Compact 38 GHz MMIC balanced vector modulators employing GaAs/InGaP HBTs

The design and performance of a 38 GHz balanced I-Q type vector modulator using HBTs as switching elements, is presented. The MMIC chip can be employed to implement direct M-PSK and M-QAM modulation schemes in order to reduce hardware complexity and cost. A novel miniature microstrip coupler geometry can be employed to further minimise the modulator´s size, yielding a circuit which only measures 1.4×1.2 mm. The balancing topology can be used to remove the parasitics of the HBTs resulting in near perfect constellations, and the compact layout can greatly reduce the cost of expensive transmitter chip area