Renowned architect Duangrit Bunnag, who won the bid to design Suvarnabhumi airport's new passenger terminal, will file defamation suits against the Engineering Institute of Thailand (EIT) and two media companies, he has said.

"We are discussing with lawyers and preparing the documents," Mr Duangrit, managing director of Duangrit Bunnag Architect Co, told the media Tuesday at a forum held by Airports of Thailand (AoT) on the terminal's design.

His company is part of DBALP Consortium, a joint venture that competed in the bid.

It also comprises Nikken Sekkei, EMS Consultants, MHPM, MSE and ARJ Consortium.

Four consortiums joined the bid and DBALP took the prize after the AoT's first winner, SA Group, was disqualified for failing to submit a price quotation.

SPAN Consultants and Sign-Tech Engineering Consultant joined forces to create SA Group. They won the highest score but ultimately lost out.

SA Group has since filed a complaint with the government claiming AoT is guilty of unfair treatment. It reportedly plans to file a petition with the Central Administrative Court.

Critics have questioned whether Mr Duangrit's architectural firm is guilty of plagiarism as the design of the new airport terminal resembles a bridge designed by world-renowned Japanese architect Kengo Kuma.

Other associations including EIT have questioned the suitability of the design and accused DBALP of other irregularities.

Mr Duangrit denied all of the accusations.

"I personally hate corruption and have been following a policy of transparency," he said.

"EIT claim our company is unfit to win the contest and that we copied the design from another project. Media companies have also reported that we are involved in graft. These stories are groundless. They were all made without any evidence to back up the allegations," Mr Duangrit said, adding he plans to sue two media outlets.

The new building will be complete with 14 airport aprons and parking areas for planes. The terminal is expected to open in 2021.