the frequency difference between the center frequency and the signal to be measured is Δf. Then the measured phase-time curve is:

[0019] φ(t)=2π·Δf·t+φ0

[0020] The frequency difference Δf can be calculated from the slope of the phase-time curve.

[0021]

[0022] Because phase measurement has errors, the frequency measurement accuracy is higher when the measurement time interval (t2-t1) is larger. When t2-t1 exceeds the period corresponding to Δf, the corresponding phase difference will exceed 2π, causing phase ambiguity in the phase difference measurement result that is an integer multiple of 2π. In order to accurately measure the frequency, the problem of phase ambiguity that is an integer multiple of 2π must be solved. The method to solve the phase ambiguity that is an integer multiple of 2π is as follows:

[0023] Calculate the number of phase abrupt changes N within the time range t1 to t2. A single abrupt change from -π to π should compensate for a phase change of -2π, and a single abrupt change from π to -π should compensate for a phase change of 2π. Generally, phase φ(t) only has abrupt changes in one direction. Considering the phase compensation, the frequency difference Δf is:

[0024]

[0025] The addition or subtraction of the compensation phase is determined by the direction of the phase change. When the signal under test is a pulse-modulated signal, the above method for solving phase ambiguity of integer multiples of 2π will encounter a problem: it is impossible to calculate how many times the phase changes during the pulse off time.

[0026] Preferably, in step S3, the pulse-modulated signal can be considered a continuous signal within the pulse width. Therefore, the frequency difference, denoted as Δf1, can be calculated using the time range within the pulse as a rough estimate of Δf.

[0027] Because the pulse width of the pulse signal is relatively narrow, the measurement accuracy of Δf1 is still relatively low.

[0028] Preferably, in step S4, the formula for calculating φ2(t) is:

[0029] φ2(t)=-2π·Δf1·t+φ(t).

[0030] Preferably, in step S5, the phase curve φ2(t) is compensated using the frequency difference Δf2 to obtain a new phase curve φ3(t), the formula of which is:

[0031] φ3(t)=-2π·Δf2·t+φ2(t)

[0032] This step can be iterated, continuously increasing the time difference and improving measurement accuracy. The frequency fine-tuning term Δfn obtained in each iteration should be accumulated.

[0033] Preferably, in step S6, when calculating the frequency difference for the first time using the phase difference and time difference between different pulses, two adjacent pulses can be selected. Subsequently, the time difference is progressively increased, for example, from adjacent pulses to intervals of 10, 100 pulses, and finally to the first and last pulses, reaching the maximum time interval and the highest measurement accuracy. The final carrier frequency measurement result of the pulse modulation signal is:

[0034] f meas = f0 + Δf1 + Δf2 + ... + Δf n .

[0035] (III) Beneficial Effects

[0036] This invention provides a method for accurately measuring the carrier frequency of a pulse-modulated signal. It has the following advantages:

[0037] This invention provides a method for accurately measuring the carrier frequency of a pulse-modulated signal. This method has the advantage of accurately measuring the carrier frequency of a pulse-modulated signal, and also has the advantages of high frequency testing accuracy and consistency with the frequency measurement accuracy of continuous wave signals.

[0038] This invention provides a method for accurately measuring the carrier frequency of a pulse modulation signal. This method can be used to measure pulse signals with irregular pulse width and period, and can also be used to measure pulse signals with high pulse repetition frequency and narrow pulse width, thus offering versatility and strong practicality. Attached Figure Description

[0039] Figure 1 This is a flowchart of a method for accurately measuring the carrier frequency of a pulse modulation signal according to the present invention;

[0040] Figure 2 A simplified schematic diagram of the spectrum analyzer for IQ acquisition in accordance with the present invention, which is a method for accurately measuring the carrier frequency of a pulse modulation signal.

[0041] Figure 3 The amplitude and phase curves of IQ acquisition for a method of accurately measuring the carrier frequency of a pulse modulated signal according to the present invention are shown.

[0042] Figure 4 This is a phase curve after coarse frequency compensation, representing a method for accurately measuring the carrier frequency of a pulse-modulated signal according to the present invention.

[0043] Figure 5 The phase curve after fine frequency compensation is shown in the method for accurately measuring the carrier frequency of a pulse modulation signal according to the present invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example:

[0046] like Figure 1-5 As shown, this embodiment of the invention provides a method for accurately measuring the carrier frequency of a pulse modulation signal, comprising the following steps:

[0047] S1. Use the spectrum measurement function of the spectrum analyzer to measure the approximate frequency of the signal, let this frequency be f0, and estimate the error range of f0 by measuring the signal bandwidth through the spectrum.

[0048] S2. Use the IQ acquisition function of the spectrum analyzer, set the center frequency to f0, the demodulation bandwidth should be greater than the signal bandwidth of the spectrum measurement, the sampling time is T, and obtain the phase-time curve and amplitude-time curve based on the IQ acquisition. The time when the amplitude is greater than a certain threshold is the pulse, and the other time is the pulse. Only the phase data within the pulse is of concern.

[0049] S3. Select the pulse with the longest duration within the pulse, and calculate the frequency difference using the method of measuring the frequency of continuous waves. Record it as Δf1 as a rough estimate of Δf.

[0050] S4. Use the frequency difference Δf1 to compensate the phase curve φ(t) to obtain a new phase curve φ2(t). The phase curve φ2(t) should be a nearly horizontal straight line within one pulse width, but the value is different for different pulses.

[0051] S5. Using the phase difference and time difference between different pulses, calculate the frequency difference again, denoted as Δf2, as a fine correction to Δf;

[0052] S6. The above steps can be iterated to continuously increase the time difference until the time difference is increased to the maximum. At this time, the measurement accuracy reaches the highest level at the current sampling time setting. The frequency fine correction term Δfn obtained in each iteration should be accumulated.

[0053] In step S1, the phase-time curve is acquired based on IQ acquisition, and the corrected frequency Δf is obtained from the phase-time curve. The final measured frequency result is f0+Δf.

[0054] In step S2, assuming the signal under test is a continuous wave signal, and the center frequency of the spectrum analyzer is set to f0 during IQ acquisition, with a frequency difference of Δf between the center frequency and the signal under test, the measured phase-time curve is as follows:

[0055] φ(t)=2π·Δf·t+φ0

[0056] The frequency difference Δf can be calculated from the slope of the phase-time curve.

[0057]

[0058] Because phase measurement has errors, the frequency measurement accuracy is higher when the measurement time interval (t2-t1) is larger. When t2-t1 exceeds the period corresponding to Δf, the corresponding phase difference will exceed 2π, causing phase ambiguity in the phase difference measurement result that is an integer multiple of 2π. In order to accurately measure the frequency, the problem of phase ambiguity that is an integer multiple of 2π must be solved. The method to solve the phase ambiguity that is an integer multiple of 2π is as follows:

[0059] Calculate the number of phase abrupt changes N within the time range t1 to t2. A single abrupt change from -π to π should compensate for a phase change of -2π, and a single abrupt change from π to -π should compensate for a phase change of 2π. Generally, phase φ(t) only has abrupt changes in one direction. Considering the phase compensation, the frequency difference Δf is:

[0060]

[0061] The addition or subtraction of the compensation phase is determined by the direction of the phase change. When the signal under test is a pulse-modulated signal, the above method for solving phase ambiguity of integer multiples of 2π will encounter a problem: it is impossible to calculate how many times the phase changes during the pulse off time.

[0062] In step S3, the pulse modulation signal can be considered as a continuous signal within the pulse width. Therefore, the frequency difference can be calculated using the time range within the pulse, denoted as Δf1, as a rough estimate of Δf. Since the pulse width of the pulse signal is relatively narrow, the measurement accuracy of Δf1 is still relatively low.

[0063] In step S4, the formula for calculating φ2(t) is:

[0064] φ2(t)=-2π·Δf1·t+φ(t).

[0065] In step S5, the phase curve φ2(t) is compensated using the frequency difference Δf2 to obtain a new phase curve φ3(t), the formula of which is:

[0066] φ3(t)=-2π·Δf2·t+φ2(t)

[0067] This step can be iterated, continuously increasing the time difference and improving measurement accuracy. The frequency fine-tuning term Δfn obtained in each iteration should be accumulated.

[0068] In step S6, when calculating the frequency difference for the first time using the phase and time differences between different pulses, two adjacent pulses can be selected. Subsequently, the time difference is progressively increased, for example, from adjacent pulses to intervals of 10, 100 pulses, and finally to the first and last pulses, reaching the maximum time interval and thus the highest measurement accuracy. The final carrier frequency measurement result of the pulse modulation signal is:

[0069] f meas = f0 + Δf1 + Δf2 + ... + Δf n .

[0070] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of accurately measuring the carrier frequency of a pulse modulated signal, characterized by: The method comprises the following steps: S1. Measure the approximate frequency of the signal using the spectrum measurement function of the spectrum analyzer, set the frequency as f0, and estimate the error range of f0 by the signal bandwidth of the spectrum measurement; S2. Use the IQ acquisition function of the spectrum analyzer, set the center frequency as f0, set the demodulation bandwidth to be greater than the signal bandwidth of the spectrum measurement, set the sampling time as T, obtain the phase-time curve and the amplitude-time curve based on the IQ acquisition, the time with the amplitude greater than a certain threshold amplitude is within the pulse, and the other time is outside the pulse; S3. Select one pulse with the longest time within the pulse, calculate the frequency difference as Δf1 by using the method of measuring the frequency of the continuous wave, and take Δf1 as the rough estimation of Δf; S4. Compensate the phase curve φ(t) using the frequency difference Δf1 to obtain a new phase curve φ2(t), and the phase curve φ2(t) is a nearly horizontal straight line within the pulse width, but the values of different pulses are different; S5. Calculate the frequency difference again by using the phase difference and the time difference between different pulses, and take Δf2 as the fine correction of Δf; S6. The above steps are iterated, the time difference is continuously expanded, and the measurement accuracy reaches the highest under the current sampling time setting when the time difference is expanded to the maximum. The frequency fine correction term Δfn obtained in each iteration is accumulated. In the step S2, assuming that the signal to be measured is a continuous wave signal, the center frequency of the spectrum analyzer is set as f0, and the frequency difference between the spectrum analyzer and the signal to be measured is Δf. The measured phase-time curve is: The frequency difference Δf can be calculated from the slope of the phase-time curve, Since there is an error in phase measurement, the frequency measurement accuracy is higher when the measurement time interval (t2-t1) is larger. When t2-t1 exceeds the period corresponding to Δf, the corresponding phase difference will exceed 2π, causing the phase ambiguity of an integer multiple of 2π in the measurement result of the phase difference. In order to accurately measure the frequency, the phase ambiguity of an integer multiple of 2π must be solved. The method for solving the phase ambiguity of an integer multiple of 2π is: Calculate the number N of times of phase φ(t) mutations in the time range from t1 to t2. The compensation phase change amount is-2π for a mutation from-π to π, and the compensation phase change amount is 2π for a mutation from π to-π. Generally, the phase φ(t) only has a mutation in one direction. The frequency difference Δf after phase compensation is: Where the addition and subtraction of the compensation phase are determined by the direction of the phase mutation. When the signal to be measured is a pulse modulated signal, the above method for solving the phase ambiguity of an integer multiple of 2π will cause that it is impossible to calculate how many times the phase mutates within the pulse-off time.

2. The method of claim 1, wherein: In the step S1, the phase-time curve is obtained based on the IQ acquisition, the correction frequency Δf is obtained from the phase-time curve, and the final measurement frequency result is f0+Δf.

3. The method for accurately measuring the carrier frequency of a pulse modulation signal according to claim 1, characterized in that: In the step S3, the pulse modulated signal is a continuous signal within the pulse width. The frequency difference within the pulse is calculated as Δf1, which is taken as the rough estimation of Δf. Since the pulse width of the pulse signal is narrow, the measurement accuracy of Δf1 is low.

4. The method of claim 1, wherein: In the step S4, the calculation formula of φ2(t) is: 。 5. The method for accurately measuring the carrier frequency of a pulse-modulated signal according to claim 1, characterized in that: In step S5, the phase curve is compensated using the frequency difference Δf2 to obtain a new phase curve φ3(t), and the formula is: This step is iterated to expand the time difference and improve the measurement accuracy. The frequency fine correction term Δfn obtained in each iteration is accumulated.

6. The method of claim 1, wherein: In step S6, the first time the frequency difference is calculated using the phase difference and time difference between different pulses, two adjacent pulses are selected. Thereafter, the time difference is expanded in turn, including from adjacent pulses to 10, 100 pulses, and finally to the first pulse and the last pulse, the time interval reaches the maximum, the measurement accuracy reaches the highest, and the final carrier frequency measurement result of the pulse modulation signal is: 。

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