Cisco 8800 Series Deployment Manual page 62

The 5 GHz channel width can be configured for 20 MHz or 40 MHz if using Cisco 802.11n Access Points and 20 MHz, 40
MHz, or 80 MHz if using Cisco 802.11ac Access Points.
If using 2.4 GHz, only channels 1, 6, and 11 should be enabled in the DCA list.
It is recommended to configure the 2.4 GHz channel for 20 MHz even if using Cisco 802.11n Access Points capable of 40 MHz
due to the limited number of channels available in 2.4 GHz.
Cisco IP Phone 8800 Series Wireless LAN Deployment Guide
62