Field symbol Runtime error

Hi,

I am usfng this but i am getitn this runtime error ?

how do i correct this ?

FIELD-SYMBOLS: <ITAB> TYPE STANDARD TABLE,

DATA: LT_TAB TYPE TABLE OF mara,

LS_TAB LIKE LINE OF LT_TAB.

LOOP AT <ITAB> INTO LS_TAB.

APPEND LS_TAB TO LT_TAB.

ENDLOOP.

I get a runtime error that, in unciode these two have to be of same structure.

I dont want to assign each and every component of field symbol to my structure

is there a direct way of doing it ?