Radio Frequency Oscillator Research Articles

Effects of power on ion behaviors in radio-frequency magnetron sputtering of indium tin oxide (ITO)

This study delves into ion behavior at the substrate position within RF magnetron discharges utilizing an indium tin oxide (ITO) target. The positive ion energies exhibit an upward trajectory with increasing RF power, attributed to heightened plasma potential and initial emergent energy. Simultaneously, the positive ion flux escalates owing to amplified sputtering rates and electron density. Conversely, negative ions exhibit broad ion energy distribution functions (IEDFs) characterized by multiple peaks. These patterns are clarified by a combination of radiofrequency oscillation of cathode voltage and plasma potential, alongside ion transport time. This elucidation finds validation in a one-dimensional model encompassing the initial ion energy. At higher RF power, negative ions surpassing 100 eV escalate in both flux and energy, posing a potential risk of sputtering damages to ITO layers.

Non-conventional resonant behavior of an unconfined magnetic domain wall in a permalloy strip

The resonant dynamic of a magnetic domain wall in a permalloy microstrip has been investigated using an innovative experimental setup that enables a simultaneous measurement of the ferromagnetic resonance and the magnetoresistance. The resonance frequency associated with the presence of the magnetic domain wall increases linearly with the external magnetic field in the range of fields where the domain wall is present in the microstrip. This linear behavior is unusual in a domain wall and not related to the standard resonant modes of a magnetic domain wall, such as breathing, twisting, or translational modes. The slope of this linear dependency is 1.38 GHz/mT, which is an incredibly large value and allows the detection of very small changes in the external magnetic field. This linear behavior opens a path for developing a highly tunable radio frequency oscillator or a magnetic sensing device where the presence of an external field is detected via small variations in the resonant frequency of the domain wall.

Integrated segmented IQ-modulator for orthogonal sampling and multi-level high-bandwidth signal generation.

Photonic-assisted signal processing of high-bandwidth signals emerges as a solution for challenges encountered in electronic-based processing. Here we present a concept for a compact, photonic-assisted digital-to-analog converter (DAC) and optical IQ-modulator in one single integrated device based on two innovative concepts: a segmented Mach-Zehnder modulator and orthogonal sampling. For electrically driving the modulator, only a single radio frequency oscillator and no pulse source or electrical DAC are required. The presented and simulated proof-of-concept device with six segments can generate a multi-level and high-bandwidth signal from low-bandwidth electronic drivers; e.g., we show the generation of a 120 Gbps data rate, 16-quadrature amplitude modulation (16-QAM, 30 Gbaud) signal solely based on low-bandwidth (5 GHz) non-return-to-zero (NRZ) signals. Integrated on a silicon photonic platform, the device provides fixable speed and bandwidth operations, positioning it as a viable solution for diverse communication systems.

Data-driven fault diagnosis method for abnormal RF oscillation of gyrotrons

Gyrotrons are vacuum electronic devices capable of generating high-power, high-frequency THz radiation. With the increasing utilization of gyrotrons in thermonuclear fusion experimental devices, achieving higher output performance and ensuring stable and reliable operation have become key development goals. However, occasional radio frequency (RF) oscillation faults inside the gyrotron during long-pulse operation hinder its stable and reliable operation. Due to the difficulty in directly observing abnormal changes within the gyrotron resonator during operation, this paper explores a data-driven approach to diagnose RF oscillation faults in the gyrotron for the first time and proposes a classification model that combines K-Nearest Neighbors and Random Forest (KNN-RForest) algorithms for fault identification. Compared with seven baseline models, the results show that our proposed KNN-RForest model has a better classification performance. It is verified that data-driven methods can effectively identify RF oscillation faults in gyrotrons. Finally, the state probabilities of the gyrotron under different power levels were predicted using the KNN-RForest model, demonstrating the application of the KNN-RForest model in identifying gyrotron RF oscillation faults, which may be helpful for setting stable operating parameters for the gyrotron to reduce the likelihood of RF oscillation faults.

Coherent multi-band MIMO radar: robustness analysis to SSMF-based RF signal delivery.

A numerical evaluation is conducted to assess the impact of distributing radio frequency (RF) signals through optical fiber links on the performance of a coherent multi-band multiple-input multiple-output (MIMO) radar system. The analysis focuses on scenarios where the antennas are widely separated in comparison to the employed signal wavelengths. The development of a model to quantify the phase noise (PN) induced on each RF band due to the signal transmission through optical fiber links between the centralized base station and each radar peripheral is described. Monte Carlo simulation results are collected to estimate the key performance indicators (KPIs) for varying standard single-mode fiber (SSMF) length and different PN contributions. The main contributors to the PN are revealed to be chromatic dispersion (CD), double Rayleigh scattering (DRS), and mechanical vibrations. In a shipborne scenario, a significant performance degradation occurs only when the length of the fiber links reaches approximately 20 km. Further, the PN impact has also been studied in a shipborne scenario to analyze the robustness of the system for worse phase noise level assumptions. The results reveal excellent robustness of the proposed centralized acquisition and processing approach in the presence of both very long fiber links and economically employed RF oscillators.

METHOD OF MINIMIZATION SIDELOBES LEVEL AUTOCORRELATION FUNCTIONS OF SIGNALS WITH NON-LINEAR FREQUENCY MODULATION

Context. At present, when creating new and upgrading existing radar systems, solid-state generator devices are widely used, which imposes certain restrictions on the peak power of probing signals. To overcome this limitation, longer duration signals with internal pulse modulation are used. The main efforts of the researchers are focused on reducing the maximum level of the side lobes of the autocorrelation function of such signals, which, without taking additional measures, has a significant level, which complicates the work of systems for detecting and stabilizing the level of false alarms. Attention is paid to signals with non-linear frequency modulation, which consist of two and three linearly frequency-modulated fragments. The maximum level of the side lobes of such signals depends significantly on the frequency-time parameters of the fragments, and therefore it is very difficult to obtain its stable value. Searching for signals with minimal side lobe level values by optimizing their time-frequency parameters is a difficult task, because changing the parameters of previous signal fragments leads to changes in the parameters of subsequent fragments
 Objective. The aim of the work is to develop a method for simplifying the search for local minima of the level of side lobes of two- and three-fragment signals with nonlinear frequency modulation by using a modified mathematical model with a whole number of periods of radio oscillations of linear-frequency modulated fragments.
 Method. The developed method is based on the proposed modification of the mathematical model, which corrects the frequencytime parameters of two- and three-fragment signals with non-linear frequency modulation by modifying the values of the frequency modulation speed while providing an integer number of complete periods of radio frequency oscillations for each of the fragments, which simplifies the process of finding local minima of the level of side lobes.
 Results. Modification of the initial mathematical model leads to the expansion of the possible range of values of frequency-time parameters, ratios of durations and frequency deviations of linearly-frequency modulated fragments and ensures stability of the mathematical model with a decrease in the maximum level of side lobes of the autocorrelation function.
 Conclusions. It has been experimentally confirmed that the use of the proposed method of modifying the input frequency-time parameters of signals with non-linear frequency modulation in the vast majority of cases reduces the maximum level of side lobes and simpli-fies the process of finding its local minima. The optimal ratios of durations and deviations of the frequency of the signal frag-ments are determined, subject to these, stable operation of the models is ensured and, in most cases, - less than the value of the maximum level of the side lobes.

The Design of a 1-6 GHz Broadband Double-Balanced Mixer.

This brief proposes a 1-6 GHz broadband double-balanced mixer. On the basis of the standard Marchand balun mixer, two techniques to enhance the performance of the mixer are proposed. Firstly, by loading capacitors, the amplitude and phase imbalance of the balun at high frequencies are improved, thereby expanding the relative bandwidth of the mixer by 0.1. Secondly, by cascading a first-order LC filter at the intermediate-frequency (IF) port, the leakage of radio frequency (RF) and local oscillator (LO) signals at the IF port is reduced by approximately 8 dB and 7 dB, respectively. This brief analyzes the various parameters that affect balun indicators and designs a broadband balun with a double-layer spiral line structure. As a result of these technologies, a 1-6 GHz double-balanced mixer is realized. The chip area is 1.13 mm × 0.95 mm, and the isolation between the IF port and the RF port is 34 dB and yields 13.5 dBm input power at 1 dB compression point (IP1 dB). The chip is fabricated via the GaAs pHEMT process.

The Design Methods and Experiments for a 220-GHz Quasi-Optical Cryogenic Schottky Subharmonic Mixer of High Performance

In this article, we present systematic design methods and experimental verifications of a 220-GHz quasi-optical cryogenic Schottky subharmonic mixer. To maximize device performance over a wide bandwidth and overcome the difficulties in conjugate matching designs, an impedance optimization-based cooperative design method is proposed for such quasi-optical mixer that includes the on-chip antenna and heterodyne mixing circuit. A coplanar waveguide (CPW) tuning network is utilized and optimized to offset the parasitic reactance effect of Schottky diodes. Besides, a dual-band log-periodic-slot integrated lens antenna is presented for coupling the radio frequency and local oscillator radiations with high efficiency. A reversed field tracing method is proposed to acquire the position and size of the equivalent Gaussian waists at both frequencies, thus offering the guidance for optimizing the substrate thickness and lens dimensions for improved antenna gain and radiation pattern. A 220-GHz quasi-optical mixer prototype was fabricated and experimentally verified at both room and cryogenic temperatures. At 134 K, the single-sideband noise factor and the conversion loss are around 4.2–8.5 and 6–11 dB over a wide intermediate-frequency bandwidth of 0.5–20 GHz, showing the superior device performance at the comparable bands.

Photon statistics and quantum phase distribution for coherent optical links in the presence of phase noise from both the laser source and the RF oscillator, and dispersion

A model of photon statistics and quantum phase distribution is analyzed for coherent optical communication links in the presence of quantum phase noise, dispersion and phase noise of the radio-frequency (RF) oscillator using an in-line optical amplifier. The quantum analysis of a dual drive Mach–Zehnder modulator and the quantum transfer function for an optical field mode across an in-line amplifier is performed by taking into account both the quantum and the classical phase noises. The resulting photon statistics are compared with the semiclassical model. We analyze the quantum phase distribution by considering the Wigner quasiprobability distribution for a coherent optical link. Here, we investigate the broadening of the quantum phase distribution due to quantum phase noise of the laser, the dispersive optical fiber, the phase noise of the RF oscillator and the inevitable noise coefficient of the optical amplifier for arbitrary amplified spontaneous emission (ASE) field modes. We analytically investigate the quantum analog to the bit error rate (BER) as a function of the laser’s linewidth, the linewidth of the RF oscillator and chromatic dispersion. The results of quantum models are compared with the semiclassical model. Quantum treatment of both the BER and variance is found to agree with prior results for a single-mode ASE field in the absence of phase noise but deviate when the effect of phase noise is considered. Including phase noise effects in the amplitude in the semiclassical treatment of the BER yields a new semiclassical expression that agrees with quantum expressions of machine precision for single-mode ASE fields.

Design of a 240 GHz on-chip dual-polarization receiver for SIS mixer arrays

We report the design of a compact dual-polarization on-chip superconductor–insulator–superconductor receiver for array applications. The planar-circuit receiver chip is comprised of the entire radio frequency (RF) signal processing chain with three main circuit components alongside some auxiliary circuits: (1) a polarization splitting 4-probe orthomode transducer (OMT) that couples the RF and local oscillator signal from free space to the chip via a drilled feedhorn; (2) two hybrids that recombine the power of each polarization from the two sets of orthogonal OMT probes; and (3) twin-junction Nb/AlOx/Nb mixers that downconvert the recombined signals to the intermediate frequency. We ensure that the four side walls of each pixel are free from obscuration, using only the top and bottom of the pixel for various connections. Consequently, the design is extendable to a large format array. In this paper, we present the detailed design of the on-chip receiver, including extensive heterodyne simulations and its potential extension into a large format array.

Immediate and Late Effects of Pulse Widths and Cycles on Bipolar, Gated Radiofrequency-Induced Tissue Reactions in in vivo Rat Skin.

Single to multiple pulse packs of bipolar, alternating current radiofrequency (RF) oscillations have been used for various medical purposes using invasive microneedle electrodes. This study was designed to evaluate the effects of pulse widths and cycles of RF pulse packs on immediate and delayed thermal tissue reactions in in vivo rat skin. RF energy at the frequency of 1 MHz and power of 70 W was delivered at each experimental setting into in vivo rat skin at 1.5-mm microneedle penetration, and then, tissue samples were obtained after 1 h and 3, 7, 14, and 21 days and histologically analyzed. A single-pulse-pack RF treatment generated coagulative necrosis zones in the dermal peri-electrode area and zones of non-necrotic thermal reactions in the dermal inter-electrode area. Multiple pulse-pack, RF-treated rat skin specimens revealed that the number and size of peri-electrode coagulative necrosis were markedly decreased by increasing the number of pulse packs and accordingly decreasing the conduction time of each pulse pack. The microscopic changes in RF-induced non-necrotic thermal reaction in the inter-electrode area were more remarkable in specimens treated with RF of 7 or 10 pulse packs than in specimens treated with RF of 1-4 pulse packs. The gated delivery of multiple RF pulse packs using a bipolar, alternating current, 1-MHz RF system using insulated microneedle electrodes efficiently generates non-necrotic thermal tissue reactions over the upper, mid, and deep dermis and subcutaneous fat in the inter-electrode areas.

Effect of Pulse Widths and Cycles on Invasive, Bipolar, and Gated Radiofrequency-Induced Thermal Reactions in ex vivo Bovine Liver Tissue.

Radiofrequency (RF) oscillations generate thermal tissue reactions, the patterns of which vary depending on the mode and efficiency of energy delivery. The aim of our study was to analyze patterns of RF-induced thermal tissue reactions according to the modes of RF delivery, including continuous and gated modes, using an alternating current, invasive bipolar RF device. RF energies at frequencies of 1 and 2 MHz were delivered at respective experimental settings into ex vivo bovine liver tissue at a 0.5-mm microneedle penetration depth. The tissue samples were then evaluated thermometrically. A histologic study was performed to evaluate RF-induced thermal tissue reactions at a 3.0-mm microneedle penetration depth. Thermal imaging study revealed homogenous, well-demarcated, square-shaped zones of RF-induced thermal reactivity on the treated area. Multivariate linear regression analysis revealed that higher temperature elevations immediately after RF treatment (∆T1) were positively associated with RF frequency, power, conduction time/pulse pack, and off-time between pulse packs and negatively associated with total off time. In the 1-MHz experimental setting, higher ∆T1 showed a positive association with power, conduction time/pulse pack, and off-time between pulse packs and a negative association with the number of pulse packs. In the 2-MHz setting, however, higher ∆T1 was positively associated with only total treatment time. Thermometric effects during bipolar and gated RF treatments are significantly associated with the frequency, power, and pulse widths and cycles of pulse packs.

Radio-frequency sheath excitation at the extremities of scrape-off layer plasma filaments, mediated by resonant high harmonic fast wave scattering

Resonant filament-assisted mode conversion (FAMC) scattering of high harmonic fast waves (HHFW) by cylindrical field-aligned density inhomogeneities can efficiently redirect a fraction of the launched HHFW power flux into the parallel direction. Within a simplified analytic approach, this contribution compares the parallel propagation, reflection and dissipation of nearly resonant FAMC modes for three magnetic field line geometries in the scrape-off layer, in the presence of radio-frequency (RF) sheaths at field line extremities and phenomenological wave damping in the plasma volume. When a FAMC mode, excited at the HHFW antenna parallel location and guided along the open magnetic field lines, impinges onto a boundary at normal incidence, we show that it can excite sheath RF oscillations, even toroidally far away from the HHFW launcher. The RF sheaths then dissipate part of the power flux carried by the incident mode, while another part reflects into the FAMC mode with the opposite wave vector parallel to the magnetic field. The reflected FAMC mode in turn propagates and can possibly interact with the sheath at the opposite field line boundary. The two counter-propagating modes then form in the bounded magnetic flux tube a lossy cavity excited by the HHFW scattering. We investigate how the presence of field line boundaries affects the total HHFW power redirected into the filament, and its splitting between sheath and volume losses, as a function of relevant parameters in the model.

Radiation Hardened Millimeter-Wave Receiver Implemented in 90-nm, SiGe HBT Technology

This article presents novel radiation hardening design techniques to substantially reduce the single-event effects (SEEs) on high-frequency receivers subject to various radiations when operating in space. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band (75–110 GHz) receiver front-end implemented in Global Foundry’s 90-nm silicon–germanium (SiGe) BiCMOS technology is used for studying SEE and investigating the effectiveness of the proposed techniques. Specifically, the mixer is modified to allow for different modes of operation in addition to introducing matching considerations between the mixer’s gain and switching stages. The receiver includes integrated high-frequency signal sources to provide the input radio frequency (RF) and local oscillator (LO) signals for full operation of the proposed millimeter-wave (mmW) receiver. Measurements are taken while the receiver is in normal operation (RF and LO are applied). The design techniques are carefully analyzed via extensive simulations using equivalent transient current pulses obtained from calibrated technology computer-aided design (TCAD) simulations. A two-photon absorption (TPA) pulsed laser experiment is used to induce transient currents in the silicon–germanium heterojunction bipolar transistor (SiGe HBT) circuit. Various devices within the mixer are hit from the back side through a hole in the designed printed circuit board (PCB). The propagated transients are then captured using a high-speed oscilloscope at the output of the receiver. The measurement results, supported by simulations and analysis, validate the robustness of the proposed radiation hardened receiver to SEE.

Noise analysis of optoelectronic oscillators in the presence of the relative intensity noise of the laser

Optoelectronic oscillators (OEOs) have recently been considered very good candidates for producing ultra-low phase noise radio frequency (RF) oscillations. One of the most important noise sources of any OEO is the relative intensity noise (RIN) of the optical field in the optical part of this system. It is the dominant noise source in some OEO cases. The initial source of the RIN is the laser; however, it may be largely enhanced in the fiber by some phenomena such as the guided entropy mode Rayleigh scattering. Here a frequency domain analysis approach is introduced to separately analyze the effect of both the low-frequency RIN (LFRIN) and the high-frequency RIN (HFRIN), i.e., the RIN around the RF harmonics, on both the phase and amplitude noises of the delay-based single-loop/dual-loop OEOs. The presented approach can take into account the RIN at both the input and the output of the optical fibers. The measured or analytical nonlinear gain function of the photodetector and the RF amplifier can be taken into account to accurately characterize the important effect of the amplitude noise to phase noise (AN-PN) conversion. It is shown that the AN-PN conversion can largely enhance the LFRIN-induced phase noise. Also, to a much lesser degree, it can enhance the HFRIN-induced phase noise. Furthermore, it is shown that the AN-PN conversion reduces the HFRIN- and LFRIN-induced amplitude noise. It is also shown that the fibers’ dispersion has a small effect on the phase/amplitude noise power induced by either LFRIN or the HFRIN, especially for smaller fiber lengths. The validity of the new analysis approach is verified by comparing its results with those of the previously published works in the literature.

600-GHz high-temperature superconducting sub-harmonic mixer coupled using a double-Y-type slot integrated lens antenna

In this paper, we present a quasi-optically coupled 600-GHz high-temperature superconducting (HTS) sub-harmonic mixer for communication and sensing applications. The mixer features an innovative double-Y-type slot integrated lens antenna, which can efficiently couple the radio frequency (RF) and local oscillator (LO) signals with a small frequency ratio by exciting the half-wave and full-wave resonant current modes on the slot, respectively. Considering the low impedance characteristics of HTS Josephson junctions, a coplanar-waveguide stepped impedance transformer is utilized for minimizing the mismatching loss. A cascaded filter network is designed to prevent the high-frequency signal leakage at both bands while coupling the intermediate-frequency (IF) signal output efficiently. Based on this antenna design and an established HTS step-edge junction technology, a 600-GHz mixer prototype was designed, fabricated and measured, which was compared with the simulation results. The achieved conversion gain and noise temperature are the best performance specs as reported to date for HTS harmonic mixers at comparable frequencies and operating temperatures.

Performance Analysis of Resonant-Fin Transistors and Their Application in RF-Circuit Design

Emerging new communication standards like 5G or 6G aggravate the circuit design of radio-frequency generation systems as they constantly increase demand on high bandwidths, low latency, and high spectral purity. The utilization of high-<i>Q</i> oscillators, however, provides a possibility of optimisation of radio-frequency oscillators regarding their phase-noise performance in the overall system. This paper analyses one of the most promising electromechanical resonator devices, the resonant fin transistor with respect to its performance and application in oscillator circuit design. Several investigations regarding its working principle, design trade-offs and limits are carried out in this work. An oscillator circuit design is given for two variants of the resonant fin transistor device together with an outlook on its performance compared to other state-of-the-art radio-frequency oscillator designs. Following the performance analyses conducted throughout this work, the fundamental limit for the <i>Q</i>-factor of this resonator is investigated, challenging the validity of functionality of the resonant fin transistor and its potential for circuit applications.

Frequency-domain analysis of dual-loop optoelectronic oscillators.

Optoelectronic oscillators (OEOs) are hybrid systems consisting of optical and radio-frequency (RF) parts that are used to produce ultralow phase noise RF oscillations. Dual-loop OEOs can overcome some problems incorporated with single-loop OEOs such as the mode-hopping phenomenon and the large spurious peaks in the phase noise. Therefore, they are usually considered the practical implementation of many OEOs. Here, a frequency-domain steady-state and phase noise analysis approach of these systems is presented, based on the conversion matrix approach. Compared with the existing time-domain analysis approaches, it requires much smaller run times. Compared with the other frequency-domain modeling approaches, such as the linear-time-invariant phase transmission models, it can take all noise-transferring phenomena between various sidebands and all amplitude-noise to phase-noise conversions and vice versa into account. Therefore, it can be regarded as a comprehensive analysis approach to dual-loop OEOs. The validity of the new approach is verified by comparing its results with those of the previously published formulations in the literature.

Design of a Low-Power Radio Frequency Unit and Its Application for Bacterial Inactivation under Laboratory Conditions

A lab-scale low-power free-running radio frequency (RF) oscillator operating at a frequency of 27.12 ± 0.50 MHz was developed to be suitable for fundamental microbiological research topics. Calibration and validation were conducted for two common foodborne pathogens in relevant microbiological growth media, i.e., Salmonella Typhimurium and Listeria monocytogenes in Tryptic Soy Broth and Brain–Heart Infusion broth, respectively. The evolution of temperature, frequency, and power consumption was monitored during treatments, both with and without bacterial cells. The setup operated within the predefined frequency range, reaching temperatures of 71–76 °C after 15 min. The average power consumption ranged between 12 and 14 W. The presence of bacteria did not significantly influence the operational parameters. The inactivation potential of the RF setup was validated, demonstrating the absence of viable cells after 8 and 10 min of treatment, for S. Typhimurium and L. monocytogenes, respectively. In future studies, the setup can be used to conduct fundamental microbiological studies on RF inactivation. The setup can provide added value to the scientific field, since (i) no consensus has been reached on the inactivation mechanisms of RF inactivation of pathogens in foods and (ii) most commercial RF setups are unsuitable to adopt for fundamental studies.

Improvement of radio frequency heating uniformity for millets by changing shape and adding polypropylene blocks

Radio frequency (RF) treatment is a burgeoning method in food processes. RF heating non-uniformity is a main obstacle for industrial implementations and influenced by the geometry of treated materials. In this study, the effect of convex-concavo shapes of the sample top surface and step shapes at the bottom of the rectangular container by adding polypropylene (PP) blocks on the heating uniformity was investigated using a 6 kW, 27.12 MHz free-running oscillator RF system. The results showed that the RF heating uniformity index values of millets decreased with increasing convex degree and decreasing concave degree of the sample top shape. Moreover, adding PP blocks at the bottom of the sample container was a better choice of improving RF heating uniformity owing to the wider adjustable range of sample sizes and better temperature distribution. This study provided a new method to improve the RF heating uniformity by simply changing the shapes of samples in either the top or bottom surface.