Compact High Power Microwave Research Articles

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.

An Overview of Multibeam Klystron Technology

The multibeam klystron (MBK) is a compact high-power microwave vacuum electronic device that features low beam voltage, high efficiency, wide bandwidth, and low volume and weight. Since the 1960s, high-performance broadband MBKs have been developed that cover the entire microwave frequency band with relative instantaneous bandwidths <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 15%, peak power <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 1 MW, average power up to 40 kW, and efficiencies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 40%. In recent years, driven by the needs of high-energy particle accelerators, ultra high frequency (UHF) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{L}$</tex-math> </inline-formula> -band MBKs with peak powers of more than 20 MW and efficiencies of nearly 80% are being developed. This article presents an overview of the development of broadband MBKs used in microwave electronic systems, such as radar and communication, and high-power MBKs used in the RF systems of particle accelerators. It also introduces the latest progress and development trends in MBKs leading to higher frequency, output power, bandwidth, efficiency, and lifetime.

PIC simulations of a frequency agile multicavity relativistic magnetron using irregular ring metamaterials driven by a transparent cathode

The design of an agile 5° irregular ring metamaterial for a 24-cavity relativistic magnetron with diffraction output (MDO) using single-stepped cavities for frequency switching is presented. By inserting six pieces of 5° irregular ring metamaterials in place of the traditional 5° vanes of a slow wave structure, the operating frequency can be tuned. When U = 400 kV high voltage is applied, with an applied magnetic field B = 0.36 T, the operating mode can be switched from the TE41 mode with a frequency of 2.585 GHz to the TE31 mode with a frequency of 2.282 GHz. The 24-cavity anode block is an electromagnetic medium which can support the operating mode working under its cutoff frequency, and the insertion of the irregular ring metamaterials alters its dispersion relation. The results suggest a new technique to achieve frequency agility by changing the dispersion relation of the electromagnetic system using a metamaterial unit cell. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for frequency agility.

PIC Simulation of the Coherent Cerenkov– Cyclotron Radiation Excited by a High-Power Electron Beam in a Crossed-Elliptical Metamaterial Oscillator at S-Band

We present an S-band high-power microwave (HPM) oscillator based on crossed-elliptical metamaterial (MTM) rings in a circular waveguide and powered by a high-power electron beam. Particle-in-cell (PIC) simulations demonstrate that when an output horn antenna of radius of 200 mm is used, an output power of 443 MW of a backward wave TE41 mode below its cutoff frequency at 2.80 GHz can be generated using a pulsed electron beam with a voltage of 990 kV and a current of 1.736 kA in a 1.8-T solenoidal magnetic field, corresponding to an electronic efficiency up to 26%. Meanwhile, another degenerate frequency of 2.80 GHz of a forward wave in the TM01 mode with an output power of 9 MW is also observed. When an output horn antenna of radius 150 mm is used, this crossed-elliptical MTM oscillator operates mainly in a forward TM01 mode at 2.80 GHz with an output power of 325 MW at an electronic efficiency of 19%, and at the same time, a backward wave TE41 mode below its cutoff frequency of 2.80 GHz with an output power of 8 MW can be observed. Simulations indicate that this slow-wave structure (SWS) consisting of a periodically crossed-elliptical MTM loaded circular waveguide can support degenerate mode operation. This result suggests that this configuration is favorable for mode switching and this work seeks to design a compact HPM source.

A compact high-power microwave TM01-TE01 mode converter

In circular waveguides, the TE01 mode has the lowest transmission loss, which is very suitable for long-distance transmission of high-power microwaves (HPMs). The output mode of HPM sources is mainly the TM01 mode; however, there are few research studies on mode converters of TM01-TE01. In this paper, a high efficiency HPM TM01-TE01 mode converter is designed; compared with the traditional TM01-TE01 mode converters, the structure of the mode converter is compact and easier to process. It is mainly composed of an input circular waveguide, a tapered rectangular waveguide, a 90° bent rectangular waveguide, and an output circular waveguide. A prototype with a center frequency of 2.4GHz is fabricated and HPM experiments are carried out. The transmission efficiency of this device reaches 99.8% in the simulation, and the measured transmission efficiency is more than 98%. Additionally, the measured power handling capacity is more than 1 GW, which is consistent with simulation. This designhas important reference significance for the designof long-distance power transmission devices and HPM mode converters.

Mode control by rearrangement of the slow wave structure in a 12-cavity relativistic magnetron with diffraction output using single-stepped cavities driven by a transparent cathode

We present the design of an agile slow wave structure for a “crab-like” A12 relativistic magnetron with diffraction output using single-stepped cavities. By regrouping the interaction region as three sets of four cavities, the TE31 operating mode is generated at 2.60 GHz with 1.0 GW output power for an applied voltage of U = 350 kV and a magnetic field of B = 0.34 T. By regrouping the interaction region as four sets of three cavities, the TE41 operating mode is generated at 2.82 GHz with 1.0 GW output power for an applied voltage of U = 355 kV and a magnetic field of B = 0.36 T. Furthermore, by regrouping the interaction region as six sets of two cavities, the TE31 mode and the TE21 mode are generated. When an applied voltage of U = 350 kV and a magnetic field of B = 0.33 T are used, its output power can be as high as 1.0 GW for the TE31 mode operating at 2.5 GHz. In addition, when an applied voltage of U = 350 kV and a magnetic field of B = 0.42 T are used, its output power can be as high as 1.0 GW with operating mode TE21 at 2.62 GHz. It was found that the rearrangement of the slow wave structure can control the operating mode and, at the same time, lower the operating condition of the beam/wave interaction compared to the traditional 12-cavity relativistic magnetron. The result suggests that this configuration is favorable for mode switching through mechanical rearrangement of the slow wave structure. This work seeks to design a compact high power microwave source for a narrowband directed microwave beam that is suitable for mode switching investigations.

A Frequency-Agile Relativistic Magnetron With Axial Tuning

A frequency-agile relativistic magnetron with axial tuning is presented. To achieve axial tuning, reentrant cavity which has two radial parts connected by a coupling hole had been introduced. Resonant frequency of this cavity configuration can be tuned by adjusting the axial length of each coupling hole without any variation of other parameters. Multi-antenna output technique had been integrated with the reentrant cavity chain to obtain high conversion efficiency in the whole tuning range. Simulation results showed that this tube had a tuning range between 1.23 GHz to 1.70 GHz, corresponding to relative bandwidth of 32% about a center frequency of 1.465 GHz. In this tuning range, the maximum output power is 1.81 GW at 1.605 GHz, corresponding to an efficiency of 54.5%. This axial tuning RM is a promising compact high power microwave source with wide tuning range.

A “crab-like” A6 relativistic magnetron with diffraction output driven by a transparent cathode

We present the design of an A6 relativistic magnetron with diffraction output (MDO) which looks like a crab and we named it the “crab-like” A6 MDO. This article shows that the crab-like A6 MDO driven by a transparent cathode can radiate the TE11 mode with an output power of about 1 GW when an optimized applied voltage of U=440 kV and magnetic field of B=0.43 T are used. Its electronic efficiency, as obtained using UNIPIC particle-in-cell (PIC) simulations, can be as high as 44% in S-band. The UNIPIC PIC code used in simulations also demonstrates that the crab-like A6 MDO can radiate both two electron spokes in the TE21 mode with an operating frequency of 2.1 GHz and four electron spokes in the TE21 mode with an operating frequency of 2.5 GHz when different magnetic field amplitudes are used for an applied voltage of U=400 kV. This result suggests that this configuration is favorable for mode switching. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for mode switching investigations.

Experimental investigation of an S-band triple cavity oscillator

The triple cavity oscillator (Tritron) is an improved high power microwave (HPM) oscillator from the dual cavity oscillator (Bitron), in which an intermediate cavity is introduced to enhance the beam modulation depth and improve the conversion efficiency by optimizing the phase between the modulated beam and the field in the intermediate cavity. There are only three cavities in the device, which makes it fit for developing compact HPM source. In this paper, an S-band Tritron is proposed and investigated experimentally. By means of adjusting the axial position of the support posts, the self-oscillation phenomenon observed in the experiment is efficiently suppressed without affecting the characteristics of the working mode. An output power of 1.8GW with the pulse width of 46ns and the frequency of 2.46GHz is obtained in the experiment under the condition of the 0.7T guiding magnetic field, and the axial length of the interaction region is only 11cm.

Compact high-power microwave divider and combiner.

A novel, compact, TM01-TE10 mode power divider and a novel, compact, four-way TE10-TM01 mode power combiner were theoretically designed and experimentally tested as a proof of principle. The theoretical and experimental S parameters are consistent with each other. High-power experiments show that their power capacities are no less than 1.5 GW and 3 GW, respectively. The devices have the merits of high power capacities and low insertion losses.

A reliable, compact, and repetitive-rate high power microwave generation system.

A compact high power microwave (HPM) generation system is described in this paper. The main parts of the HPM system are a Marx generator with a pulse forming line and a magnetron with diffraction output. The total weight and length of the system are 250 kg and 120 cm, respectively. The output microwave power of the HPM system at 550 kV of applied voltage and 0.33 T of magnetic field reaches 1 GW at 2.32 GHz of central frequency with 38 ns of pulse duration, 23% of power conversion efficiency, and Gaussian radiation pattern. In the bursts operation, both time and amplitude jitters are less than 4 ns and lower than 1.5 dB, respectively.

A New Compact High-Power Microwave Phase Shifter

A new compact low-loss fast phase-shift high-power microwave (HPM) phase shifter (PS) is proposed, designed, and cold and high-power tested. Firstly, based on solving the scattering matrix and eigenvectors, we design a novel HPM dual circular polarizer, and then a dumbbell-like metal plug driven by a high-speed servomotor is used to slide a short circuit along the dual circular polarized port to adjust the output RF phase, which varies 180 $^{\circ}$ by moving the plug with a quarter of the guided wavelength. The X-band PS has a total length of 9.5 cm and a power capacity achieved 300 MW at 30-ns HPM pulse. A fast phase shift of 310 $^{\circ}$ was achieved within 0.1 s in test, a high precision of phase shift 1 $^{\circ}$ can be realized, and the tested insertion loss was $ 0.15 dB.

A compact relativistic backward-wave oscillator with metallized plastic components

This letter presents the mechanism and realization of a compact relativistic backward-wave oscillator with metallized plastic components. The physical idea, specific structure, and the main testing results are presented. The three periods slow-wave structures with both inner and outer ripples and the coaxial extractor are designed to reduce the volume and increase the efficiency of the device. The metallized plastic components replacing the stainless steel components in the high power microwave (HPM) sources are put forward to reduce the device weight. In the initial experiment, a microwave with frequency of 1.54 GHz, power of 1.97 GW, efficiency of 33.5%, and pulse duration above 47 ns is generated, which proves that this technical route is feasible. Undoubtedly, the technical route can provide a guide to design other types of HPM sources and be benefit to the practical application of the compact HPM systems.

High Repetition-Rate Operation of a Compact Buncher for Microwaves

Recently, we have designed and built a new microwave tube; it has been given the name “Arletron.” It works in S-band, and we describe in this paper its operation. A 200-keV 1-kA annular electron beam (e-beam) is strongly bunched in a simple assembly of two pillbox cavities. The bunching occurs at the frequency of the -mode resonance of the system. An extracting cavity, inserted just downstream from the buncher, has been used to extract and to convert the kinetic energy of the beam into an RF wave that is then radiated by a conical antenna. The Arletron is a short and compact high-power microwave source whose repetition rate depends on the pulsed power system; operation at 100 Hz has been routinely achieved. The e-beam does not intercept grids or electrodes before being collected. MAGIC simulations predict that an Arletron can be, in principle, operated from S-band to C-band (2-6 GHz). Although a magnetic field is needed to propagate the beam, it is low enough to be produced by permanent magnets.

DESIGN AND EXPERIMENTS OF THE GW HIGH-POWER MICROWAVE FEED HORN

Design and optimization of high-power microwave (HPM) feed horn by combining the aperture fleld with radiation patterns are presented in the paper. The optimized feed horn in C band satisfles relatively uniform aperture fleld, power capacity higher than 3GW, symmetric radiation patterns, low sidelobes, and compact length. Cold tests and HPM experiments were conducted to investigate the radiation patterns and power capacity of the horn. The theoretical radiation patterns are consistent with the cold test and HPM experimental results. The power capacity of the compact HPM horn has been demonstrated by HPM experiments to be higher than 3GW.

Instability of relativistic electron-beam–dielectric system as a mechanism for microwave generation

The dispersion relation of relativistic rectilinear electron beam propagating along a guide magnetic field in a dielectric is investigated by cold fluid model. In such a system, due to anomalous Doppler effect, the instability occurs when the electron velocity exceeds the wave phase velocity. The growth rate and spatial growth rate are studied analytically and the nonlinear saturated efficiency is given analytically for the first time. Numerical results show that the saturated efficiency approaches about 10%–30%. The distinctive interaction mechanism is promising for the design of a new kind of compact high-power microwave generation devices.

Photon assisted field emission from a silicon emitter

A novel method for the high-frequency modulation of a semiconductor field emitter array (FEA), as needed by compact high power microwave and millimeter wave tubes, is qualitatively analyzed. The model examines a FEA held at the threshold of emission by an applied gate potential from which current pulses are triggered by the application of a laser pulse on the backside of the semiconductor. Such an arrangement produces electron bunches (“density modulation”) at GHz frequencies without suffering from the restriction in reduced emission area and small unit cell geometry imposed by the high capacitance of field emitters. The analysis proceeds by first developing an analytical model of the emission from a silicon tip using a modified WKB approach to the tunneling current, which is validated by the more exact Airy function approach to solving Schrödinger’s equation. The effects of band bending are explicitly accounted for. The resulting relations are used to estimate emission from a single hyperbolic structure, and generalized to an array where a distribution in tip radii and work function is possible. Using a simple relationship between the incident photon flux and the resultant electron density at the emission site, an estimation of the tunneling current is made. Finally, a brief description of the operation and design of such a “photon-assisted field emission device” is given.