On behalf of Wyatt Taylor: The Orx path is nomially there to do LO leakage calibration at the PA output. The transceiver IQ modulator introduces an LO leakage error, and we can do a calibration on that internally. But, the CMRR of the balun also introduces LO leakage errors, so by doing this external calibration loop, coupling off the PA and back into the ORx path, you can calibration the LO leakage for the full signal chain.
