An antenna matching system includes an electronically tunable antenna matching circuit, a first directional coupler, a first gain and phase detector, a second directional coupler, a second gain and phase detector, and a controller. The first directional coupler is configured to receive forward and reflected signals. The first gain and phase detector is configured to output a first magnitude measurement and a first phase measurement based on the signals received at the first directional coupler. The second directional coupler is also configured to receive the forward and reflected signals. The second gain and phase detector is configured to output a second magnitude measurement based on the signals received at the second directional coupler. The controller is configured to: determine circuit parameters based on the first magnitude and phase measurements; tune the matching circuit based on the circuit parameters; and check for phase error based on the second magnitude measurement.