th that is approximately twice the baseband bandwidth (equivalent to the channel bandwidth) and thus use high switch- ing frequencies, which impacts its efficiency. In this case, the power amplifier operates closer to saturation and has a higher efficiency. The overall efficiency obtained for ET is usually better than for APT, but depends on the bandwidth to be supported. The state-of-the-art ET implementations in LTE support a 40 MHz bandwidth with carrier aggregation of two contiguous 20 MHz channels; some support up to 60 MHz. In order to support up to 100 MHz channel bandwidth, ET technology will require a significant step in performance with much higher switching frequencies resulting in lower DC/DC efficiency. The improved performance compared to APT, which has no 12 5G RF Design Challenges bandwidth limitation, may be nullified until new ET techniques are developed that have improved bandwidth with good DC/DC conversion efficiency. Release 16 will probably increase Tx bandwidths to 200 MHz. Also, ET is not suitable for FR2 with 400 MHz bandwidth and the multiple PA supplies to be supported in a phase array system. 12.3.3 FR1 Frequency Bands In Release 15, 5G is specified in 30 frequency bands, out of which only 3 bands are spe- cific to 5G operation, the remaining other bands being legacy LTE bands used for NR TDD/FDD or Supplemental Uplink (SUL) operation. In this respect, the added cost in RF-FE for supporting 5G in FR1 is limited to the features introduced in Section 12.2.4 and to the support of the new bands n77/78 and n79. In some solutions, these bands are supported in a dedicated PA module. It should be noted, however, that n79 is a com- pletely new band, whereas n77/n78 can be considered as an extension of LTE Bands 42 and 43. Figure 12.10 shows the key differences compared to LTE: In LTE refarmed bands, extended channel bandwidth (CBW) support has been agreed upon for the bands n3/n80, n5, n8/n81, n39, n40, n41, n51, n66/n86, and n70 for downlink mode operation only. In bands with a short duplex d