Multi-element Antenna Research Articles

A coaxial fed flower shaped multi‐element suspended patch antenna with illumination area in the form of a ring

AbstractA multi‐element suspended microstrip patch antenna with flower shaped printed pattern excited at its centre by a coaxial feed is presented. All the radiating patch elements are electromagnetically coupled symmetrically to the same coaxial feed, thereby eliminating the need for a separate power division network. With three or more elements, the antenna beam illuminates an area in the form of a ring symmetric about the axis perpendicular to the plane of the patch elements. The antenna offers a gain in the range 5–6 dBi with a 3 dB beamwidth of about 50° in any cross‐sectional plane passing through the vertical axis. Details of the simulation studies carried out on the antenna with one to five elements and experimental results on the fabricated antennas are presented. The antenna has potential applications in remote sensing and biomedical areas, particularly for microwave imaging. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 2037–2043, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25418

Generalised selection combining diversity performance of multi-element antenna systems via a stochastic electromagnetic-circuit methodology

A stochastic electromagnetic-circuit methodology for evaluating the generalised selection combining (GSC) diversity performance of coupled and arbitrarily terminated multi-element antenna (MEA) systems when operating in Rayleigh fading environments is proposed. The methodology is based on the effective length matrix, which connects the incident electric fields to the received voltage and current vectors, and on the newly introduced stochastic generation of realistic propagation environments by means of the angular power density functions and the cross polarisation power ratio of the incoming plane waves. The generated statistical ensemble of voltage and current vectors is then used to determine the receive GSC diversity performance metrics, that is mean effective gain (MEG), envelope correlation coefficient (ρe) and effective diversity gain (EDG). Two compact MEA configurations comprising two and four printed inverted F antennas (IFA) operating in a uniform propagation scenario at the 5.2 GHz band are investigated under various GSC schemes, which include the selection (SC) and the maximal ratio (MRC) as special cases. The simulated values of MEG, ρe and EDG under the MRC scheme are in excellent agreement to those obtained from well-established closed-form methodologies.

GPS Adaptive Array Phase Compensation using a Software Radio Architecture

Digital Beam Forming and nulling are viable means of GPS array signal processing that enable multipath mitigation and provide protection against interference. As reported in the literature [1], nulling causes errors in the carrier phase and code phase measurements. The output of multi element antenna arrays (Controlled Reception Pattern Antennas – CRPAs) are subject to significant variations in their phase patterns that arise from the application of time varying adaptive array weights. This phase error can be compensated in the carrier phase tracking domain in the baseband GPS receiver. Classical approaches implement a constrained beam steering mechanism to control the phase response of the array in the look direction. An alternative approach using unconstrained adaptive array processing with compensation for the subsequent phase distortion of the GPS signal is demonstrated using a software defined GPS radio.

Downlink throughput statistics in interference-limited cellular systems with multi-element antennas

In this study, we first quantify cell-wide mean throughputs in interference-limited single-input-single-output (SISO) and multi-element antenna (MEA) cellular systems along various system-level design dimensions, including: MEA array size; frequency-reuse factor; antenna pattern (omni-directional or sectorized); degree of coding; allowable constellation size; and transmitor receive-adaptation. Next, we examine the validity of a noise-model for co-channel interference present in MEA links. Using system simulations, we show that this model is valid under all conditions, with varying levels of accuracy.

Selection-Combining Diversity Performance of Actual Multielement Antenna Systems Using the Covariance Matrix Method

Until now, the application of the covariance matrix method for evaluating the selection-combining (SC) diversity performance is restricted to the case of actual antenna systems comprising two elements. In this letter, the method is extended in order to apply to multielement antenna (MEA) systems. The performance improvement is evaluated using the effective diversity gain (EDG). Usually, EDG is measured in terms of the signal-to-noise ratio (SNR) enhancement at a specific outage probability. EDG, however, can also be measured in terms of the SNR reduction for achieving a specific average bit error rate (BER). Both EDG expressions are presented and evaluated for a compact MEA system comprising three printed inverted-F antennas (IFAs).

Design, Analysis, and Measurements of an Antenna Structure for 2.4 GHz Wireless Applications

This paper reports measured results of a multielement antenna implementation, we constructed, that performs at 2.4 GHz ISM band. Particular emphasis was given to the scattering parameters and validation characterization of this antenna structure. The constructed multielement antenna that was studied in both azimuth and elevation planes consists of a number of printed dipoles with integrated baluns. Due to its multielement construction, the proposed antenna structure is suitable for applications that require multielements nature such as MIMO, channel sounder, and digital beamforming.

Stepped frequency GPR survey with a multi-element array antenna: Results from field application on archaeological sites

The value of large scale GPR surveys to landscape archaeology is becoming increasingly important (e.g. Nishimura and Goodman, 2000; Neubauer et al., 2002; Leckebusch, 2003; Linford, 2004). However, the use of conventional single channel instrumentation requires either a significant investment of time for data acquisition or a compromise between sampling methodology and the area of coverage. The recent development of multi-channel, vehicle towed GPR arrays offers the potential to obtain very d...

Self-Optimization of femtocell coverage to minimize the increase in core network mobility signalling

Femtocells are low-cost, low-power cellular base stations that are deployed by the end user to supplement macrocellular coverage and provide high data rates in the customer's premises. In femtocell deployments, leakage of the pilot signal to the outside of a house can result in a highly increased signalling load to the core network, as a result of the higher number of mobility events caused by passing users. In this paper, the impact of these mobility events on the core network signalling load is investigated for urban areas. It is shown that without further optimization, the resulting increase in signalling is unacceptably high and as a result prevents the large-scale deployment of femtocells. Different self-optimization methods for residential femtocell coverage are investigated that can significantly reduce the resulting mobility events. First, mobility event based pilot power self-optimization is proposed for femtocells with a single antenna that matches the coverage to the size of the house and thereby can provide both good indoor coverage and a reduced level of mobility events. It is shown that the proposed coverage optimization can significantly outperform simpler methods that aim to achieve a constant cell radius. Then, this concept is further refined by using a low-cost switched pattern multi-element antenna solution. Antenna gain pattern measurements of a prototype with two patch and two inverted F antennas are presented and a corresponding feeder network is discussed. Self-optimization methods are proposed that jointly select an appropriate antenna pattern and optimize the pilot power. Finally, a second multi-element antenna solution is investigated where lobes in different directions, generated by several patch antennas, can be individually attenuated to shape the coverage. Both multi-element antenna solutions allow for a better match of femtocell coverage to the shape of each individual house, and result in a further improvement of both indoor coverage and core network signalling resulting from mobility events.

A technique for antenna configuration selection for reconfigurable circular patch arrays

This paper demonstrates a method that allows reconfigurable multi element antennas to select the antenna configuration at the receiver of a Multiple Input Multiple Output (MIMO) communication system. This antenna configuration selection scheme consists of using spatial correlation and average Signal to Noise Ratio (SNR) information to select the antenna radiation pattern at the receiver. We show that using this approach it is possible to achieve capacity gains in a multi element reconfigurable antenna system without modifying the data frame of a conventional MIMO system. We demonstrate our configuration selection algorithm through an analysis of reconfigurable circular patch antennas in realistic MIMO clustered channel models. Using this approach we also show that the functionality of the proposed selection scheme is connected to antenna parameters such as radiation efficiency, input impedance, the level of diversity between the radiation patterns of different antenna configurations, and the average system SNR. The capacity gain achievable with this configuration selection approach is calculated through numerical simulations using reconfigurable circular patch antennas at the receiver of a MIMO system that employs minimum mean square error receivers for channel estimation. The performance of the proposed method is compared to that of a MIMO system that estimates the channel transfer matrix for each antenna configuration in order to select the optimal receiver antenna radiation pattern. Channel capacity and Bit Error Rate (BER) results show the improvement offered by the proposed selection scheme relative to a conventional antenna selection technique for reconfigurable MIMO systems; in particular we show that the improvement increases with the number of configurations in the multi element reconfigurable antenna.

Eigen-Analysis of Lossy Compact Multielement Antenna Systems

In this letter, the concept of eigenmodes is applied to characterize the radiation of lossy compact multielement antenna (MEA) systems. Until now, the eigenmode analysis was performed for lossless MEA systems or for lossy ones without, however, calculating, but assuming instead, the losses within the MEA system. In this work, conversely, the radiation matrix is formed by using the realized effective length matrix, which includes the conductive and dielectric losses within the MEA systems. The total, mismatch, and radiation eigenefficiencies of five compact MEA systems comprising two to six antenna elements are deduced and discussed.

MIMO ANTENNA MODELLING USING THE EFFECTIVE LENGTH MATRICES

A hybrid electromagnetic-network analysis of the antennas- channel multiple input multiple output (MIMO) communication sub- system is presented. The analysis is based on the antenna efiective and realized efiective length matrices, which relate in a compact math- ematical way the radiated and received electric fleld intensities to the network characteristics of actual and coupled transmitting (Tx) and receiving (Rx) multi-element antenna (MEA) systems. The efiective length matrices are calculated via the active power gain and phase antenna patterns obtained by means of any full wave computational electromagnetics (CEM) fleld solver. It is shown that the realized efiec- tive length matrix is suitable for the S-parameter analysis of a MIMO communication link, while the efiective length matrix is convenient for its Z-parameter analysis. The efiective length matrix framework is ap- plied to a free space 2£2 coupled dipoles MIMO system and its results are in excellent agreement to those obtained by a Method of Moments (MoM) based fleld solver.

The Fisher–Bingham Spatial Correlation Model for Multielement Antenna Systems

In this paper, we study the effect of the elevation of incoming multipaths at a multielement antenna receiver by using a novel 3-D approach. It is shown that under a more general 3-D angle-of-arrival (AoA) model, namely, the Fisher-Bingham five-parameter (FB5) distribution, the spatial fading correlation (SFC) that is experienced between the adjacent antenna array elements decreases as the elevation increases. The FB5 distribution does not have a known series expansion, and therefore, the defining SFC integral can only numerically be evaluated. The proposed SFC function is further extended to capture the effect of multiple clusters of scatterers in the propagation channel. We, therefore, propose a mixture SFC function that is scaled according to the probability that each cluster contributes to the channel. The parameters of the individual components that constitute the mixture are estimated by using a soft expectation maximization (soft-EM) algorithm. The results indicate that the proposed model fits well with the data obtained from a multiple-input-multiple-output (MIMO) measurement campaign in the city of Ilmenau, Germany.

An efficient method for the electromagnetic analysis of slotted-waveguide antenna arrays

A rigorous method for the analysis of a broad class of multielement slotted-waveguide antenna arrays is described. The original electromagnetic problem is reduced to a system of integrodifferential equations, which is efficiently solved on the basis of the Galerkin method with consideration for the edge singularity of the electromagnetic field. The basis functions are the weighted Chebyshev polynomials of the first and second kinds. The accuracy of the obtained results is confirmed via comparison with available experimental and theoretical results. Features of the frequency characteristics of nonresonant arrays are analyzed.

Ultrawideband noise radar based on antenna arrays with signal recirculation

For radar systems using noise sounding signals with orthogonal spectra, which are radiated with the help of a multielement antenna array, a method for recirculation of noise signals in the feedback loop formed by the transmitting element, the target, and the receiving element is considered. The generalized ambiguity function is used to compare the resolutions and the sidelobe levels along the delay (range) coordinate and the angular coordinate for the cases of a linear equispaced transmitting antenna and an individual receiving antenna in the presence and in the absence of recirculation. Sparse and filled antenna arrays are analyzed for the cases of moderately wideband and ultrawideband total noise signals and different distributions of the center frequencies of partial noise signals over the array elements.

Eigenmode Analysis of Small Multielement Spherical Antennas

A numerical eigenmode solver is used to analyze the behavior of two-, four-, and six-arm small multielement spherical antennas. The resonant frequency and radiation <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor of the natural modes of the shorted antenna structure are determined from eigenmode simulations using perfectly matched layer outer boundaries. The radiation resistance of each eigenmode at resonance is determined using a multiarm feed geometry that excites the modes individually. The impedance response of the antenna when driven on a single arm can then be described as a multipole RLC network, where the component values of the network are directly related to the parameters and relative excitation amplitudes of the various eigenmodes of the antenna. A good match between the modal analysis and the full harmonic simulation is observed, and the analysis also predicts the far-field cross-polarization levels arising from energy radiated by the higher-order modes. The analysis provides physical insight into the multiresonant impedance behavior of these antennas, clearly illustrating their ultimate performance limits and yielding ideas for improved designs. The analysis can be applied towards understanding the behavior of other multielement antenna structures.

Integrating Compact Printed Antennas Onto Small Diversity/MIMO Terminals

The integration of compact printed multielement antenna (MEA) systems on small diversity and multiple input multiple output (MIMO) terminal devices operating in the 5.2 GHz industrial, scientific and medical (ISM) band is presented. The investigated MEA systems comprise up to six printed elements (inverted F and Minkowski monopole antennas) and their performance is evaluated by means of the effective diversity gain (EDG) and the 1% outage MIMO capacity. The role of the propagation environment (both outdoor and indoor) on EDG is examined, proving that the uniform scenario is a good approximation to many real environments. The tradeoff study between system's performance and number of integrated antenna elements indicates that both diversity and MIMO performance saturate when placing more than five closely spaced elements. Even the least efficient 6-element system however, can be advantageously used as a reconfigurable 2-element array under the concept of receive antenna selection, since it provides significantly improved MIMO performance over a conventional 2-element fixed one. The paper concludes with a summary of useful guidelines for the MEA design optimization procedure that emanated from this study.

Diversity Performance of Multimode Antennas in Directive Angle of Arrival Scenarios

The growing demand for wireless communications with increased spectral efficiency seeks for multi-element antenna techniques in personal communications to support high data rates by means of multiple-input multiple-output (MIMO) transmission schemes. Since the integration of multi-element antenna equipment at the mobile device needs to be well-aligned with the required form factors and aesthetical design issues, antenna array concepts with spatially decorrelated radiators are almost difficult to be implemented. Multimode antenna configurations operating with independent polarizations and different radiation patterns may substantially reduce size requirements since they do not necessarily require spatially separated phase centers. This article provides the theoretical framework for the analysis of the diversity efficiency of multimode antennas in directive angle-of-arrival scenarios. The analysis applies an idealized mathematical model of a multimode antenna based on the characterization of orthonormal, spherical harmonics. This mathematical foundation enables a detailed in-depth study of the impact of finite pattern correlation and branch power imbalances on the diversity efficiency of the multimode antenna. Based on the introduction of reliable performance metrics, the model enables a separate analysis of both effects. It serves as a guideline for the determination of the diversity efficiency when applying multimode antenna elements in mobile fading scenarios with defined angle-of-arrival scenarios.

Adaptive Transient and CW RF Interference Mitigation in HF OTH Radar: Experimental Results

Adaptive Transient and CW RF Interference Mitigation in HF OTH Radar: Experimental Results

Impact of Spatial Correlation on the Finite-SNR Diversity-Multiplexing Tradeoff

The impact of spatial correlation on the performance limits of multielement antenna (MEA) channels is analyzed in terms of the diversity-multiplexing tradeoff (DMT) at finite signal-to-noise ratio (SNR) values. A lower bound on the outage probability is first derived. Using this bound accurate finite-SNR estimate of the DMT is then derived. This estimate allows to gain insight on the impact of spatial correlation on the DMT at finite SNR. As expected, the DMT is severely degraded as the spatial correlation increases. Moreover, using asymptotic analysis, we show that our framework encompasses well-known results concerning the asymptotic behavior of the DMT.

Simulation of Multi-Element Antenna Systems for Navigation Applications

The application of user terminals with multiple antenna inputs for use with the global navigation satellite systems like Global Positioning System (GPS) and Galileo has attracted more and more attention in the past years. Multiple antennas may be spread over the user platform and provide signals required for the platform attitude estimation or may be arranged in an antenna array to be used together with array processing algorithms for improving signal reception, e.g., for multi-path and interference mitigation. In order to generate signals for testing of receivers with multiple antenna inputs and corresponding receiver algorithms in a laboratory environment, a unique hardware signal simulation tool for wavefront simulation has been developed. The signals for a number of antenna elements are first generated in a flexible user defined geometry as digital signals in baseband and then mixed up to individual RF-outputs. This paper describes the principle functionality of the system and addresses some calibration issues. Measurement setups and results of data processing with simulated signals for different applications are shown and discussed.