A self-referenced non-coherent field measurement method and system for realizing in-situ measurement of non-coherent electric field

Abstract

The application belongs to the technical field of electromagnetic wave near-field measurement and microwave photonics, and particularly relates to a self-reference non-coherent electric field measurement method and system for realizing in-situ measurement of non-coherent electric field. The method comprises an excitation and scattering unit, a radio frequency synchronous acquisition unit and a self-reference calculation control center. The core principle is to use the modulation scattering characteristics of photo-generated plasma to transfer the local field information of the antenna to be measured to a frequency shift sideband, realize the frequency domain separation of the scattering signal and the original carrier signal, and source the same independent non-coherent source and synchronously receive the sideband signal and the carrier signal. The amplitude and phase fluctuations of the source are common items of the two signals. By comparing and operating the two synchronously received signals, the common amplitude and phase fluctuations of the source are offset, and the non-coherent source stable complex electric field distribution can be obtained without establishing a phase coherent link between the measured source and the receiver.

Description

Technical Field

[0001] This application belongs to the interdisciplinary field of electromagnetic wave near-field measurement and microwave photonics, specifically relating to a self-referenced incoherent field measurement method and system for realizing in-situ measurement of incoherent electric fields. Background Technology

[0002] Near-field antenna measurement is a widely used method for evaluating antenna radiation characteristics. Compared to direct far-field measurement, near-field measurement can be performed in a more compact space. By mechanically scanning the probe in the near-field region of the antenna under test (AUT), the amplitude and phase distribution of the field are acquired point by point. The obtained complex near-field data can be used to calculate key parameters of the antenna, such as the far-field radiation pattern, gain, and polarization characteristics, using near-far-field transformation algorithms.

[0003] In traditional near-field measurement systems, accurate phase information acquisition requires the simultaneous fulfillment of two core preconditions:

[0004] 1. Phase-coherent transceiver link: A stable phase-coherent connection must be established between the source under test and the measurement receiver. This is usually achieved using a vector network analyzer (VNA) or a coherent transceiver, both of which share a unified 10MHz reference clock signal.

[0005] 2. Highly stable scanning system: During mechanical scanning, the spatial position of the probe and the connecting cable must remain sufficiently stable to avoid introducing additional phase errors.

[0006] However, as the operating frequency increases to the millimeter wave and terahertz bands, the wavelength of electromagnetic waves shortens dramatically. The measurement phase becomes extremely sensitive to positioning errors, mechanical vibrations, and cable movement. Micrometer-level position deviations can introduce significant phase errors, greatly increasing the difficulty and system cost of high-frequency near-field measurements.

[0007] Even more serious is the fact that, as modern electronic systems evolve towards integration, miniaturization, and unification, many devices under test have become completely independent operating systems. For example, active integrated antennas integrate radiating elements, local oscillators, power amplifiers, mixers, and other circuits onto the same substrate; commercial radar modules contain complete transmitters, receivers, and digital signal processing circuits; and IoT wireless terminals use system-on-a-chip (SoC) architectures to achieve wireless communication functions. The transmitters of these devices are completely enclosed within the system, unable to provide external reference clock signals or establish a phase-coherent connection with external measurement equipment, making them typical "incoherent sources."

[0008] The output signal of incoherent sources inherently exhibits random amplitude drift and phase jitter. If traditional coherent measurement methods are directly applied, the random fluctuations at the source end will completely mask the spatial phase distribution of the measured field, leading to complete distortion of the measurement results. Therefore, obtaining stable near-field electric fields for independent incoherent sources in in-situ measurement scenarios has become a core technical challenge and hot topic in the current antenna measurement field.

[0009] To address the challenges of near-field measurement of incoherent sources, scholars both domestically and internationally have conducted extensive research, proposing phase-free inversion methods that recover the phase from amplitude measurement results to obtain complete field results. The core idea of ​​these methods is to measure the pure amplitude distribution of multiple planes or probes, utilizing the physical constraints of electromagnetic wave propagation, and inverting phase information through iterative algorithms. These methods mainly include dual-plane iterative methods, plane spectral expansion methods, and source reconstruction methods. To further reduce the amount of measurement data, single-surface phase retrieval methods have also been proposed. These methods combine deterministic reconstruction strategies with band-limited field representation and optimized near-field sampling schemes to recover phase information from a single set of phase-free field data. However, existing phase-free methods are based on mechanically scanned near-field data and require phase retrieval or reconstruction algorithms, resulting in relatively long measurement and processing times. In phase-free measurements, the iterative process is prone to convergence to local optima, leading to phase ambiguity and non-uniqueness of phase solutions in the inversion results. In low signal-to-noise ratio environments, phase-free inversion results exhibit severe distortion, failing to meet the requirements of engineering-grade quantitative measurement.

[0010] For independent incoherent sources, the lack of a phase coherent link and the potential power fluctuations of the source will introduce additional errors in phase recovery and pure amplitude measurement, further reducing the reliability of the measurement results.

[0011] To improve near-field scanning efficiency, the scanning optical plasma scattering (SOPS) method has been proposed. Existing research has confirmed that SOPS can achieve efficient electromagnetic field measurement and antenna radiation characteristic diagnosis. However, existing SOPS methods are mainly geared towards coherent measurement scenarios, relying on the reciprocity principle. These methods still require the use of a vector network analyzer to construct coherent links, making them difficult to implement for incoherent measurement scenarios with independent sources and independent transmission capabilities. Traditional SOPS technology is difficult to apply to in-situ measurement scenarios involving antennas driven by independent or unstable sources, limiting the application scenarios of SOPS technology.

[0012] To date, achieving stable near-field acquisition of independent incoherent sources in in-situ measurement scenarios remains a significant technical challenge. SOPS technology possesses rapid measurement capabilities, and addressing its measurement capabilities in incoherent scenarios will have substantial engineering and industrial value. Existing technologies cannot simultaneously solve the two core problems of incoherent source phase links and dynamic disturbances from mechanical scanning. Therefore, there is an urgent need in this field for a novel measurement scheme that can physically cancel out random amplitude and phase fluctuations at the source while retaining the non-contact and high-resolution advantages of SOPS technology. Summary of the Invention

[0013] Technical Problem: The purpose of this invention is to overcome the core defects of existing incoherent source near-field measurement techniques and provide a method and system for optically controlled plasma incoherent source near-field measurement based on dual-probe self-reference. This invention generates photoinduced plasma spots on a semiconductor substrate using a modulated laser source with a certain frequency, transferring the local field information of the antenna under test to a frequency-shifted sideband. Two spatially fixed synchronous receiving probes are used to acquire the sideband signal and the original carrier signal respectively. Self-referenced complex ratio calculations are used to cancel the common source-end amplitude and phase fluctuations of the two signals, fundamentally eliminating the dependence on the coherent phase link between the source under test and the receiver, thus achieving the acquisition of the stable complex electric field near-field distribution of the incoherent source. Since the source of the field under test will have significant drift in incoherent scenarios, direct measurement will not yield a signal. Therefore, a second antenna is introduced to receive the local oscillator signal. Then, the modulation signal is used to cancel the local oscillator signal to cancel the source jitter, thereby achieving incoherent in-situ measurement using a self-referenced method.

[0014] Technical solution:

[0015] I. Optically Controlled Plasma Incoherent Source Near-Field Measurement System Based on Dual-Probe Self-Reference

[0016] The system comprises three core modules: an excitation and scattering unit, a radio frequency synchronous acquisition unit, and a self-reference solution control center. The composition, connection relationships, and functions of each module are as follows:

[0017] 1. Excitation and scattering unit: including a high-frequency modulated laser source, a high-speed beam scanning device, and a semiconductor substrate; the output end of the high-frequency modulated laser source is connected to the optical path input end of the high-speed beam scanning device through a single-mode fiber, and the output optical path of the high-speed beam scanning device is aligned with the area to be scanned on the semiconductor substrate;

[0018] High-frequency modulated laser source: A continuous fiber laser is used. The laser modulation frequency is limited by the time response of the photoinduced plasma. The plasma response time is on the order of tens of microseconds. Therefore, it is necessary to select a suitable modulation frequency to meet the requirements of the plasma response and ensure effective modulation of the scattered signal.

[0019] High-speed beam scanning device: used to control the laser beam to perform two-dimensional scanning on the surface of a semiconductor substrate. It generates a movable photo-induced plasma spot by moving the laser spot. The scanning process is controlled by a computer.

[0020] Semiconductor substrate: A semiconductor substrate capable of generating photoconductivity is used, preferably in the form of a thin sheet; the photogenerated plasma carrier lifetime generated by this semiconductor substrate is on the order of tens of microseconds, and it can respond well to laser modulation signals.

[0021] 2. Radio frequency synchronous acquisition unit: including a first fixed receiving probe, a second fixed receiving probe, and a multi-channel synchronous acquisition device; the first fixed receiving probe and the second fixed receiving probe remain stationary in spatial position throughout the measurement process and are arranged around the semiconductor substrate;

[0022] First fixed receiving probe (test channel): used to receive the frequency-shifted sideband signal generated by photogenerated plasma scattering;

[0023] Second fixed receiving probe (reference channel): used to receive the raw carrier signal radiated by the incoherent source under test;

[0024] Multi-channel synchronous acquisition equipment: Employs two clock-synchronized receivers, including but not limited to receivers, spectrum analyzers, oscilloscopes, and vector network analyzers (VNAs). A synchronization signal is used to achieve phase synchronization of the reference clocks of the two receivers; one receiving frequency of each receiver is set as a sideband frequency. The other receiver frequency is set to the carrier frequency. .

[0025] 3. Self-reference solution control center: A computer is used, which is connected to the high-speed beam scanning device, the high-frequency modulated laser source, and the multi-channel synchronous acquisition device. The computer is used to realize laser scanning control and synchronous data acquisition. Based on the dual-channel synchronous receiving signal, it completes self-reference solution to cancel the common amplitude and phase fluctuations of independent sources, and finally realizes the electric field solution of the field to be measured and the near-field distribution imaging output.

[0026] II. A Near-Field Measurement Method Based on a Dual-Probe Self-Reference Optically Controlled Plasma Incoherent Source

[0027] The measurement method is based on the above system and consists of four core steps: system initialization and configuration, frequency shift modulation and synchronization acquisition, self-reference cancellation calculation, and result output. The specific operation is as follows:

[0028] (a) System initialization configuration

[0029] 1. Place the incoherent source to be tested in the measurement area, place the semiconductor substrate in the near-field region of the antenna to be tested, and the laser beam can scan the surface of the substrate;

[0030] 2. Set the laser modulation frequency This ensures that its frequency is below the carrier response cutoff frequency of semiconductor photogenerated plasma;

[0031] 3. Configure a multi-channel synchronous acquisition device, ensuring that the center frequency of the first channel (test channel) is aligned with the carrier frequency of the source under test. With modulation frequency Frequency shift sidebands (selectable and frequency) or difference frequency The center frequency of the second channel (reference channel) is aligned with the original carrier frequency of the source under test. ;

[0032] 4. Set laser scanning parameters, including but not limited to scanning range, sampling interval, etc.

[0033] (II) Frequency shift modulation and synchronous acquisition by dual probes

[0034] 1. Activate the high-frequency modulated laser source; its output light intensity is affected by... Modulation, the output power can excite semiconductor materials to generate photogenerated plasma;

[0035] 2. Control the laser spot to scan point by point on the semiconductor substrate surface according to a preset path, at each scanning point... At this location, the photo-induced plasma spot generated by laser excitation modulates the local field information of the antenna under test to the photogenerated upper sideband frequency. This allows the sideband signal to be separated from the original carrier signal in the frequency domain;

[0036] 3. The multi-channel synchronous acquisition device synchronously acquires the sideband signals of the test channel and the carrier signals of the reference channel, and transmits the acquired complex field data to the control computer in real time for storage and subsequent processing.

[0037] (III) Self-reference cancellation and electric field calculation

[0038] The core physical principle of this invention lies in utilizing the modulation and scattering characteristics of photogenerated plasma to transfer the local field information of the antenna under test to a frequency-shifted sideband, thereby achieving frequency domain separation between the scattered signal and the original carrier signal. The sideband signal and the carrier signal originate from the same independent incoherent source and are received synchronously; the amplitude and phase fluctuations of the source are common terms in both signals. By comparing and calculating the two synchronously received signals, the common amplitude and phase fluctuations of the source are canceled out. This eliminates the need to establish a phase-coherent link between the source under test and the receiver, thus enabling the acquisition of a stable complex near-field distribution of the incoherent source.

[0039] Compared with existing incoherent source near-field measurement techniques, this invention has the following core technical advantages and beneficial effects:

[0040] 1. No phase coherent link needs to be established between the source under test and the receiver. The common amplitude drift and phase jitter of independent sources can be canceled through the dual-probe self-reference mechanism, so as to obtain the stable complex near-field distribution of incoherent sources.

[0041] 2. The dual fixed probe architecture avoids measurement errors caused by probe position, mechanical vibration and cable movement during mechanical scanning in the traditional reference probe method, and reduces the difficulty of implementing high-frequency near-field measurements.

[0042] 3. It retains the advantages of scanning optical plasma scattering (SOPS) technology, achieving efficient near-field mapping through laser scanning without the need for mechanical movement of a metal probe throughout the scanning plane.

[0043] 4. This method is applicable not only to continuous wave incoherent source measurements, but also to periodically modulated waveforms with relatively simple spectra, as long as the selected photogenerated sideband signal is isolated from other components of the original signal in the spectrum. Attached Figure Description

[0044] Figure 1 This is a diagram illustrating the overall architecture of the measurement system in this application. The optically modulated plasma on the semiconductor substrate converts the local field information of the target under test into a frequency-shifted sideband signal. A first receiving probe receives the sideband signal as the test channel, and a second receiving probe receives the original carrier signal as the reference channel. Complex near-field distributions can be obtained by comparing the two channels.

[0045] Figure 2 is a schematic diagram of the optically controlled plasma frequency shift modulation principle, showing the spectral relationship between the original carrier signal and the upper and lower sideband signals;

[0046] Figure 3 To measure the received signal spectrum distribution of Example 1 and the test results under incoherent scenarios.

[0047] Figure 4 To verify the measurement results under the condition of incoherent jitter source input in Example 1;

[0048] Figure 5 shows the measurement results of the second measurement example, where (a) is the transmitting antenna of the K-band radar module, (b) is the source power fluctuation curve, and (c) is the measured near-field amplitude and phase distribution. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The content described herein is for explanation and not limitation of the present invention. Non-creative improvements made by those skilled in the art based on the core solution of the present invention should fall within the protection scope of the present invention.

[0050] I. Optically Controlled Plasma Incoherent Source Near-Field Measurement System Based on Dual-Probe Self-Reference

[0051] The overall architecture is shown in Figure 1. The system includes three core modules: an excitation and scattering unit, a radio frequency synchronous acquisition unit, and a self-reference solution control center. The composition, connection relationship, function, and measured parameters of each module are as follows:

[0052] Excitation and scattering unit: includes a high-frequency modulated laser source, a high-speed beam scanning device, and a semiconductor substrate; the output end of the high-frequency modulated laser source is connected to the optical path input end of the high-speed beam scanning device through a single-mode fiber, and the output optical path of the high-speed beam scanning device is aligned with the area to be scanned on the semiconductor substrate;

[0053] High-frequency modulated laser source: A continuous fiber laser with a center wavelength of 980nm and an output power of 1W is used; the laser modulation frequency is limited by the time response of photo-induced plasma (about 20kHz), and is set to 10kHz in this embodiment;

[0054] High-speed beam scanning device: used to control the laser spot to scan point by point on the surface of the semiconductor substrate. In this embodiment, the scanning range is 140mm×140mm and the sampling interval is 2mm. The laser modulation frequency is limited by the time response of the photo-induced plasma. The plasma response time is on the order of tens of microseconds. Therefore, it is necessary to select a suitable modulation frequency to meet the requirements of the plasma response and ensure effective modulation of the scattered signal.

[0055] Semiconductor substrate: A semiconductor substrate capable of generating photoconductivity is used, preferably in the form of a thin sheet; the photogenerated plasma carrier lifetime generated by this semiconductor substrate is on the order of tens of microseconds, and it can respond well to laser modulation signals.

[0056] Radio frequency synchronous acquisition unit: includes a first fixed receiving probe, a second fixed receiving probe, and a multi-channel synchronous acquisition device; the first fixed receiving probe and the second fixed receiving probe remain stationary in spatial position throughout the measurement process and are arranged around the semiconductor substrate;

[0057] First fixed receiving probe (test channel): used to receive the frequency-shifted sideband signal generated by photogenerated plasma scattering;

[0058] Second fixed receiving probe (reference channel): used to receive the raw carrier signal radiated by the incoherent source under test;

[0059] Multi-channel synchronous acquisition equipment: Utilizing two vector network analyzers, phase synchronization is achieved via a 10MHz reference clock; both VNAs operate in receiver mode, with channel 1 of the first VNA aligned to the upper sideband frequency. The second VNA channel 1 is aligned with the carrier frequency. .

[0060] Self-reference solution control center: A computer is used, which is connected to the high-speed beam scanning device, the high-frequency modulated laser source, and the multi-channel synchronous acquisition device. The computer is used to realize laser scanning control and synchronous data acquisition, and completes self-reference solution based on dual-channel synchronous receiving signals to cancel the common amplitude and phase fluctuations of independent sources, and finally realizes the electric field solution of the field to be measured and the near-field distribution imaging output.

[0061] II. A Near-Field Measurement Method Based on a Dual-Probe Self-Reference Optically Controlled Plasma Incoherent Source

[0062] The measurement method is based on the above system and consists of four core steps: system initialization and configuration, frequency shift modulation and synchronization acquisition, self-reference cancellation calculation, and result output. The specific operation is as follows:

[0063] (a) System initialization configuration

[0064] 1. Place the incoherent source to be tested in the measurement area, place the semiconductor substrate in the near-field region of the antenna to be tested, and the laser beam can scan the surface of the substrate;

[0065] 2. Set the laser modulation frequency This ensures that its frequency is below the carrier response cutoff frequency of semiconductor photogenerated plasma;

[0066] 3. Configure a multi-channel synchronous acquisition device, ensuring that the center frequency of the first channel (test channel) is aligned with the carrier frequency of the source under test. With modulation frequency Frequency shift sidebands (selectable and frequency) or difference frequency The center frequency of the second channel (reference channel) is aligned with the original carrier frequency of the source under test. ;

[0067] 4. Set laser scanning parameters, including but not limited to scanning range, sampling interval, etc.

[0068] (II) Frequency shift modulation and synchronous acquisition by dual probes

[0069] 1. Activate the high-frequency modulated laser source; its output light intensity is affected by... Modulation, the output power can excite semiconductor materials to generate photogenerated plasma;

[0070] 2. Control the laser spot to scan point by point on the semiconductor substrate surface according to a preset path, at each scanning point... At this location, the photo-induced plasma spot generated by laser excitation modulates the local field information of the antenna under test to the photogenerated upper sideband frequency. This allows the sideband signal to be separated from the original carrier signal in the frequency domain;

[0071] 3. The multi-channel synchronous acquisition device synchronously acquires the sideband signals of the test channel and the carrier signals of the reference channel, and transmits the acquired complex field data to the control computer in real time for storage and subsequent processing.

[0072] (III) Self-reference cancellation and electric field calculation

[0073] The core physical principle of this invention lies in utilizing the modulation and scattering characteristics of photogenerated plasma to transfer the local field information of the antenna under test to a frequency-shifted sideband, achieving frequency domain separation between the scattered signal and the original carrier signal. The sideband signal and the carrier signal originate from the same independent incoherent source and are received synchronously; the amplitude and phase fluctuations of the source are common terms in both signals. By comparing the two synchronously received signals, the common amplitude and phase fluctuations of the source are canceled out. This eliminates the need to establish a phase-coherent link between the source under test and the receiver, thus enabling the acquisition of a stable complex near-field distribution of the incoherent source. The specific mathematical model and solution logic are as follows:

[0074] Step 1: Define the temporal eigenvalues ​​of incoherent sources

[0075] First, we define the original time-domain electromagnetic field of the incoherent source under test. Assuming the antenna under test radiates a continuous wave signal with operating frequency f_c, its local electric field at the laser irradiation position r on the semiconductor substrate can be expressed as:

[0076]

[0077] in:

[0078] : The amplitude of the local field to be measured;

[0079] : The phase of the local field to be measured;

[0080] : The center carrier frequency of the source under test.

[0081] Since the incoherent source is an independent operating system and there is no phase coherent link between it and the measurement receiver, its output signal has inherent amplitude drift and phase jitter. These fluctuations are synchronously transmitted to the optical modulation sideband signal, making it impossible to obtain an accurate and stable complex near-field distribution through direct measurement.

[0082] Step 2: Frequency shift modulation mechanism of light-controlled plasma

[0083] When the frequency is When an intensity-modulated laser irradiates a semiconductor substrate, the laser photons are absorbed by the semiconductor material and excited to generate electron-hole pairs. This causes a periodic change in the carrier concentration in the irradiated area, which in turn leads to synchronous modulation of the electromagnetic wave scattering coefficient in that area. The time-domain expression for the scattering coefficient is:

[0084] in, These are constant coefficients related to plasma scattering characteristics.

[0085] According to the principle of electromagnetic modulation, the scattered signal received by the receiving antenna Proportional to scattering coefficient With the incident local field The product of , therefore:

[0086]

[0087] Expand formula (3) using trigonometric identities:

[0088]

[0089] Therefore, it can be concluded that the received signal includes not only the carrier frequency. The background component at that location also includes a frequency of and The two frequency-shifted sideband components. These sideband components are generated by the optical scattering process and carry local amplitude and phase information of the antenna field under test. and Since the sidebands and background carrier are separated in the frequency domain, weak scattered signals can be extracted without laser switching coherent subtraction.

[0090] This principle also applies to periodically modulated waveforms with relatively simple spectra. For such waveforms, the radiated signal contains multiple discrete spectral components, each of which is shifted by optical modulation. Therefore, it is first necessary to select a spectral component as the measurement carrier. Its light-generating lateral zone It can only be used for field measurements when the sidebands generated by the original waveform components and other spectral components are separated in the spectrum.

[0091] Step 3: Dual-probe synchronization signal model

[0092] The system employs two spatially fixed receiving probes to simultaneously acquire sideband and carrier signals, respectively, thus constructing two time-synchronized measurement channels:

[0093] Test channel (sideband signal): Acquired by the first receiving probe, receiving the sideband signal generated by photogenerated plasma scattering. This signal contains both the local amplitude of the field under test at the scanning point r and... and phase The information is further superimposed with the common random amplitude drift and phase jitter terms from the source end.

[0094] Reference channel (carrier signal): Acquired by the second receiving probe, directly receiving the raw carrier signal radiated by the source under test. This signal is not modulated by plasma and only carries the common random amplitude drift and phase jitter terms at the source end.

[0095] Since the two signals originate from the same source under test and are acquired synchronously, the amplitude drift and phase jitter at the source end are common terms of the two signals, which is the core basis for achieving self-reference amplitude and phase fluctuation cancellation.

[0096] Figure 2 is a schematic diagram of the optically controlled plasma frequency shift modulation principle, showing the spectral relationship between the original carrier signal and the upper and lower sideband signals.

[0097] Step 4: Self-referenced linear cancellation operation

[0098] By comparing the two synchronously received signals, the common source-end amplitude drift and phase jitter of the two signals are canceled out. A stable near-field electric field distribution can be obtained without establishing a phase coherent link between the source under test and the receiver.

[0099] Step 5: Reconstruction of near-field electric field distribution

[0100] After traversing all scanning points to complete signal acquisition and self-reference cancellation operations, the stable near-field electric field distribution of the incoherent source under test in the scanning plane can be reconstructed.

[0101] This method is also applicable to periodically modulated waveforms with relatively simple spectra, as long as the selected photogenerated sideband signal is isolated from other components of the original signal in the spectrum.

[0102] (4) Results output and verification

[0103] After completing the measurement by traversing all scanning points, the near-field amplitude distribution spectrum and phase distribution spectrum of the incoherent source under test in the scanning plane are generated.

[0104] The following section presents two measurement examples using the system and method described above.

[0105] Measurement Example 1: Measurement Verification of Incoherent Sources for X-band Horn Antenna

[0106] This embodiment uses the above system to perform incoherent source near-field measurement verification of an X-band standard horn antenna. The antenna under test is driven by an independent signal source and does not establish a coherent connection with the measurement system. The specific steps are as follows:

[0107] 1. System initialization configuration

[0108] An X-band standard horn antenna (75mm × 56mm aperture) was placed 40mm in front of the semiconductor substrate and excited by a 10GHz continuous wave from an independent signal source with an output power of 20dBm.

[0109] Set the laser modulation frequency This is below the time response limit frequency of photoplasma on semiconductor substrates;

[0110] Configure a multi-channel synchronous acquisition device, and align the receiving frequency of the first vector network analyzer with the optically generated upper sideband signal. The receiving frequency of the second vector network analyzer is aligned with the original carrier frequency of the source under test. ;

[0111] Set the laser scanning parameters: the scanning range on the semiconductor substrate surface is 140mm×140mm, and the sampling interval is 2mm.

[0112] 2. Verification of self-reference measurement results

[0113] The laser scanning system is activated, and the laser is modulated at a frequency of 10kHz to scan the surface of the semiconductor substrate point by point. The multi-channel synchronous acquisition device simultaneously acquires the complex amplitudes of the sideband signal and the carrier signal. A single distance measurement can be completed in about 5 seconds.

[0114] To verify the ability of this invention to suppress source fluctuations, the output power of an independent signal source was manually adjusted during the scanning process to simulate source power fluctuations. Measurement results show that:

[0115] When only the test channel sideband signal is used, the measured amplitude distribution is strongly affected by the source power fluctuation, and the phase distribution becomes chaotic due to the lack of coherent links;

[0116] When using the dual-probe self-reference method of this invention, the common source fluctuations are canceled by comparing the two synchronously received signals, resulting in a stable complex near-field distribution that highly matches the benchmark results of coherent SOPS measurements. (See attached figure.) Figure 3 and Figure 4 .

[0117] For amplitude modulation and periodic pulse excitation, the measured near-field distribution is consistent with the coherent SOPS reference results, verifying the effectiveness of the method of the present invention under different excitation waveforms.

[0118] 3. Verification of in-situ measurement results when the source uses different modulation waveforms

[0119] Traditional measurements require that the antenna under test be in a state of continuous radiation. However, in actual use, the equipment is usually in a state of signal modulation. Direct measurement of radiation in incoherent scenarios under modulation has become a challenge in the field. Using the solution of this application, we can measure the radiation characteristics of the source under continuous wave (CW) excitation, amplitude modulation (AM) excitation, and periodic pulse excitation.

[0120] The modulation frequency parameters selected in this embodiment are as follows:

[0121] Continuous wave (CW) excitation: Optical modulation generates a frequency interval around the carrier frequency. The additional sideband components, the original carrier component, and the optical modulation sidebands can be received by the reference channel and the test channel, respectively.

[0122] Amplitude modulation (AM) excitation: the modulation rate is 1MHz, the modulation depth is 30%, the transmitted signal contains multiple discrete spectral components, each of which is optically modulated and offset to generate corresponding sidebands;

[0123] Periodic pulse excitation: The pulse period is 30μs and the duty cycle is 50%, which also generates multiple discrete spectral components.

[0124] Spectral analysis results show that the selected The sidebands generated by the original waveform components and other spectral components are spectrally separated, and therefore can be used for near-field measurements. Actual measurement results are as follows: Figure 3 As shown, it is currently difficult to obtain such in-situ measurements under source output modulation signals directly using existing technology.

[0125] Measurement Example 2: In-situ Measurement of K-band Commercial Radar Module

[0126] This embodiment uses the above system to perform in-situ incoherent measurements on a commercial K-band radar module, verifying the applicability of the invention in practical engineering scenarios. The specific steps are as follows:

[0127] System Configuration:

[0128] A commercial K-band radar module was placed 40mm in front of the semiconductor substrate. The module operated in 23.59GHz continuous wave transmission mode, activating only one transmit patch antenna. Its internal oscillator was an independent incoherent source with an output power of approximately -10dBm, exhibiting frequent power fluctuations.

[0129] Set the laser modulation frequency The test channel receiving frequency is aligned with the upper sideband signal of the optical generator. The reference channel receiving frequency is aligned with the original carrier frequency of the source under test. .

[0130] Measurement and calculation: Start the scanning system to complete the array data acquisition of the entire scanning area; eliminate the random amplitude and phase fluctuations of the oscillator inside the radar module through self-reference operation to obtain the near-field amplitude and phase distribution of the radar module's transmitting antenna.

[0131] Results Analysis: Refer to Figure 5In this paper, (a) is the transmitting antenna of the K-band radar module, (b) is the source power fluctuation curve, and (c) is the measured near-field amplitude and phase distribution. Although the output power of the radar module has obvious random fluctuations, the method of this invention still obtains clear and stable near-field amplitude and phase distribution.

[0132] This experiment verifies the applicability of the method of the present invention to active antennas driven by unstable independent sources in in-situ measurement scenarios.

Claims

1. A self-referenced incoherent field measurement system for in-situ measurement of incoherent electric fields, characterized in that, It includes an excitation and scattering unit, a radio frequency synchronous acquisition unit, and a self-reference solution control center; The excitation and scattering unit includes a high-frequency modulated laser source, a high-speed beam scanning device, and a semiconductor substrate; the output end of the high-frequency modulated laser source is connected to the optical path input end of the high-speed beam scanning device via an optical fiber, and the output optical path of the high-speed beam scanning device is aligned with the area to be scanned on the semiconductor substrate. The radio frequency synchronous acquisition unit is used to acquire the scattered signal of the excitation and scattering unit; The radio frequency synchronous acquisition unit includes a first fixed receiving probe, a second fixed receiving probe, and a multi-channel synchronous acquisition device; the first fixed receiving probe and the second fixed receiving probe remain stationary in spatial position throughout the measurement process and are arranged around the semiconductor substrate. The multi-channel synchronous acquisition device includes two clock-synchronized first receivers and second receivers, which respectively receive signals from a first fixed receiving probe and a second fixed receiving probe. The self-reference solution control center is connected to the excitation and scattering unit and the radio frequency synchronous acquisition unit, respectively. The system employs two spatially fixed receiving probes to simultaneously acquire sideband signals and carrier signals, respectively, thus constructing two time-synchronized measurement channels: the test channel is acquired by the first fixed receiving probe, receiving the sideband signals generated by photogenerated plasma scattering; the reference channel is acquired by the second fixed receiving probe, directly receiving the original carrier signal radiated by the source under test.

2. The self-reference incoherent field measurement system for in-situ measurement of incoherent electric fields as described in claim 1, characterized in that, The self-reference solution control center is connected to the high-speed beam scanning device, the high-frequency modulated laser source, and the multi-channel synchronous acquisition device.

3. A self-referenced incoherent field measurement method for in-situ measurement of incoherent electric fields, characterized in that, The method is implemented based on the measurement system described in claim 1 or 2, and includes the following three steps: S1: System initialization configuration, configure the multi-channel synchronous acquisition device, and align the center frequency of the first channel with the carrier frequency of the source under test. With modulation frequency The frequency shift sidebands, the center frequency of the second channel is aligned with the original carrier frequency of the source under test. The modulation frequency Below the carrier response cutoff frequency of photogenerated plasma on a semiconductor substrate; S2: Frequency shift modulation and dual-probe synchronous acquisition control the laser spot to scan point by point on the semiconductor substrate surface along a preset path. At each scanning point r, the photo-induced plasma spot generated by the laser excitation modulates the local field information of the antenna under test to the photogenerated upper sideband frequency. or This allows the sideband signal to be separated from the original carrier signal in the frequency domain; S3: Self-reference cancellation and complex amplitude electric field calculation. By comparing the two synchronously received signals, the common source-end amplitude drift and phase jitter of the two signals are canceled. After traversing all scanning points to complete signal acquisition and self-reference cancellation operation, the stable near-field complex electric field distribution of the incoherent source under test in the scanning plane is reconstructed.

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