Zero intermediate frequency terahertz near-field imaging device and method based on vector network analyzer

Abstract

The invention provides a zero-intermediate-frequency terahertz near-field imaging device and method based on a vector network analyzer, and relates to the technical field of terahertz imaging. The method comprises the following steps: generating a radio frequency signal through a vector network host and performing power division; one path radiates to a vibrating near-field probe to generate a modulation signal after frequency multiplication of the transmitting module; the other path is subjected to frequency multiplication by the receiving module to form a local oscillator signal; performing zero intermediate frequency mixing on the modulation signal and the local oscillation signal to obtain a zero intermediate frequency test signal and transmitting the zero intermediate frequency test signal back to the vector network host; setting the frequency in the vector network host as a harmonic wave of the vibration frequency of the probe so as to demodulate near-field signal data; and controlling the probe to scan and generate an image. The vector network host is used for integrating signal generation and demodulation functions, a zero intermediate frequency receiving framework is combined, the technical problems that an existing near-field imaging system is large in size and weight and low in integration level due to the fact that multiple discrete signal sources and phase-locked amplifiers are adopted are effectively solved, and miniaturization and high integration level of the system are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz imaging, in particular to a zero intermediate frequency terahertz near-field imaging device and method based on a vector network analyzer. BACKGROUND

[0002] Millimeter wave terahertz waves have important application prospects in the imaging field of nondestructive testing, material analysis and the like due to their unique penetration and spectral characteristics. However, due to the limitation of the classical Rayleigh diffraction limit, the resolution of the traditional far-field imaging technology is difficult to break through the wavelength level, and it is unable to meet the demand of high-precision and high-resolution detection of new materials. In order to break through this physical limit, the near-field imaging technology emerges as the times require, which realizes the tight focusing and detection of signals in a very close area (near field) of the sample by using a nanometer-scale probe, so as to obtain high-resolution information far beyond the diffraction limit.

[0003] At present, the existing electronic millimeter wave terahertz near-field imaging scheme usually adopts two separate microwave signal sources to cooperate with a millimeter wave terahertz spread spectrum module to generate a test signal, and a dedicated phase-locked amplifier is used to realize the reception of a weak near-field signal. Although this scheme can realize super-resolution imaging, the system composition is complex and depends on multiple separate instruments. This leads to inherent defects of the entire imaging device, such as large volume, heavy weight and low system integration, which is not conducive to the portability and wide application of the equipment. SUMMARY

[0004] In order to solve the technical problems of large system volume, heavy weight and low integration degree caused by the use of multiple separate signal sources and receiving devices in the background art, the present application provides a miniaturized and high-integration millimeter wave terahertz near-field imaging device and method by using an integrated signal generation and reception scheme based on a vector network analyzer and a zero intermediate frequency down-conversion receiving structure.

[0005] The first aspect of the present application provides a zero intermediate frequency terahertz near-field imaging device based on a vector network analyzer, comprising: a vector network analyzer host for generating a radio frequency test signal and demodulating a zero intermediate frequency test signal; a power divider connected to the host for dividing the radio frequency test signal into a first path signal and a second path signal; a millimeter wave terahertz spread spectrum transmission module connected to the power divider for frequency multiplication processing of the first path signal to generate a millimeter wave terahertz test signal; a first antenna connected to the transmission module for radiating the test signal to a near-field probe; a near-field probe for vibrating and modulating an incident signal to generate a modulated signal; a second antenna for receiving the modulated signal; A millimeter wave terahertz spread spectrum receiving module connected to the power divider and the second antenna, for multiplying the second path signal to generate a local oscillator signal, and mixing the modulated signal with the local oscillator signal to generate the zero intermediate frequency test signal; A control machine connected to the near-field probe and the vector network analyzer host, for controlling the probe to scan and generate a near-field imaging image.

[0006] Further, the mixer in the millimeter wave terahertz spread spectrum receiving module is a harmonic mixer, configured to perform Lth harmonic mixing on the modulated signal.

[0007] Further, the device further comprises a displacement table, and the millimeter wave terahertz spread spectrum transmitting module and the millimeter wave terahertz spread spectrum receiving module are respectively installed on the displacement table, and the angle between the first antenna and the second antenna and the horizontal direction is changed by adjusting the displacement table, so that the polarization direction of the millimeter wave terahertz wave electric field matches the direction of the near-field probe.

[0008] The second aspect of the present application provides a vector network analyzer-based zero intermediate frequency terahertz near-field imaging method based on the device provided by the first aspect of the present application, comprising the following steps: The vector network analyzer host generates a radio frequency test signal, and the power divider divides the radio frequency test signal into a first path signal and a second path signal; The first path signal is multiplied by the millimeter wave terahertz spread spectrum transmitting module and then radiated to the near-field probe through the first antenna; The near-field probe is controlled to vibrate to modulate the incident signal, generate a modulated signal, and receive the modulated signal by the second antenna; The second path signal is multiplied by the millimeter wave terahertz spread spectrum receiving module to generate a local oscillator signal; In the millimeter wave terahertz spread spectrum receiving module, the modulated signal is mixed with the local oscillator signal to generate a zero intermediate frequency test signal and sent back to the vector network analyzer host; The intermediate frequency frequency of the vector network analyzer host is set to be a harmonic of the probe vibration frequency to demodulate the near-field signal data; The near-field probe is controlled to scan the sample, and a near-field imaging image is generated according to the near-field signal data.

[0009] Further, the intermediate frequency frequency of the vector network analyzer host is set to be a harmonic of the probe vibration frequency, specifically, the center frequency of the intermediate frequency receiver is locked on the Mth harmonic of the probe vibration frequency, where M=1, 2,....

[0010] Further, the modulated signal is mixed with the local signal at zero intermediate frequency, specifically including: using a harmonic mixer to mix the modulated signal L times.

[0011] Further, before being radiated to the near-field probe by the first antenna, further comprising: adjusting the included angle between the first antenna and the second antenna and the horizontal direction, so that the polarization direction of the millimeter wave terahertz wave electric field matches the vibration direction of the near-field probe.

[0012] Further, the vector network analyzer host uses a single frequency synthesis source inside to generate the radio frequency test signal.

[0013] The third aspect of the application provides a computer readable storage medium, which stores a program, and the program is executed by a processor to realize the steps in the zero intermediate frequency terahertz near-field imaging method based on a vector network analyzer according to the second aspect of the application.

[0014] The fourth aspect of the application provides a computer program product, which includes software code, and the program in the software code executes the steps in the zero intermediate frequency terahertz near-field imaging method based on a vector network analyzer according to the second aspect of the application.

[0015] Compared with the prior art, the zero intermediate frequency terahertz near-field imaging device and method based on a vector network analyzer have the following beneficial effects: (1) The application uses the highly integrated signal generation, receiving and processing capabilities inside the vector network analyzer to replace the original multiple discrete devices. This design integrates the signal source, part of the receiving and demodulation functions in a single host, significantly reduces the number of external instruments, and thus realizes the technical effects of reducing the system size and weight and improving the integration level.

[0016] (2) The application innovatively adopts a zero intermediate frequency receiving architecture, and uses a flexible intermediate frequency receiver of the vector network analyzer to complete signal demodulation. This scheme eliminates the expensive special phase-locked amplifier, directly extracts the near-field information modulated by the probe in the vector network host through harmonic demodulation technology, not only reduces the system cost and complexity, but also further consolidates the technical effect of high integration level. BRIEF DESCRIPTION OF DRAWINGS

[0017] The drawings accompanying the specification are part of the disclosure and serve to further provide a further understanding of the application, the illustrative embodiments of the application and their description serve to explain the application without constituting an inappropriate limitation thereof.

[0018] Figure 1 is a schematic diagram of a zero intermediate frequency structure millimeter wave terahertz near-field imaging device based on a vector network analyzer provided by the first embodiment of the application; Figure 2 is a millimeter wave terahertz near-field imaging result map of a silicon gold sample based on a vector network analyzer provided by the first embodiment of the present application. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0020] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0021] The embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0022] All data acquisition of the present embodiment is based on compliance with laws and regulations and user consent, and legal application of data.

[0023] Embodiment one The present embodiment provides a zero intermediate frequency terahertz near-field imaging device based on a vector network analyzer, comprising: a vector network analyzer host for generating a radio frequency test signal and demodulating a zero intermediate frequency test signal; A power divider is connected to the host for dividing the radio frequency test signal into a first path signal and a second path signal; A millimeter wave terahertz spread spectrum transmission module is connected to the power divider for frequency multiplication processing of the first path signal to generate a millimeter wave terahertz test signal; A first antenna is connected to the transmission module for radiating the test signal to a near-field probe; A near-field probe is used to vibrate and modulate the incident signal to generate a modulated signal; A second antenna is used to receive the modulated signal; A millimeter wave terahertz spread spectrum receiving module is connected to the power divider and the second antenna for frequency multiplication of the second path signal to generate a local oscillator signal, and zero intermediate frequency mixing of the modulated signal and the local oscillator signal to generate the zero intermediate frequency test signal; The controller, connected to the near-field probe and the vector network analyzer host, is used to control the probe scanning and generate near-field imaging images.

[0024] Using a vector network analyzer (VNA) host as a unified signal generation and demodulation center, a power divider synchronously distributes the RF test signal to the transmit and receive paths. The transmit path generates a terahertz test signal through frequency doubling and excites the near-field probe; the receive path generates a local oscillator signal through another frequency doubling chain and performs zero-IF mixing with the scattered signal modulated by the probe, directly down-converting the near-field information in the terahertz band to an IF signal that the VNA host can directly process. The control unit coordinates scanning and data acquisition imaging. This integrated design solves the core problems of large size and low integration in traditional multi-instrument systems.

[0025] Specifically, the mixer in the millimeter-wave terahertz spread spectrum receiver module is a harmonic mixer, configured to perform L-th harmonic mixing on the modulation signal.

[0026] Harmonic mixers can use lower harmonics of the local oscillator signal to mix with radio frequency signals, allowing the local oscillator signal to operate at lower frequencies and reducing the performance requirements and cost of the local oscillator frequency multiplier. This enhances the feasibility and economy of implementing the system in the terahertz band.

[0027] Specifically, the device further includes a displacement stage, on which the millimeter-wave terahertz spread spectrum transmitting module and the millimeter-wave terahertz spread spectrum receiving module are respectively mounted. By adjusting the displacement stage, the angle between the first antenna and the second antenna and the horizontal direction is changed, so that the polarization direction of the millimeter-wave terahertz wave electric field matches the direction of the near-field probe.

[0028] By precisely adjusting the angle between the antenna and the horizontal direction, the polarization direction of the millimeter-wave terahertz wave electric field can be controlled to optimally match the physical orientation of the near-field probe. This matching maximizes the probe's modulation efficiency to the incident field and the antenna's reception efficiency to the scattered signal, thereby improving the signal-to-noise ratio and imaging quality of the entire system.

[0029] In one specific embodiment, Figure 1 A zero-IF structure millimeter-wave terahertz near-field imaging device based on a vector network analyzer is presented. Its basic components include: a vector network analyzer host, a power divider, a millimeter-wave terahertz spread spectrum transmitter module, a millimeter-wave terahertz spread spectrum receiver module, an antenna, a probe, a scanner, and a controller.

[0030] The working principle of this technical solution is as follows: the frequency synthesis source in the vector network analyzer host outputs a frequency of... The RF test signal is processed by a signal separation unit and then output to a power divider to split it into two paths. One path is input to the input interface of the frequency multiplier unit 1 in the millimeter-wave terahertz spread spectrum transmitter module 1. The frequency multiplier unit 1 multiplies the test signal N times to the millimeter-wave terahertz band, obtaining a frequency of . The millimeter-wave terahertz test signal is radiated by the millimeter-wave terahertz horn antenna 1 to the tip of the near-field probe. The near-field probe transmits the signal at a frequency of [frequency value missing]. The simple harmonic motion in the vertical direction can be used to modulate incident millimeter-wave terahertz waves, obtaining a frequency of... The modulation signal is M, where M = 1, 2, ... represents the harmonic order of the modulation signal. The probe scatters this modulation signal into free space. The horn antenna 2 receives this near-field signal and transmits it to the RF input interface of the mixer 1. By adjusting the displacement stages of the millimeter-wave terahertz spread spectrum transmitting module 1 and the millimeter-wave terahertz spread spectrum receiving module 2, the angle θ between antenna 1 and antenna 2 and the horizontal direction is adjusted so that the polarization direction of the millimeter-wave terahertz wave electric field of antenna 1 and antenna 2 matches the probe direction.

[0031] The signal from the vector network analyzer host, after being divided by the power divider, is input to the frequency multiplier unit 2 in the millimeter-wave terahertz spread spectrum receiver module 2. The frequency multiplier unit 2 multiplies the RF signal by K to obtain a frequency of... The millimeter-wave terahertz local oscillator signal is input to the local oscillator port of mixer 1 as the millimeter-wave terahertz local oscillator signal.

[0032] The Lth order (in millimeter-wave terahertz spread spectrum receiver module 2) The harmonic mixer performs zero-IF mixing between the terahertz near-field signal and the terahertz local oscillator signal to obtain a frequency of... A zero-IF test signal (M=1, 2, ...) is generated. This test signal is input to the test IF input interface of the vector network analyzer host. The vector network analyzer is set to receiver measurement mode, and the IF frequency is set to... (M=1, 2, ...), thus ensuring that the intermediate frequency receiver of the vector network analyzer host can operate at the Mth harmonic of the near-field probe vibration frequency. Demodulation and reception processing of near-field signals at frequencies (M=1, 2, ...) are performed.

[0033] The controller controls the near-field probe to scan the sample line by line, while simultaneously controlling the vector network analyzer host to transmit the millimeter-wave terahertz near-field test data from the vector network analyzer via a programmable mode. The controller then plots the obtained millimeter-wave terahertz test signals from the vector network analyzer line by line, thus obtaining the near-field imaging image of the sample.

[0034] Figure 2The results of millimeter-wave terahertz near-field imaging of a silicon-gold sample with a first-order near-field signal (M=1) based on a vector network analyzer are presented. The yellow portion on the left represents the near-field imaging results of the gold portion of the silicon-gold sample, while the blue portion on the right represents the near-field imaging results of the silicon portion. It can be seen that the contrast between the imaging results of the two materials in the silicon-gold sample is significant, indicating that this imaging device can effectively achieve millimeter-wave terahertz near-field microscopic imaging of the sample.

[0035] Compared with existing technologies, the present invention uses millimeter-wave terahertz near-field imaging technology based on a vector network analyzer, which can reduce the size and weight of the near-field imaging device and improve the integration of the millimeter-wave terahertz near-field imaging device.

[0036] Example 2 This embodiment provides a zero-IF terahertz near-field imaging method based on a vector network analyzer using the device provided in Embodiment 1, including the following steps: The vector network analyzer host generates an RF test signal, and uses a power divider to divide the RF test signal into a first signal and a second signal. The first signal is multiplied by the millimeter-wave terahertz spread spectrum transmission module and then radiated to the near-field probe through the first antenna; The vibration of the near-field probe is controlled to modulate the incident signal, generating a modulated signal that is received by the second antenna. The second signal is frequency multiplied by the millimeter-wave terahertz spread spectrum receiving module to generate a local oscillator signal; In the millimeter-wave terahertz spread spectrum receiver module, the modulation signal and the local oscillator signal are mixed at zero intermediate frequency to generate a zero intermediate frequency test signal and sent back to the vector network analyzer host. The intermediate frequency of the vector network analyzer host is set to the harmonic of the probe vibration frequency in order to demodulate the near-field signal data; The near-field probe is controlled to scan the sample, and a near-field imaging image is generated based on the near-field signal data.

[0037] By employing a series of steps—single-source power division, dual-path frequency doubling, probe modulation, zero-IF mixing, harmonic demodulation, and scanning imaging—the complex near-field imaging task is transformed into a standardized measurement process that can be efficiently executed by a vector network analyzer. This method systematically solves the operational problem of how to perform high-resolution near-field imaging using a single vector network analyzer platform.

[0038] Specifically, the intermediate frequency of the vector network analyzer host is set as a harmonic of the probe vibration frequency. Specifically, the center frequency of the intermediate frequency receiver is locked on the Mth harmonic of the probe vibration frequency, where M=1,2,...

[0039] The periodic vibration of the near-field probe modulates the terahertz field, and its useful information is carried in the harmonics of the vibration frequency. By precisely locking the center frequency of the high-sensitivity intermediate frequency receiver of the vector network detector to a specific harmonic (such as the fundamental or second harmonic), environmental noise and DC drift can be effectively filtered out, and useful signals related to the near-field characteristics of the sample under test can be selectively demodulated. This is the key to achieving high signal-to-noise ratio detection.

[0040] Specifically, the modulation signal and the local oscillator signal are mixed at zero intermediate frequency, which specifically includes: using a harmonic mixer to perform L-th harmonic mixing on the modulation signal.

[0041] By using harmonic mixing technology, the frequency and power requirements of the local oscillator signal source are reduced at the system level, simplifying the system complexity.

[0042] Specifically, before radiating to the near-field probe through the first antenna, the method further includes: adjusting the angle between the first antenna and the second antenna and the horizontal direction so that the polarization direction of the millimeter-wave terahertz wave electric field matches the vibration direction of the near-field probe.

[0043] The overall signal transmission and reception efficiency of the system can be improved by optimizing polarization matching.

[0044] Specifically, the vector network analyzer host uses a single frequency synthesis source within it to generate the radio frequency test signal.

[0045] It is ensured that the transmitted signal and the received local oscillator signal originate from the same highly stable and highly coherent reference clock. This homogeneity guarantees the phase stability of the intermediate frequency signal after mixing, enabling the vector network analyzer to perform accurate amplitude and phase measurements. This is crucial for certain quantitative near-field imaging applications that require phase information and, from a methodological perspective, strengthens the improvement in system integration.

[0046] The zero-IF terahertz near-field imaging device and method based on a vector network analyzer provided by this invention uses a single frequency synthesis source in the vector network analyzer host to simultaneously provide radio frequency test signals and local oscillator signals to the millimeter-wave terahertz spread spectrum transmission module and the millimeter-wave terahertz spread spectrum reception module, respectively. The millimeter-wave terahertz spread spectrum transmission module and the millimeter-wave terahertz spread spectrum reception module adopt a zero-IF architecture to achieve down-conversion of the near-field signal reception. This device can realize millimeter-wave terahertz near-field super-resolution microscopic imaging.

[0047] The present invention provides a zero-IF terahertz near-field imaging device and method based on a vector network analyzer. This device and method utilize a single signal source in the vector network analyzer host to split into two paths, simultaneously providing the required radio frequency (RF) signal and local oscillator (LO) signal to both the millimeter-wave terahertz spread spectrum transmitting module and the millimeter-wave terahertz spread spectrum receiving module. The millimeter-wave terahertz spread spectrum module employs a zero-IF architecture to achieve down-conversion for receiving the near-field signal. The IF frequency of the vector network analyzer host is set to the Mth harmonic of the probe modulation frequency. (M=1, 2, ...), directly realizing the demodulation and reception of near-field signals after down-conversion by the millimeter-wave terahertz spread spectrum module. This invention uses a vector network analyzer to simultaneously realize the generation of excitation signals and the demodulation and reception of near-field imaging signals, enabling super-resolution microscopic imaging of samples and improving the integration of existing millimeter-wave terahertz near-field imaging devices.

[0048] Example 3 Embodiment 3 of the present invention provides a computer-readable storage medium.

[0049] A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the zero-IF terahertz near-field imaging method based on a vector network analyzer as described in Embodiment 2 of the present invention.

[0050] The detailed steps are the same as those of the zero-IF terahertz near-field imaging method based on a vector network analyzer provided in Example 2, and will not be repeated here.

[0051] Example 4 Embodiment 4 of the present invention provides a computer program product.

[0052] A computer program product includes software code, wherein the program in the software code performs the steps of the zero-IF terahertz near-field imaging method based on a vector network analyzer as described in Embodiment 2 of the present invention.

[0053] The detailed steps are the same as those of the zero-IF terahertz near-field imaging method based on a vector network analyzer provided in Example 2, and will not be repeated here.

[0054] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0055] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0056] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0057] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0058] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0059] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0060] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A zero-IF terahertz near-field imaging device based on a vector network analyzer, characterized in that, include: The vector network analyzer host is used to generate RF test signals and demodulate zero-IF test signals; A power divider, connected to the host, is used to divide the radio frequency test signal into a first signal and a second signal; A millimeter-wave terahertz spread spectrum transmission module is connected to the power divider and is used to perform frequency multiplication processing on the first signal to generate a millimeter-wave terahertz test signal. The first antenna is connected to the transmitting module and is used to radiate the test signal to the near-field probe; Near-field probes are used to vibrate and modulate incident signals to generate modulated signals; A second antenna is used to receive the modulated signal; A millimeter-wave terahertz spread spectrum receiver module is connected to the power divider and the second antenna. It is used to multiply the frequency of the second signal to generate a local oscillator signal, and to perform zero intermediate frequency mixing between the modulation signal and the local oscillator signal to generate the zero intermediate frequency test signal. The controller, connected to the near-field probe and the vector network analyzer host, is used to control the probe scanning and generate near-field imaging images.

2. The apparatus as claimed in claim 1, characterized in that, The mixer in the millimeter-wave terahertz spread spectrum receiver module is a harmonic mixer, configured to perform L-th harmonic mixing on the modulation signal.

3. The apparatus as described in claim 1, characterized in that, The device further includes a displacement stage, on which the millimeter-wave terahertz spread spectrum transmitting module and the millimeter-wave terahertz spread spectrum receiving module are respectively mounted. By adjusting the displacement stage, the angle between the first antenna and the second antenna and the horizontal direction is changed, so that the polarization direction of the millimeter-wave terahertz wave electric field matches the direction of the near-field probe.

4. A zero-IF terahertz near-field imaging method based on a vector network analyzer using the device according to any one of claims 1-3, characterized in that, The method includes the following steps: The vector network analyzer host generates an RF test signal, and uses a power divider to divide the RF test signal into a first signal and a second signal. The first signal is multiplied by the millimeter-wave terahertz spread spectrum transmission module and then radiated to the near-field probe through the first antenna; The vibration of the near-field probe is controlled to modulate the incident signal, generating a modulated signal that is received by the second antenna. The second signal is frequency multiplied by the millimeter-wave terahertz spread spectrum receiving module to generate a local oscillator signal; In the millimeter-wave terahertz spread spectrum receiver module, the modulation signal and the local oscillator signal are mixed at zero intermediate frequency to generate a zero intermediate frequency test signal and sent back to the vector network analyzer host. The intermediate frequency of the vector network analyzer host is set to the harmonic of the probe vibration frequency in order to demodulate the near-field signal data; The near-field probe is controlled to scan the sample, and a near-field imaging image is generated based on the near-field signal data.

5. The method as described in claim 4, characterized in that, The intermediate frequency of the vector network analyzer host is set as the harmonic of the probe vibration frequency. Specifically, the center frequency of the intermediate frequency receiver is locked to the Mth harmonic of the probe vibration frequency, where M=1,2,...

6. The method as described in claim 4, characterized in that, The modulation signal and the local oscillator signal are mixed at zero intermediate frequency, specifically including: using a harmonic mixer to perform L-th harmonic mixing on the modulation signal.

7. The method as described in claim 4, characterized in that, Before radiating to the near-field probe through the first antenna, the method further includes: adjusting the angle between the first antenna and the second antenna and the horizontal direction so that the polarization direction of the millimeter-wave terahertz wave electric field matches the vibration direction of the near-field probe.

8. The method as described in claim 4, characterized in that, The vector network analyzer host uses a single frequency synthesis source within it to generate the radio frequency test signal.

9. A computer-readable storage medium, characterized in that, The storage medium stores a computer program, which, when executed by a processor, implements the zero-IF terahertz near-field imaging method based on a vector network analyzer as described in any one of claims 5 to 8.

10. A computer program product, comprising software code, characterized in that, The program in the software code performs the steps of the zero-IF terahertz near-field imaging method based on a vector network analyzer as described in any one of claims 5 to 8.

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