Spaceborne synthetic aperture radars (SARs) operating at L-band and above are nowadays a well-established tool for Earth remote sensing. In this respect, a new frontier of technological and scientific progress is represented by satellite Ka-Band SARs. Since approximately 2010, a number of European Space Agency (ESA) studies have been funded in this direction. The main identified benefit of Ka-band systems is that the short wavelength allows the implementation on a single platform of single-pass interferometry, both cross-track and along-track, with adequate interferometric sensitivity. Ka-band is also interesting due to the low penetration in media such as ice, snow, and vegetation. In principle, the 500 MHz allocation also enables high-resolution measurements. Atmospheric effects represent a severe limitation to Ka-Band SARs. Gases and water particles introduce attenuation and path delay also in clear-sky condition; raindrops also depolarization. Finally, atmospheric turbulence causes scintillation effects. Unfortunately, very few studies and experiments exist at Ka Band. With this general context, the project KaBandSARApp aims to consolidate a Ka-band SAR mission concept, linking user (product-level) observation requirements to mission requirements, and evaluating and highlighting the expected performances for a set of relevant applications. This purpose will be pursued through the development of an End-to-End (E2E) performance tool, where atmospheric effects have been simulated through a Forward Model (FM) of SAR response. This work describes the developed forward model in the general context of atmospheric effects on SAR retrieved signal. A case study relative to a quite common and light cloud (alto-stratus) will be presented and discussed.