Analysis of 220-GHz Communication Link Using A High-Order Direct-Modulation Transmitter

In this paper, an RF direct-modulation transmitter (Tx) architecture for high-speed wireless transmission is presented, which directly maps the data bits to 4M quadrature amplitude modulation (QAM) constellation. The basic principle is to vectorially synthesize M channels of QPSK modulated signals with proportional amplitudes, thereby realizing high-order QAM modulation and avoiding the use of costly digital-to-analog converters (DACs). We have designed a 220GHz sub-harmonic mixer and a 3dB branch waveguide coupler, and then built a TX three-dimensional circuit model with a carrier frequency of 220 GHz and 16QAM direct modulation, and carried out a communication link simulation verification.