A 275 GHz Active Vector-Sum Phase Shifter

Terahertz vector-sum phase shifters capable of 360^° phase control over the frequency range of 240 to 310 GHz are presented. Because the impedance mismatch of the variable-gain amplifiers employed in the phase shifter determines the flatness of the offset phases, a new broadband VGA design with its input and output impedances unaffected by dc bias is introduced. The measured results on the phase shifter fabricated using 0.25 μm InP HBT technology show incremental phase shifts of 45^° with an average RMS offset phase error of 3.6^° and insertion loss of -1 to -13 dB for eight basis dc bias states.