Conformal Antenna Optimization with Space Mapping

Designers are increasingly integrating conformal microstrip antennas into the curved structures of either air or land vehicles. Quite often, these structures are doubly curved (e.g. curved along two orthogonal surface directions). This practice necessitates the development of accurate codes versatile enough to model conformal antennas with arbitrarily shaped apertures radiating from doubly curved surfaces. Traditional planar-structure-based design techniques are not well suited for this application. A hybrid finite element-boundary integral formulation appropriate for the high-frequency analysis and design of doubly curved conformal antennas is introduced in this paper. The novelty of this approach lies in its use of an asymptotic prolate spheroidal dyadic Green’s function to model the physics of curved surface diffraction. To demonstrate the utility of this approach, the effects of curvature on the resonant frequency and input impedance of both a doubly curved conformal square and circular patch antenna are investigated. Different feed positions are also considered. Due to a paucity of published experimental data, the numerical results are benchmarked by comparison with the results for planar square and circular patch antennas. The planar results are obtained by using an experimentally validated planar finite element-boundary integral code. 296 Macon, Trott, and Kempel

In this paper, space mapping (SM) technique is combined with response surface methodology (RSM). SM is an optimization method well suited for very costly problems to find an improved design with fulfilled constraints. The SM technique use less costly models, which complements the correct models. The theory is established and compared to the corrected RSM. A multipoint version of SM is presented, where a separate evaluation is done in each iteration to improve the mapping function. Using this additional evaluation to update the mapping function, generally, the number of iterations to find the optimum solution can be reduced. Thus, the elapsed time to solve the optimization problem can be reduced if a parallel computer is utilized. Finally, one engineering optimization problem is solved to illustrate the application of SM in vehicle crashworthiness structural optimization.

A conformal microstrip antenna is highly integrated with the carrier profile, giving it the advantage of reduced carrier space. However, the processing technology for fabricating an antenna with a conformal surface is complicated and expensive owing to its irregular shape. Therefore, it is particularly important to find ways to reduce the difficulty in producing conformal conductive patterns. For the production of conformal microstrip antennas, a five-axes motion printing system is proposed to print conductive patterns on nonexpanded surfaces. The conductive pattern uses a new boundary-alignment-optimization algorithm in the printing process to improve the accuracy of the boundary of the conductive pattern by optimizing the ink-dropping points in the motion command. The short-time and low-temperature sintering of the conductive pattern by using a flash light enables it to exhibit conductive properties. This method is practically implemented to fabricate a conformal array microstrip antenna. The main and side lobes of the electric and magnetic fields in the directional pattern measured in the microwave darkroom have the same trend as in the simulation diagram. Thus, the effectiveness of this method was verified through simulation analysis and experimental results.

Designers are increasingly integrating conformal microstrip antennas into the curved structures of either air or land vehicles. Quite often, these structures are doubly curved (e.g. curved along two orthogonal surface directions). This practice necessitates the development of accurate codes versatile enough to model conformal antennas with arbitrarily shaped apertures radiating from doubly curved surfaces. Traditional planar-structure-based design techniques are not well suited for this application. A hybrid finite element-boundary integral formulation appropriate for the high-frequency analysis and design of doubly curved conformal antennas is introduced in this paper. The novelty of this approach lies in its use of an asymptotic prolate spheroidal dyadic Green's function to model the physics of curved surface diffraction. To demonstrate the utility of this approach, the effects of curvature on the resonant frequency and input impedance of both a doubly curved conformal square and circular patch antenna are investigated. Different feed positions are also considered. Due to a paucity of published experimental data, the numerical results are benchmarked by comparison with the results for planar square and circular patch antennas. The planar results are obtained by using an experimentally validated planar finite element-boundary integral code.

PurposeOptimisation in electromagnetics, based on finite element models, is often very time‐consuming. In this paper, we present the space‐mapping (SM) technique which aims at speeding up such procedures by exploiting auxiliary models that are less accurate but much cheaper to compute.Design/methodology/approachThe key element in this technique is the SM function. Its purpose is to relate the two models. The SM function, combined with the low accuracy model, makes a surrogate model that can be optimised more efficiently.FindingsBy two examples we show that the SM technique is effective. Further we show how the choice of the low accuracy model can influence the acceleration process. On one hand, taking into account more essential features of the problem helps speeding up the whole procedure. On the other hand, extremely simple auxiliary models can already yield a significant acceleration.Research limitations/implicationsObtaining the low accuracy model is not always straightforward. Some research could be done in this direction. The SM technique can also be applied iteratively, i.e. the auxiliary model is optimised aided by a coarser one. Thus, the generation of hierarchies of models seems to be a promising venue for the SM technique.Originality/valueOptimisation in electromagnetics, based on finite element models, is often very time‐consuming. The results given show that the SM technique is effective for speeding up such procedures.

Space mapping (SM) is a recognized method for speeding up electromagnetic (EM) optimization. The SM technique often requires an equivalent circuit as the coarse model. In practical cases, equivalent circuit coarse models are not always available. This letter addresses this situation and proposes a new coarse- and fine-mesh SM technique for EM optimization incorporating mesh deformation. By incorporating mesh deformation into coarse-mesh EM optimization, the coarse-mesh EM responses change continuously as the values of the geometrical design variables change. The incorporation of mesh deformation also improves the consistency between the coarse-mesh EM sensitivities and the changes in the coarse-mesh EM responses. This results in the speedup of the coarse-mesh EM optimization and potentially less SM iterations, therefore accelerating the overall SM optimization. This technique is illustrated by two microwave examples.

As it has outstanding electrical and mechanical properties, like high conductivity, durability, and flexibility, graphene may be an interesting material also for conformal and wearable antennas. Whereas mono‐atomic graphene layers have been proven to perform inadequately at microwave frequencies, in this article the performance of multilayered graphene‐based sheets (GBS) fabricated onto a polymer substrate is assessed when used as flexible planar and conformal antennas. This is accomplished through studying a simple microstrip antenna topology. Challenges related to the fabrication process of these antennas are discussed, for example adhesion issues and the occurrence of air gaps on the substrate layer. The graphene‐based technology is compared to a classical technology involving copper as metal. Bending of the antennas is also discussed. The main conclusion is that multilayered graphene does perform adequately as conductor in antennas at microwave frequencies, with the possibility of providing a slightly higher gain than copper.

This paper presents a novel configuration of a U-shaped, dual-frequency, single-feed, planar inverted-F microstrip antenna with a U-shaped slot (UU-PIFA). The antenna is well suited to telephone handsets used in today's mobile communication systems operating in both GSM and DCS 1800 bands, namely 0.9 and 1.8 GHz, respectively. An initial design is derived from an empirical approximation and a transmission line model of a rectangular microstrip antenna. The paper analyses, examines, and fine-tunes the electrical performance of the antenna, including the return loss, operating frequencies, bandwidths, input impedance, and far-field radiation patterns, by using the generalised non-uniform finite difference time domain (NU-FDTD) Maxwell solver. In addition, to increase the efficiency of the FDTD solver, the concept of domain decomposition is utilised, which enables one to eliminate redundant computational space, and thereby reduce the memory and CPU time requirements.

In this paper, we study the use of space-mapping (SM) techniques within the transmission-line matrix (TLM) method environment. Previous work on SM relies on an idealized coarse model in the design process of a computationally expensive fine model. For the first time, we examine the case when the coarse model is not capable of providing an ideal optimal response. We exploit a coarse-grid TLM solver with relaxed boundary conditions. Such a coarse model may be incapable of satisfying design specifications and traditional SM may fail. Our approach, which exploits implicit SM (ISM) and the novel output SM (OSM), overcomes this failure. Dielectric constant, an expedient preassigned parameter, is first calibrated to roughly align the coarse and fine TLM models. Our OSM scheme absorbs the remaining deviation between the implicitly mapped coarse-grid and fine-grid TLM responses. Because the TLM simulations are on a fixed grid, response interpolation is crucial. We also create a database system to avoid repeating simulations unnecessarily. Our optimization routine employs a trust region methodology. The TLM-based design of an inductive post, a single-resonator filter, and a six-section H-plane waveguide filter illustrate our approach. In a few iterations, our coarse-grid TLM surrogate, with approximate boundary conditions, achieves a good design of the fine-grid TLM model in spite of poor initial responses. Our results are verified with MEFiSTo simulations.

A design procedure for inline waveguide extracted pole filters with all-metal E-plane inserts is presented. To achieve acceptable modeling accuracy for this class of filters, an enhanced schematic-circuit-based surrogate model is developed, accounting for parasitic effects between the neighboring elements of the structure. The proposed circuit representation is used as a coarse model in a surrogate-based optimization of the filter structure with the space mapping technique as the main engine in the optimization process. Feasibility of the modeling approach is demonstrated by two filter design examples. The examples show that a low computational cost (corresponding to a few evaluations of the high-fidelity EM simulations of the filter structure) is required to obtain an optimized design.KeywordsInline filtersE-plane filtersExtracted pole filtersWaveguideModelingSurrogate optimization

The surface integral equation is adopted to analyse the characteristics of the arbitrarily arranged spherical conformal microstrip antenna array based on the moment method. The Rao–Wilton–Glisson basis function and triangle function are used to simulate equivalent current on the patch and probe, respectively. A novel basis function at the junction of wire and surface is proposed to ensure continuity of the current from probe to patch. Then, the magnetic frill loop is used as excitation source in this study, and the field on the antenna surface generated by magnetic frill loop is deduced with the help of magnetic dyadic Green's functions on the surface of sphere. For the antenna array analysis, the characteristic basis function method combined with equivalent dipole method is employed to save the consumed memory and computation time. The characteristics of several pairs of conformal spherical microstrip antennas are presented and shown to be in good agreement with data from literatures and FEKO software. At last, a result comparison between the method in this study and FEKO software is drawn to show the efficiency of this method.

FEKO is a 3D simulation tool for the analysis of electromagnetic fields. The simulation using FEKO is based on the well-known method of moments (MoM) for the Maxwell equations. FEKO can solve the problem of any structural type with a very comprehensive MoM code or tailored code. First, a radiation pattern for conformal microstrip antenna on the surface of cylinder is calculated using FEKO. In addition, the impact of conformal carrier on the radiations of microstrip antennas in different positions is simulated by FEKO. The simulation results accord with the true characteristics of conformal microstrip antennas.

In this paper, Multiport Network (MN) Model has been developed to analyze dual feed planar gap-coupled square microstrip antennas for circularly polarization. Several planar square MSA configurations have been proposed to increase both the axial ratio and impedance bandwidths with higher directivity. Only the one square patch is fed at the two orthogonal points with equal amplitude and 90/spl deg/ phase difference and others are parasitically coupled. In MN model, the dimensions of the patch are extended outwards to account for the fringing fields and the impedance matrix of the square microstrip antenna (SMSA) is obtained from its Green's function. The segmentation method is used to obtain the input impedance of the SMSA.

<span>This work investigated a miniaturized slotted conformal antenna array for multiband application. Three guard lines are incorporated to the side of main patch and top of main patch to reduce surface current for planner surface and observe the effect of guard line due to which it resonate at three frequencies in X band and Ku band to be useful for multiband. A rectangular slot is etched at center of patches to increase the current path for wide band application. A quarter wavelength feeding network is used with good agreement of impedance matching. The main lobe width and direction shows through the radiation pattern which remains stable even it is significantly curved. This structure is wrapped around a cylinder with a diameter of 41.4 mm in the circumferential direction. It is observed that the planner antenna array operating at 8.4 GHz, 11.2 GHz &18.2 GHz with a return loss of -20 dB to -45 dB with fractional BW of 25% at 3rd frequency range and the directivity from 3.4 dBi-6.8 dBi. By doing some alteration in dimensions for the conformal antenna producing fractional BW of 20% and the directivity 5.5 to 9.1 dBi at resonating frequencies of 8.4 GHz, 11.4 GHz, and 17.5 GHz. This proposed array is simulated on CST software.</span>

Composite metamaterial antenna with super mechanical and electromagnetic performances integrated by three-dimensional weaving technique