Abstract:Owing to its unique spectral characteristics, the terahertz(THz) frequency band demonstrates broad application prospects in high-resolution automotive radar, short-range high-data-rate communications, interstellar communications, and biomedical imaging. As a critical transmitting and receiving component in terahertz systems, antennas directly influence the system operating range and coverage. Current research on terahertz array antennas primarily focuses on enhancing gain and efficiency, broadening bandwidth, and beam scanning. This paper reviews the current development status and challenges of terahertz array antennas in terms of their key performance metrics, discusses recent advances in wideband high-gain antennas, beam-steering antennas, large-scale MIMO arrays, and on-chip integrated antennas, and presents an antenna array design methodology based on the Maximum Power Transfer Efficiency(MMPTE) method along with its unique advantages in terahertz antenna design, aiming to provide insights for the further advancement of terahertz array antennas.

Abstract:The research of miniaturized shared-aperture base station antennas that integrate Multiple Bands and Multiple Arrays(MBMA) have become the main research trend in current base station antenna industry. However, in the process of miniaturizing MBMA antennas, the spacing between radiators of each band is extremely compressed, the resulting electromagnetic coupling induces significant radiation pattern distortion. This paper presents a low-band shared-aperture base station antenna design with wideband scattering suppression characteristics. By integrating split-ring resonator structures on the low-band antenna radiator, the coupling high-band currents can be neutralized, thereby the influence on the high-band's radiation pattern is reduced. The experimental results show that the proposed low-band antenna element has good electrical and radiation performance in the 617~960 MHz band, achieving an impedance bandwidth of 43.5%, in-band polarization isolation of 25 dB and an average gain of (8.0±0.5) dBi. Moreover, pattern distortion in the high-band is effectively avoided, test results show that the proposed antenna exhibits excellent scattering suppression in the 1 700~2 700 MHz band. In conclusion, the proposed shared-aperture dual-band design has improved the performance in both low-band and high-band, and has high application value in MBMA base station antenna design.

Abstract:To meet the integration demands of modern electronic information systems for diverse radio functions such as detection, communication, navigation and jamming, this paper presents the design of an Super-Wideband(SWB) monopole antenna. Based on an annular monopole structure, triangular elements are loaded and subjected to multiple iterations and slotting to extend the antenna's low-frequency operating bandwidth. To mitigate the impedance matching degradation at certain frequency points after iteration, a pair of inverted L-shaped parasitic elements are loaded on both sides of the microstrip line, while rectangular slots are introduced at the end of the feeding structure. Simulation results demonstrate that the antenna achieves an operating bandwidth of 0.8~30 GHz, corresponding to a fractional bandwidth of approximately 190%. The antenna attains a peak gain of 8.5 dBi, with the gain remaining above 0 dBi across the entire frequency band. This design significantly reduces system complexity in multi-antenna configurations while achieving multifunctional co-use within a single antenna system.

Abstract:To meet the requirements of next-generation wireless communication systems, a wideband electromagnetic metamaterial antenna is proposed. A metamaterial composed of hexagonal unit cells combined with inductive stubs serves as the radiator, which, compared to the conventional quadrilateral patch cell structure, offers higher coupling capacitance and longer current paths, thereby achieving wideband design objectives. To ensure high directivity in complex electromagnetic environments during practical applications, an additional metal ground plane is introduced at the bottom of the antenna, with Polymethacrylimide(PMI) foam filling the space between this metal ground and the main ground plane. A coplanar waveguide feeding structure is adopted, eliminating one dielectric substrate layer and resulting in a simpler, more fabrication-friendly design. The final antenna dimensions are merely 48 mm×48 mm×15.1 mm(0.473λ_L×0.473λ_L×0.149λ_L, where λ_L is the wavelength corresponding to the lowest operating frequency). Measurement results demonstrate that the antenna achieves an impedance bandwidth of 41.1%(2.96~4.49 GHz) for Voltage Standing Wave Ratio(VSWR)<2, with a gain ranging from 4.5 to 7.3 dBi across the operating band and favorable directional radiation characteristics.

Abstract:Based on a tile architecture, a highly integrated Ku-band active phased array antenna capable of ±70° beam scanning is designed. The active phased array consists of a microstrip patch panel array antenna, transmit/receive(T/R)modules, beam control and feed networks, and heat sinks. The T/R modules are designed in a tile configuration, with each channel capable of simultaneously prestoring amplitude and phase compensation codes for both the receive and transmit branches. Compared with traditional brick-type T/R modules, this design significantly reduces the dimension along the RF signal propagation direction while achieving monolithic integration of 128 channels, thereby realizing miniaturization, lightweight, and high reliability. The antenna array adopts a triangular lattice arrangement, which improves the gain by approximately 1 dB at a 60° scan angle compared with conventional rectangular lattice structures. This active phased array also features the advantages of low profile, thin and lightweight design, and simple assembly/disassembly.

Abstract:At the critical stage of global communication networks evolving toward 6G, terahertz communication has become the core direction for breaking through communication capacity limits with its ultra-large bandwidth and ultra-high-speed characteristics, offering broad prospects for space-air-ground integrated scenarios. However, terahertz waves suffer from severe molecular absorption and path loss, while traditional solid-state devices have insufficient output at high frequencies, constraining industrial development. This paper reviews the core technologies of solid-state electronic communication systems and power components: at the system level, a parallel pattern has formed where III-V compound semiconductors enhance link performance and silicon-based processes explore large scale array integration; at the power component level, a complementary pattern is established between vacuum Traveling Wave Tubes(TWT) and solid-state Power Amplifiers(PA) at the device end, while binary and radial combining techniques are adopted at the circuit end to adapt to different large-scale power requirements. Finally, the evolution trend toward full mobility and integrated sensing and communication is prospected, pointing out that heterogeneous integration and novel electromagnetic mode fusion are the keys to breaking through power limits.

Abstract:With the development of terahertz time-domain spectrometers toward a large dynamic range, the system's nonlinear response has become a core bottleneck limiting the accuracy of quantitative analysis. However, traditional nonlinearity calibration methods generally suffer from issues such as optical path interference(e.g. , bulk material attenuators are prone to causing wavefront distortion), bandwidth limitations, and difficulty in metrological traceability. These problems severely restrict the standardized application of terahertz time-domain spectrometers. To address the above challenges, this study develops an attenuator with low wavelength selectivity based on the skin effect to achieve nonlinearity calibration of terahertz time-domain spectrometers. The attenuator is an Inconel 600 alloy film. By establishing a complete calibration sequence with 7 attenuation levels and constructing a three-level metrological traceability chain of "terahertz source-standard power meter-attenuator", the accuracy and traceability of the calibration results are ensured. Calibration experiments were conducted at three characteristic frequency points: 0.3 THz, 0.9 THz, and 1.6 THz. The results show that the system's nonlinearity exhibits a trend of "first decreasing and then increasing" with frequency. The system exhibits the best performance in the mid-frequency band(0.9 THz), with nonlinearity as low as 1.5%. The nonlinearity is 3.2% in the low-frequency band(0.3 THz) and increases to 7.7% in the high-frequency band(1.6 THz). Moreover, the calibration results at all frequency points comply with metrological specifications. This method effectively avoids the inherent defects of traditional attenuators, provides a high-precision and traceable technical solution for the nonlinearity calibration of terahertz time-domain spectrometers.

Abstract:In the modern electronic battlefield, the application of distributed radars enables radar systems to build a more comprehensive and complex three-dimensional combat architecture. The node radars distributed at different positions in space can adopt multiple frequency bands and working modes, possessing inherent advantages compared with single-station radars. Therefore, researching the countermeasure and anti-countermeasure of distributed radars has significant application value. This paper sorts out the current research directions and progress of technologies such as detection and anti-detection, recognition and anti-recognition, decision-making and inversion, jamming and anti-jamming, and game theory in the distributed radar countermeasure and anti-countermeasure technologies. Finally, the shortcomings of existing distributed radar confrontation and counter-countermeasures technology are summarized, and future development trends are predicted.

Abstract:To address the issues of degraded ranging accuracy and reduced robustness of radar altimeters under non-Gaussian additive noise interference, a height measurement method based on Bayesian parameter estimation is proposed. This method employs the generalized Gaussian distribution to model the characteristics of non-Gaussian noise, and combines Bayesian learning to achieve precise estimation of elevation parameters for airborne radar altimeters. Validation results from both simulation and measured data demonstrate that, compared with traditional least squares methods and existing Bayesian approaches, the proposed method improves the ranging accuracy and robustness of radar altimeter parameter estimation under non-Gaussian additive noise interference, providing reliable technical support for high-precision parameter estimation under complex noise conditions.

Abstract:Radar signal recognition is one of the critical tasks in modern radar electronic warfare systems. Traditional radar signal recognition methods primarily rely on experienced operators and sophisticated signal processing techniques. With the continuous advancement of radar technology, the quantity and variety of radar signals in the electromagnetic environment are increasing and overlapping with each other. When identifying mixed known and unknown radar signals, conventional recognition methods often suffer from low recognition accuracy and poor generalization capability. This paper proposes a method based on one-Dimensional Convolutional Neural Network (1D-CNN) for recognizing mixed known and unknown radar signals. Through recognition experiments on three simulated Pulse Description Word(PDW) datasets of mixed known and unknown radar signals with varying complexity levels, the recognition accuracy reaches no less than 89.5%, which verifies the feasibility of the proposed method.

Abstract:To acquire terrain elevation profiles, terrain tracking methods are commonly adopted to extract topographic height information. Terrain tracking is divided into two stages: coarse tracking and retracking. Coarse tracking roughly obtains the Above Ground Level(AGL) via airborne navigation and positioning devices, whereas retracking is a process that uses algorithms to retrieve AGL parameters from the echo waveform with high precision. Most existing retracking algorithms are based on the Least Squares(LS) method, Maximum A Posteriori(MAP) method, and Variational Bayesian Expectation-Maximization(VB-EM) method. However, the LS method tends to overfit during the fitting process, resulting in degraded extraction accuracy; the MAP method does not suffer from overfitting but fails to yield a closed-form solution; the VB-EM method avoids overfitting and can obtain a closed form solution for the posterior probability density, yet its operation is complex, computationally intensive, and prone to getting trapped in local optima. To address these issues, this paper establishes a reliable elevation-change retracking algorithm framework based on a Bayesian-driven model combined with Markov Chain Monte Carlo(MCMC) sampling. The proposed Bayesian retracking algorithm not only avoids overfitting but also obtains a closed-form posterior probability solution, while requiring a relatively small computational burden. Applying this method to perform retracking calculations on radar echoes, the final measurement error is on the order of only one range bin; converted to a measurement altitude of 3 000 m, the error is merely 0.2%.

Abstract:This paper investigates the distributed fusion estimation problem for Multi-Sensor Multi-Rate(MSMR) systems subject to hybrid network attacks and correlated noises. The state update rate is a positive integer multiple of the observation sampling rate, and different sensors sample uniformly at different rates. The system noise is correlated with the observation noise at the same time instant. Hybrid network attacks may occur during the transmission of sensor observations to remote estimators, and a predictive compensation model is established to address this phenomenon. Through model transformation and state iteration, a unified and concise model is constructed at the observation sampling points. Using the innovation analysis method, optimal Local Filters(LFs) are derived at both observation sampling points and state update points, respectively. Furthermore, the estimation error cross-covariance matrices between any two local filters are derived, and a matrix-weighted Distributed Fusion Filter(DFF) is proposed. Simulation results verify the effectiveness of the proposed algorithms.

Abstract:In the fields of spacecraft, particle accelerators, microwave devices and electric vacuum devices, the secondary electron emission characteristics of metal materials are one of the key factors affecting equipment and devices, so the research on its modification methods and technologies has important scientific research significance and broad application prospects. It is a potential technical method to modify the secondary electron emission characteristics of metal materials by metal ion beam irradiation. In this paper, the changes of secondary electron emission characteristics of copper under different irradiation effects such as surface morphology, internal defects and ion implantation are simulated by Monte Carlo method. The results show that surface pit defects are a significant factor to inhibit the secondary electron emission yield of metal materials, which can be reduced by more than 70%, while surface peak morphology can enhance the secondary electron emission coefficient, which can be increased by more than 60%. The suppression effect of internal defects on secondary electron emission is relatively weak, only about 13%. The inhibition effect of ion implantation will only be effective on the shallow surface, which is similar to plating a film with low emissivity on the metal surface. The research results provide guidance for the design of ion beam irradiation modification technology for secondary electron emission characteristics of metal materials.