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Microwave applications, such as microwave ovens and mobile phones, are ubiquitous and indispensable in modern society. As the utilization of microwave technology is becoming more widespread, the effects of microwaves on living organisms and physiological processes have received increased attention. This study aimed to investigate the effects of microwaves on calcium carbonate biomineralization as a model biochemical process. A magnetron oscillator was used to generate 2450 MHz microwaves because magnetrons are relatively inexpensive and widespread. We conducted transmission electron microscopy (TEM), atomic force microscopy (AFM), TEM-electron energy-loss spectroscopy (EELS), dynamic light scattering (DLS), and high-performance liquid chromatography (HPLC) measurements to analyze the calcium carbonate precipitates. Our findings showed the formation of string-like precipitates of calcium carbonate upon microwave irradiation from one direction, similar to those obtained using a semiconductor oscillator, as reported previously. This implied that the distribution of the frequency had little effect on the morphology. Furthermore, spherical precipitates were obtained upon microwave irradiation from two directions, indicating that the morphology could be controlled by varying the direction of microwave irradiation. Magnetrons are versatile and also used in large-scale production; thus, this method has potential in medical and industrial applications. [ABSTRACT FROM AUTHOR]

Dynamic nuclear polarization (DNP) is one of the most powerful and versatile hyperpolarization methods to enhance nuclear magnetic resonance (NMR) signals. A major drawback of DNP is the cost and complexity of the required microwave hardware, especially at high magnetic fields and low temperatures. To overcome this drawback and with the focus on the study of nanoliter and subnanoliter samples, this work demonstrates 200 GHz single chip DNP microsystems where the microwave excitation/detection are performed locally on chip without the need of external microwave generators and transmission lines. The single chip integrated microsystems consist of a single or an array of microwave oscillators operating at about 200 GHz for ESR excitation/detection and an RF receiver operating at about 300 MHz for NMR detection. This work demonstrates the possibility of using the single chip approach for the realization of probes for DNP studies at high frequency, high field, and low temperature. Cutting the cost and complexity of the microwave devices is crucial for expanding the applications of DNP enhanced NMR. Researchers introduce microsystems where the generation/detection of 200 GHz microwaves occur locally on a 1 mm2 silicon chip. [ABSTRACT FROM AUTHOR]

In this paper, a novel microwave oscillator is developed at frequencies of 5.7 and 7.5 GHz through the application of Negative Resistance and Harmonic Balance theory. The design process involves leveraging the Agilent Advance Design System (ADS) tool, ensuring exceptional electromagnetic (EM) performance. The utilization of microstrip circuit elements enhances the overall performance of the oscillator structure. Following optimization and co-simulation of nonlinear models for the compact Planar Microwave Oscillator (62 x 38 mm²), highly satisfactory results are obtained. Quantitatively, the measured output powers at 5.7 and 7.5 GHz are determined to be 9.5 dBm and 7.05 dBm, respectively. These power levels are particularly relevant for C band applications spanning 4 to 8 GHz, including areas such as satellite communication, radar, and wireless networks. [ABSTRACT FROM AUTHOR]

Purpose: The primary aim of this paper is to present a novel design approach for a ring voltage-controlled oscillator (VCO) suitable for L-band applications, whose oscillation frequency is less sensitive to power supply variations. In a few decades, with the advancement of modern wireless communication equipment, there has been an increasing demand for low-power and robust communication systems for longer battery life. A sudden drop in power significantly affects the performance of the VCO. Supply insensitive circuit design is the backbone of uninterrupted VCO performance. Because of their important roles in a variety of applications, VCOs and phase locked loops (PLLs) have been the subject of significant research for decades. For a few decades, the VCO has been one of the major components used to provide a local frequency signal to the PLL. Design/methodology/approach: First, this paper chose to present recent developments on implemented techniques of ring VCO design for various applications. A complementary metal oxide semiconductor (CMOS)-based supply compensation technique is presented, which aims to reduce the change in oscillation frequency with the supply. The proposed circuit is designed and simulated on Cadence Virtuoso in 0.18 µm CMOS process under 1.8 V power supply. Active differential configuration with a cross-coupled NMOS structure is designed, which eliminates losses and negates supply noise. The proposed VCO is designed for excellent performance in many areas, including the L-band microwave frequency range, supply sensitivity, occupied area, power consumption and phase noise. Findings: This work provides the complete design aspect of a novel ring VCO design for the L-band frequency range, low phase noise, low occupied area and low power applications. The maximum value of the supply sensitivity for the proposed ring VCO is 1.31, which is achieved by changing the VDD by ±0.5%. A tuning frequency range of 1.47–1.81 GHz is achieved, which falls within the L-band frequency range. This frequency range is achieved by varying the control voltage from 0.0 to 0.8 V, which shows that the proposed ring VCO is also suitable for low voltage regions. The total power consumed by the proposed ring VCO is 14.70 mW, a remarkably low value using this large transistor count. The achievable value of phase noise is −88.76 dBc/Hz @ 1 MHz offset frequency, which is a relatively small value. The performance of the proposed ring VCO is also evaluated by the figure of merit, achieving −163.13 dBc/Hz, which assures the specificity of the proposed design. The process and temperature variation simulations also validate the proposed design. The proposed oscillator occupied an extremely small area of only 0.00019 mm2 compared to contemporary designs. Originality/value: The proposed CMOS-based supply compensation method is a unique design with the size and other parameters of the components used. All the data and results obtained show its originality in comparison with other designs. The obtained results are preserved to the fullest extent. [ABSTRACT FROM AUTHOR]

Low phase noise oscillators are key building blocks of many high-end microwave systems. This work introduces a phase noise reduction mechanism through a gain driven polariton platform, where coherent coupling is used to suppress frequency distribution around the carrier, effectively reducing the phase noise. The design process for achieving low phase noise performance is outlined, and three prototypes are constructed, all of which feature key components, such as gain-embedded planar microwave cavity, yttrium iron garnet, and magnets. In particular, the first prototype is used to showcase the phase noise reduction mechanism, while the second prototype, a fixed-frequency oscillator working at 3.544 GHz, exhibits phase noise levels of −117 and −132 dBc/Hz at 10 and 100 kHz offset frequencies, respectively. The third prototype offers a tuning range from 2.1 to 2.7 GHz, while maintaining phase noise levels comparable to the second prototype. [ABSTRACT FROM AUTHOR]

Low guiding magnetic fields are favored for high-power microwave sources in practical applications for the sake of compactness and miniaturization, especially for permanent magnet packaging to replace the bulky and heavy solenoid system. A novel focusing cathode is proposed in a V-band transit-time oscillator to reduce the requirement for guiding magnetic fields. Particle-in-cell simulation results indicate that in the diode region, the radial electric field and electron beam current are reduced with the focusing cathode, further leading to improved transmission of the electron beam under a low guiding magnetic field. With an input of diode voltage of 393 kV, a beam current of 5.25 kA, and a low guiding magnetic field of 0.6 T, the transit-time oscillator outputs a microwave with an average power of 566 MW and a frequency of 58.6 GHz, resulting in a conversion efficiency of 27.3%. The proposed V-band transit-time oscillator with a focusing cathode can also stably work under a large range of input voltage and magnetic field, desired for further research with permanent magnet packaging. [ABSTRACT FROM AUTHOR]

Brillouin lasing has been widely applied to microwave oscillators, optical gyroscopes, optical sensors, and other fields owing to its strong and flexible dynamics. Microspheres with ultrahigh quality factors and small mode volume are very suitable for generating Brillouin lasing, but it is difficult to integrate them on a chip. Here, we utilize subwavelength grating waveguide as a photonic coupler to connect the silica microsphere with a silicon chip and realize on-chip backward Brillouin lasing. It is experimentally indicated that when the on-chip pump power reaches 24.8 mW, the backward Brillouin lasing with an on-chip slope efficiency of 5% will be excited. Our method makes it easier to realize on-chip Brillouin acousto-optic interaction and greatly expands the application range of microspheres. [ABSTRACT FROM AUTHOR]

In order to expand the range of mechanical tuning of generation frequency in a subgigawatt Cherenkov microwave oscillator, it is proposed to use а configuration of relativistic backward-wave oscillator (BWO) having no reflectors with the radiation output in the direction opposite to the electron beam. In a numerical experiment using KARAT electromagnetic PiC code, it is demonstrated that in this case, due to only variation of the slow-wave structure (SWS) period, it is possible to change the oscillation frequency by tens of percent preserving the TM01 operation mode. The frequency tuning range is thereby limited from below by the lower boundary of the SWS passband, near which the BWO oscillation regime is displaced by the orotron regime, and from above by high-frequency excitation of the competing TM02 mode. A moderately relativistic microwave oscillator is simulated with a tuning band between 2.73 and 4.15 GHz (frequency ratio 1.52) at the (−3 dB) level of the maximum microwave power (520 MW at 3.85 GHz). The feeding electron beam having 460 keV particle energy and 4.7 kA current is transported by the magnetic field with an induction of 1.0 T. Additional simulations demonstrate that the frequency tuning range is extendable to approximately an octave at the cost of lower generation efficiency. [ABSTRACT FROM AUTHOR]

This article shows the design of two different low phase noise (LPN) planar X-band frequency oscillators using two various microstrip filters (MFs). These two MFs act as a frequency stabilization part in the loop of the microwave oscillator. The first one, the modified Jerusalem MF (MJ-MF), is based on the Jerusalem scheme. The second one, the complementary modified Jerusalem MF (CMJ-MF), is complementary of the MJ-MF. Finally, by employing the branchline coupler, the LPN MF oscillator is achieved. The MJ-MF (narrowband filter) LPN X-band oscillator operates at 8.17 GHz and denotes a phase noise (PN) of −161 dBc/Hz at 1-MHz frequency offset. The CMJ-MF (wideband filter) LPN X-band oscillator operates at 8.14 GHz and mentions a PN of −157 dBc/Hz at 1-MHz frequency offset. [ABSTRACT FROM AUTHOR]

A cross-band frequency hopping high power microwave (HPM) oscillator with permanent magnet package was proposed. The oscillator comprises of an inner Ku-band hollow oscillator and an outer C-band coaxial oscillator. By comparing with other cross-band HPM oscillators, this device is quite compact and high efficiency, for the guiding magnetic field is as low as 0.43 T, which is provided by a 74 kg permanent magnet. Since the cathode can be adjusted telescopically to produce annular electron beams at different radius, different bands HPMs can be generated in the inner and the outer slow wave structure. Verified by particle-in-cell simulation, a HPM with a frequency of 7.8 GHz and a power of 3.1 GW is achieved for C-band, corresponding to a power efficiency of 45%. Respectively, a Ku-band HPM output with a frequency of 14.4 GHz and a power of 1.3 GW were obtained, corresponding to a power efficiency of 45%. [ABSTRACT FROM AUTHOR]

The frequency hopping technology is one of the most significant research directions for high-power microwave (HPM) devices. This paper presented a novel HPM oscillator with frequency hopping across C, X, and Ku bands based on magnetic field tuning. A coaxial transit time oscillator (TTO) is nested onto the outer conductor of the hollow relativistic Cherenkov microwave oscillator, which forms a dual electromagnetic structure with a single-annular cathode. When the electron beam is guided by gradient magnetic fields, it interacts with TTO to produce Ku-band HPMs. If the gradient magnetic field changes into the uniform magnetic field, the electron beam would enter the relativistic Cherenkov microwave oscillator, and the frequency of generated microwaves decreases, which are decided by the strength of the magnetic fields according to the cyclotron resonance absorption theory. In the particle-in-cell simulation, when the diode voltage and gradient magnetic field are 580 kV and 0.5 T, respectively, a Ku-band HPM output with a frequency of 13.9 GHz and a power of 2.09 GW is obtained, corresponding to power efficiency of 42%. When the magnetic field transforms into uniform, the device produces an X-band HPM output with a frequency of 9 GHz and a power of 2.4 GW at a diode voltage of 683 kV and a magnetic field of 0.7 T. When the voltage and magnetic field strength are increased to 699 kV and 1.5 T, respectively, the device generates a C-band HPM output with a frequency of 4.5 GHz and a power of 2.1 GW. The corresponding conversion efficiency of the X-band and C-band Cherenkov microwave oscillators is 35% and 30.7%, respectively. [ABSTRACT FROM AUTHOR]

Coupled microwave oscillators could be potentially considered a good replacement for the feed network of frequency‐diverse arrays. However, previous studies showed that the stability region for a mutually weak‐coupled oscillator array in the Mode Lock State (MLS) is too small to be practical. Besides, by increasing the coupling strength or reducing the initial natural frequency of the oscillators, the current analytical methods lose their accuracy. The final steady‐state and dynamic of a non‐linear Van‐der‐Pol medium‐coupled oscillator array in the MLS is investigated. By using the Kuramoto Model results in analysing the biological cells, an alternative approach is suggested and investigated in the entrainment region for the mode‐locked microwave oscillator array. This approach is accurate even for medium‐coupled oscillator arrays, where the locking range to the beat frequency ratio is greater than 0.1. The stability of the oscillator in this region is investigated by imposing some perturbations in the form of phase noise on the initial signals. Also, the optimum initial condition to design large arrays is investigated using the analysis results. In the described initial conditions for small beat frequencies, the simulation results show that the stability region is much greater than the large beat frequency region. This capability initiates a new practical approach for implementing Frequency Diverse Arrays. [ABSTRACT FROM AUTHOR]

Magnetic droplet solitons are dynamical magnetic textures that form due to an attractive interaction between spin waves in thin films with perpendicular magnetic anisotropy. Spin currents and the spin torques associated with these currents enable their formation as they provide a means to excite non-equilibrium spin-wave populations and compensate their decay. Recent years have seen rapid advances in experiments that realize and study magnetic droplets. Important advances include the first direct x-ray images of droplets, determination of their threshold and sustaining currents, measurement of their generation and annihilation time, and evidence for drift instabilities, which can limit their lifetime. This perspective discusses these studies and contrasts these solitons to other types of spin-current excitations, such as spin-wave bullets, and static magnetic textures, including magnetic vortices and skyrmions. Magnetic droplet solitons can also serve as current controlled microwave frequency oscillators with potential applications in neuromorphic chips as nonlinear oscillators with memory. [ABSTRACT FROM AUTHOR]

Spin Hall nano-oscillators (SHNOs) are promising candidates for new microwave oscillators with high durability due to a small driving current. However, conventional SHNOs with an in-plane precession mode require a bias field for stable oscillations, which is not favored in certain applications such as neuromorphic computing. Here, we propose and theoretically analyze a bias-field-free SHNO with an in-plane hard axis and an out-of-plane precession mode by solving the Landau–Lifshitz–Gilbert equation analytically and numerically. We derive formulas for driving currents and precession frequency and show that they are in good agreement with numerical simulation results. We show that our proposed SHNOs can be driven by much smaller bias current than conventional spin torque nano-oscillators. [ABSTRACT FROM AUTHOR]

The inherent nonlinear magnetization dynamics in spintronic devices make them suitable candidates for neuromorphic hardware. Among spintronic devices, spin torque oscillators such as spin transfer torque oscillators and spin Hall oscillators have shown the capability to perform recognition tasks. In this paper, with the help of micromagnetic simulations, we model and demonstrate that the magnetization dynamics of a single spin Hall oscillator can be nonlinearly transformed by harnessing input pulse streams and can be utilized for classification tasks. The spin Hall oscillator utilizes the microwave spectral characteristics of its magnetization dynamics for processing a binary data input. The spectral change due to the nonlinear magnetization dynamics assists in real-time feature extraction and classification of 4-binary digit input patterns. The performance was tested for the classification of the standard MNIST handwritten digit data set and achieved an accuracy of 83.1% in a simple linear regression model. Our results suggest that modulating time-driven input data can generate diverse magnetization dynamics in the spin Hall oscillator that can be suitable for temporal or sequential information processing. [ABSTRACT FROM AUTHOR]

Herein voltage and frequency controlled thin film transistors fabricated by depositing SeO2 onto germanium thin crystals are reported. For these devices measurements of the current-voltage characteristics revealed a biasing dependent rectification ratios. The devices showed metal-oxide-semiconductor character under reverse biasing conditions. In addition, the biasing dependent capacitance and conductance spectral studies in the frequency domain of 20M-1000MHz has shown the possibility of switching the capacitance and negative conductance from negative mode to positive mode. The features of the Ge/SeO2 devices make them attractive for use in electronic circuits as parasitic capacitive circuit elements, noise reducers, signal amplifiers and microwave oscillators. [ABSTRACT FROM AUTHOR]

A dual-cavity opto-mechanical microwave oscillator (OM-MO) for microwave photonic (MWP) generation with ultra-narrow linewidth based on radial (R) guided acoustic modes of a single-mode fiber (SMF) is proposed and investigated experimentally. The dual-cavity OM-MO consists of a 5 km SMF main ring, which provides forward stimulated Brillouin scattering (FSBS) gain, and a 300 m SMF subring that achieves single-frequency output of the R07 guided acoustic mode based MWP (R07-MWP) with Vernier effect. At 300 mW 980 nm pump threshold power, the 319.79 MHz R07-MWP is generated by adjusting polarization controllers based on nonlinear polarization rotation effect, corresponding to the 7437th harmonic of the 43 kHz cavity round trip frequency. The 3 Hz ultra-narrow linewidth of R07-MWP is achieved by decreasing the intrinsic linewidth of the passive ring resonator. The acoustic-mode and longitudinal-mode suppression ratios reach 22 and 36 dB, respectively. Within 20 min of the stability experiment, the power and frequency stability fluctuation of the R07-MWP are ±1 dB and ±0.05 MHz, respectively. This ultra-narrow linewidth MWP generation technology has great potential in the communication field, especially in long-distance wireless communication transmission. [ABSTRACT FROM AUTHOR]

This study denotes a procedure of a small phase noise (SPN) oscillator employing three different substrate integrated waveguide (SIW) resonators as a frequency stabilization‐component. The SIW resonator as modifying phase noise (PN) is investigated and branchline coupler in the feedback loop is presented. The design technique to attain SPN usage for optimized efficiency is proposed. Then, three different X‐band SIW oscillators using a packaged GaAs FET transistor are planned. Due to the PN and compacting, the miniaturized conventional SIW (MCSIW) oscillator is selected. This MCSIW oscillator operates at 8.15 GHz, mentions a PN of −169 dBc/Hz at 1‐MHz frequency‐offset. [ABSTRACT FROM AUTHOR]

High-power microwave sources have been widely applied for material processing in scientific research and manufacturing. The development of stable, high-frequency, high-power microwave sources is essential for achieving efficient microwave processing. This study proposes using a square doubly reentrant coupled-cavity as the slow-wave resonant structure in a K-band extended interaction oscillator (EIO). This design allows for ease of fabrication and high-power capability. The EIO is designed to operate in single 0-mode. The simulation results show that the competing π/5-mode can be effectively suppressed by properly choosing the width and location of the output coupler. The simulation and experiments successfully demonstrate stable, single-mode, tunable, high-performance operation of the EIO. The experimental measurements show a maximum output power of 1.776 kW (18.56% electronic efficiency), and a wave frequency of 24.324 GHz at a beam voltage of 17.4 kV and beam current of 550 mA. The EIO microwave source is suitable for interdisciplinary applications that require higher heating rates and greater uniformity. [ABSTRACT FROM AUTHOR]

A compact Ku-band triaxial klystron amplifier (TKA) with three cascaded single-gap bunching cavities is proposed for the sake of high output efficiency at low seed injection power. The three bunching cavities are specially designed with optimal external quality factors and specific drift tube length to suppress the self-oscillation of these cavities. By decreasing the coupling coefficients and increasing the frequency interval of the three cavities, the asymmetric mode competition can be successfully eliminated in 3D particle-in-cell simulation. The compact TKA is demonstrated to be capable of producing the Ku-band high power radiation with a peak power of 580 MW corresponding to an efficiency of 31 % and a pulse duration of nearly 100 ns in typical experiments. Furthermore, the seed injection power and axial length of the proposed device are reduced to 9 kW and 10 wavelengths, respectively. [ABSTRACT FROM AUTHOR]

In this letter, a parallel‐feedback dual‐band voltage‐controlled oscillator (DVCO) with low phase noise and a wide tuning range is proposed. The DVCO is composed of two tunable filters associated with four switches and an active device. By controlling four switches, the oscillation frequency can be switched and oscillated in one of two bands. The employed tunable filter with maintained passband shape and wide frequency tuning range (FTR) is beneficial to designing wideband DVCO with low phase noise. Owing to the maintained frequency response, the sharp phase variation and high in‐band group delay can be maintained during the filter tuning process, which can enhance the phase noise improvement. Moreover, the sharp phase variation can realize the phase compensation in a wide FTR when tuning the DVCO. To develop a DVCO with a simple circuit scheme, the two‐pole tunable filters with two different FTRs are designed. For verification, the proposed DVCO is designed, manufactured, and measured. The measurement results show that each band of the DVCO has a tuning range of 1.97–2.58 GHz (27.8%) and 2.934–3.468 GHz (16.7%), respectively. For the lower band, the phase noise at 100 kHz and 1 MHz frequency offset is better than −99.2 and −126.4 dBc/Hz, respectively. While for the upper band, the phase noise at 100 kHz and 1 MHz frequency offset is better than −101.2 and −127.4 dBc/Hz, respectively. [ABSTRACT FROM AUTHOR]

Based on microwave heating, a monolithic low-power temperature-programmable high-precision microheater is implemented for thermotherapy. The microwave heater is designed and fabricated in 0.18- $\mu \text{m}$ CMOS process. The $Q$ -factor of the on-chip inductor that serves as the heat applicator would be degraded by the bioimpedance load effect when the heating target is in the vicinity of the microwave heater. Because of such bioimpedance load effect, the electric field around the heat applicator is decreased, which limits the heating efficiency of the microwave heater. To improve the heating efficiency, a bioimpedance load effect compensation technique is adopted to enhance the electric field around the heat applicator. Moreover, a time-to-digital converter (TDC)-based temperature sensor with a sensing resolution of 0.052 is employed to realize the thermostatic function with the precision of ±0.1 °C. Consuming 136 mW, the power amplifier of the heater delivers the output power of 25.36 mW (14 dBm). The heating rate of 0.24 °C/min and heating efficiency of 34.4 J/°C are achieved. [ABSTRACT FROM AUTHOR]

This article analyses the effect of noise and nonlinearity in optoelectronic phase-locked loops (OEPLLs). The OEPLL phase-locks a microwave oscillator on the envelope of the optical pulse train from a mode-locked laser (MLL). The phase detector of this type of OEPLL is called a balanced optical microwave phase detector (BOMPD) and operates in a mixed electro-optical domain. The main noise sources in a BOMPD, such as shot noise of photodiodes, generation-recombination noise of photodiodes, relative intensity noise of the laser, and noise of the bias voltage applied to the BOMPD. are discussed. The nonlinear behavior of the BOMPD with respect to the intensity of the optical field and the amplitude of the RF voltage is discussed. An OEPLL that can lock on the harmonics and interharmonics of the MLL repetition rate is demonstrated. The OEPLL has an in-band phase noise of below −150 dBc/Hz at 100-kHz offset frequency for a carrier frequency of 10 GHz. This phase noise level is 10–20 dB better than state-of-the-art commercial frequency synthesizers. [ABSTRACT FROM AUTHOR]

This letter reports the successful development of an S-band short-length, high-efficiency, coaxial cavity multi-beam relativistic klystron amplifier (CCMB-RKA). The simulation in one-dimensional genetic algorithm, capable of giving high-efficiency parameters, predicted 67% efficiency of CCMB-RKA, taking the interaction length as 600 mm, beam voltage as 420 kV, and beam current as 230 A. However, for accurate results, the CCMB-RKA was simulated again using three-dimensional code CHIPIC, taking RF input power, beam voltage, and beam current as 4.4 kW, 420 kV, and 3.22 kA ($= {14} \times {230}$ A, 14 being the beam number), respectively, predicting the output power, gain, and efficiency of the device as 810 MW, 53 dB, and 60%, respectively. Finally, the designed CCMB-RKA was built and experimented with. Through 20 groups of the comparative experiments, the GW-level RF output power of the device, typically, 1.027 GW (peak), 60 ns pulse was demonstrated with 55% efficiency, 370 phase jitter, and 53 dB gain, taking the RF input power, beam voltage, and beam current as 4.8 kW, 453 kV, and 4.1 kA, respectively. The results establish the potential of the CCMB-RKA developed for high-power microwave applications. [ABSTRACT FROM AUTHOR]

A scheme for generating oscillations based on an exceptional point of degeneracy (EPD) is proposed in two-coupled resonators made of two coupled transmission lines terminated on balanced gain and loss, exhibiting a double pole. The EPD is a point in the parameter space of the system at which two or more eigenmodes coalesce in both their eigenvalues (here, resonance frequencies) and eigenvectors. We show that a finite-length single transmission line terminated with gain and loss possesses no degeneracy point, whereas second-order EPDs are enabled in two finite-length coupled transmission lines (CTLs) terminated with balanced gain and loss. We demonstrate the conditions for EPDs to exist for three different termination configurations with balanced gain and loss, and show the eigenfrequency bifurcation at the EPD following the fractional power expansion series related to the Puiseux series. We study the oscillatory regime of operation assuming the gain element is nonlinear, and the extreme sensitivity of the degenerate self-oscillation frequency to perturbations and how it compares with the sensitivity of the linear-gain case. Finally, we show that the sensitivity of the EPD-CTL resonator is much higher than the one of a single-TL resonator. The very sensitive EPD based oscillator can be used as sensors when very small variations in a system shall be detected.

The transmission delay in an accurate time-transfer system using an optical fiber is calculated by accurately measuring the roundtrip delay of the fiber. The delays in the forward and backward paths of the transmission line must be identical to achieve a highly accurate transmission delay compensation. The effect of chromatic dispersion, which occurs when the optical wavelengths of the forward and backward signals are different, and the effect of backscattering, which occurs in the fiber, are crucial and must be considered for higher accuracy. In this study, we present a fiber transmission delay measurement method that uses optical signals of the same wavelength for the forward and backward paths to overcome these problems. Signal separation can be achieved between the forward and backward signals and between the transmission and backscattered signals by shifting the modulation frequency of a sub-carrier of the optical signal at the remote station. The experimental results demonstrate that a highly accurate time-transfer of more than 1 ns can be expected over a 250 km fiber transmission. [ABSTRACT FROM AUTHOR]

In this article, the effect of microwave leakage into the diode region on the suppression of backward current in a relativistic backward wave oscillator (RBWO) operating at low magnetic field is investigated by the theoretical analysis, particle-in-cell (PIC) simulation, and experiments. The theoretical results show that some backward electrons are absorbed by the cathode holder due to microwave leakage, and as the microwave power increases, the microwave frequency increases, and the guiding magnetic field decreases, it will promote the absorption of electrons. The PIC simulations based on the first principle reveal that the leakage microwave partially suppresses the backward current and the suppression is enhanced when the incidence TM02 is dominant. In the ${X}$ -band dual-mode RBWO packaged with permanent magnet experiments, a microwave pulse with the power of 3.9 GW, the frequency of 9.93 GHz, and the efficiency of 33% was measured when the diode voltage was 820 kV and diode current was 14.5 kA. [ABSTRACT FROM AUTHOR]

We present a novel configuration for an axial virtual cathode oscillator (Vircator) operating in the ${C}$ -band and designed for high output power applications. In order to enhance the efficiency, we have employed a geometry with up to seven reflectors along the drift space. While in previous research works this optimization process has been performed only varying the reflectors radii while using a fixed distance between reflectors, in our work we propose an optimization in terms of both reflectors radii and distances. Our optimized structure for the axial Vircator is able to provide an efficiency up to 15.6% and an output power of 1.6 GW in the ${C}$ -band, with a working voltage of 510 kV and a cathodic current of 24 kA. [ABSTRACT FROM AUTHOR]

In this article, low phase noise microwave oscillators based on elliptic resonators have been reported. Eight different designs of elliptic oscillators in various frequency bands such as L and X have been compared with each other and the results of them have been presented. The parameters such as active devise, elliptic resonator, oscillation frequency, output power, phase noise, and figure-of-merit are considered. In the end, the low phase noise X-band oscillator based on elliptic filter and branchline coupler is having better results of phase noise among the other elliptic microwave oscillators. [ABSTRACT FROM AUTHOR]

We report a novel temperature sensor based on a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) and temperature-to-time mapping. In the proposed scheme, a narrow bandpass electrical filter is inserted into the FDML OEO cavity. The temperature information is mapped to the time interval of the output pulses due to the temperature-sensitive bidirectional scanning property of the FDML OEO. Compared with other OEO-based temperature sensors, the proposed scheme avoids the needs of wideband electrical spectrum analyzers, since the temperature-sensitive output pulses can be interrogated using a low-speed oscilloscope working under sub-Nyquist sampling condition. In the proof-of-concept experiment, a high sensitivity of 8.166 μs/°C and resolution of 0.03°C is achieved, demonstrating a good temperature sensing performance. [ABSTRACT FROM AUTHOR]

The realization of photonic microwave oscillators using optomechanical cavities has recently become a reality. By pumping the cavity with a blue-detuned laser, the so-called phonon lasing regime - in which a mechanical resonance is amplified beyond losses - can be reached and the input signal gets modulated by highly-coherent tones at integer multiples of the mechanical resonance. Implementing optomechanical cavities on released films with high index of refraction can lead to optical modes at telecom wavelengths and mechanical resonances in the GHz scale, resulting in highly-stable signals in the microwave domain upon photodetection. Owing to the extreme compactness of such cavities, application in satellite communications (SATCOM) seems highly appropriate, but no experiments have been reported so far. In this paper, an optomechanical microwave oscillator (OMO) built on a micron-scale silicon optomechanical crystal cavity is characterized and tested in a real SATCOM testbed. Using a blue-detuned laser, the OMO is driven into a phonon lasing state where multiple harmonics are generated, reaching tones up to 20 GHz. Under this regime, its practical applicability, remarkably addressing its performance as a photonic local oscillator, has been validated. The results, in addition with the advantages of extreme compactness and silicon-technology compatibility, make OMOs very promising candidates to build ultra-low weight photonics-based microwave oscillators for SATCOM applications. [ABSTRACT FROM AUTHOR]

A magnetron is one of the most common microwave power generators used in commercial or industrial applications. There are a few methods for optimizing the magnetron to enhance its efficiency, which include the selection of the building materials, increasing the resonant cavity, enlarging operation space size, and modifying the anode structure. This article proposes the modification of magnetron cathode for high-frequency and low-power applications using gallium nitride (GaN)-coated cathode replacing the current barium oxide (BaO) coat. The highlighted optimization is intended to modify the control of magnetron electron drift velocity, heat dissipation, operation frequency, and power generation. Simulation and experimental results have been extracted at 2.45 GHz to generate 5 W microwave power and tested for over 30 ft. of power transmission using a rectenna interface, which results in an efficiency of 88.37%, compared with 51.8% using BaO coat. [ABSTRACT FROM AUTHOR]

Simulation of high-power microwave source devices generally uses parallel algorithms to speed up the operation. In recent years, with the upgrade of parallel technology, the parallel efficiency of the particle simulation software has been further improved. Existing MPI-2 parallel technology of particle simulation software CHIPIC realizes the access to the local memory space of other processes through message passing. The new version of the MPI-3 standard provides the shared memory feature, which allows the data to be directly called by each process in the shared memory window, which reduces the information transmission. In this paper, based on the shared memory feature of MPI-3, the electromagnetic particle simulation parallel algorithm and dynamic load balancing algorithm are designed in the particle simulation software. The implementation of the two algorithms can improve the parallel efficiency from different aspects. The RKA and magnetic isolation oscillator high-power microwave devices are used as the test models. The test results show that the electromagnetic particle simulation parallel algorithm based on the shared memory feature of MPI-3 can improve the efficiency of the software by up to 44%. The efficiency of the dynamic load balancing algorithm based on MPI-3 can also be improved by up to 38%. [ABSTRACT FROM AUTHOR]

A V-band coaxial relativistic transit-time oscillator (TTO) with shallow corrugated output structure operating in TM02 mode is presented. Compared with the deep corrugated output structure, the power handling capacity of the device with shallow corrugated output structure is higher. In particle-in-cell (PIC) simulation, a 403 MW output microwave at 59.10 GHz is obtained with beam voltage of 400 kV, beam current of 5.0 kA under the guiding magnetic field of 1.0 T. The maximum surface electric field in the device is 1.8 MV/cm. Compared with the maximum surface electric field in deep corrugated devices, the maximum surface electric field decreases by 38%. In experiment, a microwave output with power of 258 MW, frequency of 59.04 GHz and pulse duration of 16.0 ns is obtained with diode voltage of 410 kV and beam current of 5.1 kA. The microwave output power and pulse width are significantly improved compared with the previous deep corrugated structure. [ABSTRACT FROM AUTHOR]

The emission uniformity of explosive emission cathodes is important to the operation of high power microwave generators. Although this concept seems to be widely accepted, the concrete influence of cathode emission uniformity on microwave generation has not been researched in detail and many conclusions on this matter are ambiguous due to the lack of solid evidence. This paper makes an effort to research this issue with particle-in-cell simulations about an X-band relativistic backward wave oscillator. To keep the diode impedance unchanged, an emission model in which each emission cell is artificially assigned a specific current density is adopted. The emission non-uniformity is simulated in three ways: spaced emission, large-area no-emission, and local enhanced emission. The simulation results uncover three phenomena: first, no significant influence is found for the cathode emission uniformity on the microwave starting time as long as no obvious mode competition is excited by emission non-uniformity; second, bad emission uniformity may bring about reduction of microwave power, but this may not happen when the emission non-uniformity is just localized to a few discrete strong emission points; third, under specific circumstances, the emission non-uniformity may lead to the excitation of mode competition, which can significantly delay the starting time and lower the microwave power. [ABSTRACT FROM AUTHOR]

Various electrodynamic models of a combustion chamber with an initiated subcritical streamer discharge used to ignite a combustible air/fuel mixture are considered. To localize the discharge in the working chamber, initiators based on half-wave electromagnetic vibrators with resonant properties are applied. The dependencies of the structure of the electric field forming the discharge on the geometric parameters of the discharge initiator are obtained, and integration of the combustion chamber with the generator of microwave radiation is discussed. Calculations are performed for various orientations of the discharge initiator with respect to the optical axis of the chamber. Possibilities for further enhancement of the electric field at the poles of the initiator of a developed streamer discharge are discussed. The results obtained confirm the possibility of using subcritical streamer discharge in high-pressure combustion chambers. The ways of increasing the resulting electromagnetic field at the vibrator poles to form discharge with a developed streamer structure are determined. The results obtained are potentially important to study ignition and combustion of air/fuel mixtures induced by the subcritical streamer discharge. [ABSTRACT FROM AUTHOR]

A novel structure of low phase noise and high output power monolithic microwave integrated circuit (MMIC) oscillator is presented in order to use it in 5G applications. The oscillator is based on the ED02AH process which allows us to design a microwave oscillator keeping a minimum size which is impossible to have it using other technologies since microwave oscillators are sensitive components above 20 GHz. The oscillator is studied, designed, and optimized on a GaAs substrate from the OMMIC foundry using the advanced design system (ADS) simulator in order to obtain a miniaturized oscillator (1.1×1.3 mm²) generating two signals of different frequencies fo1=26 GHz and fo2=30 GHz. The objective is to design an oscillator with high output power and low phase noise while respecting its specifications. The optimization of the proposed microwave oscillator shows satisfying results. Indeed, at 26 GHz and 30 GHz, the output powers are respectively 13.33 dBm and 14.89 dBm. The oscillator produces a sinusoidal signal of 1.5 V and 1.75 V amplitude respectively at 26 GHz and 30 GHz. The oscillator phase noise at fo1 and fo2 resonance frequencies using the liquid crystal (LC) resonator shows respectively -109 dBc/Hz and -110 dBc/Hz at 10 MHz offset. [ABSTRACT FROM AUTHOR]

Masers as telecommunication amplifiers have been known for decades, yet their application is strongly limited due to extreme operating conditions requiring vacuum techniques and cryogenic temperatures. Recently, a new generation of masers has been invented based on optically pumped spin states in pentacene and diamond. In this study, we pave the way for masers based on spin S = 3/2 silicon vacancy (VSi) defects in silicon carbide (SiC) to overcome the microwave generation threshold and discuss the advantages of this highly developed spin hosting material. To achieve population inversion, we optically pump the VSi into their mS = ±1/2 spin sub-states and additionally tune the Zeeman energy splitting by applying an external magnetic field. In this way, the prerequisites for stimulated emission by means of resonant microwaves in the 10 GHz range are fulfilled. On the way to realising a maser, we were able to systematically solve a series of subtasks that improved the underlying relevant physical parameters of the SiC samples. Among others, we investigated the pump efficiency as a function of the optical excitation wavelength and the angle between the magnetic field and the defect symmetry axis in order to boost the population inversion factor, a key figure of merit for the targeted microwave oscillator. Furthermore, we developed a high-Q sapphire microwave resonator (Q = 104-105) with which we find superradiant stimulated microwave emission. In summary, SiC with optimized spin defect density and thus spin relaxation rates is well on its way of becoming a suitable maser gain material with wide-ranging applications. [ABSTRACT FROM AUTHOR]

To investigate photoinduced phenomena in various materials and molecules, ultrashort pulsed x-ray and electron sources with high brightness and high repetition rates are required. The x-ray and electron's typical and de Broglie wavelengths are shorter than lattice constants of materials and molecules. Therefore, photoinduced structural dynamics on the femtosecond to picosecond timescales can be directly observed in a diffraction manner by using these pulses. This research created a tabletop ultrashort pulsed electron diffraction setup that used a femtosecond laser and electron pulse compression cavity that was directly synchronized to the microwave master oscillator (∼3 GHz). A compressed electron pulse with a 1 kHz repetition rate contained 228 000 electrons. The electron pulse duration was estimated to be less than 100 fs at the sample position by using photoinduced immediate lattice changes in an ultrathin silicon film (50 nm). The newly developed time-resolved electron diffraction setup has a pulse duration that is comparable to femtosecond laser pulse widths (35–100 fs). The pulse duration, in particular, fits within the timescale of photoinduced phenomena in quantum materials. Our developed ultrafast time-resolved electron diffraction setup with a sub-100 fs temporal resolution would be a powerful tool in material science with a combination of optical pump–probe, time-resolved photoemission spectroscopic, and pulsed x-ray measurements. [ABSTRACT FROM AUTHOR]

In this article, an axially partitioned magnetically insulated line oscillator (MILO) to generate high-power microwave (HPM) with two frequencies in different bands is presented. The electromagnetic characteristics of the dual band MILO (DBMILO) in the absence of an electron beam are investigated to ensure the resonance condition. The RF performance of the device is analyzed through particle-in-cell (PIC) simulation. The proposed DBMILO is designed to operate in $S$ - and $X$ -bands for the input dc voltage and current of 500 kV and 56 kA, respectively. A peak RF power of ~3.6 GW with peak power conversion efficiency of ~12.8% at 3.4 and 10.1 GHz is detected through PIC simulation. Practical concerns with the HPM source, such as RF breakdown and anode plasma generation at the beam collector in the proposed design, are also explored, along with possible solutions. [ABSTRACT FROM AUTHOR]

This article presents a work on development of a high-power radio pulse generator, which is a gyromagnetic nonlinear transmission line (GNLTL) in which periodically placed NiZn ferrites are saturated by an axial magnetic field produced by permanent magnets periodically placed inside the transmission line. Structurally, the line is a corrugated coaxial waveguide with permanent NdFeB magnets placed inside the inner conductor of the line. The transmission line geometry was optimized using numerical simulation by finite-difference time domain (FDTD) method. The excitation of high-frequency oscillations in the developed transmission line at central frequency of 1 GHz and above is shown experimentally using ferrite rings with 45 and 28 mm outer and inner diameters. The maximum peak power of microwave oscillations obtained in the experiments is 110 MW at the central frequency 1.3 GHz. The obtained RF power is comparable to that of more common GNLTL with continuous filling by ferrite rings having the same transverse size. [ABSTRACT FROM AUTHOR]

A copper helical coil antenna was developed, characterized, and optimized for 2.45 GHz operations supplied by a microwave semiconductor oscillator. The application field of interest is laser-induced breakdown spectroscopy enhanced by microwave. Simulations using the Ansys HFSS demonstrate the superior localized E-field strength of the helical coil antenna, compared with other antenna-type structures. Simulation results show that E-field strength at the tip of the antenna has a logarithmic trend for increasing the coil pitch. The optimum pitch is 5 mm for a coil diameter of 6.5 mm upon consideration of the system compactness. Despite the antenna's open-circuit end, the presence of target samples does not interfere with the E-field and H-field distribution of the antenna and the surrounding environment. Applications in microwave-enhanced laser-induced breakdown spectroscopy (MWLIBS) confirm the importance of the antenna reflector. The electric field strength was over 100 times higher than the previous capacitor-like antenna. The antenna configuration angle was then experimentally optimized for maximum enhancement effects in the spectrochemical analysis of Al2O3. The antenna angle of 60° from the laser beam propagation achieved maximum enhancement in the emission signal of Al I. [ABSTRACT FROM AUTHOR]

Introduction/purpose: Detailed theoretical and experimental studies have been carried out in order to investigate the problem of a phase stability in electrodynamically uncoupled Gunn oscillators. Methods: The influence of modulating pulse instabilities has been investigated by means of computer simulation in the framework of a nonlinear one-dimensional theoretical model of the GaAs Gunn diode semiconductor active region. Experimental observations were also conducted including microwave measurements and antenna far-field estimation. They confirm the main theoretical results and extend the key work conclusions. Results: It was shown that the initial phase of the microwave oscillation out of the Gunn oscillator is independent of internal noises of the semiconductor structure and can be fixed only by the modulating voltage pulse. Conclusion: Gunn-diodes based microwave oscillators were stabilized using the leading edge of the voltage pulse from the modulating power supply. These results open up serious prospects for designing antenna phased arrays based on Gunn oscillators without mutual feedback (electrodynamically independent). [ABSTRACT FROM AUTHOR]

Based on a dual-loop optoelectronic oscillator (OEO) with Vernier effect, a scheme of fiber Bragg grating (FBG) interrogation system with an improved scale factor has been proposed and experimentally demonstrated. Functioning as the optical carrier of the OEO, the reflection signal of two cascaded FBGs is divided into two optical beams by using a wavelength division multiplexer (WDM). The two optical beams at different wavelengths travel along single mode fibers with different lengths. After combined together by another WDM, the two optical beams go through a section of dispersion compensation fiber (DCF). The oscillating frequency shift of the OEO is determined by the overall time delay, which is affected by the wavelength change of the sensing FBG. Thus, the wavelength change of the sensing FBG can be converted into the oscillating frequency shift of the OEO. Furthermore, due to the length difference between the two optical beams, an obvious Vernier effect has been generated in the frequency response of the OEO. By detecting the frequency shift of the envelope peak of the frequency response curve, the sensitivity of the sensing interrogation can be enhanced greatly. A proof-of-concept OEO-based FBG sensor for axial strain sensing experiment is performed. The experimental results show that the sensitivity is about 0.31 KHz/μϵ for a single-loop OEO. By employing Vernier effect, the sensitivity can be improved to -11 KHz/μϵ, which is 35 times higher than that of the single-loop OEO.

An all-optical microwave oscillator based on parity-time symmetry was proposed and experimentally demonstrated. It mainly consists of a big feedback loop, an active small loop and a polarization-dependent Sagnac loop. The microwave seed signal originates from the beating between the continuous wave and the Stokes wave. The function of microwave envelope detection and feedback modulation are implemented through cross gain modulation of two semiconductor optical amplifiers. By employing the parity time symmetry loops and the Vernier effect, the single mode selectivity capability of the oscillator has been enhanced, and a single mode microwave signal with high quality can be generated. In the experiment, a highly quality microwave signal with a frequency of 10.71 GHz was generated. The single side band phase noise can reach −94.1 dBc/Hz@10 kHz and the side mode suppression ratio of the generated microwave signal reaches 41 dB. Compared to the previously reported all-photonic microwave oscillator, the single side band phase noise is improved by 7 dB at a frequency offset of 10 kHz, and by 20 dB at a frequency offset of 100 Hz. The results indicate that our proposed scheme significantly improves the quality of the generated microwave signals. • This manuscript provides a feasible pure optical scheme to generate microwave photonic signal source. • The parity time symmetry loops can significantly enhance the single mode selectivity capability of the oscillator. • The SSB is improved by 7 dB at a frequency offset of 10 kHz, and by 20 dB at a frequency offset of 100 Hz. [ABSTRACT FROM AUTHOR]

A super klystron-like relativistic backward wave oscillator (RBWO) is presented. In the device, the distributed Cherenkov radiation generated in the slow wave structure (SWS) is absorbed by the electron bunch in the last corrugation and re-accelerated, creating high-energy electrons that overcome the space-charge repulsion force to further compress the bunch length and maximize the fundamental harmonic current, contributing to the extremely efficient microwave generation in the extraction cavity through concentrated transition radiation. A novel elliptical extraction cavity is used to improve the power capacity. A soft magnet is inserted to precisely control the beam path, which provides a higher beam kinetic energy to be extracted and a stronger electric field that interacts with the tighter bunch. In the experiment, as the diode voltage was 585 kV and diode current was 7.5 kA, a microwave pulse with a power of 2.9 ± 0.3 GW measured in the radiation field, a frequency of 8.23 GHz, and a pulse duration of 22 ns was obtained. The corresponding efficiency is up to 66 ± 8%, which is an experimental record for GW-class relativistic vacuum electronic devices. [ABSTRACT FROM AUTHOR]

A preliminary investigation on S-band multiport relativistic magnetron (RM) is carried out, which is targeted at the application of high-power microwave (HPM) phased array system. For such system, the phase synchronization and stabilization of sources are crucial. In the proposed multiport RM, the HPMs in four independent output ports are extracted from the same resonant system, thus having the same amplitude and phase naturally. Moreover, the output mode of such multiport RM is fundamental mode, which can achieve Gaussian radiation in the far field directly. Since mode convertors and phase-locked units are no longer necessary, it is beneficial to the miniaturization of HPM phased array system. To further control the phase of output signals, a wide side dimension adjustable phase shifter used for this multiport RM is designed, which could achieve 180° phase shift with a power handling capacity of 568 MW. Particle-in-cell (PIC) simulation of such multiport RM combined with phase shifters applied a diode voltage of 450 kV is carried out. When all output signals are adjusted to be in- phase, an average output power of 265 MW in each port can be obtained, corresponding to a power conversion efficiency up to 65%, and the relative phase differences are controlled within ±2.4%. [ABSTRACT FROM AUTHOR]

An oscillator is a vital component as the energy source in microwave telecommunication system. Microwave oscillators designed using Gunn diode have poor DC to RF efficiency. IMPact Ionization Avalanche Transit-Time diode (IMPATT) oscillators have the drawback of poor noise performance. The transistorized oscillators have a limitation to the maximum oscillation frequency which means that they cannot be used for oscillators designed for high frequencies. To design negative series feedback Dielectric Resonator Oscillator (DRO), the resonant unit uses a dielectric resonator (DR) since it is small in size, light in weight, has high-Quality (Q) factor, better stability and also it is inexpensive. It has the benefits of low-phase noise, low cost, miniaturization, high stability, applicable for devices designed at high frequencies and had already been widely applied, so the research on microwave dielectric oscillator has also been one of the focus of today's microwave integrated circuits. DRO is widely used in electronic warfare, missile, radar and communication systems. The DRO incorporates High-Electron Mobility Transistor (HEMT) as an active device since it offers higher power-added efficiency combined with excellent low-noise figures and performance. The entire circuit of DRO using HEMT at 26 GHz is designed using Agilent Advanced Design System (ADS) software. In this, DRO different measurements of parameters are done such as output power which is typically + 1 1 dBm for 26 GHz DRO, phase noise at 10 kHz offset for 26 GHz DRO it is 80 dBc/Hz. The frequency pushing and frequency pulling for 26 GHz DRO its typical values are 30 kHz/V and 1 MHz, respectively. [ABSTRACT FROM AUTHOR]

In the application of microwave heating, how to design and optimize a microwave cavity to improve heating uniformity is still a challenge. In this work, a shape optimization algorithm based on the arbitrary Lagrangian–Euler (ALE) method is developed to optimize the geometry of the microwave cavity. By introducing the ALE method, the precise boundary shape is obtained through optimization on the premise that the cavity structure topology remains unchanged to improve the heating uniformity. A 2-D model and a 3-D model are used to illustrate the proposed method in detail. The results of the 3-D model show that compared with the initial design, the heating uniformity of the optimal design is improved by 95%, and the heating efficiency is also improved by 29%. At the same time, the optimized boundary shape is 3-D printed for experimental verification, and the temperature is measured through the experiment, which verifies the rationality and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]