th the top panel being located right in front of the ear, placing the panel on the back side, and ensur- ing that beams are directed away from the head is the best strategy to minimize body exposure. In case panel switching is not an option, P-MPR and restrictions on the max- imum uplink duty cycle are additional schemes considered to comply with maximum permissible exposure (MPE) safety requirements. This, in turn, may imply dedicating a proximity sensor for each antenna panel. The number of antenna module also heavily depends on the UE form factor and the choice of cover materials. The impact of materials on the antenna performance is exac- erbated by the fact that the trend in UE thickness is pushing for ever thinner devices, thereby leaving little gap between the display glass and the back cover material. For example, 3D simulations in [5] show how the LCD screen may impact the radiated beam pattern. Data in [1, 16] show that the when panel is in a "sandwich" between two glass layers (LCD screen and glass back cover), not only are implementation losses 1-2 dB higher with a glass than with a plastic cover, but glass also tends to scatter radiation pat- terns, providing amplification in certain directions and attenuations in others. Low-end devices with a plastic back cover might therefore be able to deliver good performance with only two panels, while for high-end devices, where both the glass back cover and metallic bezels are used, it might be necessary to use three or even four modules, with a combination of face/back and edge modules. The higher the number, the better the chance of mitigating MPE and blockage as well as meeting SC, but this comes at the expense of signal routing complexity since two intermediate frequency lines are required per panel, and at the expense of cost. Details of the implementation of the first-generation "high-end" mmWave-capable smartphones are available in the public domain and are examples of OEMs choosing three [17] or four antenna modules [18]. 12.7 Summary From many viewpo