Narrow Band High Power Microwave Research Articles

High-Power Microwave Pulse-Induced Failure on Unmanned Aerial Vehicle System

With the wide application of unmanned aerial vehicles (UAVs), more attention has been paid to the safe operation of UAVs in complex electromagnetic environments. In this article, we investigate the impact of high-power microwave (HPM) pulses on three types of typical commercial UAVs. We established the HPM irradiation experiment system first and obtained the responses of UAVs under the HPM attack with different electric field strengths. The flight logs and the damage analysis reports indicate that the damaged components of the type I UAV and the type II UAV are the rotor motor and the electronic speed controller. The experiment results prove that L-band narrowband HPM microwave has strong backdoor coupling effects on UAVs. The damage mechanism of UAVs by the HPM is studied by simulation. The simulation results show that an HPM pulse will cause a high-voltage pulse coupled to the cable connecting the electronic speed controller and the rotor motor, which caused the electronic speed controller to send out a false signal that caused the rotor motor speed to rise sharply, eventually making the rotor motor to burn out. Experiment results show that strengthening electromagnetic protection on the cable can effectively prevent HPM damage to UAVs. The simulation results match the experiment results and the damage analysis reports. Finally, some suggestions are provided to improve the UAV’s anti-HPM capability.

Progress in narrowband high-power microwave sources

Even after 50 years of development, narrowband high-power microwave (HPM) source technologies remain the focus of much research due to intense interest in innovative applications of HPMs in fields such as directed energy, space propulsion, and high-power radar. A few decades ago, the main aim of investigations in this field was to enhance the output power of a single HPM source to tens or hundreds of gigawatts, but this goal has proven difficult due to physical limitations. Therefore, recent research into HPM sources has focused on five main targets: phase locking and power combination, high power efficiency, compact sources with a low or no external magnetic field, high pulse energy, and high-power millimeter-wave generation. Progress made in these aspects of narrowband HPM sources over the last decade is analyzed and summarized in this paper. There is no single type of HPM source capable of excellent performance in all five aspects. Specifically, high pulse energy cannot be achieved together with high power efficiency. The physical difficulties of high power generation in the millimeter wave band are discussed. Semiconductor-based HPM sources and metamaterial (MTM) vacuum electron devices (VEDs) are also commented on here. Semiconductor devices have the advantage of smart frequency agility, but they have low power density and high cost. MTM VEDs have the potential to be high power efficiency HPM sources in the low frequency band. Moreover, problems relating to narrowband HPM source lifetime and stability, which are the important determinants of the real-world applicability of these sources, are also discussed.

Design and experimental demonstration of a circularly polarized mode converter for high-power microwave applications.

A novel mode converter that can transform coaxial transverse electromagnetic (TEM) mode into circularly polarized TE11 (CPT) mode was developed and experimentally studied with high-power microwave (HPM). The mode conversion is realized by two steps. First, the TEM mode is converted into linearly polarized TE11 (LPT) mode by the webbed-shaped balun structure. Second, the LPT mode is transformed into the CPT mode with the insertion of circular-arc diaphragms in a circular waveguide. In this paper, the principle of a mode converter working at 1.57 GHz is demonstrated, as well as the experimental results. The experimental and simulation results are in good agreement. At the central frequency, the conversion efficiency is more than 99.5%, the measured axial ratio approximates to 1.39 dB, and the power handling capacity is in excess of 1.5 GW. These measured results meet the demand for narrow-band HPM source application.

Tunable Electrically Small Conical Folded Dipole Antenna Used as a Mesoband High-Power Microwave Source

High-power microwave (HPM) moderate-band (MB) sources combine simple design concepts seen in ultrawideband (UWB) sources, but with longer pulses to produces higher energy spectral densities. These factors allow the designs to be more compact and less complicated than many narrowband HPM sources. In this letter, we will demonstrate from both simulation and experimental results the operation of a electrically small, tunable, self-resonant, mesoband source utilizing a conical folded dipole antenna as the energy storage and radiating element. The system is based on a previous design for an HPM folded helix antenna that has a resonant frequency of 46 MHz and is charged to 70 kV. The design presented here utilizes a tunable capacitance that allows the resonant frequency to be tuned between 52 and 87 MHz with ka =0.58 at the lowest resonant frequency.

Investigation of a metallic photonic crystal high power microwave mode converter

It is demonstrated that an L band metallic photonic crystal TEM-TE11 mode converter is suitable for narrow band high power microwave application. The proposed mode converter is realized by partially filling metallic photonic crystals along azimuthal direction in a coaxial transmission line for phase-shifting. A three rows structure is designed and simulated by commercial software CST Microwave Studio. Simulation results show that its conversion efficiency is 99% at the center frequency 1.58 GHz. Over the frequency range of 1.56-1.625 GHz, the conversion efficiency exceeds 90 %, with a corresponding bandwidth of 4.1 %. This mode converter has a gigawatt level power handling capability which is suitable for narrow band high power microwave application. Using magnetically insulated transmission line oscillator(MILO) as a high power microwave source, particle-in-cell simulation is carried out to test the performance of the mode converter. The expected TE11 mode microwave output is obtained and the MILO works well. Mode conversion performance of the converter is tested by far-field measurement method. And the experimental result confirms the validity of our design. Then, high power microwave experiment is carried out on a Marx-driven Blumlein water line pulsed power accelerator. Microwave frequency, radiated pattern and power are measured in the far-field region and the results agree well with simulation results. The experiment also reveals that no microwave breakdown or pulse shortening took place in the experimental setup.

An Electrically Small Conical Folded Dipole Antenna for Use as a Compact, Self-Resonant Mesoband High-Power Microwave Source

Mesoband (MB) high-power microwave (HPM) sources use fast-risetime switches to trigger weak resonators in order to create a damped sinusoidal waveform. MB sources are more compact and less complicated than narrowband HPM sources, and they possess increased energy spectral density per pulse relative to ultrawideband HPM sources. In this paper we consider the design of a MB HPM system that operates at the low end of the VHF spectrum (below 50 MHz) that is based on a self-resonant, electrically small antenna (ESA). The ESA is based on a conical folded helix design. It is slowly charged up to high voltage, and it is then switched using a fast-rise time switch to convert the stored static energy into radiated electromagnetic fields. Here we show the design, modeling, and preliminary experimental results of the source operating as low as 38 MHz at an electrical size of ka = 0.43, where a is the radius of a sphere circumscribing the source. Experimental results are obtained in the far field for a charge voltage of 30 kV.

Waveguide‐based combining S‐band high power microwaves

Incoherent power combining system is a promising technique for enhancing the output power level of narrow-band high-power microwave devices, and waveguide-based combiner usually has the virtues of high transmission efficiency, proper bandwidth and high power-handling capacity within a compact structure. A specific cross-junction combiner is proposed for combining the S/S band microwave beams, and the detailed simulation and experimental results are presented. The investigations show that the combiner realises integration of GW level power combination and mode conversion from two microwave sources simultaneously.

Design of a metallic photonic crystal high power microwave mode converter

Electromagnetic properties of a two-dimensional metallic photonic crystal in a transmission line is analyzed, and a compact TEM-TE11 high-power microwave mode converter which takes this type of sturcture for phase-shiftting is presented. An L band TEM-TE11 mode converter is optimized using the commercial software cst microwave studio. Its conversion efficiency is 98% at the center frequency of 1.58 GHz. Over the frequency range of 1.56–1.625 GHz, the conversion efficiency exceeds 90%, with a corresponding bandwidth of 4.1%. This mode converter has a gagawatt level power handling capability, thus it is suitable for narrow band high-power microwave application. Using magnetically insulated transmission line oscillator as a high-power microwave source, particle-in-cell simulation is carried out to test the performance of the mode converter. It is found that the proposed mode converter works well with this narrow band high power microwave device.

Investigation on the power combination of the relativistic magnetrons with axial extraction

The relativistic magnetron with axial extraction, also known as magnetron with diffraction output (MDO), is an important device for the miniaturization and compaetification of magnetron. It is also promising to be one of the most compact narrow band high power microwave sources. Based on the manners and traits of the MDO directly radiating the quasi-TE11 mode in axial direction, the investigation of the power combination of double MDOs with a horn antenna is carried out. After discussing the combination ways and results, a modified configuration is proposed for improving the radiation directivity. Finally, the results show that when the adjacent double MDOs have an open angle of 7 and the common horn antenna has the parameters of h = 600 mm and r = 340 mm, the mode reflection coefficient of the power combination system is 0.31, the maximum gain is 21.5 dB, the radiation mode is TE11.

T-junction waveguide-based combining high power microwave beams

Waveguide-based combining microwave beams is an attractive technique for enhancing the output capacities of narrow-band high power microwave devices. A specific T-junction combiner is designed for combining the X/X band microwave beams, and the detailed combining method and experimental results are presented. In the experiments, two microwave sources which can generate gigawatt level microwaves are driven by a single accelerator simultaneously, and their operation frequencies are 9.41 and 9.60 GHz, respectively. The two microwave beams with durations of about 35 ns have been successfully combined, and no breakdown phenomenon occurs.

Modified magnetic field distribution in relativistic magnetron with diffraction output for compact operation

A modified magnetic field distribution in relativistic magnetron with diffraction output (MDO) for compact operation is proposed in this paper. The principle of how the modified magnetic field confines electrons drifting out of the interaction space is analyzed. The results of the particle-in-cell (PIC) simulations of the MDO with the modified magnetic field distribution show that the output power of the MDO is improved, and the long cylindrical waveguide used for collecting the drifting electrons can be omitted. The latter measure allows the horn antenna of the MDO to produce more focused energy with better directivity in the far field than it does with the long cylindrical waveguide. The MDO with the modified magnetic field distribution promises to be the real most compact narrow band high power microwave source.

Choosing optimum method for the efficient design of a relativistic magnetron with diffraction output

The relativistic magnetron with diffraction output (MDO) is promising to be the most compact narrow band high power microwave source. In this paper, based on the theory of S-parameters, a method named “choosing optimum” is proposed for the efficient design of the MDO in any wave band. By means of S-parameters, the π-TE31 mode conversion efficiencies of an S band MDO are calculated and then verified by three-dimensional particle-in-cell simulations. In order to illustrate the advantage of the choosing optimum method, the S-parameters of another L-band MDO are computed in a wide range of structure parameters and two results are chosen with detail information. Compared with the conventional method, the choosing optimum method is not only a shortcut, but also a convenient and easy way for choosing the high efficient MDOs in any wave band to meet the needs of different applications.

An efficient mode conversion configuration in relativistic magnetron with axial diffraction output

Relativistic magnetron with diffraction output, also known as magnetron with axial extraction, is a favorite in exploring the most compact narrow band high power microwave source. For further improving power conversion efficiency and radiation pattern without diminishing the compactness, this paper proposed an efficient mode conversion configuration in an S-band π-mode operating relativistic magnetron with diffraction output. The whole device has a total length of 290mm and a maximum diameter of 260mm. In three-dimensional particle-in-cell (PIC) simulation, an optimized outcome that the power conversion efficiency can reach 43% corresponding to 4.2GW output and the radiation pattern is similar to TE11 mode is achieved.

First Trials with a 45 GW Cable-Based Pulsed-Power Generator

The output from narrow-band high-power microwave (HPM) sources, such as the virtual cathode oscillator (vircator) and the magnetically insulated line oscillator (MILO), is strongly dependent on the voltage pulse feed. A rectangular, flat-top voltage pulse can be achieved by the use of a transmission line as a pulse-forming unit. The development in high-voltage cable technology has made them useful as parts of high-voltage and high-power generator systems. The generator is designed to deliver a 200 ns voltage pulse of 500 kV into a 10 Omega unmatched load with an electric power of 25 GW. The generator has an impedance of 2 Q. The primary energy storage of the generator consists of a 50 kV, 20 U capacitor bank. The 50 kV is discharged into a transformer that charges a pulse-forming line to 550 kV. When charged, the pulse-forming line is discharged into the load via a spark gap. This paper presents results from initial testing of the generator.