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In order to obtain near-metal-insensitive antenna for closed-space wireless communications, the impedance characteristics of U-shaped folded monopole antenna is investigated in detail. In this Letter, the near-metal-insensitive means antenna VSWRs are hardly influenced by the near object, especially metal. The simulated and measured results show that the proposed higher impedance model has stronger near-metal-insensitiveness than the conventional middle impedance model. The simulated and measured results show that the antenna gains of higher impedance models are 3 dB greater at maximum than those of middle impedance models, when metal plane approaches. References [1] T. Kobayashi, "Measurements and characterization of ultra wideband propagation channels in a passenger-car compartment," IEICE Trans. "Comparisons of simulated and measured electric field distributions in a cabin of simplified scale car model," IEICE Trans.

This paper studies loop antennas over artificial magnetic conductor (AMC) surfaces with the objective of designing a dual-band RF energy harvesting antenna. The AMC surface is well known to achieve low-profile and higher-gain wire antennas. From a practical point of view, impedance matching is of paramount importance to achieve highly efficient reception of weak ambient RF energy. Firstly, the driving-point impedance of a loop antenna over an AMC surface was studied, where a conventional method using image theory to estimate the impedance was found to be not always useful for loop antennas. As the AMC surface is within the reactive near field, mutual coupling between the antenna and the AMC unit cells is significant, which the conventional method does not take into account. We then proposed a novel use of a polarization dependent AMC surface for dual-band RF energy harvesting. An AMC surface with a rectangular unit cell was adopted for two orthogonal polarizations with different frequencies. Finally, the AMC surface and the loop antennas were successfully implemented as a dualband energy harvesting panel together with RF-to-DC conversion circuits and a power management circuit.

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