A CL65 AFTER TAKEOFF AND GEAR RETRACTION DELCARED AN EMER AND DIVERTED DUT TO CHRONIC EICAS WARNING

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ACFT HAD A PREVIOUSLY RPTED NOSEWHEEL STEERING PROB EARLIER THAT DAY; BUT I HAD SINCE COMPLETED AN SGF ROUND TRIP WITHOUT INCIDENT. UPON GEAR RETRACTION; EICAS MESSAGE 'STEERING INOP' POSTED. WE WERE STILL IN THE TERMINAL AREA OF ZZZ AND WE ASKED FOR VECTORS TO RESOLVE A PROB FROM ATC. I RAN THE QRH; BUT THE MESSAGE RE-POSTED. I NOTIFIED COMPANY OPS ZZZ AND COORDINATED OUT RETURN TO ZZZ WITH DISPATCH VIA COMMERCIAL RADIO. WE NOTIFIED ATC THAT WE WOULD BE LNDG WITHOUT NOSEWHEEL STEERING AND WOULD NEED A RWY WITH FAVORABLE WINDS AND THAT WE WOULD BE STOPPING ON THAT RWY TO WAIT FOR A TOW TO THE GATE. I DECLARED AN EMER. ACFT LANDED WITHOUT INCIDENT AND WE STOPPED ON THE RWY. THE ACFT WAS TOWED TO THE GATE. CALLBACK CONVERSATION WITH RPTR ACN 506138 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE NOSE STEERING SYS ON THE CL65 IS A FLY-BY-WIRE OR ELECTRONIC STEERING WITH NO CABLES TO THE COCKPIT TILLER. THE RPTR STATED ENRTE TO ZZZ HAD THE EICAS WARNING 'STEERING INOP' AND FOLLOWED THE QRH WHICH ADVISES SWITCHING NOSE STEERING OFF. THE RPTR SAID THIS AIRPLANE HAD PREVIOUS RPTS ON NOSEWHEEL STEERING AND WAS SIGNED OFF WITH VARIOUS REPAIRS. THE RPTR STATED PRIOR TO ARR AT ZZZ AN EMER WAS DECLARED AND LNDG WAS UNEVENTFUL. THE RPTR AID ZZZ MAINT REPLACED A NOSE STEERING CTL UNIT. THE RPTR STATED AFTER MAINT THE AIRPLANE WAS DISPATCHED TO ABC AND BACK TO ZZZ AND THE NOSE STEERING OPERATED NORMALLY. THE RPTR STATED THE ACFT WAS DISPATCHED AGAIN TO XXX AND AFTER TKOF AND LNDG GEAR RETRACTION THE EICAS 'STEERING INOP' WARNING APPEARED. THE RPTR SAID ANOTHER EMER WAS DECLARED; LANDED AND TOWED TO THE GATE. THE RPTR STATED A LOGBOOK MAINT RPT WAS WRITTEN AND A VERBAL RPT GIVEN TO MAINT. THE RPTR STATED THAT MAINT NEVER ADVISED THE CREW WHAT COMPONENT OR ACTION WAS TAKEN TO INSURE A POSITIVE FIX.