Adaptive Optimization Framework for Antenna Structure Design

Abstract

As terahertz and subterahertz technologies continue to develop, there is an increasing need for compact antennas with broad bandwidth, stable impedance matching, and reliable directional response. The micro circular log periodic antenna, or MCLPA, is a promising candidate because its self similar geometry can support wideband operation within a com-pact planar structure. However, its design is controlled by several coupled geometric param-eters, including the number of rings, scaling factor, angular spans, and tooth thickness. These parameters interact in a nonlinear way, which makes manual optimisation difficult and often requires many full wave electromagnetic simulations. This thesis presents an Efficient Self Adaptive Optimiser, or ESAO, for simulation guided antenna design under limited computational resources. Instead of using fixed objec-tive weights throughout the search, the proposed framework evolves both antenna parame-ters and objective priorities during the optimisation process. The framework combines sev-eral adaptive components, including feature salience analysis, surrogate assisted candidate screening, multi fidelity evaluation, hybrid search strategies, progressive dimensionality re-duction, and convergence control. Together, these components allow the optimiser to focus simulation effort on more informative regions of the design space while still maintaining sufficient exploration. The proposed method is applied to the design of an MCLPA operating in the millimetre wave and subterahertz range. Simulation results show that the optimised design improves the operating bandwidth and maintains stable realised gain and impedance matching com-pared with the initial seed design. The final design uses eight log periodic elements with a scaling factor of 0.78 and achieves a simulated operating band from approximately 60.3 GHz to 100.4 GHz, with an average realised gain of 6.1 dBi and a minimum reflection coef-ficient of minus 37.1 dB. To support the simulation results, selected MCLPA samples were fabricated on silicon substrates and tested using a blackbody radiation source, PTFE optical components, and high impedance voltage readout. Because calibrated terahertz power measurement and vec-tor network analysis were not available for the fabricated samples, the experimental study focuses on relative voltage response rather than absolute antenna gain or responsivity. The measured results show repeatable voltage changes under blocked and unblocked radiation conditions, an overall increase in response with blackbody temperature, and orientation de-pendent behaviour. These observations provide practical evidence that the fabricated MCLPA responds to incident broadband radiation and that the simulation guided design is physically meaningful. Overall, this work contributes a practical optimisation framework for expensive elec-tromagnetic design problems and demonstrates its use through the design, fabrication, and relative experimental characterisation of an MCLPA. The results suggest that adaptive opti-misation can reduce manual design effort while also providing interpretable relationships between antenna geometry and electromagnetic performance.