A Theoretical Analysis of Symmetrical Matching for NFC Antennas

Symmetrical matching has been widely used for near field communication antennas because it can achieve a higher transmission bandwidth, increase operating volume (including distance and area) in reader/writer mode, and reduce influence of component tolerance, etc. However, a fundamental theoretical analysis of symmetrical matching has not been reported yet. In this article, a rigorous definition of symmetrical matching is given. Given antenna parameters and target matching impedance, conditions to implement symmetrical matching and expressions to theoretically calculate the matching component values are derived for the first time. Some useful features of symmetrical matching related to bandwidth, detuning, and phase are also revealed. Experimental results can well match these derived theoretical results. These derived results are important for application in the explanation of phenomena associated with symmetrical matching, in the selection of an optimal target matching impedance to improve operating volume, in the implementation of automatic transmission power control, and in the tuning of pseudo-differential antennas, etc.