Antenna efficiency is a measure of radiated power relative to total antenna power including losses. nRF9160 does not set requirements to antenna radiation parameters, but antenna efficiency is an important parameter in low power devices as it directly impacts the radiated and received power and thus current consumption and coverage.
An omnidirectional antenna and a relatively low peak gain is the most desirable solution for an IoT device as a terminal device's orientation will usually vary.
Network operators may require Over-the-Air (OTA) testing of the device (see Conductive tests) and may have specific antenna efficiency requirements or requirements for the parameters that are related to the efficiency of different device categories.
To get certified by a regulatory body, the device must pass RF exposure evaluation. Each regulatory body has their own set of permitted antenna radiation parameters. The maximum allowed power density limits for radiation can be used to derive the maximum gain limits for an antenna. For more information, see Antenna tests.