Explicit Size Reduction Research Articles

Cost-Efficient EM-Driven Size Reduction of Antenna Structures by Multi-Fidelity Simulation Models

Design of antenna systems for emerging application areas such as the Internet of Things (IoT), fifth generation wireless communications (5G), or remote sensing, is a challenging endeavor. In addition to meeting stringent performance specifications concerning electrical and field properties, the structure has to maintain small physical dimensions. The latter normally requires searching for trade-off solutions because miniaturization has detrimental effects on antenna characteristics, including the impedance matching, gain, efficiency, or axial ratio bandwidth. Furthermore, explicit size reduction is more demanding than optimization with respect to other figures of merit. On the one hand, it is a constrained task with acceptance thresholds set on the bandwidth, gain, etc. On the other hand, optimum solutions are normally located at the boundary of the feasible region, traversing of which is a difficult problem by itself. The necessity of using full-wave electromagnetic (EM) analysis for antenna evaluation only aggravates the problem due to high computational costs associated with numerical optimization algorithms. This paper proposes a procedure for expedited optimization-based miniaturization of antenna structures involving trust-region gradient search and multi-fidelity EM simulations, as well as implicit handling of design constraints using a penalty function approach. The assumed model management scheme is associated with the convergence status of the optimization process with the lowest fidelity model employed at the early stages of the algorithm run and the discretization density of the structure gradually increased to reach the high-fidelity level towards the end of the run. This allows us to achieve a considerable computational speedup without compromising the reliability. Our methodology is demonstrated using two broadband microstrip antennas. The obtained CPU savings exceed seventy percent as compared to the reference procedure involving high-fidelity model only.

Explicit Size-Reduction of Circularly Polarized Antennas Through Constrained Optimization With Penalty Factor Adjustment

Modern communication systems of high data capacity incorporate circular polarization (CP) as the preferred antenna radiation field configuration. In many applications, integration of the system circuitry with antennas imposes size limitations on CP radiators, which makes their development process a challenging endeavor. This can be mitigated by means of simulation-driven design, specifically, constrained numerical optimization. Majority of the performance-related constraints are expensive to evaluate, i.e. require full-wave electromagnetic (EM) analysis of the system. Their practical handling can be realized using a penalty function approach, where the primary objective (antenna size reduction) is complemented by contributions proportional to properly quantified constraint violations. The coefficients determining the contribution of the penalty terms are normally set up using designer’s experience, which is unlikely to render their optimum values in terms of the achievable miniaturization rates as well as constraint satisfaction. This paper proposes a procedure for automated penalty factor adjustment in the course of the optimization process. Our methodology seeks for the most suitable coefficient levels based on the detected constraint violations and feasibility status of the design. It is validated using two CP antenna structures. The results demonstrate a possibility of a precise constraint control as well as superior miniaturization rates as compared to the manual penalty term setup.

Miniaturisation of wideband antennas by means of feed line topology alterations

It is a common practice to achieve reduction of wideband antenna size by incorporating appropriate geometrical modifications into conventional antenna topologies (e.g. monopoles or uniplanar structures). The authors investigate a particular type of modification, which is changing the geometry of the feed line. The two basic geometries include a taper and a stepped-impedance line. They carry out systematic investigations concerning the effect of these feed line geometries on obtainable antenna miniaturisation rates. For the sake of generality, feed line geometries of various complexities are considered (from two to six sections). An automated adjustment of antenna geometry parameters through numerical optimisation is performed to ensure design optimality for each combination of antenna/feed structure. The optimisation process is formulated as an explicit size reduction task with a constraint on the maximum in-band reflection level. The investigations are performed using two selected ultra-wideband monopoles. The results indicate clear advantage of the stepped-impedance feed line over the tapered one. On the other hand, considerable size reduction can be obtained by increasing the geometrical complexity of the feed line, although the design problem becomes more challenging due to the increased number of antenna parameters. Numerical results are validated experimentally for selected antenna prototypes.

Simulation‐driven size‐reduction‐oriented design of multi‐band antennas by means of response features

This study addresses the problem of explicit size reduction of multi-band antennas by means of simulation-driven optimisation. The principal difficulty of electromagnetic (EM)-based miniaturisation of multi-band antennas is that several resonances have to be controlled independently (both in terms of their frequency allocation and depth) while attempting to reduce physical dimensions of the structure at hand. The design method of choice in this work is feature-based optimisation (FBO) framework. The methodology has been shown as appropriate for handling multi-band antenna responses. The primary objective of the optimisation process is the footprint area of the antenna. At the same time, design requirements pertinent to reflection characteristics are handled by means of a penalty function approach. The properties of the FBO framework, namely ‘flattening’ of the functional landscape, allows to keep the design optimisation costs at acceptable levels of few dozens of evaluation of the EM simulation model of the antenna. For the sake of demonstration, two antenna structures are considered, a dual-band patch antenna, and a triple-band dipole antenna. Considerable size-reduction ratios are achieved, over 50% and almost 30% for the first and the second structures, respectively. Numerical results are validated experimentally.

Feasible space boundary search for improved optimisation‐based miniaturisation of antenna structures

This study describes an enhanced procedure for electromagnetic-simulation-based miniaturisation of antenna structures. The proposed methodology utilises formulation of the antenna design as non-linear minimisation problem oriented towards explicit size reduction with constraints imposed on the reflection response of the structure at hand. The primary idea is to explore the boundary of the feasible region so as to allow efficient identification of a constrained optimum that ensures satisfaction of the prescribed matching requirements for the structure at hand. The proposed algorithm overcomes the issues related to the standard formulation involving a penalty function approach, where high non-linearity of the objective function in the vicinity of the optimum may lead to finding a sub-optimal design. For the sake of demonstration and verification, three examples of ultra-wideband antennas are considered. In all cases, the proposed methodology leads to smaller footprints and better control of the in-band matching compared to the benchmark algorithm, i.e. gradient-based search with implicit reflection response control through a penalty function approach.

Structure and EM‐driven design of novel compact UWB slot antenna

In this study, a structure and design optimisation procedure of a novel compact ultra-wideband (UWB) slot antenna has been presented. In order to achieve small size of the structure and maintain acceptable electrical performance, a sufficiently large number of geometry parameters have been introduced. These include a stepped-impedance feed line and a meandered slot with all of dimensions being parameterised and subject to optimisation. All parameters are simultaneously adjusted using automated electromagnetic (EM)-simulation-driven optimisation algorithm. The design process is oriented towards explicit size reduction of the antenna structure. Penalty function approach is utilised to control the reflection response. In order to reduce the computational cost of the optimisation process, variable-fidelity EM models are utilised. The footprint of the optimised antenna is only 8.93 × 17.9 mm (160 mm2) while maintaining reflection below the –10 dB threshold in the entire UWB frequency range. The antenna has been favourably compared with the state-of-the-art compact structures in terms of the size. The obtained numerical results are supported by measurements of the fabricated antenna prototype.

Simulation-driven design of compact ultra-wideband antenna structures

Purpose – The purpose of this paper is to investigate strategies and algorithms for expedited design optimization and explicit size reduction of compact ultra-wideband (UWB) antennas. Design/methodology/approach – Formulation of the compact antenna design problem aiming at explicit size reduction while maintaining acceptable electrical performance is presented. Algorithmic frameworks are described suitable for handling various design situations and involving simulation models without and with response gradients available. Numerical and experimental case studies are provided demonstrating feasibility of solving real-world miniaturized antenna design tasks. Findings – It is possible, through appropriate combination of the global and local optimization methods, surrogate modeling techniques and response correction methods, to find optimum dimensions of antenna structures that minimize antenna size while maintaining acceptable electrical performance. Design optimization can be performed at practically feasible computational costs. Research limitations/implications – The study summarizes recent advances in miniaturization-oriented design optimization of UWB antennas. The presented techniques reach far beyond the commonly used design approaches based on parameter sweeps and similar hands-on methods, particularly in terms of automation, reliability, and reduction of the computational costs of the design processes. Originality/value – The proposed design problem formulation and algorithmic frameworks proved useful for rapid design of compact UWB antenna structures, which is extremely challenging when using conventional methods. To the knowledge, this is the first attempt to efficient solving of this type of design problems, especially in the context of explicit antenna size reduction.

Compact UWB monopole antenna for internet of things applications

A structure of a compact ultra-wideband monopole antenna has been presented. The antenna consists of a microstrip-fed rectangle radiator as well as a ground plane with a rectangle slit and an L-shaped stub. The critical factor in achieving a small size is a careful design procedure involving numerical optimisation of all geometry parameters of the antenna aiming at explicit size reduction while maintaining acceptable electrical performance. The final design exhibits dimensions of only 9.45 × 18.5 mm and a footprint of 175 mm 2 . Experimental validation and comparisons with competitive designs are also provided.

Structure and design optimisation of compact UWB slot antenna

A structure and computationally efficient design optimisation procedure of a novel miniaturised UWB slot antenna has been proposed. Upon geometry parameter adjustment, the structure exhibits a very small footprint of just 161 mm2. This has been achieved by introducing sufficient number of degrees of freedom, including the parameterised multi-section slot and a multi-section load of the feed line as well as efficient numerical optimisation of all relevant geometry dimensions of the structure. The design process has been formulated as explicit size reduction problem. The electrical performance parameters (here, a maximum in-band reflection) are controlled by suitably defined constraints. The final design has been verified through full-wave electromagnetic simulation as well as physical measurements of the fabricated antenna prototype.

Fast EM-Driven Size Reduction of Antenna Structures by Means of Adjoint Sensitivities and Trust Regions

In this letter, a simple yet robust and computationally efficient optimization technique for explicit size reduction of antenna structures is presented. Our approach directly handles the antenna size as the main design objective, while ensuring satisfactory electrical performance by means of suitably defined penalty functions. For the sake of accuracy, the antenna structure is evaluated using high-fidelity EM simulation. In order to maintain computational efficiency of the design optimization process, it is carried out using cheap adjoint sensitivities and trust region framework utilized as convergence safeguard. Our technique is illustrated through a design of a compact quasi-isotropic dielectric resonator antenna and a UWB monopole. Numerical results are supported by physical measurements of a fabricated prototype.