Energy-Efficient Array Transmitters Through Outphasing and Over-the-Air Combining

In this paper, a combinerless outphasing architecture for multiantenna transmitters with analog beamforming is presented and analyzed. The outphasing transmitter facilitates the use of highly power efficient switch-mode power amplifiers (PAs), while the combinerless structure further simplifies and improves the power efficiency of the design. The combining of the component outphasing signals in such a system then occurs over-the-air, at the receiver antenna. We consider two cases, one where the transmit outphased signals are alternately fed to the individual antennas and another where they are grouped in subarrays, and derive the analytical expressions for the total power beampatterns in both cases. Additionally, we carry out extensive simulations to verify the beampattern results and to evaluate the inband and out-of-band emission characteristics of the system, in terms of error vector magnitude (EVM) and total radiated power (TRP)-based adjacent channel leakage ratio (ACLR). We also consider these metrics under gain and phase mismatches in the transmitting antenna branches. The simulation results indicate that the system is able to attain good EVM results, while also the TRP-based ACLR limits imposed by 3GPP can be met if substantially large number of antennas are employed.