Mid Sweden University

The paper describes the application of a computer intensive methodology to evaluate antenna susceptibility to random physical damage for a dipole and a bow-tie antenna. For each randomly generated damage pattern antenna parameters are simulated and a statistical comparison is performed. Computer intensive statistical methods like the Bootstrap, used here for postprocessing, make fewer initial assumptions than classical statistical methods when modelling a problem, and are robust against small deflections from these assumptions. The bias-corrected and accelerated (BCa) Bootstrap method is used for confidence interval estimates. The dipole antenna is found to be more robust to numbers of small (similar to 100th of a wavelength) circular holes penetrating the structure than the bow-tie antenna.

In a previous paper, (Olsson, Sidén, and Koptioug, "Robustness comparison of bow-tie and dipole antennas," IEE Proceedings Microwaves, Antennas and Propagation, vol. 151, no 6, Dec. 2004, pp. 525-529), it was shown that the dipóle antenna is more robust than the bow-tie antenna, with same radiator aperture area, to numbers of small randomly positioned holes penetrating the structures. In present paper it is shown that for a small number of holes the bow-tie antenna is more robust due to lower hit probability in high current density areas. The results show that the bow-tie feed is more robust for a small amount of damage, whereas the strip dipole feed (of width w and thickness t, with w ≫ t) is more robust in general terms, and particularly for larger number of damages.

Is it possible to produce a planar dipole-like antenna with a reduced conductive area without any loss in either robustness or performance? The objective is to reduce the amount of expensive conductor to be used when applying a meshing technique to the printing of antennas. In this context, robustness means that the characteristics are maintained when the antenna is damaged, for example if it is scratched. This is particularly important for radio frequency identification tags in logistic systems. A general antenna robustness evaluation methodology, based on numerical simulations of a large number of randomly damaged antennas, is used for the antenna comparisons. The antenna performance degradation, based on the return loss (S11) at 868MHz, is monitored for some basic planar antennas. Finally, we show that it is possible to produce robust low-cost antennas using wire replacements for the solid planar antennas and thus, provided that the robustness requirement is moderate, replace the solid antenna with a thin conductor analogue.

We address the question of robustness of damaged microstrip antennas, the damage being either penetrating, caused by fragment impact, or floating, caused by manufacturing imperfections. A simple analytic expression is derived to facilitate the prediction of robustness. To verify this expression a Monte Carlo method, based on a general 3D electromagnetic solver, is used to evaluate the robustness of the antennas. The simulations are verified by measurements and supplementary simulations in an alternative electromagnetic solver, using the finite difference time domain method (FDTD). The agreement between the simulated results and the analytic expression is found to be good in a qualitative comparison.