We present the design of a bistatic High Spectral Resolution Lidar (HSRL) aiming at measuring the aerosol phase function for applications in Ultra High Energy Cosmic Ray experiments. The expectation is to give accurate data for the aerosol phase function, needed to correct the Extended Air Shower (EAS) signal of air-fluorescence detectors for the air Cherenkov contamination, caused mainly by the aerosols. In this work we mainly focus on the design principles of the HSRL receiver for recording the aerosol to molecular scattering ratio as a function of height. We present results from testing an SLM CW diode laser of 120 mW at 532 nm, to be used as a LIDAR emitter in the transmitting telescope, and verify the design coherence length according to the manufacturer. As receiver we consider a system two different Fabry-Perot etalons having free spectral ranges 0.1cm−1 and 1cm−1 respectively, corresponding to the molecular and aerosol channels. The fringe patterns are analyzed over 2π polar angle range using appropriate algorithms.