Estimation of probability density function using spectral analysis

The authors present a new bound on the estimation of the probability density function of random signals, using Woodward's theorem, correlation techniques and spectral analysis. The proposed method is based on the spectral analysis of the random process     

Direction of arrival estimation using adaptive directional time-frequency distributions

Time-frequency distributions (TFDs) allow direction of arrival (DOA) estimation algorithms to be used in scenarios when the total number of sources are more than the number of sensors. The performance of such time–frequency (t–f) based DOA estimation algorithms depends on the resolution of the underlying TFD as a higher resolution TFD leads to better separation of sources in the t–f domain. This paper presents a novel DOA estimation algorithm that uses the adaptive directional t–f distribution (ADTFD) for the analysis of close signal components. The ADTFD optimizes the direction of kernel at each point in the t–f domain to obtain a clear t–f representation, which is then exploited for DOA estimation. Moreover, the proposed methodology can also be applied for DOA estimation of sparse signals. Experimental results indicate that the proposed DOA algorithm based on the ADTFD outperforms other fixed and adaptive kernel based DOA algorithms.     

Asymmetric probability density function of a signal withinterferometric crosstalk

An asymmetric probability density function due to the beating of interferometric crosstalk and amplifier spontaneous emission noise in a system with optical preamplifier is observed experimentally and explained theoretically. An accurate derivation of the probability density function of the photocurrent in the presence of N incoherent homodyne interferers is presented, for the first time, to explain the asymmetry. The model is compared with the experiment and is shown to be in excellent agreement     

Statistical cellular Gaussian scatter density channel model employing a directional antenna for mobile environments

The statistical Gaussian scatter density model (GSDM) is used to evaluate the effects on the Doppler power density spectrum (PDS) when a directional antenna at base station (BS) is employed. We derive the angle of arrival (AOA) probability density function (pdf ) of the multipath components at the mobile station (MS). The AOA pdf at the MS and the PDS, are compared with those for the Clarke's model and the macrocell circular model. We demonstrate that the circular model overestimates the probability of scatterers with AOA near to the line of sight (LoS), resulting in a poorer estimation of the PDS unlike the Gaussian model.     

Plasma density measurement using a frequency sweeping short antenna

A new scheme has been developed to measure the plasma density directly with the use of a short antenna driven by a sweeping frequency RF source and biased by a variable negative dc voltage.     

Estimation of the spatial correlation function and angular spectrum by using a multiantenna system

A closed formula based on representing the angular spectrum in the Fourier basis was obtained for computing the correlation coefficients of signal fadings in elements of the multiantenna system. The method of estimating the expansion coefficients of the angular spectrum with subsequent evaluation of the spatial correlation function was proposed.     

采用EBG地的低剖面微带定向天线设计

对具有金属地的微带定向天线,低剖面设计面临着工作频带窄的难题。采用蘑菇形EBG结构代替微带定向天线的常规金属地,利用EBG地对特定频率电磁波的同相反射特性,在保持天线工作频带条件下,缩减天线微带基板的厚度,实现低剖面设计。以一只工作频点为5.8 GHz的2×2微带阵列天线为例,该阵列天线的辐射单元采用分形结构以进一步提升天线带宽。仿真计算和实际测试表明:该微带阵列天线在采用低剖面设计后,微带基板厚度由原1.0 mm降至0.25 mm,而天线的定向辐射方向图、增益和工作带宽基本保持不变。     

The estimation of a probability density function from measurements corrupted by Poisson noise (Corresp.)

The estimation of a probability density function from measurements corrupted by independent additive Poisson noise is considered. An estimate is derived that is asymptotically unbiased and consistent in the quadratic mean. Also, a practical realization of the estimator is given.     

The probability density function for the output of a correlator with band-pass input waveforms

A general expression is obtained for the characteristic function for the output of a correlator with narrow-band inputs. This general expression is applicable to cases in which the input signals are sinusoidal and have arbitrary amplitudes and phases, and in which the noise inputs are partially correlated. The probability density function for the output is obtained for three special cases, one of which corresponds to a situation that often arises in practice. This practical situation is that in which the signal inputs have the same amplitude and phase, and the noise inputs have the same rms value but are uncorrelated.     

一种新型自适应天线的波达方向估计特性分析

针对杜惠平(1999)提出的一种基于菲涅尔相位修正聚焦结构的多波束自适应天线,利用最大似然估计算法实现了这种自适应天线的空间来波方向估计,考虑了信躁比、快拍次数和阵元间距等参数对估计结果的影响,分析了估计的统计性能及其克拉美-罗界,所做工作适用于透射型和反射型菲涅尔区板天线。仿真计算与有关文献理论分析结果吻合较好,表明本文建立的菲涅尔区天线波达方向估计模型的有效性。     

应用定向天线测量无线信道角度功率谱

针对无线信道角度功率谱测量问题,提出了一种简单而新颖的测量方法.利用定向天线进行方位角扫描的功率测量,观测值、天线方向图和角度功率谱之间构成第一类Fredholm积分方程,通过求解积分方程可以得到角度功率谱.利用低通滤波器对观测数据进行预处理可以克服解积分方程的病态问题,改变滤波器参数并结合最小均方误差准则,可以得到角度功率谱的最小均方误差估计.仿真结果验证了该方法的有效性.     

Traveling wave optical modulator using a directional coupler LiNbO3waveguide

Fabrication methods for low drive voltage and broad-band LiNbO3waveguide directional coupler optical modulator are described. Optical waveguides were prepared by conventionaly Ti in-diffusion into LiNbO3c-cut plate. To obtain wide-band frequency response, traveling wave electrodes were used. Electrode characteristic impedance measured by time domain reflectometry method coincided well with the calculated value by conformal mapping. Measured electrode conductor losses followed square root of frequency. To reduce electrode conductor losses, asymmetric and 3-μm thick Al electrodes were used. Directional coupler optical modulator frequency response was analyzed, using the phase difference average value along the propagation directions. Calculated value by this method coincided well with measured value obtained by a swept frequency technique. The characteristics of this modulator at the 1.317-μm wavelength are as follows: 100 percent modulation voltage is 4 V, extinction ratio is 17 dB, optical insertion loss is 5.4 dB, 3-dB bandwidth is 3.6 GHz, and rise time is about 400ps.     

SAR amplitude probability density function estimation based on a generalized Gaussian model.

In the context of remotely sensed data analysis, an important problem is the development of accurate models for the statistics of the pixel intensities. Focusing on synthetic aperture radar (SAR) data, this modeling process turns out to be a crucial task, for instance, for classification or for denoising purposes. In this paper, an innovative parametric estimation methodology for SAR amplitude data is proposed that adopts a generalized Gaussian (GG) model for the complex SAR backscattered signal. A closed-form expression for the corresponding amplitude probability density function (PDF) is derived and a specific parameter estimation algorithm is developed in order to deal with the proposed model. Specifically, the recently proposed "method-of-log-cumulants" (MoLC) is applied, which stems from the adoption of the Mellin transform (instead of the usual Fourier transform) in the computation of characteristic functions and from the corresponding generalization of the concepts of moment and cumulant. For the developed GG-based amplitude model, the resulting MoLC estimates turn out to be numerically feasible and are also analytically proved to be consistent. The proposed parametric approach was validated by using several real ERS-1, XSAR, E-SAR, and NASA/JPL airborne SAR images, and the experimental results prove that the method models the amplitude PDF better than several previously proposed parametric models for backscattering phenomena.     

The correlation properties of the arrival angles of a wave reflected by an inhomogeneous scattering layer

The correlation properties of the arrival angles of a plane wave that is obliquely incident on a randomly inhomogeneous refracting medium are considered. The spatial autocorrelation coefficients of the azimuthal and polar angles at the exit from the layer are determined and numerically analyzed. The coefficients are obtained in the incidence plane and in the plane perpendicular to it. It is shown that, when the medium is characterized by a statistically isotropic permittivity, the correlation characteristics of arrival angles are anisotropic.     

An approximate but accurate analysis of the dielectric wedge antenna fed by a slab waveguide using the local mode theory and Schelkunoff equivalence principle

A computationally efficient method to obtain design parameters for tapered radiators is presented. The method uses a local mode theory in conjunction with the Schelkunoff equivalence principle. Radiation patterns of directive gain for dielectric wedge antennas of varying lengths and different dielectric constants are presented. Both the TE and TM cases are considered. The method is validated by comparison with data obtained from a recently developed more rigorous mode-matching method. Excellent agreement is obtained over the physically important angular range from endfire to broadside for the TE case and over the angular range spanned by the major lobe for the TM case.     

Envelope probability density function of the sum of signal, noise and interference

A new closed-form expression of the envelope probability density function for the sum of signal, Gaussian noise and c.w. interference is found.     

General probability density function of packet service times for computer networks

The letter presents derivations of a generalised probability density and distribution functions of packet service times for computer communication networks. Included in the derivation are the effects of message segmentation into packets and the effects of control traffic. We also present the first and the second moments of the packet service times. These expressions can be used in modelling and analysis of computer networks by assigning appropriate values to various parameters.     

Comparison of measured and calculated antenna sidelobe couplingloss in the near field using approximate far-field data

Computer programs presently exist to calculate the coupling loss between two antennas provided that the amplitude and phase of the far field are available. It is shown that when this far-field information is not available it is possible to specify approximate far fields from a knowledge of the sidelobe of each antenna along the axis of separation and the electrical size of each antenna. The ENVLP computer program developed by M.H. Francis and A.D. Yaghjian (ibid. vol.AP-34, p.952-5, July 1986) was modified for this purpose. Measurements of near-field coupling loss between two moderately sized microwave antennas were made to determine the effectiveness of using approximate sidelobe level data instead of the detailed far fields. Comparison of the measured and computed coupling indicates that the use of approximate far fields gives an estimate of the coupling loss with an uncertainty of about ±5 dB     

一种小型化超短波单极子天线设计

超短波天线在舰船飞机上应用很广,天线的小型化有利于提升其隐蔽性、稳固性,因此对天线的小型化设计显得异常重要。采用加载集总元件和宽带匹配网络的方式,设计了一款新型超短波天线。将宽带匹配网络做成一个微带电路结构与天线辐射单元直接相连的一体化设计,进一步减小了天线的长度;采用 Matlab 和 HFSS 软件联合仿真,并运用遗传算法优化计算全部集总元件的具体数值。天线在100 MHz~400 MHz频段范围内的驻波系数 VSWR(电压驻波比)小于3,水平方向全向辐射。天线和匹配网络总的物理长度仅为255 mm,实现了小型化的要求。制作了天线实物并测量,实测天线参数与仿真参数吻合较好,达到了设计目标。