Apparatus and methods for radio frequency front-ends are provided. In certain configurations, a radio frequency front-end includes ultrahigh band (UHB) transmit and receive modules employed for both transmission and reception of UHB signals via at least two primary antennas and at least two diversity antennas, thereby supporting both 4×4 receive MIMO and 4×4 transmit MIMO with respect to one or more UHB frequency bands, such as Band 42, Band 43, and/or Band 48. The radio frequency front-end can operate with carrier aggregation using one or more UHB carrier frequencies to provide flexibility in widening bandwidth for uplink and/or downlink communications.