DC 9 CREW ACCEPTS VECTOR ISSUED TO ANOTHER ACFT IN ORD AIRSPACE.

Narrative

WE WERE ON A HDG OF 090 DEGS AND AT 5000 FT MSL DSNDING TO 4000 FT MSL. WE WERE ON VECTORS FOR THE ILS VISUAL APCH TO RWY 22R AT ORD. I WAS FLYING THE ACFT. THE FO RESPONDED TO A RADIO CALL AND I HEARD HIM READ BACK THE CLRNC OF 'TURN R 180 DEGS AND INTERCEPT THE RWY 22R LOC.' BUT; WHAT I DIDN'T HEAR WAS OUR CALL SIGN. I THOUGHT MAYBE I MISSED SOMETHING. WHEN I STARTED THE TURN AND SAW WHERE THE ARPT AND RWY WERE; I REALIZED THIS DIDN'T SEEM RIGHT. WE WERE DIRECTLY N OF THE ARPT AND IN NO POS TO INTERCEPT RWY 22R LOC. THEN I ASKED THE FO TO ASK APCH CTL WHAT HDG WE WERE SUPPOSED TO BE ON. AT THE SAME TIME APCH CTL REALIZED WE WERE NOT ON THE CORRECT HDG; SO HE TURNED US TO A HDG OF 045 DEGS TO RE-ENTER DOWNWIND AND TO STOP OUR DSCNT AT 4500 FT MSL. THERE WERE NO CONFLICTS WITH ANY OTHER TFC BECAUSE THE OTHER ACFT WAS DOWN AT 3500 FT MSL. WE WERE VECTORED TO INTERCEPT RWY 22R LOC AND LANDED WITHOUT FURTHER INCIDENT. THERE WERE SEVERAL THINGS THAT LED UP TO THIS PROB. I BELIEVE I SHOULD HAVE BEEN LISTENING TO THE RADIO XMISSIONS. I SHOULD HAVE QUESTIONED THE FO; OR BEEN MORE DIRECT IN ASKING THE FO TO VERIFY THE CLRNC AGAIN IF I DIDN'T HEAR IT. A COUPLE OF ACFT HAD SIMILAR SOUNDING CALL SIGNS; AND RADIO CONGESTION.