Showing papers on "RF power amplifier published in 2020"

300-GHz-Band 120-Gb/s Wireless Front-End Based on InP-HEMT PAs and Mixers

Abstract: We developed a 300-GHz-band 120-Gb/s wireless transceiver front-ends (TRX) using our in-house InP-based high-electron-mobility-transistor (InP-HEMT) technology for beyond-5G. The TRX is composed of the RF power amplifiers (PAs), mixers, and local oscillation (LO) PAs which are all packaged in individual waveguide (WG) modules by using a ridge coupler for low-loss WG-to-IC transition. RF PAs are designed using the low-impedance inter-stage-matching technique to reduce the inter-stage matching loss of the amplifier stages, and the back-side DC line (BDCL) technique is used to simplify the layout and to improve the gain of the PAs. The fabricated RF PAs show a high output 1-dB compression point of more than 6 dBm from 278 to 302 GHz. The mixers are used for both up- and down-conversion in the transmitter and receiver. These mixers are designed to have high conversion gain (CG) over the wideband even after packaging by enhancing the isolation between the RF and IF ports. The measured CG of mixer module is −15 dB, and the 3-dB IF-bandwidth is 32 GHz. The LO PAs are also designed using the BDCL technique so that they can supply the required LO power to the mixers. The TRX with these InP building blocks enables the data transmission of a 120 Gb/s 16QAM signal over a link distance of 9.8 m.

Textile-Based Large Area RF-Power Harvesting System for Wearable Applications

Abstract: In this article, we demonstrate flexible and lightweight textile-integrated rectenna arrays for powering wearable electronic devices. We propose a method to exploit large clothing-areas to integrate arrays consisting of $2\times2$ and $2\times3$ rectenna elements. Each element comprises a patch antenna and a rectifier which are fabricated using embroidery of conductive thread on the textile substrates. The rectifier used single-diode circuit configuration and showed a radio frequency (RF)-to-dc conversion efficiency of 70% for an applied input RF-power of 8 dBm at its input port. We also present several tests to demonstrate the applicability of the rectenna array. Specifically, in boosted-Wi-Fi modality, a dc power of $600~\mu \text{W}$ was collected at 10 cm from the source and $80~\mu \text{W}$ was collected at 60 cm from the source. These demonstrations show the proposed system’s applicability for charging and powering low-power wearable electronic devices.

A Triple-Band High-Gain Multibeam Ambient RF Energy Harvesting System Utilizing Hybrid Combining

Abstract: Overcoming the challenge of battery recharging and replacement in industry Internet-of-Things (IoT) applications is considered by proposing the design of a triple-band high-gain multibeam ambient radio frequency (RF) energy harvesting system utilizing hybrid combining. The novelty of the design is that it simultaneously exploits frequency, space, and polarization to maximize the harvested RF energy. Wideband hybrid combining is proposed, which enables the harvesting of energy at low RF power densities while maintaining the wide frequency and space coverage necessary for ambient RF energy harvesting. The antenna design consisting of 16-ports has an average area per port of $0.3\lambda \times 0.3\lambda$ (where $\lambda$ is the freespace wavelength at 1.8 GHz) and is demonstrated to achieve a wide relative bandwidth of 38.5% covering the GSM-1800, UMTS-2100, and WiFi frequency bands. Hybrid combining of the 16-port antenna provides multiple antenna beams each with up to 11 dBi antenna gain and these provide broad beam coverage. The design for the rectifiers, using multistub impedance matching, is also provided and these are shown to be efficient over the frequency bands of interest. Measurements in an anechoic chamber demonstrate that the proposed energy harvesting system can provide an output dc voltage of more than 755 mV, an output dc power of more than $-$ 6.4 dBm and RF-to-dc efficiencies greater than 40% when the power density is more than 1400 $\mu \mathrm{W}/\mathrm{m}^{2}$ . It is also shown that the proposed system can provide output dc power of 80 $\mu \mathrm{W}$ and 7.3 $\mu \mathrm{W}$ in real outdoor and indoor ambient environments, respectively.

A Compact Source–Load Agnostic Flexible Rectenna Topology for IoT Devices

Abstract: This article presents a new compact lightweight radio frequency (RF) energy harvesting system. The system relies on a dual-tapered transmission line-based matching network that stretches the rectification capability of an integrated Schottky diode. This topology is demonstrated on a 2.4 GHz rigid harvesting system with a resulting power conversion efficiency that reaches up to 58% over 0 dBm input RF power. Its performance is compared with a reference rectifier that relies on a typical open circuit shunt-stub matching network. The rectifier along with a miniaturized monopole antenna is then tailored for a flexible substrate with a resulting efficiency around 50% at 0 dBm input power. The rectifier exhibits an almost flat efficiency over the 2.3–2.5 GHz frequency span despite wide load variations. The system is characterized in multiple bent configurations featuring high and stable performance. It is demonstrated that for different bent states, the proposed flexible harvester does not display large variations in harvested power. Thus, the presented rectenna demonstrates the remarkable combination of compactness, flexibility, and stability. Equipped with these features, such rectifier can be plugged into a variety of sensors, even on wearable surfaces, which makes it ideal for Internet of Things (IoT) applications.

Near-Field Wireless Power Transfer to Deep-Tissue Implants for Biomedical Applications

Abstract: Wireless power transfer (WPT) plays critical roles in powering deep-tissue implants, which also contributes to several emerging advances for biomedical engineering. To enable a high-power density region in implants, this article presents a method, termed the self-phasing technology, to focus electromagnetic fields from various paths at a deep-tissue spot. By performing the phase-conjugated operation on the incident signal and then retransfer back to the source, coherent RF power can be achieved without learning the precise or even dynamic locations of sources and concerning inhomogeneous medium perturbations. An external slot antenna array placed above skin surface 4 mm is considered as a transmitter and an implanted rectenna consisting of a magnetic resonant coil and an RF-to-dc rectifier circuit is treated as a receiver. The conversion efficiency of the rectifier circuit is optimized within the received power range and the measured efficiency of 50% can be achieved at 0 dBm. To visualize the transceiver effects of the integrated system under safety thresholds, a light-emitting diode (LED) is soldered at the terminal of the rectenna and measurements show that smooth drive can be achieved. Certain brightness of LED can demonstrate that the self-phasing technology can support WPT for biomedical applications.

A Sensitive Triple-Band Rectifier for Energy Harvesting Applications

Abstract: This paper presents a novel sensitive triple-band power rectifier for RF energy harvesting systems. The proposed rectifier can simultaneously harvest RF energy from GSM-900, GSM-1800, and Wi-Fi-2450 bands at relatively low and medium ambient power densities. Previously, a few multi-band rectennas have been reached a stable conversion efficiency overall frequency bands of interest because of the nonlinearity and the distinct input impedance of the rectifying circuit at these frequencies. The originality of this paper is on the improved impedance matching technique that enhances the efficiency and performance of the rectifier. The proposed high-efficiency triple-band rectifier consists of three parallel branches. Each branch comprises an input matching circuit designed to provide maximum RF power transferred to rectifying diodes, a single voltage doubler using Schottky diode HSMS-2852, and a DC-pass filter to smooth the DC output voltage. A prototype of the proposed rectifier circuit is fabricated and tested to verify its performance against the simulation results. With an optimum load resistance of 3.8 kΩ at -10 dBm input power level, the measured RF to DC conversion efficiency achieves 33.7%, 21.8%, and 20% at 0.9, 1.8 and 2.45 GHz respectively. The efficiency is above 46.5 % overall bands of interest under 0 dBm input power.

Collaboratively Harvesting Ambient Radiofrequency and Thermal Energy

Abstract: In this paper, an ambient power harvester with a single-diode device is proposed for simultaneously scavenging both radiofrequency (RF) and thermal energy in a mixed and cooperative manner. This cooperative harvesting process is theoretically examined through a proposed model of the diode and then validated by simulation and measurement. In the proposed cooperative power harvester, the harvested dc voltage from a thermal source is used to bias the diode for improving the diode's RF-to-dc power conversion efficiency (PCE). An accurate analytical model of the Schottky diode is developed for specifying the constraining parameters of RF-to-dc PCE and accurately predicting diode's performances in a low RF power range $({ \leq - \text{25}\;{\text{dBm}}})$ , respectively. The calculated results are found to be in a good agreement with the simulated ones obtained by the harmonic balance simulator in the advanced design system. For demonstration and validation, the proposed mixed cooperative power harvester is designed and prototyped on the basis of diode SMS7630. A total measured output dc power around 0.8 μ W is obtained with an RF-to-dc PCE around 33.4%, when the two injecting power sources at the diode are both −30 dBm. In addition, rectennas with and without a matching network are both fabricated and tested. By eliminating the L matching network, the rectenna is found to offer a higher dc output power. The proposed mixed cooperative power harvester is hoped to find potential real-world applications in an ambient atmosphere with RF coverage and temperature gradient. It not only helps to produce a higher power but also provides a reliable way of improving the resilience of dc power production.

Novel Drain-Connected Field Plate GaN HEMT Designs for Improved V BD – R ON Tradeoff and RF PA Performance

Abstract: TCAD studies are performed to develop physical insights into the breakdown behavior of drain-connected field plate-based GaN HEMTs. Using the developed insights, to mitigate the performance bottleneck caused by the lateral drain-connected field plate design, we have proposed novel vertical-field-plate designs. The proposed designs alleviate the channel electric field by uniformly distributing it vertically into the GaN buffer region. As a result, the proposed vertical and dual-field-plate design offer ${2} \times $ and ${3} \times $ improvements in breakdown voltage, respectively, compared with the design without field plate. Similarly, compared with a design with a lateral field plate, a 50% improvement in the breakdown voltage was seen with dual-field-plate architecture. RF power amplifier (PA) performance extracted using load-pull simulations demonstrates an improved RF PA linearity at higher drain bias, improved output power, efficiency, and PA gain for HEMTs with dual- and vertical-field-plate designs.

Directional Radiation Technique for Maximum Receiving Power in Microwave Power Transmission System

Abstract: Directional radiation (DR), a distinguishing feature of a microwave power transmission (MPT) system, suitably shapes and properly steers an intensified beam toward a specific target area. Coupling more radiated energy to the receiving aperture, DR technique benefits system efficiency and brings great flexibility, which entails further investigation. This article addresses DR realization from a system perspective. A novel architecture of MPT transmitter is proposed, which equips the system with multiple independently controlled RF power outputs and serves as a solid hardware basis for DR realization. Three DR algorithms are also introduced, providing convenient methods to obtain maximum receiving power for the receiver via software control. A 915 MHz/100 W MPT transmitter is fabricated in the lab, and an MPT verification platform is also constructed. Proposed architecture and algorithms are fully verified with experiments, which show a good performance in DR realization.

Efficient Rectifier for Wireless Power Transmission Systems

Abstract: This article describes a full-bridge rectifier and a receiving antenna array for operation within an innovative wireless power transmission (WPT) system. A high-power transmitter using circularly polarized free-space waves and based on a retrodirective antenna array technology is also employed to boost the overall received RF power at the input of the rectenna. To the best of our knowledge, the proposed rectifier circuit and active antenna configuration are the first demonstration of a high-power beam tracking system for WPT scenarios, being different from previously reported near-field coupling and other lower power harvesting schemes. The main focus of this article is the rectifier design, its bench-top measurements, and operation in such a retrodirective, self-tracking microwave system. A novel approach based on in-phase multitone input signals is also developed to improve rectifier efficiency. The rectifier size is 4.5 cm by 2 cm and can offer more than 86% and 75% RF-to-dc rectification efficiency at 27 dBm for an input signal at 1.7 and 2.4 GHz, respectively. This rectifier circuit component can also be employed in other communication applications or WPT systems, for example, to convert to dc received RF signals or power in the radiating near- and far-field in order to wirelessly charge the batteries of home electronics, such as smartphones, tablets, or Internet of Things (IoT) devices.

Proposition of deposition and bias conditions for optimal signal-to-noise-ratio in resistor- and FET-type gas sensors.

Abstract: In the field of gas sensor studies, most researchers are focusing on improving the response of the sensors to detect a low concentration of gas. However, factors that make a large response, such as abundant or strong adsorption sites, also work as a source of noise, resulting in a trade-off between response and noise. Thus, the response alone cannot fully evaluate the performance of sensors, and the signal-to-noise-ratio (SNR) should additionally be considered to design gas sensors with optimal performance. In this regard, thin-film-type sensing materials are good candidates thanks to their moderate response and noise level. In this paper, we investigate the effects of radio frequency (RF) sputtering power for deposition of sensing materials on the SNR of resistor- and field-effect transistor (FET)-type gas sensors fabricated on the same Si wafer. In the case of resistor-type gas sensors, the deposition conditions that improve the response also worsen the noise either by increasing the scattering at the bulk or damaging the interface of the sensing material. Among resistor-type gas sensors with sensing materials deposited with different RF powers, a sensor with low noise shows the largest SNR despite its small response. However, the noise of FET-type gas sensors is not affected by changes in RF power and thus there is no trade-off between response and noise. The results reveal different noise sources depending on the deposition conditions of the sensing material, and provide design guidelines for resistor- and FET-type gas sensors considering noise for optimal performance.

Circularly Polarized Retrodirective Antenna Array for Wireless Power Transmission

Abstract: A retrodirective antenna (RDA) array for wireless power transmission (WPT) is presented. Applications include the wireless charging of mobile phones and other handheld devices. The reported RDA defines an active high-power transmitter module that retrodirects a received beacon tone back to a mobile unit by circularly polarized (CP) free-space radiation. In addition, this RDA architecture uses a network of four subarrays, defined by a total of 16 radiating patch elements, in an effort to boost the transmit gain while also reducing the supporting RF hardware requirements when compared to a more conventional RDA. Measurements and simulations in the reactive near-field of the system are in agreement in terms of the tracking capabilities of the high-power CP-RDA. Power levels in excess of 27 dBm were measured at 2.4 GHz at a receiver module, and when this RF power was rectified, more than 350 mW at dc was observed. To the best knowledge of the authors, this is the first demonstration of a WPT system using a mixer-based analog RDA. Previous low-power demonstrations were more complex computer-controlled systems that did not offer any real-time tracking ability. Other applications for the proposed RDA include target tracking, sensor charging, and other WPT systems.

High Efficiency Power Amplifier for IoT Applications: RF Path

Abstract: IoT devices must remain operational for 10 years with one set of batteries. Most power is typically consumed by an RF power amplifier, which is necessary for transmitting data over a wireless radio channel in 5G networks. For this reason, the task of increasing the efficiency of an RF power amplifier is relevant. High efficiency can be achieved by using active element switching modes in combination with “synthetic” amplification methods. This article analyzes the energy characteristics of a Class D switching power amplifier with a filter for two configurations: voltage mode and current mode for various transistor saturation times (Duty Ratio). Based on the analysis of time diagrams, integral equations are written, the solution of which allows us to derive calculation formulas. The results of calculations are presented. It is shown that the mode of working with meanders is most advantageous, while the VMCD circuit should work at τsat≤π, and in the CMCD circuit should work at τsat≥π.

11.7 A Voltage-Tolerant Three-Level Buck-Boost DC-DC Converter with Continuous Transfer Current and Flying Capacitor Soft Charger Achieving 96.8% Power Efficiency and 0.87µs/V DVS Rate

Abstract: In recent years, buck-boost converters have been widely utilized for battery-powered mobile systems such as RF power amplifiers, battery chargers, and LED drivers. However, in a wide battery voltage range, they face challenges including dynamic voltage scaling (DVS), wide load current range, and dynamic line/load transients while ensuring reliability for an industrial usage. To resolve these issues, the conventional buck-boost (CBB) converter should overcome the characteristic of discontinuity in the output transfer current (OTC) which causes degradation of loop dynamics and transient response. Several past works with continuous OTC have been proposed to resolve these problems, but their voltage conversion ratios are limited [1], [2]. Moreover, in [3], [4], a high-voltage (HV) process, which necessitates large active area and incurs high fabrication cost, is required to withstand voltage stresses over 10V (2×V IN ) applied across power switches. To overcome the above challenges, this paper proposes a voltage-tolerant three-level buck-boost (TLBB) converter. The TLBB has continuous OTC and uses only normal 5V CMOS devices for its switches. In addition, a voltage-tolerant dual channel-interleaved three-level buck-boost (DTLBB) converter is suggested for applications [5] requiring a wide range of load current and high conversion ratio while supporting fast DVS transition.

A Thermal/RF Hybrid Energy Harvesting System With Rectifying-Combination and Improved Fractional-OCV MPPT Method

Abstract: This paper presents a thermal/RF hybrid energy harvester. The energy harvesting system can scavenge energy from a thermoelectric generator (TEG) and a radio-frequency (RF) energy source simultaneously, and deliver the combined power to a single load. Two techniques are employed in the system to increase the end-to-end efficiency; the rectifying-combination technique is proposed to eliminate the power loss associated with a dedicated AC-DC converter before the combiner and an improved fractional open-circuit voltage (FOCV) maximum power tracking (MPPT) is considered for a high average efficiency. A dynamic power path control extracts the maximum RF power from a cross-coupled differential rectifier, and also behaves as an AC/DC energy combiner. The thermal/RF harvester system achieves a measured peak end-to-end power conversion efficiency (PCE) of 63.4%. The shorter sampling time of 26ms every 16s for the proposed FOCV MPPT method reduces the long charging tail required to refresh the sampling capacitor, resulting in a an improved average efficiency of 82.2% for the thermal harvester. Fabricated in 0.18 $\mu \text{m}$ CMOS technology, the prototype operates at a thermal input voltage ranging from 40 mV to 400 mV and an RF power from −18 dBm to −3 dBm and delivers an output voltage of 1.8 V. The total area of the fabricated circuit prototype is 1.22 mm2.

Impact of Input Nonlinearity on Efficiency, Power, and Linearity Performance of GaN RF Power Amplifiers

Abstract: The impact of input nonlinearity due to the nonlinear C GS - $V$ GS profile on load harmonic tuned power amplifier (PA) performance is qualitatively discussed. It is experimentally validated by pulsed vector load pull measurements that both Class B and Class F PA operation are quite sensitive to the source second harmonic (Z 2S ) termination with an efficiency delta of ∼40%. In contrast, Class F−l PA shows relatively robust performance with an efficiency delta of ∼10% versus Z 2S terminations. Thus, we identify the ‘good’ and ‘bad’ design space of Z 2S terminations on the Smith chart for load harmonic tuned PA classes. In addition, this paper identifies a design space continuum for Z 2S terminations other than a short for Class F−l PA which results in consistent efficiency, output power, and improved linearity.

Multi-Phase Three-Level Buck Converter with Current Self-Balancing for High Bandwidth Envelope Tracking Power Supply

Abstract: Envelope Tracking (ET) is a power supply modulation technique for a radio frequency power amplifier (RFPA), primarily employed to improve its efficiency This paper presents the design and performance analysis of a two-phase three–level buck converter, then compares it with its two-level counterpart for ET power supply application Gallium Nitride (GaN) MOSFETs switching at 25 MHz are selected as power stage devices and Zero Voltage Switching (ZVS) technique is used for better efficiency A fourth-order ZVS - low pass filter (LPF) is designed to track a 20 MHz large bandwidth envelope signal and also to maintain the current self-balancing in the multi–phase converter system The efficiency of the proposed design peaks 975 % at 115 W and has an average efficiency of 945 % at 26 W Simulation results evince precise tracking of 20 MHz, 4G LTE envelope signal with 10 dB Peak-to-Average Power Ratio (PAPR) Performance analysis indicates that the three-level option has improved average power efficiency for higher bandwidth ET applications

Wireless Power Transfer System for Battery-Less Sensor Nodes

Abstract: For the first time, the design and implementation of a fully-integrated wireless information and power transfer system, operating at 24 GHz and enabling battery-less sensor nodes, is presented in this paper. The system consists of an RF power source, a receiver antenna array, a rectifier, and a battery-less sensor node which communicates via backscatter modulation at 868 MHz. The rectifier circuits use commercially available Schottky diodes to convert the RF power to DC with a measured efficiency of up to 35%, an improvement of ten percentage points compared with previously reported results. The rectifiers and the receive antenna arrays were jointly designed and optimised, thereby reducing the overall circuit size. The battery-less sensor transmitted data to a base station realised as a GNU Radio flow running on a bladeRF Software Defined Radio module. The whole system was tested in free-space in laboratory conditions and was capable of providing sufficient energy to the sensor node in order to enable operation and wireless communication at a distance of 0.15 metres.

High-speed graded-channel AlGaN/GaN HEMTs with power added efficiency >70% at 30 GHz

Abstract: The authors report on highly scaled 60 nm gate length graded-channel AlGaN/GaN high electron mobility transistors (HEMTs) with a record power added efficiency (PAE) of 75% at 2.1 W/mm power density at Vdd = 10 V and the PAE of 65% at 3.0 W/mm power density at 30 GHz at Vdd = 14 V. Under two-tone power measurement, the graded-channel AlGaN/GaN HEMTs demonstrated similar power performance with peak PAE >70% at 30 GHz. This novel channel design shows great promise for high-efficiency millimetre-wave (mmW) power amplifiers up to 3 W/mm RF power density operation.

On-Demand Real-Time Optimizable Dynamic Model Sizing for Digital Predistortion of Broadband RF Power Amplifiers

Abstract: In this article, we present a dynamic model sizing approach for digital predistortion (DPD) of broadband radio-frequency power amplifiers. By employing a novel model structure adaptation algorithm, the DPD model structure can be adaptively adjusted during its real-time deployment to keep the optimum size and complexity under different operation conditions. Power consumption of DPD can be reduced by on-demand automatic model structure adaptation instead of reusing the same model structure for all power levels and band allocations. To realize dynamic model sizing, the adaptation algorithm explores new potential terms based on prior knowledge of the model structure and prunes the DPD model with a stepwise backward regression method. Experimental results show that the algorithm can quickly find the optimum model structure when the operation condition changes. During the adaptation, it can also maintain robust linearization performance with a relatively low computational complexity and thus demonstrates itself as a suitable solution to the linearization of future broadband wireless systems.

Toward high voltage radio frequency devices in β-Ga2O3

Abstract: The path to achieving integrated RF and power conversion circuitry using the β-Ga2O3 material system is described with regard to the materials high Johnson's RF figure of merit. Recent results, including large signal data at VD = 50 V, are provided, showing progress in achieving high-voltage RF operation. Additionally, progress in achieving high-gain devices through gate length scaling is also benchmarked by a record RF power device with a gate length of 0.5 μm achieving a 2.1 GHz μm f T − L G product. These results are compared with state-of-the-art RF devices, and the expectations for β-Ga2O3 at this point in its maturity throughout this Letter with future milestones laid out to measure progress. The conclusion includes near- and long-term projections for β-Ga2O3 devices for RF based on the results and projected milestones presented.

NB-IoT and GNSS All-In-One System-On-Chip Integrating RF Transceiver, 23-dBm CMOS Power Amplifier, Power Management Unit, and Clock Management System for Low Cost Solution

Abstract: This article presents a fully integrated stand-alone narrowband Internet-of-Things (NB-IoT) and global navigation satellite system (GNSS) system-on-chip (SoC). It aims for an all-in-one system to integrate all necessary blocks such as an RF transceiver, a power management system (PMIP), and a clock management system and to save a bills-of-material (BOM) cost. An RF transceiver is integrated to support multi-band cellular IoT and GNSS with a CMOS RF power amplifier transmitting 23-dBm output power. A PMIP, including bucks, a boost, and low-dropout regulators (LDOs), is integrated to support coin cell or AAA battery and to support a wide input supply voltage range from 2.5 to 5 V. In addition, clock management system is embedded with a digitally controlled crystal oscillator (DCXO), a relaxation oscillator (RCO), and temperature sensor units (TSUs). It is fabricated in a standard 28-nm CMOS process and its size is 24.6 mm2. The power consumption of always-on-block is 15 $\mu \text{W}$ , and the sleep current consumption is less than 10 $\mu \text{A}$ at 3.8 V.

Beamforming Optimization for MIMO Wireless Power Transfer with Nonlinear Energy Harvesting: RF Combining versus DC Combining

Abstract: In this paper, we study the multiple-input and multiple-output (MIMO) wireless power transfer (WPT) system so as to enhance the output DC power of the rectennas. To that end, we revisit the rectenna nonlinearity considering multiple receive antennas. Two combining schemes for multiple rectennas at the receiver, DC and RF combinings, are modeled and analyzed. For DC combining, we optimize the transmit beamforming, adaptive to the channel state information (CSI), so as to maximize the total output DC power. For RF combining, we compute a closed-form solution of the optimal transmit and receive beamforming. In addition, we propose a practical RF combining circuit using RF phase shifter and RF power combiner and also optimize the analog receive beamforming adaptive to CSI. We also analytically derive the scaling laws of the output DC power as a function of the number of transmit and receive antennas. Those scaling laws confirm the benefits of using multiple antennas at the transmitter or receiver. They also highlight that RF combining significantly outperforms DC combining since it leverages the rectenna nonlinearity more efficiently. Two types of performance evaluations, based on the nonlinear rectenna model and based on realistic and accurate rectenna circuit simulations, are provided. The evaluations demonstrate that the output DC power can be linearly increased by using multiple rectennas at the receiver and that the relative gain of RF combining versus DC combining in terms of the output DC power level is very significant, of the order of 240% in a one-transmit antenna ten-receive antenna setup.

Vector Decomposed Long Short-Term Memory Model for Behavioral Modeling and Digital Predistortion for Wideband RF Power Amplifiers

Abstract: This paper proposes two novel vector decomposed neural network models for behavioral modeling and digital predistortion (DPD) of radio-frequency (RF) power amplifiers (PAs): vector decomposed long short-term memory (VDLSTM) model and simplified vector decomposed long short-term memory (SVDLSTM) model. The proposed VDLSTM model is a variant of the classic long short-term memory (LSTM) model that can model long-term memory effects. To comply with the physical mechanism of RF PAs, VDLSTM model only conducts nonlinear operations on the magnitudes of the input signals, while the phase information is recovered by linear weighting operations on the output of the LSTM cell. Furthermore, this study modifies the LSTM cell by adding phase recovery operations inside the cell and replacing the original hidden state with the output magnitudes that are recovered with phase information. With the modified LSTM cell, a low-complexity SVDLSTM model is proposed. The experiment results show that the proposed VDLSTM model can achieve better linearization performance compared with the state-of-the-art models when linearizing PAs with wideband inputs. Besides, in wideband scenarios, SVDLSTM model with much fewer parameters can present comparable linearzation performance compared to VDLSTM model.

Simons Observatory Microwave SQUID Multiplexing Readout: Cryogenic RF Amplifier and Coaxial Chain Design

Abstract: The Simons Observatory (SO) is an upcoming polarization-sensitive cosmic microwave background experiment on the Cerro Toco Plateau (Chile) with large overlap with other optical and infrared surveys (e.g., DESI, LSST, HSC). To enable the readout of $${\mathcal {O}}$$(10,000) detectors in each of the four telescopes of SO, we will employ the microwave SQUID multiplexing technology. With a targeted multiplexing factor of $${\mathcal {O}}$$(1000), microwave SQUID multiplexing has never been deployed on the scale needed for SO. Here we present the design of the cryogenic coaxial cable and RF component chain that connects room temperature readout electronics to superconducting resonators that are coupled to transition edge sensor bolometers operating at sub-Kelvin temperatures. We describe design considerations including cryogenic RF component selection, system linearity, noise, and thermal power dissipation.

A Photonic-Based Wideband RF Self-Interference Cancellation Approach With Fiber Dispersion Immunity

Abstract: A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity is proposed. A dual-drive Mach–Zehnder modulator (DD-MZM) in a dual-polarization binary phase-shift keying (DP-BPSK) modulator is used as an optical interference canceller, which cancels the self-interference from the received signal and generates two optical sidebands of the signal of interest (SOI) in the received signal. Another DD-MZM in the DP-BPSK modulator is used to provide a pure optical carrier. By combing the optical signals from the two DD-MZMs and beating them at a photodetector, the SOI can be recovered. In addition, if the SOI needs to be transmitted in optical fiber, the power fading effect caused by fiber dispersion can be overcome by simply introducing a proper phase shift to the pure optical carrier. An experiment is performed. RF self-interference cancellation (SIC) with a bandwidth up to 2 GHz is experimentally demonstrated and a cancellation depth of more than 20 dB is achieved even if the bandwidth of the self-interference is about 2 GHz. The SIC with 25-km fiber transmission and the RF power of the SOI after 25-km fiber transmission are also demonstrated, which proves that the SIC has very good immunity to fiber dispersion and the SOI can be transmitted without power fading.

Development of fundamental power couplers for 166.6 MHz superconducting quarter-wave beta = 1 proof-of-principle cavities.

Abstract: Superconducting 166.6 MHz β = 1 cavities of quarter-wave geometry have been chosen for a high energy photon source, a 6 GeV diffraction-limited synchrotron light source currently under construction in Beijing. Five cavities will provide the required 5.4 MV radio frequency (rf) voltage and 900 kW beam power. Each cavity will be equipped with one fundamental power coupler (FPC), delivering a minimum rf power of 180 kW to the beam. A 50 Ω coaxial structure with one planar warm window was employed. Its location was carefully selected to avoid electron bombardments on the ceramic window due to potential cavity field emission while preserving the required strong coupling. Focusing on optimized heat loads, a compact geometry was pursued to allow assembly with the cavity in a class 10 clean room, thus minimizing contamination. Two prototype FPCs have been fabricated and examined with high power on room-temperature test stands. The couplers were tested up to 50 kW continuous wave (cw) limited by the available solid-state amplifier. The rf conditioning was conducted initially in travelling-wave mode and later in a standing-wave setup with the variable phase of the reverse wave. All rf surfaces were thus exposed to a high field equivalent to 200 kW cw traveling wave. Being the most critical component, the window-inner-conductor assembly was conditioned up to 150 kW at 650 MHz on a hybrid test stand. Multipacting barriers were encountered as predicted and can be processed by rf conditioning. The design, fabrication, and high-power tests of the first 166.6 MHz FPCs are presented.

Solving the Time- and Frequency-Multiplexed Problem of Constrained Radiofrequency Induced Hyperthermia.

Abstract: Targeted radiofrequency (RF) heating induced hyperthermia has a wide range of applications, ranging from adjunct anti-cancer treatment to localized release of drugs. Focal RF heating is usually approached using time-consuming nonconvex optimization procedures or approximations, which significantly hampers its application. To address this limitation, this work presents an algorithm that recasts the problem as a semidefinite program and quickly solves it to global optimality, even for very large (human voxel) models. The target region and a desired RF power deposition pattern as well as constraints can be freely defined on a voxel level, and the optimum application RF frequencies and time-multiplexed RF excitations are automatically determined. 2D and 3D example applications conducted for test objects containing pure water (rtarget = 19 mm, frequency range: 500–2000 MHz) and for human brain models including brain tumors of various size (r1 = 20 mm, r2 = 30 mm, frequency range 100–1000 MHz) and locations (center, off-center, disjoint) demonstrate the applicability and capabilities of the proposed approach. Due to its high performance, the algorithm can solve typical clinical problems in a few seconds, making the presented approach ideally suited for interactive hyperthermia treatment planning, thermal dose and safety management, and the design, rapid evaluation, and comparison of RF applicator configurations.

Sampling Rate Reduction for Digital Predistortion of Broadband RF Power Amplifiers

Abstract: In this article, we present a novel technique to build digital predistorters that can linearize broadband power amplifiers (PAs) using reduced sampling rates. In contrast to conventional digital predistortion (DPD) where oversampling is necessary to avoid aliasing effect, the proposed method cancels the aliasing distortion using a sliced multistage cancellation scheme. A large reduction of sampling rate can be achieved in digital implementation of DPD, significantly reducing power consumption and implementation cost. Experimental results show that a DPD with a sampling rate of merely $1.5\times $ , instead of $5 \times $ , signal bandwidth, can still produce satisfactory performance within the linearization bandwidth but consume only one-third of power, compared with that using the conventional approaches. The proposed technique provides a promising solution for the next-generation 5G systems, where large signal bandwidths are required.

Rectifiers’ Design and Optimization for a Dual-Channel RF Energy Harvester

Abstract: This paper presents the design and implementation of two front-ends for RF (Radio Frequency) energy harvesting, comparing them with the commercial one—P2110 by Powercast Co. (Pittsburgh, PA, USA) Both devices are implemented on a discrete element board with microstrip lines combined with lumped elements and are optimized for two different input power levels (−10 dBm and 10 dBm, respectively), at the GSM900 frequencies. The load has been fixed at 5kΩ, after a load-pull analysis on systems. The rectifiers stages implement two different Schottky diodes in two different topologies: a single diode and a 2-stage Dickson’s charge pump. The second one is compared with the P2110 by generating RF fields at 915 MHz with the Powercast Powerspot. The main aim of this work is to design simple and efficient low-cost devices, which can be used as a power supply for low-power autonomous sensors, with better performances than the current solutions of state-of-the-art equipment, providing an acceptable voltage level on the load. Measurements have been conducted for input power range −20 dBm up to 10 dBm; the best power conversion efficiency (PCE) is obtained with the second design, which reaches a value of 70% at 915 MHz. In particular, the proposed device exhibited better performance compared to the P2110 commercial device, allowing a maximum distance of operation of up to 22 meters from the dedicated RF power source, making it suitable even for IoT (Internet of Things) applications.