Six-port QPSK demodulator for optimal K-band multiport amplifier calibration

A wideband six-port-based demodulator is proposed and applied as a quadrature phase shift keying (QPSK) demodulator for optimal K-band multiport amplifier (MPA) calibration circuitry. The proposed six-port demodulator adopts wideband ring hybrids for optimal 180° phase balance in local oscillator signal paths. In addition, a voltage-controlled reflection-type phase shifter and an attenuator are integrated into the six-port structure to ensure accurate magnitude and phase balance over broadband operation, resulting in optimal phase and amplitude error detection for the MPA system. To verify the proposed structure, RF demodulation of the K-band QPSK modulated signal was demonstrated for purpose of MPA calibration.