Radio Frequency Interference (RFI) is an increasing problem in Microwave Radiometry, particularly for Earth Observation, because the antennas are pointing towards the Earth. RFI has been observed at L-band in ESA's SMOS (Soil Moisture and Ocean Salinity) Earth Explorer mission, as well as in NASA's SMAP (Soil Moisture Active and Passive) and Aquarius missions, as well as in AMSR-E and WindSat missions at 10.7 GHz and 18.7 GHz [1]. Therefore, dedicated on-board systems are nowadays a must to detect and remove contaminated measurements, improving radiometric accuracy, and increasing the spatial coverage. In this work, a novel detection technique, specially tailored for Synthetic Aperture Interferometric Radiometers (SAIR), is proposed and its performance analysed. It is based on the change of the shape of the crosscorrelation function at lags different from zero under the presence of RFI. The performance of the proposed technique is compared to other common RFI detection algorithms, and its limitations and advantages are discussed. Post-correlation detection performance is found to out-perform other commonly used algorithms such as Kurtosis. In addition, it presents some convenient properties for its practical application in correlation and real aperture radiometers.