互耦效应下端射阵机载雷达STAP方法研究

互耦效应是阵列天线一个固有的重要属性,而端射阵天线由于其特殊的主波束指向以及抑制栅瓣所要求的小阵元间距,其阵列间存在的互耦效应比侧射阵更加严重.本文首先分析了互耦效应对端射阵天线方向图的影响,构建了存在互耦效应下的天线方向图模型;然后给出了考虑互耦效应的杂波模型并分析了互耦对端射阵机载雷达杂波谱以及STAP（Space-Time Adaptive Processing）性能的影响;最后提出了一种基于杂波协方差矩阵重构的互耦效应补偿方法.计算机仿真验证了所提方法的有效性.     

Complete RF system model for analysis of compact MIMO arrays

A framework to analyze compact arrays for multiple-input-multiple-output (MIMO) is presented. Many handheld devices require very compact arrays. Small spacings between the antennas lead to mutual coupling, which decreases the efficiency of the antennas and therefor the signal-to-noise ratio and leads to correlated signals at the antennas. Both effects are completely taken into account in this framework; thus, it allows for a fair comparison of different antenna arrays for MIMO. It is distinguished between MIMO systems for multiplex transmission or pure beamforming, which have different requirements for the antennas. Different compact array configurations, which exploit spatial, polarization, and pattern diversity, are discussed and compared. For practical purposes, it is also shown how to connect this framework to standard path-based channel models.     

Performance of a Multiple HAP System Employing Multiple Polarization

In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to increase the data rates in HAP communication systems. We will also investigate the effects of spatial correlation and mutual coupling between the separate antenna elements on system performance. Simulation results show that although the capacity is degraded by correlation and mutual coupling, we still achieve significant capacity gain compared to the single HAP case. In addition, we evaluate the performance of the system for different separation angles between HAPs, and determine the optimal separation angle that maximizes the total capacity of the system.     

Measured MIMO Capacity and Diversity Gain With Spatial and Polar Arrays in Ultrawideband Channels

This paper experimentally investigates the performance of multiple-input multiple-output (MIMO) systems in indoor ultrawideband (UWB) channels. The improvement in robustness and information rate due to spatial and polar antenna arrays is evaluated. The subchannel correlation, power gains of supported eigenmodes, and branch power ratios are analyzed. The polar arrays are found to experience lower correlation than that of spatial arrays. SNR gains of up to 3 and 5 dB are reported with 1times2 and 1times3 spatial arrays, respectively; the latter is shown to double the coverage range. The mutual information capacity is found to scale almost linearly with the MIMO array size, with very low variance. It is confirmed that the device compactness achieved by the polar array comes with only a small penalty in the achievable capacity and SNR gain compared to the spatial array. The multiple-antenna UWB techniques explored in this paper offer the potential for high-data-rate, robust communications.     

共享孔径交错稀疏阵列天线互耦误差建模与校正

共享孔径交错稀疏阵列天线是实现多功能阵列天线的有效途径。现有的参数化互耦消除方法都是针对均匀阵列天线展开的,其研究的互耦矩阵都是规则的方阵,对共享孔径交错稀疏阵列天线的互耦矩阵模型并不适用。在充分考虑共享孔径交错稀疏阵列天线中子阵内互耦的“稀疏”和“方位依赖”的特殊性后,通过将常规的互耦矩阵扩展表示为“非方”的“增广互耦矩阵”来对交错稀疏阵列天线子阵内和子阵间的耦合效应进行建模,并通过“增广互耦矩阵”的参数化估计最终实现了共享孔径交错稀疏阵列天线互耦误差的建模与校正。仿真结果证实了所提方法的有效性和可行性。     

Smart antennas based on spatial multiplexing of local elements (SMILE) for mutual coupling reduction

A new method for reducing mutual coupling in a smart antenna array using patch antenna elements is proposed. In a recently introduced smart antenna architecture, the spatial multiplexing of local elements (SMILE) scheme, the newly proposed array feed network affects mutual coupling. It is demonstrated that proper design of the feed network may reduce mutual coupling significantly, yielding nearly ideal radiation characteristics. Numerical solutions are used to study and optimize the currents on the surface of a four-element C-band patch antenna array and feed network. Radiation patterns of the same array with different feed networks are also computed. Results show a reduction in sidelobe level of several decibels, increased accuracy in beam pointing during scan, and improved depth and placement.     

Mutual coupling in multi-element array antennas and its influence on MIMO channel capacity

The effects of mutual coupling between receive elements in a multi-element antenna on multiple-input multiple-output (MIMO) system capacity are reported. The results are based upon analysis of mutual coupling calculated for a measured linear array of five printed dipole elements with 0.56 of a wavelength spacing. It is shown that the presence of mutual coupling at the receive array antenna leads to additional correlation between spatial channels and results in a loss of MIMO system capacity.     

ESPAR array design for the UHF RFID wireless sensor communication system

In this paper, in order to improve the received signal strength (RSS) and signal quality, three arrays of electronically steerable parasitic array radiator (ESPAR) antennas are suggested for the ultra-high frequency (UHF) radio frequency identification (RFID) communication and sensing system applications. Instead of the single antenna, the array antennas have recently been widely used in many communication systems because of their peak gains, better radiation patterns, and higher radiation efficiency. Also, there are some important issues to use the antenna array like high data rates in wireless communication systems and to better understand the many targets or sensors. In this article, a wireless sensor network (WSN) is being investigated to overcome multipath fading and interference by antenna nulling technology that can be achieved through beam control ESPAR array antennas. The proposed ESPAR array antennas exhibit higher gains like 9.63, 10.2, and 12 dBi and proper radiation patterns from one array to another. Moreover, we investigate the mutual coupling effect on the performance of array antennas with different spacing (0.5λ, 0.75λ, λ) and configurations. It is found that the worst mutual coupling reduced by −28 to −34 dB for 2 × 2 array, −3 to −43 dB for 2 × 3 array, and finally −42 dB to −51 dB due to the antenna spacing from 0.5λ to λ. Thus, these suggested antennas could effectively be applied in the WSN communication systems, internet of things (IoT) networks, and massive wireless and backscatter communication systems.     

Efficient detectors for MIMO-OFDM systems under spatial correlation antenna arrays

This work analyzes the performance of implementable detectors for the multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) technique under specific and realistic operation system conditions, including antenna correlation and array configuration. A time-domain channel model was used to evaluate the system performance under realistic communication channel and system scenarios, including different channel correlation, modulation order, and antenna array configurations. Several MIMO-OFDM detectors were analyzed for the purpose of achieving high performance combined with high capacity systems and manageable computational complexity. Numerical Monte Carlo simulations demonstrate the channel selectivity effect, while the impact of the number of antennas, adoption of linear against heuristic-based detection schemes, and the spatial correlation effect under linear and planar antenna arrays are analyzed in the MIMO-OFDM context.     

混合BMO算法用于紧耦合甚低频直立阵去耦优化

提出了一种基于混合蝴蝶交配优化（butterfly mating optimization，BMO）算法抑制阵列天线互耦的新方法.该方法首先根据建立的阵列天线的非线性优化模型，对优化变量进行分组排序，利用二进制BMO算法对模型馈线进行稀布优化；其次，为平衡全局搜索和局部寻优能力，在标准BMO算法的基础上赋予蝴蝶个体均匀混沌初始化和自适应变位移机制，对天线结构进一步优化.将所提方法应用于二元甚低频（very low frequency，VLF）紧耦合伞形天线阵，结果表明:所提方法能够有效改善相控时阵元的辐射电阻，组阵增益接近理论值，提升了阵列天线的波束合成性能.该方法为大型阵列天线互耦抑制提供了新思路.     

On the empirical optimization of antenna arrays

Empirical optimization is an algorithm for the optimization of antenna array performance under realistic conditions, accounting for the effects of mutual coupling and scattering between the elements of the array and the nearby environment. The algorithm can synthesize optimum element spacings and optimum element excitations. It is applicable to arrays of various element types having arbitrary configurations, including phased arrays, conformal arrays and nonuniformly spaced arrays. The method is based on measured or calculated element-pattern data, and proceeds in an iterative fashion to the optimum design. A novel method is presented in which the admittance matrix representing an antenna array, consisting of both active and passive elements, is extracted from the array's element-pattern data. The admittance-matrix formulation incorporated into the empirical optimization algorithm enables optimization of the location of both passive and active elements. The methods also provide data for a linear approximation of coupling as a function of (nonuniform) element locations, and for calculation of element scan impedances. Computational and experimental results are presented that demonstrate the rapid convergence and effectiveness of empirical optimization in achieving realistic antenna array performance optimization.     

On uplink CDMA cell capacity: mutual coupling and scattering effects on beamforming

It has been shown that code-division multiple-access (CDMA) systems that employ digital beamforming and base station antenna arrays have the potential to increase capacity significantly. Therefore, accurate performance prediction of such systems is important. We propose to take the electromagnetic behavior of the base station antenna array into account, as well as its impact on wireless channel propagation. Specifically, the wideband channel introduces scattering, while the mobile environment causes Doppler fading, which in turn degrades power controllability. We develop a more accurate performance analysis of antenna arrays, where the performance degradation in digital beamforming, due to the combination of mutual coupling, scatter and imperfect power control, and its impact on uplink CDMA system capacity is quantified. A Rayleigh fading amplitude with varying angle-of-arrival spread is assumed, and maximum signal-to-noise ratio beamforming weights are used. These weights are further correlated with mutual coupling at the base station array. Despite the degradation due to the combination of mutual coupling, scattering, and imperfect power control, significant capacity increases are possible.     

Adaptive MIMO Transmission for Exploiting the Capacity of Spatially Correlated Channels

We consider a novel low-complexity adaptive multiple-input multiple-output (MIMO) transmission technique. The approach is based on switching between low-complexity transmission schemes, including statistical beamforming, double space-time transmit diversity, and spatial multiplexing, depending on the changing channel statistics, as a practical means of approaching the spatially correlated MIMO channel capacity. We first derive new ergodic capacity expressions for each MIMO transmission scheme in spatially correlated channels. Based on these results, we demonstrate that adaptive switching between MIMO schemes yields significant capacity gains over fixed transmission schemes. We also derive accurate analytical approximations for the optimal signal-to-noise-ratio switching thresholds, which correspond to the crossing-points of the capacity curves. These thresholds are shown to vary, depending on the spatial correlation, and are used to identify key switching parameters. Finally, we propose a practical switching algorithm that is shown to yield significant spectral efficiency improvements over nonadaptive schemes for typical channel scenarios     

Reconfigurable antenna solution for MIMO-OFDM systems

A reconfigurable microstrip dipole antenna solution for multiple-input multiple-output (MIMO) communication systems making use of orthogonal frequency division multiplexing (OFDM) is presented. When applied to closely spaced antenna arrays, this method can increase link capacity. The benefits of this novel antenna solution are demonstrated by channel capacity measurements taken in an indoor environment with a 2/spl times/2 MIMO system.     

三维空间MIMO信道接收天线阵列互耦效应及系统容量分析

针对非频率选择性瑞利衰落MIMO(multiple-input multiple-output)信道,建立了接收天线阵列的三维空间信道模型,将MIMO的一般信道建模推广到三维空间域。在建模过程中利用天线阵列在互耦效应下的等效网络模型,推导出三维空间域模型下的互耦相关性的通用表达式,阐明了互耦效应下相关性与无互耦相关性之间的关系。应用通用表达式分析了当接收端为不同的天线阵列结构时,入射信号的中心到达角和角度扩展分别对于在互耦效应下信道容量的影响。分析结果验证了不同的角度扩展对于互耦相关性的影响,揭示了在互耦效应下影响系统容量的主要因素为入射信号的平均中心到达角。     

一种应用于4G/5G频段的新型8×8频率可重构MIMO系统设计

文章提出一种可应用于4G/5G工作频段且应用分集技术解耦的8×8频率可重构MIMO系统。八天线阵列中包括4个可切换于2.6 GHz频段和3.5 GHz频段的频率可重构天线模块以及4个应用于3.5 GHz频段的5G模块。由于频率可重构技术的应用,该系统可满足网络传输速率等多种要求,进一步提高终端设备的空间利用率和系统应用的灵活性。文章给出了MIMO系统切换前后的S参数和包络相关系数等参数的计算结果,结果显示出多天线阵列的可应用性。     

多输入多输出信道容量研究及天线优化

多输入多输出(MIMO)技术是第三代合作伙伴(3GPP)长期演进(LTE)等先进无线通信技术的关键。MIMO无线系统的大容量实现和其他性能的提高均极大地依赖于MIMO低空间相关度和天线优化配置。根据电磁学的基本理论,基于空间信道模型(SCM)分析了LTE MIMO系统的空间相关性和信道容量。在分析信道容量过程中,结合了互耦情况的信道容量模型并进行了修正。结果表明:在城市微小区和郊区宏小区环境移动台天线间距d_MS=0.4 λ,下行4×4阶天线配置能达到零相关度和12.5 bps/Hz(城市微小区)、10.5 bps/Hz(郊区宏小区)的信道容量。这些配置能广泛应用于LTE系统终端天线阵列中。     

Design and performance analysis of side by side,echelon and H‐shaped multiple printed dipole antennas for wireless local area network application

An array of printed dipole antennas for wireless local area network applications is designed and simulated using ads software. In MIMO system, numbers of antenna elements are used in different configuration. This paper presents the simulated results of printed dipole antennas in side by side 4‐element array, echelon and H‐shaped dipole array configurations. The designed antenna is characterized by measuring return loss, radiation pattern, directivity, and gain and also presented the simulated capacity results of different array configurations. The mutual coupling between the dipoles of different orientations is included to make simulation more realistic. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of coupling accumulation in antenna arrays

Mutual coupling between antenna elements in a phased array causes array performance to vary with scan angle. Large impedance mismatch and radiation loss can occur in certain critical directions for which the steering phase advances match the antenna coupling delays. At these critical scan angles, many coupling contributions add inphase to produce a large impedance mismatch and minimum radiation from the array. Several different phased arrays have exhibited scanning "blind" regions that appear to be a consequence of coupling accumulation. A large, flat, homogeneous antenna array is analyzed, and a relationship is found between the critical scan angles and phase of the mutual coupling coefficients. Extensive measurements on arrays of horn antennas have shown radiation minima that correlate with coupling phase measurements and with theory.     

Optimization of Antenna Array Structures in Mobile Handsets

A study of the capacity of multiple-element antenna systems is presented with particular emphasis on the effects of mutual coupling between the antenna elements. As the total size of the array is often fixed and limited, the correlation of fading as well as the mutual coupling of two elements separated in index by some value$l$increases. In this paper, at first with the assumption that the length of the linear array of antenna elements and the number of antenna elements at the receiver are fixed, the capacity with coding, without coding, and the symbol error rate (SER) of space-time coding are investigated. The results obtained show that for the mean signal to noise ratio at the receiver of$rho = 20$dB, the linear array of three antenna elements is the optimum choice if the total length of the array is in the range of$0.3lambda$–$0.86lambda$, while in the case of channel state information (CSI), this range is$0.25lambda$–$0.6lambda$. The effects of the signal-to-noise ratio (SNR) and number of the base station antenna elements on the capacity of the fixed-length linear arrays are also discussed. Next, it is assumed that the number of antenna elements at the transmitter and receiver are equal. Simulation results show the number of antenna elements for maximizing the capacity.