This manuscript is presenting various research works on the modeling of the propagation of electromagnetic waves (EMW) in complex environments. The work includes numerical and analytical modelling of EMW interactions in the maritime environment, in the troposphere and then the ionosphere, natural environments whose effects on EMW propagation are sensitive to microwave frequencies. In this work, numerical modeling of the propagation by resolution of the Parabolic Wave Equation (PWE) is central. It will be applied to different propagation environments, for different types of applications (radar, telecommunication or positioning by GNSS radio navigation). The effects of refraction and atmospheric scintillation (tropospheric, ionospheric), interactions with ground or sea surface will then be illustrated. The presentation will be complemented by examples of application to active remote sensing of the atmosphere (retrieval of vertical refraction index profiles by inversion of radar echoes or GNSS signals in Radio-Occultation geometry, characterization of tropospheric turbulence by GNSS). The prospects for work envisaged are centered on the problems of EMW propagation in the ionosphere, with the main objectives of characterizing the turbulent fluctuations in the electron density of the ionospheric plasma, their occurrence, modelling and prediction of ionospheric scintillations.