This is the factory replacement antenna.

Use this Antenna from DJI as a spare or replacement for your O4 Air Unit Pro. As a whole, the O4 Air Unit Pro lets you add FPV capabilities to non-FPV-capable drones. The antenna is an essential component for the system's transmission module, supporting enough bandwidth to stream real-time footage up to 1080p resolution at 100 fps and 15ms latency in Racing mode. It also works with the optional transmission module to provide a stable signal via automatic multichannel frequency selection.