I took apart an older Atheros card and looked through the specs with this in mind a year or so ago. I can't remember the exact chips, but it was from the 5k series. There was a separate RF front end chip that did analog up/down conversion between the ISM bands and an intermediate frequency. The IF ran from the RF front end to a chip that contained the ADC/DAC. Unfortunately, this chip also did PHY, implemented in hardware, and I couldn't figure out a way to get access to raw samples. You can implement your own MAC in software, but you're stuck with PHY. The RF chip might be handy for other purposes, but there are plenty of other good options there.