These spectral masks are defined in IEEE specification 802.11a, 802.11b, and 802.11g. Wireless LAN (WLAN) transmitters are required to meet these masks and FCC Part 15 (15.247, 15.205, and 15.209) unlicensed equipment specifications simultaneously.
These spectral masks can of course be found in the IEEE802.11 document, but they are sometimes difficult in a Web search.
IEEE 802.11b WLAN Spectral Masks
IEEE 802.11a WLAN Spectral Masks