Hi there, these guys here have one
Praxsym: Practical Systems Engineering The PM2458. It covers the 2.4 GHz, 5.3 GHz, and 5.8 GHz bands and is around $1400USD. I looked around quite a bit to try and fined one cheaper but could not. After that there is only very expensive Fluke or comparable models for about $7000 NZD and up. I did list the PM-2458 on our website but had no interest.
As 2.5GHz in not part of the Wifi standard you would probably have to get a general SWR meter. I would be interested as well if anyone finds a good portable unit that is easy to use on the field. I could still get the PM-2458 if anyone is interested.
Cheers, Dale
Go Wireless NZ