The 802.11a standard was released in 1999 , around the same time that 802.11b was released. Where 802.11b only supports data transfer rate of 11 Mbps, for which most routers and wireless cards were manufactured at that time using the same 802.11b standard .
This is why 802.11b became more popular than 802.11a for many years. In 2003, the 802.11a standard was digested by 802.11g which used the same 2.4 GHz band as 802.11a, but it supported transfer rates up to 54 Mbps.
NOTE For an 802.11a connection to occur, each device that is present in the wireless network must support the 802.11a standard otherwise the connection is not possible.
For example, if a base station broadcasts an 802.11a signal, then only those computers with Wi-Fi cards that support 802.11a can only recognize the base station.
It has been seen that many routers are backward compatible with older standards, so it is necessary to manually configure them so that some routers can work with older 802.11a and 802.11b devices.