ML-Surrogate-Assisted Design Optimisation of a Microstrip Patch Antenna

A 2.45 GHz inset-fed microstrip patch on FR-4 is simulated with the free FDTD solver openEMS on 120 training and 30 independent test designs (W, L, y0), 198 real runs in all. A Gaussian-process surrogate predicts resonance, S11 depth and bandwidth in microseconds; a search runs on it and every candidate is re-simulated. The deployed model (GP residual) has a mean f0 error of 0.50 % on the test plan; the analytic formula is off by 1.24 % in f0 on average (11.51 % at most, correlation 0.960), worse than the deployed surrogate (0.50 %). The final design (route gp_infill) is W = 42.53, L = 28.41, y0 = 7.59 mm. openEMS gives f0 = 2.4488 GHz (-0.05 % from 2.45 GHz), S11 = -34.8 dB, bandwidth 63 MHz: f0 is within 2 % of the target and S11 is below -15 dB. By the strict objective, the best re- simulated design is 'MLP + 100,000 random candidates, frequency weighted 10 x' (f0 2.4492 GHz, -0.03 %, S11 -35.3 dB, 1 extra EM run(s) after the data), a surrogate route. The best classic route is 'Nelder-Mead directly on openEMS, 20 real runs, no data set' (2.4433 GHz, S11 -36.8 dB, 20 EM run(s) after the data, no data set). The textbook formula alone gives f0 2.4181 GHz (-1.30 %) and S11 -9.6 dB, i.e. above -10 dB, not matched; hand rules on the simulator meet both targets at simulator run 2 (of 3 runs); Nelder-Mead meets both at its run 9; the surrogate route needs its 120 training runs before the first search, so its first verified design costs 121 runs. For this one design task the surrogate's plan is therefore NOT cheaper than the classic routes. Its value is elsewhere: a map of the whole design space that answers any other target frequency or tolerance question at once, instant re-targeting (microseconds), and an uncertainty estimate. No other finished project in this series uses openEMS or antenna electromagnetic simulation. No antenna was fabricated or measured.

Category: Electronics and Communication Engineering

Electronics & Communication Engineering Project E14 from ProTechSC Academy, with graphical abstract, video demonstration and project guidance.