Wideband Array Research Articles

THE DESIGN OF AN OPTICAL TIME STEERED ANTENNA BASED ON A NEW INTEGRATED TRUE TIME DELAY UNIT

In the framework of wide-band and ultra wide-band array antennas, an Optical Time Steered Antenna (OTSA) is presented, by considering the design strategies of a new True Time Delay (TTD) Control Unit in the Beam Forming Network (BFN). The unit has high reliability, low crosstalk, low switching time and potential low cost, being based on a low cost technology. Furthermore, due to its compactness and modularity, it can be easily grouped with other ones to make a control unit of large arrays. Difierent strategies and working conflgurations of the TTD control unit are presented as a trade-ofi among hardware complexity, insertion loss reduction and beam control capability. The design of an OTSA prototype is discussed by considering a realistic model simulating the behavior of a real world antenna and accounting for unavoidable non-realities, such as random, periodic and systematic errors introduced by each device exploited in the OTSA as well as mutual coupling between radiating elements. An optimal trimming strategy, able to compensate at best for BFN errors and based on the use of suitably located trimmers, is presented. Among other cases, to enlighten the potentialities of the OTSA, an all optical architecture providing a difierence beam squint free pattern is also proposed.

Analytical Model and Practicle Validation of Phase Variation of Reflect Array Antenna

Reflection phase properties of reflect array antenna design in the X-band frequency range has been addressed in this work. An analytical model for obtaining the required reflection phase from individual reflect array elements to form a planar wave in front of the periodic aperture has been presented. A unit cell patch element representing an infinite reflect array modeled based on FEM using the waveguide simulator demonstrated that there is no significant influence on the scattering parameters of reflect array resonant elements until the angle of incidence is increased up to 40 degrees. A Figure of Merit (FoM) has been defined for the comparison of the reflection phase curves of reflect arrays modeled with different dielectric substrates and the results are compared in terms of bandwidth performance and static linear phase range. Furthermore reflect array unit cell patch elements have been fabricated in X-band frequency range using different he practical validation of the waveguide scattering parameter measurements of unit cell reflect array elements. The measured results demonstrated an improvement in FoM and reflect array bandwidth performance with an increase in substrate thickness.

DESIGN OF A UWB COMBINED ANTENNA AND AN ARRAY OF MINIATURIZED ELEMENTS WITH AND WITHOUT LENS

In this paper, the design of an array of wideband combined antenna elements is presented. A TEM horn antenna is combined with magnetic dipoles to obtain a wideband element with a bandwidth from 180MHz to 30GHz. The element is then miniaturized in order to be placed in a two by two array, and then the optimized values of the horizontal and vertical spacings are calculated. To enhance the array bandwidth, a lens is placed in front of each element. This leads to an increase in the bandwidth from 0.2 to 10GHz while no grating lobes appear over the bandwidth. The combined element is fabricated and the simulation results are verifled by the measured data. Furthermore, simulation results for the return loss, radiation patterns and antenna gain for the 2 £ 2 array are presented.

A SHAPED-BEAM SERIES-FED APERTURE-COUPLED STACKED PATCH ARRAY ANTENNA

A shaped-beam series-fed aperture-coupled stacked patch array antenna at X-band is presented. To improve the array bandwidth, two-port aperture-coupled stacked patch antennas, which are suitable for the series-fed array conflguration, are presented as the radiating elements. To ofier the pattern design and optimization progresses more ∞exibility, a uniformly spaced array conflguration is applied in the shaped-beam pattern design, instead of the conventional nonuniformly spaced array conflguration. The experimental results show that, in a 7.6% bandwidth, the main beam shape of the array maintains in good agreement with the design goal, and the side lobe level maintains lower than i18dB.

Synthesis of power patterns for wideband arrays including mutual coupling

A power pattern synthesis technique for a wideband array including mutual coupling (MC) is proposed. A frequency-dependent MC (FDMC) matrix is obtained accurately via the complex curve fitting technique. With the FDMC matrix the mutual coupling effect is included in the synthesis procedure automatically, resulting in an MC-compensated frequency-invariant power pattern.

Analytical Description and Design of Printed Dipole Arrays for Wideband Wide-Scan Applications

Wideband arrays of printed dipoles with inter-element loads are investigated. A closed-form expression for the active input impedance of the array element is derived with a spectral domain approach. The procedure is based on an extension of the Green's function formulation for arrays of connected dipoles to the case of dipoles coupled via loads. The accuracy of the formulation is investigated with the aid of parametric analyses. The model can be used in the preliminary design of wideband printed dipoles for the dimensioning of the radiating elements. The procedure remains accurate also for arrays of dipoles that are not tightly coupled, for which and the current along the element assumes a resonant-like sinusoidal distribution.

Wideband Array Signal Detection Algorithm Based on Power Focusing

针对无源侦察系统的实时性应用需求，该文提出了一种基于功率聚焦的宽带阵列信号检测算法。利用均匀线阵接收信号的相位变化信息，通过改进的二重FFT 算法将各阵元接收信号的功率聚焦到信号到达角 (DirectionOf Arrival, DOA)。在此基础上，推导了聚焦后各角度上噪声数据的概率密度函数，构造了具有恒虚警特性的检验统计量和相应的检测门限，并推导了不同虚警率和信噪比条件下的理论检测概率。该算法聚焦过程计算复杂度较小，检测过程不依赖于信号先验信息，检测结果还可为后续的精确角度测量提供初值。仿真实验表明，该算法对弱信号具有较好的检测效果。

Superstrate-Enhanced Ultrawideband Tightly Coupled Array With Resistive FSS

An efficient low-profile ultrawideband tightly coupled array employing a resistive frequency selective surface (FSS) and a superstrate is introduced. The FSS suppresses destructive ground plane interference, resulting in an increase in the array bandwidth by a factor greater than two. A superstrate is used to alleviate losses due to the resistive FSS. It is shown that a properly designed superstrate reduces losses by about 2.5 dB. The proposed array, which employs tightly coupled bowtie elements, achieves very low profile <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(0.055\lambda_{\rm low})$</tex> </formula> , 21:1 bandwidth, and radiation efficiency greater than 73% across the band. This paper presents the analysis and design of the array, particularly the FSS and superstrate. To validate the design, measurements of a prototype array are presented as well.

Wide-Band Wide-Coverage Linear Array of Four Semi-Circular Sector Horns

A linear array antenna consisting of four semi-circular sector horns is proposed to achieve wide-band and wide-coverage radiation characteristics. The array can operate over a wide frequency band from 850 MHz to 2570 MHz and cover a wide range of 120° in the azimuth plane. Each semi-circular sector horn is fed by a centred coaxial probe loaded with a conducting cylinder to obtain a wide-band and symmetric radiation pattern of vertical polarization. Measured and simulated results of a designed array show its potential applications for base stations serving wide-range mobile users and other wide-band spectrum-monitoring systems.

메타재질구조의 UWB 전력 분배기를 이용한 광대역 배열 안테나를 위한 급전부 설계

In this paper, a new method is suggested to reduce the size of a wide-band array antenna. The power-divider for the feeding structure is made compact as with the help of a novel Metamaterial UWB bandpass filter. This power divider is clearly different from others in that the proposed design uses microstrip structured Composite Right and Left-Handed (CRLH) filters, while others use two dielectric layers or long tapered transmission lines. In order to validate the proposed design method, the circuit and full-wave simulated results of the power divider with the Metamaterial UWB filters are compared to each other, and the Metamaterial properties of the structure are shown with the electric field at the ZOR and dispersion diagram. Furthermore, the antenna performance of the fabricated antenna with the power divider is measured and compared with the prediction. Also, the size reduction effect by the proposed scheme is addressed.

Wideband beamforming for multipath signals based on frequency invariant transformation

It is well known that the performance of conventional adaptive beamformers degrades severely due to the presence of coherent or correlated interferences (multipath propagation) and various techniques have been developed to improve the performance of the beamformer. However, most of the work in the past has been focused on the narrowband case. In this paper, the wideband beamforming problem in the presence of multipath signals is addressed, with a novel approach proposed by employing a pre-processing stage based on the frequency invariant beamforming (FIB) technique. In this approach, the received wideband array signals are first processed by an FIB network, and then a traditional narrowband adaptive beamformer or an appropriate instantaneous blind source separation (BSS) algorithm can be applied to the network outputs. It is shown that with the proposed structure, cancellation of the desired signal is reduced, leading to a significantly improved output signal to interference plus noise ratio (SINR).

Design of Wideband Concentric-Ring Arrays with Three-Dimensional Beam Scanning Based on the Optimization of Array Geometry

Absract Optimization design of wideband concentric-ring arrays for three-dimensional beam scanning with a minimum peak side-lobe level is addressed in this article. To obtain three-dimensional beam scanning with the lowest peak side-lobe level over a wide bandwidth, concentric-ring array geometries, i.e., radius and inter-element spacing of each ring, are optimized. Optimal array geometries are solved via the differential evolution algorithm, and the results are presented for wideband concentric-ring arrays with different scan angles. The peak side-lobe level of the optimal wideband concentric-ring arrays dropped significantly compared to the periodic arrays after geometry optimization was performed. In addition, the comparison with the periodic wideband array shows that not only does the optimal wideband concentric-ring array have a comparable directivity, but the number of elements is also saved.

Constrained Pareto Optimization of Wide Band and Steerable Concentric Ring Arrays

A multi-objective evolutionary algorithm that explicitly introduces the management of a single or multiple constraints on the solutions of an electromagnetic problem is presented in this paper. The proposed strategy is based upon a modified genetic algorithm which evaluates the strength of a solution by considering both the match to the desired performance (objectives) as well as the satisfaction of specific requirements imposed to the design (constraints). The key issue is represented by the adaptive constraints management and its influence on the selective pressure of the genetic algorithm. The procedure is applied to the optimization of concentric ring arrays. Several design examples of steerable and wideband arrays are provided to prove the flexibility and reliability of the approach. A particular emphasis is given to the changes in array performance when the same objectives are requested but different kinds of constraints are forced.

Antenna Requirements for Software Defined and Cognitive Radios

Antenna requirements for software defined radio (SDR) and cognitive radio (CR) systems are reviewed and the resulting challenges are discussed. Both concepts imply capabilities for operation over very wide bandwidths, of the order of one decade in some cases. This then becomes the main challenge for antenna designers. However, as the concepts evolve, some systems will work over limited bandwidths and existing or extended bandwidth antennas will be used. In the Paper the concepts are explained. As bandwidth is a major concern, the fundamental limits of performance are restated. For handheld radio antenna bandwidth and efficiency at low frequencies is the main problem. Both in the terrestrial fixed infrastructure and in space communication the difficulty of designing very wideband arrays to give the pattern control necessary for interference minimization is significant. In defence applications external handset antennas are seen to be necessary and extension to very wide bandwidths is also seen to be challenging. It is concluded that there is steady progress towards the realization of both SDR and CR, and this is throwing up very significant antenna challenges.

Low-Cost Wideband Microstrip Arrays With High Aperture Efficiency

Three novel two-dimensional wideband arrays of microstrip E shaped patches are designed for use in a 10% frequency range around the 2.45 GHz ISM band. The proposed arrays are intended to serve as subarray in a switchable outdoor antenna that has to be low-cost and very compact. The scan in the horizontal plane is performed by using switching between six subarrays covering 180 degrees. The main design criterion was a combination of the bandwidth with an aperture efficiency as high as possible, since this allows to minimize occupied space. The design is based on a method of moments algorithm in combination with a particle swarm optimization. CST MW Studio was employed for validation purposes before manufacturing. A very good agreement was achieved between simulated and measured results. The maximum measured aperture efficiencies of the last two arrays are 105% and 86%, respectively, which is considerably higher than what has been reported up to now in literature for wideband microstrip arrays.

A wideband linear array with reduced number of antenna elements

AbstractAn X‐band linear array antenna with reduced number of elements is presented. To suppress the sidelobe level using fewer array elements, the synthesis of a nonuniform antenna array has been implemented with the matrix pencil method (MPM) that can provide the excitation and location distribution to miniaturize the array dimension. A comparison with the conventional array antennas with uniform and conventional distributions is conducted to demonstrate the performance of the proposed wideband array, which also experimentally verifies the feasibility of the MPM. The developed array antenna is suitable for portable devices, mini mobile platforms, and low‐tier unmanned vehicles. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1846–1848, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26962

Bayesian Focusing for Coherent Wideband Beamforming

In this paper, we present and study a Bayesian focusing transformation (BFT) for coherent wideband array processing, which takes into account the uncertainty of the direction of arrivals (DOAs). The Bayesian focusing method minimizes the mean-square error of the transformation over the probability density functions (pdfs) of the DOAs, thus achieving improved focusing accuracy over the entire bandwidth. In order to solve the Bayesian focusing problem, we derive and utilize a weighted extension of the wavefield interpolated narrowband generated subspace (WINGS) focusing transformation. We provide a closed-form expression for the optimal BFT and extend it to the case of directional sensors. We then consider a numerical computation scheme of the BFT in the angular domain. We show that if an angular sampling condition is satisfied then the angle domain approximation yields the optimal BFT. We also treat the important issue of robust focused minimum variance distortionless response (MVDR) beamformer. We analyze the sensitivity of the focused MVDR to the focusing errors and show that the array gain (AG) is inversely proportional to the square of the signal-to-noise ratio (SNR) for large values of the SNR, and highly sensitive to the focusing errors. In order to reduce this sensitivity we generalize the popular narrowband diagonal loaded MVDR to the focused wideband case, referred to as the Q-loaded focused MVDR wideband beamformer. We derive a closed-form analytic expression for the AG of the Q-loaded focused MVDR beamformer which depends on the focusing transformations. A numerical performance evaluation and simulations demonstrate the advantage of the BFT over that of other focusing transformations, for multiple source scenarios.

A Multiport Impedance-Matching Feed Network for Directional Antennas

The proposed multiport impedance-matching feed network simultaneously optimizes the operating bandwidth and gain of a two-element superdirective antenna array. Maximum directivity of an N-element isotropic radiator approaches N2 as the element spacing approaches zero. Additionally, the operating bandwidth of superdirective antenna arrays is narrowband. Utilizing a multiport impedance-matching network will increase the operating bandwidth. Special consideration is required in designing the circuit so that the losses introduced by the matching network do not significantly degrade the absolute gain of the antenna array.

Design and Analysis of Printed Yagi-Uda Antenna and Two-Element Array for WLAN Applications

A printed director antenna with compact structure is proposed. The antenna is fed by a balanced microstrip-slotline and makes good use of space to reduce feeding network area and the size of antenna. According to the simulation results of CST MICROWAVE STUDIO software, broadband characteristics and directional radiation properties of the antenna are explained. The operating bandwidth is 1.8 GHz–3.5 GHz with reflection coefficient less than −10 dB. Antenna gain in band can achieve 4.5–6.8 dBi, and the overall size of antenna is smaller than0.34λ0×0.58λ0. Then the antenna is developed to a two-element antenna array, working frequency and relative bandwidth of which are 2.15–2.87 GHz and 28.7%, respectively. Compared with antenna unit, the gain of the antenna array has increased by 2 dB. Thus the proposed antenna has characteristics of compact structure, relatively small size, and wideband, and it can be widely used in PCS/UMTS/WLAN/ WiMAX fields.

Wideband DOA estimation from the sparse recovery perspective for the spatial-only modeling of array data

This communication utilizes a sparse recovery technique named “least absolute shrinkage and selection operator” (LASSO) to formulate and solve the problem of direction-of-arrival (DOA) estimation for far-field wideband sources. The spatial-only modeling for wideband array output is employed when the sources have flat spectra, and the DOA estimation problem in this model can be transformed into a sparse recovery problem. Via the LASSO technique, an optimization problem is constructed and solved by second-order cone (SOC) programming to obtain the DOA estimates. Numerical simulations are also provided in contrast with those existing algorithms using the spatial-only model.