The striker has arrived from Blackburn Rovers and could face Liverpool in today's early kickoff.
McKenna said: “We think Sam brings a lot of different qualities to the squad and is an experienced player who has worked extremely hard over the years to improve his game and to become more and more effective as a player.
“That was shown last year with the fantastic season he had at Blackburn with the goals he scored throughout the campaign, including one at Portman Road of course.
“He has a real feel for scoring goals and works so hard for the team both on and off the ball. He knows many of the players here, as well as some of the staff and has ties to the club and to the area.
“This is a move that works for all parties and he has rightfully earned the chance to play in the Premier League, which I know he is delighted to do at this club.
“His arrival gives us another really versatile forward player who can operate in different roles and systems, giving us a big goal threat and plenty of other qualities to add to the team.”