Computationally feasible narrow‐band antenna modeling using response features

Accurate and low‐cost models of input characteristics are of primary importance from the point of view of efficient design of antenna structures. Yet, the modeling problem is difficult because reflection responses are highly nonlinear functions of frequency and change considerably when adjusting antenna dimensions. Conventional approximation‐based models require massive datasets and often fail to provide required accuracy. This work demonstrates a possibility of dramatic reduction of the number of training samples, which is achieved by reformulating the modeling problem in a space of appropriately defined response features. The key factor is that dependence of feature point coordinates (both frequency and level) on antenna dimensions is less nonlinear than for the standard responses (S‐parameters vs. frequency). Our methodology permits construction of reliable surrogates using much smaller datasets than those required by conventional approaches. Experimental validation indicates that our models provide accuracy that is sufficient for practical antenna design.     

Expedited simulation‐driven design optimization of UWB antennas by means of response features

In this work, a method for fast design optimization of broadband antennas is considered. The approach is based on a feature‐based optimization (FBO) concept where reflection characteristics of the structure at hand are formulated in terms of suitably defined feature points. Redefinition of the design problem allows for reducing the design optimization cost, because the dependence of feature point coordinates on antenna dimensions is less nonlinear than for the original frequency characteristics (here, S‐parameters). This results in faster convergence of the optimization algorithm. The cost of the design process is further reduced using variable‐fidelity electromagnetic (EM) simulation models. In case of UWB antennas, the feature points are defined, among others, as the levels of the reflection characteristic at its local in‐band maxima, as well as location of the frequency point which corresponds to acceptable reflection around the lower corner frequency within the UWB band. Also, the number of characteristic points depends on antenna topology and its dimensions. Performance of FBO‐based design optimization is demonstrated using two examples of planar UWB antennas. Moreover, the computational cost of the approach is compared with conventional optimization driven by a pattern search algorithm. Experimental validation of the numerical results is also provided.     

Rapid design optimization of antennas using space mapping and response surface approximation models

A computationally efficient method for design optimization of antennas is discussed. It combines space mapping, used as the optimization engine, and response surface approximation, used to create the fast surrogate model of the optimized antenna. The surrogate is configured from the response of the coarse‐mesh electromagnetic model of the antenna, and implemented through kriging interpolation. We provide a comprehensive numerical verification of this technique as well as demonstrate its capability to yield a satisfactory design after a few full‐wave simulations of the original structure. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Fast simulation‐driven antenna design using response‐feature surrogates

In this article, a computationally efficient procedure for electromagnetic (EM)‐simulation‐driven design of antennas is presented. Our methodology is based on local approximation models of the antenna response, established using a set of suitably selected characteristic features rather than the entire response (such as reflection versus frequency). The approximation model is utilized to verify the level of satisfying/violating given performance requirements, and to guide the optimization process towards a better design. By exploiting the fact that the dependence of the response features on the designable parameters of the antenna of interest is simple (close to linear or quadratic), the feature‐based optimization converges faster than conventional optimization of frequency‐based EM‐simulated responses. In order to further speed up the design, coarse‐discretization simulations are utilized to estimate the feature gradients with respect to adjustable parameters of the problem at hand. The optimization algorithm is embedded in the trust‐region framework for safeguarding convergence. The proposed technique is demonstrated using two antenna examples. In both the cases, the optimum design is obtained at the computational cost corresponding to a few high‐fidelity EM antenna simulations. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:394–402, 2015.     

Reduced‐cost microwave filter modeling using a two‐stage Gaussian process regression approach

A technique for the reduced‐cost modeling of microwave filters is presented. Our approach exploits variable‐fidelity electromagnetic (EM) simulations, and Gaussian process regression (GPR) carried out in two stages. In the first stage of the modeling process, a mapping between EM simulation filter models of low and high fidelity is established. The mapping is subsequently used in the second stage, making it possible for the final surrogate model to be constructed from training data obtained using only a fraction of the number of high‐fidelity simulations normally required. As demonstrated using three examples of microstrip filters, the proposed technique allows us to reduce substantially (by up to 80%) the central processing unit (CPU) cost of the filter model setup, as compared to conventional (single‐stage) GPR—the benchmark modeling method in this study. This is achieved without degrading the model generalization capability. The reliability of the two‐stage modeling method is demonstrated through the successful application of the surrogates to surrogate‐based filter design optimization. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:453–462, 2015.     

Fast simulation‐driven feature‐based design optimization of compact dual‐band microstrip branch‐line coupler

Design of miniaturized microwave components is a challenging task. On one hand, due to considerable electromagnetic (EM) cross‐couplings in highly compressed layouts full‐wave EM analysis is necessary for accurate evaluation of the structure performance. Conversely, high‐fidelity EM simulation is computationally expensive so that automated determination of the structure dimensions may be prohibitive when using conventional numerical optimization routines. In this article, computationally efficient simulation‐driven design of a miniaturized dual‐band microstrip branch‐line coupler is presented. The optimization methodology relies on suitably extracted features of a highly nonlinear response of the coupler structure under design. The design objectives are formulated in terms of the feature point locations, and the optimization is carried out iteratively with the linear model of the features utilized as a fast predictor. The entire process is embedded in the trust‐region framework as convergence safeguard. Owing to only slightly nonlinear dependence of the features on the geometry parameters of the circuit at hand, the optimized design satisfying prescribed performance requirements is obtained at the low computational cost of only 24 high‐fidelity EM simulations of the structure. Experimental validation of the fabricated coupler prototype is also provided. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:13–20, 2016.     

Multi‐objective design optimization of antennas for reflection,size, and gain variability using kriging surrogates and generalized domain segmentation

Cost‐efficient multi‐objective design optimization of antennas is presented. The framework exploits auxiliary data‐driven surrogates, a multi‐objective evolutionary algorithm for initial Pareto front identification, response correction techniques for design refinement, as well as generalized domain segmentation. The purpose of this last mechanism is to reduce the volume of the design space region that needs to be sampled in order to construct the surrogate model, and, consequently, limit the number of training data points required. The recently introduced segmentation concept is generalized here to allow for handling an arbitrary number of design objectives. Its operation is illustrated using an ultra‐wideband monopole optimized for best in‐band reflection, minimum gain variability, and minimum size. When compared with conventional surrogate‐based approach, segmentation leads to reduction of the initial Pareto identification cost by over 20%. Numerical results are supported by experimental validation of the selected Pareto‐optimal antenna designs.     

Reliable design optimization of microwave structures using multipoint‐response‐correction space mapping and trust regions

Space mapping (SM) is one of the most efficient simulation‐driven design technologies used in microwave engineering to date. It includes so‐called output SM that ensures exact matching between the EM‐evaluated microwave structure under consideration (fine model) and its surrogate at the current design. The standard, single‐point output SM exploits the fine model data at a single design and is not able to align the models' sensitivity. Here, a multipoint response correction is proposed that generalizes the concept of output SM. By using a design‐variable‐dependent correction term and exploiting all available fine model information, the proposed technique provides exact match between the surrogate and the fine model at several designs. This retains the benefits of output SM but also enhances sensitivity matching between the two models, which results in improved performance of the SM optimization process. The efficiency of the propose approach is demonstrated using several microwave design problems. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Design of defective electromagnetic band‐gap structures for use in dual‐band patch antennas

Generally, the surface wave of an antenna can be suppressed by integrating the electromagnetic band‐gap (EBG) structures. However, to achieve this effect, the EBG cells must be reasonably designed, otherwise it may lead to performance degradation instead. In this article, a dual‐band pinwheel‐shaped slot EBG structure is proposed. When applied to a patch antenna, defects are introduced into 3 rows of the EBG unit cells. The proposed antenna, incorporating EBGs designed with structural defects, to radiate at 4.9 and 5.4 GHz is simulated and tested. The measured results show that the ?10‐dB bandwidth of the proposed EBG antenna is extended by 41% and 25.4% at low frequency and high frequency, respectively. In addition, the peak gain of the proposed EBG antenna is increased by 2.44 dB at 4.9 GHz and 2.86 dB at 5.4 GHz with >40% efficiency. When compared with the periodic EBG antenna, this antenna is more effective. Thus, these experimental results show that the performance of the EBG antenna can be improved by interrupting the periodicity of the EBGs structures.     

Slot line fed dual‐band dipole antenna for 2.4/5.2 GHz WLAN applications

A printed slot line fed dual‐band coplanar dipole antenna having a dimension of 0.40λ_g × 0.20λ_g suitable for both 2.4 and 5.2 GHz (IEEE 802.11 b/g and 802.11 a) WLAN application is presented. The structure comprises of a slot line fed symmetrical L strips to achieve dual‐band operation. Design equations of the antenna are developed and validated on different substrates. The simulation and experimental results show that the proposed antenna exhibits good impedance match, gain, and stable radiation patterns in both the frequency bands. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2012.     

Novel offset‐fed dual‐band aperture‐dipole composite antenna: Operating principle and design approach

Operating principle and design approach of a novel dual‐band aperture‐dipole composite antenna are proposed. It is shown that multiple operating modes can be simultaneously excited by employing offset‐feeding technique at first. After the behavior of each mode is studied, the operating principle of the antenna is analyzed and described. Then, an improved dual‐band aperture‐dipole composite antenna is formed and it is designed by using the proposed approach. The antenna is experimentally verified. It is demonstrated that two operating bands for radiation are ranged from 2.36 to 2.58 GHz and from 4.1 to 15.72 GHz, respectively, in which the reflection coefficient are both 相似文献   

Design of dual‐mode dual‐band rectangular waveguide filtering antenna

A dual‐mode dual‐band rectangular waveguide filtering antenna with fourth‐order Chebyshev response is presented. First, design equations and processes of filtering networks are presented. Then, filtering antenna is constructed through cross‐shaped slot for radiation instead of the output port of filtering networks. A pair of degenerated modes are exploited in waveguide resonator design to miniaturize the whole size and form two passbands. In addition, the bandwidth can be adjusted flexibly in proper range. A prototype at C‐band is fabricated and measured, showing two operation channels of 5 to 5.05 GHz and 5.1 to 5.15 GHz with high rejection between two bands. Good agreement is achieved between the simulations and measurements, showing excellent performance in terms of filtering, out‐of‐band rejection, and gain in bands.     

An efficient dual‐band filter‐antenna design based on simplified integration methodology

In this article, a newly developed filter‐antenna synthesis and realization methodology is applied to design a planar dual‐band filtering antenna. The synthesis method is derived based on the filter synthesis theory. As a result, a coupling coefficient expression is formulized more precisely specially for the antenna matched to the filter, which is essentially different from that in filter coupling. The synthesized circuit is realized by an efficient parameters extraction process. A third‐order dual‐band filtering antenna integrated with two dual‐mode 8‐shaped resonators and a dual‐inverted‐L antenna is then implemented for example to illustrate the design procedure. The integration method facilitates an efficient and practical filter‐antenna design without complicated parameters evaluation process. Finally, the proposed filtering antenna with simple structure and controllable frequencies is developed with the use of the investigated formulations and extraction curves. The circuit is realized for 2.5/3.45‐GHz WiMAX‐band applications. The tested results agree well with the simulations, showing good passbands selectivity and out‐of‐band rejection are attained.     

Gap‐coupled designs of star shape microstrip antennas for dual band and wide band circular polarized response

Gap‐coupled designs of star‐shape microstrip antennas for dual band and wide band circular polarized response are proposed. An angular displacement between fed and parasitic patches yields the optimum separation between patch orthogonal resonant modes to yield circular polarized response. In dual band design, axial ratio bandwidth of 8% is obtained whereas wideband design gives axial ratio bandwidth of nearly 29%. Proposed configurations exhibit broadside pattern with peak gain of more than 7 dBi. Resonant length formulations for star shape patch and for their dual and wide band designs are presented. They provide guidelines for redesigning similar antenna at different frequency.     

A Dual‐band and dual‐polarized antenna array for 2G/3G/LTE base stations

A dual‐band antenna array is proposed for the application of base station (BS) in 2G/3G/long term evaluation (LTE) mobile communications. This antenna consists of two independent ±45° dual‐polarized arrays, one of which operates from 1.71 to 2.17 GHz, and the other of which is designed from 2.5 to 2.69 GHz. The proposed BS antenna array has a high isolation of greater than 29 dB and high front‐to‐back ratio of more than 26 dB at the operating frequencies. The measured peak gain is 17.9 and 18.1 dBi for the lower and upper bands, respectively, and the cross polarizations isolation (CPI)(within ±60º of the mainlobe) is 16 dB lower than the broadside co‐polarization. It was confirmed that the proposed antenna array meets the communication standards in China. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:154–163, 2016.     

Analysis of circular polarization antenna design trade‐offs using low‐cost EM‐driven multiobjective optimization

Circular polarization (CP) antennas are vital components of modern communication systems. Their design involves handling several requirements such as low reflection and axial ratio (AR) within the frequency range of interest. Small size is an important criterion for antenna mobility which is normally achieved as a by‐product of performance‐oriented modifications of the structure topology. In this work, multiobjective optimization is used in order to identify and analyze design trade‐offs for miniaturized CP antenna including the antenna capability for maintaining small size while retaining acceptable levels of other performance figures. We use a population‐based metaheuristic algorithm to obtain a set of designs which represent the best attainable compromise between the imposed requirements. To maintain a low optimization cost, the algorithm is executed on a cheap approximation model and the results are further corrected to bring them to the EM model accuracy level. Here, the analysis is carried out for a planar CP antenna. Achievable size reduction of the considered structure—while maintaining acceptable performance—is around 11%. Antenna performance in terms of in‐band reflection and AR varies from ?14 to ?10 dB and from 1.3 to 3 dB, respectively. The numerical results are validated by measurements of fabricated antenna prototypes.     

Precise control of reflection response in bandwidth‐enhanced planar antennas

In this work, the issues of bandwidth enhancement of planar antennas and the relevance of precise and automated response control through numerical optimization have been investigated. Using an example of a planar antenna with parasitic radiator we illustrate possible effects of even minor modifications of the antenna geometry (here, applied to the ground plane) on its reflection performance. In particular, a proper handling of geometry parameters may lead to considerable broadening of the antenna bandwidth. For the sake of computational efficiency, the adjustment of geometry parameters is carried out using surrogate‐based optimization methods exploiting coarse‐discretization EM simulations as the underlying low‐fidelity antenna model. Additionally, suitably defined penalty function allows us to precisely control the maximum in‐band reflection so that sufficient margin to accommodate possible manufacturing tolerances can be achieved. The optimized designs of the two antenna structures considered in this work exhibit over 1.75 GHz (>31%) and 2.15 GHz (>38%) bandwidth, respectively, for the center frequency of 5.6 GHz. Simulation results are validated using measurements of the fabricated prototypes. Comparison with state‐of‐the‐art designs is also provided. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:653–659, 2016.     

Electromagnetic band‐gap structured printed antennas: A feature‐oriented survey

Wireless communication systems are playing an important role in different sectors of human society. Printed antennas are considered as the critical enabling technologies for these systems. The technology related to the design and development of printed antennas have been continuously improved from the structural view of configuration to antenna features improvement. Electromagnetic bandgap (EBG) structures have played a significant role in improving the features of printed antennas. In this paper, authors have restricted a feature–oriented comprehensive survey on EBG‐structured printed antennas. This type of survey is primarily required for the beginner working on EBG structures/EBG‐structured printed antennas. Such a survey process is rarely carried out in the open literature to the best of authors' knowledge. The proposed survey process is confined only to five different feature classifications; bandwidth improvement, gain improvement, dual‐band/multi‐band characteristics, band‐notch characteristics, and compact and low profile, respectively.     

A dual‐band eight‐antenna multi‐input multi‐output array for 5G metal‐framed smartphones

A dual‐band eight‐antenna array operating in the long‐term evolution (LTE) band 41 (2.496‐2.69 GHz) and 3.5‐GHz band (3.3‐3.7 GHz) for fifth‐generation (5G) metal‐framed smartphone is presented. The proposed dual‐band antenna array is composed of four identical dual‐antenna building blocks (DABBs). Each DABB consists of two identical antenna elements with a neutralization line between them. The antenna array is simulated, fabricated, and measured. The isolations are better than 10.5 dB and 11.0 dB in the low band (LB; LTE band 41) and high band (HB; 3.5‐GHz band). The total efficiencies are 41% to 54% and 46% to 64% in the two operation bands, respectively. In addition, the measured envelope correlation coefficients are less than 0.11 and 0.06, the calculated channel capacities are better than 34.5 and 36.3 bps/Hz in the LB and HB, respectively. Furthermore, four hand‐grip scenarios are investigated, and results show that proposed antenna array can maintain excellent multiple‐input multiple‐output performances in all scenarios.     

Phase‐spacing optimization of linear microstrip antenna arrays using simulation‐based surrogate superposition models

A technique for simulation‐driven optimization of the phase excitation tapers and spacings for linear arrays of microstrip patch antennas is presented. Our technique exploits two models of the array under optimization: an analytical model which is based on the array factor, as well as an electromagnetic (EM) simulation‐based surrogate model of the entire array. The former is used to provide initial designs which meet the design requirements imposed on the radiation response. The latter is used for tuning of the array radiation response while controlling the array reflection response as well as for validation of the final design. Furthermore, the simulation‐based surrogate model allows for subsequent evaluation of the array responses in the beam scanning operation at negligible computational costs. The simulation‐based surrogate model is constructed with a superposition of simulated radiation and reflection responses of the array under design with only one radiator active at a time. Low computational cost of the surrogate model is ensured by the EM‐simulation data computed with coarse meshes. Reliability of the model is achieved by means of suitable correction carried out with respect to the high‐fidelity array model. The correction is performed iteratively in the optimization process. Performance, numerical efficiency, and accuracy of the technique is demonstrated with radiation pattern synthesis of linear arrays comprising 32 microstrip patch antennas by phase‐spacing optimization. Properties of the optimal designs in the beam scanning operation are then studied using the superposition models and compared to suitably selected reference designs. The proposed technique is versatile as it also can be applied for simulation‐based optimization of antenna arrays comprising other types of individually fed elements. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:536–547, 2015.