High Power Microwave Generation Research Articles

Dynamic characteristics of a coaxial magnetic switch modulating pulse forming networks.

Pulsed power generators utilizing magnetic switch technology within the 100ns scale have become widespread for surface treatment, high power microwave generation, and food processing, in which the dynamic characteristics of the magnetic switch perform an important function. The saturation process, electric field between layers, and energy loss are closely associated with the applied time scale of the magnetic core, which affects the dynamic characteristics of the switch. However, compared with the study within the microsecond scale, the dynamic characteristics of magnetic switches within the 100ns scale have not been studied in depth. In this paper, the dynamic characteristics of a coaxial magnetic switch modulating pulse forming networks (PFNs) are studied via both field-loop co-simulation and scaled experimental test. It is found that increasing PFN section number (Ns) leads to an acceleration in the saturation process of the core, which helps understand the switch performance of the magnetic core more clearly. With respect to a specific magnetic switch based on a ferromagnetic core, it is quantitatively analyzed that increasing Ns from 1 to 10 leads to a 16.1% reduction in core saturation time (tsat), a 13.4% increase in eddy loss (EET), and a 5.7% rise in maximum interlamination field strength (Emax) under the 100ns scale; however, tsat is reduced by 19.3%, EET increases by 5.2%, and Emax rises by 2.3% under the microsecond scale. The results could provide a design reference for magnetic switches in pulsed power generators.

Enhancing power capacity and performance of wide-drift-channel transit-time oscillators for long-pulse high-power microwave generation

This paper addresses the challenge of extending the pulse duration of high-power microwave (HPM) sources, a critical focus in HPM technology. Transit-time oscillators (TTOs) typically modulate electron beams by forming standing waves through the cutoff of the TM01 mode in the modulation cavity. This study proposes enhancing the power capacity of TTOs by widening the drift channel. To enhance modulation capability without compromising power capacity, front and rear reflectors are strategically introduced. In particle-in-cell simulations, the device exhibits an output power of 1.65 GW at a frequency of 12.6 GHz, with an efficiency of 33.6%. The saturation time for the output microwave is 30 ns, and the maximum internal electric field strength is 860 kV/cm. The presented TTO, with design improvements, offers a promising solution for applications requiring prolonged pulse durations in high-power microwave sources.

Revisiting the Luce diode in the context of recent research on multi-vircators with dielectric reflectors

Recently, in a series of articles Mumtaz, Choi, and others [i.e., S. Mumtaz and E. Choi, IEEE Electronic Device Lett. 43, 1756 (2022)] studied a relativistic gridded vircator with one or more dielectric anodes, in which considerable increase in the efficiency of high-power microwave (HPM) generation compared to ordinary vircators was observed. This is very important since the main disadvantage of vircators is their low efficiency. It was suggested that the repelling of electrons by the initial impacting electron charge collected on the dielectric reflectors forms a multi-vircator, which increases HPM production. The present article reports the results of experiments and numerical simulations, which show that this mechanism does not result in high multi-vircator efficiency. Similar dielectric anodes were investigated 50 years ago in a configuration known as the Luce diode, in which collective acceleration of ions was studied. It was also known that the operation of the Luce diode is accompanied by a HPM burst, which was never measured. Results of experiments and simulations in various configurations based on a gridded vircator and dielectric reflectors confirm the existence of high-energy ion acceleration. Unfortunately, none of these configurations produce HPM of higher efficiency than a regular gridded vircator.

Experimental study on influence of temperature on breakdown in a waveguide cavity

Radio frequency (RF) breakdown is one of the crucial factors limiting the power capacity of high-power microwave (HPM) generators. In this paper, a waveguide cavity has been designed to study quantitatively the influence of temperature on high-gradient RF breakdown. The two planes of the waveguide cavity are divided into a strong-field side and a weak-field side with the feeding of microwave signals. The temperature of the strong-field side of the waveguide cavity can be adjusted from ambient temperature (25 °C) to 435 °C by loading a resistive wire heater. The breakdown threshold of the waveguide cavity decreases apparently with the increase in the temperature. The breakdown threshold at 408 °C is 751 kV/cm, which is about 150 kV/cm lower than that at ambient temperature. In addition, the higher the temperature, the more pronounced the pulse shortening. Under the same microwave power injection, the averaged pulse width of HPM after passing through the waveguide cavity at 408 °C is equal to 17.6 ns, shortened by about 1/3 compared to that at ambient temperature. The quantitative study of the influence of temperature on the RF breakdown provides a new guideline for exploring breakdown suppression methods in HPM generators.

Recent progress of parameter-adjustable high-power photonic microwave generation based on wide-bandgap photoconductive semiconductors

Recent progress of parameter-adjustable high-power photonic microwave generation based on wide-bandgap photoconductive semiconductors

Analysis and simulation of X-band high-power microwave generation based on T-shaped four-period slow-wave structure

In this study, a T-shaped, four-period resonant slow-wave structure is optimally designed, and its high-frequency performance is comprehensively analyzed in theory. By using the image theory, the T-shaped waveguide unit is transformed into an equivalent ridge waveguide configuration. The high-frequency characteristics of the equivalent ridge waveguide, such as resonant frequency and structure of the T-shaped waveguide are analyzed by using equivalent circuit theory. The analysis has confirmed that in the ridge waveguide, starting from the second-highest order mode, the frequency points of the even-order modes are very consistent with those of the T-shaped waveguide; however, the odd-order modes have no such corresponding mode in the T-shaped waveguide, for they do not fulfill the electric boundary conditions required by the image method. On this basis, a T-shaped four-period resonant slow-wave structure is constructed, and its dispersion characteristics are analyzed to determine the resonant modes and frequencies, as well as the range of mode synchronization voltages. Simulations are subsequently performed to validate the effectiveness of the relativistic extended interaction radiation source, which includes the novel T-shaped periodic resonant slow-wave structure. Advanced three-dimensional particle simulations, in conjunction with optimization techniques show that a high-power microwave output at a frequency of 9.8 GHz, is achieved, which can delivers an average power of 71.4 MW. This output is attained under the conditions of a 448 kV beam voltage, 400 A beam current, and a 0.4 T uniform axial magnetic field, with an electron efficiency reaching 39.8%. This structure, characterized by the T-shaped waveguide, is demonstrated to be capable of producing high-efficiency, high-power microwaves with fewer periods, presenting a compact and efficient solution for generating high-power microwaves in advanced scientific applications.

A Cross-Band High-Power Microwave Generator With Wide Frequency Tunability Based on a Relativistic Magnetron and a Radial Transit-Time Oscillator

A Cross-Band High-Power Microwave Generator With Wide Frequency Tunability Based on a Relativistic Magnetron and a Radial Transit-Time Oscillator

New Electromagnetic Threat Protection Systems

The issues discussed in the article refer to a new category of military operations - electronic warfare (EW). In the context of EW, the high-power microwave (HPM) technology currently enables remote disturbances of operations lasting until the circuit is reset or the electronic system is destroyed. The article examines the problem of protection and defence against using HPM pulses. The research used a compact HPM generator developed at the Polish National Centre for Nuclear Research. It has a power of 3MW, an operating frequency of 2.9 GHz and a 3 μs pulse duration, emitted with a repetition rate of 1, 50, 100 and 250 Hz. The developed HPM pulse protection systems were subjected to intense field exposure in the open space of the training ground, in its land and sea sections, and in the circuit with a reverberation chamber. The distribution of the generated field on each measurement station was tested using a high-power D-dot probe, from which the data was transferred to the recording system via an optical fibre link. In all cases, this distribution turned out to be repetitive. The field probe with a logger was used for measurements inside composite structures. Unprotected electronic systems in hobby drones, mobile phones, cameras and systems using sensors based on micro-mechanical units were exposed. An analysis was conducted to check the operation of electronic circuits, effects caused and phenomena occurring during exposures to intense microwave radiation. It was found that the developed system meets the design assumptions in conditions similar to actual exposure to HPM weapons. Screening efficiency has been determined for various spatial configurations of radiation beam incidence. The presented systems for the protection and defence against the effects of HPM weapons implemented in the technology of composite hybrid absorbers enable effective elimination of electromagnetic pulse effects.

The Method of Reducing the Guiding Magnetic Field of High-Band O-Type High-Power Microwave Generator

When the O-type high-power microwave (HPM) generator is extended to the high band, reducing the intensity of the guiding magnetic field is an effective means for their development toward lightweight and miniaturization. Through the study of the electron beam, the overmoded coaxial structure and piecewise magnetic field are considered to decrease the magnetic field requirements. The former diminishes the demand for the guiding magnetic field by affecting the space density of the electron beam and the space-charge-limited current. The latter replaces the uniform magnetic field, which ensures the effective transmission of the electron beam and lowers the weight of the coil. A Ku-band coaxial Cerenkov oscillator with the overmode ratio of 4.2 is taken as the example. The piecewise magnetic field with the magnetic flux density of 0.4–0.6 T is used for particle-in-cell (PIC) simulation. The diode voltage is 460 kV, the injection power is 3.6 GW, and the final output microwave power is 1.55 GW, with the corresponding power efficiency of 43%. The microwave frequency is 14.3 GHz and the spectrum is pure. The simulation results prove the effectiveness of these methods and explore the geometry of the permanent magnet packaging.

Guest Editorial The Nineteenth Special Issue on High-Power Microwave and Millimeter-Wave Generation

Guest Editorial The Nineteenth Special Issue on High-Power Microwave and Millimeter-Wave Generation

Investigation on a coaxial HPM generator with low magnetic field

A Ku band coaxial high power microwave generator with a low magnetic field was investigated without mode competition in this paper. Mode competition is avoided physically by adopting a two-cavity extractor instead of a three-cavity extractor to eliminate the resonance between the modulation slow wave structure and the extractor slow wave structure at any unexpected frequency except the working frequency. Moreover, the efficiency of the device increases due to the separation process of energy extraction and electron collection by adopting the inner conductor collecting structure. Particle simulation results showed that when the magnetic flux density is 0.6 T, the diode voltage is 560 kV, and the diode current is 8 kA, we get 1.55 GW microwaves with an efficiency of 35% and a frequency of 14.7 GHz. Experimental investigation is carried out based on the physical design and simulation results. 1.0 GW microwaves are obtained, and the frequency is 14.8 GHz in the experiment when the magnetic flux density is 0.64 T, the diode voltage is 590 kV, and the diode current is 8.5 kA. No obvious hint of electron emission or bombardment is observed at the surface of the generator after 10 thousand pulses, and the advantage of this kind of generator working in a low magnetic field is proved.

Investigation of a Novel Biperiodic Reltron for High-Power Microwave Generation

A novel configuration of a reltron, referred to as the biperiodic reltron, has been proposed to generate gigawatts-level RF radiation. It uses a modified modulation cavity, in which double-side coupled modulation cavities are biperiodically associated instead of a single-side coupled modulation cavity as in the conventional case. All three feasible resonating modes, i.e., 0, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $</tex-math> </inline-formula> /2, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $</tex-math> </inline-formula> modes, generated concurrently at the two different resonant frequencies provided a good field stability against unwanted perturbations. With the input beam current and voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 53 kA and 400 kV, respectively, the proposed biperiodic reltron has predicted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 12-GW RF power generation with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 57% efficiency using particle-in-cell (PIC) simulation.

Test of KW Class Photonic Microwave Generation Using Vanadium-Compensated 6H-SiC PCSS and Burst-Mode-Operation Pulse Laser

Photoconductive semiconductors operating in linear mode can be used for adaptive high-power microwave (HPM) generators by modulating incident light. This paper presents the design scheme and preliminary test results of a narrowband kW class adaptive photonic microwave generator by employing a wide-bandgap semi-insulating 6H-SiC photoconductive semiconductor and a burst-mode laser. The experimental scheme of the generator is described along with the circuit simulation of the radio frequency generator. The laser operated at a wavelength of 532 nm with a pulse width of 100 ns and a repetition rate of 100 Hz. The laser modulates the frequencies of the generated microwave, and preliminary tests are conducted in the frequency range of 0.8–1.2 GHz. The maximum output microwave power of the designed scheme reaches up to 2.6 kW when the bias voltage is 10 kV. The results confirm that this method can be used for high-power frequency-adjustable microwave signal generation. The microwave source system presented in this paper has continuously adjustable frequency and flexible waveform control.

A novel compact solid-state high power pulse generator based on magnetic switch and square waveform pulse transformer.

The high power pulse generators have been widely used in high power microwave generation and plasma physics research. In this paper, a novel compact solid-state high power pulse generator is studied, numerically and experimentally. The generator is mainly composed of the primary energy supply, the magnetic pulse compressor, the Blumlein type low-impedance pulse forming network, and the square waveform pulse transformer. Especially, design considerations for a solid-state high power pulse generator are proposed. Experimental results show that pulses with a peak power of 2 GW, a duration of 150ns, and a repetitive rate of 10Hz are continuously achieved on a dummy load. The dimension is Φ60 × 210cm2, and the average power density reaches ∼5 W/L. Experimental results show reasonable agreement with numerical analysis.

CNT/Cu composite cathode: A new approach to long lifetime for explosive emission cathode

Carbon nanotube (CNT) cathodes have attracted much attention in recent years due to the advantages of large field enhancement factor and low emission threshold. However, the severe ablation under intense emission makes the lifetime short and therefore limits the application in the field such as high power microwave generation. To resolve this problem, this paper proposes to mix CNTs with metals, and a novel CNT/Cu composite cathode is manufactured. The lifetime experiments under voltage of 940 kV and repetition frequency of 20 Hz demonstrate that the lifetime of the CNT/Cu composite cathode is over 3 × 105 pulses, which is much longer than that of the normal copper cathode by at least one order of magnitude. The microscopic morphology analysis reveals that the CNT micro-protrusions and whiskers should be vital for the good emission property of the new cathode.

A 1-MV low-jitter high-reliability multi-stage equal breakdown probability gas switch

This paper presents the development of a novel megavolt-class equal breakdown probability (EBP) multi-stage self-discharge gas switch for high power microwave generation with low breakdown jitter and high reliability. With the joint distribution of breakdown probability for ‘n’ identical stages of EBP gas switch, the advantages of diminishing the breakdown jitter and omitting the complex breakdown order problem are hence disclosed in considerable details with the aid of probability computation method. Based on theoretical analysis, a 5 stages 1-MV EBP multi-stage gas switch is designed in which periodic cog profile cathode is proposed to further decrease the breakdown jitter. The performances of EBP switch are tested at the repetition rate of 1,10,20,50 Hz over 1000 successive pulses with breakdown jitter as low as 2.7% ,energy efficiency as high as 90% and pulse rising time as low as 5 ns. The overall performance of EBP gas switch shows great potential in compact and reliable high power microwave generating system.

The Characteristics of the Second and Third Virtual Cathodes in an Axial Vircator for the Generation of High-Power Microwaves

A virtual cathode oscillator or vircator is a vacuum tube for producing high-power microwaves (HPM). The efficiency of the vircator has been a difficult task for decades. The main reasons for low efficiency are intense relativistic electron beam (IREB) loss and few or no interactions between IREB and HPM. In this case, forming multiple virtual cathodes may be beneficial in overcoming these constraints. By reusing the axially propagating leaked electrons (LE), we could confine them and form multiple virtual cathodes (VCs). This article discussed the characteristics of newly formed VCs based on simulation results. The formation time of new VCs was discovered to be highly dependent on the reflector position and the density of LE approaching their surfaces. Furthermore, multiple VC formation in the waveguide region does not affect conventional VCs’ position or forming time. The emission mode of the generated HPM was TM01 with single and multiple VCs and remained unaffected. The formation of multiple VCs positively influenced the axial and radial electric fields. When compared to a single VC, the axial and radial electric field increased 25.5 and 18 times with multiple VCs. The findings suggested that forming multiple VCs could be a future hope for achieving high vircator efficiency.

Study on temperature distribution and response of electron collector in high-power microwave generator

Relativistic backward wave oscillator is a high-power microwave generator with great application potential. Since a large amount of waste electron are deposited on the collector, the temperature of the collector rises, which reduces the safety and stability of relativistic backward wave oscillator. The collector temperature characteristics are calculated by using the Fourier thermal conduction model and the phase change heat transfer model. A method to reduce the collector temperature and shorten the retardation time is obtained. The results show that the collector temperature, water temperature, and vapor volume fraction show periodic fluctuation. The collector temperature can be reduced by increasing the working pressure, increasing the volume flow rate, decreasing the channel width, and increasing the thermal conductivity of the collector material. The temperature response of the collector thermal conduction is synchronized with the thermal interaction in the nanosecond's order. There is a retardation time for the convection and phase change heat transfer. The convection heat transfer retardation time is about 5 ms, and the phase change heat transfer retardation time is about 10 ms. The thermal conductivity, channel diameter, and volume flow rate have great effects on the heat dissipation, so they are the major influence factors of retardation time.

Nonlinear Transmission Line Performance as a Combined Pulse Forming Line and High-Power Microwave Source as a Function of Line Impedance

Nonlinear transmission lines (NLTLs) offer compact, low-cost, all solid-state high-power microwave (HPM) generation. This article experimentally investigates the RF output power for composite-based 10, 25, and 50 Ω NLTLs used as a combined pulse forming line and HPM source. We manufactured coaxial NLTLs containing 10% barium strontium titanate and 15% nickel zinc ferrite encased in polydimethylsiloxane. The output voltage and power in the time and frequency domains, respectively, showed that the 10 Ω NLTL generated the greatest RF output. The 25 Ω NLTL generated greater output power from 500–1100 MHz than the 50 Ω NLTL. This occurs because reducing the NLTL impedance induces a larger transient current for a given charging voltage. This transient current corresponds to a stronger transient magnetic field, which facilitates magnetic moment alignment to allow for coherent magnetic moment rotation to occur. This setup eliminates the separate pulse forming network and magnetic field bias that typically occurs in other NLTL systems, which provides additional flexibility in tuning the NLTL impedance and reducing device footprint.

A SIX-PORT MEASUREMENT DEVICE FOR HIGH POWER MICROWAVE VECTOR NETWORK ANALYSIS

The changes experienced in technology due to the third industrial revolution have over the years contributed immensely to the development of efficient devices and systems. As a result, solutions have been provided to challenges encountered in the heating industry. However, higher efficiency and better performance has undoubtedly been highly sort after. This paper presents the complete industrial development of a new system of a microwave device for use in S-band networks (2.45 GHz ISM band in this application): a vector network analyzer (VNA). The VNA, which is designed based on the six-port measurement principle, provides accurate measurements of both magnitude and phase of the load reflection coefficient. The device is designed to have high power handling capabilities and works under the full operating conditions of high-power microwave generators. Initial measurements show that the device perform stable and can perform temperature-independent measurements over protracted periods. The system is suited for on-line monitoring and control of network parameters in industrial waveguide applications..