A small-sized broadband transient pulse electric field measurement system

Abstract

The present invention discloses a small, broadband transient pulse electric field measurement system, belonging to the field of transient electromagnetic pulse measurement technology. The system comprises a front-end sensor and a receiver; the front-end sensor comprises a shielding box, an electrically small short-pole antenna, a high-resistance integrator, a variable-gain operational amplifier, an electro-optical direct modulation circuit, a temperature sensor, a front-end power management system, a front-end controller, and a wavelength-division multiplexing optical communication link. The expansion of the measurement system's upper limit is related to the thickness and radial dimensions of the shielding box; when the shielding box thickness is reduced while the radial dimensions are increased, the impact of high-frequency electromagnetic scattering from the shielding box's sidewalls on the measurement results can be effectively reduced. The system has a frequency response range of 300Hz to 3GHz and a 60dB electric field time-domain measurement dynamic range. It can achieve true-to-original waveform measurement of transient electromagnetic pulses ranging from hundreds of V / m to hundreds of kV / m. It also features automatic transmission link insertion loss compensation, automatic gain temperature drift compensation, online status monitoring, and sensitivity adjustment functions, and has high environmental adaptability and ease of use.

Description

Technical Field

[0001] The invention belongs to the technical field of transient electromagnetic pulse measurement, and in particular relates to a small broadband transient pulse electric field measurement system. Background Art

[0002] Research on transient electromagnetic pulse measurement technology is relatively mature both domestically and internationally. According to publicly available literature, existing measurement techniques primarily include active electro-optical electric field transmission measurement systems, integrated electro-optical crystal electric field measurement systems, TEM horns, D-Dots, and microstrip transmission structures. Baum et al. first developed a broadband D-Dot electric field sensor in 1978, but this type of sensor is an electric field differential type, which suffers from baseline drift during numerical integration. In 2021, Zhang Jiahong et al. completed the design of a miniature integrated optical waveguide electric field sensor with a bandwidth of 100 kHz to 10 GHz, but the system's response flatness was poor. Zhu Sitao et al. developed an ultra-wideband electromagnetic pulse radiation field measurement system with a 4 ns time window, using a constant impedance TEM horn as a receiving antenna. In 2021, Liu Yifei et al. completed research on a sensitivity-self-calibrating pulse electric field measurement system based on optical fiber transmission and developed an active electro-optical electric field measurement system with a bandwidth of 1.38 GHz. The aforementioned transient electromagnetic pulse measurement technologies all have their own relative technical advantages and practical applications. Compared to other measurement technologies, electric field measurement systems based on active electro-optics offer the advantages of original waveform measurement, no time window restrictions, low cost, and a simple structure. However, the bandwidth upper limit of existing publicly available technical indicators is relatively low, which cannot meet the requirements of transient fast pulse electric field measurement applications. Current scientific research activities have carried out technical research on this type of measurement system, and the design of "a small transient pulse electric field measurement system" with a bandwidth of 10kHz to 1GHz has been completed. However, the system bandwidth cannot meet the general measurement requirements of conventional LEMP, UWS, etc.

[0003] Based on this, it is of great significance to develop a broadband transient active electro-optical field measurement system to further broaden the application scope of this type of measurement system and improve the universality of transient electromagnetic pulse measurement technology. Summary of the Invention

[0004] The purpose of the present invention is to develop a small, wide-band, and highly environmentally adaptable transient pulse electric field measurement system to solve the bandwidth upper limit problem of this type of measurement system, expand the system response lower limit, optimize the system's environmental adaptability and instrumentation design, and simultaneously meet the universal measurement needs of transient pulse radiation electric fields such as lightning, static electricity, and ultra-wide spectrum electromagnetic pulses.

[0005] In order to achieve the above objectives and solve the above technical problems, the technical solutions of the present invention are as follows:

[0006] A small broadband transient pulse electric field measurement system includes a front-end sensor 1 and a receiver 2;

[0007] The front-end sensor 1 consists of a shielding box 3, an electrically small short-pole antenna 4, a high-resistance integrator 5, a variable-gain operational amplifier 6, an electro-optical direct modulation circuit 7, a temperature sensor 8, a front-end power management 9, a front-end controller 10, and a wavelength division multiplexing optical communication link 11;

[0008] The receiver is composed of a wavelength division multiplexing optical communication link 11, a link insertion loss compensation circuit 12, a photoelectric conversion circuit 13, a back-end controller 14, and a back-end power management circuit 15;

[0009] The shielding box 3 is composed of a hollowed-out metal cavity and is used to shield the circuit board inside the front-end sensor and as a reference ground plane for the electrically small short-pole antenna 4. The expansion of the measurement upper limit of the measurement system is related to the thickness and radial size of the shielding box 3. The thickness and radial size of the shielding box 3 are designed according to the bandwidth upper limit required by the actual measurement task. When the thickness of the shielding box 3 is reduced, the radial size is increased, that is, the distance from the vertical side wall of the shielding box 3 to the antenna is increased, which can effectively reduce the impact of high-frequency electromagnetic scattering from the side wall of the shielding box on the measurement results.

[0010] The electric short pole antenna 4 is placed in the center of the shielding box 3 and adopts the form of a monopole or dipole to couple the environmental electric field. Its output is connected to the high-resistance integrator 5 to integrate the induced signal and obtain the original waveform signal of the electric field.

[0011] The high-impedance integrator 5 is sequentially connected to a variable-gain operational amplifier 6, an electro-optical direct modulation circuit 7, and a wavelength-division multiplexing optical communication link 11. It attenuates and amplifies the electric field signal coupled by the electrically small short-pole antenna 4, and converts the coupled electric signal into an analog intensity-modulated optical signal for interference-free transmission. The high-impedance integrator 5 is composed of a FET-input operational amplifier or a transistor, and should have a relatively flat amplitude-frequency / phase-frequency response within the designed frequency band and sufficient phase margin.

[0012] The variable gain operational amplifier 6 is controlled by the front-end controller 10 and can attenuate or amplify the coupled electrical signal to adjust the system sensitivity;

[0013] The electro-optical direct modulation circuit 7, which consists of an electro-optical direct modulation circuit and an automatic optical power control circuit, can adjust the output static optical power based on the temperature information obtained by the temperature sensor 8 and the temperature drift calibration data. In combination with the link insertion loss compensation circuit 12, it can compensate for the system sensitivity offset introduced by temperature changes in real time.

[0014] The optical signal output by the electro-optical direct modulation circuit 7 is transmitted via optical fiber to the link insertion loss compensation circuit 12 and the photoelectric conversion circuit 13, which demodulates the analog intensity modulated optical signal and restores the ambient electric field waveform;

[0015] The link insertion loss compensation circuit 12 is composed of a voltage-controlled optical attenuator or optical amplifier based on PID closed-loop control, and is used to dynamically attenuate or amplify the static optical power output by the electro-optical direct modulation circuit 7 to a fixed static optical power value, thereby automatically compensating for the sensitivity offset caused by the optical fiber link insertion loss and the temperature drift of the sensor sensitivity;

[0016] Front-end power management 9 and back-end power management 15 are used for powering on the measurement system, voltage division power supply, lithium battery charging and power monitoring;

[0017] The front-end controller 10 and the back-end controller 14 are system-on-chips composed of single-chip microcomputers, which are used to complete the digital communication between the front-end sensor 1 and the receiver 2;

[0018] The wavelength division multiplexing optical communication link 11 is composed of a serial-to-optical communication circuit and an optical wavelength division multiplexer. It uses wavelength division multiplexing to integrate the analog modulated optical signal output by the electro-optical direct modulation circuit 7 and the uplink and downlink digital communication optical signals, thereby realizing a single optical fiber connection between the front-end sensor 1 and the receiver 2, thereby improving the ease of use of the measurement system.

[0019] The measurement system controls the front-end sensor 1 through the buttons of the receiver 2 or the host computer, adjusts the gain of the variable gain operational amplifier 6, realizes the sensitivity adjustment of the measurement system and monitors the state parameters of the front-end sensor 1 in real time, and controls the low-power sleep and wake-up of the front-end sensor 1.

[0020] Furthermore, when testing an electric field with a relatively high field strength, the electrically small short-pole antenna 4 is parallel to the mirror plane of the measurement system shielding box 3 , that is, the receiving antenna is an open coaxial antenna.

[0021] Furthermore, the hardware integration of the high-resistance integrator 5 is achieved by voltage division between the equivalent capacitance of the antenna and the equivalent load capacitance. When a bias resistor of 100 megohms is used, the low-frequency measurement lower limit of the measurement system can be reduced.

[0022] Furthermore, when designing for a lower low-frequency response of the measurement system, the load resistance in the high-resistance integrator 5 can be increased, a DC-coupled subsequent active link can be used as much as possible, and multiple ultra-wideband capacitors can be used in the AC-coupled active link to reduce insertion loss. When using a high-resistance integrating resistor, the bias stability design of the input stage of the high-resistance integrator 5 must be fully considered.

[0023] Furthermore, when designing a system for a higher bandwidth frequency band, it is necessary to reduce the length of the feeding coaxial section and not use load capacitance to keep the resonant frequency away from the design frequency of the measurement system. At the same time, a damping resistor is added between the electrically small short-pole antenna 4 and the high-resistance integrator 5 to optimize the upward amplitude-frequency response curve caused by resonance and improve the response flatness of the measurement system.

[0024] Furthermore, the link insertion loss compensation circuit 12 uses a variable optical attenuator or an optical amplifier to compensate for temperature drift and link insertion loss.

[0025] Furthermore, the specific implementation steps for real-time compensation of link insertion loss in the test system are as follows:

[0026] Performing constant control on the output static optical power of the electro-optical direct modulation circuit 7;

[0027] Detecting the received static photocurrent of the photoelectric conversion circuit 13 and using it as the feedback quantity of the analog negative feedback control;

[0028] Based on the received static photocurrent and the locally set reference value, the offset error is obtained, and based on PID control, the attenuation or gain of the variable optical attenuator or optical amplifier is dynamically controlled to complete the real-time compensation of the link insertion loss in the simulated closed loop.

[0029] Furthermore, the specific implementation steps of the test system temperature drift compensation are as follows:

[0030] Use temperature assessment method to obtain system sensitivity temperature drift data;

[0031] Temperature sensor 8 obtains the internal temperature of the sensor;

[0032] Real-time dynamic adjustment of the static optical power output by the electro-optical direct modulation circuit 7 so that the static optical power is equal to 1 / G E (T) remains constant with temperature; where G E (T) is the optical modulation gain of the ambient electric field.

[0033] Furthermore, when the polarization of the receiving antenna is mismatched with that of the incident electric field, the electrically short-pole antenna 4 needs to adopt a symmetrical dipole mode to remove the common-mode scattering.

[0034] Furthermore, the shape of the shielding box 3 adopts a circular or square shielding box mechanical structure, which can effectively reduce the influence of the side wall electromagnetic scattering on the antenna receiving amplitude-frequency response.

[0035] The effective benefits of the present invention are as follows:

[0036] 1. The broadband transient pulse electric field measurement system of the present invention greatly improves the measurement response bandwidth of this type of measurement system by optimizing the shielding structure and high-resistance integration circuit of the front-end sensor, and can realize universal measurement of transient pulse electric fields such as lightning, static electricity, and ultra-wide spectrum electromagnetic pulses;

[0037] 2. The broadband transient pulse electric field measurement system of the present invention automatically compensates for system sensitivity changes introduced by link insertion loss in real time through link insertion loss compensation control based on received static optical power feedback, thereby improving the system's environmental adaptability and instrumentation level.

[0038] 3. The broadband transient pulse electric field measurement system of the present invention solves the problem of system-level sensitivity temperature drift through system sensitivity temperature drift compensation based on temperature feedback, avoids the high power consumption caused by conventional laser constant temperature control, greatly improves the measurement accuracy of the measurement system, and extends the standby time under the same battery capacity;

[0039] 4. Based on the technical route of the broadband transient pulse electric field measurement system of the present invention, the design of a measurement system with higher bandwidth indicators (>5GHz) can be realized. Compared with other types of broadband measurement systems, it has the characteristics of low noise, high dynamic range, high environmental adaptability, and low cost.

[0040] The present invention's compact, broadband transient pulse electric field measurement system boasts a frequency response range of 300Hz to 3GHz and a 60dB dynamic range (SNR>5) for electric field time-domain measurement. It can accurately measure transient electromagnetic pulses ranging from hundreds of V / m to hundreds of kV / m. It also features automatic transmission link insertion loss compensation, automatic gain drift compensation, online status monitoring, and sensitivity adjustment, offering high environmental adaptability and ease of use. Furthermore, based on the technical solutions of the present invention, the measurement system's bandwidth can be further expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a functional structure diagram of the small broadband transient pulse electric field measurement system of the present invention;

[0042] Figure 2 Schematic diagram of the typical shielding box mechanical structure and its electromagnetic scattering according to the present invention;

[0043] Figure 3 This is the antenna receiving and high-resistance integration equivalent circuit diagram of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be explained and illustrated in detail below with reference to the accompanying drawings and embodiments.

[0045] The present invention belongs to the technical field of transient electromagnetic pulse measurement, and specifically relates to a small broadband transient pulse electric field measurement system, which can be used for measuring transient pulse radiation electric fields such as lightning, static electricity and ultra-wide spectrum electromagnetic pulses.

[0046] The purpose of the present invention can be achieved by the following technical solutions:

[0047] A small broadband transient pulse electric field measurement system, such as Figure 1 As shown, it includes a front-end sensor 1 and a receiver 2;

[0048] The front-end sensor 1 consists of a shielding box 3, an electrically small short-pole antenna 4, a high-resistance integrator 5, a variable-gain operational amplifier 6, an electro-optical direct modulation circuit 7, a temperature sensor 8, a front-end power management 9, a front-end controller 10, and a wavelength division multiplexing optical communication link 11;

[0049] The receiver is composed of a wavelength division multiplexing optical communication link 11, a link insertion loss compensation circuit 12, a photoelectric conversion circuit 13, a back-end controller 14, and a back-end power management circuit 15.

[0050] The bandwidth of the measurement system mainly depends on the optimized design of the shielding box 3, the electrically small short-pole antenna 4 and the high-resistance integrator 5, and the remaining parts can be realized by adopting mature technical solutions.

[0051] Shielding box 3, consisting of a hollowed-out metal cavity, serves as a shield for the front-end sensor's internal circuit board and as a reference ground plane for the electrically short-pole antenna 4. Electromagnetic analysis indicates that electromagnetic scattering from shielding box 3 is a significant factor affecting the upper bandwidth limit of the measurement system. Shielding box 3 requires a thinner physical structure with larger radial dimensions to minimize the impact of high-frequency electromagnetic scattering from the box's sidewalls on the measurement results. Furthermore, when the receiving antenna and the incident electric field are polarized mismatched, the receiving antenna's reference mirror will also generate significant high-frequency scattering, severely limiting the system's bandwidth expansion and the fidelity of the measured waveform. In this case, electrically short-pole antenna 4 must adopt a symmetrical dipole configuration to eliminate this common-mode scattering.

[0052] The electric short pole antenna 4 is placed in the center of the shielding box 3 and adopts the form of monopole or dipole to couple the environmental electric field. Its output is connected to the high-resistance integrator 5 to integrate the induced signal and obtain the original waveform signal of the electric field.

[0053] The high-resistance integrator 5 is sequentially connected to the variable-gain operational amplifier 6 and the electro-optical direct modulation circuit 7, and converts the coupled electrical signal into an analog intensity-modulated optical signal for interference-free transmission.

[0054] The variable-gain op amp 6, controlled by the front-end controller 10, has a 32dB gain adjustment range and can attenuate or amplify the coupled electrical signal to adjust system sensitivity. The electro-optical direct modulation circuit 7, consisting of an electro-optical direct modulation circuit and an automatic optical power control circuit, uses temperature information obtained by the temperature sensor 8 and temperature drift calibration data to adjust the output static optical power. In conjunction with the link insertion loss compensation circuit 12, it compensates for system sensitivity drift introduced by temperature changes in real time.

[0055] The optical signal output by the electro-optical direct modulation circuit 7 is transmitted via the optical fiber to the link insertion loss compensation circuit 12 and the photoelectric conversion circuit 13, which demodulates the analog intensity modulated optical signal and restores the ambient electric field waveform.

[0056] Link insertion loss compensation circuit 12, comprised of a voltage-controlled optical attenuator or optical amplifier using PID closed-loop control, dynamically attenuates or amplifies the static optical power output by electro-optical direct modulation circuit 7 to a fixed static optical power value. This automatically compensates for sensitivity shifts caused by fiber link insertion loss and sensor temperature drift, improving the system's environmental adaptability and ease of use.

[0057] Front-end power management 9 and back-end power management 15 are responsible for powering up the measurement system, providing voltage-splitting power, charging the lithium battery, and monitoring power levels. Front-end controller 10 and back-end controller 14, system-on-chips comprised of single-chip microcomputers, facilitate digital communication between front-end sensor 1 and receiver 2.

[0058] The measurement system can control the front-end sensor 1 through the buttons of the receiver 2 or the host computer to adjust the gain of the variable gain operational amplifier 6 to achieve sensitivity adjustment; monitor the status parameters of the front-end sensor 1 in real time, such as power level, temperature and other information; and control the low-power sleep and wake-up of the front-end sensor 1.

[0059] The wavelength-division multiplexing optical communication link 11, consisting of a serial-to-optical communication circuit and an optical wavelength-division multiplexer, uses wavelength-division multiplexing to integrate the analog modulated optical signal output by the electro-optical direct modulation circuit 7 with the uplink and downlink digital communication optical signals. This enables a single-fiber connection between the front-end sensor 1 and the receiver 2, improving the system's ease of use.

[0060] The technical solution of the present invention is further described in detail below through embodiments and drawings.

[0061] Example 1

[0062] A small broadband transient pulse electric field measurement system, such as Figure 1 As shown, it includes a front-end sensor 1 and a receiver 2. The front-end sensor 1 is composed of a shielding box 3, an electrically small short-pole antenna 4, a high-resistance integrator 5, a variable-gain operational amplifier 6, an electro-optical direct modulation circuit 7, a temperature sensor 8, a front-end power management 9, a front-end controller 10, and a wavelength division multiplexing optical communication link 11; the receiver is composed of a wavelength division multiplexing optical communication link 11, a link insertion loss compensation circuit 12, an optoelectronic conversion circuit 13, a back-end controller 14, and a back-end power management 15.

[0063] The shielding box 3, consisting of a hollowed-out metal cavity, serves as the electromagnetic shielding for the internal circuits of the front-end sensor and as the reference ground plane for the short-pole antenna 4. Electromagnetic analysis of the shielding box shows that the electromagnetic side walls of the shielding box will generate scattering when encountering the ambient electric field. The equivalent radiation source of a typical shielding box (12×12×1cm) is as follows: Figure 2 As shown. At the receiving antenna, the time domain expression of the Z-direction component of the scattered field is approximately given by equation (1):

[0064]

[0065] The scattered field consists of the differential, proportional, and integral terms of the incident ambient electric field. Further analysis and calculation of Equation (1) show that at higher frequencies (>1 GHz), the differential term dominates the scattered field on the sidewall perpendicular to the incident field and is approximately proportional to the sidewall height. On the sidewall parallel to the incident field, the proportional term dominates the scattered field, and the scattered field intensity is much smaller than that on the perpendicular sidewall.

[0066] From formula (1), we can further know that Figure 2 Under a shielding box, the impact of vertical sidewall scattering on the antenna's reception characteristics is primarily influenced by the thickness h of the shielding box 3 and the distance from the vertical sidewall to the antenna (i.e., the shielding box's half-width a / 2), and this impact increases with increasing frequency. This is also one of the most significant factors that severely restrict the upper bandwidth of this type of measurement system. When the thickness of the shielding box 3 is in the 1-3 cm range, which is electrically small relative to the 2-6 GHz frequency range, electromagnetic scattering from the sidewall is difficult to eliminate using a gradual slope transition.

[0067] In order to reduce the impact of the side wall scattering of the shielding box 3 on the antenna receiving characteristics, a thinner shielding box thickness is required to reduce the intensity of the total equivalent scattering source; since the scattered field radiation decays approximately at 1 / r, increasing the distance from the vertical side wall to the antenna further reduces the scattered field intensity reaching the antenna.

[0068] Attachment Figure 2 When the mechanical dimensions of the shielding box 3 are reduced from 12 × 12 × 3 cm to 12 × 12 × 1 cm, the electromagnetic scattering from the shielding box 3 reduces the antenna's receive amplitude-frequency response from approximately ±1.4 dB to ±0.4 dB in the DC to 3 GHz frequency range, and from approximately ±2.3 dB to ±0.6 dB in the DC to 6 GHz frequency range. When designing measurement systems with higher requirements, the thickness h can be further reduced and the width a increased to minimize scattering from the shielding box 3's sidewalls.

[0069] In addition, since vertical sidewall scattering plays a dominant role in the sidewall integrated scattering, the shape of the shielding box can be optimized and a circular or square shielding box mechanical structure can be used to effectively reduce the impact of sidewall electromagnetic scattering on the antenna receiving amplitude-frequency response.

[0070] At this time, when measuring the electric field waveform with a bandwidth above 1 GHz and a large mismatch in electric field polarization, the electromagnetic scattering suppression design of the receiving antenna reference ground plane must also be considered.

[0071] In the case of polarization mismatch, in addition to scattering from the sidewalls of the shielding box 3, the reference plane of the receiving antenna also generates electromagnetic scattering, which affects the measurement results and gradually worsens with increasing polarization mismatch angle. Electromagnetic simulation results show that when the shielding box has structural dimensions of 12×12×1cm and the electric field polarization mismatch angle is 30°, the electromagnetic scattering reduces the measurement system bandwidth to 1.6GHz and severely distorts the antenna coupling waveform. Further electromagnetic calculation and analysis show that this electromagnetic scattering is approximately equal in amplitude and opposite in direction on both sides of the shielding box, indicating common-mode interference.

[0072] To address the above-mentioned electromagnetic scattering interference, a symmetrical dipole form needs to be adopted based on a common-mode suppression circuit, thereby broadening the application of electric field measurement systems based on active electro-optical types in wide bandwidths and large mismatch angles.

[0073] By adopting this technical approach, the impact of electromagnetic scattering from the shielding box on measurement results can be effectively reduced, resolving the bandwidth limitations of this type of measurement system and further increasing the bandwidth to 3-6 GHz. Furthermore, the upper bandwidth limit of the measurement system is also limited by the bandwidth of subsequent active links, such as the high-resistance integrator 5 and the electro-optical direct modulation circuit 7.

[0074] The electrical length of the electrically short-pole antenna 4 is generally required to be 1 / 10 of the wavelength of the highest design frequency. Furthermore, during high-field field testing, the electrically short-pole antenna 4 can be aligned parallel to the measurement system shielding box 3, effectively creating an open coaxial antenna for the receiving antenna. Its receiving characteristics can be analyzed using electromagnetic reciprocity equivalence, with sensitivity proportional to the natural logarithm of the feed aperture radius.

[0075] The electrically small short-pole antenna 4 is connected to a high-resistance integrator 5, which can be equivalent to a series antenna equivalent capacitor C. ant and parasitic inductance L ant , and its equivalent receiving circuit is shown in Figure 3. The high-resistance integrator 5 is composed of a FET input operational amplifier or a transistor, and should have a relatively flat amplitude-frequency / phase-frequency response within the design frequency band and have sufficient phase margin.

[0076] The hardware integration of the high-resistance integrator 5 is achieved through the equivalent capacitance C of the antenna. ant and the equivalent load capacitance C eq-load Voltage division is achieved, such as Figure 3 The equivalent circuit is shown in Figure 2. The equivalent load capacitance C eq-load The equivalent capacitance C of the feeding coaxial line coax 、PCB parasitic capacitance C parasite , load capacitance C load , transistor input capacitance C in Bias resistor R load Provides input bias current for the active transistor gate of high-resistance integrator 5. At this time, the low-frequency lower limit of the measurement system is approximately calculated by equation (2).

[0077]

[0078] Use a bias resistor R of 100 megohms load , which can reduce the low-frequency measurement limit of the measurement system. For example, when the equivalent load capacitance is 4pF and the integration resistance is 200MΩ, the -3dB low-frequency limit of the measurement system is about 200Hz, which meets the low-frequency measurement requirements of conventional LEMP.

[0079] When designing for a lower-frequency measurement system, the load resistor in high-resistance integrator 5 can be increased, DC-coupled subsequent active links can be used whenever possible, and multiple ultra-wideband capacitors can be used in parallel for AC-coupled active links to reduce insertion loss. Furthermore, when using high-value integrating resistors, full consideration must be given to the bias stability design of the input stage of high-resistance integrator 5.

[0080] Equation (3) gives the transfer function between the output of the high-resistance integrator 5 and the incident electric field when the frequency is greater than 1 GHz, where h eq_ant (ω), S shield (ω), G amp (ω) are the effective receiving height of the ideal electrically small antenna, the effect of the shielding box 3 on the antenna reception, and the gain of the buffer FET operational amplifier.

[0081]

[0082] Due to the parasitic inductance L of the short pole 4 and the feeding port ant&coax The existence of , and the equivalent LC resonance, make the high-resistance integrator 5 unstable or self-excited oscillation, its resonant frequency is shown in formula 4. When designing a system with a higher bandwidth, it is necessary to reduce the length of the feeding coaxial section and not use load capacitance to make the resonant frequency away from the design frequency of the measurement system. In addition, add an appropriate damping resistor R between the electrically small short-pole antenna 4 and the high-resistance integrator 5 damp ,like Figure 3 As shown in the figure, the upward curvature of the amplitude-frequency response curve caused by resonance is optimized to improve the response flatness of the measurement system.

[0083]

[0084] The high-resistance integrator 5 is respectively connected to a variable gain operational amplifier 6, an electro-optical direct modulation circuit 7 and a wavelength division multiplexing optical communication link 11 to attenuate and amplify the electric field signal coupled by the electrically small short-pole antenna 4 and perform electro-optical conversion.

[0085] The variable gain operational amplifier 6 can increase the system's measurement dynamic range without significantly increasing the system's noise floor. The electro-optical direct modulation circuit 7 has an automatic optical power control function to ensure stable system operation.

[0086] The analog intensity modulated optical signal output by the electro-optical direct modulation circuit 7 is transmitted to the receiver via the optical fiber, and then passes through the wavelength division multiplexing optical communication link 11 for optical wavelength filtering and branching. It is then connected to the link insertion loss compensation circuit 12 and the optoelectronic conversion circuit 13 for optoelectronic conversion, thereby completing the measurement of the ambient electric field.

[0087] The gain of the optical transmission link is affected by the temperature drift of the laser's modulation efficiency, the temperature drift of the op amp / low-noise amplifier's gain, and the optical attenuation of the analog optical intensity modulation link. To address these issues, the link insertion loss compensation circuit 12 uses a variable optical attenuator or optical amplifier to compensate for the aforementioned gain temperature drift and link insertion loss. Equation (5) gives the expression for the measurement system output and the ambient electric field:

[0088] V out (t) = [1 + E in (t)G E (T)]P0A fiber A VOA G OE (5)

[0089] Where:

[0090] P0 represents the static optical power output by the electro-optical direct modulation circuit 7, which has been automatically controlled.

[0091] G E (T) is the optical modulation gain of the ambient electric field (including the gains of the high-resistance integrator 5, the variable gain operational amplifier 6, and the electro-optical direct modulation circuit 7), which has a temperature drift characteristic;

[0092] A fiber Introducing insertion loss into the optical transmission link;

[0093] A VOA is the attenuation or gain of a variable optical attenuator or optical amplifier;

[0094] G OE is the photoelectric conversion gain of the photoelectric conversion circuit 13 .

[0095] From formula (5), we can know that under given test conditions, the modulation depth of the simulated light intensity [1+E in (t)G E (T)] / P0 remains constant. Therefore, the variable optical attenuator or optical amplifier can be controlled in real time based on analog negative feedback to make the link attenuation A fiber A VOA is constant, that is, the input static light P0A of the photoelectric conversion circuit 13 fiber A VOA is a fixed value P const , as shown in formula (6), ultimately achieving real-time compensation of link insertion loss in the measurement system.

[0096]

[0097] The real-time compensation of the system link insertion loss is specifically implemented as follows: 1) constant control of the output static optical power of the electro-optical direct modulation circuit 7; 2) detection of the received static photocurrent of the photoelectric conversion circuit 13, and use it as the feedback quantity of the analog negative feedback control; 3) based on the received static photocurrent and the locally set reference quantity, the offset error is obtained, and based on PID control, the attenuation or gain of the variable optical attenuator or optical amplifier is dynamically controlled to complete the analog closed-loop real-time compensation of the link insertion loss.

[0098] From formula (6), we can see that in order to achieve the system gain temperature drift compensation, it is necessary to ensure that G OE P const and 1 / G E The temperature drift of (T) remains consistent. The receiver is used indoors and the photoelectric conversion gain G can be ignored. OE Temperature drift changes, at this time, as long as the input static optical power P of the photoelectric conversion circuit 13 is guaranteed const and 1 / G E (T) temperature drift changes remain consistent, the temperature drift compensation of the system sensitivity can be achieved.

[0099] The specific implementation of system sensitivity temperature drift compensation is as follows: 1) using temperature assessment to obtain system sensitivity temperature drift data; 2) the temperature sensor 8 obtains the internal temperature of the sensor; 3) real-time dynamic adjustment of the static optical power output by the electro-optical direct modulation circuit 7 so that the static optical power P0 is consistent with 1 / G E (T) remains consistent with the change of temperature, as shown in formula (6), completing the feedback compensation of the system sensitivity temperature drift compensation.

[0100]

[0101] At this time, the measurement system realizes automatic sensitivity temperature drift compensation and link insertion loss compensation, ensuring the consistency of the measurement system's sensitivity in various usage environments, and improving the system's environmental adaptability and ease of use.

[0102] Due to the special electromagnetic design of the shielding box 3, the front-end sensor cannot carry a high-capacity battery. Based on this technology route, automatic dynamic sensitivity temperature drift compensation can effectively reduce the high power consumption caused by constant temperature control of the laser, effectively extending the service life of the front-end sensor.

[0103] The front-end controller 10 is responsible for reading temperature data from the front-end sensor, dynamically adjusting and controlling static optical power, controlling the gain of the variable-gain op amp 6, controlling the front-end power management 9, performing power monitoring, low-power sleep, and wakeup, and receiving and executing relevant commands sent by the receiver. The back-end controller 14 monitors receiver status parameters such as system compensation status and receiver power level, and forwards commands between the host computer and the front-end sensors.

[0104] The wavelength division multiplexing optical communication link 11 adopts wavelength division multiplexing technology to complete the integration of analog modulated optical signals and digital optical signals, realize single-fiber connection between front-end sensors and back-end receivers, and improve the integration of the measurement system.

Claims

1. A small broadband transient pulse electric field measurement system, characterized in that: It includes a front-end sensor (1) and a receiver (2); The front-end sensor (1) comprises a shielding box (3), an electrically short-pole antenna (4), a high-resistance integrator (5), a variable-gain operational amplifier (6), an electro-optical direct modulation circuit (7), a temperature sensor (8), a front-end power management (9), a front-end controller (10) and a wavelength division multiplexing optical communication link (11); The receiver is composed of a wavelength division multiplexing optical communication link (11), a link insertion loss compensation circuit (12), a photoelectric conversion circuit (13), a back-end controller (14), and a back-end power management (15); The shielding box (3) is composed of a hollowed-out metal cavity and is used for shielding the circuit board inside the front-end sensor and as a reference ground plane for the electrically small short-pole antenna (4); the expansion of the measurement upper limit of the measurement system is related to the thickness and radial size of the shielding box (3); the thickness and radial size of the shielding box (3) are designed according to the bandwidth upper limit required by the actual measurement task, and when the thickness of the shielding box (3) is reduced, the radial size is increased, that is, the distance from the vertical side wall of the shielding box (3) to the antenna is increased, which can effectively reduce the influence of high-frequency electromagnetic scattering of the side wall of the shielding box on the measurement result; The electric short pole antenna (4) is placed in the center of the shielding box (3) and is in the form of a monopole or dipole for coupling the environmental electric field. Its output is connected to a high-resistance integrator (5) to integrate the induced signal and obtain the original waveform signal of the electric field; The high-resistance integrator (5) is sequentially connected to a variable-gain operational amplifier (6), an electro-optical direct modulation circuit (7), and a wavelength-division multiplexing optical communication link (11), and performs attenuation amplification on the electric field signal coupled by the electrically small short-pole antenna (4), and converts the coupled electric signal into an analog intensity-modulated optical signal for interference-free transmission. The high-resistance integrator (5) is composed of a FET input operational amplifier or a transistor, and should have a relatively flat amplitude-frequency / phase-frequency response within the designed frequency band and have sufficient phase margin. A variable gain operational amplifier (6), controlled by a front-end controller (10), is capable of attenuating or amplifying the coupled electrical signal to achieve system sensitivity adjustment; The electro-optical direct modulation circuit (7) is composed of an electro-optical direct modulation circuit and an automatic optical power control circuit. The electro-optical direct modulation circuit (7) can adjust the output static optical power according to temperature drift calibration data based on temperature information obtained by the temperature sensor (8), and can compensate for the system sensitivity offset introduced by temperature change in real time in combination with the link insertion loss compensation circuit (12); The optical signal output by the electro-optical direct modulation circuit (7) is transmitted via an optical fiber to a link insertion loss compensation circuit (12) and a photoelectric conversion circuit (13), which demodulates the analog intensity modulated optical signal and restores the ambient electric field waveform; A link insertion loss compensation circuit (12) is composed of a voltage-controlled optical attenuator or an optical amplifier based on PID closed-loop control, and is used to dynamically attenuate or amplify the static optical power output by the electro-optical direct modulation circuit (7) to a fixed static optical power value, thereby automatically compensating for sensitivity offset caused by optical fiber link insertion loss and sensor sensitivity temperature drift; Front-end power management (9) and back-end power management (15), used for power-on, voltage-dividing power supply, lithium battery charging and power monitoring of the measurement system; The front-end controller (10) and the back-end controller (14) are systems on a chip composed of single-chip microcomputers, and are used to complete digital communication between the front-end sensor (1) and the receiver (2); The wavelength division multiplexing optical communication link (11) is composed of a serial port to optical communication circuit and an optical wavelength division multiplexer, and uses wavelength division multiplexing to integrate the analog modulated optical signal output by the electro-optical direct modulation circuit (7) and the uplink and downlink digital communication optical signals, thereby realizing a single optical fiber connection between the front-end sensor (1) and the receiver (2), thereby improving the convenience of use of the measurement system; The measurement system controls the front-end sensor (1) through a button of a receiver (2) or a host computer, adjusts the gain of a variable-gain operational amplifier (6), realizes sensitivity adjustment of the measurement system, monitors the state parameters of the front-end sensor (1) in real time, and controls the low-power sleep and wake-up of the front-end sensor (1).

2. A small broadband transient pulse electric field measurement system according to claim 1, characterized in that: When testing an electric field with a relatively high field strength, the electric short-pole antenna (4) is parallel to the mirror surface of the measurement system shielding box (3), that is, the receiving antenna is an open coaxial antenna.

3. A small broadband transient pulse electric field measurement system according to claim 1, characterized in that: The hardware integration of the high-resistance integrator (5) is achieved by voltage division between the equivalent capacitance of the antenna and the equivalent load capacitance. When a bias resistor of 100 megohms is used, the low-frequency measurement lower limit of the measurement system can be reduced.

4. A small broadband transient pulse electric field measurement system according to claim 1, characterized in that: When designing for a lower low-frequency response of the measurement system, the load resistance in the high-resistance integrator (5) can be increased, a DC-coupled subsequent active link can be used as much as possible, and multiple ultra-wideband capacitors can be used to reduce insertion loss for the AC-coupled active link. When a high-resistance integral resistor is used, the bias stability design of the input stage of the high-resistance integrator (5) must be fully considered.

5. A small broadband transient pulse electric field measurement system according to claim 1, characterized in that: When designing a system for a higher bandwidth frequency band, it is necessary to reduce the length of the feeding coaxial section and not use a load capacitor so that the resonant frequency is far away from the design frequency of the measurement system. At the same time, a damping resistor is added between the electrically small short-pole antenna (4) and the high-resistance integrator (5) to optimize the upward curvature of the amplitude-frequency response curve caused by the resonance and improve the response flatness of the measurement system.

6. A small broadband transient pulse electric field measurement system according to claim 1, characterized in that: The link insertion loss compensation circuit (12) adopts a variable optical attenuator or an optical amplifier to compensate for temperature drift and link insertion loss.

7. A small broadband transient pulse electric field measurement system according to claim 6, characterized in that: The specific implementation steps of the real-time compensation of link insertion loss of the measurement system are as follows: Performing constant control on the output static optical power of the electro-optical direct modulation circuit (7); Detecting the received static photocurrent of the photoelectric conversion circuit (13) and using it as a feedback quantity for analog negative feedback control; Based on the received static photocurrent and the locally set reference value, the offset error is obtained, and based on PID control, the attenuation or gain of the variable optical attenuator or optical amplifier is dynamically controlled to complete the real-time compensation of the link insertion loss in the simulated closed loop.

8. A small broadband transient pulse electric field measurement system according to claim 6, characterized in that: The specific implementation steps of the measurement system temperature drift compensation are as follows: Use temperature assessment method to obtain system sensitivity temperature drift data; The temperature sensor (8) obtains the internal temperature of the sensor; Real-time dynamic adjustment of the static optical power output by the electro-optical direct modulation circuit (7) so that the static optical power is equal to 1 / G E (T) remains constant with temperature; where G E (T) is the optical modulation gain of the ambient electric field.

9. A small broadband transient pulse electric field measurement system according to any one of claims 1 to 8, characterized in that: When the receiving antenna and the incident electric field polarization are mismatched, the electrically short-pole antenna (4) needs to adopt a symmetrical dipole method to remove common-mode scattering.

10. A small broadband transient pulse electric field measurement system according to any one of claims 1 to 8, characterized in that: The shape of the shielding box (3) adopts a circular or square shielding box mechanical structure, which can effectively reduce the influence of the electromagnetic scattering of the side wall on the antenna receiving amplitude-frequency response.

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