In this paper, a frequency-selective absorber with large-angular stability under oblique incidence is present. The absorptivity of the structure can be reached to maximum by impedance matching and parameter optimization method under a specific angle (40 degrees), which ensures an excellent absorption response within 60 degrees oblique incidence. This method solves the problem that the absorptivity of traditional absorbers deteriorates with the increase of incident angle. The absorber consists of a three-layer structure: two lossy layers and a metal ground layer, the equivalent circuit model is discussed and the operating frequency band is widened by generating electric resonances and magnetic resonances. Due to the high symmetry of the structure, the absorber has good polarization insensitivity. Numerical simulation shows that from 4.4 to 20 GHz, the absorptivity of the structure is above 90% within 40 degrees oblique angle of incidence. Finally, the design plays an important role in military stealth and preventing electromagnetic interference.

The letter presents a low-windage omnidirectional antenna for high-speed aircraft in the UHF and L bands. It combines a planar biconical antenna with a printed tape parasitic branch monopole antenna. Upgrading the traditional restricted-length biconical antenna to a double-layer planar design meets the compact, lightweight, and low windage requirements of airborne use. To enhance bandwidth and meet the lightweight, compact criteria of high-speed aircraft, the planar-printed monopole antenna integrates parasitic stubs and loop antenna concepts. Experimental results exhibit excellent isolation between antenna elements, with over 15 dB segregation and operational spectrum return loss of 27% and 18% at 10 dB. The voltage standing wave ratio is below 2, with less than 5 dB variation in the horizontal radiation pattern across frequency bands. The antenna, measuring 20 mm x 190 mm x 270 mm and weighing around 0.5 kg, holds great promise for high-speed aircraft applications.

为解决在雷达脉冲压缩过程中通过海明窗、汉宁窗等加权方式降低旁瓣而引起主瓣展宽、分辨率下降的问题,提出了一种以常用窗函数为基窗函数的改进窗函数非线性组合法.首先,相较于基窗函数,基于窗函数加权脉冲压缩的原理,证明窗函数线性组合法在主瓣展宽不变时可获得更好的旁瓣抑制能力;并在此基础上进一步证明改进的窗函数非线性组合法具有更优的旁瓣抑制能力.然后,通过对改进的窗函数非线性组合法在三角窗、汉宁窗、海明窗、布莱克曼窗等作为基窗函数时的脉冲压缩性能仿真与分析,验证了该方法使用不同基窗函数均可在主瓣展宽不变、信噪比损失增加低于0.5 dB的前提下,将峰值旁瓣相比凯塞窗降低4dB以上、相比几种常用窗函数降低7dB以上.最后,通过多目标的仿真实验验证,相比于不同的基窗函数,改进窗函数非线性组合法具有更优的弱小目标检测能力.

The characterization of targets by electromagnetic (EM) scattering and underwater acoustic scattering is an important object of research in these two related fields. However, there are some difficulties in the simulation and measurement of the scattering by large targets. Consequently, a similarity study between acoustic and EM scattering may help to share results between one domain and the other and even provide a general reference method for the simulation of scattering characteristics in both fields. Based on the method of physical optics, the similarity between the EM scattering of conductors and the acoustic scattering of soft/hard targets and the similarity between the EM scattering of dielectrics and the acoustic scattering of elastics are studied. In particular, we derive how to transfer quantities from one domain into another so that similar scattering patterns arise. Then, according to these transfer rules, the EM scattering and acoustic scattering of three typical targets with different types of boundaries were simulated and measured, and the simulated EM scattering and acoustic scattering curves were found to be in perfect agreement, with correlation coefficients above 0.93. The correlation coefficients between the electromagnetic and acoustic scattering patterns were above 0.98, 0.91, and 0.65 for three typical targets. The simulated and measured scattering results verify the proposed similarity theory of EM and acoustic scattering, including the transfer from one domain into the other and the conditions of EM and acoustic scattering, and illustrate that the acoustic scattering characteristic of the target can be simulated using the EM scattering based on the derived conditions and vice versa.

A low-profile circularly polarized folded reflectarray antenna (CPFRA) with linearly polarized (LP) feed antenna is presented in this paper. Polarizing grid usually used as the subreflector of traditional FRA is replaced by a polarization-sensitive frequency selective surface (FSS) in the CPFRA design. The polarization-sensitive FSS is designed to convert the LP incidence into the CP wave within its passband while reflecting the orthogonal LP incident wave over its operating frequency band. A CPFRA prototype was designed for Ka band satellite communications uplinks with its performance demonstrated in this paper. Good performance of the proposed CPFRA has been achieved with its 3dB axial ratio (AR) frequency band covering from 28.9 to 30.6GHz and 3dB gain frequency band from 28.8 to 32.7GHz. Additionally, the proposed CPFRA retains the excellent characterisits of FRA as high efficiency, low profile, etc.

In the acoustic scattering and characteristic tests of large targets and large-scale transducers, in order to meet the plane wave conditions, the larger test distance is often required. It is a greater difficulty for the testing laboratories with limited space. In order to compact the testing distance and solve the problem of requiring a long distance for large-scale target scattering and large-scale transducer testing, based on the principle and application of microwave compact test rang system and the approximation of electromag-netic wave and acoustic wave, an underwater acoustic compact range test system (ACTRS) is proposed. The developed ACTRS uses a parabolic main reflector to obtain a plane wave at a short distance. Compared to the traditional underwater acoustic test system, the space distance is effectively compacted and the conversion process is reduced. Moreover, as the main device in the proposed ACTRS, the air-cavity with resin honeycomb structure was selected as the basic unit cell of the main reflector for the good underwater acoustic reflection performance. In addition, the edge sawtooth structure was selected to reduce the interference of edge diffraction in the quiet zone. Subsequently, the main reflector was sim-ulated, trial-produced and measured. The measurement result shows good agreement with the simula-tion result. Finally, based on the proposed main reflector, the ACRTS was constructed for the object scattering and transducer directivity measurements. The test results were consistent with the simulation and the manufacturer's manual data. Overall, the designed ACTRS can be used for large-scale target scat-tering and transducer directivity testing, providing a new reference for exploration of acoustic measure-ment methods.(c) 2023 Elsevier Ltd. All rights reserved.

A bandpass negative group delay（NGD）passive circuit based on defect ground structure（DGS）and substrate integrated waveguide（SIW）-matched is developed in the paper. The NGD DGS topology is originally built with notched cells associated with self-matched substrate waveguide elements. The DGS design method is introduced as a function of the geometrical notched and SIW via elements. Then, parametric analyses based on full wave 3-D electromagnetic S-parameter simulations were considered to investigate the influence of DGS physical size effects. The design method feasibility study is validated with fully distributed microstrip circuit prototype. Significant bandpass NGD function performances were validated with 3-D simulations and measurements with-1.69 ns negative group delay value around 2 GHz center frequency over 33.7 MHz NGD bandwidth. Insertion loss is 4.37 d B, and reflection loss reaches 41.5 d B.

Velocity aliasing is unavoidable for millimeter-wave cloud radar (MMCR) due to its short wavelength. In the vertically pointing MMCR, a special aliasing state called half-folding will cause the traditional postprocessing dealiasing methods used for weather radar, including the dual-PRF method, to fail. In this paper, we propose a method that applies the dual-PRF technique to spectral dealiasing. By utilizing the property that the true velocity difference between peaks should be the same in both PRFs, our method is able to solve a special case of half-folding caused by multiple peaks, which is ignored by other spectral dealiasing methods. The special case, which we call implicit half-folding, occurs in the presence of multiple peaks in a Doppler power spectrum, where none of the peaks are folded, and they appear to be in the same Nyquist interval, whereas the peaks are actually not in the same Nyquist interval. Observations from a 94 GHz vertically pointing MMCR called TJ-II were used to demonstrate various aliasing cases, including the implicit half-folding case. As a result, our method successfully solved all aliasing cases while the other method failed when the implicit half-folding case occurred.

A new method using three dimensions of cloud continuity, including range dimension, Doppler dimension, and time dimension, is proposed to discriminate cloud from noise and detect more weak cloud signals in vertically pointing millimeter-wave cloud radar observations by fully utilizing the spatiotemporal continuum of clouds. A modified noise level estimation method based on the Hildebrand and Sekhon algorithm is used for more accurate noise level estimation, which is critical for weak signals. The detection method consists of three steps. The first two steps are performed at the Doppler power spectrum stage, while the third step is performed at the base data stage. In the first step, a new adaptive spatial filter combined with the Kuwaraha filter and the Gaussian filter, using the ratio of mean to standard deviation as the adaptive parameter, is applied to initially mask the potential cloud signals to improve the detection performance at the boundary of cloud and noise. Simulations of boundary cases were performed to compare our adaptive filter and normal Gaussian filters. Box filters are used in steps two and three to remove the remaining noise. We applied our method to cloud radar observations with TJ-II cloud radar at the Nanjing University of Information Science & Technology. The results showed that our method can detect more weak cloud signals than the usual methods, which are performed only at the Doppler power spectrum stage or the base data stage.

A W-band dual-beam low side-lobe level antenna with a shared slotted waveguide radiating layer was designed by the authors. The proposed antenna consists of a symmetrical dual ports feed network layer located on two sides of the antenna, a novel shared symmetrical 4 x 32 slotted waveguide array radiation layer, and a bottom layer. The compact slot distance was adjusted to achieve deflection of the radiation pattern and reduce the radiation grating lobes. Good antenna radiation efficiency and port isolation were obtained by optimising the position of the slots at the radiation layer. A low side-lobe level (SLL) was obtained using Taylor distribution was used in the design of the offset of each slot. The optimised antenna was fabricated and measured. Based on measurement results, the designed antenna has a 24.8 dBi far-field gain, -17/-25.5 dB E/H plane side lobe level, and 19.8 degrees beam deflection at 94 GHz. The performances of the two ports were in good agreement with each other, and the measured isolation was above 14.5 dB at 94 GHz.

Objective Known as frequency-selective surfaces (FSSs), artificial electromagnetic metamaterials are periodic structures that selectively transmit or reflect electromagnetic waves. However, traditional passive FSSs with fixed electromagnetic filtering characteristics have limitations in complex modern environments. To this end, active frequency-selective surfaces (AFSSs) with switchable, reconfigurable, and tunable functionalities have caught attention for their flexible electromagnetic wave control capabilities. Although many researchers have devoted considerable efforts to developing AFSS structures with various advantageous features, limited attention has been paid to independent control of different polarizations. To satisfy the demand for polarization independent control in various applications, we propose a novel AFSS structure with four operating modes. The design allows independent modulation of transmission and reflection for TE or TM polarized wave at different frequency bands, providing dual-polarization transmission, TE or TM single-polarization transmission, and full-polarization shielding functionalities. Furthermore, the AFSS structure demonstrates excellent angular stability, ensuring almost consistent performance within an incidence range of 0 degrees-45 degrees for all operating modes. This characteristic is vital for practical applications that require stable functionality under varying incident angles. Finally, the presented polarization independent multi-mode AFSS structure exhibits promising potential in spatial filtering and radome applications that require specific polarization control. Methods We propose a novel multi-mode switchable AFSS structure with polarization independent control capability and excellent angular stability. The design involves a multi-layer filtering structure that enables the desired polarization independent control functionality. Specifically, we carefully design orthogonal top and bottom FSS structures to independently control TE and TM polarizations. Meanwhile, by integrating PIN diodes between adjacent unit cells in the top and bottom layers, we achieve the capability to switch among different operating modes. To enhance the understanding of the structure's working mechanism, we build TE and TM equivalent circuit models of the unit cell for analysis, with various polarized incident waves considered. Subsequently, we investigate the changes in the real and imaginary parts of the impedance for both transmission and shielding modes, providing valuable insights into transmission window generation. Furthermore, we present detailed TE and TM polarized transmission and reflection results for each operating mode at various incident angles. Additionally, we visualize the corresponding electric field distribution to effectively illustrate the working states. This comprehensive analysis highlights the versatility and adaptability of the proposed structure. Finally, to emphasize its advantages, we compare the proposed AFSS structure with some recent similar designs. The comparison demonstrates the unique strengths and benefits of our approach, making it a promising candidate for diverse applications requiring independent polarization control. Results and Discussions The proposed structure provides multi-mode switchability and polarization independent control, enabling four operating modes including dual-polarization transmission, TE polarization transmission and TM polarization reflection, TE polarization reflection and TM polarization transmission, and full-polarization shielding. In the transmission mode, the real parts of the TE and TM polarized input impedance of the structure closely match 377 Omega at 3. 6 GHz and 4. 6 GHz respectively, with their imaginary parts approaching zero. Both of them effectively match the air impedance, and consequently efficient transmission of both polarizations is achieved at these frequencies (Fig. 4). The structure achieves mode switching by adjusting the bias states of the top and bottom PIN diodes, ensuring that each mode exhibits highly stable performance independent of the others. Additionally, the structure demonstrates sound angular stability within an incidence range of 0 degrees-45 degrees (Fig. 5). Based on these functionalities, the proposed structure has great application prospect in spatial filtering, antenna enclosures, and other relevant fields. Conclusions We present a novel polarization independent control multi-mode switchable frequency-selective surface filter/shield. The structure is designed based on the equivalent circuit model with a multi-layer FSS architecture, where PIN diodes are loaded on the top and bottom layers to achieve independent control of TE and TM waves. By setting different bias voltages on the diodes, the structure can switch among the four operating modes, enabling transmission or reflection control of TE and TM waves. In the transmission mode, the structure forms low-insertion-loss transmission windows at center frequencies of 3. 6 GHz and 4. 6 GHz for TE and TM waves respectively. In the shielding mode, electromagnetic waves are prevented from penetrating the structure. Within the incident angle range of 0 degrees- 45 degrees, each mode exhibits stable performance, and the working states of different polarizations are not affected by other modes. In conclusion, the multi-mode reconfigurable AFSS design has promising application potential in wireless communication systems.

针对新一代天气雷达数据存在风轮机杂波污染问题,统计分析了 5种雷达基数据特征量,风轮机杂波具有较高的反射率因子隆起度和水平通道信噪比隆起度以及较大的速度奇异率,其信号质量指数接近1,谱宽接近0或大于7.0m·s-1.以特征量统计结果为基础,使用模糊逻辑算法对雷达基数据中的风轮机杂波进行特征识别,结果显示,模糊逻楫算法能有效地把风轮机杂波从各种强度的气象降水回波和固定地物杂波中识别出来.针对被识别出来的风轮机杂波,使用区域平均插值方法对雷达基数据中的风轮机杂波进行剔除,杂波剔除结果显示,气象降水条件下获得了较好的风轮机杂波剔除效果.

A 94 GHz pulse Doppler solid-state millimeter-wave cloud radar (MMCR), Tianjian-II (TJ-II), has been developed. It reduces the size and cost using a solid-state power amplifier (SSPA) and a single antenna. This paper describes the system design, including hardware and signal processing components. Pulse compression, segmented pulse, and dual pulse repetition frequency (PRF) technologies are employed to overcome the limitations imposed by the low power of the SSPA and the high frequency of 94 GHz. The TJ-II also features a dual-polarization, high-gain antenna for linear depolarization ratio detection and a time-division receive channel to improve channel consistency and save on costs. To achieve high flexibility and low interference in signal transmission and reception, the TJ-II uses software-defined radio technology, including direct digital synthesis, digital downconversion, and bandpass sampling. A series of Doppler power spectrum processing methods are proposed for detecting weak cloud signals and improving scene adaptability.

In this paper, a 94 GHz dual-polarization high-isolation cassegrain antenna feed by a diagonal horn antenna is designed. The antenna consists of a D = 540 mm main reflector, sub-reflector, and dual-port dual-polarization diagonal horn feed antenna. To obtain similar feed horn E-H radiation patterns, gain, high polarization, and port isolation, a dual-port diagonal horn was designed in the feed. The measured antenna gains are 50.85 dBi and the side-lobe levels are −24.5 dB at E-H radiation patterns of two ports at 94 GHz, respectively. The VSWRs of port 1 and port 2 are less than 1.5:1 in the range 93.2–95.3 GHz, which meets the working requirements of frequency modulated continuous wave and pulse cloud radars. And the isolation between the two ports is above −50 dB, whereas the polarization isolation of each port is above 40 dB. The proposed W-band antenna is a suitable candidate for the dual-polarization cloud radars.

随着机动目标的高速化、小型化发展,对于雷达的测量精度也提出了更高的要求.鉴相测速能够达到波长级的测量精度,其技术难点主要包括相位提取和解相位模糊.为了降低鉴相测速对信噪比的要求,本文提出了一种基于调频傅里叶变换的改进型鉴相测速方法.首先建立变脉冲重复周期的回波模型,对回波信号进行互相关FFT处理,提取峰值点得到模糊相位;其次对互相关FFT结果进行调频傅里叶变换,得到速度和加速度的粗估计值;然后根据单帧解相位模糊法,对模糊数修正值进行遍历,找出最优解,得到优化后的解模糊相位;最后采用鉴相测速,得到速度的精确值.仿真实验证明了该方法的可行性和有效性.

Abstract. A set of Doppler power spectrum processing methods for TJ-II, a vertical sensing 94 GHz millimeter-wave cloud radar(MMCR), is proposed to distinguish clouds and enhance the data quality. The noise level is estimated by a modified segment method with 2-D segments. A two-step cloud signal mask method is proposed to distinguish clouds and noise. A Gaussian filter with adaptive standard variance is used to improve detection performance at the boundary of clouds and noise. Square signal blocks were constructed to test our method. Velocity dealiasing is carried out combined with a pre-dealiasing processing and the dual Pulse Repetition Frequency (PRF) technique to address a particular phenomenon called half-folded in MMCRs, which can not be fixed by post-processing at the base datum stage. Some observations of TJ-II are used to demonstrate our method. A comparison between our method as pre-processing and the method as post-processing proposed by Key Laboratory for Semi-Arid Climate Change of the Ministry of Education and College of Atmospheric Sciences, Lanzhou University, was carried out using one-day observation. It was found that our method shows some advantages in cloud base detection.

It is important to monitor the take-off and landing of civil aircraft using passive detection methods. Due to the strict aircraft safety requirements and the electromagnetic environment around an airport, using too many active detection methods should be avoided. Using an aircraft’s microwave radiation signal detection is very advantageous because it does not actively emit signals and has a strong cloud penetration, suitable for all-weather observation. This paper introduces a synthetic aperture microwave radiation system for monitoring the take-off and landing of civil aircraft, which is characterized by real-time two-dimensional imaging, and the image refresh rate can reach 10 ms, which meets the high refresh rate requirements for aircraft imaging. Applicable system parameters and antenna array distribution scheme and imaging algorithm are given. Then the paper focuses on the error analysis and correction method of the system. The correction method is simple and fast, which avoids the disadvantage that the error needs to be corrected regularly in the laboratory environment, and is suitable for airport application. Finally, the simulation and experimental results show that this technology can be used for real-time monitoring of civil aircraft during take-off and landing, and it is a practical means to assisting landing.

随着低轨(LEO)通信卫星业务需求的增加,低轨卫星需要使用Ka频段进行通信.本文针对低轨卫星采用Ka频段可能与在轨的高轨卫星发生同频干扰问题,采用基于链路分离角的空域分隔方法进行干扰规避的角度间隔分析.分别从不同干扰场景、地面站分布情况来分析对干扰角度间隔的影响,并在此基础上提出该角度间隔范围内,低轨卫星需采取的干扰规避措施.

本文提出一种新型低副瓣自适应波束形成算法,解决了传统自适应波束形成器在干扰和高信噪环境下算法性能急剧下降的问题,并降低了快拍数对算法稳健性的影响.该算法基于标准Capon波束形成器,利用消除空域噪声的方法提高期望矢量的重估精度,并结合功率估计算法重构出干扰噪声协方差矩阵;然后使用特征干扰相消算法二次重构噪声协方差矩阵得到最优权值,增强算法在低样拍下的稳定性;最后对最优权值进行切比雪夫加权和二次约束实现了零陷加宽.仿真实验结果表明:新算法计算量小,旁瓣电平低,降低了在干扰运动和导向矢量失配时快拍数和信噪比对性能的影响.

为在高频率选择性和大带宽的前提下实现小型化,提出一种紧凑非对称双枝节加载的易级联多模谐振滤波器.采用微波网络级联方法,分析优化设计了中心频率为6 GHz的单级、两级和三级多模谐振宽带滤波器.测试结果表明,该滤波器在5.41 mm×7.61 mm(0.21λg×0.29λg)有效尺寸下,带外抑制优于40 dB,损耗小于2.6 dB,相对带宽大于33％.该滤波器具有小型化、宽带、带外抑制强等优点,有利于通信系统和固态雷达收发机的小型化设计.