Intense solar activity is a major driver of hazardous space weather. The associated processes, including strong electromagnetic radiation, plasma ejections, and high-energy particle acceleration, can significantly disturb the Sun-Earth environment within a short time and further trigger a series of chain effects such as ionospheric disturbances and high-frequency communication interruptions, thereby posing serious threats to critical sectors including aviation, aerospace, and telecommunications. With the continuous advancement of space technology, society has placed increasingly higher demands on space-weather monitoring with high accuracy and reliability. Consequently, the development of high-performance solar radio observing systems has become an important approach to improving space-weather forecasting and mitigation capabilities. In solar physics, radio emissions at different frequencies correspond to radiation mechanisms occurring at different heights and under different plasma-density conditions in the solar atmosphere. Therefore, obtaining observational data with the broadest possible frequency coverage is not only crucial for revealing the acceleration mechanisms of high-energy electrons in solar flares, but also provides important support for understanding the spatiotemporal evolution of solar eruptions. From the perspective of instrumentation development, it is thus of great significance to establish solar radio observing systems with broader frequency coverage and higher temporal and spectral resolutions. This paper systematically reviews the development of solar radio observing instruments worldwide, summarizes the structural characteristics of representative radio telescopes and spectrometers from the decimeter, centimeter, to millimeter wavelength bands, and compares their system designs, signal-processing chains, and frequency coverage. On this basis, the current status of solar radio observing facilities is analyzed, and the key technical bottlenecks and future development trends are discussed. It is hoped that this review will provide useful references for the planning, design, and key-technology development of future solar radio observing systems.

Using high-resolution data from the Chashan Broadband Solar Radio Spectrometer at meter wavelengths of the Chinese Meridian Project-Phase II, C. Li et al. identified a novel fine spectral structure of solar radio bursts, termed periodic beaded stripes, and proposed a generation mechanism. Here we report additional events and develop a quantitative method to determine the physical conditions in the emission region. Periodic stripes tend to occur in the postphase of flares and are associated with complex magnetic configurations. They repeat on subsecond timescales and show similar to 0.1 s bead-like modulations, often accompanied by low-frequency absorptions. Modeling the chained stripes with linear kinetic theory of the double plasma resonance (DPR) instability constrains the source-region magnetic field to 0.2-1.7 G and the plasma density to (1-7) & times; 108 cm-3. The former follows the drift of individual stripes, and the latter tracks the overall trend. This study summarizes the key properties of periodic beaded stripes and establishes a quantitative DPR-based framework for coronal diagnostics.

Solar radio bursts from decimeter to centimeter wavelength originate from radiations from coherent to incoherent mechanism. This spectral domain hosts a rich variety of fine structures that encode critical information about energetic electron beams, coronal magnetic fields, and ambient plasma conditions-key elements for understanding particle acceleration and energy release during solar flares. To exploit this diagnostic potential, a broadband observing system with high time and frequency resolution is essential. In this study, we designed and developed the Chashan Broadband Solar Decimetric Spectrometer (CBSdm), which enables high-precision observation of solar radio bursts in the 3-6 GHz frequency band. The system employs a 6 m parabolic antenna with a log-periodic dipole array feed, and utilizes nanosecond-level microwave switching technology to construct a dual-channel analog receiving chain (3.1-4.4 GHz/4.6-5.9 GHz). Real-time spectral processing is achieved via a 14-bit 3 GSPS analog-to-digital converter and an Field Programmable Gate Array-based digital backend. Key performance metrics include a noise figure of 2 dB, sensitivity of -77.9 dBm@2.6 GHz, and system linearity better than 0.998. Relative calibration was performed and cross-validated with data from the Learmonth Observatory. Since its deployment in 2023 October, the system has successfully captured X-class flare events, with dynamic spectra exhibiting typical continuum features and multi-frequency synchronous evolution. The coordinated observations of CBSdm (3-6 GHz) and CBScm (6-15 GHz) provide continuous gyrosynchrotron spectra covering the optically thick to thin transition, enabling diagnostics of flare magnetic fields and nonthermal electron distributions.

With the increasing volume of solar radio spectrogram observation data, deep learning-based recognition and detection of solar radio bursts have become a key research direction. However, most studies on meter-wave solar radio spectrogram recognition and detection rely on proprietary datasets, and publicly available datasets remain scarce. To address this issue and facilitate the use of public datasets for deep learning model validation, thereby promoting the development of automatic detection methods for meter-wave solar radio spectrogram, we propose a new solar radio spectrogram dataset. The dataset is constructed from meter-wave solar spectrogram observation data from the Learmonth Observatory in Australia and the meter-wavelength observing system of the Chashan Solar radio Observatory (CSO) of Shandong University. Experimental results demonstrate that the proposed dataset effectively supports the recognition and detection of solar radio spectrograms, providing essential data resources for the intelligent recognition of solar radio burst features.

An ultrawideband, optically transparent metamaterial absorber (MMA) was designed and fabricated, employing a convolutional neural network (CNN) in conjunction with a particle swarm optimization algorithm (PSO). The CNN enables a rapid prediction of reflection coefficients, thereby significantly simplifying the design process. PSO performs global optimization to fine-tune structural parameters based on CNN predictions, achieving configurations that meet specified absorption targets. The combination of CNN and PSO has formed an innovative reverse inverse process, which can achieve on-demand design of the MMA according to the desired absorption spectra. The designed MMA employs an optically transparent indium tin oxide (ITO) conductive film. With a thickness of 8.5 mm, the absorber achieves absorptivity exceeding 95% across the ultrawideband frequency range from 14.2 to 37.8 GHz, corresponding to a relative bandwidth of 90.8%, and exhibits excellent angular stability. Based on the simulation results, physical prototypes with dimensions of 250 x 250 mm2 were fabricated. Experimental measurements demonstrate strong agreement with the simulated reflection coefficients and confirm the broadband absorption performance. The proposed MMA exhibits both high optical transparency and efficient broadband electromagnetic absorption, making it highly suitable for applications in multispectral stealth technology and electromagnetic compatibility engineering.

Abstract During rocket launches, atmospheric disturbances significantly impact the ionosphere, generating Traveling Ionospheric Disturbances (TIDs). These disturbances can affect radio communications and navigation systems and may pose risks to high‐speed aerospace vehicles. By analyzing TIDs induced by SpaceX rocket launches, this study aims to understand the ionospheric response to rocket launches and explore potential high‐speed flight trajectories. This work investigates 153 Falcon rocket launch events from January 2023 to June 2024. First, ionospheric data undergoes preprocessing, where the Savitzky‐Golay filter and Butterworth filter are applied to extract ionospheric disturbances caused by rocket launches, and disturbance images are subsequently generated. Next, the occurrence time, duration, and spatial extent of these disturbances are analyzed, and TID images are manually labeled. Finally, using the labeled TID images, a deep learning‐based ionospheric disturbance detection model is trained with a target detection algorithm. This model achieves an identification accuracy of approximately 83% in detecting TIDs within TEC images.

The detection of solar radio bursts (SRBs) is of great significance for solar physics research and space weather forecasting. In recent years, intelligent recognition and detection of SRBs based on deep learning has become an important research direction in solar radio studies. However, due to the complex characteristics of solar radio spectrograms and the presence of strong noise interference, the detection accuracy of SRBs still needs to be further improved. In this paper, observational data from the Learmonth Observatory of Australia and the Chashan Solar Observatory (CSO) of Shandong University are used to construct a meter-wave SRB dataset. Then, the You Only Look Once 11 network is improved to enhance the detection performance for different types of SRBs (Type II, III, IIIs, IV, and V SRBs). Experimental results demonstrate that the proposed method effectively improves the detection accuracy of SRBs. Finally, the trained detection model is integrated into a self-developed intelligent solar radio observation data analysis system, which is further deployed at the CSO to realize automatic burst identification and physical parameter extraction from observational data. This provides an intelligent data analysis tool for solar radio research. By comparing the burst parameters extracted by manual statistics and intelligent detection, the intelligent detection method is shown to meet the requirements. Therefore, this study promotes the integration of artificial intelligence and solar radio research, providing valuable experience for the development of large-scale models in the field of space science.

To meet the calibration requirements of the 50-70 GHz solar flare millimeter-wave spectrometer designed by Shandong University, this study develops a low-cost truncated-cone array blackbody radiation source. The source achieves an average emissivity of 0.9996 across the operational band and ensures surface temperature uniformity better than 0.3 degrees C. Electromagnetic simulations based on the finite integration technique (FIT) were conducted to optimize cone height, array periodicity, and absorber coating thickness, while thermal simulations confirmed that the truncated geometry effectively reduces axial temperature gradients and improves brightness temperature uniformity with only a slight reduction in emissivity. An FPGA-based brightness temperature control system further enabled stable regulation within +/- 0.27 degrees C. Experimental validation included both a two-point calibration and a solar-blackbody comparison. These results provide qualitative validation that the proposed truncated-cone array blackbody can be applied as a calibration reference for solar observations. Future work will focus on 3D-printed modular arrays to enhance uniformity, reproducibility, and multichannel adaptability.

Spike-type III burst pairs represent a distinct class of solar radio emissions in which clusters of spike-like bursts appear atop the high-frequency onset of type III bursts. Using high time–frequency resolution data from the Chashan Broadband Solar radio spectrometer at meter wavelengths (CBSm), we present the largest statistical study to date of such events, comprising 502 spike–type III pairs from 35 events recorded between November 2023 and October 2025. We find that spike-like clusters systematically precede their associated type III bursts by 0.5–3 s in time (∼87% of pairs) and by 3–30 MHz in frequency (∼80%), a temporal and spectral offset that differs from earlier reports. The spike-like clusters exhibit diverse morphologies, including point-like, blob-like, drifting, and diffuse structures, with durations of ∼0.5–5 s and bandwidths of 15–150 MHz. Bidirectional drifting structures with rates of ∼20–100 MHz s−1 are observed, consistent with source motion both toward and away from the Sun. Furthermore, spike emission is predominantly strongly circularly polarized, with more than 64% of clusters showing maximum polarization exceeding 0.6, in stark contrast to the generally weak polarization of type III bursts. These findings point to an origin of the spike radiation in a multi-scale, inhomogeneous, and highly dynamic electron-acceleration region, providing novel observational constraints on the mechanisms underlying coherent solar radio bursts.

The radioheliograph employs synthetic aperture imaging techniques to achieve high-resolution observations of the Sun. Enhanced synchronization among the antenna elements significantly improves the dynamic range (DR) of the resulting images. This article presents a digital receiver system designed for solar radio observations, which utilizes a rubidium atomic clock to ensure precise synchronization. Combined with high-accuracy delay compensation, the system implements a fully digital and distributed synchronous acquisition architecture. The processing core is based on an XCKU115 FPGA, which enables high temporal resolution (<1 ms) and high spectral resolution (<3 MHz)-both essential for accurate radio spectral measurements. The experimental results demonstrate that the system achieves two-level, four-scale delay compensation with an error of less than 10 ps, while the overall timing accuracy across the full signal chain remains about 100 ps. This work provides a foundation for the development of next-generation radioheliographs, offering high applicability and system scalability.

Interferometry technology stands out as a significant trend in radio observation systems, where correlators act as pivotal components responsible for real-time data processing. Responding to the operational needs of Shandong University Chashan Solar Radio Observatory's 39.540-GHz solar radio binary interferometer, a 1.25-Gs/s FX-type digital correlator was developed. Following a modular framework, the digital correlator comprises three core modules: data acquisition, correlation processing, and data transmission. Additionally, it incorporates adjustable delay compensation and amplitudephase consistency calibration functionalities to ensure precise signal alignment and system coherence. The coherent noise injection method is employed to assess inherent amplitudephase discrepancies in the analog front end (AFE), while real-time compensation calibration factors are implemented in FPGA to rectify the amplitudephase consistency of the AFE. Experimental design and validation were executed, showcasing that the correlator, featuring dual channels, a 1.25-Gs/s sampling rate, and 14-bit resolution, achieves an adjustable delay compensation accuracy of 0.8 ns. Post-amplitudephase consistency calibration of the AFE links reveals an amplitude error of approximately +/- 0.2 dB and a phase error of approximately +/- 7 degrees, indicating notable calibration efficacy. Subsequently, the RTL design of the digital correlator presented in this article was verified, confirming the logical coherence of the RTL design and validating the accuracy of the correlation output results through experimental design. The development of this correlator not only finds application in other interferometric measurement system scenarios but also establishes a research groundwork for future digital correlator advancements in the comprehensive aperture solar imager slated for development by the research group.

During solar flare eruptions, millimeter-wave radiation is emitted, which is highly efficient and sensitive to high-energy electrons, allowing for the extraction of unique magnetic field information. Therefore, we have developed a 50–55 GHz solar millimeter-wave radiometer system. The system employs a 50 cm diameter Cassegrain antenna to receive circularly polarized solar radiation signals. These signals enter the analog front-end system, where they undergo power division, filtering, and detection operations, resulting in voltage signals. Subsequently, the signals are processed by the digital receiver for analog-to-digital conversion and smoothing and are finally transmitted to the host computer via the RS422 protocol to display the intensity of solar radiation. The system’s performance metrics are as follows: a noise figure of <2.5 dB, system linearity ≥0.9999, a time resolution range of 0.001–1 s, and a dynamic range exceeding 30 dB. The system began routine observations in 2024 October and successfully captured the world’s first 50 GHz band solar flare data in December. Currently, the system is effectively observing during the 25th solar activity maximum period, which is expected to provide valuable data for solar physics research.

This study designed a kind of novel triple-band, low-profile, shared-aperture, and high-gain cavity antenna by incorporating an artificial magnetic conductor (AMC) metamaterial. An AMC metamaterial plate capable of acting as mu-negative metamaterials (MNGs) at three distinct frequencies was developed; serving as the covering layer of the cavity antenna, this plate was constructed with three patch antennas as radiation sources. Fabricated in the printed circuit board technology, the antenna was thoroughly tested in an anechoic chamber, and the experimental outcomes demonstrated excellent congruence with the simulation data. Notably, operating at 6.33, 9.48, and 10.80 GHz, the three radiation sources of the antenna can effectively share a single radiation aperture, achieving impressive gains of 14.2 dBi, 17.3 dBi, and 12.3 dBi, respectively. As a breakthrough, this technology overcomes the limitation of traditional cavity antennas, which are often constrained to single-frequency operation. Furthermore, the antenna cavity developed in this study boasts a minimal thickness of only 10 mm, significantly slimmer than the conventional half-wavelength thickness limit of resonant cavities. In summary, by combining such advantages as low profile, triple-frequency capability, high gain, and extensive integration, this innovative antenna meets the requirements for antenna components in the new generation of wireless communication systems.

Solar flares, coronal mass ejections, and other solar radio burst phenomena release substantial amounts of solar radiation energy, resulting in adverse space weather conditions and posing significant hazards in space. Spectrum analysis conducted manually or with traditional image processing algorithms is limited by low efficiency and accuracy. This paper investigates solar radio burst detection methods and their applications. Five solar radio burst detection methods—Continuous-3 σ , Sum Flux-3 σ , Continuous Slope, Sum Flux Slope, and Sum Flux Continuous-3 σ —are developed and validated using data from the Japanese NoRP and the Australian Learmonth Solar Radio Observatory. The results show that all five methods can detect solar radio bursts to some degree. Considering the combined metrics of success rate, false detection rate, and real-time performance, the Sum Flux Continuous-3 σ method is deemed the optimal method among the five. Additionally, the Sum Flux Slope method, which is not reliant on historical data, demonstrates superior universality. Finally, we implement the Sum Flux Slope method on a 39.5–40 GHz two-element interferometer, achieving real-time solar radio burst detection in the upper computer software. The method also includes functionalities for email alerts, burst information recording, and control parameter adjustment, confirming its effectiveness and practicality. Test results demonstrate the method’s effectiveness in real-time solar radio burst detection.

Solar eruptions, including flares and coronal mass ejections, are the most energetic phenomena in the solar system. These explosive events accelerate high-energy particles and generate electromagnetic radiation from radio to gamma-ray wavelengths, producing heliospheric disturbances and acting as primary drivers of space weather hazards. Wide-band solar radio observations, spanning decameter to centimeter wavelengths, constitute a key component of the Chinese Meridian Project (CMP) for tracking and monitoring solar eruptions from the Sun's atmosphere into interplanetary space. The technique of solar radio imaging spectroscopy is still challenging and new. The Mingantu Spectral Radioheliograph (MUSER) with three arrays at low (30-400 MHz), intermediate (400 MHz-2 GHz), and high (2-15 GHz) frequency bands images the solar atmosphere in 3D from the top-chromosphere up into the mid-corona. The solar radio spectrometers include a Metric Wavelength Solar Radio Spectrometer (90-600 MHz) at Chashan in Shandong province, together with the three Decameter-Metric to Centimetric Wavelength Solar Radio Spectrometers at the MUSER site, offering spectrum monitoring ability across a super wide band from 30 MHz up to 15 GHz. The overall design, some technical details, calibration method, and performance with some preliminary data of these facilities are described.

Solar radio bursts are a major source of space weather hazards. Thus, developing solar observation systems is essential. The heliograph, based on synthetic aperture imaging and a dual interferometer, enables high-resolution solar imaging, offering rich spatial information beyond conventional radio spectrometers. The performance of a synthetic aperture heliograph depends critically on time-frequency synchronization among multiple antennas. On this basis, we have conducted research on fiber time-frequency synchronization. The research allows the long-distance transmission and synchronization of signals generated by the rubidium atomic clock via optical fiber. Analysis and testing demonstrated that the research achieved frequency stability of 7 × 10 ^−13 /1 s and an accuracy of 0.466 ppm. After compensation, the average time difference achieved 4.6 and 5.4 ps for frequency and time standard signal, respectively. These results not only indicate that our scheme meets the requirements of the synthetic aperture heliograph but also demonstrate good applicability and scalability, providing a solid foundation for the future development of solar observation systems.

A novel fine spectral structure in solar radio bursts has been discovered using the Chashan broadband solar radio spectrometer at meter wavelengths (CBSm), an instrument of the Chinese Meridian Project-Phase II (CMP-II). The structure features periodic narrow-band stripes with a typical recurrence time < 1 s (occasionally reaching 8 s), often drifting from high to low frequencies and accompanied by absorptions, with trailing stripes appearing at the end of preceding ones. Some stripes exhibit periodic beaded (or pearl-like) enhancements with a periodicity of similar to 0.1 s. The beaded stripes are reported for the first time ever. Data from the DAocheng Radio Telescope (DART) indicate a radio emission brightness temperature exceeding 10(9) K, originating above brightening loops in active region AR 13664. We proposed a novel generation mechanism of the periodic stripes on the basis of the double plasma resonance (DPR) instability, and explained the beaded substructure in terms of modulation by low-frequency magnetohydrodynamic (MHD) waves. The study highlights the CBSm's capability to detect high-resolution fine spectral structures and offers novel insights into the emission mechanism and source characteristics of solar radio bursts.

The challenge of receiver nonlinearity in radio observation systems results in diminished system linearity, dynamic range, and sensitivity, particularly in low-amplitude and linear regions. To address these issues, this article proposes a digital postcompensation calibration method based on a nonlinear model of radio receivers. By using nonlinear digital postcompensation technology, we analyze the nonlinear effects exhibited by radio receivers. A nonlinear model of radio receivers is constructed using empirical data. The compensation-linearized output is generated by compensating for the observed input of the radio observation system's output response through the inverse model of the nonlinear model. Subsequently, the receiver response compensates for the difference between the actual radio receiver response and the response corresponding to linear gain, thereby eliminating nonlinear distortion and achieving real-time digital postcompensation linearization of these effects. We introduce a method for modeling the nonlinear behavior of radio receivers based on empirical data, along with a nonlinear postcompensation linearization approach rooted in this model. Experimental validation via radio observation systems reveals a mean square error of approximately 0.8226% between the model output and the system response. Furthermore, the nonlinear postcompensation linearization method, which is based on the nonlinear model of radio receivers, significantly enhances system linearity, particularly in the low-amplitude region and nonlinear region. The amplitude response difference of the system, concerning the quiet sun and cold space, shifts from approximately 5 dB to approximately 11 dB, thereby amplifying the sensitivity of the solar radio observation system.

ABSTRACT We present a study of wave processes in sunspots from active regions NOAA 11131 on 2010 December 10 and NOAA 12565 on 2016 July 14 observed by SDO/AIA in the 1600, 304, and 171 Å temperature channels. To study the spatial structure of the resonance cavities previously found by Jess et al., we applied spectral data processing techniques such as pixelized wavelet filtering and mode decomposition. For the first time, we found stable regions as waveguides of the oscillations in the sunspot umbra, occupying specific frequency ranges without spatial overlap. The sizes of these regions depend on the frequency oscillations, and the maximum frequency coincides with the values of the harmonics of the main oscillation mode. Frequency drifts were observed in the band occupied by these regions, with different spectral slopes depending on the location of the sources in the sunspot umbra. We suggest that the observed distribution of wave sources in the umbra is a set of resonant cavities where successive amplification of oscillations at selected multiple harmonics is observed. The distribution of sources at low frequencies indicates the influence of the atmospheric cut-off due to the inclinations of the magnetic field lines.

This paper studies the causes and distribution of reconstruction errors in subtractive dither structure and provides solution to minimize these errors. We present the generation of reconstruction errors in two types of quantization, namely mid-riser and mid-tread, with their corresponding distributions. We then construct a 12-bit pipeline analog to digital converters (ADC) simulation model and use a 16-bit digital to analog converter (DAC) to convert the dither sequence into analog signals. We perform statistical analysis on the resulting data, verify the accuracy of the distribution, and find that reconstruction error only occurs when the dither signal accuracy surpasses that of the ADC. Additionally, we find that mid-tread quantization has the lowest probability of reconstruction error. Finally, we analyze the impact of reconstruction error on the signal to noise ratio (SNR) and spurious free dynamic range (SFDR) at various input frequencies. Our findings show that the reconstruction errors' effect on the SFDR and SNR of the input signal is less than 1 dB.