Cellular Direct-connect In-Building Amplifier, with Outdoor Omni-directional Antenna
Drawing showing an example of a direct-connect bidirectional amplifier connection between a 4G/5G router or modem to an omnidirectional antenna for better cellular reception for indoor use. The direct attach amp is important for maximum power transfer and the omni antenna is used when you don't know the direction of maximum received signal strength. Other components include surge protector and a Wi-Fi router if the cellular device has no Wi-Fi capability.
See more on techniques to improve cellular signal.