Quadrature phase shift keyed/bi-phase shift keyed modulator

A phase modulator for discretely varying the phase of an input carrier signal between at least four different phase states and providing a phase modulated carrier output signal, said phase modulator comprising:

• first and second transmission line segments, where each of said first and second transmission line segments includes first and second terminating end regions, and where the length of said first and second transmission line segments differ by a first selected difference value;
• first and second switch means coupled to said first and second transmission line segments, wherein said first switch means includes a carrier signal input means adapted for receiving an input carrier signal, and said second switch means includes an output means, and wherein each of said first and second switch means includes a control input means for receiving a selected control signal for causing said input carrier signal to conduct through a selective one of said first and second transmission line segments from said input means to said second switch means output means thereby providing an intermediary carrier signal;
• third and fourth transmission line segments, where each of said third and fourth transmission line segments includes first and second terminating end regions, and where the length of said third and fourth transmission line segments differ by a second selected difference value;
• third and fourth switch means coupled to said third and fourth transmission line segments, wherein said third switch means includes an input means for receiving said intermediary carrier signal, and said fourth switch means includes an output means for providing an output carrier signal, and wherein each of said third and fourth switch means includes a control input means for receiving a selected control signal for causing said intermediary carrier signal to conduct through a selective one of said third and fourth transmission line segments from said input means of said third switch means to said output means of said fourth switch means;
• an amplifier means biased into saturation, said amplifier means having input means electrically coupled to said output means of said fourth switch means, and an amplifier output for providing said phase modulated carrier output signal having a substantially constant selected phase state phase over a narrow bandwidth;
• and
• where
• said first difference value is substantially π/2, and said first difference value is substantially defined by:
• β2L2−β1L1
• and,
• said second difference value is substantially π, and said second difference value is substantially defined by:
• β4L4−β3L3
• where
• L1, L2, L3, & L4=path length of said first, second, third, and fourth transmission line segments, respectively,
• βn=ω0/(νph)n, real part of propagation constant (1/cm), where n corresponds to a respective one of said transmission line segments L1 through L4;
• ω0=2πf0, radians, and
• f0=desired center frequency of operation.