PLT HAS NMAC IN UNCTLED ARPT TFC PATTERN.

Narrative

I MADE AN APCH FROM THE NE TO SANTA PAULA ARPT; MADE THE APPROPRIATE ANNOUNCEMENT AND APCHED ON THE UPWIND LEG AT 2000 FT MSL. THIS UPWIND WAS EXTENDED 1 MI TO THE SW OF THE RWY WHILE I LISTENED TO AN AIRPLANE APCHING ON AN EXTENDED L DOWNWIND FROM THE SW. THE 2 OF US ACKNOWLEDGED ONE ANOTHER WITH ME SAYING THAT I WOULD FOLLOW HIM (AND BOTH OF US ANNOUNCING EVERY POS IN THE PATTERN). I TURNED BASE AS THE OTHER PLANE WAS ALMOST OVER THE NUMBERS AND AS I BANKED FROM BASE TO FINAL; LOOKED TO THE APCH PATH OF RWY 22 ONLY TO SEE A LARGE TWIN FLYING DOWN FINAL 100-150 FT UNDER MY R WING. SUDDENLY HE TURNED L AND STARTED TO CLB AND MY CORRECTIVE ACTION WAS TO CLB AND TURN BACK TO THE R. LATER IT WAS DISCOVERED THAT HE NEVER SAW MY PLANE; BUT REACTED TO THE AIRPLANE ON THE RWY AND INSTEAD OF DOING A GAR STRAIGHT AHEAD HE DID A 180 DEG TURN TO THE L. THERE WERE NEVER ANY ANNOUNCEMENTS FROM THE TURN AIRPLANE. AFTER LNDG AND WATCHING HIM DO YET ANOTHER 180 DEG TURN AND COME ON BACK STRAIGHT IN; I WENT OVER TO SPEAK WITH HIM AND FIND OUT WHAT HE WAS DOING! HE HAD FLOWN THROUGH SPECIAL FLT RULES AREA AND HEARD NOTHING ON HIS RADIOS AND CONTINUED TO MAKE A STRAIGHT-IN TO RWY 22 SANTA PAULA. HE SAID THAT HE HAD NEVER BEEN TO THIS ARPT AND DID NOT KNOW THE PROC. I AM A RADIO TECHNICIAN AND OFFERED TO LOOK AT HIS RADIOS. THERE WAS NOTHING APPARENTLY WRONG WITH THEM. HE PROBABLY WAS NOT VERY FAMILIAR WITH THEIR OP AND THE AUDIO PANEL OP. THE FLT INSTRUCTOR FRIEND WHO WAS RIDING WITH ME TOOK THE OPPORTUNITY TO REMIND HIM OF FAR PART 91.103. ALL AVAILABLE INFO ABOUT A FLT SHOULD BE KNOWN; INCLUDING WHAT KIND OF PATTERN ENTRY IS PREFERRED AT A SPECIFIC ARPT AND WHY!