While I agree with the "this may be a bridge too far" remarks above, I also know the feeling of wanting to do something I "can't", and have spent happy hours not getting where I wanted to go.
And so, in that spirit...
Maybe "the answer", if you really want to go the RF route, is a highly directional RF receiving antenna (do they exist?) mounted to rotate, a bit like a radar dish... hmm Radar.... and use a combination of signal strength and antenna's direction to generate the wanted info?
But all of that from someone who knows nothing about radio, it must be said.
Of course that approach depends on the receiver giving a signal STRENGTH indicatoin, which previous posters have said will be difficult.
The little "RF link" modules which might be tempting aren't tri-state... the receiver can't tell you "sender sending 1"/ "sender sending 0"/ "no signal seen".
To use one of those would entail yet more complexity (=ways to go wrong, be slow)
You'd set the sender to send a square wave of a set frequency. And then "ask" the receiver: "Are you seeing that frequency, or not?" If seeing frequency, antenna is pointed towards sender. If not, not.
Of course, that "solution" assumes that there will be no reflections of the sender's signal off of, say, a wall....