This paper presents a broadband Doherty power amplifier (DPA) design with an octave bandwidth based on a new load network consisting of a quasi-lumped impedance transformer for the carrier amplifier, a multiple resonance circuit for the peaking amplifier, and a broadband post-matching network. The quasi-lumped impedance transformer and the multiple resonance circuit were designed based on accurate equivalent circuits for internal components inside the packaged transistor. Based on power bandwidth analysis, optimum susceptance provided by the multiple resonance circuit at the peaking amplifier, was obtained. The proposed broadband DPA was designed using 45 W gallium-nitride high electron mobility transistor for both carrier and peaking amplifiers. For continuous-wave signals in frequency range of 0.9 to 1.8 GHz, the implemented broadband DPA exhibited a drain efficiency of 54.2% to 73.4% at peak output power of 49.7 to 51.4 dBm and a drain efficiency of 41.7% to 58.0% at output back-off of 6 dB. For the down-link long-term evolution signal with a channel bandwidth of 10 MHz and a peak-to-average power ratio of 6.5 dB, a drain efficiency of 41.3% to 57.4% and an adjacent channel leakage power ratio of -22.5 to -30.2 dBc at an average output power of 43.2 to 449 dBm were achieved at an octave bandwidth.

This paper presents a reconfigurable radio frequency to direct current (RF-DC) converter operating at 902 MHz frequency designed to efficiently harvest RF signals and convert into useable DC voltages for RF energy harvesting applications. The proposed scheme employs a dual-path, a series (lowpower) path and a parallel (high-power) path, to maintain high power conversion efficiency (PCE) over wide input power range. The dual-path is composed of two identical rectifier blocks utilizing internal threshold voltage cancellation (IVC) technique to efficiently compensate the threshold voltage of the transistors used as rectifying devices. An adaptive control circuit (ACC) consisting of a comparator, an inverter and three switches is used in the proposed scheme. The ACC activates the series path or the parallel path to maximize the harvested power based on the input power range. The proposed scheme is designed and fabricated in a 180 nm complementary metal-oxide semiconductor (CMOS) technology. The measurement results show that PCE of the proposed circuit is above 20% from -18 dBm to -5 dBm, maintaining 13-dB input power range with peak PCE of 33% at -8 dBm for 200 kΩ load resistance. The proposed circuit demonstrates -20.2 dBm sensitivity across 1 MΩ load resistance while producing 1 V output DC voltage.

This article presents a high-efficiency fast transient constant on -time (COT) control dc–dc buck converter for the Internet of Things applications. The current reused current sensor is proposed to enhance the loop stability and improve the power conversion efficiency at light load. Input current is sensed and added to the feedback voltage of the dc–dc converter to increase the sensed output ripple voltage. Fast transient dc-offset cancelation technique is introduced to achieve a fast transient recovery time and to cancel the output dc offset. This chip is fabricated with a 0.13- μ m CMOS process. A standard supply voltage of 7–15 V is applied to produce the output voltage of 5–5.33 V. The total die area is 2 mm × 1.5 mm. The settling time is 17 μ s. The transient recovery time from light to heavy load and from heavy load to light load are 3 μ s and 2.7 μ s, respectively, with a maximum dc offset of 3.5 mV. The overshoot voltage is 85 mV and the undershoot voltage is 72 mV. The peak efficiency of the proposed design is 95.56% at 0.5 A and efficiency at the light load of 10 mA is 84.60%.

The retroreflective method has been used as a radio—frequency (RF) beamforming method for massive antenna array, for wireless communication systems, radars, and microwave power transfer (MPT) systems. In particular, the retroreflective method is suitable for optimum beamforming for both near—and far—field zones. Each transmitter (Tx) and receiver (Rx) circuit in the Tx array has its own phase offset, which should be calibrated for optimum retroreflective operation. This paper presents a simple and effective phase offset calibration method for the retroreflective beamforming arrays using a one—by—one basis optimum phase searching method with a receiver at a reference point. To verify the proposed method for a massive retroreflective array, a 5.2 GHz short— and mid—range (~ 4 m) MPT system, including a Tx array based on 8x8 antennas and an Rx using 6 antennas (5 rectennas for power reception, and 1 additional for pilot transmission) for charging mobile handsets was implemented. Optimal retroreflective beamforming from the Tx array, which was calibrated using the proposed method, was experimentally verified for angles of within ±45° degrees for both xz— and yz—planes. The implemented Tx and Rx circuits achieved a received dc power of about 100 mW at a distance of 4 m.

This article presents a Doherty power amplifier (DPA) based on asymmetric cells with a complex combining load (CCL). In this study, a new and intuitive design technique using the Smith chart is proposed for developing the load network of the CCL-DPA. The peaking amplifier consists of a larger cell size compared to that of the carrier amplifier in order to achieve higher power gain and peak output power in comparison with the conventional CCL-DPAs based on symmetric cells. For verification purposes, the proposed asymmetric CCL-DPA was designed and implemented using 6- and 10-W GaN-HEMTs for the carrier and peaking amplifiers, respectively. For the 1.68-GHz continuous-wave signal, the asymmetric CCL-DPA exhibited a power-added efficiency (PAE) of 68.0% and a drain efficiency (DE) of 73.9% at a peak output power of 43.5 dBm. When an output power back-off of 9.5 dB was used, a PAE of 52.0% and a DE of 54.7% were achieved. Using the long-term evolution signal with a peak-to-average power ratio of 9.6 dB and a signal bandwidth of 10 MHz, a PAE of 53.6%, a DE of 56.4%, and a power gain of 13.5 dB were obtained at a power level of 34.0 dBm. Using a digital predistortion technique, an adjacent channel leakage power ratio of -48 dBc was achieved at the same power level.

This letter proposes a novel capacitively coupled microstrip comb-line array (CCMCA) antenna for millimeter-wave band applications. The proposed antenna has the advantages of low profile, low cost, and ease of fabrication for the millimeter-wave band. By adjusting the gaps between the radiating strips and feeding line, an antenna with low sidelobe level can easily be designed. To verify the suitability of the proposed antenna for millimeter-wave applications, two arrays (1 x 18 and 4 x 18) were designed and developed at the design frequency of 79 GHz. The measured results show good agreement with the simulated ones in terms of reflection characteristics and radiation patterns. In addition, the CCMCA antenna has stable beam direction even with frequency change, compared to a conventional series-fed microstrip rectangular patch array antenna.