Passive microwave remote sensing encompasses techniques well suited for use in systems with limited power budget, due to the low consumption linked to reception-only operation. Some examples of these techniques include Microwave Radiometry (MWR), Global Navigation Satellite Systems Reflectometry (GNSS-R), and Radio-Frequency Interference (RFI) detection algorithms. Small satellite missions including these instruments, such as FSSCat, have proven the value of passive remote sensing techniques with high revisit times due to the low orbits, and the possibility to horizontally scale the mission with more satellites. The Flexible Microwave Payload (FMPL) used in the FSSCat mission has continued development within the RITA Payload project, and it is now being used in Drone-based platforms to provide in-situ data using space-proven acquisition algorithms. In this work, the development of a drone-based FMPL will be presented. © 2022 IEEE.