Quadrature frontend with directional coupler for RF reflection coefficient measurements

A Cartesian approach reflection coefficient measurement block based on a directional coupler and four quadrature mixers is presented in this work. The block was designed for use in an automatic impedance matching system in the ultra-high frequency range. Simulations, including parasitics, resulted in an average error of 3.4% full-scale and indicate a high potential of the approach for an implementation in integrated circuit technology. Measurements on a discrete setup demonstrate a maximum error of 28% full-scale and prove the usefulness of the approach.