Output Of Antenna Array Research Articles

24 GHz Flexible Antenna for Doppler Radar-Based Human Vital Signs Monitoring.

Noncontact monitoring of human vital signs has been an emerging research topic in recent years. A key approach to this monitoring is the use of the Doppler radar concept which enables real-time vital signs detection, resulting in a new class of radar system known as bio-radar. The antennas are a key component of any bio-radar module and their designs should meet the common requirements of bio-radar applications such as high radiation directivity and mechanical flexibility. This paper presents the design of a four-element antenna array on a flexible liquid crystal polymer (LCP) substrate of 100 μm thickness and εr of 3.35. The designed antenna array can be used with a 24 GHz bio-radar for vital signs monitoring in a non-contact manner. It features a relatively compact size of 36.5 × 53 mm2 and measured gain of 5.81 dBi. The two vital signs: breathing rate (BR) and heart rate (HR) of two human subjects are detected with relatively good accuracy using the fabricated antenna array and radio frequency (RF) output power of −3 dBm from a distance of approximately 60 cm. The effect of bending on the antenna performance is also analyzed.

Weight Vector Fluctuations in Adaptive Antenna Arrays Tuned Using the Least-Mean-Square Error Algorithm with Quadratic Constraint

We present the results of statistical analysis of an adaptive antenna array tuned using the least-mean-square error algorithm with quadratic constraint on the useful-signal amplification with allowance for the weight-coefficient fluctuations. Using the perturbation theory, the expressions for the correlation function and power of the output signal of the adaptive antenna array, as well as the formula for the weight-vector covariance matrix are obtained in the first approximation. The fluctuations are shown to lead to the signal distortions at the antenna-array output. The weight-coefficient fluctuations result in the appearance of additional terms in the statistical characteristics of the antenna array. It is also shown that the weight-vector fluctuations are isotropic, i.e., identical in all directions of the weight-coefficient space.

A Computationally Efficient Iterative MLE for GPS AOA Estimation

This paper presents a computationally efficient algorithm for GPS signal angle of arrival (AOA) estimation based on an iterative maximum likelihood estimator (iMLE) operating on an antenna array output. The iMLE has global convergence and therefore can estimate the true AOA MLE, regardless of the initial value, and has a simple mathematical form without any derivative or matrix decomposition computation. Simulations are performed for signals with different antenna array parameters, and the performances are compared with that of conventional MUSIC and CAPON methods. The results demonstrate that the iMLE can achieve better noise performance even with a small number of antenna elements. The paper also presents a tracking mode for the iMLE that further improves its performance for signals with low signal-to-noise ratio (SNR) and greatly extends its application into weak GPS signal or multipath environments.

Biologically Inspired Coupled Antenna Array for Direction-of-Arrival Estimation

We propose to design a small-size antenna array having high direction-of-arrival (DOA) estimation performance, inspired by the Ormia ochracea's coupled ears. The female Ormia is able to locate male crickets' call accurately, for reproduction purposes, despite the small distance between its ears compared with the incoming wavelength. This phenomenon has been explained by the mechanical coupling between the Ormia's ears, modeled by a pair of differential equations. In this paper, we first solve the differential equations governing the Ormia ochracea's ear response, and convert the response to the prespecified radio frequencies. Using the converted response, we then implement the biologically inspired coupling as a multi-input multi-output filter on a uniform linear antenna array output. We derive the maximum likelihood estimates of source DOAs, and compute the corresponding Cramer-Rao bound on the DOA estimation error as a performance measure. We also consider a circular array configuration and compute the mean-square angular error bound on the three-dimensional localization accuracy. Moreover, we propose an algorithm to optimally choose the biologically inspired coupling for maximum localization performance. We use Monte Carlo numerical examples to demonstrate the advantages of the coupling effect.

Spectral correlation characteristics of an adaptive Antenna array tuned by the Hebb algorithm with allowance for the weight-vector fluctuations

In this paper, we present the results of statistical analysis of the characteristics of an adaptive antenna array tuned by the Hebb algorithm with allowance for the weight-vector fluctuations in the case where signals with different levels of autocorrelatedness of the input-signal readouts arrive at the antenna array. Expressions for the correlation function of the output signal and the power spectral density at the antenna-array output are obtained. It is shown that fluctuations lead to distortions of the output signal of the adaptive antenna array and appearance of additional terms in the formulas for these characteristics.

The effect of fluctuations of weighting coefficients on the statistical characteristics of an adaptive antenna array tuned according to the Hebb algorithm

The results of analyzing the statistical characteristics of the weighting vector of an adaptive antenna array tuned according to the Hebb algorithm, which is one of the classical learning algorithms used for tuning of artificial neural networks, are presented. The analysis is performed with consideration for fluctuations of the weighting vector. It is shown that fluctuations lead to distortions of the antenna-array output signal and to the mismatch effect (the presence of the residual power at the antenna output) that arises owing to fluctuations of weighting coefficients. In an adaptive antenna array tuned according to the Hebb algorithm, the overcompensation effect is not observed.

A Blind Space-Time Constrained Minimum Output Energy Detector for DS-CDMA Communication System

In this paper, a blind space-time (ST) multiuser detector, called ST constrained minimum output energy (ST-CMOE) detector, is proposed. It can be viewed as an extension of the CMOE method ( Proc. Globecom, p. 379, 1994), and therefore it is immune to near-far effect. It processes the antenna array output jointly in spatial and temporal domain. Simulation results show that the proposed algorithm can outperform the space-CMOE detector proposed by Wang and Poor ( IEEE Trans. Signal Process. vol. 47, p. 2356, 1999) which process the received signal in spatial and temporal domain separately. It can also outperform the ST subspace detector proposed by Chkeif (IEEE Trans. Commun. vol. 48, p. 729, 2000), which, although processes the received signal jointly in spatial and temporal domains, suffers from the mismatch problem in the multipath environment. The simulation results also show that the proposed ST-CMOE detector can achieve the same performance as the training-based ST minimum-mean-square-error detector. In order to reduce the computational load and adapt to dynamic multiple-access channels, an adaptive algorithm is presented. The computational load of this adaptive detector is comparable to Hu's method (IEEE Trans. Signal Process . vol. 52, p. 1862, 2004), while it does not require any initial training or channel estimation in the multipath environment. Simulation results show that the proposed adaptive ST-CMOE detector can work well in a dynamic multiple-access channel, where interferences may enter or leave the channel at any time

Weight vector fluctuations in adaptive antenna arrays with nonlinear function in a feedback loop

We present the results of statistical analysis of adaptive antenna arrays with nonlinear function in the feedback loop, which are adjusted by an algorithm for recurrent inversion of a sample estimate of the input-signal correlation matrix with allowance for the weight-coefficient fluctuations. Using the perturbation-theory methods in the first (Born) approximation, we obtain expressions for the correlation function and power of the output signal of an adaptive antenna array and a formula for the covariance matrix of the weight-coefficient vector. The weight-coefficient fluctuations are shown to result in signal distortions at the antenna-array output and appearance of additional terms in the statistical characteristics of the antenna array. These terms are second-order infinitesimals with respect to adaptation coefficient. Fluctuations are first-order infinitesimals and, thus, are much greater in an antenna array without nonlinear function in the feedback loop. It is also shown that the weight-vector fluctuations are anisotropic, i.e., they are absent in the constraint direction, minimal in the interference direction, and maximal in all other directions.

A Blind Adaptive QR-Based Lattice Multi-Channel Filter for CellularBase-Station TDMA Transceivers with Antenna Arrays

A new adaptive algorithm for blind interference rejection and multipath mitigation is studied and applied to antenna array processing in TDMA cellular communication systems. It is shown how the estimation of multiple signals from different sources by means of a multi-sensor receiver can be formulated as a multi-channel deconvolution problem. The proposed method is based on High-Order Statistics (HOS) processing of the baseband vector samples at the antenna array output. The similarity between the cumulant-based solution and the standard multi-variable Least Squares solution is exploited to derive an efficient adaptive algorithm based on the vector lattice architecture. The algorithm is numerically stable, considerably less complex than other existing multi-channel methods using HOS processing and exhibits rapid convergence with respect to blind array processing algorithms using simple gradient-based minimization procedures.

An adaptive algorithm for antenna array low-rank processing in cellular TDMA base stations

A new adaptive algorithm for blind interference rejection and multipath mitigation is studied and applied to antenna array processing in the reverse channel of a time-division multiple-access (TDMA) cellular communication system. The method is based on higher order statistics (HOS) processing of the baseband vector samples at the antenna array output. The similarity between the cumulant-based solution and the standard multivariable least-squares solution is exploited to derive an efficient adaptive algorithm based on a low-rank processing architecture. The algorithm exhibits good tracking and enhanced identification capability with respect to traditional least-squares methods.