Well, each antenna needs to be sensitive enough to pick up the signals at all. You also need very high data rates for producing interference fringes with 1.3 m

Well, each antenna needs to be sensitive enough to pick up the signals at all. You also need very high data rates for producing interference fringes with 1.3 mm waves, which is probably one of the reasons why a satellite like RadioAstron works at longer wavelengths.