Application of multi-objective fractional factorial design for ultra-wideband antennas with uniform gain and high fidelity

An efficient design methodology is presented for developing ultra-wideband (UWB) antennas with uniform gain and high fidelity. The major challenge for designing UWB antennas is to simultaneously meet all the frequency-domain and time-domain performance criteria including good impedance matching throughout the operational frequencies, relatively uniform gain over the UWB, and high waveform fidelity on pulse-preserving capabilities. If the framework of Pareto-based evolutionary algorithms is adopted, it may require thousands of tests to find an optimum structure due to the blind-search feature. In this study, all the requirements of UWB antenna design can now be efficiently achieved by the proposed methodology, which integrates the processes of fractional factorial design of experiments and Derringer's desirability functions into a multi-objective optimisation technique. The detailed procedure and its capability are demonstrated by an UWB planar monopole antenna design which comprises nine design parameters. By performing merely 64 predefined simulations, the optimum antenna structure is determined with an excellent impedance matching by 2:1 voltage standing wave ratio and a relatively constant gain (2.48-5.04 dBi) over the frequency band of 3.1-10.6 GHz. Meanwhile, the time-domain distortion is greatly reduced in comparison with the reference design which simply optimises the characteristic of impedance matching.