and operation in band 41. In all other cases, the UE is mandated to support simultaneous dual uplink transmissions. It is worth noting that even if an EN-DC combination is SUO eligible, SUO is only allowed for operating carrier frequencies and channel BW for which a direct hit occurs. As a result, operators who plan to deploy 5G in a "difficult" EN-DC band combination may not necessarily have to pay the SUO penalty. Operators need to perform a detailed IMD analysis based on their spectrum holdings to determine if direct hit applies. Take, for example, the case of DC_5_n66 shown in Figure 12.6 for which a direct IMD 2 hit occurs to band 5 DL carrier 886 MHz when n66 is modulated at 1727 MHz and band 5 at 841 MHz; that is, SUO is allowed (IMD2 = 1727 - 841 = 886 MHz). However, if band 5 is deployed at 830 (UL)/875 (DL) MHz, the IMD2 does not overlap band 5 DL, and therefore the UE must support dual uplink transmissions. LTE B5 DL freq. [MHz] 875 LTE B5 UL freq. [MHz] 830 Direct hit - complete overlap Partial overlap IMD adjacent to victim No overlap Figure 12.6 Example of detailed IMD2 analysis for DC_5_n66 or DC_66_n5. Direct hits have been derived assuming 5 MHz CBW for each RAT and 1 MHz raster. 12 5G RF Design Challenges Dual connectivity in 5G is also specified for NE-DC, where NR is the Master Cell Group (MCG) and LTE the Secondary Cell Group (SCG), and NN-DC, which combines both 5G CA (for example, with 2 FR1 bands with n2-n5) and 5G dual uplink connectivity between FR1 and FR2 bands, for example, nl-n257. 12.2.4 New Features Impacting UE RF Front-End 12.2.4.1 Impact of Beam Forming in FR2 While beamforming can be implemented with a large number of antenna elements at the gNb, Figure 12.7 shows that the limited volume of modern smartphones and shrink- ing area for additional antennas creates new trade-off challenges to deliver sufficient spherical coverage with a limited number of mmWave antenna panels. For beam correspondence (BC), Release 15 assumes dual-polarized signal paths and a minimum of two antenna 