Highly placed sources said they have completed the final report and it might be filed next week before the Special CBI court.
The allegations of corruption and other irregularities have been denied by Dayanidhi Maran.
The agency had sought information from Malaysian authorities through Letters Rogatory but it did not get satisfactory details, after which the judicial requests were sent again.
The sources, however, said they had enough information on the basis of which they could file the charge sheet.
It was alleged by former Aircel Chief C Sivasankaran that Maran had as the then Telecom Minister favoured Maxis-group in the takeover of his company and in return investments were made by the company through Astro network in Sun TV owned by the Maran family.
CBI had told the Supreme Court that during Maran's tenure there was "deliberate delay" in providing letter of intent to Sivasankaran.