Radar altimeters use frequency modulated continuous wave (FMCW) and the bandwidth is 20 to 170 MHz (the larger the chirp, the more accurate it can be). It's ex

Radar altimeters use frequency modulated continuous wave (FMCW) and the bandwidth is 20 to 170 MHz (the larger the chirp, the more accurate it can be). It's extremely difficult to have a 170 MHz wide filter at 4.3 GHz with a brick wall response out of band. https://www.ntia.doc.gov/files/ntia/publications/compendium/4200.00-4400.00_01MAR14.pdf https://www.ntia.doc.gov/files/ntia/publications/compendium/...