The Beacon Frame format is as provided below:
FIG Courtesy: 802.11 Wireless Networks: The Definitive Guide, 2nd Edition
As can be seen from the pictorial representation above – the beacon frame consists of mandatory fields and optional fields. The Mandatory fields are those fields that are required for the proper working of the network.
Optional fields are those Information Elements/fields that provide information on the support of various features in the network.
For a more exhaustive list of information elements and beacon frame fields – kindly refer the IEEE Std 802.11TM-2012 document–section 8.3.3.2 beacon frame format