HF antenna for non-contact reading of electronic tags, has two concentric spiral coils with opposite sense on a PCB substrate, both contributing to radiation of interrogation signal

摘要

The antenna comprises two coupled inductances (L1, L2), preferably formed as PCB tracks, which are in the form of concentric opposite-sense spirals so that circulating currents (i1, i2) are in phase opposition. The outermost inductor (L1) has a variable matching capacitor (C) connected in series with it and a fixed capacitor (C12) in parallel with this combination, the second inductor being connected to the junction of the two capacitors. Both inductors contribute to antenna radiation, raising its efficiency.