RF Output Power Research Articles

Performance enhancement of frequency-doubling gyroklystron amplifier by magnetic field tapering

A uniform magnetic field across the device is often used to analyze gyroklystron. In this paper, a tapered magnetic field is applied across the two-cavity 35 GHz frequency-doubling gyroklystron to improve its performance. Device performance is compared between tapered and uniform magnetic field cases using particle-in-cell code “CST.” The result confirms that the tapered magnetic field significantly improves the device performance parameters such as output power, efficiency, gain, and bandwidth compared to uniform magnetic field conditions. With a 1.6-kW driver power, 306 kW RF output power along with 22.8 dB gain is achieved for a tapered magnetic field case, while 227 kW RF output power along with 21.5 dB gain is achieved for a uniform magnetic field case. When the magnetic field is uniform, the efficiency and bandwidth of a gyroklystron are approximately 21.6% and 100 MHz, respectively; however, for the tapered magnetic field, it can rise to 29.1% and 120 MHz, respectively. Device efficiency results suggest that a tapered magnetic field improves energy transfer from the electron beam to the RF field. A parametric study for both magnetic field cases examines the effect of magnetic field strength, beam current, beam voltage, and pitch factor on the device. This detailed research recommends optimizing frequency-doubling gyroklystron performance with tapered magnetic fields.

Design and simulation of a Ka-band frequency doubling gyroklystron amplifier

The design methodology of a Ka-band frequency doubling two cavity gyroklystron has been discussed in this paper. In this study, the amplifier’s design and simulation are accomplished by employing nonlinear analysis and validated using particle-in-cell simulation techniques. The output cavity functions in the TE02 mode at two times the input signal frequency at the second harmonic of the cyclotron frequency, while the input cavity is powered by a 17.5 GHz source and functions in the TE01 mode at the first harmonic of the cyclotron resonance. The device’s performance has been examined both in the presence and in the absence of a beam. A number of factors were taken into account in order to optimize the interaction structure dimension to reach the device’s targeted performance. By adjusting the structural features and electron beam parameters, the device’s RF output power is assessed in an effort to increase efficiency. Simulation results estimate that the device displays a gain of 21.5 dB, an efficiency of 21.6%, a power of 227 kW, and a −3 dB bandwidth of ∼0.3%.

Design of a dual-mode transverse deflecting structure using neural network and multiobjective algorithms

Shanghai Synchrotron Radiation Facility/Shanghai Soft X-ray FEL Facility is currently developing an advanced variable polarization transverse deflecting structure TTDS (two-mode transverse deflecting structure) using a dual-mode rf structure concept. Driven by two different rf power sources, this novel TDS works using both the HEM11 and HEM12 modes for simultaneous vertical and horizontal deflections, consequently, it can provide a time-varying polarization of the electrical field at ultrafast speeds. It is capable of producing circular and elliptical polarizations as well as flexible vector combinations through amplitude and phase modulation from a low-level rf system. The work presented in this paper is focused on the analysis and design of the variable polarization TDS, consisting of dual-mode cells and two dual-mode couplers. Designing and optimizing for dual-mode design and optimization is complex; consequently, an advanced optimization procedure based on neural networks and multiobjective algorithms has been developed. This improves the accuracy and efficiency of the rf structure design process. Through iterations, the dual-mode cells in the final design are optimized for high impedance and other rf performance criteria for both the HEM11 and HEM12 modes. The two couplers for rf power input and output are also optimized. Based on the optimized design and rf sensitivity analysis, the mechanical design has been completed and is now ready for manufacture. Published by the American Physical Society 2024

Modified Uni-Traveling-Carrier Photodetector with Its Optimized Cliff Layer.

We have designed the MUTC-PD with an optimized thickness of cliff layer to pre-distort the electric field at the front side of the collection layer. With the optimized MUTC-PD design, the collapse of the electric field will be greatly suppressed, and the electrons in its collection layer will gradually reach their peak velocity with the growing incident light power. Moreover, as the incident light intensity increases, the differential capacitance also declines, thus the total bandwidth grows. It will make the MUTC-PD achieve high-speed and high-power response performance simultaneously. Based on simulation, for 16μm MUTC-PD with a 70 nm cliff layer, the maximum 3 dB bandwidth at -5 V is 137 GHz, compared with 64 GHz for the MUTC-PD with a 30 nm cliff layer. The saturation RF output power is 27.4 dBm at 60 GHz.

Performance improvement studies of axially partitioned dual band magnetically insulated line oscillator

In magnetically insulated line oscillator (MILO)s, a proportion of device current is responsible for the self-generated magnetic field that aids electron flow confinement in the anode cathode gap, thereby suitable RF generation. The device currents should not be high due to its direct impact on device efficiency, and electron energy depositions at load can lead to anode plasma formation. Also, the lower currents can facilitate the device to operate at larger voltages and/or for longer operational times. In this article, couple of axially partitioned dual band MILOs (DBMILO) designs that operate at lower device currents in comparison with the existing axially partitioned DBMILOs in the literature is presented. For one design with the radius of the slow wave structure (SWS), i.e., RSWS = 40 mm, the injection of the DC electron beam parameters 505 kV and 49 kA, generated an output RF power of ∼5.8 GW oscillating at 3.71 and 10.16 GHz (S-and X- bands) concurrently with ∼23.8% conversion efficiency. However, the other design (RSWS = 40.6 mm) at beam voltage 505 kV and device current of 47 kA generated an output RF power of >3.85 GW oscillating at 3.5 and 10.5 GHz, concurrently, where the frequencies are harmonically related. Thus, the proposed designs yielded significant device current reduction to ∼47 and ∼49 kA from ∼56 kA (existed), respectively, thereby drop of 16% and 12.5% to its counter designs, respectively. Also, there is substantial reduction in the electron energy depositions, thus the occurrence of anode plasma formations. Moreover, the peak conversion efficiency is enhanced to 23.4% and 16.4%, from 12.8%.

Electrical feedback system for enhancing the RF power of photodetector.

In this paper, we propose a system for enhancing the RF output power of the photodetector, especially the power of fundamental tune and second-order harmonic, by feeding back part of the RF signal through an electrical feedback circuit. As a result of bias modulation and opto-electric mixing, the RF output power can be effectively enhanced. The structure of uni-traveling carrier photodetector (UTC-PD) is employed in this work. With the RF enhancement system, the power of fundamental tune and second-order harmonic improve by 6.4 dB and 9.9 dB respectively, under the condition of 26 dBm input optical power, 3 V bias voltage, and 14 GHz input optical signal. Further, it was observed that third-order harmonic appeared under the influence of this system.

Design of Novel Photodetector Array in Optical Communication Systems and Optimization of Signal Processing Algorithm

This study aims to enhance the high-speed and high-power performance of photodetectors, focusing on the epitaxial layer structure of photodetector arrays. The epitaxial structure of the photodetector involves a P–I–N structure with InAlAs/InGaAs heterostructures. InAlAs is used as the P-region material, and a dual-waveguide photodetector array is designed with a core diameter of 20 μm. The optical coupling is achieved through normal incident vertical illumination. Additionally, a novel structure of a dual-core symmetrically connected photodetector array is proposed, altering the electrode structure and core arrangement to maintain consistent distances for the output signals from the cores to the device’s output terminal. In order to address the issue of minimum bit error rate in optical communication systems under conditions of optical noise and limited energy efficiency of received optical signals, a photodetector array signal processing algorithm is proposed. The experimentally designed dual-core symmetrically connected P–I–N photodetector array achieves a 3 dB bandwidth of 15.37 GHz at an average photocurrent of 5 mA. Furthermore, it maintains a 3 dB bandwidth of 11.67 GHz at a high-power operating state of 50 mA, with an alternating current (AC) saturation current of 56 mA and a saturated RF output power of 1.11 dBm at 11.67 GHz. In comparison, the improved dual-core traveling-wave photodetector array at 11.67 GHz only achieves an AC saturation current of 38 mA and a saturated RF output power of 2.66 dBm. The signal processing algorithm for the selected dual-core symmetrically connected P–I–N photodetector array demonstrates that employing a method of merging array elements reduces the system’s computational complexity with minimal impact on the system’s power consumption.

High-Efficiency Industrial 130 kW cw Solid-State RF Amplifier for 1.3 GHz

A new 1.3 GHz solid-state high-power RF amplifier (SSA) has been built for the Lighthouse project in close cooperation between Cryoelectra and RI Research Instruments. The amplifier was developed by Cryoelectra as a scalable compact system with an RF-power density of 40kW/m2. Its industrial design is very reliable and easy to maintain. The SSA delivers a continuous RF output power of more than 130 kW with a wall-plug efficiency of 63% and with very low phase noise. The power is generated by 40 patented RF amplifier modules each containing 8 GaN transistor units. Their outputs are combined by a coaxial 8-way combiner in the center of the module. Each module is connected to the 4x9-way cable-free waveguide combiner network and can be exchanged in the event of fault within minutes thanks to quick connectors. A sophisticated control system continuously monitors the state of all components for reliable machine and personnel protection.Despite all the challenges encountered during development and production, the SSA was built and handed over to the client in the shortest possible time. It passed the acceptance test on site exceptionally well.

Commissioning of MW class Gyrotron Test Facility at ITER-India & Demonstration of ITER relevant RF performance (1MW for 1000 s at 170 GHz)

ITER-India, as a part of its in-kind commitments to ITER project, has a mandate to deliver two “Gyrotron” based RF Source sets with state-of-the-art specifications (170 GHz, 1MW, 1000 s), for ECRH (Electron Cyclotron Resonance Heating) applications. With an aim to bench mark the integrated system performance, a MW class Gyrotron Test Facility has been developed at ITER-India under Phase-1 of the project execution plan. The facility has been developed with all necessary auxiliary systems and services such as the Low Voltage and High Voltage Power Supplies; Control, Protection and Monitoring Systems; RF Diagnostic Systems; Cooling and Vacuum Services etc. Further, a test Gyrotron with ITER relevant specifications (1MW, 170 GHz, 1000s) along with a set of dummy loads and waveguide components have been procured from M/s. Gycom, Russia, and fully integrated with the test facility. Detailed Site Acceptance Tests of the Test Gyrotron have been conducted at the newly developed ITER-India Gyrotron Test Facility (IIGTF). An output RF power of 1MW at 170 GHz for 1000 s with RF efficiency of about 50% has been successfully demonstrated during these tests there by validating the ITER relevant performance

Fabrication of UTC PDs Having High RF Power Output Efficiency

Fabrication of UTC PDs Having High RF Power Output Efficiency

Enhanced bandwidth of a lateral-pin Ge/Si avalanche photodiode using inductive gain peaking

Lateral-pin germanium silicon avalanche photodiodes (APDs) offer great potential for improving performance, cost-effectiveness, and versatile production processes for large-capacity data communication applications. However, excessive avalanche multiplication noise limits the increase in bandwidth. In this study, we propose and design the integrated peaking inductors to enhance the bandwidth of a lateral pin Ge/Si APD without compromising the direct current (DC) characteristics. By introducing the spiral inductor to counteract the capacitive effect of APD, the RF output power at high frequency can be effectively increased, thus improving the photodiode bandwidth. The impact of different sizes of inductors and APDs on the performance was experimentally investigated. The resulting APDs, with Ge lengths of 20μm (Ge20) and 45μm (Ge45), provided low dark currents of 11 nA and 27 nA, and primary responsivities of 0.85 A/W and 1.05 A/W at −1 V, respectively. A small inductor (375 pH) exhibited greater bandwidth enhancement than a large inductor (622 pH) and the Ge20 APD achieved a bandwidth of up to 78 GHz. For the larger Ge45 APD, the bandwidth was maintained above 50 GHz, even close to the breakdown voltage, and a high gain-bandwidth product of up to 609 GHz was calculated by an avalanche multiplication gain of 11.7. This result may provide ideas for balancing the speed and sensitivity of lateral-pin APDs used in high-speed optical communications.

Velocity selective spin labeling using parallel transmission.

Ultra-high field (UHF) provides improved SNR which greatly benefits SNR starved imaging techniques such as perfusion imaging. However, transmit field (B1 + ) inhomogeneities commonly observed at UHF hinders the excitation uniformity. Here we show how replacing standard excitation pulses with parallel transmit pulses can improve efficiency of velocity selective labeling. The standard tip-down and tip-up excitation pulses found in a velocity selective preparation module were replaced with tailored non-selective kT -points pulse solutions. Bloch simulations and experimental validation on a custom-built flow phantom and in vivo was performed to evaluate different pulse configurations in circularly polarized mode (CP-mode) and parallel transmit (pTx) mode. Tailored pTx pulses significantly improved velocity selective labeling fidelity and signal uniformity. The transverse magnetization normalized RMS error was reduced from 0.489 to 0.047 when compared to standard rectangular pulses played in CP-mode. Simulations showed that manipulation of time symmetry in the tailored pTx pulses is vital in minimizing residual magnetization. In addition, in vivo experiments achieved a 44% lower RF power output and a shorter pulse duration when compared to using adiabatic pulses in CP-mode. Using tailored pTx pulses for excitation within a velocity selective labeling preparation mitigated transmit field artifacts and improved SNR and contrast fidelity. The improvement in labeling efficiency highlights the potential of using pTx to improve robustness and accessibility of flow-based sequences such as velocity selective spin labeling at ultra-high field.

Thermal dissipation enhancement in flip-chip bonded uni-traveling carrier photodiodes.

The thermal properties of modified uni-traveling carrier (MUTC) photodiode flip-chip bonded to AlN and diamond are simulated. The thermal impedance of InGaAs is the primary source of internal heating. An n-down epitaxial structure is designed to improve thermal dissipation. Compared to the conventional p-down configuration, the n-down MUTCs bonded to diamond, or AlN submounts achieved 145% and 110% improvement in dissipated power density at thermal failure, respectively. The improved thermal characteristics presage higher RF output power before thermal failure.

6G energy‐efficient systems based on arrays combined with dielectric lenses

AbstractIt is demonstrated that combining phased array antennas with dielectric lenses constitutes a suitable solution to increase the energy efficiency in next‐generation communication systems. A dielectric lens is designed to increase the gain of an array antenna working in the 3GPP n257 band (26.5–29.5 GHz). The simulated results demonstrate that the dielectric lens increases the gain between 0.4 and 1.3 dB in a large scanning range from 0° to 60° at 28 GHz; meaning that the output RF power can be decreased by up to 26% for a same equivalent isotropic radiated power required from the base station.

Microwave wireless power transfer system using a dual-dielectric resonator oscillator

Non-radiating wireless power transfer (WPT) systems have found extensive applications in science and technology. This paper reports the design, simulation, and implementation of a compact single-port (DC to RF) WPT system composed of two coupled dielectric resonators (DR). The DR on the transmitter side, in combination with a transistor amplifier and a series feedback circuit, forms a dielectric resonator oscillator for microwave power generation. The DR on the receiver side is coupled to the transmitter DR such that the circuit can be considered as a dual-dielectric resonator oscillator or DDRO. The DDRO is designed for optimum power transfer to the output port. The measured RF output power of the proposed WPT system at 7.5 GHz for a 10 mm spacing between the transmitting and receiving DR is measured to be 13.07dBm at a DC voltage of 3.3 V and a supply current of 32.3 mA, which shows a good agreement with our proposed method of analysis. The available bandwidth at the operating frequency of 7.5 GHz is measured to be 150 MHz which provide a relatively wide bandwidth for simultaneous data transmission.

A Compact Repetitive Marx Generator for Generating Intense Electron Beams for HPM Sources

A 500 kV, 80 Hz repetition rate compact Marx generator has been designed and developed for producing high intense relativistic electron beams for high-power microwave (HPM) sources. This Marx generator comprises eight bipolar stages (16 stages of unipolar) using energy storage capacitors for achieving improved performance in repetition mode operation. The maximum charging voltage per stage is 50 kV, producing an erected voltage of 800 kV. However, the load voltage will vary according to the impedance of the load connected across the generator. Custom-designed energy storage capacitors were developed to allow voltage reversal of up to 30%–50%, enabling the system to deliver a higher current. A small pulse transformer-based triggering unit with an output voltage of 30 kV was used for triggering the generator. The system’s performance was tested in pulse repetition frequency (PRF) mode with resistive and diode loads and achieved a repetition rate of 80 Hz. An energy density of ~460 J/m3 was achieved in the developed system. A vircator device was connected and tested to benchmark the Marx generator for its repetitive and burst mode operations. The test results show the measured RF output power of 100 MW.

Bias Current Modulation of DC and RF Properties of AlmGa1‐m∼GaN Heterojunction IMPATT at Sub‐Millimeter Wave Frequency

AbstractLarge signal RF properties of double drift region (DDR) Impact Avalanche Transit Time (IMPATT) device based on AlmGa1‐m∼GaN heterojunction (HT) are investigated and their variation with bias currents has been presented here. These RF properties and their modulation will significantly validate the acceptability of the particular HT in the sub‐millimeter wave frequency domain. Avalanche noise plays the prime ground for making the IMPATT diode basically noisy and tunneling decays the performance of the device, as we move towards the higher frequency range like the sub‐millimeter frequency. These setbacks can be done with if the homojunction (HM) is replaced by heterojunction. This authenticates the choice of heterojunction over homojunction. Here, the author takes 500 GHz as the frequency of concern in the sub‐millimeter wave range. Here, two complementary heterojunctions of AlmGa1‐m∼GaN is taken with m = 0.4 or the mole fraction of Al in the alloy being 40% and their RF results are compared with two homojunctions of GaN and AlGaN for double drift region (DDR) IMPATT diode. Outcomes indicate that HT diodes surpass the high‐frequency performance of HM diodes if compared on the basis of dc to RF conversion efficiency and output power due to the influence of large amplitude ac signal. It is also observed that with increasing bias voltage dependent current, which is varied from 20 × 108to 40 × 108Am−2, the efficiency of conversion together with the power output increases. These results will be very important for further research in this domain.

Design of High-Speed UTC-PD With Optimization of Its Electron Transit Performance and Parasitic Capacitance

An 1500 nm thick collector layer is adopted in the uni-travelling-carrier photodiode (UTC-PD) to reduce the PD's capacitance, while the PD's diameter is set to be 20 μm for better saturation performance and optical coupling characteristic of a signal from a single mode fiber. By optimizing biasing voltage and input light intensity, the electric field intensity in the collector layer would be controlled to make the photo-generated electron in the UTC-PD transiting at around its peak drift velocity in the collector layer and at the same time to make the UTC-PD obtaining it minimum capacitance. Together with the optimization of the doping distribution in UTC-PD's cliff layer and its collector layer, the UTC-PD's high-speed performance and saturation performance can be further improved. An optimized 20 μm diameter UTC-PD with a simulated 106 GHz 3 dB bandwidth and 21.02 dBm output RF power at 25 GHz is designed. It proposes a discussion to realize high speed, high saturation performance UTC-PD together with high coupling efficiency from a single mode optical fiber by bringing the electric field determined drift velocity performance of its uni-traveling- carrier, the electron, into full play.

Simulation and design of a high-speed and high-power modified uni-traveling carrier photodiode based on the electric field distribution in the depletion region.

A modified uni-traveling carrier photodiode with an electric field control layer is proposed to achieve high-speed and high-power performance at a lower bias voltage. By inserting the 10nm p-type InGaAs electric field control layer between the intrinsic absorption layer and space layer, the electric field distribution in the depleted absorption layer and depleted non-absorption layer can be changed. It is beneficial for reducing power consumption and heat generation, meanwhile suppressing the space-charge effect. Compared with the original structure without the electric field control layer, the 3dB bandwidth of the 20µm diameter novel structure, to the best of our knowledge, is improved by 27.1% to 37.5GHz with a reverse bias of 2V, and the RF output power reaches 23.9dBm at 30GHz. In addition, under 8V bias voltage, the bandwidth reaches 47.3GHz.

Load-Modulated Balanced Amplifier: From First Invention to Recent Development

The RF power amplifier (PA) is a unit in wireless transmitters that strengthens the signal to combat losses in transmission by converting dc electric power to the added RF output power. Over the past decades, with the rapid development of wireless communications, high-efficiency PA design has become one of the most popular topics in both academic research and industrial development as the PA consumes a high portion of the transmitter energy, and thus its power efficiency directly impacts the system performance. In addition, because the PA is the main source of distortion generated by the transmitter, linearity is another concern in PA design, particularly in wideband systems <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> .