DIRECT-CARRIER modulation is expected to find widespread use in commun
ications transceivers, since it promises lower cost and smaller system
size due to reduced hardware requirements, By using a microwave-monol
ithic-integrated-circuit (MMIC) phase shifter and variable attenuator
to provide phase and amplitude control, a single-chip transmitter desi
gn aimed at indoor radio applications achieves direct-carrier modulati
on in the 17/18-GHz frequency range, The first part of a two-part arti
cle describes the various circuit topologies available for implementin
g the phase shifter and variable attenuator, examining the performance
and fabrication characteristics of the candidate designs.