MMIC balanced vector modulators for millimetre-wave digital communications applications [HEMT ICs]

There is considerable demand for low cost, high performance, millimetre-wave transmitters for digital communications applications. Direct carrier modulation is an ideal solution to this challenge since it minimises the complexity of the mm-wave subsystems. In this paper the design and performance of balanced MMIC vector modulators operating at 38 GHz are described. It is shown that the balanced bi-phase amplitude modulator elements yield accurate constellations with broadband operation from 20 to 40 GHz. 16-QAM modulation can be produced directly at 38 GHz using this technique, with no fine tuning required. With careful calibration of the vector modulator very high precision can be achieved, and 256-QAM signals have been generated to demonstrate this capability.