Once the operational frequency bands and device concept are known, the antenna selection process or custom antenna design work can start. Deciding between using an external or internal integrated antenna is one of the first choices that must be made.
An external antenna is not as size limited as an internal one and is therefore likely to have better performance. But when considering the routing between the nRF91 Series device and the antenna, such as a long coaxial cable, and the desirable radiation properties of the terminal antenna, the difference in the performance of an external and a well-designed internal antenna can be small.
Usually, the design constraints of a small IoT device exclude the use of an external antenna. As the dimensions of the board and layout mainly determine the performance of an integrated antenna, antenna design should be considered in the earliest phase possible during the device concept phase.