Resonant Meta-Surface Superstrate for Single and Multifrequency Dipole Antenna Arrays

The design of a multifrequency dipole antenna array based on a resonant meta-surface superstrate is proposed. The behavior of a single element that is closely placed to a meta-surface is experimentally investigated. The proposed meta-surface is based on resonating unit cells formed by capacitively loaded strips and split ring resonators. By tuning a dipole antenna to the pass band of the meta-surface, the physical area is effectively illuminated enhancing the radiation performance. The gain, radiation efficiency and effective area values of the whole configuration are compared to the ones obtained with a single dipole without superstrate. Radiation efficiency values for the proposed configuration of more than 80% and gain values of more than 4.5 plusmn 1 dB are obtained. Based on this configuration, simulated results of a multifrequency antenna array are presented. Distinctive features of this configuration are high isolation between elements (20 dB for a distance of lambda₀/4), and low back radiation.     

Dielectric cover effect on rectangular microstrip antenna array

A theoretical model to analyze a covered rectangular antenna with an arbitrary dielectric constant superstrate is developed. The antenna is simulated by the radiation of two magnetic dipoles located at the radiating edges of the patch. The Green's function of an elementary magnetic dipole in a superstrate-substrate structure, utilizing spectral-domain analysis, is formulated, and the surface-wave and radiation field are computed. An improved transmission line model, which considers the stored energy near the radiating edges and the external mutual coupling, is used to compute the input impedances and radiation efficiency. Design considerations on the superstrate thickness and its dielectric constant are discussed. Experimental data for a single element and a 4×4 microstrip array is presented to validate the theory     

Highly efficient dipole antenna with planar meta-surface

The radiation performance of a dipole antenna closely placed to a planar meta-surface based on parallel short dipoles and continuous wires is presented. Owing to the uniform illumination of the superstrate, an enhancement of gain up to 6.8 dBi is obtained, the thickness of the whole system being 0.135 lambda_o and the aperture efficiency 82%.     

Experimental verification of the reduction of coupling between dipole antennas by using a woodpile substrate

In this paper, the mutual coupling between dipole antennas placed on top of a woodpile structure is experimentally investigated. The coupling between dipoles backed by a woodpile substrate is compared with that obtained when the dipole antennas are placed on a dielectric substrate and when they radiate into free space. On average, between 2 and 7 dB reduction of the mutual coupling is achieved with respect to the dielectric substrate case when the woodpile substrate is used. The free space coupling is also reduced in the H-plane configuration case. However, the E-plane coupling slightly increases due to modification of the radiation pattern. Imaging array applications could potentially benefit from the use of EBG substrates due to the improved isolation between pixels.     

Analysis of mutual coupling between a finite phased array ofdipoles and its feed network

The mutual coupling effects between a finite phased array of dipoles and its feed network are analyzed. The feed network is typically a corporate feed consisting of split-tee power dividers cascading to form a certain power distribution over the aperture. A simple iterative approach is used to solve the interaction between elements and feed. The radiation of a finite dipole array are first found for a given voltage excitation. These radiation impedances are then used as loads for the feed network, and the n+1 port network problem is analyzed. Due to the interaction between the feed network and dipoles, the antenna parameters such as mismatch, antenna pattern, and gain are all affected. These effects can be determined from the analysis of the network representation. Numerical results for a typical phased array with a corporate feed show that the resultant VSWR of the feed pattern degradation is due to the mutual coupling effects     

Decoupling Efficiency of a Wideband Vivaldi Focal Plane Array Feeding a Reflector Antenna

A focal plane array (FPA) feeding a reflector can be used to achieve a large field of view (FOV) with overlapping simultaneous beams. In order to provide a continuous FOV over more than an octave bandwidth, the inter-element spacing in the FPA has to be electrically small over large parts of the band. This will inevitably result in strong mutual coupling effects between the array elements. On transmit, the total lost power due to mutual coupling can be quantified by the decoupling efficiency, a term recently introduced for antenna arrays. This paper presents measured decoupling efficiencies of a Vivaldi element FPA operating between 2.3 and 7 GHz. The radiation patterns of the FPA are calculated for two beam excitations by using measured embedded element patterns, and the corresponding decoupling efficiencies are evaluated by using measured $S$ -parameters between all element ports. The FPA is assumed to illuminate a deep reflector with $F/D=0.35$ , and the overall reflector aperture efficiencies are computed. The decoupling efficiencies are also determined through the measurements of the total radiation efficiencies in a reverberation chamber, which includes material absorption losses.      

计入阵元间互耦影响的阵列方向性图综合

基于自适应天线理论，在考虑了天线阵中阵元间互耦影响的情况下，对均匀和非均匀直线阵列的方向性图进行了综合，并讨论了加权值幅度和相位误差对天线阵列方向性图的影响。     

Design and performance analysis of side by side,echelon and H‐shaped multiple printed dipole antennas for wireless local area network application

An array of printed dipole antennas for wireless local area network applications is designed and simulated using ads software. In MIMO system, numbers of antenna elements are used in different configuration. This paper presents the simulated results of printed dipole antennas in side by side 4‐element array, echelon and H‐shaped dipole array configurations. The designed antenna is characterized by measuring return loss, radiation pattern, directivity, and gain and also presented the simulated capacity results of different array configurations. The mutual coupling between the dipoles of different orientations is included to make simulation more realistic. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of finite arrays of axially directed printed dipoles on electrically large circular cylinders

Various arrays consisting of finite number of printed dipoles on electrically large dielectric coated circular cylinders are investigated using a hybrid method of moments/Green's function technique in the spatial domain. This is basically an "element by element" approach in which the mutual coupling between dipoles through space as well as surface waves is incorporated. The efficiency of the method comes from the computation of the Green's function, where three types of spatial domain Green's function representations are used interchangeably, based on their computational efficiency and regions where they remain accurate. Numerical results are presented in the form of array current distributions, active reflection coefficient and far-field pattern to indicate the efficiency and accuracy of the method. Furthermore, these results are compared with similar results obtained from finite arrays of printed dipoles on grounded planar dielectric slabs. It is shown that planar approximations, except for small separations, can not be used due to the mutual coupling between the array elements. Consequently, basic performance metrics of printed dipole arrays on coated cylinders show significant discrepancies when compared to their planar counterparts.     

Mutual coupling in multi-element array antennas and its influence on MIMO channel capacity

The effects of mutual coupling between receive elements in a multi-element antenna on multiple-input multiple-output (MIMO) system capacity are reported. The results are based upon analysis of mutual coupling calculated for a measured linear array of five printed dipole elements with 0.56 of a wavelength spacing. It is shown that the presence of mutual coupling at the receive array antenna leads to additional correlation between spatial channels and results in a loss of MIMO system capacity.     

相控阵天线的耦合激励系数及盲点研究

为了深入探讨相控阵天线单元间的相互耦合,以阵列天线单元S参数为基础,分别分析了振子形式辐射单元和缝隙形式辐射单元组成阵列的辐射单元之间的耦合关系,并利用天线单元的耦合激励系数分析计算了阵中单元的有源辐射方向图。对阵列中每个单元的耦合激励系数的幅度和相位进行了分析,发现平行排列单元和轴向排列单元的耦合激励系数的相位存在差异,平行排列时激励单元与相邻单元间的相位相差较小,这种差异是阵列产生盲点的主要因素。     

High-Efficiency Angled-Dipole Antennas for Millimeter-Wave Phased Array Applications

A high-efficiency microstrip-fed endfire angled-dipole antenna has been developed for millimeter-wave phased array applications. The antenna is built on both sides of a Teflon substrate (epsiv_r = 2.2) and this allows a wideband feed from the single-ended microstrip line to the differential dipole. The design results in wide radiation patterns for scanning purposes with a gain of around 2.5 dB at 20-26 GHz and a cross-polarization level of < -15 dB at 24 GHz. A mutual coupling of < -23 dB is measured between adjacent elements with 6.8 mm center-to center spacing (0.50-0.54 lambda₀ at 22-24 GHz). A variant of the angled-dipole antenna with a magnetic ground plane edge was also developed, and shows a measured gain of > 6 dB at 23.2-24.6 GHz and very low mutual coupling between elements (<-23 dB for a 6.8 mm spacing). Both antennas result in a radiation efficiency of > 93% when referenced to the microstrip line feed (including mismatch loss). The usefulness of these antennas as phased array radiators is demonstrated by several eight-element linear arrays at 22-24 GHz with scan angle up to 50 degrees. The application areas are in automotive radars and high data-rate communication systems.     

Performance of adaptive array antenna with arbitrary geometry in the presence of mutual coupling

The effect of the mutual coupling between the array elements on the performance of the adaptive array antennas (AAA) is investigated when the actual received voltages which include the mutual coupling are directly used to estimate the weight vector based on the adaptive algorithm. The output signal-to-interference-noise ratio (SINR), the convergence of the adaptive algorithm and the synthesized pattern are evaluated to study the effect due to the existence of the mutual coupling. It is found that the mutual coupling affects the antenna adaptive gain, but does not affect the adaptive processing. It is also found that the mutual coupling does not always degrade the iterative convergence of the adaptive algorithm. It is proved that any invertible matrix for compensating the mutual coupling cannot improve the output SINR. It is also indicated that the radiation pattern can be correctly synthesized in the presence of the mutual coupling by introducing the universal steering vector (USV) whose element corresponds to the array element pattern.     

Effect of Coupling Phase on Mutual Injection Locking Range in Coupled Oscillator Arrays

The performance of a coupled oscillator array depends critically on the coupling network. Determination of the optimal coupling phase depends on the oscillator equivalent circuit and the location of mutual coupling between the oscillators. In this paper, the authors examine the effects of coupling phase on the mutual injection locking range. Three element coupled oscillator arrays (COAs) were mutually coupled at two different locations, with each coupling location presenting a different resonance to the coupling network, and the optimal coupling phase required to generate a linear phase shift in the range of $-90^{circ}$ to 90$^{circ}$ was determined. For each coupling location, when the coupling phase was off by 180$^{circ}$ , the arrays were shown to lock with a limited range and operate in a mode other than the in-phase mode.      

Signal bandwidth consideration of mutual coupling effects on adaptive array performance

The effect of mutual coupling on the performance of a least mean square (LMS) adaptive array using dipole elements is analyzed in consideration of the signal bandwidth. The purpose here is to illustrate quantitatively the significance of the effect of mutual coupling. The results show that the effect in the broad-band signal cases is much greater than that in the narrow-band cases, particularly when few antenna elements are used.     

EBG Superstrate Array Configuration for the WAAS Space Segment

Two different electromagnetic bandgap (EBG) superstrate array antenna configurations, intended for the Wide Area Augmentation Service space segment, are presented in this paper. The described antenna configurations take advantage of the directivity enhancement produced by a semireflective sheet placed parallel to a metallic ground plane. The first design presented is realized using a 2$,times,$ 2 circularly polarized (CP) patch array illuminating an EBG superstrate composed of a square pattern of circular holes etched in a thin metallic sheet. The second design consists of a 2$,times,$ 2 CP helix array feeding a hexagonal pattern of holes etched into a metallic EBG superstrate. Both configurations have been designed, breadboarded, and measured, and excellent agreement between simulations and measurements has been recorded. The accurate control of the antenna pattern phase center variation with both the frequency and the antenna field of view, necessary for the intended navigation antenna application, has been the principal challenge of this work. The EBG technology designs presented here are simpler than conventional navigation antennas and can lead to cost reduction, beamforming network simplification, and height reduction while offering similar radio-frequency performances to equivalent products realized in conventional technology.      

Effects of coupling accumulation in antenna arrays

Mutual coupling between antenna elements in a phased array causes array performance to vary with scan angle. Large impedance mismatch and radiation loss can occur in certain critical directions for which the steering phase advances match the antenna coupling delays. At these critical scan angles, many coupling contributions add inphase to produce a large impedance mismatch and minimum radiation from the array. Several different phased arrays have exhibited scanning "blind" regions that appear to be a consequence of coupling accumulation. A large, flat, homogeneous antenna array is analyzed, and a relationship is found between the critical scan angles and phase of the mutual coupling coefficients. Extensive measurements on arrays of horn antennas have shown radiation minima that correlate with coupling phase measurements and with theory.     

MIMO系统中互耦影响分析

文章简要概括了MIMO系统及其信道容量，并基于矩量法重点分析了MIMO系统中天线阵元间的互耦作用对每个天线阵元辐射方向图的影响。结果表明互耦能使每个天线阵元的方向图发生畸变，所以在应用射线追踪法构建MIMO系统的信道矩阵时必须考虑互耦的影响以提高计算精度。     

Calculation of antenna mutual coupling from far radiated fields

Mutual coupling between a pair of identical array elements is calculated from far field radiation. The reaction theorem is used on a single element to carry out a mutual coupling calculation. Evaluation of the reaction integral over a spherical surface surrounding a single waveguide element produces results better than the conventional aperture surface integral when using far fields. The method provides a simple tool for the estimate of mutual coupling given knowledge of the far field radiation of a single element. This is of great advantage during the development of array elements of unusual geometry, where analysis or other measurement techniques are difficult or less convenient.<>     

Analysis of planar strip geometries in a substrate-superstrate configuration

A moment method procedure is used to analyze the behavior of several different configurations consisting of planar strips in a substrate-superstrate geometry. These include the microstrip transmission line, center-fed dipole, the mutual impedance between two dipoles, and the transmission-line coupled dipole. In each case some of the basic superstrate effects are discussed.