A method and device for testing linear deviation of high-speed frequency modulation signals

Abstract

The present invention discloses a method and device for testing the linear deviation of a high-speed frequency-modulated signal. The high-speed frequency-modulated signal to be tested is modulated into the optical domain by a high-speed electro-optical modulator. A high-speed adjustable optical delay line is used to split the optical signal into two signals with differential delays. The mixed output is detected in the optical domain. After filtering out the down-converted signal and phase-detecting the low-frequency signal output by a DDS, a high-speed ADC performs data acquisition, reception, and analysis. By varying the delay of the high-speed adjustable optical delay line and the corresponding low-frequency signal frequency generated by the DDS, and performing multiple measurements, the sampled data is fitted with a polynomial to determine the linear deviation of the high-speed frequency-modulated signal to be tested. The present invention has a simple structure, high measurement accuracy, and is easy to implement.

Description

Technical Field

[0001] The present invention belongs to the field of high-frequency and high-speed signal processing, and in particular relates to a method and device for testing linear deviation of a high-speed frequency modulation signal. Background Art

[0002] With the advancement of radar detection technology, increasingly stringent requirements are being placed on radar performance indicators such as range, resolution, and measurement accuracy. Compared to traditional pulse radar, linear frequency modulated continuous wave (LFMCW) radar transmits signals with a time width significantly greater than the target echo delay, and the transmitter and receiver operate simultaneously, eliminating range blind spots. Furthermore, because LFMCW signals have a very large time-bandwidth product and possess far greater energy than pulse signals, they offer enhanced detection capabilities, making them widely used in high-precision ranging and imaging.

[0003] The theoretical range resolution of LFMCW radar is ,in is the speed of light, and B is the sweep bandwidth. Therefore, the sweep bandwidth determines the highest range resolution that the radar can achieve. However, due to the non-ideal characteristics of the device, the LFMCW signal output cannot be completely linear.

[0004] Linearity represents the degree to which the frequency of a linear frequency modulation (LFM) signal deviates from its ideal frequency. This affects not only the ranging accuracy of an LFMCW radar but also its actual range resolution. When the transmitted signal is an ideal LFM, the difference frequency signal between the transmitted signal and the target echo signal is a single-frequency signal within one LFM cycle. However, when it is an imperfect LFM, the difference frequency signal spectrum will have a certain bandwidth, potentially making it impossible to distinguish adjacent targets. Furthermore, in the presence of strong transmitted signal leakage or reflections from large targets, weaker target signals may be drowned out by the phase noise of the stronger signal. Spurious signals can interfere with the radar's normal operation, leading to false alarms. Therefore, evaluating the linearity of high-speed FM signal sources is of great practical significance.

[0005] Traditional FM signal linearity measurement methods can be mainly divided into the following two categories: (1) Static measurement method. This method is based on a fixed DC voltage and the measured discrete value of the output frequency to obtain a static FM characteristic curve. The disadvantage is that the working state of the FM source at this time is different from the actual working state and cannot reflect the true working characteristics. (2) Instantaneous frequency measurement method. This method divides the signal into two paths with differential delay and mixes them. The instantaneous frequency of the mixed signal is calculated by signal processing methods such as phase difference method, wavelet transform method, phase-locked loop method, etc. However, these methods often have limitations. The phase difference method is too sensitive to noise, the wavelet transform method requires the selection of an appropriate scale, and the phase-locked loop method has a response time problem. (3) Phase measurement method. This method also divides the signal into two paths with differential delay and mixes them, but does not directly measure the instantaneous frequency. Instead, it uses a low-frequency signal output by a high-stability signal source that matches the differential delay to perform phase detection and solve the frequency deviation of the original FM signal. The signal processing process of this method is relatively simple and can intuitively reflect the linear deviation of the FM source during operation. Summary of the Invention

[0006] In view of the above, the present invention proposes a method and device for testing the linear deviation of a high-speed frequency modulation signal, which can measure the linear deviation of a high-speed frequency modulation signal.

[0007] A method and device for testing linear deviation of a high-speed frequency modulation signal, the device used in the method comprising:

[0008] Laser (1), high-speed frequency modulation signal to be measured (2), Mach-Zehnder modulator (3), 1×2 optical coupler (4), high-speed adjustable optical delay line (5), 2×1 optical coupler (6), high-stability reference source (7), photodetector (8), electric amplifier (9), low-pass filter (10), signal generator (11), phase detector (12), high-speed ADC acquisition card (13);

[0009] The invention is characterized in that: the high-speed frequency modulation signal (2) to be measured is modulated onto the optical signal generated by the laser (1) through the Mach-Zehnder modulator (3), and is divided into two paths through the 1×2 optical coupler (4). 、 Output, where After passing through the high-speed adjustable optical delay line (5), the two signals are controlled to have a differential delay of Then the two signals are combined into one signal through a 2×1 optical coupler (6) and input into a photodetector (8). The two optical sideband optical signals are mixed in the optical domain and converted into electrical signals. Then, the down-converted signals are filtered out through an electrical amplifier (9) and a low-pass filter (10) in sequence. The signal generator (11) controls the differential delay of the high-speed adjustable optical delay line (5). The corresponding low-frequency signal is output, and the low-frequency signal and the down-converted signal are phase-detected by a phase detector (12). The high-speed ADC acquisition card (13) performs data acquisition based on the synchronization signal provided by the high-speed frequency modulation signal (2) to be measured, and is used for subsequent data processing in the host computer. The high-stability reference source (7) is responsible for providing a reference signal to the high-speed frequency modulation signal (2) to be measured and the signal generator (11).

[0010] Furthermore, the Mach-Zehnder modulator (3) operates in a carrier suppression (minimum point) state, the optical carrier component is suppressed, and the output only contains a sideband signal, which is used to modulate the high-speed frequency modulation signal (2) to be measured into the optical domain.

[0011] Furthermore, the high-speed adjustable optical delay line (5) is composed of a plurality of sub-delay units and an electrical control module, each sub-delay unit includes two optical switches and two delay optical fibers of different lengths, and the electrical control module controls the direction of the optical switch, thereby providing a continuously adjustable optical delay amount.

[0012] Furthermore, the photoelectric detector (8) detects the two optical sideband optical signals after the combination. Perform beat frequency and input optical power , after optical detection, the difference frequency signal of the two signals is output.

[0013] Furthermore, the low-frequency signal generated by the signal generator (11) has a frequency of ,in is the frequency sweep slope of the high-speed FM signal (2) to be measured, The differential delay is set for the high-speed adjustable optical delay line (5).

[0014] Furthermore, during each measurement, the differential delay is guaranteed. Much smaller than the frequency modulation period Under the premise of multi-scale change of the delay of the high-speed adjustable optical delay line (5), and the frequency of the low-frequency signal generated by the corresponding signal generator (11) is adjusted, and the synchronization signal provided by the high-speed frequency modulation signal (2) to be measured is used as the start mark of the measurement to perform measurement, obtain the frequency deviation data corresponding to the current differential delay and wait for further data processing.

[0015] Furthermore, the data processing method includes:

[0016] For all differential delays In the example, each differential delay The corresponding set of discrete sampling data output by the phase detector , first remove all sampling times in The invalid points other than , and then all the sampling points of the groups are averaged according to the corresponding sampling time, that is , get the processed average discrete data At this time, a polynomial fitting is performed on the sequence, the error is calculated based on the least squares method, and the gradient descent method is used to optimize the objective function. Considering that the actual frequency deviation is concentrated in the low-order terms, in order to avoid overfitting, the highest power of the polynomial is selected to be 5 or less. The final polynomial curve represents the linear deviation of the signal to be measured.

[0017] Based on the above technical solution, the present invention has the following beneficial technical effects:

[0018] (1) The present invention measures the linear deviation of high-speed frequency modulation signals based on the phase measurement method, which does not require a complex signal processing process to calculate the instantaneous frequency and is more suitable for real-time linearity calculation of high-speed frequency modulation signals.

[0019] (2) The present invention adopts a multi-scale delay measurement method with high measurement accuracy, which can effectively suppress random noise in the measurement process and minimize measurement gaps.

[0020] (3) The DDS bandwidth required by the present invention is relatively small, easy to purchase, and easier to implement in actual measurement scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the specific structure of the device of the present invention.

[0022] In the figure: 1—laser, 2—high-speed FM signal to be measured, 3—Mach-Zehnder modulator, 4—1×2 optical coupler, 5—high-speed adjustable optical delay line, 6—2×1 optical coupler, 7—high-stability reference source, 8—photodetector, 9—electrical amplifier, 10—low-pass filter, 11—signal generator, 12—phase detector, 13—high-speed ADC acquisition card. DETAILED DESCRIPTION

[0023] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 Schematic diagram of the specific structure of the method and device for testing the linear deviation of high-speed frequency modulation signals of the present invention. Figure 1 As shown, the device used in the method includes: a laser (1), a high-speed frequency-modulated signal to be measured (2), a Mach-Zehnder modulator (3), a 1×2 optical coupler (4), a high-speed adjustable optical delay line (5), a 2×1 optical coupler (6), a high-stability reference source (7), a photodetector (8), an electric amplifier (9), a low-pass filter (10), a signal generator (11), a phase detector (12), and a high-speed ADC acquisition card (13).

[0025] In this embodiment, it is assumed that the high-speed frequency modulation signal (2) to be measured is as follows in the first cycle:

[0026]

[0027] in is the starting frequency , is the frequency sweep slope , represent Frequency deviation at time , the initial phase is ignored at this time. The high-speed frequency modulation signal (2) to be measured is modulated onto the optical signal generated by the laser (1) by the Mach-Zehnder modulator (3). At this time, the carrier suppression modulation method is adopted. It is assumed that the electric field of the optical signal generated by the laser (1) is expressed as:

[0028]

[0029] set up , then the electric field of the output optical signal is expressed as:

[0030]

[0031] in is the Bessel function, The optical signal is split into two paths by a 1×2 optical coupler (4), one of which passes through a high-speed adjustable optical delay line (5) to introduce differential delay. , the electric fields corresponding to the two signals are:

[0032]

[0033]

[0034] The two optical signals are combined through a 2×1 optical coupler (6), and their optical power is:

[0035]

[0036] The combined signal is input to the photodetector (8) for beat frequency to achieve optical domain mixing and converted into an electrical signal, which then passes through the electrical amplifier (9) and low-pass filter (10) to output a down-converted signal. :

[0037]

[0038] in for The amplitude factor, represents the difference frequency, Represents the phase constant. At this time, set the low-frequency signal output by the signal generator (11) Frequency is :

[0039]

[0040] in for The amplitude factor, for The initial phase of . At this time, the phase detector (12) outputs :

[0041]

[0042] Where K is the gain coefficient of the phase detector. During the measurement process, ensure It is much smaller than the frequency modulation period T, so the first term in equation (5) can be expressed as follows:

[0043]

[0044] At this time, the frequency offset of the high-speed FM signal to be measured can be derived by sampling the output of the phase detector (12). sampling,

[0045] In this embodiment, due to The size of will affect the resolution of the phase detector (12) output. When the value is larger, the output resolution of the phase detector (12) is large, and when When the phase detector (12) is small, the output resolution is small. At the same time, since the measurement process is only applicable to ,when When it is larger, it will be This interval produces a large measurement gap. Taking the above factors into consideration, this embodiment adopts multi-scale delay to measure the linear deviation of the high-speed frequency modulation signal.

[0046] During each measurement, from small to large, while ensuring the differential delay The delay of the high-speed adjustable optical delay line (5) is adjusted under the premise that the delay is much smaller than the frequency modulation period T, and the frequency of the low-frequency signal output by the corresponding signal generator (11) is changed at the same time, and the synchronization signal provided by the high-speed frequency modulation signal (2) to be measured is used as the start mark of the high-speed ADC acquisition card (13) measurement.

[0047] For all differential delays In the example, each differential delay The corresponding set of discrete sampling data output by the phase detector First, remove all sampling times between The invalid points other than , and then all the sampling points of the groups are averaged according to the corresponding sampling time, that is , get the processed average discrete data At this time, a polynomial fitting is performed on the sequence, the error is calculated based on the least squares method, and the objective function is optimized using the gradient descent method; considering that the actual frequency deviation is concentrated in the low-order terms, in order to avoid overfitting, the highest power of the polynomial is selected to be 5 or less.

[0048] The fitted polynomial curve represents the linear deviation of the high-speed frequency modulation signal (2) to be measured. Based on the curve, relevant indicators including linearity can be calculated.

[0049] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for testing linear deviation of a high-speed frequency modulation signal, the device used in the method comprising: Laser (1), high-speed frequency modulation signal to be measured (2), Mach-Zehnder modulator (3), 1×2 optical coupler (4), high-speed adjustable optical delay line (5), 2×1 optical coupler (6), high-stability reference source (7), photodetector (8), electric amplifier (9), low-pass filter (10), signal generator (11), phase detector (12), high-speed ADC acquisition card (13); The invention is characterized in that: the high-speed frequency modulation signal (2) to be measured is modulated onto the optical signal generated by the laser (1) through the Mach-Zehnder modulator (3), and is divided into two paths E by the 1×2 optical coupler (4). out1 、E out2 Output, where E out2 After passing through the high-speed adjustable optical delay line (5), the differential delay of the two signals is controlled to be τ, and then the two signals are combined into one signal through the 2×1 optical coupler (6) and input into the photodetector (8). The two optical sideband optical signals are mixed in the optical domain detection and converted into electrical signals, and then sequentially passed through the electrical amplifier (9) and the low-pass filter (10) to filter out the down-converted signal. The signal generator (11) outputs the corresponding low-frequency signal according to the differential delay τ controlled by the high-speed adjustable optical delay line (5). The low-frequency signal and the down-converted signal are phase-detected by the phase detector (12). The high-speed ADC acquisition card (13) performs data acquisition according to the synchronization signal provided by the high-speed frequency modulation signal (2) to be measured, and is used for subsequent data processing in the host computer. The high-stability reference source (7) is responsible for providing a reference signal to the high-speed frequency modulation signal (2) to be measured and the signal generator (11); During each measurement, under the premise of ensuring that the differential delay τ is much smaller than the frequency modulation period T, the delay of the high-speed adjustable optical delay line (5) is changed in multiple scales, and the frequency of the low-frequency signal generated by the corresponding signal generator (11) is adjusted. The synchronization signal provided by the high-speed frequency modulation signal (2) to be measured is used as the start mark of the measurement to perform the measurement, obtain the frequency deviation data corresponding to the current differential delay and wait for further data processing.

2. The high-speed frequency modulation signal linear deviation testing method according to claim 1, wherein: The Mach-Zehnder modulator (3) operates in a carrier suppression minimum point state, the optical carrier component is suppressed, and the output only contains a sideband signal, which is used to modulate the high-speed frequency modulation signal (2) to be measured into the optical domain.

3. The method for testing linear deviation of a high-speed frequency modulation signal according to claim 1, wherein: The high-speed adjustable optical delay line (5) is composed of a plurality of sub-delay units and an electric control module. Each sub-delay unit includes two optical switches and two delay optical fibers of different lengths. The electric control module controls the direction of the optical switch to provide a continuously adjustable optical delay.

4. The method for testing linear deviation of a high-speed frequency modulation signal according to claim 1, wherein: The photoelectric detector (8) detects the two optical sideband optical signals E after the combination. out1 、E out2 Perform beat frequency, input optical power P=(E out1 +E out2 )*(E out1 +E out2 ) * , after optical detection, the difference frequency signal of the two signals is output.

5. The method for testing linear deviation of a high-speed frequency modulation signal according to claim 1, wherein: The low-frequency signal frequency f generated by the signal generator (11) d =s*τ, where s is the frequency sweep slope of the high-speed frequency modulation signal (2) to be measured, and τ is the differential delay set by the high-speed adjustable optical delay line (5).

6. The method for testing linear deviation of a high-speed frequency modulation signal according to claim 1, wherein: Data processing methods include: For all differential delays [τ1, τ2…τ l , for each differential delay τ k the corresponding set of discrete sampling data of the phase detector outputs where n ≤ T*f s ; first, remove all invalid points with sampling times outside τ < t < T, and then average all groups of sampling points in sequence according to the corresponding sampling times, that is to obtain the processed average discrete data At this time, perform polynomial fitting on the average discrete data, calculate the error based on the least squares method, and use the gradient descent method to optimize the objective function. Considering that the actual frequency deviation is concentrated in the low-order terms, to avoid overfitting, the highest power of the polynomial is selected to be 5 or less. The finally obtained polynomial curve represents the linear deviation of the signal to be measured.

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