A transmitter and method for determining impedance measurement in an active radio frequency transmitter of an antenna are provided. Voltage and current samples are obtained from a modulating signal delivered to an antenna. The voltage and current samples are converted from analog to digital format, and decimation occurs to reduce the number of samples. Complex demodulation is performed of each of the voltage and current samples to baseband levels and decimation of the voltage and current samples is performed to reduce the number of samples. An impedance estimate can then be estimated from the voltage and current samples.