High-Efficiency Transmitter With Over-the-Air Combination by Dual-Feed Antenna

This letter presents a high-efficiency transmitter (Tx) based on a power amplifier (PA) and antenna co-design using an over-the-air (OTA) combination. A dual-feed single-aperture antenna enables the voltage-coherent recombination of two independently amplified signals in the far field through edge-loaded antenna design, generating in-phase radiation fields. A decoupling structure is introduced to enhance the port-to-port isolation while simultaneously enabling tuning of the antenna second-harmonic input impedance. Together with a shared output matching network (OMN), the antenna load provides appropriate fundamental and second-harmonic impedances for both branch PAs, enabling high-efficiency operation without additional harmonic control circuits. In the 3.45–3.55-GHz band, both branch PAs achieve 74%–76.5% saturated drain efficiency (DE) with the antenna load. Under excitation by a 20-MHz orthogonal frequency-division multiplexing (OFDM) signal with an 8.5-dB peak-to-average power ratio (PAPR), the Tx achieves 78.3% average efficiency, an adjacent channel power ratio (ACPR) below −45 dBc after digital predistortion (DPD) in the field-of-view (FOV) direction.