In this study, we propose a digital beamforming system for microwave power transfer with a real-time beam-scanning algorithm for tracking a moving receiver. To perform scanning, each channel in the transmitter generates and converts a baseband signal for the allocated beam direction based on the pilot slots in a frame structure. An initial timer reset process and a preamble are included in the algorithm to maintain time synchronization among units of the scanning period in a wireless environment. The average received power is simulated, and the optimal frame configuration is derived by considering the proportion of an energy transmission slot in the frame. For experimental verification, we design a 4 × 4 digital beamforming system operating at 5.8 GHz and a receiver. The scanning performance is experimentally validated with various numbers of scanning beams and placements of the receiver. Moreover, when radiating 16 W of RF power, an RF power of 100 mW or more is received in all sections for the scenario of the receiver moving in a 1 m distance using 1 second period beam scanning. The proposed microwave power transfer system with a real-time beam scanning algorithm is verified to track the moving receiver in a wireless environment and perform optimal microwave power transfer.

This paper proposes a receiving array antenna with a trapezoidal configuration that combines multiple rectifier circuits for wide-angle reception. The proposed receiving antenna system consists of three antenna elements operating at 5.8 GHz and the same number of rectifier circuits. To resolve the degradation in power transmission efficiency caused by misalignment, the receiving array antenna is designed in a trapezoidal configuration, and a quasi-air substrate is adopted for each antenna to achieve a high gain with the required beamwidth. All antenna elements in this system have measured reflection coefficients of less than -10 dB, and the overall beam coverage of the system is 205°. The power measurements of the receiving system are performed at 5° intervals within the beam coverage, and the results demonstrate that power is reliably received within the beam coverage through the proposed receiving antenna system.

The demand for multireceiver microwave power transfer (MPT) is increasing, driving research on enhancing both transmission efficiency and received power. To achieve this, both the power conversion efficiency (PCE) at multiple energy receivers (ERs) and the output power capability of the energy transmitter (ET) must be considered. This article proposes a multitone signal design for MPT using multidirectional multisine waveforms in a planar array antenna, which maintains high peak-to-average power ratio (PAPR) at the ERs while reducing PAPR at the ET via envelope shaping and phase offset optimization. Simulation and experimental results using a 16-channel digital beamforming system confirm that the proposed method improves both ER-side PCE and ET-side power capability. Under a three-directional MPT scenario, the proposed method reduced the average PAPR at central ET elements by 0.55 dB with two-tone signals compared to conventional continuous wave (CW) transmission, resulting in ER-side PCE improvements of 4.0 and 5.6 percentage points under 430 and $680~\Omega $ loads, respectively. With four-tone signals, it maintained a similar PAPR to CW while achieving PCE improvements of 3.4 and 8.4 points under the same load conditions. It also showed reduced nonlinear distortion under high transmit power, enhancing system performance on both the transmit and receive sides.

This paper presents a multibeam hybrid beamforming (MHBF) architecture for microwave power transfer (MPT), enabling wireless power delivery to multiple receivers with a reduced number of RF chains. The proposed architecture decouples beam control into the horizontal and vertical dimensions, where horizontal multibeams are generated in the baseband through digital precoding, while the vertical beam direction is controlled by a Butler-matrix-based analog beamformer. In particular, multibeam transmission is achieved using multi-tone signals with distinct phase weights assigned to each tone, enabling beams to be steered toward different directions, while the Butler-matrix-based analog beamformer provides vertical beam-steering capability. Compared with fully digital beamforming (DBF), MHBF enables simultaneous multibeam formation in the horizontal domain with fewer RF chains, thereby reducing hardware overhead and system complexity. To validate the proposed architecture, a 5.8 GHz prototype was designed and fabricated. The experimental results demonstrate three-beam and four-beam operation under a transmit power of 30.57 dBm, while the average received RF power in the single-beam case was 12.11 dBm at a distance of 1 m. In the three-beam and four-beam cases, average received RF power levels of 7.3 dBm and 6.1 dBm per beam were achieved, respectively. RF-to-DC conversion measurements under 430 $\Omega$ and 680 $\Omega$ load conditions further showed average PCE values of up to 38.77% and 35.05% for the three-beam and four-beam cases, respectively. These results confirm the feasibility of simultaneous multibeam wireless power delivery and its potential as an effective solution for multi-receiver operation with reduced RF-chain requirements.

Conventional Doherty power amplifiers (DPAs) often suffer from performance degradation due to inaccurate load modulation, primarily caused by relying on idealized fixed current ratio and neglecting the intricate nonlinearities of practical transistors. This paper proposes a generalized and systematic design methodology for asymmetric DPAs (ADPAs) based on load-pull-driven current ratio ( $\delta$ ) optimization. By identifying a specific $\delta$ that satisfies the carrier amplifier's optimal impedance conditions at both saturation and output power back-off (OBO), the proposed method establishes the desired load modulation trajectory linking the OBO and saturation impedance conditions. The proposed design methodology effectively bridges the gap between active device characterization and matching network synthesis by deriving $\delta$ directly from load-pull data. To verify the proposed approach, two ADPA prototypes targeting 6-dB and 9-dB OBO were designed and fabricated at 2.45 GHz. The 6-dB prototype achieves a measured saturated output power of 45 dBm with a peak drain efficiency of 72.3~\%, while maintaining 68.5~\% drain efficiency at 6-dB OBO. The 9-dB prototype achieves 43.82~dBm output power with 71.87~\% drain efficiency at saturation and 73.75~\% drain efficiency at 9-dB OBO. These results demonstrate that the proposed design methodology provides an effective and scalable design solution for high-performance ADPAs.