Yes. Directional antenna with EXTREMELY low bitrates so that the bits have a long time to accumulate any noise out of the signal. Specifically its at 160 bits per second at a transmit frequency of 8 GHz.
160 bits per second is actually pretty high. As comparison the German radio time signal used by parts of Europe sends out 1 bit per second: https://en.wikipedia.org/wiki/DCF77
Yeah, at the time the probes were launched, 160bps would have been a fairly respectable transmit rate between two computers connected by a cable, located in the same city!