Mutual Coupling in Phased Arrays: A Review

The mutual coupling between antenna elements affects the antenna parameters like terminal impedances, reflection coefficients and hence the antenna array performance in terms of radiation characteristics, output signal-to-interference noise ratio (SINR), and radar cross section (RCS). This coupling effect is also known to directly or indirectly influence the steady state and transient response, the resolution capability, interference rejection, and direction-of-arrival (DOA) estimation competence of the array. Researchers have proposed several techniques and designs for optimal performance of phased array in a given signal environment, counteracting the coupling effect. This paper presents a comprehensive review of the methods that model and mitigate the mutual coupling effect for different types of arrays. The parameters that get affected due to the presence of coupling thereby degrading the array performance are discussed. The techniques for optimization of the antenna characteristics in the presence of coupling are also included

Enhanced Direction of Arrival Estimation through Electromagnetic Modeling

Engineering is a high art that balances modeling the physical world and designing meaningful solutions based on those models. Array signal processing is no exception, and many innovative and creative solutions have come from the field of array processing. However, many of the innovative algorithms that permeate the field are based on a very simple signal model of an array. This simple, although powerful, model is at times a pale reflection of the complexities inherent in the physical world, and this model mismatch opens the door to the performance degradation of any solution for which the model underpins. This dissertation seeks to explore the impact of model mismatch upon common array processing algorithms. To that end, this dissertation brings together the disparate topics of electromagnetics and signal processing. Electromagnetics brings a singular focus on the physical interactions of electromagnetic waves and physical array structures, while signal processing brings modern computational power to solve difficult problems. We delve into model mismatch in two ways; first, by developing a blind array calibration routine that estimates model mismatch and incorporates that knowledge into the reiterative superresoluiton (RISR) direction of arrival estimation algorithm; second, by examining model mismatch between a transmitting and receiving array, and assessing the impact of this mismatch on prolific direction of arrival estimation algorithms. In both of these studies we show that engineers have traded algorithm performance for model simplicity, and that if we are willing to deal with the added complexity we can recapture that lost performance

Evaluation and Analysis of Array Antennas for Passive Coherent Location (PCL) Systems

Passive Coherent Location (PCL) systems use a special form of a radar receiver that exploits the ambient radiation in the environment to detect and track targets. Typical transmissions of opportunity that might be exploited include television and FM radiobroadcasts. PCL implies the use of a non-radar electromagnetic sources of illumination, such as commercial radio or television broadcasts also referred as transmitters of opportunity. The use of such illumination sources means that the receiver needs to process waveforms that are not designed for radar purposes. As a consequence, the receivers for PCL systems must be much more customized than traditional receivers, in order to obtain the most appropriate and best signal. Since antennas are the eyes of the receivers, processing of an incoming signal starts with the antennas. Yet, because PCL system is non-traditional, there has not been much work done in the evaluation of the antennas, even though PCL systems have some demanding constraints on the antenna system. During this research various array antenna designs will be studied by their radiation patterns, gain factors, input impedances, power efficiencies and other features by simulating these arrays in the computer environment. The goal is to show the better performance of the array antennas compared to traditional Yagi-Uda antennas that are currently used for PCL systems

PERFORMANCE ANALYSIS OF DIRECTION OF ARRIVAL ESTIMATION FOR A 3-D UNIFORM VOLUME ARRAY

In this thesis, performance analysis of direction of arrival estimation using an antenna array is performed. We apply methods and concepts commonly used in 1-d linear and 2-d planar arrays to create a 3-d isotropic, uniform volume array. We compare and contrast the effectiveness of a 1-d, 2-d, and 3-d uniform isotropic array to observe the advantages of each. We incorporate the effect of element factor when using half-wave dipole antenna elements rather than isotropic point sources for the elements in our array. We also consider the polarization of the incident wave impinging upon the array. We build three 3-d orthogonal arrays of colinear dipoles and evaluate their performance using two estimation techniques over varying angles of incidence and power levels. The estimation techniques utilized are the maximum likelihood estimation (MLE) and minimum variance distortionless response (MVDR), which are compared against the Cramér–Rao bound (CRB). Performance analysis of these arrays corresponding to the two estimation techniques is performed and summarized. The results show the benefits and limitations of a uniform 3-d antenna array over others.Approved for public release; distribution is unlimited.Lieutenant, United States Nav

Stochastic framework for evaluating the effect of displaced antenna elements on DOA estimation

We establish a statistical framework for investigating the influence of correlated random displacements of antenna elements in a uniform circular antenna array (UCA) on the distribution of direction-of-arrival (DOA) estimates. More specifically, we apply a stochastic collocation method formodeling the sparse UCA root-MUSIC-DOA estimates as polynomial expansions of the random displacements. Compared to Monte-Carlo simulations, this approach yields a speedup of about 40 for the case of a displacement of two antenna elements

The LWA1 Radio Telescope

LWA1 is a new radio telescope operating in the frequency range 10-88 MHz, located in central New Mexico. The telescope consists of 258 pairs of dipole-type antennas whose outputs are individually digitized and formed into beams. Simultaneously, signals from all dipoles can be recorded using one of the instrument's "all dipoles" modes, facilitating all-sky imaging. Notable features of the instrument include high intrinsic sensitivity (about 6 kJy zenith system equivalent flux density), large instantaneous bandwidth (up to 78 MHz), and 4 independently-steerable beams utilizing digital "true time delay" beamforming. This paper summarizes the design of LWA1 and its performance as determined in commissioning experiments. We describe the method currently in use for array calibration, and report on measurements of sensitivity and beamwidth.Comment: 9 pages, 14 figures, accepted by IEEE Trans. Antennas & Propagation. Various minor changes from previous versio