In this article, a pattern synthesis methodology for lossy antennas is proposed based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> -port characteristic mode analysis (CMA), with the radiation efficiency of the antenna guaranteed at the same time. Reactive loads are chosen as physical implementations. To perform <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> -port CMA, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> ports are first added to the lossy and lossless structures to obtain the impedance matrices. Modal efficiencies are then calculated, based on which the locations of the feed and the loads are selected. With the characteristic solutions and one set of modal weighting coefficients (MWCs), where inefficient modes have been excluded, the corresponding loads and radiation pattern can be determined. Afterward, an objective function considering physical implementation and the target pattern is established and optimized. With optimal MWCs, the lumped components loaded at each port are calculated and implemented. The method is applied to an arm-worn smartwatch antenna operating at GPS L1 band, which aims at radiating toward the sky direction for reliable link with satellites. Following the proposed method, the power radiated toward the target area has been increased by more than 40% compared with the original design. The total efficiency is above −6.1 dB when it is worn on a Cellular Telecommunications Industry Association (CTIA) arm. The prototype of the proposed antenna (Prop. Ant) has been fabricated and measured, which showed similar performances to the simulated one both in free space and in the arm-worn scenario.

Pattern Synthesis for Lossy Antennas Based on N-Port Characteristic Mode Analysis

In this article, a pattern synthesis methodology for lossy antennas is proposed based on <inline-formula> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula>-port characteristic mode analysis (CMA), with the radiation efficiency of the antenna guaranteed at the same time. Reactive loads are chosen as physical implementations. To perform <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>-port CMA, <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> ports are first added to the lossy and lossless structures to obtain the impedance matrices. Modal efficiencies are then calculated, based on which the locations of the feed and the loads are selected. With the characteristic solutions and one set of modal weighting coefficients (MWCs), where inefficient modes have been excluded, the corresponding loads and radiation pattern can be determined. Afterward, an objective function considering physical implementation and the target pattern is established and optimized. With optimal MWCs, the lumped components loaded at each port are calculated and implemented. The method is applied to an arm-worn smartwatch antenna operating at GPS L1 band, which aims at radiating toward the sky direction for reliable link with satellites. Following the proposed method, the power radiated toward the target area has been increased by more than 40% compared with the original design. The total efficiency is above −6.1 dB when it is worn on a Cellular Telecommunications Industry Association (CTIA) arm. The prototype of the proposed antenna (Prop. Ant) has been fabricated and measured, which showed similar performances to the simulated one both in free space and in the arm-worn scenario.

Pattern Synthesis for Lossy Antennas Based on N-Port Characteristic Mode Analysis

Battlefield electromagnetic environment has become more and more complex under the background of information war. Strong interfering signals have seriously affected the quality of communication and reliability of information. To weaken or even eliminate the effect of the unwanted signal to the wanted one, genetic algorithm (GA) is utilized to optimize element current amplitudes in obtaining the needed radiation pattern of adaptive linear array antenna under intensive interference environment. Details on structure of the system, radiation pattern formulation, and application of the genetic algorithm are given, and simulation examples are also demonstrated to show the effectiveness of the GA approach. advantages are such that the optimized amplitudes can be directly used in the engineering without further discretization, and that the ratio of maximum amplitude to minimum one is moderate which makes it easy to feed the antenna.

Optimizing Adaptive Linear Array Antenna Pattern Under Intensive Interference Environment Using Genetic Algorithm

The E-plane- and H-plane-coupled linearly polarized (LP) multi-input–multi-output (MIMO) dielectric resonator antenna (DRA) arrays are investigated. It is found that by adjusting the dimensions of DRA, the <inline-formula> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula>-field of the coupled element can be made out of phase with that of the excited element for both arrays. Based on this discovery, a self-decoupled circularly polarized (CP) MIMO DRA array is devised based on the polarization orthogonality of the coupled and excited DRAs. Without using any additional decoupling structure, the array can achieve either an extremely low coupling level of about −45 dB within a bandwidth of 10% or a broad decoupling bandwidth of 20.1% with a coupling level of about −27 dB by simply adjusting the antenna dimensions. Furthermore, a four-element MIMO array is proposed, yielding a 6.7% operating bandwidth with <inline-formula> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert < -10$ </tex-math></inline-formula> dB, <inline-formula> <tex-math notation="LaTeX">$\vert \text{S}_{21}\vert < -20$ </tex-math></inline-formula> dB, and AR < 3 dB. The universality of the proposed decoupling method is, therefore, verified.

Design of Self-decoupled Circularly Polarized MIMO Dielectric Resonator Antenna Array Based on Polarization Orthogonality

The sub-structure characteristic modes (CMs) can be used to describe the localized modal behavior of antenna systems, giving us more degrees of freedom to explore the resonance characteristics of antennas. Due to this attractive property, the sub-structure CM analysis is gaining more and more research interest in antenna engineering. On the other hand, handling the loss and spurious-mode issues in the sub-structure CM formulations for lossy composite structures is still a challenging task and further studies are needed. In this article, following the generalized theory of CM, a novel surface-integral-equation (SIE)-based sub-structure CM formulation is developed. In the proposed sub-structure CM equation, a new sub-structure-oriented right-hand side weighting matrix is strictly formulated, which is exclusively related to the radiated power. Eigen solutions of the CM equation can clearly separate contributions of the radiated, dissipated, and reactive powers of full structure, giving important physical insights into the radiation-and-loss mechanisms of antennas whose working modes are desired to be confined to the designated part. Two numerical examples, the Yagi–Uda dielectric resonator antenna (DRA) with and without loss, and the chassis of mobile device with a human hand, are presented to validate the effectiveness of the proposed formulation.

An Alternative Surface-Integral-Equation-Based Sub-Structure Characteristic Mode Formulation for Lossy Composite Structures

Lossy dielectric substrate affects the performance of a nearby perfect electric conductor (PEC) antenna. This letter presents a set of formulae for characteristic mode analysis (CMA) of composite PEC and lossy dielectric objects. It is based on the volume-surface integral equation and substructure treatment that separates the radiation and dissipation powers of the composite structure. A narrow PEC plate (that represents a dipole antenna) is placed in proximity of a thick, lossy dielectric material, and CMA of this structure is presented as an example. The separation gap between the PEC and dielectric objects affects the resonance and radiation efficiency of the antenna, and it is shown that CMA accurately captures those effects. The influence of dielectric loss on the modal orthogonality is discussed. Since the PEC item dominates over the coupling one in the substructure operator, the computed modes maintain good orthogonality with low-loss dielectrics. Owing to the physical insights of CMA, it has many potential applications associated with lossy materials.

Characteristic Mode Formulations of Composite PEC and Lossy Dielectric Objects

In this paper we present the detailed performance of GA-ABF technique (genetic algorithm based adaptive beamforming) under different interference/noise environment First, the GA-ABF's performance under stationary scenario is analyzed in terms of different interferences power, different direction of arrival, and different element channel noise Afterward, the tracking ability of GA-ABF is demonstrated in circumstance where a group of interferences with distinct power change their directions of arrival randomly at certain time interval Finally, two approaches aimed at improving the effectiveness and rate of convergence of GA-ABF are outlined quantitatively towards suppressing multiple random interferences within the framework of standardized genetic algorithm so that no further complex GA operations is involved

On the performance of genetic algorithm based adaptive beamforming

Electromagnetic properties of an array antenna are inevitably affected by random magnitude and phase errors in the feeding network. Polynomial chaos expansion (PCE) method can analyze such problems, but the number of numerical quadrature grows rapidly with stochastic dimensionality for solving the PCE coefficients. An improved PCE algorithm is proposed to improve the computational efficiency. A large array is decomposed into several small groups those can be efficiently treated by the PCE method. Stochastic quantification of the whole array is achieved by the superposition of grouped results. In addition, the proposed method can integrate with the method of moments to treat real-world arrays. The results computed by this method agree with those of Monte Carlo, and the computational time is reduced by two orders of magnitude for a dipole array with 64 elements.

Stochastic Quantification of Array Antennas With Random Feeding Errors Using an Improved Polynomial Chaos Expansion Method

Radiation patterns of a phased array tend to be affected by random excitation errors. In this paper, a unified neural network (UNN) architecture is presented to study the statistical characteristics of radiation patterns. Benefited from the inherent symmetry of the array manifolds and efficient data preprocessing, the UNN architectures are almost identical for planar arrays consisting of 4–10 000 elements except for a slight difference existed in the output layer. Therefore, this merit avoids repetitive selections of training hyperparameters and network architectures. This method can efficiently treat the problems with multiple observation points in order to obtain statistical radiation patterns, and an analytic or closed-form solution is not required. Moreover, it can combine with the method of moments (MoM), which takes account of the element pattern and mutual coupling effects. The trained UNN models can predict the probability density function (PDF) of radiation characteristics at any spatial location. Numerical results show that the UNN and Monte Carlo (MC) results are comparable in accuracy. 

Statistical analysis of phased arrays with random excitation errors using a unified neural network architecture

In this paper we envision the evolvable antenna array system (EAA) based on the development of tunable or reconfigurable antenna element and the concepts that drawn from evolvable hardware. The general system architecture and the working scheme of EAA system are outlined. Two different ways of evolving: element-level evolving and array-level evolving are illustrated by examples. Further discussions in terms of the system implementation and performance improvement are then followed.

Envision of evolvable antenna array

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