A radio frequency (RF) circuitry includes a device that taps a transmission line and picks up some of electromagnetic signals traveling in both directions. The RF circuitry includes a first detector, a second detector, a third detector, and a processor. The first detector measures a power of a first portion of the tapped electromagnetic signal travelling in one direction. The second detector measures a power of a first portion of the tapped electromagnetic signal travelling in the other direction. The third detector measures a power of a combined signal which includes a second portion of the tapped electromagnetic signal travelling in the one direction and a second portion of the tapped electromagnetic signal travelling in the other direction. The processor determines, based on outputs from the detectors, a relative magnitude and a relative phase of the electromagnetic signals.