Isn't it possible to use a laser as an "antenna" that transmits data? This would save quite a lot of mass since you don't need a large dish.
The only problem I can think of is how would you modulate the signal to encode bits? But lasers can modulate their signal somehow, can't they? I'm pretty sure that you could use amplitude modulation, or at the very least, on/off key.
EDIT: Another problem is that lasers won't be able to receive any signal, so a dish is necessary for the probe to receive signals with a reasonable gain.