MIL FGT ON VECTOR FOR VISUAL APCH DSNDED BELOW ASSIGNED ALT AND HAD CLOSE PROX WITH ANTENNAS.

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SIMULTANEOUS ILS APCHS WERE IN USE TO RWY 28L&R WITH MODERATE TO HVY TFC. FGT INBOUND REQUESTED A VOR 28L APCH; AS HE WAS NOT ILS EQUIPPED; WITH THE FEEDER CTLR. THE SUPVR MADE THE DECISION THAT I WOULD VECTOR THE FGT FOR A VISUAL APCH TO RWY 28L SINCE I WAS WORKING ARR S POS. THE VOR 28L APCH WAS NOT AN OPTION THEN AS THE FINAL APCH COURSE INTERSECTS BOTH RWY 28L&R ILS FINAL APCHS. THE VISUAL APCH ALSO SHOULD NOT HAVE BEEN AN OPTION AS A 15 BROKEN CEILING IS 300 FT BELOW VISUAL MINIMUMS. WHEN I QUESTIONED THE SUPVR ON THE MINIMUMS HE SAID GO AHEAD AND RUN THE VISUAL APCH; IT'S GOOD ENOUGH FOR HIM. AT APPROX 12 MI E OF THE ARPT; I ISSUED FGT AN ALT OF 2500 FT. AT THIS POINT HE DSNDED TO 17 MSL AND I LOST RADIO WITH HIM. I WAS ABLE TO REESTABLISH RADIO COM WITH THE FGT ON THE BACKUP XMITTER; BUT NOT UNTIL AFTER HE PASSED BTWN 2 2100-FT MSL ANTENNAS. I THEN CLBED HIM TO 2500 FT MSL; WHERE HE SAW RWY 28L ON ABOUT A 3 MI FINAL. HE WAS THEN ISSUED THE VISUAL APCH CLRNC. INSTEAD OF COMPLYING WITH THE SUPVR; I SHOULD HAVE SUGGESTED THAT WE HOLD THE FGT UNTIL VISUAL MINIMUMS WERE AVAILABLE OR TFC WAS LIGHT ENOUGH FOR THE VOR 28L APCH TO BE USED.