QPSK detection using glow discharge detector and a photodiode for millimeter-wave and terahertz communication

The terahertz gap (0.1-10 THz) is an attractive frequency band for new applications. In wireless communication, it can serve as a high capacity link. The lack in use of that gap exists due to a lack of available commercial communications technology systems in that region. We have found that neon indicator lamps or glow discharge detectors (GDD) can be used as simple and very inexpensive detectors in that frequency gap. In modern modulation techniques, the signal phase should be recovered. This article is a proof of concept of detection of quadratic amplitude modulated millimeter-wave signals by a GDD and photodiode using a heterodyne detection method.