Microwave 16-QAM Modulator and Demodulator for 2.4 GHz Band Utilizing 4x4 Butler Matrices

This paper investigates the usability of $4 \times 4$ Butler matrices for 16-QAM modulation and demodulation. The presented theoretical analysis shows that an appropriate choice of demodulator matrix input ports not only allows for using of non-matched power detectors without causing performance degradation, but also significantly reduces design complexity The measurements of the manufactured circuits yield excellent electrical parameters and a good resemblance between the obtained and ideal constellation, confirming the efficacy of Butler matrices as 16-QAM modulators and demodulators.