Near-field and far-field shared structure for NFC and CNSS applications
This study presents a shared structure for both near- and far-field operations using magnetic resonance coupling and electromagnetic radiation. The proposed structure is composed of a rectangular loop and two monopoles. A duplexer is designed to route the near- and far-field signals. For far-field operation, both dual-band resonance and dual-sense circular polarisation required by the compass navigation satellite system (CNSS) are achieved. For near-field operation, a wireless communication link operating at 13.56 MHz is established. The effect of matching distance on the transmission performances is studied and the optimal matching network is obtained. The proposed design is fabricated and verified experimentally. In the far-field regime, it can achieve 10 dB impedance bandwidths of 17.2 and 15.8% and 3 dB axial ratio bandwidths of 4.6 and 12.8% and the two CNSS bands are fully covered. In the near-field regime, an average transmission coefficient of 0.59 is achieved within the operation range of 5-30 mm by the proposed design. The obtained good performance reveals that the proposed shared structure is suitable to be applied in handheld devices for near-field communication and CNSS applications.