y wide bandwidths avail- able at mmWave frequencies set forth serious challenges for the data converters and the data conversion interfaces between the analog and digital domains in both receivers and transmitters. 5.7 Sub-6 GHz Transceiver and Antenna Design Considerations The evolution of 4G to 5G and the reliance on the existing technology allows several LTE solutions to be integrated into the initial rollout of the NR, providing immediate benefits without waiting for future releases. The early rollouts are also supported by the use of 728 Chapter 5 EN-DC functionality where an NR gNB is always associated with an LTE eNB. In Rel-15 NR, 4X4 downlink MIMO, particularly at frequencies above 2.5 GHz, which include n77/ 78/79 and B41/7/38, will be mandatory. The presence of four MIMO layers not only enables extended downlink data rates but also means there will be four separate antennas in the UE. An additional feature that is driven by mobile operators, however not mandatory, is the deployment of 2 X 2 uplink MIMO. Having 2 X 2 uplink MIMO in UE requires two 5G NR transmit PAs to transmit from separate antennas. This is particularly beneficial in cases where higher frequency TDD spectrum (in sub-6 GHz) is used as is the case with n41, n77, n78, and n79 as well as other TDD bands. The effective doubling of the uplink data rate enables shorter uplink bursts and flexible use of the 5G frame timing to increase the number of downlink slots, potentially increasing downlink data rates. However, when the downlink data rate increases, the uplink is challenged by the requirement of fast feedback from the UE [28]. A further use of the available second transmit path is a new transmission mode known as 2TX coherent transmission. This effectively uses the principles of diversity, which are strongly leveraged on the downlink side of the network and enable up to 1.5-2 dB of addi- tional transmit diversity gain, which is critical to address the fundamental uplink-limited network performance. Such improvements in uplink translate i