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.     

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。     

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.     

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.     

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.     

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.     

平板缝隙天线的计算机辅助设计

基于边值积分方程方法的小型平面缝隙阵的机助设计方法。这种计算方法是严格的。但即使对于小型阵，计算量也相当大。对小型阵提出缝列与耦合分支分别设计的方法，并给出模型实验结果。实验结果表明，对于一般指标的方阵，这种方法是可行的。对于低分瓣和超低旁瓣阵，尤其大型阵，还需以严格计算代替大量实验，去寻求简化计算的经验方法，建立一种半经验的机助设计方法。     

Guided Waves on a Planar Helix

Considered here is a planar structure comprising a pair of parallel arrays of periodically spaced conducting strips which conduct in different directions in the two arrays. The guiding properties of this planar structure are found to be similar, in one case, to those of circular tape helices. While in general, different dielectric media are assumed in the sandwiched and outer regions, the special cases studied are 1) the case in which air constitutes both the media, 2) the normal-helix case in which the inner medium is a solid dielectric and the outer medium is air, and 3) the "inverted-helix" case with the two media interchanged.     

Generalized Three Dimensional Coprime Array for Two-Dimensional DOA Estimation

Wireless Personal Communications - In this paper, we extend the coprime planar array to coprime cubic array and propose a three dimensional coprime array (TDCA) for two-dimensional direction of...     

Finite-Element Solution of Planar Inhomogeneous Waveguides for Magnetostatic Waves

A unified numerical approach based on the finite-element method is described for the solution of planar inhomogeneous waveguides for magnetostatic waves. Both magnetostatic volume wave and magnetostatic surface wave modes are treated. The validity of the method is confirmed by calculating the magnetostatic wave modes of layered YIG films. The numerical results of inhomogeneous YIG films with alpha-power magnetization profile are also presented, and the effects of magnetization inhomogeneities on the delay characteristics and potential profiles for magnetostatic forward volume wave, magnetostatic backward volume wave, and magnetostatic surface wave modes are examined.     

Synthetic-Aperture Radar Based on Nonsinusoidal Functions: IX ?Array Beam Forming

For sinusoidal waves with bandwidth zero, one obtains the classical formula ? = ? ?/ L = ?c/fL for the resolution angle of a sensor array, where L is the length of the array, ? the wavelength, f the frequency, and c the phase velocity of the wave, while ? is a constant whose value is usually chosen to be 1. Waves with the time variation of a rectangular pulse of duration ?T yield the resolution angle e = 2?cf?P/PN, where P/PN is the signal-to-noise ratio and ?f = 1/2?T the nominal bandwidth of the pulse; the same result holds for coded pulse sequences, such as Barker codes or complementary codes, if the main lobe of their auto-correlation function has the shape of a triangle with rise time ?T. Hence, the resolution angle e can be reduced by increasing the signal power, as well as by increasing the array length L or the bandwidth ?f. For sinusoidal waves, an increase of the signal power brings no reduction of the resolution angle. The trade between signal power and frequency bandwidth is of interest whenever the attenuation increases rapidly with frequency, e.g., in high-resolution all-weather radar or in underwater acoustic beam forming.     

一种改进的两维阵列数字单脉冲测角方法

针对两维阵列数字单脉冲测角,提出一种改进的方法,首先完成一组无等效孔径变化效应的偏差测量,然后通过高阶多项式拟合进一步实现方位和俯仰联合测角,以改善测角误差性能.通过分析无等效孔径变化效应偏差角与方位和俯仰差之间的关系,得到了相应的测角方法;并通过仿真验证了该方法是有效的.