A modified QPSK modulation technique for direct antenna modulation (DAM) systems

Direct antenna modulation (DAM) has been proposed to overcome the bandwidth limitation of high Q resonating antennas by decoupling the stored energy from the coupled or radiated energy. It, however, due to its switching nature, imposes a zero voltage or zero current switching condition to the modulation technique at the symbol transition in order to achieve high radiation efficiency. Simple on-off keying (OOK) based on monocycle RF pulses was used in the past. In this paper, higher order phase shift keying modulation techniques are proposed for DAM systems. The so-called modified QPSK modulation technique can maintain zero current switching conditions at the symbol transitions while creating the four quadrant phases to represent different symbols. Simulations for a near field communication (NFC) system employing such modulation techniques have demonstrated better transmission performance judged by the eye diagrams.