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 μ m 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.