DI-524 wireless router no signal missing antenna

I have a DI-524 wireless router that has a signal when it's wired, however it's missing it's antenna so I can't get any wireless signal.  I have a Mac book and my os is 10.4.  My question is where can I find an antenna for this router, and apprx how much will this run me?  Also when there is no antenna connected to the router would it produce a signal at all?  I only ask because I wouldn't want to go out an buy an antenna and find out that the router just isn't producing any signal.  Thanks for your help