OS X :: Losing Wireless Network Connection

I am running into a headache with my wireless network connections. When I close my laptop to put it to sleep, I often lose my network connection. It is easy enough to reconnect; I simply try to connect to a web page, get network diagnostics, and re-enter my password (and click on the "remember password" box). All works great -- until I next close the laptop. It happens all the time at one site, sometimes at home (using Time Capsule), and seldom at the church where I volunteer.

I have checked all my settings and can't figure out what's going on. If my poor memory is correct, I didn't use to have this problem, but it has been going on for the last couple of months. I know I could keep the sucker open, but I want to save power by putting it to sleep -- and the desk where I work at home has a sliding drawer so it has to be closed to close the drawer. (And my network connections are all in the desk also.) I've posted this question to the Apple forum but haven't gotten any replies there other than a couple of followup questions. I am using Time Capsule as my router and I have updated the software