The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) aboard Mars Express marked the beginning of orbital low-frequency radar exploration of the Martian subsurface, enabling the detection of deep dielectric discontinuities and the mapping of polar layered deposits and potential water reservoirs. Conceived within the technological constraints of the late 1990s, its architecture reflects the state of power electronics, digital processing and RF integration available at that time. Subsequent planetary radar sounders progressively evolved this paradigm. The higher-frequency approach of SHARAD improved vertical resolution at reduced penetration depth, introducing enhanced digital processing strategies. RIME, designed for the JUICE mission, reintroduced low-frequency deep sounding with modernized electronics, increased onboard processing capability and improved system integration.