A 275 GHz Active Vector-Sum Phase Shifter

Terahertz vector-sum phase shifters capable of 360 degrees 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 mu m InP HBT technology show incremental phase shifts of 45 degrees with an average RMS offset phase error of 3.6 degrees and insertion loss of -1 to -13 dB for eight basis dc bias states.