The Ka-band Radar Interferometer (KaRIn) is an altimeter used to measure water surface heights and one instrument aboard the NASA/French Space Agency (CNES)/Canadian Space Agency (CSA)/United Kingdom Space Agency Surface Water and Ocean Topography (SWOT) satellite. KaRIn is a near-nadir (+/- 2.7° look angle) swath-based instrument that measures the highly reflective water surface. The look angles at the altitude of the satellite enable swath coverage of about 120 km (from 10 to 70 km in cross-track distance on both sides of the nadir track). The instrument acquires measurements at Ka-band (35.75 GHz) with two Ka-band synthetic aperture radar (SAR) antennae at opposite ends of a 10-m boom. The KaRin instrument consists of the KaRIn Digital Electronics Subsystem (KDES), the Radio Frequency Unit (RFU), the High Power Amplifier (HPA), and the Deployable Antenna Assembly.