A Self-Steering Array for Nonsinusoidal Waves

A self-steering array system is described for beam forming with nonsinusoidal waves. The array system electronically steers a main beam in the direction of the source from which the wavefront is arriving without prior knowledge of the source locatiora. The principle of monopulse tracking radar is applied to the array system so that the angular coordinate of tihe source can be determiined with respect to the array axis. If the source is in rmotion, it can be tracked on pulse-to-pulse bases. Finally, the self-steering array system is advanced further to suppress the additive thermal noise presenit with the incoming signals, and to achieve good angular resolution and accuracy.     

Two-Dimensional Planar Array for Digital Beamforming and Direction-of-Arrival Estimations

A compact uniplanar design of 2-D antenna arrays is presented for digital beamforming (DBF) and direction-of-arrival (DOA) estimations. The array is based on switchable microstrip slot antennas that are series fed in one dimension and parallel fed in the other dimension. In conjunction with spatial multiplexing of local elements (SMILE) techniques, the array is able to use both the series- and parallel-fed antennas for 2-D beamforming and DOA estimations. The combination of series and parallel feeding provides a simple way of constructing 2-D DBF arrays with a simple and uniplanar feed network. Other advantages are its low cost and compatibility with a microwave integrated circuit process for the receiver system. A 4 $times$ 4 receiving array test bed at a 5.5-GHz operating frequency is fabricated, and DBF and DOA tests on this test bed are successfully demonstrated.      

Antennas for Nonsinusoidal Waves: II-Sensors

The use of the basic large-current radiator?discussed in a previous paper?and the Hertzian electric dipole as sensor is investigated. If the sensor works into a large resistive load, typically implemented by an emitter follower, its output voltage varies like the electric field strength, while a capacitive load produces an output voltage proportionate to the integral of the field strength. The maximum energy is transferred to a load impedance that is equal to the radiation resistance of the antenna. This is the same result as in the case of sinusoidal waves, but the radiation resistance for nonsinusoidal waves differs from that for sinusoidal waves. An effective aperture can be defined, which is again analogous, but not equal, to the same concept used for sinusoidal waves.     

Three-Dimensional Antenna Patterns for Nonsinusoidal Waves

Array beam forming with nonsinusoidal waves allows a trade-off between signal power, frequency bandwidth, and array size for a small resolution angle. In addition, one can derive various antenna patterns with desiralble features for achieving good angular resolution. Such patterns are peak-amplitude, peak-power, ramp-duration, flat-duration, energy, and slope patterns that have been derived for linear arrays. In this paper, the principle of beam forming with noise-free nonsinusoidal waves received by rectangular planar arrays is discussed. Three-dimensional peak-amplitude, energy, and slope patterns are derived for planar arrays with 4 × 4, 8 × 8, 16 × 16, and 32 × 32 sensor elements.     

Two-Dimensional Beamforming with Nonsinusoidal Signals

A two-dimensional beamforming technique is presented for two-dimensional arrays of (N × N) sensors receiving plane wavefronts with nonsinusoidal time variations in the form of a single rectangular pulse of duration T or in the form of a coded sequence of rectangular pulses with nominal time duration T. The three-dimensional energy pattern has a main beam for small angles of incidence and a number of sidelobes for large angles of incidence. For wavefronts with rectangular time variations, the maximum sidelobe has the magnitude 1/N and, for coded time variations, the maximum sidelobe exceeds 1/N. The magnitude of the sidelobes of the energy pattern can be decreased by increasing the number of sensors in the array. The resolution angle can be decreased by the ratio (N1/N2) when the number of sensors is increased from (N1 × N1) to (N2 × N2) and it can be decreased by the ratio (T1/T2) when the nominal time duration is decreased from T2 to T1. Waveform distortion results in a degradation of the resolution angle.     

Nonsinusoidal Waves in Rectangular Waveguides

It is widely believed that a waveguide behaves like a lossless dispersive medium, which implies that only sinusoidal waves can be transmitted without distortions. This is correct for the particular solutions of Maxwell's equations that have been in use since Rayleigh's original investigation in 1897. More general solutions can be found that show that a large class of nonsinusoidal periodic waves can be transmitted distortion-free by a lossless waveguide. These solutions are readily derived for rectangular waveguides by means of the Fourier series, while a generalization of the Fourier series is required for cylindrical waveguides.     

Nonsinusoidal Waves in Cavity Resonators

It has been shown that nonsinusoidal waves can propagate dispersion-free in loss-free waveguides. This situation opens the possibility of nonsinusoidal waves existing distortion-free in cavity resonators. A general solution of Maxwell's equations for nonsinusoidal waves in rectangular cavity resonators is derived. For the special case of a square wave, the electric and magnetic field strengths as functions of time and space are analyzed in detail. The implication of this analysis is that square waves or other periodic nonsinusoidal waves with various periods T can be separated by cavity resonators just as sinusoidal waves with various periods T can be separated. This paper is part of an ongoing effort to advance the technology of antennas and associated circuits for nonsinusoidal electromagnetic waves.     

基于子阵划分的二维穿墙MIMO阵列设计

穿墙三维成像中,不同的阵列构架会直接影响阵列性能及其适用环境。利用等效阵列原理设计二维多输入多输出(MIMO)阵列,在具体分析一维STVA阵列具有最短物理尺寸的原理上,提出了利用子阵划分的方法解决等效阵列到MIMO阵列的去卷积问题。针对去卷积后得到多种MIMO阵列构型的择优问题,提出了综合尺寸的概念,利用子阵划分后的部分信息衡量去卷积后MIMO阵列的物理尺寸,最后将这种方法推广至二维MIMO阵列,设计出适用于穿墙成像的二维UWB-MIMO阵列,利用仿真实验验证了其在穿墙三维成像中的优异性能。     

Antennas for Nonsinusoidal Waves. I. Radiators

During the last years numerous applications of nonsinusoidal electromagnetic waves have been discussed in this TRANSACTIONS. The next step is the implementation of these applications. It is generally accepted that the antennas pose the greatest diMculty. In a series of papers on radiators, sensors, and arrays, we will investigate antennas, both theoretically and experimentally. Sufficient information is provided to permit anybody who is equiped for work with pulses of about I-ns duration to build simple radiators and sensors.     

一种平面阵的非均匀子阵划分方法

大型相控阵雷达阵元数目众多,系统结构复杂,在实际中一般采用子阵结构,以减少通道数和设计成本。均匀划分的子阵级波束形成会产生栅瓣和栅零点;设计合理的非均匀划分方法可以有效的抑制栅瓣和栅零点,缺点是旁瓣较高和自适应性能下降。本文针对等幅平面阵提出了一种简单的非均匀划分子阵的方法,能够打乱子阵排列的周期性,有效降低了子阵级方向图的旁瓣。仿真验证了该方法的有效性。     

Radiation of Nonsinusoidal Waves by a Large-Current Radiator

The calculation of the electric and magnetic field strength produced by a radiator is usually done only for distances large compared with the geometric dimensions of the radiator. This approach makes it Impossible to obtain exact relations between the power fed to the radiator by the driver, the voltage between the radiator terminals, the power radiated to or received from the near zone, and the power radiated to the far zone. This paper develops a solution for the large-current radiator that can be evaluated numerically by computer for any distance, and thus permits the calculation of the power flowing at any time through the surface of the radiator. The knowledge of this power is the basis for the design of efficient radiators.     

A Bifocal Focused Two-Dimensional Frequency-Scanned Array

A 2D frequency-scanned array focused in the near-field zone is analyzed. A method for the synthesis of this array ensuring perfect field focusing in two points at two frequencies is proposed. Array scanning in two planes (longitudinal and transverse) is analyzed with the use of an approximate model. The motion trajectory of the focal spot (scanning arc) and optical aberrations associated with scanning are studied. Different variants of determination of the scanning arc, using the criterion of the maximum field intensity and the criterion of the maximum aperture efficiency of the array, are considered. It is shown that application of bifocal arrays can improve main quality indices as compared to those of single-focus arrays.     

平面天线阵快速正交投影波束形成算法

针对大型平面天线阵列下样本数据含有期望信号时，正交投影（OP）波束形成算法不再适用的问题，提出一种新的基于阻塞矩阵的正交投影快速波束形成算法。该算法首先构造阻塞矩阵从样本信号中阻塞掉期望信号，再对阻塞后的样本信号进行施密特（GS）正交化得到重构后的干扰子空间，最后在此基础上实现正交投影波束形成。新算法适用于任意阵型的二维均匀平面阵，在小快拍数下能快速计算出自适应权重。仿真结果表明，无论是弱干扰信号还是强干扰信号，该算法都具有很好的抗干扰性能。     

两维LED阵列初探

本文阐述大型两维发光二极管(LED)阵列的设计、制造及其在虚拟显示象源中的应用.利用双台面蚀刻工艺,由铟镓铝磷(InGaAlP)系材料制成LED象素.边长为10μm的正方形LED在峰值发射波长约650nm时,外量子效率为0.5%,亮度达10fL,而阵列功耗仅为2.9mW.LED阵列由240行×144列(～VGA/8)个象素组成,象素节距为20μm,显示速度每秒60帧,按行主导矩阵寻址方式来驱动.象素在恒定电流下以脉宽调制来驱动,灰度达16级.本文对阵列亮度的均匀性作了分析.取样图象、图形及灰度图象皆证明,LED阵列可用作虚拟显示的单色象源.     

任意平面阵列的干扰抑制

本文提出一种任意平面阵列抑制干扰的方法.对任意平面阵列的接收信号进行多次正交变换,然后对变换后信号的自相关矩阵求平均值,所得矩阵应用最大信号与干扰加噪声功率比准则求得抑制干扰的权值.计算机模拟实验表明,该方法能有效抑制干扰且对干扰信号之间的相关特性没有要求.     

一种稳健的机载面阵雷达非均匀杂波抑制方法

在非均匀杂波和密集目标环境下,由于没有足够的独立同分布(IID)训练样本,传统空时自适应处理(STAP)方法的杂波抑制性能严重下降。针对以上问题,该文提出一种对阵元误差稳健的机载面阵雷达非均匀杂波抑制方法。该方法首先根据雷达系统参数先验知识构造杂波表示基矩阵。然后在考虑阵元误差的情况下,基于最小二乘准则迭代地估计杂波表示系数和阵元误差,最后利用估计得到的最优杂波表示系数和阵元误差直接在阵元脉冲域进行杂波对消。该方法无须估计待检测单元统计特性;没有孔径损失;不需要训练样本;即使在距离模糊情况下也能有效地抑制密集目标环境下机载面阵雷达回波数据中的非均匀杂波。仿真结果验证了该文方法的有效性。

     

Incoherent Two-Dimensional Array Modulation Transceiver for Photonic CDMA

This paper proposes a novel incoherent optical code-division multiple-access (OCDMA) transceiver design, as a promising network access employing a newly introduced prime code family named as double-padded modified prime code as spreading sequences, based on the 2-D optical modulation scheme deploying frequency and polarization shift keying. Hereafter, it is referred to as F-PolSK. The novel F-PolSK-OCDMA system has been accurately analyzed taking into account the presence of 1) optical amplified spontaneous emission noise; 2) electronic receiver noise; 3) photo-diode shot-noise; and 4) multiple-access interference (MAI). The application of the optical tapped-delay lines at the receiver as a CDMA-decoder has also been investigated. The evaluation of 2-D array modulation in conjunction with OCDMA indicates that the binary combination of this hybrid scheme enhances the overall system performance. The results reveal that the proposed architecture can easily accommodate greater number of users and consume less power as compared with previous schemes. On the other hand, in polarization modulation since the optical beam power is constant, the system has immunity against the self- and cross-phase modulations. Besides, the system security is much enhanced due to 2-D advanced modulation in optical domain.     

平面阵MIMO雷达发射方向图设计方法

针对现有MIMO雷达发射方向图设计方法无法直接推广到平面阵MIMO雷达的问题,在平面阵方向图可以由水平和垂直方向的线阵方向图合成的思想基础上,该文提出一种应用基波束和概率选择方法设计平面阵MIMO雷达发射方向图的方法。该方法首先将期望方向图沿方位角累加,形成1维俯仰角方向图,建立垂直方向线阵的俯仰角基波束集合和该集合元素的概率选择优化模型;其次针对每个俯仰角对应的1维方位角期望方向图,建立水平方向线阵的方位角基波束集合和该集合元素的概率选择优化模型;最后合成2维基波束集合和集合中元素的选择概率,并求得平面阵MIMO雷达的发射方向图和发射信号。该方法中的优化问题都是凸问题,可以求得全局最优解。     

一种平面印刷电控波束扫描天线阵

该文设计了一种平面印刷偶极子波束扫描寄生阵列天线,可用于移动终端设备以提高通信质量和系统容量。通过改变加载在寄生单元中的电抗值可以控制天线的最大辐射方向。天线基本结构用电磁场全波软件设计,所需加载的电抗值通过差分进化算法(DE)优化得出。实测的天线主波束方向在xoy平面内-34~38之间扫描;在各方向上,中心工作频率上的增益在3.6~4.9 dBi之间变化,反射系数小于-10 dB的频带在5.63~5.96 GHz之间,带宽为330 MHz。实测结果表明,天线具有良好的波束扫描性能,采用的设计和优化方法准确高效。