Impact of receiver´s frequency response in GNSS reflectometers

Global Navigation Satellite System´s (GNSS) opportunity signals reflected over the surface of the Earth can be used for altimetry, sea state determination... So far, GPS signals scattered over the Earth´s surface have been cross-correlated with a local replica of the transmitted signal (typically the GPS available C/A code) shifted in frequency (Δf_d) and in delay (τ). However, it is not possible to achieve the full potential of these signals due to the unavailability of the large bandwidth codes. To overcome this problem, the direct and reflected signals can be cross-correlated. However, to improve the SNR high gain antennas are required and they must be steerable so as to point to the direct satellite and to the specular reflection point. Differences between the receivers´ frequency responses impact the overall frequency response, and may distort the ideal observables. This work presents the analytical computation of the GNSS reflectometer observables in the above conditions and will compare them to the ideal ones, so as to be able to properly specify the receivers´ frequency response.