High-power Signal Research Articles

Underdetermined blind source separation method of high-power microwave signals based on parametrically optimal variational modal decomposition

Abstract Reconnaissance and identification of enemy military targets in modern battlefields are becoming increasingly difficult. A high-power microwave signal separation method based on parameter-optimal variational modal decomposition (VMD) is proposed. Firstly, three different electromagnetic signals are mixed with high-power microwave signals and superimposed with additive Gaussian white noise as the mixed signals, and at the same time, a cubic nonlinear function and a limiting threshold function are introduced to process the mixed signals to simulate the complex battlefield electromagnetic signals intercepted by the receiver. Secondly, the Sparrow Search Algorithm (SSA) is used to globally optimize the decomposition parameters of the VMD algorithm, which decomposes the single-channel observation signal into a number of eigenmode functions. The VMD algorithm decomposes the single-channel observation signal into several intrinsic mode functions, then reconstructs the multidimensional observation signals, performs the singular value decomposition of the autocorrelation matrix of the multidimensional observation signals, estimates the number of source signals of the single-channel observation signals and calculates the correlation coefficients of the Intrinsic Mode Functions (IMFs) with the single-channel observation signals, so as to reconstruct the multichannel observation signals. Finally, the Joint Approximate Diagonalization of Eigenmatrices (JADE) algorithm is used for blind source separation of the multichannel observation signals. Simulation results show that the correlation coefficient between the separated signal and the high-power microwave source signal obtained by this method is 0.9015, and the method has good effectiveness and feasibility.

Electrochemical Impedance Spectra Measurements and Analysis of Polymer Electrolyte Membrane Electrolysis on Short Stack

Energy storage is becoming increasingly urgent as the share of fluctuating renewable energies increases in order to utilize the full potential of power plants and stabilize the grid in times of lower yields. Water electrolysis is therefore a promising solution for converting energy into hydrogen, which offers the opportunity of long term, even seasonal energy storage, albeit with lower round-trip efficiency compared to established battery technology.In a comparative technology assessment among AEM, SOEC, PEM, and AEL Polymer Electrolyte Membrane electrolysis excels in terms of power density >2 A/cm² and partial load stability, although it has disadvantages in terms on precious metal usage in catalysts and highly conductive corrosion resistant coatings for porous transport layers.In this work the method of electrochemical impedance spectroscopy will be investigated to gain insight into kinetics and transport processes at different operation conditions. Furthermore, we will investigate degradation losses and establish a state of health monitoring at a short stack level. Since stack designs for atmospheric PEM-Electrolysis enables easy single cell voltage monitoring the Impedance response to a superimposed applied AC-current signal can be picked up from each cell individually. Yet, the large footprint of “technical cells” leads to very low overall impedance thus making signal pickup and analysis more challenging compared to single cell or RDE measurements on small active area. Applying a precise high power signal, precise measurement of small AC contributions at a high DC background and the reduction of interferences with other components such as interferences from the power line or ripples in the DC part as well as temporal and spatial homogeneity of the sample under test are posing constraints for the recording and interpretation of electrochemical impedance spectra.We studied different setups of power electronics with add-on impedance spectrometers, both in serial and parallel configuration. The test object, shown in figure1b), was a 282 cm² active area PEM-electrolysis short stack of 3 cells derived from a an open source “generic PEM fuel cell stack” design which was operated at atmospheric pressure in a Greenlight G200 test rig (figure1a)) modified for electrolysis operation. A zahner IM6 impedance spectrometer in combination an EL1000 was used for the modulation of the alternating current signal. For comparison AC-modulation using a tunable AC frequency generator already implemented in the DC Power supply was studied. The current and voltage signals in this setup were recorded and analyzed using a high-speed transient recorder. The resulting impedance spectra of both devices are shown in Figure 1c) at different current densities. The spectra recorded were analyzed by standard methods via assignment of equivalent circuits. We studied the reproducibility and assignability of different time constants to different processes and equivalent circuit parameters depending on the operating conditions and the actuation amplitudes.From the results of these studies, we derived optimization potential for the electrolysis stack design. Furthermore, we studied degradation processes as a consequence of accelerated stress tests providing a data basis for electrolyzer stack operation and predictive maintenance. Figure 1

A Sturdy Shield: Enhancing 6G Fronthaul with Quantum-Security

Abstract: With the emergence of smart devices and the Internet of Things (IoT), 5G has been developed to meet the growing demand for transmission speeds and bandwidth. 5G overcomes the limitations of previous generations of technology, offering significant improvements in speed, latency, and stability. However, with the advancement of computational capabilities and the advent of quantum computers, security issues have become a pressing concern. Current technologies in 5G fronthaul rely on intrinsic security technologies, which are difficult to defend against quantum computer-based attacks. Consequently, this paper proposes a future mobile fronthaul architecture, such as 6G, which builds upon the 5G fronthaul network architecture while introducing quantum communication based on the BB84 protocol. This architecture enhances privacy protection and improves resistance to eavesdropping while maintaining the original performance. Additionally, the paper models the architecture to explore its noise resistance, using forward and backward spontaneous Raman scattering power as indicators, and demonstrates the system's feasibility under the influence of high-power 6G signals. The potential applications of this architecture are also examined. The results indicate that the quantum-secure 6G fronthaul network represents a significant breakthrough. It not only meets the stringent security requirements of modern communication but also enables a wide range of applications, paving the way for a safer and more interconnected digital future.

Calorimetric Measurements of a High-Power RF Signal

Development of a high-power RF signal meter based on the method of calorimetric measurements, which in some cases is the only possible one is presented. The device is as a system of elements exchanging either energy or information, the operation and interconnection of which ensures the stability of its functioning. The main elements of the device are: a coordinated load and a two-circuit water-air cooling system that convert RF energy first into thermal electrical energy, and then into internal energy of the coolant (working fluid). The measurement and control system provides information display on the monitor and generation of internal control signals. The work focuses on the process of converting electromagnetic energy into internal energy of the coolant, since the matched RF load is integrated into the cooling system and requires special design and technological solutions to ensure efficient operation. A cooling and measurement system has been designed to test the developed RF absorber with a power of up to 5 kW. The parameters of the cooling system were determined based on minimizing the time to achieve thermal equilibrium (time to establish readings) and the set parameters (input temperature no more than 35 °С, temperature difference no more than 40 °С). Based on calculations of the electrodynamic model constructed by the partial domain method, the geometric dimensions were determined at which the voltage standing wave ratio of the load in the operating frequency range (from DC to 1300 MHz) will be the smallest. The article presents the results of designing a high-frequency wattmeter cooled by a liquid (water), examines the thermophysical processes occurring in it and the influence of the presence of a coolant in the cooling circuit.

Broadband nonlinear delay and sum (NL-DAS) for baseline-free damage imaging using a sparse sensor network

The Delay and Sum (DAS) method is a well-known damage imaging technique in sparse array guided wave imaging. However, the DAS method requires prior knowledge on the stable baseline state, which makes it ineffective under different operational or environmental conditions, e.g. temperature and moisture, and altered experimental settings, e.g. degraded bonding quality of sensors.This paper proposes a Nonlinear Delay and Sum (NL-DAS) method which does not require prior knowledge about the baseline state, but instead exploits the presence of nonlinear wave/defect interactions. Relatively high-power broadband sweep sine signals are supplied to a sparse sensor array to activate a multitude of nonlinear wave/defect interactions. Application of time–frequency filtering to the response signals allows the isolation of damage-induced broadband nonlinear responses. The isolated broadband nonlinear response signals are subsequently decomposed into a series of narrowband tone burst responses from which a set of damage maps are constructed. To improve the quality of the constructed damage maps, an automated framework is proposed to obtain the frequency-dependent directional group velocities without requiring prior knowledge on material properties. Finally, the resulting set of damage maps is fused into a single broadband NL-DAS damage map.The proposed broadband NL-DAS approach is demonstrated on a simulation dataset, generated with 3D Finite Element method, which is representative for a cross-ply carbon fiber reinforced polymer (CFRP) containing a delamination defect. The damage imaging performance is studied for different test conditions in terms of (i) signal-to-noise ratio, (ii) number of sensors and (iii) excitation bandwidth. Experimental validation is illustrated on a CFRP plate containing a barely visible impact damage, and on a CFRP A320 component with a disbond at one of the stiffeners.

Broadband infrared imaging governed by guided-mode resonance in dielectric metasurfaces

Nonlinear metasurfaces have experienced rapid growth recently due to their potential in various applications, including infrared imaging and spectroscopy. However, due to the low conversion efficiencies of metasurfaces, several strategies have been adopted to enhance their performances, including employing resonances at signal or nonlinear emission wavelengths. This strategy results in a narrow operational band of the nonlinear metasurfaces, which has bottlenecked many applications, including nonlinear holography, image encoding, and nonlinear metalenses. Here, we overcome this issue by introducing a new nonlinear imaging platform utilizing a pump beam to enhance signal conversion through four-wave mixing (FWM), whereby the metasurface is resonant at the pump wavelength rather than the signal or nonlinear emissions. As a result, we demonstrate broadband nonlinear imaging for arbitrary objects using metasurfaces. A silicon disk-on-slab metasurface is introduced with an excitable guided-mode resonance at the pump wavelength. This enabled direct conversion of a broad IR image ranging from >1000 to 4000 nm into visible. Importantly, adopting FWM substantially reduces the dependence on high-power signal inputs or resonant features at the signal beam of nonlinear imaging by utilizing the quadratic relationship between the pump beam intensity and the signal conversion efficiency. Our results, therefore, unlock the potential for broadband infrared imaging capabilities with metasurfaces, making a promising advancement for next-generation all-optical infrared imaging techniques with chip-scale photonic devices.

Finite element analysis of a Helmholtz transducer jointly driven by a trilaminar ring and a piezoelectric circular tube

Abstract Crosswell seismic survey can image the crosswell geological anomalies with high resolution in 3D. To effectively conduct crosswell seismic survey, it is necessary to use a seismic source capable of transmitting low-frequency and high-power signals in a compact size. In this paper, a novel Helmholtz transducer is proposed, which utilizes both the bending vibrations of the trilaminar ring and the radial vibrations of the piezoelectric circular tube to simultaneously drive the vibration of the Helmholtz liquid cavity. This design reduces the resonant frequency of the liquid cavity while enhancing the transmitting voltage response at the liquid cavity resonant frequency. The influence of the inner radius of the trilaminar ring, the outer radius of the ceramic ring and the length of the piezoelectric circular tube on the liquid cavity resonant frequency and the transmitting voltage response at the liquid cavity resonant frequency is simulated using the finite element method. The simulation results provide a theoretical foundation for optimizing the design of such transducers.

Testing and Analysis of PIM Performance in a Passive DAS Network - Experimental Approach

Passive intermodulation (PIM) poses a significant challenge in telecommunication networks, with potentially severe impacts on network performance and signal integrity if not addressed during the initial deployment phase. This study investigates PIM levels within a passive distributed antenna system (DAS) network for cellular mobile radio communication across multiple floors of a building. The network comprises coaxial cables, connectors, splitters, combiners, and antennas structured in a systematic plan. This work used the experimental method to test for PIM in the network used for this investigation. Designed as a multicarrier system, it handles RF signals across frequencies of 700/850MHz, 1900MHz, 2100MHz, and 2600MHz. On-site PIM testing was conducted during the network deployment phase to analyze the behavior of high-power RF signals. Utilizing Kaelus iQA-1921C and iQA 850C series PIM analyzers, tests were conducted following known industry codes and standards. High RF power was preset to 43dBm for full band, 35dBm for high bands, and 25dBm for low band. The test equipment was calibrated on high PIM load and low PIM load. Test points were selected at both vertical and horizontal subsystem cabling structures, focusing on riser cables. The standard baseline performance PIM levels was set to -150dBc. The analysis focused on examining the characteristics of PIM signals captured via time-domain PIM traces, investigating the impact of altering the frequency of the two-tone signal on the IM3 frequency component, and highlighting the importance of selecting an appropriate frequency for the two-tone signal that is not positioned near the edges. Results were based on pass or fail test, and resolution measures were taken to mitigate interference.

Design of X-Band Circulator and Isolator for High-Peak-Power Applications.

This paper presents a design of a X-band circulator-isolator for handling high-peak-power applications. The device consists of two cascade-connected ferrite circulators, with one dedicated to transmission and the other to small-signal reception coupled with high-power signal isolation. To improve the power capacity, a layer of poly-tetra fluoroethylene (PTFE) film is placed above and below the circulator's and the isolator's center conductors. Measurement results show that the device is capable of withstanding a peak power of 7000 W, with an insertion loss of <0.3 dB at the transmitting port. Similarly, it sustains a peak power of 6000 W with an insertion loss of <0.5 dB at the reception port. Moreover, the proposed design achieved isolation between the transmitting and receiving ends of >20 dB with a VSWR < 1.2 at each port. Thermal analysis shows that the maximum relative ambient temperature rise is 15.11 ∘C. These findings show that the proposed device achieves low-loss transmission of high-peak-power signals in the transmit channel and reverse isolation of high-peak-power signals in the receive channel.

Substitution modification mechanism of YIG ferrite with a high spin-wave linewidth via fast relaxation Dy3+ ion doping and sintering modulation

YIG ferrites are often used as nonreciprocal materials in microwave ferrite devices because of their low microwave magnetic and dielectric losses. To comply with the trend of planarization and integration of microwave systems, YIG ferrites are required to withstand higher powers. In this study, we investigated the variation in material microwave properties with material composition and microstructure. The experimental results show that doping the material with high-relaxation ions Dy3+ combined with modulating the sintering holding time can effectively improve the material’s high-power microwave signal withstanding capability, and YIG ferrite with a spin-wave line width of 18.7 Oe is obtained. In addition, when the average grain size of the material is controlled within 5 μm, the effect of the average grain size on the spin-wave linewidth is more noticeable than that of Dy3+ substitution.

Microwave gain-assisted optical limiter in molecular magnets.

We investigate the optical properties of a crystal of molecular magnets within the microwave frequency range. It is shown that in the presence of a static magnetic field and applying a coupling laser field in the microwave region, reverse saturable absorption in the microwave domain can be induced in molecular magnets. Notably, the intensity and detuning of the coupling laser field are shown to exert significant control over electromagnetically induced optical limiting (OL). Thus, the OL behavior can safeguard the active sensors in seekers against the saturation as they approach microwave sources. What we believe to be a novel optical limiting phenomenon is introduced, wherein the crystal amplifies noiselessly weak input microwave fields in the linear region of the optical limiter while attenuating intense input fields. Consequently, these findings suggest the potential for actively controlling radars or seekers by exploiting a gain-assisted optical limiter to detect microwave sources with weak signals. The static magnetic field, acting as a pivotal parameter, significantly influences the attainment of OL performance across a broad spectrum of microwave frequencies. We anticipate that the outcomes of this investigation could be applied in microwave photonics to enhance the ranging capabilities of missile seekers or radars via the identification of weak signal targets. Additionally, the research highlights the protective capabilities of microwave sensors against high-power microwave signals. Finally, the open aperture Z-scan technique is employed to confirm the induced gain-assisted optical limiting behavior in molecular magnets.

AI-DRIVEN TRANSFORMER NETWORKS IN SHARED SPECTRUM FOR ENHANCED SIGNAL PROCESSING FOR NONLINEAR RECEIVERS

Communication systems face challenges from high-power adjacent channel signals, or blockers, inducing nonlinear behavior in RF front ends. Ensuring robust performance in the presence of blockers is crucial for IoT and other spectrum-consuming devices coexisting with advanced transceivers. This paper proposes a flexible, data-driven solution using a Deep Belief Network (DBN) to mitigate third-order intermodulation distortion (IMD) during demodulation. Numerical evaluations of AI-enhanced receivers employing DBN as an IMD canceler and demodulator show significant improvements in bit error rate (BER) performance. The effectiveness of DBN varies with RF front end characteristics, notably the third-order intercept point (IP3).

Noise equalization scheme based on probabilistic shaping and complex-valued ANN for dual-polarization continuous spectrum NFDM system with high-order modulation formats

In dual-polarization continuous spectrum nonlinear frequency division multiplexing (DP-CS NFDM) systems, the presence of noise destroys the independence between subcarriers in the nonlinear spectral domain (NSD). Additionally, as the modulation order and the number of subcarriers increase, the signal power increases and the effect of noise on the performance of the system becomes more severe. In this paper, we propose a noise equalization scheme based on probabilistic shaping (PS) and complex-valued neural network (c-ANN) for dual-polarization transmission CS NFDM system with high-power signals. The scheme utilizes PS to reduce the distribution probability of high-power constellation points of the signal with high-order modulation format, to decrease the peak-to-average power ratio of the continuous spectrum subcarriers and the average power of the signal, which can achieve the suppression and equalization of the amplifier spontaneous emission (ASE) noise and the processing noise. In addition, the scheme uses the c-ANN to effectively reduce the correlation between subcarriers caused by the noise and improve the system performance. The effectiveness of the proposed scheme is verified in the DP-CS NFDM system, and the simulation results show that the Q-factor gain is enhanced by roughly 1.1 dB and 0.8 dB for the number of subcarriers of 128 and 256, respectively, compared to the classic nonlinear Fourier transform (NFT) scheme. Among them, with different noise figure (NF) and satisfying the 7% forward error correction (FEC) threshold, the 512QAM signal with an entropy of 8 after equalization increase the transmission distance by 80 km longer than that of uniform 256QAM signals for the number of subcarriers of 128. Compared with the joint scheme based on PS and real-valued neural network (r-ANN), this scheme has better equalization performance at the same complexity, and the complexity can be reduced by 50% under the same performance.

The conceptual design of the high-efficiency 400 kW solid-state power station at 352 MHz for the European spallation source

Abstract This paper introduces an innovative conceptual design of a 400 kW solid-state power amplifier (SSPA) station and presents preliminary measurements for the key components. Recent advancements and benefits of solid-state technology have made the prospect of replacing vacuum tubes increasingly appealing. Historically, a significant challenge was the limited output power capacity of individual solid-state transistors, necessitating the integration of numerous units to generate high-power microwave signals in the range of hundreds of kilowatts. However, modern transistors capable of producing over 2 kW of output power have emerged, facilitating this transition. Another weak point was low power efficiency in high-power operating mode. The advanced rugged technology (ART) of solid-state devices enables the utilization of these transistors in nonlinear and switching operating classes, thereby enabling the creation of high-efficiency high-power amplifiers. In this conceptual design, 264 SSPA modules based on ART, each with a power output of 1.6 kW, are combined. The measurements revealed a single SSPA capable of delivering up to 2 kW output power with a power efficiency of 73% at frequency of 352 MHz. Due to the minimal losses during module combination and working SSPA in Class-C operation mode, the power efficiency of the station is expected to closely mirror that of a single module.

A Unified Rate-Splitting Framework for Secure Spectrum Sharing via Joint Precoding Optimization

To handle the security problem of cognitive radio (CR) systems, secondary users (SUs) are able to be designed to assist the primary user (PU) in secure transmission. To realize the spectrum sharing among CR users, we adopt the rate-splitting multiple access (RSMA) properly, with nonorthogonal multiple access (NOMA) and space division multiple access (SDMA) as its special cases. In this article, we set up a unified rate-splitting framework to guarantee the safe spectrum sharing through multiple multiaccess strategies, without the knowledge of wiretap channels. The precoding vectors at the transmitter are conjointly designed to boost the transmission of common stream, which is from both PU and SU. Besides, the private stream of the downlink CR system can be well secreted in the high-power common signal. As for NOMA and SDMA, when the message of SU is regarded as the friendly jamming signal, the security transmission requirement of PU can be similarly guaranteed via precoding design. Simulations validate that the rate-splitting framework we established can be effective in ensuring the spectrum sharing security for the secure users through RSMA, and the security for NOMA and SDMA is also able to be promoted through adjusting our designed framework.

Bayesian safety surveillance with adaptive bias correction.

Postmarket safety surveillance is an integral part of mass vaccination programs. Typically relying on sequential analysis of real-world health data as they accrue, safety surveillance is challenged by sequential multiple testing and by biases induced by residual confounding in observational data. The current standard approach based on the maximized sequential probability ratio test (MaxSPRT) fails to satisfactorily address these practical challenges and it remains a rigid framework that requires prespecification of the surveillance schedule. We develop an alternative Bayesian surveillance procedure that addresses both aforementioned challenges using a more flexible framework. To mitigate bias, we jointly analyze a large set of negative control outcomes that are adverse events with no known association with the vaccines in order to inform an empirical bias distribution, which we then incorporate into estimating the effect of vaccine exposure on the adverse event of interest through a Bayesian hierarchical model. To address multiple testing and improve on flexibility, at each analysis timepoint, we update a posterior probability in favor of the alternative hypothesis that vaccination induces higher risks of adverse events, and then use it for sequential detection of safety signals. Through an empirical evaluation using six US observational healthcare databases covering more than 360 million patients, we benchmark the proposed procedure against MaxSPRT on testing errors and estimation accuracy, under two epidemiological designs, the historical comparator and the self-controlled case series. We demonstrate that our procedure substantially reduces Type 1 error rates, maintains high statistical power and fast signal detection, and provides considerably more accurate estimation than MaxSPRT. Given the extensiveness of the empirical study which yields more than 7 million sets of results, we present all results in a public R ShinyApp. As an effort to promote open science, we provide full implementation of our method in the open-source R package EvidenceSynthesis.

A Novel ppb-Level Sensitive and Highly Selective Europium-Based Diketone Luminescent Sensor for the Quantitative Detection of Aluminum Ions in Water Samples

A novel Eu(tta)3([4,4′-(t-bu)2-2,2′-bpy)] complex (tta-thenoyltrifluoroacetone), a ratiometric luminescent-based optical sensor for the quantitative determination of aluminum ion, is synthesized and characterized using XRD and 1H NMR. The XRD data reveal the slightly distorted octahedral structure. The complex displays a bright red emission at 613 nm in methanol which is characteristic of europium (III) complexes. Upon the addition of Al3+ ions, the red emission disappears, and a new blue emission at 398 nm emerges, manifesting the ratiometric nature of the complex. The turn-off of the red emission and turn-on of the blue emission are attributed to Eu-Al trans-metalation, as supported by Raman data that show the emergence of Al-O vibrations at 418, 495, and 608 cm−1 concomitant with the disappearance of Eu-O and Eu-N bond vibrations. Most aluminum sensors are known to suffer from interferences from other metals including Cu2+, Co2+, and Cd2+. However, the sensor reported here is tested for 11 common cations and shows no interference on sensitivity. To the best of our knowledge, this is the first known Eu-based luminescence sensor that successfully exhibited the ability to detect aluminum ions in ppb levels in aqueous environments. The calculated Al3+ binding constant is 2.496 × 103 ± 172. The complex shows a linear relationship in the range of 0–47.6 ppb (1.76 × 10−6 M) Al3+ and the limit of detection (LOD) is 4.79 ppb (1.77 × 10−7 M) in MeOH. ICP-OES is used for validation of the sensor complex in water and then it was used for quantitative detection of Al3+ ions in water as a real-life application. The complex can accurately detect Al3+ ions in the range of 4.97–24.9 ppb (1.84 × 10−7 M–9.2 × 10−7 M) with an LOD of 8.11 ppb (2.99 × 10−7 M). Considering that the aluminum ion serves no recognized function within the human body, its accumulation can lead to severe neurological disorders, including Parkinson’s and Alzheimer’s diseases. With the LOD value significantly lower than the WHO-recommended maximum permissible level of 200 ppb for aluminum in drinking water, even without high-power laser-aided signal enhancement, the sensor shows promise for detecting trace amounts of aluminum contamination in water. Therefore, it can significantly aid in the monitoring of even the smallest aluminum ion contamination in drinking water, industrial effluents, and natural water bodies.

Synchronization of quantum communications over an optical classical communications channel.

Precise synchronization between a transmitter and receiver is crucial for quantum communications protocols such as quantum key distribution (QKD) to efficiently correlate the transmitted and received signals and increase the signal-to-noise ratio. In this work, we introduce a synchronization technique that exploits a co-propagating classical optical communications link and tests its performance in a free-space QKD system. Previously, existing techniques required additional laser beams or relied on the capability to retrieve the synchronization from the quantum signal itself; this approach, however, is not applicable in high channel loss scenarios. On the contrary, our method exploits classical and quantum signals locked to the same master clock, allowing the receiver to synchronize both the classical and quantum communications links by performing a clock-data-recovery routine on the classical signal. In this way, by exploiting the same classical communications already required for post-processing and key generation, no additional hardware is required, and the synchronization can be reconstructed from a high-power signal. Our approach is suitable for both satellite and fiber infrastructures, where a classical and quantum channel can be transmitted through the same link.

Research on simulation method for nonlinear effects of airborne SAR electromagnetic interference

In order to simulate the nonlinear interference effect of high-power electromagnetic signals on airborne Synthetic Aperture Radar (SAR) imaging, the walk–stop geometric modeling of airborne SAR was established, and the range time-domain pulse coherence method was used to simulate SAR echo. By establishing a SAR receiver RF channel model, the interference mechanism of high-power electromagnetic signals is combined on RF front-end devices, the nonlinear effects on the echo signal when high-power electromagnetic signals enter the receiver are simulated, and finally the range Doppler algorithm is used to image the echo signal and the interference signal. A method for evaluating the interference effect of high-power electromagnetic signals on airborne SAR imaging using the correlation coefficient of images was proposed. The results showed that the change in the correlation coefficient of images before and after interference relative to the interference signal ratio was consistent with the image interference effect. The correlation coefficient showed a stepped trend with the change in the interference signal ratio, and there was a saturation effect after the interference effect reached a certain level.

Tunable, coherent optical comb source via on-chip bidirectional coupling.

A tunable comb source is demonstrated through gain switching on a three-sectioned photonic integrated circuit (PIC). The PIC consists of two mutually coupled lasers connected by a passive waveguide. One of these is a tunable, two-section, single mode laser. The second laser is a simple Fabry-Perot cavity laser which can be phase-locked with the single mode laser via bidirectional coupling. Frequency combs are produced by gain switching the Fabry-Perot laser by applying a high-power radio frequency signal. Combs are generated with line spacings ranging from 3.5 to 8 GHz. The on-chip bidirectional coupling causes the comb to also be generated in the two-section device. Despite the lack of on-chip optical isolation between the lasers, the resulting combs are stable. Numerical simulations using a delay-differential model reproduce the results and reveal the important role played by the short delay times inherent to on-chip integration in this stability.