Channel Capacity Between Antenna Arrays— Part I: Sky Noise Dominates

Space–time coding techniques can be used to achieve very high spectral efficiencies in highly scattering environments using multiple transmit and receive antennas. At the remote station, there is usually a more limited space allotted to the antenna array than at the base station. Since the spectral efficiency improves with the number of antennas, one is interested in how many antennas can be crammed into the limited space on the remote station. This paper (Part I of II) addresses some of the issues which affect the allowable density of antennas in the remote station. In particular, the mutual impedance between antenna elements in the remote array and the correlation between the signal and noise fields received by these elements are analyzed for their impact on the channel capacity achievable by such arrays. In particular, we assume the transmitter is radiating from$n_T$elements of uncoupled half-wave dipoles and knows nothing of the channel. A formula is given for the maximum channel capacity to a receiving array of$n_R$elements, coupled to each other in the presence of ambient noise or interference with a uniform angle of arrival distribution. This formula neglects amplifier noise in the receivers. It is shown that the channel capacity is already determined at the terminals of the receiving array, and can not be improved by internal coupling networks following the receiving array. When the propagation is by means of full three-dimensional scattering, the channel capacity is unaffected by mutual coupling in the receiving array.     

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.     

Ultrawideband noise radar based on antenna arrays with signal recirculation

For radar systems using noise sounding signals with orthogonal spectra, which are radiated with the help of a multielement antenna array, a method for recirculation of noise signals in the feedback loop formed by the transmitting element, the target, and the receiving element is considered. The generalized ambiguity function is used to compare the resolutions and the sidelobe levels along the delay (range) coordinate and the angular coordinate for the cases of a linear equispaced transmitting antenna and an individual receiving antenna in the presence and in the absence of recirculation. Sparse and filled antenna arrays are analyzed for the cases of moderately wideband and ultrawideband total noise signals and different distributions of the center frequencies of partial noise signals over the array elements.     

Prediction of noise and interference cancellation with a moving compact receiver array in an indoor environment

An interference and noise cancellation technique based on a reference signal is studied for a compact receiver antenna array placed in an indoor environment. The exact active element pattern method is used to model the radiation characteristics of the array, including mutual coupling between the antenna elements. A two-dimensional ray-tracing technique describes the signal propagation in the indoor environment for a moving receiving antenna.     

S模式交叠信号的PA分离算法性能分析

为了提升高密度信号背景下对S模式应答的接收能力,投影算法(PA)在阵列接收的基础上采用投影技术分离S模式交叠信号,因其具有良好的稳定性和实用性而成为经典的信号分离方法。首先,分析了PA算法针对的问题在各种空中流量密度下的发生概率;其次,在PA算法的基础上推导了交叠信源数检测与信号到达方向的关系,进一步分析了信号到达角(DOA)与噪声增益之间的关系,并说明了信号DOA对分离后的信号解码的影响;最后,以均匀线阵(ULA)为例仿真说明了信号DOA对信源数检测、噪声增益的影响。结果表明,对于两个S模式交叠的情况,PA算法在六阵元ULA下可以达到80%以上的检测成功率,并有较好的分离效果。     

Antenna excitation for maximum gain

The problem of obtaining the excitation of an antenna array for maximum power gain is considered in terms of network parameters defined at the input terminals. The reciprocal problem of loading an antenna for maximum absorption area is also considered. The network parameters may be either calculated by solving appropriate boundary value problems, or measured on arrays already constructed. Some procedures for experimentally determining the excitation for maximum gain are presented. If the array elements are closely spaced, supergain antennas are obtained. Formulas for estimating the frequency sensitivity, orQ, of such supergain arrays are given, and the gain-bandwidth product is discussed.     

Modélisation d’une antenne-réseau et traitement optimal

An array antenna is modeled after a linear multipole filter, one part of which is connected to a distant source, radiating in a specified direction, while the relations between the other parts are characterized by the antenna admittance matrix. This modeling technique is applied to an array of parallel linear wire antennas. It is shown how the array admittance matrix can be evaluated numerically by a discrete quantization of the Maxwell’s equations with the proper boundary conditions (Harrington’s method of moments). The admittance matrix is then used to formulate the optimum signal processing for transmission (maximization of antenna gain, with or without constraints) and for reception (maximization of signalto-noise ratio). Along with the model of the array antenna that is submitted, a method of signal processing is developed in which accurate estimates are included of the losses that occur within the array elements as well as of the coupling between elements and of the noise arising in the receiving system. The antenna designer can thus optimize the geometric configuration of the array and study the phenomenon of superdirectivity with a more realistic approach than was hitherto possible.     

Features of formation of the patterns of a monopulse active phased array antenna with a dome lens

A method for the control of the transmission coefficients of antenna elements of a system comprising an active phased array antenna (APAA) and a dome lens, which ensures formation of a deep boresight null of the elevation difference pattern, is proposed. The effect of the control method on the characteristics of receiving monopulse channels of the APAA depending on the intrinsic noise of antenna elements is analyzed. The results of the well-known theory of reception of a nonplane wave by an antenna with continuous aperture are extended to the case of an array antenna.     

一种旋转可控式二元AIS 八木天线阵列

为改善自动识别系统(AIS)数据丢失问题、增大AIS 基站通信距离、解决通信覆盖区域单一的问题, 针对传统AIS 全向天线和定向天线的不足,研究出旋转可控式二元八木天线阵,每个阵元都由八木天线组成,通过电控可以使两个阵元同步旋转,也可以分别旋转。当两八木天线平行时,天线阵增益最大,经测试可达近17 dBi。做了AIS 信息接收实验,天线可以接收距长江口50 海里以内水域的AIS 信息。通过各自旋转并改变天线阵元的角度,可以实现方向图的快速切换。对八木天线进行理论分析,利用基于有限元算法的HFSS 进行仿真,仿真结果与实验结果相近。该天线阵既确保了天线增益,又能通过电控来实现波束快速转换,较一般天线通信距离更长,且能灵活控制通信覆盖范围,对AIS 可靠的数据交换及海事监管具有一定的参考价值。     

Direction of Arrival Estimation in the Presence of Noise Coupling in Antenna Arrays

The direction of arrival (DOA) estimation problem in the presence of signal and noise coupling in antenna arrays is addressed. In many applications, such as smart antenna, radar and navigation systems, the noise coupling between different antenna array elements is often neglected in the antenna modeling and thus, may significantly degrade the system performance. Utilizing the exact noise covariance matrix enables to achieve high-performance source localization by taking into account the colored properties of the array noise. The noise covariance matrix of the antenna array consists of both the external noise sources from sky, ground and interference, and the internal noise sources from amplifiers and loads. Computation of the internal noise covariance matrix is implemented using the theory of noisy linear networks combined with the method of moments (MoM). Based on this noise statistical analysis, a new four-port antenna element consisting of two orthogonal loops is proposed with enhanced source localization performance. The maximum likelihood (ML) estimator and the Cramer-Rao lower bound (CRLB) for DOA estimation in the presence of noise coupling is derived. Simulation results show that the noise coupling in antenna arrays may substantially alter the source localization performance. The performance of a mismatched ML estimator based on a model which ignores the noise coupling shows significant performance degradation due to noise coupling. These results demonstrate the importance of the noise coupling modeling in the DOA estimation algorithms.     

Selecting array configurations for MIMO systems: an evolutionary computation approach

This paper presents an antenna selection method for multiple-input multiple-output wireless systems. By exploitation of the channel transfer matrix, the antenna selection criterion is the maximization of the instantaneous capacity achieved using a specific number of transmitting and receiving antenna array elements. For each environment, the proposed method applies a genetic algorithm which seeks the most advantageous subset of antenna elements. The results are based on measured and simulated channels and show that the proposed method selects array configurations that yield superior performance compared to the arrays usually employed. Furthermore, comparative analysis results are presented, with respect to a state-of-the-art algorithm.     

一种新型圆极化可重构天线

本文利用最大功率传输效率法(MMPTE),通过4个相同左旋圆极化贴片单元作为子阵来实现阵列天线圆极化可重构。通过在被设计阵列(作为发射阵列)远场区引入极化控制接收天线,可以将整个收发系统看作一个无线功率传输系统,这样就可以把阵列天线的设计问题转换为一个天线之间的传输效率最优化的问题。通过调节接收天线的极化方式和接收位置,可控制被设计阵列的极化方式和扫描角度。与传统做法不同的是,被设计阵列单元的极化方式确定时,通过改变接收天线的极化方式,阵列还能产生与单元极化相反的极化方式,同时两种极化方式所得的增益差距在1dBi以内。本文以中心频率在2.45GHz的左旋圆极化单元组成的十六单元阵列为例,说明如何实现阵列左右旋极化的可重构以及+/-60°的扫描功能。     

星载数字波束形成系统中阵元位置误差的分析

阵列天线的阵元位置误差能够造成数字波束形成系统性能的严重恶化。引起阵列天线导引矩阵失配的原因很多,阵元位置误差是最重要的因素之一。首先从物理的角度对阵元位置误差进行了理论建模,提出了阵元位置误差的圆柱形不确定度模型。作为整个天线系统误差构成的重要一环,对阵元位置误差造成的接收信号相位误差进行了量化分析,给出了相互关系。最后就如何消除阵元位置误差的影响进行了讨论。     

Receiving Phased Antenna Array Based on Injection-Locked Harmonic Self-Oscillating Mixers

A 4 times 1 element receiving phased antenna array is presented with phase-shifter elements based on injection-locked harmonic self-oscillating mixers. Each phase-shifter element provides the double functionality of variable phase-shifter and down-converter. The phase-shifts applied to the input signals coming from the different antenna patch elements can be selected by dc control signals in a continuous range of 450deg. The required dc control voltages are calculated for the different incident angles by means of harmonic balance simulations. The influences of phase-shift and conversion gain errors on the beam-steering frequency performance of the antenna are studied. Also illustrated is how the phase-shifter parameters can be optimized in order to minimize the frequency scanning. A 4 times 1 element receiving phased antenna array, with an input frequency band centered at 11.25 GHz and the output frequency band centered at 1.5 GHz, has been manufactured for the experimental validation of the simulated results. A beam scanning range from -23deg to 23deg has been experimentally obtained.     

Smart antennas in wireless systems: uplink multiuser blind channeland sequence detection

Space-division multiple-access (SDMA) schemes have been proposed to increase the capacity of wireless communication systems by simultaneously transmitting and receiving multiple co-channel signals through different spatial channels. We address the uplink (remote users to the base station antenna array) blind channel and sequence identification problem for an SDMA system. We show that multiuser blind identification can be accomplished by exploiting the spatial and temporal diversities of an antenna array system. In particular, a recursive estimation algorithm is developed to recover multiple signals from intersymbol interference (ISI) and co-channel interference (CCI) by taking advantage of a special structure of the array output and the finite-alphabet property of digital communication signals. The implementation of the proposed approach in practical applications is discussed, and field experiments have been conducted to demonstrate the effectiveness of the proposed algorithm     

Space-time cross-correlation functions for antenna array elements in a noise field

The importance of designing a radar (or communications) receiver to operate effectively in the presence of spatial noise creates the necessity for determining the space-time cross-correlation functions between antenna array elements. A representation of a general, polarized, nonisotropic noise process is used to determine the cross-spectral densities and cross-correlation functions between arbitrarily oriented dipole antenna array elements in the presence of a noise field only. Several examples have been worked out for isotropic noise to show the variation of the cross-correlated noise function vs. the spatial separation of the dipoles. One important result is that the noise cross correlation is shown to be a function of the receiver element spatial orientation when the elements are dipoles. For certain spatial orientations between dipoles it is possible to reduce the noise cross correlation between these antenna array elements to zero.     

通信天线信道容量机电耦合建模及阵元位置灵敏度分析

以相控阵天线为代表的下一代通信基站天线正在向着高频段、高增益、高密度、高指向精度方向发展,机械结构因素对通信系统信道质量的影响与制约越来越明显、机电耦合问题越来越突出.为有效保证复杂环境下5G/6G通信容量目标的实现,本文针对通信基站相控阵天线的机电热耦合问题,建立了融合阵元位置偏移、姿态偏转及温度分布等因素的基站天线信道容量机电耦合模型,可据此快速评估射频器件发热环境下通信指标退化情况;构建了阵列天线电场强度与信道容量对阵元随机位置误差的灵敏度模型,分析比较了不同工作条件下各阵元随机位置误差对通信指标的影响规律.     

Evaluation of adaptive phased array antenna, far-field nullingperformance in the near-field region

A theory for analyzing the behavior of adaptive phased array antennas illuminated by a near-field interference test source is presented. Conventional phased array near-field focusing is used to produce an equivalent far-field antenna pattern at a range distance of one to two aperture diameters from the adaptive antenna under test. The antenna is assumed to be a linear array of isotropic receive elements. The interferer is assumed to be a bandlimited noise source radiating from an isotropic antenna. The theory is developed for both partially and fully adaptive arrays. Results are presented for the fully adaptive array case with single and multiple interferers. The results indicate that near-field and far-field adaptive nulling can be equivalent. The adaptive nulling characteristics studied in detail are the array radiation patterns, adaptive cancellation, covariance matrix eigenvalues, and adaptive array weights     

Optimal Antenna Radiation Characteristics for Diversity and MIMO Systems

This paper proposes a method for determining the antenna element radiation characteristics that maximize diversity gain given a specific power angular spectrum of the propagation environment. The method numerically constructs the eigenfunctions of the covariance operator for the scenario subject to constraints on the radiated power and allowable level of supergain. The discussion also focuses on how the resulting radiation characteristics approximately optimize average capacity for multiple-input multiple-output communications. Computational results reveal that optimal antenna characteristics can provide significantly more diversity gain than that offered by the characteristics of a simple design. An example computation using genetic algorithm optimization demonstrates that a numerically optimized practical design can be designed whose performance is relatively close to that of the optimal array.      

Performance of Electrically Small Array Receiving Systems in the Presence of Noise

The performance of broad band electrically small beamed receiving arrays operating in the high-frequency band (3 to 30 MHz) and in a random noise environment is studied. The concepts of system noise figure (SNF) and signal-to-noise ratio improvement factor (SNIF) are proposed as criteria for comparing one array antenna receiving system to any reference antenna system when the conditions of operation are defined. Graphical representations of SNIF for the two- and four-element antenna systems versus a single-element system are presented. SNIF is shown to depend on the geometry of the array, on the phasing network, and on the ratio of atmospheric noise power to internal system noise power.