EMC modeling approach to the design of micro magnetic radiators

In the recent days, small magnetic radiators are becoming more and more important, for a large variety of applications involving the use of ultra-small transmission bandwidths. Primary destinations of these radiators are represented by RFID technology, wireless sensor networks, data tracking, environment monitoring, where they can be used not only in free-space conditions, but also inside complex electromagnetic media. As a matter of fact, the antenna is an essential component that impacts the efficiency of the transmission, the size of the device, and the bandwidth operability. In this paper we introduce an analytical procedure, deduced by a typical EMC modeling approach, that allows the design of magnetic antennas with arbitrary shape and extremely reduced dimensions. The technique is based on a multi-conductor transmission lines approach: the matching circuit is configured by constructing, together with the antenna, a curvilinear three-conductors transmission line; hence, the matching impedance is computed analytically, without any optimization procedure, by a multi-conductor model. The procedure can be applied to any antenna geometry, even very complex ones, e.g., with fractal shape. Simulations have been compared to measurements, proving a good agreement. The major characteristic is represented by the capability to realize a 50 ohm radiator, without the insertion of a passive matching circuit. In this way, a relatively high efficiency is obtained, even if for an extremely narrow band, but the obtained (narrow) bandwidth is sufficient, especially for the mentioned applications. Since the design procedure is analytical, it can be efficiently applied to design and synthesize antennas in the free space, but also in general media. For this reason, the configuration can be efficiently proposed for the realization of the terminal unit when it is embedded inside lossy, complex material.