Switched Non-uniformly Distributed-Turns Coil antenna for dual-band operation

A switched Non-uniformly Distributed-Turns Coil (NDTC) dual-band antenna for near- and far-field regions of propagation in Radio Frequency IDentification (RFID) reading applications is presented. The operation mode alternate is realized by introducing micro electro-mechanical system (MEMS) switches to a previously reported NDTC design´s radiating element. The final design uses the MEMS to switch between bands, the 13.56MHz of the high frequency (HF) and the 866.6MHz of the ultra-HF (UHF), and the near- and far-field operations as a result. The radii of inner turns of the NDTC were earlier optimized using non-uniformly distributed turns of the coil for maximum magnetic-field (H-field) in the near-field, and the switching allows for the far-field where extended RFID reading ranges are sought using a single antenna unit. Simulated results corroborate the claim and show robust H-field and good radiation efficiency of the antenna.