802.11a is an extension of the IEEE 802.11 standard designed to operate in the 5 GHz frequency band (specifically from 5.15 to 5.35 GHz and from 5.725 to 5.825 GHz). It was developed to provide higher data rates and reduce interference compared to the earlier 802.11b standard, which operates in the 2.4 GHz band, however 802.11a has a shorter range and poorer wall-penetration characteristics due to its higher frequency.
802.11a offers a maximum data rate of 54 Mbit/s using Orthogonal Frequency Division Multiplexing (OFDM) modulation. This higher data rate made it suitable for applications that require faster wireless connectivity.
One of the challenges of using the 5 GHz band is the potential for interference with radar systems and other licensed users. To mitigate this, 802.11a devices are required to incorporate mechanisms for detecting radar signals and avoiding interference. Additionally, transmit power control is employed to reduce the interference potential.

In summary, 802.11a was developed to provide higher data rates in the 5 GHz band but faced challenges related to radar interference, then 802.11h was introduced to address these challenges by implementing regulatory compliance mechanisms such as DFS and TPC, ensuring the coexistence of wireless networks and radar systems in the 5 GHz band.