Bhanu,
Define a local variable of type CL_ABAP_CHAR_UTILITIES=>HORIZONTAL_TAB.
LV_TAB TYPE CL_ABAP_CHAR_UTILITIES=>HORIZONTAL_TAB
LOOP AT GT_DATATAB INTO GS_DATATAB.
CONCATENATE GS_DATATAB-FIELD1
GS_DATATAB-FIELD2
..............
GS_DATATAB-FIELDN
INTO LV_STRING SEPARATED BY LV_TAB.
TRANSFER LV_STRING TO lv_filename.
ENDLOOP.
Thanks,
Vikram.M