Global Navigation Satellite Systems – Reflectometry (GNSS-R) is a relatively new remote sensing technique that benefits from GNSS signals as signals of opportunity as a bistatic radar. These signals can be processed as a scatterometer by measuring the relative scattered power, as an altimeter by measuring the relative delay between the direct and the scattered signals, and as an unfocused Synthetic Aperture Radar (SAR) with very short coherent integration times (typically a few millisecons). Wider bandwidth signals provide an opportunity to increase the performance of some GNSS reflectometry applications (i.e. altimetry). The Microwave Interferometric Reflectometer (MIR) is an instrument developed at UPC to compare different GNSS-R techniques, notably the conventional and interferometric ones, and assess the capabilities of these new signals and bands of the GPS and Galileo systems (L1/E1 and L5/E5). This paper describes the MIR beamforming system.