A transmitter architecture and methodologies supporting uplink inter-band carrier aggregation (CA). In various embodiments, first and second baseband signals are provided to a plurality of passive mixers that selectively combine the baseband signals with differing local oscillation signals to produce outbound RF signals of at least first and second RF frequencies. Depending on the relevant CA mode of operation, the outbound RF signals are amplified and selectively coupled to at least one transmitting antenna for respective transmission over a plurality of frequency bands.