Router recommendation for simultaneous Client Mode and Access Point

Hi,

I'm looking for a router which has the capability of acting as a wireless client to one SSID and also broadcasting it's own SSID with it's own DHCP subnet.

The one router I have is currently doing this as it has 2 radios - 2.4Ghz and a 5Ghz. It uses 1 radio as a client and another for the AP, but it can then only connect as a client to 2.4Ghz network and distribute a 5Ghz AP.

Are there any routers out there anyone can recommend that have this functionality? Are dual radios required and can I get around the frequency band limitation?

The reason I want to do this is because I want the devices connected wirelessly to the router (acting as client and AP) to be hidden from the main router - hence the need for separate subnet, but via a wireless connection.

Thanks for any help.