Hi OmChandra L,
Use function module SAP_CONVERT_TO_XLS_FORMAT instead of GUI_DOWNLOAD to convert your internal table into excel sheet.
Coding:
CALLFUNCTION'SAP_CONVERT_TO_XLS_FORMAT'
EXPORTING
i_filename = <Filename with extension .xlsx >
TABLES
i_tab_sap_data = <Internal_table>
EXCEPTIONS
conversion_failed = 1
OTHERS = 2.
IF sy-subrc <> 0.
MESSAGEID sy-msgid TYPE sy-msgty NUMBER sy-msgno
WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
ENDIF.
Thanks & Regards,
T. Prasanna Kumar