In this letter, a two-coil wireless power transfer system is analyzed mathematically to obtain optimal source and load impedances, which are the most important factors that affect system efficiency. In addition, a near-zero refractive index metamaterial slab with a negative permeability was inserted between two resonant coils close to the transmitter to improve the efficiency in a large range. Finally, the wireless energy transfer system with the metamaterial slab was designed, fabricated and measured to evaluate the analysis method. The power transfer efficiency of 73.1% with the optimal impedances was enhanced to 81.3% using a 5 × 5 array metamaterial slab at the frequency of 13.56 MHz and the distance of 20 cm between the transmitter and the receiver.

Microstrip patch antenna (MPA) with loading of shorting pins expressed as a high gain and planar structure. The inductive effect of shorting pin tunes up the resonant frequency leading to increase the electrical size of antenna and, in consequence, its radiation directivity is enhanced. This work proposes a new configuration of MPA with loading of via holes to achieve gain enhancement. The field distribution is analyzed to optimize position of via holes. A prototype of proposed MPA is fabricated and shows excellent realized gain of 11.3 dBi that enhance about by 1.3 dB in comparison to the previous work.

A new approach to designing a broadband and highly efficient class-E power amplifier based on nonlinear shunt capacitance analysis is proposed. The nonlinear shunt capacitance method accurately extracts optimum class-E power amplifier parameters, including an external shunt capacitance and an output impedance, at different frequencies. The dependence of the former parameter on the frequency is considered to select an optimal value of external shunt capacitor. Then, upon determining the latter parameter, an output matching network is optimized to obtain the highest efficiency across the bandwidth of interest. An analytical approach is presented to design the broadband class-E power amplifier of a MOSFET transistor. The proposed method is experimentally verified by a 140-170 MHz class-E power amplifier design with maximum added power efficiency of 82% and output power of 34 dBm.Key Words: Broadband, Class-E Power Amplifier, MOSFET Transistor, Nonlinear Output Capacitance, PAE. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ

Class-E power amplifiers have found widespread application because of their design simplicity and high-efficiency operation. The nonlinear characteristic of the switching device significantly affects the power amplifier performance, although this is often neglected in theoretical analyses. In this paper, a class-E power amplifier with a shunt capacitance composed of nonlinear and linear capacitance has been mathematically analyzed to obtain the frequency limitation that governs maximum efficiency operation. The analytical method is presented to determine the effective operating frequency for any model of MOSFET device. The practical power amplifier circuit, using a MRF282 MOSFET, was implemented to verify the validity of the theoretical analysis.

This work presents a method used for designing a broadband class-E power amplifier that combines the two techniques of a nonlinear shunt capacitance and a low quality factor of a series resonator. The nonlinear shunt capacitance theory accurately extracts the value of class-E components. In addition, the quality factor of the series resonator was considered to obtain a wide bandwidth for the power amplifiers. The purpose of using this method was to produce a simple topology and a high efficiency, which are two outstanding features of a class-E power amplifier. The experimental results show that a design was created using from a 130 to 180 MHz frequency with a bandwidth of 32% and a peak measured power added efficiency of 84.8%. This prototype uses an MRF282SR1 MOSFET transistor at a 3-W output power level. Furthermore, a summary of the experimental results compared with other high-efficiency articles is provided to validate the advantages of this method.Key Words: Broadband, Class-E Amplifier, High PAE, Nonlinear Capacitance. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ