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This paper demonstrates the analysis of a long-distance high-power microwave wireless power transmission (MWPT) system based on asymmetrical resonant magnetron and cyclotron-wave rectifier. In the system, the novel magnetron with the asymmetrical resonant cavity, the straps, and the output loop coupling circuit can effectively promote the beam–wave interaction, suppress the mode competition, and enhance the output coupling, which results in a 400 kW output microwave power with a conversion efficiency of 45%. The transceiver Cassegrain antenna system with its simple structure, high conversion efficiency, and high power capacity can attain an integral power transmission efficiency of 2.6% at 10 km distance. The cyclotron-wave rectifier with high efficiency and single-tube high power capacity can achieve 85% microwave to DC conversion efficiency. Finally, the long-distance high-power MWPT system can achieve 8.5 kW DC power with about 1% DC–DC transmission efficiency at the operating 2.45 GHz frequency and for the 10 km distance. Such a system is likely a potential and attracting solution to remotely power the fuel-free aerial vehicle from the ground, can also provide electrical power to an isolated mountain top or an island, and even an alternative to transmit the power from space solar power satellite in geostationary orbit to the ground.

In this article, a parallel-circuit class-EF power amplifier with a shunt quarter-wave transmission-line for driving signals with arbitrary duty cycles is proposed and investigated. At the particular condition of duty cycle = 1/3, the values of the elements in the output network, as well as, some critical design parameters are analyzed and optimized. This leads to a series of significant improvements in the peak drain voltage ( V max), the maximum operating frequency ( f max), and the power output capability ( cp ). Furthermore, in order to verify the advantage of the proposed new amplifier and its feasibility in realistic situations, a proof-of-concept circuit is designed and fabricated. Finally, at the operating frequency of 3.59 GHz, excellent performance has been achieved with the power-added efficiency of 79.9% and output power of 40.7 dBm.

In this article, an artificial neural network (ANN)-based large-signal model (LSM) of AlGaN/GaN high electron mobility transistors (HEMTs) with accurate buffer-related trapping effects characterization and modeling is proposed. A hybrid small-signal parameter-extraction method for AlGaN/GaN HEMTs is used to acquire the parasitic parameters. To simplify the modeling procedure of the drain–source current $I_{\mathrm{ ds}}$ , an ANN-based model associated with the empirical equations taking into account the trapping effects, self-heating effects, and breakdown issue is developed. The low-frequency dispersions related to the buffer-related trapping effects have been well modeled by using a new empirical equation, which has been verified by small-signal S-parameters. Also, a new thermal factor $K_{T}$ and an improved Shockley diode equation are given in the proposed model as well. The developed LSM has been fully verified by a $2\times 100\,\,\mu \text{m}$ AlGaN/GaN HEMT with the pulsed I–V, small-signal S-parameters, power sweep, and load—pull measurements.

In this work, the properties of a two-tone signal driven concurrent power amplifier (CPA) are analyzed extensively. Firstly, the characteristics of two-tone signals are discussed to explain the nonlinearity and efficiency of two-tone signal driven CPA. Secondly, a method of how to solve the efficiency of a two-tone signal driven CPA is proposed in this paper with a detailed calculation procedure and complete theory. Finally, a general empirical expression to calculate the drain efficiency (DE) of CPA versus the frequency ratio and the amplitude ratio of the two carriers is proposed. Simulation results and experimental verifications are given to validate the proposed analytical formulation to predict the efficiency of CPAs when driven with balanced or imbalanced two-tone signals.

Power amplifier (PA) models, such as the neural network (NN) models and the multilayer NN models, have problems with high complexity. In this article, we first propose a novel behavior model for wideband PAs, using a real-valued time-delay convolutional NN (RVTDCNN). The input data of the model is sorted and arranged as a graph composed of the in-phase and quadrature ( I/Q ) components and envelope-dependent terms of current and past signals. Then, we created a predesigned filter using the convolutional layer to extract the basis functions required for the PA forward or reverse modeling. Finally, the generated rich basis functions are input into a simple, fully connected layer to build the model. Due to the weight sharing characteristics of the convolutional model's structure, the strong memory effect does not lead to a significant increase in the complexity of the model. Meanwhile, the extraction effect of the predesigned filter also reduces the training complexity of the model. The experimental results show that the performance of the RVTDCNN model is almost the same as the NN models and the multilayer NN models. Meanwhile, compared with the abovementioned models, the coefficient number and computational complexity of the RVTDCNN model are significantly reduced. This advantage is noticeable when the memory effects of the PA are increased by using wider signal bandwidths.

This paper presents a mathematical model of the optimal fundamental load modulation design space for Class-X harmonically tuned power amplifiers (PAs). Starting from Class-X PA with maximally flat waveform, the optimal fundamental load trajectory that maintains constant high efficiency for different output power back-off level is obtained. Optimal fundamental load trajectory with different sets of second and third harmonic impedances are studied and verified with harmonic load-pull measurement. By carefully choosing the second and third harmonic load impedance, the optimal fundamental load trajectory can cross the real axis, which provides more flexibility in amplifier design. A 10W Cree GaN transistor, CG2H40010F, is measured at 800 MHz. The measured load-pull contours locate on the calculated optimal fundamental trajectory which validates the theory proposed in this work.

In this paper, a new method is presented to analyze the bandwidth performance of power amplifiers (PAs) including the Class-A/B/J Continuum for dynamic load modulation (DLM). Due to the introduced biasing operation factor $p$ , the analysis of bandwidth performance of DLM Class-J PAs can be extended to other modes, such as deep Class-AB mode. With the help of MATLAB software, the relationship between the drain efficiency (η) and output power back-off (OPBO) at the current generator plane (CGP) is demonstrated clearly. At the CGP, the proposed method indicates that when $p = 0$ , the fractional bandwidth (FBW) of DLM PAs is improved from 73% to 141% compared with the results at the extrinsic plane (EP). When $p$ is increased to 0.2, the FBW of DLM PAs can be improved from 141% to 156%. Furthermore, the proposed method in this work provides clear guideline to do a general analysis on the bandwidth performance of DLM PAs including the Class-A/B/J Continuum, and it also provides potential theoretical guidance for engineers to design wideband DLM PAs.

An analytical method is proposed to reduce the memory effects and third-order intermodulation distortions for improving the linearity of wideband power amplifier (PA). An excellent linearity can be obtained by reducing the second-harmonic output power levels and reducing the envelope voltage components in the megahertz range. An improved wideband Chebyshev low-pass matching network including the bias network is analyzed and designed to validate the proposed method. The measured results indicate that a wideband high-efficiency linearized PA is realized from 1.35 to 2.45 GHz (fractional bandwidth = 58%) with power added efficiency of 60–78%, power gain of 10.8–12.3 dB, and output power of 40.0–41.2 dBm. For a 20 MHz LTE modulated signal, the adjacent channel leakage ratios (ACLRs) of the proposed PA with digital pre-distortion (DPD) linearization are −55.7 ~ −53.9 dBc across 1.5–2.4 GHz at an average output power of 32.4–33.6 dBm. For a 40 MHz two-carrier LTE modulated signal, the ACLRs of the proposed PA with DPD linearization are −51.1 ~ −48.2 dBc at an average output power of ~30.5 dBm in the frequency range from 1.5 GHz to 2.4 GHz.

This paper proposes a new theory for harmonically tuned power amplifiers (PAs) with maximally flat waveforms, Class-X PAs. This class has been developed to achieve maximally flat waveforms. In this class, the relationship between the fundamental load impedance and the independently set second- and third-harmonic load impedances is established to maintain constant output power with constant efficiency. This relationship sets an optimum fundamental load design space when the second- and third-harmonic impedances are varied simultaneously and independently of each other. By varying the second- and third-harmonic impedances independently, higher flexibility in the design of broadband PAs is obtained. The theory of Class-X PA and its broadband characteristics were validated with an experimental design example using a Cree’s 10-W Gallium Nitride (GaN) device. This design showed a measured drain efficiency higher than 70% and output power within 3-dB variation over more than one-octave bandwidth.

In this paper, a novel planar compact coupled-line circuit is proposed to design a single-ended-to-balanced power divider (PD) that can be used in numerous balanced circuits and systems. By using the matrix transformation between the mixed-mode (MM) scattering parameters and the single-ended scattering parameters, the constraint rules are deduced to realize the performance of equal power division with in-phase, good input (output) port matching, high isolation between two balanced outputs, high suppression of the common-mode (CM) noise, as well as the mode-conversion suppression between differential-mode signals and CM noise. Then, the closed-form design equations are derived using the even- and odd-mode analysis. Finally, a microstrip PD, which works at 1 GHz, is designed and fabricated. The measured (simulated) operating relative bandwidth is 37% (38%) from 0.76 (0.83 GHz) to 1.13 GHz (1.21 GHz). The consistency between the simulated and measured MM scattering parameters verifies the correctness of the design theory.

This letter presents a new antenna topology to implement the load modulation in the Doherty transmitter, which resulted in enhancing the bandwidth compared to previous works. The active load modulation is realized by using a monopole array antenna, which serves as both Doherty combiner and wave radiator. The load impedances of amplifiers can be dynamically tuned through the mutual coupling of the array elements. Detailed design equations and procedures are developed. For verification, a Doherty transmitter operating at 1.95–2.10 GHz has been designed and fabricated using GaN HEMT transistors. The prototype transmitter exhibited a power-added efficiency of 53% at peak power level and maintained an efficiency of 43% at 6.8-dB backoff, over the frequency band of 1.95–2.10 GHz.

A novel design space of load modulated (LM) continuous Class-B/J power amplifiers (PAs) is proposed, and a detailed mathematical analysis is presented. The combination of LM technique and continuous mode is introduced to enhance the wideband performance of LM PAs. An inversely proportional relationship between $Z_{L}$ and $C_{\mathrm {out}}$ is derived, which indicates that the nonlinear $C_{\mathrm {out}}$ can affect the optimal load impedances at output power backoff (OPBO) and the design parameter $\beta $ should be appropriately adjusted. The measured results of a PA prototype show that the PAE is 39%–45% under LM when OPBO = 5 dB across 1.6–2.4 GHz. Compared with the same PA with fixed $V_{\mathrm {var}}$ , the proposed PA with optimum $V_{\mathrm {var}}$ at 2 GHz achieves a PAE improvement with 11% when OPBO = 5 dB.

In this article, a Ka-band narrowband multilayer bandpass filter (BPF) centered at 34.5 GHz is presented, where a hybrid structure of two substrate integrated waveguide (SIW) cavities with slots and CPW is used to meet the good filtering capability and compact size. Benefiting from the 3-D circuit layout, the proposed filter can effectively overcome a vital drawback of large circuit size of traditional filter, and be used in system-in-package application. The circuit size of the filter excluding feed lines is about 0.5λg by 0.5λg, where λg is the guided wavelength at the central frequency of 34.5GHz. Simulated results show that the filter has the 3dB bandwidth of 0.86 GHz (FBW = 2.5%) and insertion loss of 1.7 dB at central frequency. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1395–1398, 2016

A novel reliable small signal model parameter extraction of asymmetric GaN-based Heterojunction Field Effect Transistors (HFETs) is proposed in this paper. An efficient systematic searching procedure based on pinch-off and cold weak-forward S-parameters has been developed to consider the asymmetric structure of GaN HFETs and find the optimal values of the gate and drain pad capacitances Cpg and Cpd. Considering that the depletion region extension is varied with the gate bias voltage V gs slightly even below pinch-off voltage, the obtained initial values of the extracted parameters are optimized by artificial bee colony (ABC) algorithm to improve the reliability of parameter extraction. The developed parameter extraction method shows excellent accuracy and reliability. The proposed procedure can be extended to asymmetric GaN devices with various process technologies. The developed approach has been validated by an asymmetric 0.15 μm GaN HFET over a wide range of bias conditions and frequencies., 2018 13th European Microwave Integrated Circuits Conference (EuMIC), September 23-25, 2018, Madrid, Spain

A dual-band bandpass filter (BPF) using varactor-loaded square split ring resonator is proposed to realize the dual-band frequency response and one high-selective tunable passband. This resonator is mainly composed of a pair of the square split ring, two varactors and an open stub $(l=\lambda/4@f_{even})$ . By placing an open stub at the center position of the proposed resonator, the odd-mode resonance $f_{\text{odd}}$ is split into two modes, as $f_{\text{odd}1}$ and $f_{odd2}$ , which can be used to form a high-selectivity passband. The two distinct odd/even-mode resonances can be generated independently and used to realize the first-/second-passbands. The simulated results indicate that the center frequency of the first-passband can be tuned from 1.15 to 1.45 GHz with a 3-dB constant bandwidth of $110\pm 10 \ \text{MHz}$ . meanwhile, the center frequency of the second-passband is fixed at 2.2 GHz with a 3-dB fractional bandwidth of 8.6-11.4%.

The impact of knee voltage effect and soft turn-on characteristic of the practical transistor on the design space of load modulated (LM) continuous Class-B/J power amplifiers (PAs) is analyzed and improved design space is proposed in this paper. For LM continuous Class-B/J PAs with a practical transistor, the knee voltage effect has a noticeable effect on the dynamic load-lines when the dynamic load modulation at the current generator plane (CGP) is proceeding. The chosen load impedance of LM continuous Class-B/J PAs with optimum output power and efficiency at the 0 dB output power back-off (OPBO) can be affected by the knee voltage effect. The soft turn-on characteristic can lead to a non-null drain quiescent current at Class-B/J mode, which limits the dynamic OPBO range with high efficiency. Based on the Pedro load-line theory, the improved design space of LM continuous Class-B/J PAs can offer a more accurate prediction on the efficiency contours and provide more effective theory guidance in designing high-efficiency LM PAs.

A novel X-band frequency synthesizer for array radar system is presented in this paper. This frequency synthesizer is based on a Phase Locked Loop (PLL) with mixer structure. The synthesizer consists of multiple Direct Digital Synthesizers (DDSs), Voltage Controlled Oscillators (VCOs) and PLLs. The PLL is used as the system reference clock to the DDS and local reference signal to the mixer. DDSs generate two reference signals: one is for the Phase Frequency Detector (PFD) and the other provides the reference signal to the PLL. According to this structure, the frequency synthesizer with excellent performance for array radar system is developed. The experimental results indicate that the output of frequency synthesizer is low phase noise (

The analysis on the design space at the intrinsic plane for dynamic load modulated (DLM) continuous Class-B/J power amplifier (PA) is presented in this paper. The proposed intrinsic design space extends the classical design space of the continuous Class-B/J power amplifier which is the special case operated at the saturated power, and it indicates a potential that DLM continuous Class-B/J PA can achieve broadband performance. Based on the proposed intrinsic design space, DLM PA can maintain high efficiency at a large dynamic range of output power. A 15 W GaN HEMT device CGH60015D provided by CREE is used to verify the proposed design space at three frequencies of 1.5 GHz, 2.0 GHz and 2.5 GHz. The measured drain efficiency and output power by load-pull measurements show that the proposed design space can give a distinct guideline for engineers to choose the optimal load impedances at the intrinsic plane for developing DLM PAs.

This paper presents a broadband, high efficient RF power amplifier (PA) in class-J mode by using a compact output matching structure. Different from traditional structure, the compact output structure is consisted of harmonic-control matching network and fundamental matching network to make the output matching network. Using the commercial device, GaN HEMT Cree's CGH40010, this continuous class-J PA realizes a 50% relative bandwidth with simulated drain efficiency of 71%–74.7% in the frequency range of 1.79–2.21 GHz.

The design of continuous and reconfigurable Doherty power amplifier (DPA) using tunable comb structure is presented in this paper. Two Cree GaN HEMTs with 10-W peak envelope power are employed to design the continuous and reconfigurable DPA. Layout simulation results show that the continuous and reconfigurable DPA achieves a power-added efficiency (PAE) of 40%–60% at the peak power and a PAE of 30%–40% at the 6-dB backoff point from the saturated output power from 0.81GHz to 1.35GHz.

The design of a reconfigurable continuous Class-F power amplifier (PA) is presented in this paper. A varactor-based output matching network is used to design the reconfigurable continuous Class-F PA. By employing the CREE 10W GaN HEMT device CGH40010F, the design is verified by simulation. The layout simulation results show that more than 50% efficiency is obtained from 0.9GHz to 1.45GHz. In each reconfigurable band with a bandwidth of 200MHz, the power gain is within 10.6±1.0dB.

`New' Class-E solutions are proposed by varying three different design parameters which are introduced in the voltage and current equations in order to extend the Class-E `design space', of which the `new' solutions can apply to optimal and suboptimal operation. The design procedure of suboptimal Class-E power amplifier (PA) is analysed in details and then a suboptimal Class-E PA based on GaN HEMT CGH40010F is designed to prove the correctness of the `new' solutions. The measured maximum output power of 39.6 dB, power-added-efficiency of 74.7% and drain efficiency of 78.9% were obtained at 2.6 GHz with a 28 dBm input power. These measurement results show that a similar or better level of efficiency and output power that are reported for optimal Class-E PAs at lower frequencies using the same transistor, and the presented `new' solutions extend the `design space' of Class-E PA. This paper give engineers more degrees of freedom to design Class-E PA.

In the above paper, the author presents theoretical analysis of coupling coefficient of coupled-line using the asymmetrically loaded resonator. The coupling coefficient is critical to control the bandpass-to-bandstop transformation and bandwidth. However, some errors have been found, which may affect the readers’ understanding and they will be indicated in this letter.

In this paper, the implementation of an X band Tx-to-Rx leakage cancellation network to achieve bandwidth improvement and high isolation performance is presented. The circuit architecture and leakage cancellation theory are described in detail. The operation principle of leakage cancellation network is based on phase cancellation technique. This architecture is made up of three two-section Wilkinson power dividers and a hybrid-ring, which miniaturizes the leakage cancellation network, compared with conventional ferrite circulators. The proposed architecture has been completely implemented and measurements have been carried out for verification. The simulated bandwidth is presented with 83% fractional bandwidth above 30dB isolation, and the corresponding measured fractional bandwidth is 31.2%. Meanwhile, the simulated bandwidth is presented with 16% fractional bandwidth above 40dB isolation, and the corresponding measured fractional bandwidth is 6.4% The measured peak isolation is 46.2dB@9.361GHz. Although the measured fractional bandwidth is decreased, the high isolation bandwidth between Tx port and Rx port based on the circuit architecture proposed in this paper, is still enhanced, especially compared with other conventional high isolation networks.

This paper presents a new method to design high efficiency and wideband power amplifier (PA). Based on the output parasitics network of MOSFET, this method shifts the optimum load impedances from the intrinsic plane to the package plane, which are obtained by the continuous PA theory and then rectified elaborately by multi-harmonic bilateral-pull technology, in order to make the second harmonic load impedances in high efficient region as well as the fundamental load impedances with high power added efficiency (PAE) and output power. A simulated example based on the GaN HEMT device CGH40010F is designed to verify the proposed method.

This paper presents that the maximum operating frequency of sub-harmonic Class-E amplifier not only depends on the transistor duty ratio, but also relies on the slope of switch voltage when the transistor turns on. When dc supply voltage, output power and shunt capacitance are specified, the maximum operating frequency increases as the slope of switch voltage increases. On the contrary, it increases as the transistor duty ratio declines.

In the above paper, the author proposes a filter configuration with a configurable-pole response, which can achieve two-, three-, and four-pole states. However, some errors have been found, which may affect the readers’ understanding and they will be indicated in this letter.