Microwave Amplifiers Research Articles

Suppression of Self-Excitation by a Local Absorber in a Relativistic Plasma Microwave Amplifier

Suppression of Self-Excitation by a Local Absorber in a Relativistic Plasma Microwave Amplifier

Rapidly Enhanced Spin-Polarization Injection in an Optically Pumped Spin Ratchet

Rapid injection of spin polarization into an ensemble of nuclear spins is a problem of broad interest, spanning dynamic nuclear polarization (DNP) to quantum information science. We report on a strategy to boost the spin-injection rate by exploiting electrons that can be rapidly polarized via high-power optical pumping. We demonstrate this in a model system of nitrogen-vacancy center electrons injecting polarization into a bath of ${}^{13}\mathrm{C}$ nuclei in diamond. We deliver $>20$ W of continuous, nearly isotropic, optical power to the sample, constituting a substantially higher power than in previous experiments. Through a spin-ratchet polarization transfer mechanism, we show boosts in spin-injection rates by over 2 orders of magnitude. Our experiments elucidate bottlenecks in the DNP process caused by rates of electron polarization, polarization transfer to proximal nuclei, and spin diffusion. This work demonstrates opportunities for rapid spin injection employing nonthermally generated electron polarization, and has relevance to a broad class of experimental systems, including in DNP, quantum sensing, and spin-based MASERs (microwave amplification by stimulated emission of radiation).

Review of the development of the hydrogen maser technique and a brief introduction to its space applications

Since 1960, when the first hydrogen frequency standard, the microwave amplification by stimulated emission of radiation (maser), was developed in the laboratory of Norman Ramsey at Harvard University, the performance of its frequency stability and technique development have been closely related to scientific research. A variety of H-maser designs have been developed for the demands of space science applications, including the deep space network (DSN) and the gravity probe (GP) experiment. H-maser is one of three well-developed microwave atomic frequency standards and is widely used worldwide in both ground and on-board-based settings. Along with upgrades to the frequency stability performance of the H-maser, improved knowledge of the world has also been reported.

Сравнительный анализ методов измерения тепловых параметров интегральных СВЧ-усилителей мощности на биполярных транзисторах

A brief analysis of methods and features of measuring thermal parameters of integrated microwave power amplifiers on bipolar transistors (BT) is presented. The hardware and software complex implementing the method of measuring the thermal parameters of the amplifier according to OST 11 0944-96 and the original modulation method is described. In both methods, the temperature of the active region of BT crystals is determined by a change in a certain temperature-sensitive parameter (TSP) of BT when they are heated by pulsed power. The results of comparative measurements of the thermal resistance of the junction-housing of the L-band integrated microwave amplifier on silicon BT are presented. The optimal duration of the heating pulses in the standard method was determined based on the analysis of the previously measured transient thermal characteristics of the amplifier. To exclude the influence of transients when switching the amplifier from the heating mode to the measurement mode, the temperature of the BT crystal at the end of the heating power pulse was determined by interpolating the results of several TSP measurements under the assumption that the crystal cooling curve has a root character. It is shown that the results of measuring the thermal resistance of the junction-housing of an integral microwave amplifier by both methods are in good agreement with each other.

Development of Quantum Limited Superconducting Amplifiers for Advanced Detection

Ultralow-noise microwave amplification and detection play a central role in different applications, going from fundamental physics experiments to the deployment of quantum technologies. In many applications the necessity of reading multiple detectors, or cavities or qubits, calls for large bandwidth amplifiers with the lowest possible noise. Current technologies are based on High Electron Mobility Transistors and Josephson Parametric Amplifiers. Both have limitations, the former in terms of the minimum noise, the latter in terms of bandwidth. Superconducting Traveling Wave Parametric Amplifiers (TWPAs) have the potential of offering quantum limited noise and large bandwidth. These amplifiers are based on the parametric amplification of microwaves traveling along a transmission line with embedded nonlinear elements. We are developing superconducting TWPAs based both on Josephson junction arrays (Traveling Wave Josephson Parametric Amplifiers) and on nonlinear kinetic inductance (Dispersion Engineered Traveling Wave Kinetic Inductance Amplifiers). Our goal is to achieve large bandwidth (in the 5 to 10 GHz range), large gain (more than 20 dB), large saturation power (more than −50 dBm), and near quantum limited noise (noise temperature less than 600 mK). Current achievements in the design and development of the high performance TWPAs are here reported and discussed, together with current limitations and possible future developments.

Bimodal Approach for Noise Figures of Merit Evaluation in Quantum-Limited Josephson Traveling Wave Parametric Amplifiers

The advent of ultra-low noise microwave amplifiers revolutionized several research fields demanding quantum-limited technologies. Exploiting a theoretical bimodal description of a linear phase-preserving amplifier, in this contribution we analyze some of the intrinsic properties of a model architecture (i.e., an rf-SQUID based Josephson Traveling Wave Parametric Amplifier) in terms of amplification and noise generation for key case study input states (Fock and coherents). Furthermore, we present an analysis of the output signals generated by the parametric amplification mechanism when thermal noise fluctuations feed the device.

Phase diffusion and noise temperature of a microwave amplifier based on single unshunted Josephson junction

High-gain microwave amplifiers operating near quantum limit are crucial for development of quantum technology. However, a systematic theoretical modeling and simulations of their performance represent rather challenging tasks due to the occurrence of colored noises and nonlinearities in the underlying circuits. Here, we develop a response theory for such an amplifier whose circuit dynamics is based on nonlinear oscillations of an unshunted Josephson junction. The theory accounts for a subtle interplay between exponentially damped fluctuations around the stable limit cycle and the nonlinear dynamics of the limit cycle phase. The amplifier gain and noise spectrum are derived assuming a colored voltage noise at the circuit resistor. The derived expressions are generally applicable to any system whose limit cycle dynamics is perturbed by a colored noise and a harmonic signal. We also critically assess reliabilities of numerical methods of simulations of the corresponding nonlinear Langevin equations, where even reliable discretization schemes might introduce errors significantly affecting simulated characteristics at the peak performance.

Second law analysis of MHD Carreau fluid flow through a microchannel with thermal radiation

The present work projects on constructing a Carreau fluid to investigate the entropy rate for a magnetohydrodynamic (MHD) steady fluid flow in a micro-channel. The second law of thermodynamics and rheological expressions of Carreau fluid are considered. This theoretical study is relevant to a microchannel heat sink, a microchannel heat exchanger, a microwave amplifier manufacturing process, medicine, renewable energies, polymer extrusion, nuclear reactors, fiber production refrigeration, and electrical cooling. The numerical simulations were computed with the Finite element method. The graphical illustrations were constructed to examine the effect of various physical quantities for entropy, Bejan number, velocity, and temperature conditions. Simulated results show that entropy and Bejan number (Be) have the escalating behavior of the magnetic parameter.

An Innovative Odd-Power Divider by means of a Triple FinLine Waveguide to Microstrip Transition

This paper outlines a novel approach to design a waveguide to microstrip Finline transition, that allows a division by three of the RF power traveling inside a rectangular waveguide. The possibility of obtaining and odd power division of microwave and millimeter wave signals with such Finline transition is completely unexplored yet harbinger of great opportunities. Starting from a 3D CAD model of the structure and continuing with Electromagnetic simulations, the obtained results completely describe a transition able to achieve an almost perfect power splitting by three. Multyphisics simulations, show an intrinsic resistance to vibrations of such transition, allowing it to be installed on aircraft or satellites modules. Thanks to this achievement a total new kind of power devices will come next, exploiting this odd power division in fact, it will be possible to realize different types of microwave amplifiers, increasing the efficiency and decreasing the occupied size. At the Author’s best knowledge it is the first time a divider by three Finline transition is reported in literature.

A Convolutional Neural Network for Human Motion Recognition and Classification Using a Millimeter-Wave Doppler Radar

Human movement detection based on millimeter-wave radar sensors is a technology of interest in various areas such as for smart surveillance, security, behavioral biometrics, biomedical systems, robotics, etc. This paper shows the feasibility and effectiveness of using a compact 24 GHz Doppler radar with a built-in low-noise microwave amplifier (LNA) for detecting and extracting signals coming from human motion. Reliability and accuracy is assessed based on a comprehensive theoretical analysis, and on simulation results followed by experimental investigations. A continuous wavelet transform (CWT) is used to decompose in-phase and quadrature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I/Q}$ </tex-math></inline-formula> ) baseband signals to extract information about the dynamics of the system. The dataset consists of 1000 recordings in 8 motion classes (standing, walking, sitting, etc.). We propose to apply a two-channel convolutional neural network (CNN), which is composed of two CNN channels, for learning high-level features from time-domain signals and CWT spectrograms. One channel has four one-dimensional (1D) convolutional and pooling layers, and the other channel is made of three two-dimensional (2D) convolutional and pooling layers. In addition, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I/Q}$ </tex-math></inline-formula> signals are denoised by using Savitzky-Golay filtering, and both noisy and denoised signals are used as input signals for deep learning data augmentation purpose. We achieved an overall classification accuracy rate of 98.85% in motion classification for a two-branch CNN architecture, and an accuracy rate of 95.3% for a one-branch 2D-CNN. Our results show that a dual-channel CNN model can greatly increase the classification capabilities of human motion recognition and classification, and the proposed method can be effectively used with various radar signal classifications.

Stability criteria of two-port networks, application to thermo-acoustic systems

System theory methods are developed and applied to introduce a new analysis methodology based on the stability criteria of active two-ports, to the problem of thermo-acoustic instability in a combustion appliance. The analogy between thermo-acoustics of combustion and small-signal operation of microwave amplifiers is utilized. Notions of unconditional and conditional stabilities of an (active) two-port, representing a burner with flame, are introduced and analyzed. Unconditional stability of two-port means the absence of autonomous oscillation at any embedding of the given two-port by any passive network at the system's upstream (source) and downstream (load) sides. It has been shown that for velocity-sensitive compact burners in the limit of zero Mach number, the criteria of unconditional stability cannot be fulfilled. The analysis is performed in the spirit of a known criterion in microwave network theory, the so-called Edwards-Sinsky's criterion. Therefore, two methods have been applied to elucidate the necessary and sufficient conditions of a linear active two-port system to be conditionally stable. The first method is a new algebraic technique to prove and derive the conditional and unconditional stability criteria, and the second method is based on certain properties of Mobius (bilinear) transformations for combinations of reflection coefficients and scattering matrix of (active) two-ports. The developed framework allows formulating design requirements for the stabilization of operation of a combustion appliance via purposeful modifications of either the burner properties or/and of its acoustic embeddings. The analytical derivations have been examined in a case study to show the power of the methodology in the thermo-acoustics system application.

Theory of drain noise in high electron mobility transistors based on real-space transfer

High electron mobility transistors are widely used as microwave amplifiers owing to their low microwave noise figure. Electronic noise in these devices is typically modeled by noise sources at the gate and drain. While consensus exists regarding the origin of the gate noise, that of drain noise is a topic of debate. Here, we report a theory of drain noise as a type of partition noise arising from real-space transfer of hot electrons from the channel to the barrier. The theory accounts for the magnitude and dependencies of the drain temperature and suggests strategies to realize devices with lower noise figure.

Design and Test of Innovative Three-Couplers-Based Bandpass Negative Group Delay Active Circuit

An innovative design method of bandpass (BP) negative group delay (NGD) active circuit is developed. The BP NGD topology consists originally of octopole and hexapole coupled line (CL) couplers. The NGD active circuit is validated by a prototype implemented in hybrid technology. The measured results are in good agreement with simulations. The CL-based passive circuit generates BP NGD performance with simulated and measured results showing NGD level of approximately -12 ns having 1.97 GHz center frequency with -11 dB transmission coefficient and -16 dB reflection coefficient. To compensate the loss, active circuit was fabricated by cascading the passive circuit with a microwave amplifier. Subsequently, the previous BP NGD performance is achieved with 0 dB gain. Moreover, a notable active microwave device characterization is performed with the NGD prototype via nonlinear measurements. It was found that the tested NGD prototype operates with 10-dB noise figure, 21 dBm P1dB compression, 29 dBm and 41 dBm OIP3.

Microwave Optomechanically Induced Transparency and Absorption Between 250 and 450 mK

High-quality microwave amplifiers and notch-filters can be made from microwave optomechanical systems in which a mechanical resonator is coupled to a microwave cavity by radiation pressure. These amplifiers and filters rely on optomechanically induced transparency (OMIT) and absorption (OMIA), respectively. Such devices can amplify microwave signals with large, controllable gain, high dynamic range and very low noise. Furthermore, extremely narrowband filters can be constructed with this technique. We briefly review previous measurements of microwave OMIT and OMIA before reporting our own measurements of these phenomena, which cover a larger parameter space than has been explored in previous works. In particular, we vary probe frequency, pump frequency, pumping scheme (red or blue), probe power, pump power and temperature. We find excellent agreement between our measurements and the predictions of input/output theory, thereby guiding further development of microwave devices based on nanomechanics.

Changes in the characteristics of semiconductor structures of microwave amplifiers under the action of pulsed laser radiation

The effect of pulsed laser radiation on the change in the parameters of semiconductor structures of field-effect transistors with a Schottky gate with an operating frequency range of 1.5-8 GHz and integrated amplifiers with an operating frequency range of 0.4-6 GHz is studied. Laser radiation with 25 ns pulse duration, incident on the transistor crystal, creates a pulsed photocurrent. It is shown that the amplitude of the pulsed photocurrent is three times higher than the operating transistor current. The current-voltage characteristics of the field-effect transistor were measured in the mode of pulsed laser radiation. The amplitude dependence of the pulsed photocurrent in semiconductor structures on the power of laser radiation for various wavelengths of 1.06 μm and 0.53 μm is studied. It is shown that as a result of the action of pulsed laser radiation on semiconductor structures, a short disappearance of the amplification of the high-frequency signal at the amplifier output occurs. Keywords: laser radiation, transistor, microwave amplifier, photocurrent, current-voltage characteristic.

Characterization Technique to Reveal Critical Resonances in Nonlinear RF Circuits

The presence of critical resonances can significantly impact the stable and robust operation of microwave amplifiers, leading to spurious oscillations in the worst case. In this work, a technique based on noise measurements performed with a spectrum analyzer is presented to experimentally characterize these resonances. Broadband white noise is injected into the input of the circuit, so the critical resonances are clearly revealed above the noise floor of the measuring instrument, without the need of exigent settings and far from the bifurcation point. In addition to detecting potentially risky resonances, the actual position of the critical poles on the pole-zero map can be estimated from these noise measurements by applying pole-zero identification techniques. The noise injection technique has been tested in two nonlinear prototypes in microstrip technology: an analog frequency divider and an <inline-formula> <tex-math notation="LaTeX">${L}$ </tex-math></inline-formula>-band amplifier.

РАЗРАБОТКА РЕТРАНСЛЯТОРА ДЛЯ УСТРОЙСТВА КОНТРОЛЯ ИЗМЕНЕНИЯ СОСТАВА ВОЗДУШНОЙ СРЕДЫ

This work is part of a project to create a device for monitoring changes in the composition of the air environment. The article describes the main elements of the repeater unit included in the measuring device. The results of modeling the developed band-pass filter, which is part of the waveguide path of the repeater, are presented. Experimental studies of the filter and circulator parameters are also carried out. The technical capabilities of the electronic part of the repeater unit, namely microwave amplifiers and a controlled phase shifter, are described.

Ultra-Low Phase Noise Measurement of Microwave Sources Using Carrier Suppression Enabled by a Photonic Delay Line

We propose and demonstrate a photonic delay line based carrier suppression interferometer system for measuring the phase noise of microwave sources. We show both theoretically and experimentally for the first time that carrier suppression is capable of suppressing the effects of the residual phase noise of the microwave amplifiers and the relative intensity noise of light in the system by up to 70 dB, and therefore effectively eliminates the contributions of these noise sources to the noise floor of the phase noise measurement system. Using a 2-km photonic delay line, we achieved phase noise measurement floors of −126 dBc/Hz at 1 kHz and −152 dBc/Hz at 10 kHz around a 10 GHz carrier, respectively, which are 15 and 20 dB lower than those of a frequency discriminator based phase noise measurement system using the same length of fiber delay and the same optical and microwave components. The noise floor of −152 dBc/Hz at 10 kHz is also 8 dB and 17 dB lower than those of a Keysight E5052B phase noise measurement system with 100-times cross-correlation and without cross-correlation, respectively. Even lower phase noise floors are expected for such a carrier suppression system if microwave phase shifters with lower residual phase noise or a longer photonics delay line are used.

Performance characteristics of bistable active ring resonators based on ferrite films

A bistability phenomenon in a ring resonator consisting of a delay line on surface spin waves and a microwave amplifier has been experimentally investigated. It is shown that an enhancement of the gain coefficient above a specified value provides an appearance of a hysteresis at the resonator transmission characteristic. A frequency range of the bistability broadens due to an increase of the gain coefficient as well as the external magnetic field. While the value of the gain is limited from above by a transition of the ring into a self-oscillating regime, an increase in the magnetic field from 1150 Oe up to 3150 Oe provides an expansion of the frequency range of the hysteresis from 77 kHz to 185 kHz.

Quasiballistic electron transport in cryogenic SiGe HBTs studied using an exact, semi-analytic solution to the Boltzmann equation

Silicon–germanium heterojunction bipolar transistors (HBTs) are of interest as low-noise microwave amplifiers due to their competitive noise performance and low cost relative to III–V devices. The fundamental noise performance limits of HBTs are thus of interest, and several studies report that quasiballistic electron transport across the base is a mechanism leading to cryogenic non-ideal IV characteristics that affect these limits. However, this conclusion has not been rigorously tested against theoretical predictions because prior studies modeled electron transport with empirical approaches or approximate solutions of the Boltzmann equation. Here, we study non-diffusive transport in narrow-base SiGe HBTs using an exact, semi-analytic solution of the Boltzmann equation based on an asymptotic expansion approach. We find that the computed transport characteristics are inconsistent with experiments, implying that quasiballistic electron transport is unlikely to be the origin of cryogenic non-ideal IV characteristics. Our work helps to identify the mechanisms governing the lower limits of the microwave noise figure of cryogenic HBT amplifiers.