The airFiber 4X (SKU AF-4X), is a high-performance radio designed to work in the licensed 4.9GHz band, also known as the public safety band, so a license is required to use those radios in the US.
US units operate from 4,940MHz to 4,990MHz, and International units (only for export) can operate from 4.7-4.99GHz.
The AF-4X works with any 4.9GHz-capable MIMO antenna. It is compatible with the Ubiquiti airFiber Dish 30dBi and 34dBi models, as well as the RocketDish 30dBi and 34dBi antennas. Unfortunately, since those antennas have been designed for the 5GHz band, the performance in the 4.9GHz range is lower. Therefore, it's important to consider this and use the following values in your calculations and in the data you enter into the airFiber 4X Wireless tab.
The AF-5G23-S45 antenna is not recommended for the 4.9GHz, since the antenna gain for that antenna at 4.9GHz is around 17-18dBi.
Note: Remember that is very important to get a license to use any 4GHz frequency, otherwise you will be breaking the law