In a multibeam radar sensor apparatus having at least two transmission/reception channels, whose signal paths each include an antenna and a mixer, at least one first mixer is configured bidirectionally as a transfer mixer, and at least one second mixer is switchable from a first into a second operating state; in the first operating state, the mixer is bidirectionally configured as a transfer mixer, and in the second operating state, the mixer being configured in an at least approximately isolating manner as a receiving mixer. In addition, in a method for determining a distance and/or a speed of a target, a radar signal is transmitted in a direction of the target and a reflected radar echo is received, for which at least two transmission/reception channels are used whose signal paths each include an antenna and a mixer; at least one mixture is switched over from a first into a second operating state, in order to use the mixer, in the first operating state, bidirectionally as a transfer mixture, and, in the second operating state, in an at least approximately isolating manner as a receiving mixer.