High Frequency Operation Research Articles

A New Predictive Current Control With Reduced Current Tracking Error and Switching Frequency for Multilevel Inverters

The forward Euler's integration method is widely used to compute the trajectories of the control variables in conventional predictive current control (PCC) techniques. However, the computational error caused by the forward Euler's method proportionally increases with the sampling time. Hence, the current tracking ability of conventional PCC techniques deteriorates when operating with a large sampling time. Furthermore, the conventional PCC methods produce more switching transitions to reduce the current tracking error, thereby leading to a high switching frequency operation. To overcome these problems, Heun's integration method is proposed for the PCC in this article. The proposed method has predictor and corrector stages to minimize the computational error caused by the large sampling time during the prediction process of the control variables. Thereby, the proposed Heun's method-based PCC techniques produce fewer switching transitions to minimize the current tracking error. Consequently, this results in a decrease in switching frequency. The proposed PCC method is applied to a four-level multilevel inverter (4L-MLI). The discrete-time system models are developed using Heun's integration method to implement the proposed PCC. The working philosophy of the proposed method is demonstrated through the dSPACE/DS1103 controlled 4L-MLI laboratory prototype. The experimental performance of the proposed PCC is compared with that of the conventional PCC in terms of average switching frequency, current tracking error, current harmonic distortion, and transient response time.

Channel Estimator and Nonlinear Detector for mmWave Beamformed OTFS Systems in High Mobility Scenarios

Real-time data-intensive applications in highly mobile environments with high data rates and low latency are one of the key requirements for beyond fifth-generation (5 G) communications. Towards this end, a combination of the millimeter wave (mmWave) band with large available spectrum and orthogonal time-frequency space (OTFS) modulation, which offers robust performance in high mobility scenarios, can be envisioned as a promising solution. However, employing OTFS in the mmWave frequency band is challenging in presence of nonlinear distortions attributed to radio frequency (RF) power amplifier (PA) and complex equalization involved in OTFS receiver in the delay-Doppler domain. The nonlinearity effect of PA is inevitable in mmWave systems due to the high operating frequency and large bandwidth. The nonlinear distortions induce interference and make the target distribution analytically intractable. In this paper, we propose a receiver design for mmWave OTFS systems that aims to address the challenges posed by the nonlinear distortions of the RF PA. The proposed receiver design leverages the use of a large-scale antenna array to decouple the received signal into multiple branches through beamforming. Specifically, we first derive the input-output relation in the delay-Doppler domain with nonlinearity. Then, a combination of maximal-ratio combining (MRC) and iterative particle filter (PF)-based nonlinear detector is proposed to address the issue. We also design a pilot pattern considering the additional interference from the PA impairment. Furthermore, we reformulate the threshold-based channel estimation to incorporate the nonlinearly distorted pilot in its estimation process. Extensive numerical results demonstrate the proposed algorithm's reliability and superiority over existing digital predistorters (DPD) and conventional linear detectors.

High-Frequency Performance Characteristics of the Double-Gate Schottky Barrier Tunnel Field Effect Transistor in Analog and Radio-Frequency Applications

In this paper, a novel structure of Double Gate Schottky Barrier Tunnel Field Effect Transistor (DG-SBTFET) has been designed and simulated. The DG-SBTFET has two sources (NiSi) and two gate metals with an HfO2. Silvaco-TCAD simulator has been used for investigating the analog and radio frequency performance of the DG-SBTFET. The proposed device (DG-SBTFET) is compared with the conventional devices in terms of electrical parameters including ION current, ION/IOFF ratio, RF performance including transconductances (gm), cut-off frequency (f T ), transit time (r), gain bandwidth product (GBP), transconductance generation factor (TGF), and transconductance frequency product (TFP). Further, we simulate the linearity characteristics of the DG-SBTFET device is compared it with other conventional devices, including the second-order voltage intercept point (VIP2), third-order voltage intercept point (VIP3), and third-order input intercept point (IIP3). Hence, the proposed device (DG- SBTFET) is suitable for low-power and high-frequency applications.

A new single modulating and single carrier‐based predictive current control technique for single‐phase quadruple boost multilevel inverter topology

SummaryA new floor function single carrier‐based modulated model predictive current control (F2‐SCM2PC2) technique has been proposed in this paper by considering traditional single‐phase quadruple boost switched capacitor‐based multilevel inverter (QB‐SCMLI) topology. Conventionally, the implementation process of single modulating and single carrier‐based pulse width modulation (PWM) techniques are very much complex and finite control set‐based model predictive control (FCS‐MPC) technique inherently operates with variable switching frequency (VSF) operation, which is not suitable for industrial applications. To alleviate the aforementioned issues, a new generalized closed‐loop F2‐SCM2PC2 technique has been proposed. It consists of a simple PWM implementation process and can easily be integrated with a predictive algorithm, thereby providing a constant switching frequency (CSF) of operation. The particular single modulating and single carrier‐based PWM technique with floor function is also suitable for low and high switching frequency (LSF‐HSF) operations. The validation of floor function‐based PWM technique in open‐loop and closed‐loop F2‐SCM2PC2 techniques has been effectively verified through experimentation on QB‐SCMLI topology with consideration of resistive–inductive load.

Analysis and Classification of Charge Trapping States in β-Ga2O3 Mosfets Using I-V and C-V in Dark and Illumination Conditions

Beta-gallium oxide (β-Ga2O3) is a promising ultra-wide bandgap semiconductor for high power applications. Its breakdown electric field of 8 MV cm-1, a Baliga figure of merit 3-10 times larger than that of SiC and GaN, and the ability to be grown from the melt make it highly attractive for the semiconductor industry. Significant improvements have been made in β-Ga2O3 device performance for both high power and high frequency operation. Currently, aluminum oxide (Al2O3) is the preferred gate dielectric for β-Ga2O3 transistors due to its electron and hole barriers, and similar atomic structure. Process optimizations to improve the interface quality has been explored by chemical treatments1 to the β-Ga2O3 surface before dielectric deposition, during the deposition of Al2O3, and with post-deposition annealing. Therefore, there is a desire to understand and classify defects at and near the Al2O3/β-Ga2O3 interface. Here, we report on a study of the Al2O3/β-Ga2O3 interface and border traps in planar depletion-mode β-Ga2O3 MOSFETs using DC I-V and C-V measurements in dark and under illumination with wavelengths from 730 nm (1.7 eV) to 230 nm (5.4 eV). The MOSFETs are fabricated on a 50 nm Si-doped epitaxial layer with a target doping concentration of 2.4 x 1018 cm-3 grown on a (010) semi-insulating β-Ga2O3 substrate. A Ti/Al/Ni/Au metal stack is deposited and annealed to form the Ohmic contacts. Plasma-assisted atomic layer deposition (PE-ALD) is used to deposit the 20 nm Al2O3 gate dielectric. The fabricated transistor structures have a LG of 1.94 µm, LS of 0.5 µm, and LD varying from 0.5 µm, 5.5 µm, and 10.5 µm. Measurements were performed at room temperature. Most FETs exhibited a threshold voltage of approximately -4 V, high linearity, and ION/IOFF ratios between 107 – 109. Using the conductance method, we extract an interface trap state density, Dit, of 3 x 1011 eV-1 cm-2 up to 0.44 eV below the conduction band. Illumination is used to obtain deep trap concentration and behavior. We observe little to no change in IV and CV curves for wavelengths above 365 nm but see a significant voltage shift in the CV curves for illumination wavelengths between 365 nm (3.4 eV) to 230 nm (5.4 eV), indicating significant activated traps from 3.4 eV below the conduction band. We will present the analysis of photo-assisted CV and stress-CV curves at various wavelengths to obtain densities of fixed, fast, and slow trap states and discuss their impact on device performance.

(Digital Presentation) Analysis of MIS-HEMT Kink Effect in Saturation Region

The High Electron Mobility Transistor (HEMT) has been widely used in the field of power electronics and high frequency operation since 1983 (1), while presenting a simple circuit design for analog applications (2, 3), and for extreme harsh environments as well (3, 4). However, HEMTs presents a problem with gate leakage and current collapse which can be solved by introducing an insulator between the gate and semiconductor while maintaining the high performance, hence the Metal Insulator Semiconductor High Electron Mobility Transistor (MIS-HEMT) appears as a solution. The AlGaN/GaN heterostructures forms, at the interface, a sheet with high electron density (2DEG – 2 Dimension Electron Gas), which also presents a high electron mobility. The MIS structure presents a well know conduction between source and drain. As a result, the MIS-HEMT device presents multiple conductions. The focus of this work is to study how the multiple conductions of the MIS-HEMT impact on the output characteristics.The studied devices are, a MIS-HEMT with the gate insulator composed of a 2 nm Si3N4, and a GaN MOSFET of 25 nm of Al2O3 as the gate insulator, both devices were fabricated at imec Leuven – Belgium, and have the same dimensions: gate width of 5 µm and gate length of 600 nm. Their respective schematics are presented at figure 1.The drain current (IDS) as a function of drain voltage (VDS) for a MIS-HEMT (left) and GaN MOSFET (right) with multiple overdrive voltage (VGT) is presented in figure 2. The VDS ranges for these devices are different because they have different saturation points, although it is possible to notice that the MIS-HEMT shows greater current drive when compared to MOSFET considering the same VDS, which is likely due to the formation of the 2DEG as the main conducting mechanism in the MIS-HEMT.Previous works (5 – 8) showed that the MIS-HEMT have multiple conduction mechanisms dependent on VGT, and figure 3 shows the effect of those multiple conductions on the output current of the device where it is very likely that one of those conductions have different VDS sat. It is possible to notice higher values of IDS with increasing VGT, as expected. However, for high enough VGT, there is an anomalous IDS increase (kink) in the saturation region, that occurs due to the different conduction mechanism (MOS and HEMT conductions). This effect will be called as MIS-HEMT kink effect (MH kink effect). This MH Kink effect occurs when the HEMT conduction mechanism overcomes the MOS conduction.The output conductance (gD) as a function of VDS for the MOSFET is presented in figure 4. Figure 5 shows gD as a function of VDS for multiple VGT for the MIS-HEMT, where it is possible to see a peak in the gD (in saturation region) shifting to the right for increasing VGT, caused by the MH kink effect.In order to better visualize, the VDS value for which the MH kink takes place, it is plotted as a function of VGT in figure 6. It is possible to see that as VGT increases, the MK kink effect shifts for higher VDS values, thanks to the higher electron density in 2DEG making the HEMT conduction less dependent on VDS. Figure 1

A snap-through vibration-rotation modulation mechanism for high-performance low frequency energy harvester

Ambient low frequency (LF) vibrations are ubiquitous but their efficient utilization is still an open issue. To tackle this problem, this paper reports an ingenious vibration–rotation (V-R) modulation mechanism that is realized by introducing a reset spring and a pair of magnets to the conventional rack-and-pinion mechanism. By taking advantage of the magnets-enabled snap-through dynamics, the V-R mechanism can convert LF-vibrations to fast rotation. Under a pressed depth of 10 mm and trigger frequency of 2.0 Hz, a high rotation speed of 1230 rpm can be achieved by the snap-through V-R mechanism in combination with a pawl-ratchet mechanism, which is 1.4 times higher than that enabled by the linear counterpart. A rotor-based vibration energy harvester (R-VEH) designed with the snap-through V-R mechanism can generate high voltage of 4.3 V and large power of 10.8 mW as excited at 2.5 Hz. The snap-through R-VEH can also sustain the continuous work of a hygrothermograph by tapping the irregular LF-vibration of a treadmill (even with a small amplitude of roughly 2.5 mm). The snap-through R-VEH is thus a potential technology for the efficient harvesting of pervasive LF-vibrations toward self-driven sensing systems.

A laterally excited bulk acoustic resonator with scattering vias in electrodes

Laterally excited bulk acoustic resonators (XBARs) using interdigital electrodes are currently limited in potential 5G applications due to the accompanied spurious modes and small capacitance. This Letter presents an XBAR with scattering vias in electrodes, named SV-BAR. The non-parallel boundaries thoroughly disrupt the coherent formation of standing waves in the lateral direction, thereby suppressing the higher-order spurious modes. The duty factor of SV-BAR is optimized as 0.5 using COMSOL Multiphysics finite element analysis for the 50 Ω impedance matching. The SV-BAR is fabricated using a 390 nm Z-cut LiNbO3 on an insulator substrate and exhibits an impressive ratio of Zp/Zs near 64.5 dB, a Kt2 of 21.80% at 4.762 GHz, as well as a large value f · Bode_Qmax · Kt2 (3.43 × 1011). The measured temperature coefficient of frequency is −69.8 ppm/°C, which can be compensated using SiO2 thin films. The SV-BAR provides an effective solution for high-performance radio frequency filters for 5G communication.

Enhanced the Efficiency of AC to DC Power Adapter

AC to DC Power adapter or power converter is a vital area of research nowadays is efficiency enhancement. In this research work we designed two circuit of 45 watt AC to DC power adapter and we used different diode in both circuit. First circuit which we designed which we considerd as real circuit and we used 1N4148 diode in this circuit full bridge rectifier. And simulate this circuit in LTSPICE software. After analysis the result and using the latest Efficiency Enhancement, High-Frequency Operation, Wide Bandgap Semiconductors, Miniaturization and Integration, eliability and Lifetime, Digital Control Techniques, Power Factor Correction, Renewable Energy Integration, Multi-Port Converters, Harmonic Distortion and EMI, Smart Grid and Demand Response, Environmental Impact and Sustainability, Biomedical Applications, and Safety and Standardization factors because These areas of research collectively contribute to the advancement of AC to DC power conversion technology, making it more efficient, reliable, and adaptable to the evolving needs of various industries. We design second circuit which we consider as ideal circuit we used MURS320 diode ideal circuit full bridge rectifier. And we simulate this circuit in LTSPICE software and analysis the simulation result. We get 2.5% efficiency in ideal circuit of 45 watt AC to DC power adapter

An Analytical Model of Dynamic Power Losses in eGaN HEMT Power Devices.

In this work, we present an analytical model of dynamic power losses for enhancement-mode AlGaN/GaN high-electron-mobility transistor power devices (eGaN HEMTs). To build this new model, the dynamic on-resistance (Rdson) is first accurately extracted via our extraction circuit based on a double-diode isolation (DDI) method using a high operating frequency of up to 1 MHz and a large drain voltage of up to 600 V; thus, the unique problem of an increase in the dynamic Rdson is presented. Then, the impact of the current operation mode on the on/off transition time is evaluated via a dual-pulse-current-mode test (DPCT), including a discontinuous conduction mode (DCM) and a continuous conduction mode (CCM); thus, the transition time is revised for different current modes. Afterward, the discrepancy between the drain current and the real channel current is qualitative investigated using an external shunt capacitance (ESC) method; thus, the losses due to device parasitic capacitance are also taken into account. After these improvements, the dynamic model will be more compatible for eGaN HEMTs. Finally, the dynamic power losses calculated via this model are found to be in good agreement with the experimental results. Based on this model, we propose a superior solution with a quasi-resonant mode (QRM) to achieve lossless switching and accelerated switching speeds.

A compact Balanced Antipodal Vivaldi Antenna with improved phase center stability for imaging and ultrawideband localization applications

This paper introduces a phase center stability improved Balanced Antipodal Vivaldi Antenna (BAVA) loaded with ‘I’ shaped non-resonant director array. The proposed antenna operates from 6 GHz to 18 GHz with S11 less than −10 dB and addresses the issue of phase reversal. The rectification of phase reversal produces enhanced phase center stability. Standard deviation is used to find least dispersed set of the phase center span calculated by varying design parameters of the director through a parametric study. By effective circumventing of phase reversal through improved coupling between the signal and ground planes, the proposed antenna achieves a maximum of 65.31% of improvement of phase center stability when compared to the reported Vivaldi antennas. In addition, further fine tuning of H-plane phase center stability for phi-components of about 6.5% at higher frequencies of operation is also attained using a meander-line section in the feed. With a size of 3.2λ0×1.6λ0×0.02032λ0 mm3, the proposed antenna exhibits sustained radiation patterns. Where λ0 is free space wavelength at 12 GHz. Full wave simulation of the design using CST microwave studio and experimental validation with a fabricated prototype are carried out.

Fracture Imaging and Response Characterization of the High-Definition Oil-Based Mud Borehole Imagers Through Modeling and Inversion

The new-generation, high-definition oil-based mud borehole imagers measure button impedances, which are often inverted to produce images of the formation resistivity, formation permittivity, and sensor standoff. These images, each reflecting a unique aspect of the downhole media, can provide a comprehensive understanding of the reservoir’s secondary porosity, i.e., fractures and vugs. To understand and validate the inversion behavior on fractures and vugs, synthetic logs of axisymmetric 2D fractures and vugs are generated and inverted. While the inverted medium properties follow the variation of the fracture-filling materials, the inverted standoff is shown to be a reliable indication of the fracture open/closed conditions. Specifically, an increased inverted standoff would always appear for mud-filled open fractures, which is further validated by laboratory measurements on artificial fractures and vugs. Numerical tests indicate that mineral-filled fractures may also lead to some variations on the inverted standoff when the resistivity contrast between the mineral-filling material and the host formation is high. Therefore, an elevated standoff may also be associated with a mineral-filled fracture. The modeling and inversion help reveal the connection between the response of the inverted parameters and the actual fracture characteristics. When the fractures are open and filled with mud, the inversion obtains an equivalent standoff at the fractures. This equivalent standoff increases not only with fracture width but also with the resistivity of the host formation. As a result, a fracture may have varying amplitudes in different formation layers. The fracture modeling and inversion also allow us to understand the prevalent existence of conductive fractures observed in the field. It is commonly thought that the resistivity of oil-based mud is always higher than that of the formation. However, this is only true at traditional operating frequencies. Because of mud dispersion, the mud resistivity is different at the two operating frequencies. For an open, mud-filled, resistive fracture to turn conductive, the formation resistivity only needs to exceed the mud resistivity at the higher operating frequency, which is typically on the order of a few 100 Ω·m instead of many 1,000 Ω·m at the lower operating frequency. As a result, an open fracture could be easily conductive in one layer but resistive in another formation layer.

A PVT tolerant low power wide tuning range differential voltage controlled oscillator design in 90 nm CMOS technology

This paper presents a three-stage low power and wider tuning range differential ring-oscillator with dual control voltages. This design permits lower tuning gain using dual control voltage (VTUNE 1 and VTUNE 2) to achieve high operation frequency. The dual voltage control enables a large bias current into the circuit. The proposed DRO has been implemented in 90 nm CMOS technology, whose performance results show a very high output frequency range which includes lower frequency band (LFB) and higher frequency band (HFB) from 0.007 GHz to 13.48 GHz. This DRO shows power consumption from 0.001 mW to 2.307 mW and phase noise of −92.27 dBc/Hz @ 1MHz offset. The figure of merit (FoM) for this DRO turns out to be −179.98 dBc/Hz. In addition, process corner analysis, Monte Carlo analysis, temperature sweep analysis, and stability analysis has been performed to find the robustness of the circuit.

Compact Wideband Groove Gap Waveguide Bandpass Filters Manufactured with 3D Printing and CNC Milling Techniques.

This paper presents for the first time a compact wideband bandpass filter in groove gap waveguide (GGW) technology. The structure is obtained by including metallic pins along the central part of the GGW bottom plate according to an n-order Chebyshev stepped impedance synthesis method. The bandpass response is achieved by combining the high-pass characteristic of the GGW and the low-pass behavior of the metallic pins, which act as impedance inverters. This simple structure together with the rigorous design technique allows for a reduction in the manufacturing complexity for the realization of high-performance filters. These capabilities are verified by designing a fifth-order GGW Chebyshev bandpass filter with a bandwidth BW = 3.7 GHz and return loss RL = 20 dB in the frequency range of the WR-75 standard, and by implementing it using computer numerical control (CNC) machining and three-dimensional (3D) printing techniques. Three prototypes have been manufactured: one using a computer numerical control (CNC) milling machine and two others by means of a stereolithography-based 3D printer and a photopolymer resin. One of the two resin-based prototypes has been metallized from a silver vacuum thermal evaporation deposition technique, while for the other a spray coating system has been used. The three prototypes have shown a good agreement between the measured and simulated S-parameters, with insertion losses better than IL = 1.2 dB. Reduced size and high-performance frequency responses with respect to other GGW bandpass filters were obtained. These wideband GGW filter prototypes could have a great potential for future emerging satellite communications systems.

LiNbO3 Surface Acoustic Wave Resonators with Large Effective Electromechanical Coupling

This paper reports an LNO surface acoustic wave (SAW) resonator based on a shear horizontal mode with high operating frequency over 3 GHz, large electromechanical coupling of 33.54%, Q factor of 380, and a relatively good figure of merit (FOM) of 127. Combing crystal-ion-slicing (CIS) technology with a room temperature bonding method, a 4-inch single crystalline LNO thin film on silicon is prepared successfully. The influence of damaged LNO film on crystalline quality and SAW performance is comprehensively analyzed. After totally removing the damaged layer, the electromechanical coupling and Q factor is significantly improved. The high-performance SAW resonator possesses the potential to meet the requirements of SAW filters for the fifth-generation (5G) communication in terms of high frequency, large bandwidth, and a high-quality factor.

Experimental and numerical study of a liquid metal magnetohydrodynamic generator for thermoacoustic power generation

Combining a thermoacoustic cycle engine with a liquid metal magnetohydrodynamic (LMMHD) generator will result in a thermal power generation system with no mechanical moving parts and high reliability. This disruptive technology has drawn much attention in space nuclear power generation, especially in recent years. It requires an LMMHD generator to work at a higher frequency than conventional LMMHD generators targeted for ocean wave energy conversion. However, the operating characteristics and loss mechanisms of LMMHD generators at high operating frequencies remain poorly understood, and experimental characterization of such a generator is lacking. In this work, a three-dimensional transient numerical analysis of a high-frequency LMMHD generator is performed based on multi-physics field simulation software COMSOL, to understand the operating characteristics of the generator, and the effects of inlet velocity, load resistance, and operating frequency on the generator’s performance. Furthermore, an LMMHD generator prototype was designed, constructed, and tested under different inlet velocities, load resistances, and frequencies by using a linear compressor for the first time. When the operating frequency and inlet velocity are 15 Hz and 4.3 m/s, the output voltage and current of the generator prototype reached 113 mV and 1720 A, with an output power of 68 W at a corresponding acoustic-to-electric efficiency of 24 %. A discrepancy between the numerical predictions and the experimental results was found, which gave insight into where further improvements can be made. This work reveals the operating characteristics and losses mechanism of LMMHD generators operating at higher frequencies and contributes to the development of high-efficiency generators for thermoacoustic power generation.

Flexible FPGA 1D DCT hardware architecture for HEVC

In this work, we propose a flexible 1D DCT hardware design with a constant throughput of 32 pixels per cycle for all transform block (TB) size modes. The design supports all TB sizes defined in the HEVC standard. Flexibility is achieved by multiplexing only the outputs, which results in lower data path delays compared to other proposed designs. Also, the additional partial butterfly units are transferred to the output of transformation cores. The transformation operation is done in a single stage to minimize the latency of the design and reduce hardware usage. The highly parallel input reduces the need for a very high operational frequency, which is suitable for low-power FPGA designs. Four different reusable transformation cores are used that are designed using parallel Multiple Constant Multiplication (MCM) units to further reduce the calculation time. The design was implemented on the Virtex UltraScale + device. The implementation has hardware usage of 21,818 LUTs, and it can reach the maximal throughput of 4.90 Gsps at the working frequency of 153 MHz which is enough to support the video resolutions of up to 8192 × 4320@60fps. Comparison with the other works shows that DCT FPGA implementation without DSPs can reach the performance of the ASICs with trade-offs in power consumption.

Low-Profile Planar Ultrawideband Modular Antenna Array Loaded With Parasitic Metal Strips

A low-profile dual-polarized planar ultrawideband modular antenna (PUMA) array is proposed in this paper. The overall profile is as small as 11.4 mm (0.228λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> is the free-space wavelength at the highest operating frequency) based on element sizes 25 × 25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0.5 × 0.5λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>high</i></sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and a large operating frequency bandwidth achieved by loading lossless parasitic metal strips between the dipole patch and the ground plane. The loop-mode resonance that causes deterioration of the port isolation around the lowest operating frequency is comprehensively analyzed and suppression methods are proposed. To further reduce the overall profile, a metasurface-based wide-angle impedance matching (MS-WAIM) layer is introduced. The surface waves guided by the MS-WAIM layer during wide-angle scanning in H-plane are suppressed by cutting properly-sized square holes at critical positions. The calculated results show that the proposed infinite array can scan up to ±60° in E/H-planes with active VSWRs below 2.9 within 2–6 GHz and orthogonal port isolations beyond 20 dB. A 12 × 11 array prototype is fabricated and reasonable agreement is achieved between the calculated and measured results.

Microcontroller-Based Trapezoidal Slope Compensation Technique for Peak Current Mode Control at MHz Frequencies

Slope compensation is necessary for the peak cur-rent mode control technique to ensure the stability of the power converter. Micro-controllers (μCs) existing in the market implement the slope compensation using built-in digital to analog converters (DACs). DACs exhibit finite transient times, which can be negligible when the μCs are used to control the power converters at switching frequencies in the order of a few hundreds of kHz. However, for high device switching frequency (HDSF) operation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq 1\, \rm{MHz}$</tex-math></inline-formula> ), the DAC transient time becomes significant and can make it difficult, if not impossible, to achieve the conventional ramp slope compensation. Hence, in this paper, a novel concept of ‘trapezoidal’ slope compensation is proposed by considering the transient time of the μC. A detailed analysis is performed to understand the effect of the transient period on the converter stability. The proposed technique is validated with an experimental prototype of 400 W at 1 MHz switching frequency and it is shown to ensure stability of the converter at all operating points within the specification.

Modeling and Operation of Series-Parallel Resonant Load in Industrial RF Dielectric Heating Application

Radio Frequency (RF) based heating application is used in multiple industries like drying cross-laminated woods, food and packaging, melting silicon etc. These industrial RF heating plants operate at frequencies of 6.78 MHz, 13.56 MHz, or 27.12 MHz (ISM band). Historically, the high frequency requirement has forced the industry to rely on vacuum tube based RF generator, which are only 60% efficient. Modern semiconductors like wide bandgap (WBG) devices have achieved the high frequency operation that is required to replace the inefficient vacuum tubes. However, a comprehensive study of load network for an industrial RF heating plant has not been undertaken such that an existing plant can be retrofitted with semiconductor based turn-key solution. In this paper the authors present design equations for an industrial RF dielectric heating load structure and suggest necessary modifications required to replace vacuum tube RF generator with voltage source converter (VSC). A new figure of merit (FOM) is defined that impacts the load structure efficiency. Finally, a small-scale prototype load is manufactured as a case study. The prototype demonstrated an output power of 750 W at 6.76 MHz with an overall efficiency of 90% from DC input to RF load which can not be achieved with a vacuum tube technology.