arXiv subjects

Changjun Liu

Publications and source records attributed to Changjun Liu.

18 recordsLinked to original sources

arXiv2026

A C-band microwave rectifier without capacitors for microwave power transmission

A microwave rectifier at 5.8 GHz without any capacitors is presented, which owns a measured MW-to-DC conversion efficiency of 68.1%. A harmonic rejection filter and a DC pass filter, which replace lumped capacitors in conventional microwave rectifiers, are applied to suppressing the harmonics produced by an HSMS-286 Schottky diode during rectifying. At the fundamental frequency, a microstrip impedance transformer which contains a shunt {\lambda}g/8 short-ended microstrip transmission line and two short series microstrip transmission lines are applied to compensating the imaginary impedance of the diode and matching the input impedance of the rectifier. The measured MW-to-DC conversion efficiency agrees well to the simulated results. The novel rectifier without any lumped passive elements may be applied for power transmission system at higher microwave frequencies.

physics.app-ph↗

arXiv2026

Second- and Third-Harmonic Backscatter Through a Bandstop Filter Using Defected Ground Structure

In this brief, a novel harmonic-backscatter-rectifier (HBR) is introduced for simultaneous rectification and harmonic-based uplink. The proposed (HBR) employs a rectifier to generate both DC power and the harmonic carriers for backscattering communication, and a dual-band reconfigurable band-stop filter using defected ground structure(DGS) to modulate the second and third harmonics with low-power consumption and same input impedance at f0 all the time. As a proof of concept, an HBR prototype operating at 1.85 GHz was designed and experimented. An uplink data rate of 8Mbps (4Mbps x 2 ) was achieved when the HBR was fed with -10 dBm RF power, and the data modulation consumed less than 27.7pJ/bit. In addition, a passive harmonic tag was implemented with the proposed HBR and a low-power binary sequence generator, which demonstrated a continuous uplink of 12 kbps at -6 dBm RF power.

physics.app-ph↗

arXiv2026

An Adaptive Power Division Strategy for Nonlinear Components in Rectification

This letter presents a novel adaptive power division strategy, which uses two rectifying diodes with nonlinear impedance characteristics that are configured in parallel to function optimally at their individual power levels. Through the strategic adjustment of the input admittance, the conductance of the low-power diode decreases progressively with increasing power, while the conductance of the high-power diode increases correspondingly. This conductance-based power allocation method ensures that the power is rectified consistently by the most appropriate diode, regardless of the power level, and, thus, enables efficient rectification across an extended range. This letter presents a rectifier typology to substantiate the proposed strategy. Experimental results confirm the efficiency of the adaptive power division strategy, with the rectifier showing efficiency in excess of 60% from 5 to 29.5 dBm, giving a power dynamic range of 24.5 dB.

physics.app-ph↗

arXiv2026

Harmonic-Recycling Rectification Based on Novel Compact Dual-Band Resonator

Harmonic generation during radio frequency (RF)-dc conversion causes performance degradation of a microwave rectifying circuit. To suppress and recycle the harmonic power, this letter proposes a novel compact dual-band resonator (DBR) based on a microstrip coupled transmission line. It presents open-circuits at the second and third harmonic frequencies, which effectively block the higher order harmonic for power recycling. The conventional input cascading filters for harmonic rejection can be eliminated, simplifying the circuit topology and reducing loss. Theoretical analyses were carried out and corresponding equations were formulated for the proposed DBR. For validation, two rectifying circuits with/without the DBR operating at 2.2 GHz were fabricated and tested. Using the proposed DBR at 10 dBm RF power, the suppression of the second and third harmonic powers is enhanced by 18.4 and 7.6 dB, respectively. Besides, an improvement of RF-dc power conversion efficiency (PCE) was observed; specifically, PCE reached 73.2% at 10 dBm compared to 71.6% obtained from an equivalent rectifier.

physics.app-ph↗

arXiv2026

Experimental study on an S-band near-field microwave magnetron power transmission system on hundred-watt level

A multi-magnetron microwave source, a metamaterial transmitting antenna, and a large power rectenna array are presented to build a near-field 2.45 GHz microwave power transmission system. The square 1 m2 rectenna array consists of sixteen rectennas with 2048 Schottky diodes for large power microwave rectifying. It receives microwave power and converts them into DC power. The design, structure, and measured performance of a unit rectenna as well as the entail rectenna array are presented in detail. The multi-magnetron microwave power source switches between half and full output power levels, i.e. the half-wave and full-wave modes. The transmission antenna is formed by a double-layer metallic hole array, which is applied to combine the output power of each magnetron. The rectenna array DC output power reaches 67.3 W on a 1.2 ohm DC load at a distance of 5.5 m from the transmission antenna. DC output power is affected by the distance, DC load, and the mode of microwave power source. It shows that conventional low power Schottky diodes can be applied to a microwave power transmission system with simple magnetrons to realise large power microwave rectifying.

physics.app-ph↗

arXiv2025

High-Efficiency Octave Bandwidth Rectifier for Electromagnetic Energy Harvesting

This letter presents the design and implementation of a compact high-efficiency octave microwave rectifier. A key highlight is the novel segmented impedance matching method, a unique approach that expands the rectifier bandwidth. The diode reactance is initially regulated by a series short-ended microstrip line. Impedance-compensated structures, characterized by varying admittance properties across an extensive frequency range, partition the operating frequency band into two segments based on the input impedance, thereby minimizing impedance variation. Ultimately, the input impedance is matched by a novel triple-band matching network. An octave rectifier was fabricated and measured. Results demonstrate that the rectifier achieves over 50% efficiency over 1.3-2.55 GHz fractional bandwidth 64.9% at 0-dBm RF input power. Even with a decrease in input power to -10 dBm, the rectifier maintains over 30% efficiency.

physics.app-ph↗

arXiv2025

Enhancing Microwave Heating Uniformity in Cavities Using a 2-bit Coding Metasurface

A novel method for enhancing microwave heating uniformity using a 2-bit coding metasurface is proposed. This metasurface is specially designed to scatter incident waves into multiple directions at 2.45 GHz rather than just one, significantly improving the electric field distribution uniformity within a cavity, and eliminating the need to redesign the cavity itself or modify the power excitation. Simulated results demonstrate a reduction in the coefficient of variation (COV) of potato temperature from 0.694 to 0.461, indicating enhanced heating uniformity while maintaining efficiency. Additionally, the measured potato temperatures show excellent agreement with the simulated results, validating the effectiveness of the proposed method.

physics.app-ph↗

arXiv2025

Modeling and Experiments of an Injection-Locked Magnetron With Various Load Reflection Levels

In this article, we investigate the performance of an injection-locked 5.8-GHz continuous-wave magnetron with various load reflection levels. The load reflection is introduced to an equivalent magnetron model to theoretically evaluate the system performance. The effects of different load reflection levels on the magnetron's output are numerically analyzed. Experiments are performed while the load reflection is varied using an E-H tuner between a magnetron and a circulator. A narrower locking bandwidth is observed under constant injection power with increasing load reflection. The proper-mismatched system suppresses its sideband energy, thereby reducing phase noise. The experimental features qualitatively validate the theoretical analyses results. The investigation results also provide guidance for advanced applications in communication and high-energy physics based on injection-locked magnetrons.

physics.app-ph↗

arXiv2025

Modular Multirotary Joints SPS Concept-Challenges and Design Considerations

As a major space based energy infrastructure in response to the challenge of climate change, space solar power SSP has attracted extensive international attention for more than 55 years. Recently, various SSP concepts have been proposed, aiming to efficiently harvest gigawatts of solar power over Earth geostationary orbit and transmit it to the Earth wirelessly. Based on the multirotary joints solar power satellite MR SPS concept proposed in 2014, this article presents an updated modular MR SPS concept, together with the challenges and design considerations. The primary objective is to address the challenges associated with long distance dc electric power transmission and exceptionally high precision microwave power transmission. The MMR SPS employs multiple modules, each further including a solar subpanel and an antenna subpanel. The solar subpanel and antenna subpanel in each module are connected with each other via conductive rotary joints with a much shorter distance compared with that in the MR SPS concept. As a result, lower voltage in electric power transmission is allowed, which significantly reduces the complexity of the system and increases its reliability. Retroreflective beamforming is employed to ensure the accurate steering of the microwave power beam to the ground receiving aperture. For the first time, this article analyzes and validates the performance of using retroreflective beamforming to compensate for antenna position deviations through a numerical calculation model that includes near field effects. Additionally, this article outlines the transportation and assembly methods, along with the considerations of the full life cycle cost for an MMR SPS.

physics.app-ph↗

arXiv2025

Compact High-Efficiency All-Polarization Rectenna for Wireless Power Transmission

In this letter, we present an innovative design for a compact, high-efficiency all-polarization receiving rectenna tailored for wireless power transmission. This rectenna, which integrates an antenna with two same rectifier units, employs direct conjugate matching of antenna impedance to rectifier impedance. This approach eliminates the necessity for an external impedance-matching network, thereby reducing the overall dimensions of the rectenna. The implementation of virtual ground concept streamlines the design of the rectifier's output filter. The low-profile antenna, engineered for operation at 2.45 GHz, demonstrates high conversion efficiency across all polarization angles. The measured RF-to-DC efficiency exceeds 63% for all polarization angles, achieving a peak efficiency of 82.2%.

physics.app-ph↗

arXiv2025

Theoretical and experimental development of a high-conversion-efficiency rectifier at X-band

Voltage doubler rectifiers are usually applied to systems with high voltage and low current requirement. An X band voltage doubler rectifier has been developed with 72% conversion efficiency. To the best of our knowledge, the obtained rectifying efficiency is the maximum reported to date at X band with Schottky diodes. The working characteristics of the diodes in the voltage doubler rectifier are analyzed in detail. Closed-form equations of diode input impedance and rectifying efficiency are presented and validated using Advanced Design System simulations. The matching network design of the proposed rectifier is based on the closed-form equations. The preliminary rectifying efficiency is predicted by the closed-form equations as well. Measured and simulated results are in good agreement.

physics.app-ph↗

arXiv2025

A Reconfigurable Circuit Strategy and Its Application in Low-Power Rectifier for Ambient Energy Harvesting

In ambient electromagnetic energy harvesting systems, the input power to the rectifier is low. To improve rectification efficiency, Schottky diodes, which are sensitive to low power, are commonly selected as rectifying devices to convert microwave power into dc power. However, low-power rectifying diodes typically have low reverse breakdown voltages, making them susceptible to reverse breakdown under high power conditions. This letter proposes a low-power rectifier with reconfigurable function. The rectifying diode is connected in parallel with the p-i-n diode. At low input power, the output dc voltage is low, and the p-i-n diode remains off, having no impact on the rectifier operation. As the input power increases, the p-i-n diode turns on, causing change in circuit structure and impedance mismatch. This leads to increased reflected power, thereby preventing the rectifying diode from receiving excessive power. In addition, the turn-on voltage of the p-i-n diode is lower than the reverse breakdown voltage of the rectifying diode, protecting it from reverse breakdown.

physics.app-ph↗

arXiv2025

Study on Improving Microwave Heating Uniformity Based on Phase-Frequency Simultaneous Modulation Technique

Conventional microwave heating techniques are limited due to inherent thermal point residency effects and inadequate control over the heating process. A novel method is proposed to enhance microwave heating uniformity using the injection-pulling technique. In this method, the injection-pulling technique is used to achieve simultaneous modulation of both the output phase and frequency of the magnetron, thereby extending the locking bandwidth of the injection-locking technique. The output characteristics of the injection-pulled magnetron were validated through numerical calculations and experiments. Microwave heating experiments were conducted under both a five-cup water load and an absorbent paper load. Compared with conventional injection-locking frequency sweeping, the proposed method not only expands the sweeping bandwidth from 8 to 18 MHz but also further improves heating uniformity, offering more options for magnetron applications in microwave heating.

physics.app-ph↗

arXiv2025

High-Efficiency Isolator-Free Magnetron Power Combining Method Based on H-Plane Tee Coupling and Peer-to-Peer Locking

Magnetrons are widely used as high-performance microwave sources in microwave heating, microwave chemistry, and microwave power transmission due to their high efficiency, low cost, and compact size advantages. However, the output power of a single magnetron is limited by its resonant cavities, posing a physical constraint. High-efficiency coherent power combining based on the injection-locking technique effectively overcomes this limitation and meets the demand for higher output power. Nevertheless, using isolators, such as circulators, introduces significant insertion loss, and the injection signal sources and phase shifters increase the system size, cost, and complexity in a conventional magnetron power combining (MPC) system. A novel method is proposed to utilize the coupling between two ports of an H-plane tee to achieve peer-to-peer injection locking magnetrons. Meanwhile, an asymmetric phase compensation is realized using a section of waveguide to adjust the magnetron output characteristics. Theoretical and numerical analyses provided qualitative insight into the system output behavior. Subsequently, an experimental system was developed for verification. In the experiments, the system achieved maximum microwave power combining efficiencies 90.2%, 93.6%, and 93.6% at electrical waveguide lengths corresponding to 90, 135, and 225, with output powers of 1650, 1260, and 1610 W, respectively, without the use of any isolators or external injection sources. The experimental results show good agreement with numerical calculations. This method offers the advantages of low cost, compact size, and low loss, providing a new approach for developing high-performance MPC systems in the future.

physics.app-ph↗

arXiv2025

Design of a High-Power and High-Efficiency GaN-HEMT VCO Based on an Inverse Class-F Amplifier

This letter proposes a high-power and high-efficiency GaN-HEMT voltage-controlled oscillator. The VCO consists of a coupled-line coupler, an inverse class-F amplifier, and a novel frequency-tunable stepped-impedance resonator. Using a harmonic control circuit and a parasitic parameter compensation circuit, the power amplifier operates in the inverse class-F state to achieve high efficiency. The feedback circuit uses a coupled-line coupler instead of the traditional coupling capacitor to control feedback power precisely. The measurement results show that the VCO with an oscillation frequency of 2.41-2.45 GHz achieves a maximum conversion efficiency of 74.5% at 2.44 GHz and an output power of 40.2 dBm. It is a candidate for the microwave source in a wireless power transmission system.

physics.app-ph↗

arXiv2025

A Novel Class-F 2.45/5.8 GHz Dual-Band Rectifier for Wireless Power Transmission

This letter proposes a high-efficiency dual-band class-F rectifier for wireless power transmission (WPT). The rectifier comprises a dual-band harmonic termination network, a dual-band matching network, a single Schottky diode, and a dc pass filter. A theoretical analysis of the harmonic termination network is performed to improve the rectifying efficiency. The network exhibits good class-F operation by controlling the second and third harmonics in dual bands. A rectifier operating at 2.45 and 5.8 GHz was designed, fabricated, and measured for validation. The measurements show maximum RF-dc conversion efficiencies of 74.9% and 61.9% with 200 and 500{\Omega} loads at 2.45 and 5.8 GHz, respectively. The proposed rectifier achieves dual-band harmonic control with high efficiency.

physics.app-ph↗

arXiv2025

A High-Efficiency Microwave Power Combining System Based on Frequency-Tuning Injection-Locked Magnetrons

To increase the power level and energy utilization rate of injection-locked magnetron sources, a dual way 1-kW S-band magnetron microwave power combining system with high combining efficiency was proposed and validated. A waveguide magic-Tee was used to achieve power combining and to provide a pathway for the reference signal. This system utilizes the power-dividing characteristic of a magic-Tee to lock two magnetrons. Frequency tuning is applied to adjust the phase difference between the two magnetrons' signals so as to achieve a high combining efficiency. Experimental results indicate that the microwave power combining efficiency of the proposed system reaches 94.5%. The attenuation of microwave power is caused only by the waveguides and magic-Tee. Our investigation provides a guideline for future high-power microwave combining systems with low losses.

physics.app-ph↗

arXiv2021

Deep Probabilistic Time Series Forecasting using Augmented Recurrent Input for Dynamic Systems

The demand of probabilistic time series forecasting has been recently raised in various dynamic system scenarios, for example, system identification and prognostic and health management of machines. To this end, we combine the advances in both deep generative models and state space model (SSM) to come up with a novel, data-driven deep probabilistic sequence model. Specifically, we follow the popular encoder-decoder generative structure to build the recurrent neural networks (RNN) assisted variational sequence model on an augmented recurrent input space, which could induce rich stochastic sequence dependency. Besides, in order to alleviate the inconsistency issue of the posterior between training and predicting as well as improving the mining of dynamic patterns, we (i) propose using a lagged hybrid output as input for the posterior at next time step, which brings training and predicting into alignment; and (ii) further devise a generalized auto-regressive strategy that encodes all the historical dependencies for the posterior. Thereafter, we first investigate the methodological characteristics of the proposed deep probabilistic sequence model on toy cases, and then comprehensively demonstrate the superiority of our model against existing deep probabilistic SSM models through extensive numerical experiments on eight system identification benchmarks from various dynamic systems. Finally, we apply our sequence model to a real-world centrifugal compressor forecasting problem, and again verify its outstanding performance by quantifying the time series predictive distribution.

cs.LG↗