Miniaturized low cost 30 GHz monolithic balanced BPSK and vector modulators: Part I

The design and performance of a monolithic microwave balanced biphase ampli tude modulator operating at 30 GHz is presented. The MMIC chip, which measu res only 1.1. mm x 0.9 mm. employs direct carrier modulation to reduce hard ware complexity and cost. A novel microstrip coupler geometry has been used to obtain a very compact layout. By employing a balanced topology, the par asitics of the cold FET switching elements can be removed, resulting in bro adband operation with a near-perfect constellation. Furthermore, a monolith ic balanced vector modulator, which measures 1.25 mm x 1.45 mm, can be real ized by operating two modulators in quadrature, producing satisfactory quad rature phase-shift keying (QPSK) and 16-quadrature amplitude modulation (QA M) performance. This article, the first of a two-part series, discusses the advantages of using direct carrier modulation at mm-wave frequencies. The active device characterization and detailed circuit analysis of both the si ngle-state and balanced modulators are presented.