A new phase conjugator circuit architecture suitable for retrodirective array applications is described and demonstrated. The architecture is based on fourth-order subharmonically pumped mixers and requires a local oscillator (LO) frequency at half the radio frequency (RF). Measurements of a prototype phase conjugator operating at an RF input and intermediate frequency (IF) output of 3.47 and 3.57 GHz have shown an RF-to-IF conversion loss of 21.4 dB, RF-to-IF isolation of 26.4 dB, and isolation between the IF and twice the LO of 59.8 dB. A technique to quantitatively measure the phase conjugate signal that does not rely on retroreflection is also detailed.
