Characterisation of antenna substrate properties using surrogate-based optimisation

In the current study, the authors present a technique to characterise the permittivity and loss tangent of an antenna substrate. In this method, an error function is formulated with measured data and a set of simulation data on the antenna's impedance and bandwidth. Subsequently, a surrogate-based optimisation code is used to intelligently search for the substrate parameters that minimise the error function. The validity of the method is demonstrated by experiments on wearable patch antennas with felt substrates. The results show that the method is effective in retrieving the permittivity and loss tangent of the antenna substrate using the antenna itself as the test fixture. Thus, there is no need to prepare additional resonators or transmission-line fixtures as in conventional substrate characterisation methods.