Output Power Gain Research Articles

Output Power and Gain Monitoring in RF CMOS Class A Power Amplifiers by Thermal Imaging

The viability of using off-chip single-shot imaging techniques for local thermal testing in integrated radio frequency (RF) power amplifiers (PAs) is analyzed. With this approach, the frequency response of the output power and power gain of a Class A RF PA is measured, also deriving information about the intrinsic operation of its transistors. To carry out this paper, the PA is heterodynally driven, and its electrical behavior is down converted into a lower frequency thermal field acquirable with an InfraRed lock-in thermography (IR-LIT) system. After discussing the theory, the feasibility of the proposed approach is demonstrated and assessed with thermal sensors monolithically integrated in the PA. As crucial advantages to RF-testing, this local approach is noninvasive and demands less complex instrumentation than the mainstream commercially available solutions.

Analysis of Interconnection Schemes for PV Systems Operating under Shadow Conditions

The output power of a PV system consisting of multiple strings and arrays of PV modules reduces drastically as shading increases on it. The shaded module in a string limits the output current of the entire string thereby reduces its output power. Different techniques are used for the optimal interconnection of modules in a PV system that not only helps in reducing the deteriorating effects of partial shading but also enhances the output power of the overall PV system. The performance and the cost analysis of different interconnection schemes including series-parallel (SP), honeycomb (HC), bridge-linked (BL), and total cross tied (TCT) with bypass diode are presented. Commonly existing shading patterns including diagonal (DI), short wide (SW), long wide (LW), short narrow (SN) and short wide (SW) are evaluated. Results show that TCT exhibits better output power under all shade patterns. For a typical 4A—4 PV system operating under diagonal shading condition, 15.1% gain in output power can be achieved through TCT connection in comparison to conventional SP interconnection. Further, it has been found that the cost of extra conductors incurred due to TCT connection can be recovered through enhanced energy output within three quarters of the year.

Investigation of the photodarkening of Yb-Li co-doped silica fiber

In this work, we systematically studied the mitigation of photodarkening (PD) in ytterbium-doped silica fiber co-doped with lithium (Li). Adding a proper concentration of Li+ ions to the core glass composition, the PD-induced excess loss can be reduced by 25%. The results showed that the effect on numerical aperture and laser efficiency was very small. Compared with the sodium (Na) co-doped Yb/Al silica fiber at the same concentration, the mitigation of the PD effect through Li+ and Na+ ions co-doping was analyzed and discussed. Furthermore, a hypothesis was proposed for the mechanism of alkali metal Li and Na co-doping to mitigate the PD effect. More effective core composition and doping concentration were proposed to provide guidance of high output power gain fiber preparation.

Thermodynamic analysis of combined cycle power plant using regasification cold energy from LNG terminal

Being increasingly used clean fuel, liquefied natural gas (LNG) release large amount of cold energy during its regasification process, which can be used for performance augment and energy saving towards regasification of LNG. In this paper a triple pressure Combined Cycle Power Plant (CCPP) with the application of the regasification cold energy is thermodynamically analyzed through energy and exergy principles. Three options were considered to investigate the effects of cold energy on thermodynamic performance of CCPP as a function of ambient temperature. The first option consists of utilization of cold energy for gas turbine (GT) inlet air cooling in the gas cycle (GC), the second option for cooling the condenser circulating water in the steam turbine cycle (STC) and the third option is a combined process of cold energy utilization in both GC and STC. The three presented options highlight the use of two heat exchangers one in GC and second in STC intended for utilization of LNG cold energy in CCPP. It is found that the gain in power output is significant from ambient air temperature 29 °C–45 °C (around 8.5% to 10.5%) and the gain in exergy efficiency is 0.09%–2.2% compared to the base case.

Very high open-circuit voltage in dual-gate graphene/silicon heterojunction solar cells

Two dimensional (2D) layered materials and their heterojunctions with other materials are attracted because of their remarkable electrical and optical properties. In particular, graphene/semiconductor Schottky heterojunction is used for high performance solar cells. Here, we demonstrated very high open circuit voltage (Voc) in graphene/silicon heterojunction solar cell by dual-gate electric field application. The low density of states near Dirac point in graphene allows large modulation of graphene Fermi-level and corresponding Schottky barrier in a graphene/silicon junction. The top and bottom gate electric fields independently adjust the built-in potentials of respective upper and lower silicon energy band to induce higher band bending (1.22 eV) than the bandgap (1.12 eV). As a result, a maximum Voc of 0.94 V is achieved at the − 8 V of top-gate voltage and 10 V of bottom-gate voltage, exceeding highest known Voc for previous graphene/silicon solar cell (Voc = 0.61 V) and the S-Q Limit (0.84 V) of conventional silicon solar cell – a thermodynamic limit for the energy conversion efficiency of solar cells with a single band gap energy. The ratio of output power gain to input gate power (ΔPG/ΔPC) is approximately 1012–1014 with negligible power consumption in the gate (PC = 1 fW/cm2–10 pW/cm2), resulting in the significant advances in the power generation (PG = 40 mW/cm2).

Performance evaluation of a partially admitted axial turbine using R245fa, R123 and their mixtures as working fluid for small-scale organic Rankine cycle

Zeotropic mixtures and turbine expander were two hot topics in organic Rankine cycle (ORC) field recently. However, few researches referred the design of turbine expander with zeotropic mixtures. In this paper, R245fa, R123 and three mixtures (0.25R245fa/0.75R123, 0.5R245fa/0.5R123, 0.75R245fa/0.25R123) are used as working fluid to investigate the performance of a partially admitted turbine consisting of 3 nozzles and 30 blades. The mean-line diameter of turbine is 0.1 m and the height of blade is 14 mm. The 3D simulation are carried out with ANSYS CFX using k-omega turbulence model and SRK real gas model. Results show that turbine has maximum power output of 8.1336 kW and maximum efficiency of 55.3% with pure R245fa used as working fluid. When the mass fraction of R245fa is 0.25, mixture has the maximum glide temperature of 3 K, while turbine has maximum power output gain of 7.87%, maximum mass flow rate gain of 3.57%, maximum Ma number of 2.19 and maximum mass flow rate of 0.5287 kg/s. The results of system analysis coupling with the designed turbine show that the maximum thermal efficiency, maximum net work and minimum exergy destruction factor are 6.15%, 7.6771 kW and 2.41 respectively for the best working condition.

A 28-GHz Symmetrical Doherty Power Amplifier Using Stacked-FET Cells

A two-stage Ka-band Doherty power amplifier (DPA) using a stacked field-effect transistor (FET) cell is presented. We demonstrate, for the first time, the two critical parameters in a stacked-FET topology that must be designed specifically for a Doherty operation: the gate capacitance and the bias voltage of the stacked transistor. The two parameters strongly determine the DPA output power, power-added efficiency (PAE), and power gain flatness. Furthermore, we also demonstrate a dual-driver topology to boost the amplifier gain without scarifying PAE, and a proposed bias circuitry to deal with the high gate leakage current of an enhancement mode (E-mode) process. The stacked-FET DPA prototype is fabricated in an E-mode 0.15- $\mu \text{m}$ gallium arsenide (GaAs) process to verify the concept. At 28 GHz, the 2.9 mm $\times1.7$ mm integrated chip exhibits a measured gain of 14.4 dB, an output power of 28.7 dBm, with an associated 37% peak PAE and 27% PAE at 6-dB power back-off. To the best of the authors’ knowledge, the DPA achieves among the highest gain and highest power density of all reported DPAs at millimeter-wave frequencies.

Improve the performance of solar modules by reflectors

Solar energy is one of the most significant renewable energy sources, in both its applications thermal and photovoltaic, world needs. Iraq is one of the countries with the abundance of this type of energy, where annual solar activity reaches about 2000kWh/m2/year on the horizontal surface. In the present work a solar collectors with V-trough concentrator system were designed and fabricated with geometric concentration ratios two suns to get an extra electric output power. The experiment was carried out in Al-Zwraa Company in Baghdad. The main results indicated that the solar concentrator system caused to increase the short circuit current due to increase the amount of incident solar radiation on the solar modules, and thus increase in output power. As a comparison with reference module, the gain in output power, at solar noon, exceeded 48%. It can be concluded that the use of V-Trough concentrator system coupled with solar module systems can result in a favourable cost-benefit ratio.

Integrated Microstrip Meander Line Traveling Wave Tube Based on Metamaterial Absorber

An integrated microstrip meander line (MML) slow-wave structure (SWS) comprised of an MML SWS and compact wideband metamaterial absorber (MMA) is proposed and demonstrated theoretically and experimentally in this paper. The MMA consists of metallic rectangular resonators with a metallic ground plane and a separating dielectric layer. Simulation results show that the MMA has multidistinctive absorption peaks; the bandwidth at 56-GHz peak frequency is reach up to 30 GHz. The integrated MML SWS can provide flatter gain response of output power than that made by the MML SWS with a traditional resistive coating attenuator. Experimental results are in close agreement with simulation results. A traveling wave tube (TWT) is simulated based on this integrated MML SWS. The output power of this TWT is 48.21 W at 33 GHz corresponding to a maximum gain of 30.3 dB; the output power gain is greater than 25 dB across the entire working frequency range.

Tunable differential modal gain in FM-EDFA system using dual pumping scheme at 100 Gbps system capacity

In this manuscript, we demonstrate a few-mode system by tailoring of ring-doped EDFA index profile to mitigate the effect of differential modal gain under the presence of ten spatial linearly polarized modes. The FM-EDFA system also gives better output power spectra, gain spectra and optical signal-to- noise ratio of an individual mode for wide range of wavelength window (C-band) and BER below $$10^{-10}$$10-10 at 100 Gbps. Moreover, the better performance in FM-EDFA system is achieved by selecting mode bidirectional pumping scheme.

High-Voltage DC-DC Converter Topology for PV Energy Utilization—Investigation and Implementation

This paper exploited the utilization of photovoltaic (PV) energy system with high-voltage (HV) output DC-DC converter. Classical boost converters are used for both renewable energy integration and HV applications, but limited by reducing output/efficiency in performance. Moreover, as parasitic elements suppress the power transfer ratio, converter needs to maximize the PV energy utilization. This investigation study focused to include additional parasitic elements (voltage-lift technique) to a standard DC-DC buck converter and to overcome all the above drawbacks to maximize the PV power generation. The proposed power circuitry substantially improves the output power gain transfer ratio and a prototype hardware module is implemented using industrial standard DSP TMS 320F2812. Numerical simulation development followed by an experimental prototype implementation is carried out in this investigation. A set of numerical and experimental results is provided in this paper, which show close conformity with the theoretical background.

Electrical and optical properties of laser irradiation treated vertical light‐emitting diodes

A comparative analysis of the properties of vertical light-emitting diodes (VLEDs) fabricated using different surface treatment schemes was conducted. Compared with a conventional VLED, a light output power increase of 24.8% for an injection current of 350 mA was achieved by an n-type-gallium nitride (GaN)-based VLED with a thin undoped GaN layer and microsized protrusions produced by krypton fluoride laser irradiation using an energy density of 600 mJ/cm2. This was accomplished without noticeable degradation of the electrical properties of the device. Further, potassium hydroxide wet etching of the VLED surface increased the light output power gain to 47.3% for the same injection current.

Topology reconfiguration for optimization of photovoltaic array output

As more utility scale photovoltaic (PV) power plants are installed, there is a need to improve monitoring and management of PV arrays. A procedure is presented here for optimizing the electrical configuration of a PV array under a variety of operating conditions. Computer simulations and analysis with synthetic and real data are presented in this paper. The performance of the optimization system is evaluated for a variety of partial shading conditions using a SPICE circuit simulator. In general, a 4%–5% gain in power output is achievable by employing active switching in order to reconfigure the array’s electrical configuration.

Effect of Gate Insulator Thickness on RF Power Gain Degradation of Vertically Scaled GaN MIS-HEMTs at 40 GHz

We present an initial study of the RF reliability of SiN x/InAlN/AlN/GaN MIS-HEMTs with a molecular-beam epitaxy deposited SiN x gate insulator thickness varying from 0 (Schottky gate) to 6 nm. T-gate devices with 120 nm gate length were stressed under continuous-wave 40-GHz large-signal RF operation, biased in class AB with $V_{DS} = \mbox{20} \mbox{V}$ . Degradation in large-signal output power gain was observed to various degrees for all devices. For structures with a 3- or 6-nm gate insulator thickness, output power degraded by approximately 1 dB or less after 250 h of operation. A rapid decrease in output power was observed for structures with a 1-nm gate insulator or a Schottky gate, with a 1-dB decrease in output power within the first 10 h of operation. Degradation in output power was associated with a reduction in drain current, likely caused by hot-electron-related trapping as the drain current was fully recoverable after exposing the devices to UV light. Simulations show that as the gate insulator thickness is reduced, the peak lateral electric field in the channel increases, which would be consistent with an increase in hot-electron-related degradation.

A 77-GHz FMCW Radar System Using On-Chip Waveguide Feeders in 65-nm CMOS

This paper presents a 77-GHz radar system using a transmitter (Tx) and receiver (Rx) integrated with on-chip waveguide feeders in 65-nm CMOS. The newly proposed on-chip waveguide feeder shows the insertion loss of about 2 dB and more than 30% bandwidth. Additionally, both the Tx and Rx are integrated with internal ×10 frequency multipliers. Therefore, a radar system can be easily implemented without sensitive millimeter-wave packaging technology by mounting the Tx and Rx chips on the waveguide aperture. The interconnections for the low-frequency reference and baseband signals can be realized on the low-cost FR-4 printed circuit board. The radar system shows 9-dBm output power and 13-dB down-conversion gain from the waveguide port.

High-Power RF Testing of 1-MW, 352.2-MHz Continuous Wave Klystron Amplifier

A 1-MW, 352.2-MHz continuous wave (CW) radio frequency (RF) test stand based on TH 2089 klystron amplifier is developed and tested up to its rated power. Klystron amplifier demands stringent performances from its beam bias power supply for its proper operation. A novel crowbar less solid-state modular topology is adopted for -100-kV, 25-A dc beam bias power supply and its achieved performance parameters are presented in this paper. Wire burn test, which is crucial for CW klystron amplifier, was conducted on this power supply to ensure that its stored energy during klystron arcing is less than 20-J. The criterion for the selection of test wire is also presented. A real-time control system is developed for proper sequence of operation of various power supplies as well as for control and monitoring of crucial parameters of this test stand. The testing of this high-power klystron amplifier is quite involved in nature and various tests have been carried out under several operating conditions before it is employed in the high-power RF test stand. This paper studies and analyzes the effect of variations of various parameters on the performance of this high-power klystron amplifier. Variation of output power and RF gain against RF input power as well as variation of RF phase over beam voltage is presented. Variations of RF output power against frequency, beam voltage, beam current, and mod-anode voltage are also presented. Heat run test was conducted on this klystron amplifier for 24 h to ensure its reliability.

Experiments on a Ku-band gyrotron traveling-wave-tube amplifier with a tapered waveguide

A Ku-band gyrotron traveling-wave-tube (gyro-TWT) amplifier was investigated. To obtain a wide operating bandwidth, we used a two-stage tapered rectangular waveguide interaction circuit. An electron beam of 27 keV and 3.56 A was produced from a double-anode magnetron-injection-gun (MIG). The measured frequency bandwidth over 10 dB gain in the linear operation region was found to be 18%. The gyro-TWT’s saturated output power was 14.9 kW at 14.4 GHz, corresponding to a saturated output power gain of 27.4 dB and an efficiency of 15.5%. The measured experimental results were in agreement with those of non-linear numerical simulations.

Maximizing concentrated solar power (CSP) plant overall efficiencies by using spectral selective absorbers at optimal operation temperatures

Selective absorbers for CSP plants to suppress thermal losses and to increase the efficiency is a promising topic and strong scientific efforts have been spent on how to design and realize such materials. However, there has been no comprehensive optimization analysis of the overall efficiency of CSP plants with selective absorbers.We performed a comprehensive computational parameter study of operation temperature and optical properties of the absorber and investigated their effect on the overall plant efficiency in dependence of sun light concentration up to C=2000 suns. Optimal operation temperatures were shown not to exceed 1383K. By using selective absorbers instead of a black body or currently used materials, our assessment yields a potential electrical power output gain of up to around 35%. Our investigations also provide the optical parameters of an ideal (perfect selective) absorber. Its optimal cut off wavelength λcut lies around 2.4μm for concentration factors below 120 and above 600 suns. For C in the range of 120–600 suns the value of the cut off wavelength is 1.79μm. Simulating non-ideal (realistic) absorption properties, it was found that the strongest influence is caused by high absorption at low wavelengths. Low emittance at longer wavelengths plays a less important role. Also the sharpness of the transition from high absorption to low emittance plays a minor role regarding overall plant efficiency. As a rule of thumb, the cut-off wavelength should be at around 2.4μm when assuming realistic (non-ideal) spectral selectivity. Finally, the theoretical maximum overall efficiency of a CSP plant achievable by an ideal selective absorber was calculated to up to 73% at 2000 suns and even up to 65% for a selective absorber with realistic optical properties.

Design, fabrication and measurement of a novel 140 GHz folded waveguide based on SU-8 UV-LIGA technology

In an RF MEMS field, a folded waveguide is the core structure of a traveling wave tube as a slow-wave structure. 140 GHz is an important atmospheric working window. In this paper, the dispersion property and interaction impedance of a novel 140 GHz folded waveguide were analyzed and simulated using CST Microwave Studio. The beam–wave interaction in the folded waveguide was also simulated, using CST Particle Studio. The output power gain of the folded waveguide reached 24.5 dB at 140 GHz when the emission voltage was 12.7 kV and the emission current was 0.15 A. The simulation process provided structure parameters for further micromachining. Furthermore, to analyze the effect of structure fabrication errors, CST was used to simulate the dispersion and interaction impedance by adding tolerance to some important structure parameters. Finally, multi-step SU-8 UV-LIGA technology was adopted for micromachining the folded waveguide. To ensure adhesion between the SU-8 photoresist and substrate, a thin TiO2 film was formed on the surface of the Ti substrate. In the end, test results showed that the reflection coefficient S11 and transmission coefficient S21 were near −28.1 dB and −1.2 dB respectively. Moreover, the output power gain was close to 23 dB at 140 GHz. Good accordance between the simulation and experimental results indicated a reasonable design and high precision of microfabrication by SU-8 UV-LIGA technology.

Bifacial photovoltaic panels field

Bifacial solar cells may produce more output energy than mono-facial solar cells because both sides of the cell, front and rear, can absorb solar radiation. This occurs when the nearby ground or other artificial surfaces are highly reflective. A gain in output power of 5–20% has been reported in the literature for special applications. The present article deals with the calculation of the annual incident irradiation on a solar field comprising of bifacial photovoltaic panels deployed in multiple rows and separated by a distance between the rows. These types of fields are designed for large scale solar electricity production. The calculation of the annual incident irradiation is compared between two types of deployments: (a) bifacial photovoltaic panels installed with an optimal tilt angle facing south, (b) bifacial photovoltaic panels installed vertically and facing the east-west direction. The study shows that bifacial photovoltaic panels installed with an optimal tilt angle may produce 32% more energy than vertical bifacial photovoltaic panels, for the same environmental conditions. On the other hand, more vertical collectors can be installed in fields with the same field dimensions.