High Power Microwaves

The rapid proliferation of unmanned aerial vehicles (UAVs) and precision-guided munitions (PGMs) has fundamentally altered the tactical landscape of modern security, creating a state of permanent asymmetric threat. Small, cost-effective drones, often referred to as loitering munitions, now bridge the capability gap between traditional reconnaissance platforms and high-velocity guided missiles. In contemporary theaters of conflict, particularly in Eastern Europe, drones costing between $2,000 and $30,000 have demonstrated the capacity to engage and destroy high-value assets, forcing defenders to utilize interceptor missiles costing upwards of $1 million per engagement. This economic and tactical asymmetry poses a profound threat to strategic infrastructure, cultural heritage, and soft targets like schools and places of worship. Traditional air defense architectures, optimized for high Radar Cross Section (RCS) and high-velocity targets, frequently struggle against autonomous swarms characterized by low-altitude flight, rapid maneuverability, and irregular spatial formations.

Project NUSRET conceptualizes a revolutionary defensive posture: the invisible electromagnetic minefield. This system does not rely on expendable kinetic interceptors but instead establishes a persistent, distributed field of high-power microwave (HPM) energy capable of laying "mines in the air".  By synthesizing high-frequency electromagnetic pulses with advanced protocol-layer cyber-attacks, NUSRET seeks to provide a comprehensive shield against diverse threats, ranging from commercial quadcopters to ground-launched guided projectiles and cluster munitions. The objective is a "one-to-many" engagement model that neutralizes entire swarms simultaneously while adhering to stringent safety and legal frameworks for operation in civilian-adjacent zones.

Particularly in the modern geopolitical context, the prevention of armed UAV and drone attacks—which damage strategic and cultural heritage, cause mass casualties in schools, or result in fatalities at places of worship—is of critical importance.

High-power microwave, HPM, systems can be used as non-lethal weapons with the ability to destroy or disturb electronics, by damaging internal circuits and inducing high currents. Today microwave sources are being developed with peak powers exceeding 1 GW, one of these devices is the vircator, a narrowband source which is unique to the HPM community. In order to understand and develop microwave sources like the vircator it is necessary to have computer models, as simulations gives an invaluable understanding of the mechanisms involved during operation, saving time and development costs. This thesis presents the results from a theoretical analysis and a simulation study using a well known electromagnetic particle-in-cell code, Computer Simulation Technology Particle Studio. The results are then compared to measured data from a HPM system, the Bofors HPM Blackout. The results show that CST PS can be used to design and study the coaxial vircator with good results.

In this research, a compact multi-layer microstrip antenna for Multiple-Input Multiple-Output (MIMO) systems with dualband circular polarization capability has been designed, simulated, and fabricated. The antenna structure employs separate coupling networks for each frequency band, each comprising a hairpin resonator, a straight slot, and a U-shaped groove. This configuration enables the establishment of two signal paths with the requisite phase difference to feed the patch. By applying a ±90° phase shift, the antenna achieves dual-band circular polarization operation. The principal innovation of this work is the implementation of a multi-layer feeding network that ensures an axial ratio below 3 dB, achieved through the combined action of the straight slot and U-shaped groove to excite a circular polarization resonance mode. The antenna exhibits right-hand and left-hand circular polarization characteristics in different frequency bands. Simulation and experimental results validate the antenna's performance, demonstrating impedance bandwidths of 3.0-4.2 GHz and 5.5-6.6 GHz, with near-complete circular polarization coverage across the first band. The gain response increases linearly with frequency, achieving an average value of 5 dB.

A helical (Slow Wave Structure SWS) traveling wave tube (TWT) operating in the C bandwidth was designed using CST software. Based on modelling, TWT components were produced. Conductor support rod rings were used to matching the impedance line and provide ease of assembly. According to the modelling, the signal gain was determined as 30 dB. In addition, Time Domain Reflectometer (TDR) analyses were performed to observe the effect of mounting rings on impedance improvements with the help of software. As a result, it has been determined that the support rod rings, which have not been used before in C band helix TWT systems, positively affect the ease of assembly and impedance improvement.

Metamaterials (MTMs) are synthetic materials designed to have characteristics that "may not be readily available in nature," such as negative permittivity, reversed Doppler Effect, reversed Cherenkov Effect, and negative Refractive Index. These characteristics have motivated researchers to analyze and investigate the use of MTMs for modelling high-power microwave (HPM) radiation sources. One of the most potential HPM sources is an annular beam-driven Backward-Wave Oscillator (BWO) based on the Cerenkov mechanism. The devices that use the Cerenkov mechanism are preferred due to their larger bandwidth. Its high output power and repetition operations make it a promising source. In this paper, an annular beam-loaded metamaterial BWO is simulated in order to investigate and comment on the possibility of metamaterial or metamaterial-inspired structures replacing the slow-wave structures (SWSs) in vacuum tube devices. Performance parameters of several BWO configurations loaded with different metamaterial-inspired conductor rings are compared to rippled SWS-based BWOs. The results suggest that fewer metamaterial rings with solid cross-section (CS) inside the BWO lead to a closer match in generated output power and frequency with the output power generated using a rippled SWS.

The dispersion relation of semicircularly corrugated slow-wave structure (SCCSWS) is calculated and verified numerically using synthetic technique. The metallic periodic structure resonates at discrete frequencies when both ends of it are shorted and excited properly. From the discrete frequencies of the axial modes of the resonant cavity, continuous dispersion curve for both the fundamental and the higher order passband modes (TM 01-TM 03) are generated. The generated dispersion curve is compared with the analytical results, which agree excellently with a maximum deviation of 1.33% for TM 01 mode, 1.94% for TM 02 mode, and 1.30% for TM 03 mode. The electromagnetic field patterns of SCCSWS in both radial and axial direction are also calculated and compared with analytical field patterns. Comparative results validate both the obtained dispersion relation and field patterns of SCCSWS, which can be employed as viable alternative of the existing slow-wave structure (SWS) in high-power microwave devices.

The dispersion relation of beam-free trapezoidally corrugated periodic metallic slow wave structure (TCSWS) has been numerically verified using a synthetic technique. The dispersion curves for both the fundamental and the higher order passband modes (TM 01-TM 03) are computed for an axisymmetric-corrugated structure. The periodic structure resonates at specific frequencies when shorted appropriately at both ends. From the specific frequency values of these resonant peaks, a dispersion curve is determined for each transverse magnetic (TM) mode. The obtained dispersion curve is compared with both the experimental and analytical results using the same number of periods. The comparisons with analytical results and their experimental counterpart agree excellently with a maximum deviation of 1.94% for the TM 01 mode, 1.29% for the TM 02 mode and 2.38% for the TM 03 mode. The radial and longitudinal electromagnetic field patterns of TCSWS are also calculated and compared with analytical field patterns for a six-period slow wave structure. Comparative results validate both the obtained dispersion curves and field patterns of TCSWS.

E-band (71-76 GHz and 81-86 GHz) is widely used for wireless point to point links with a few Gigabit/second data rate. E-band front-ends are powered by solid state amplifiers with about 1 W output power per module. This level of output power limits range and spectral efficiency in rain condition and has to be compensated by high gain antennas or backup low frequency links with reduced capacity. The availability of tens of Watts of transmission power would allow higher spectral efficiency and long range, and the use of lower gain antennas for multibeam and area coverage. Millimeter wave Traveling Wave Tubes (TWTs) are gaining interest due to their higher power, more than one order of magnitude, in comparison to solid state devices. Helix TWTs, typically built at microwaves, are very arduous to fabricate due to the extremely small diameter of an helix at E-band. This paper reports the design and fabrication of the first ever Eband TWT based on a full metal slow wave structure, the double corrugated waveguide. The TWT is designed to provide about 70 W power and more than 35 dB gain in the 71-76 GHz band. A test TWT using a single section interaction structure is in the final assembly phase as proof of concept with about 2 W output power. The E-band TWT performance will open new perspectives in the availability of long range wireless links with multi-Gb/s data rate needed for enabling 5G and 6G new networks.

E-band (71-76 GHz and 81-86 GHz) is already used for point to point links with a few Gigabit/second data rate. Front-ends are powered by solid state amplifiers with about 2-3 W output power. This output power values limit range and spectral efficiency and have to be compensated by high gain antennas. The availability of tens of Watt would allow higher spectral efficiency and long range, and the use of lower gain antennas for multibeam and area coverage. This paper reports the design and the initial fabrication of the first ever E-band Traveling Wave Tube (TWT) based on the double corrugated waveguide. A test short interaction structure TWT is in assembly phase as proof of concept with about 2 W output power. The final TWT is designed to provide about 70 W power and about 40 dB gain.

The need of high data rate can be satisfied only by wide frequency bands in the millimetre wave region. This paper presents the design of a G-band (215-250 GHz) Traveling Wave Tube with 40 dB gain for wireless communications, based on the double corrugated waveguide. The structure of the TWT is based on a single section, instead of the typical configuration of two sections with a sever used at microwave frequency. This is possible due to the high losses at those frequency that permit a stable behaviour. This paper reports both cold and hot simulations.

To improve the performance of a broadband traveling-wave tube (TWT), a helix pitch profile incorporating a section with reduced phase velocity followed by a positive phase-velocity taper is used. A simple technique to design a pitch profile of this kind is elaborated upon and later applied to an existing 6-18-GHz uniform pitch mini-TWT to improve its interaction efficiency. By using the newly designed helix, a TWT is developed, which shows increases in electronic efficiency and output power up to 8.75% points and 2.6 dB (75 W), respectively. Further application of this method to another uniform pitch baseline tube results in similar improvements.

Nowadays, due to the concern regarding the environment, energy-efficiency performance in microwave ovens are required. This paper presents the output performance enhancement of domestic microwave oven. The power output and efficiency of the oven is calculated by using the test procedure discussed in the IEC 60705. The main component for the efficiency enhancement of oven are vanes type continuous wave magnetron and the high voltage circuit. As per the literature, 3-D particle in cell modelling in CST studio suite software is used for the modelling of the magnetron to examine the performance of the magnetron. The geometrical parameters of the magnetron are changes to achieve the desired efficiency for the oven. Further, modelling of the π quadruple model of non-linear transformer with doubler circuit has been done in MATLAB Simulink environment. The simulated and the experimental data has been collected and compared. It is found that there is approximately less than 5% variation in the simulated and the experimental results. Also, the performance of the oven has been enhanced approximately by 4.5%.

The measurements of microwave pulses of gigawatt power level have a lot of constraints. A receiving antenna is a starting and core point of the measurement system. Waveguide based and dipole antennas have a limited wide bands, while the use of commercially available wideband antennas is restricted by their maximum peak power acceptances. The design of the wide band antenna with the small effective area was proposed. The characteristics of prototype were obtained in numerical simulations with ANSYS HFSS software and by calibration tests in the frequency band of 1-13 GHz. It has the effective area about the 1 mm2 in X-band and square-law dependence on the wavelength in a wide band. The cross polarization rate is more than 60 dB at the centre position and not less than 30 dB within the range of ±5 0 in azimuth and elevation angle. The wide beam radiation pattern forces a user to discriminate reflected signals. This antenna could greatly simplify the measurement system, replacing a set of narrow band antennas that connected to several recording channels.

The main objective of the paper is to make an efficient design of the input and output coaxial coupler for a helix TWTs. An approach has been developed for the efficient design and analysis of the coaxial couplers in the practical situation. Normally multi-section impedance transformer approach is used for any wide band coupler. For a space helix TWT, coupler should be wide bandwidth and small size. In this case coupler is matched with helix slow wave structure and the standard 50-ohm connectors. The simulated return loss (dB) profile for different type of couplers is obtained by using Ansoft HFSS, CST microwave studio and compares those with experimental results. The tip loss design at sever ends for the input and the output section has been also optimized.

The fabrication of slow wave structures for millimeter wave Traveling Wave Tubes (TWT) poses significant difficulties and requires high accuracy processes. The EU H2020 TWEETHER project proposes a Point to Multipoint (PmP) distribution wireless W-band (92 -95 GHz) system for backhaul for small cells in the future 5G scenario and fixed access, based on a folded waveguide W-band TWT. The cost of TWTs and feasible high volume production are key parameters for millimeter wave network front ends. This paper explores possible new approaches for reducing the fabrication cost of millimeter wave slow wave structures for TWTs based on the SU-8 casting and low cost CNC milling process.

Radial line slot array (RLSA) antennas used to generate circular polarization, are categorized as high-efficiency plane array antennas. In these antennas, the second-layer wave-guide is filled with a dielectric material to eliminate the grating lobes caused by the array structure. All input power to the antenna must pass through a confined space that includes dielectric, air, and metal. This space has corners where the intensity of the electric field would be very high and, therefore, at high powers, would reduce the power transmission capacity of the antenna. For this reason, instead of using a dielectric in the space between the two wave-guides, a slow radial wave structure is used. In this paper, first, a mathematical analysis of the slow-wave structure is performed based on the Fluke theory. Next, a slow-wave structure is designed, simulated, and optimized for use in a 10.2 GHz radial line slot array antenna.The simulation results showed that the minimum reflection coefficient is-20 dB, and its bandwidth is 251 MHz. Finally, a prototype of the simulated antenna was constructed using the proposed structure. The antenna power analysis showed that the minimum tolerable antenna power is 625 MW.

The W-band pulsed traveling-wave tubes (TWTs) are known to play a crucial role in the high-resolution radars due to their wide bandwidth and high output power. This paper presents some experimental results of an ultrawide bandwidth W-band pulsed TWT with folded-waveguide circuits fabricated by ultraviolet lithography, electroplating, and molding. A prototype tube has been tested, showing a gain of over 30 dB from 94 to 110 GHz and saturated output power of over 100 W from 94 to 101.8 GHz, with an electronic efficiency of 2.86%-4.08%. Limited by the drive power, the prototype's unsaturation output power is over 60 W from 101.8 to 110 GHz.

The European Commission Horizon 2020 ULTRAWAVE, "Ultra capacity wireless layer beyond 100 GHz based on millimeter wave Traveling Wave Tubes", aims to exploit portions of two frequency bands in the millimetre wave spectrum, the D-band (141-148.5 GHz) and the G-band (275-305 GHz) for creating a very high capacity layer. Due to the high atmosphere and rain attenuation, high transmission power is needed to provide a useful transmission range. Traveling Wave Tubes are the only devices that can provide the multi-Watt transmission power above 100 GHz. In this paper, the design of the Double Corrugated Waveguide (DCW), as slow wave structure, for a novel D-band TWT, for wireless communications, will be described.

The fabrication of slow wave structures for millimeter wave Traveling Wave Tubes (TWT) poses significant difficulties and requires high accuracy processes. The EU H2020 TWEETHER project proposes a Point to Multipoint (PmP) distribution wireless W-band (92 -95 GHz) system for backhaul for small cells in the future 5G scenario and fixed access, based on a folded waveguide W-band TWT. The cost of TWTs and feasible high volume production are key parameters for millimeter wave network front ends. This paper explores possible new approaches for reducing the fabrication cost of millimeter wave slow wave structures for TWTs based on the SU-8 casting and low cost CNC milling process.

Mode conversion of high-power electromagnetic microwave (HPEM) was successfully accomplished using a coaxialbeam rotating antenna (COBRA) in an X-band relativistic backward-wave oscillator (RBWO). The mode conversion from the TM 01 mode to the circularly polarized TE 11-likeness mode was identified by both cold test and hot test. To observe whether mode conversion is effective or not, the radiation pattern of TE 11-likeness mode by COBRA lens was compared with the case of the radiation pattern of TM 01 mode using simple horn antenna. Their radiation patterns could be described by fluorescent lamps. The experimental results of radiation pattern measurements are shown to be in a reasonable agreement with the simulated one. The maximum value of RF output power appeared at the center of COBRA lens from the experimental results. Index Terms-Coaxial beam rotating antenna (COBRA), highpower electromagnetic (EM) microwave (HPEM), mode conversion, relativistic backward-wave oscillator (RBWO).

The measurements of microwave pulses of gigawatt power level have a lot of constraints. A receiving antenna is a starting and core point of the measurement system. Waveguide based and dipole antennas have a limited wide bands, while the use of commercially available wideband antennas is restricted by their maximum peak power acceptances. The design of the wide band antenna with the small effective area was proposed. The characteristics of prototype were obtained in numerical simulations with ANSYS HFSS software and by calibration tests in the frequency band of 1-13 GHz. It has the effective area about the 1 mm2 in X-band and square-law dependence on the wavelength in a wide band. The cross polarization rate is more than 60 dB at the centre position and not less than 30 dB within the range of ±5 0 in azimuth and elevation angle. The wide beam radiation pattern forces a user to discriminate reflected signals. This antenna could greatly simplify the measurement system, replacing a set of narrow band antennas that connected to several recording channels.

Nowadays, due to the concern regarding the environment, energy-efficiency performance in microwave ovens are required. This paper presents the output performance enhancement of domestic microwave oven. The power output and efficiency of the oven is calculated by using the test procedure discussed in the IEC 60705. The main component for the efficiency enhancement of oven are vanes type continuous wave magnetron and the high voltage circuit. As per the literature, 3-D particle in cell modelling in CST studio suite software is used for the modelling of the magnetron to examine the performance of the magnetron. The geometrical parameters of the magnetron are changes to achieve the desired efficiency for the oven. Further, modelling of the π quadruple model of non-linear transformer with doubler circuit has been done in MATLAB Simulink environment. The simulated and the experimental data has been collected and compared. It is found that there is approximately less than 5% variation in the simulated and the experimental results. Also, the performance of the oven has been enhanced approximately by 4.5%.

This paper presents a Vlasov antenna with optimized reflector position and angle suitable for high power microwave applications. With the proposed configuration, the reflector is directly attached to the waveguide, which is an advantage and makes it simpler to radiate in the direction of the axis of the waveguide. Bevel-cut and Step-cut Vlasov antennas, designed for operation at 3 GHz, are used to validate the effect of the reflector. In addition to proper radiation of the direction of maximum radiation, the optimized reflector results in increased antenna gain and reduced half-power beamwidth.

This paper describes a theoretical characterization of a Transverse Electric (TE)-polarized vortex beam antenna in the microwave range. The main body of the antenna consists of a cylindrical waveguide that is excited by a traveling-wave current ring feeder. A new design of the feeder is proposed. Closed-form formulas are obtained for the fields and the antenna input impedance following a conventional derivation based on the electric vector potential. A detailed dispersion analysis is used for accurate evaluation of the relevant spectrum and propagation properties. The effectiveness of the theoretical derivations is validated via full-wave numerical simulations.

This paper presents antenna designs with improved performance and characteristics for applications requiring high levels of microwave power. One such application is in the remote neutralization of landmines and unexploded ordnance, which is part of a wide research program on Humanitarian Demining. A description of this program is included in this paper. Two types of antennas are dealt with in this work: Vlasov and the slotted waveguide antennas. A Vlasov antenna with a curved cut is first introduced. This novel cut shape is more suitable for high power microwave (HPM) applications and results in increased antenna gain and good sidelobe level and half-power beamwidth. Bevel-cut and step-cut Vlasov antennas with optimized reflector position and angle are also reported. The optimized reflector is directly attached to the waveguide making the Vlasov antenna, which gives a simpler design. It also offers the advantages of a better control over the direction of maximum radiation, an increased antenna gain and a reduced half-power beamwidth. Corrugations are used inside slotted waveguide antennas in two configurations: one leading to a much smaller reflection coefficient at the antenna input, which is essential for HPM, and the second resulting in antenna size reduction by shifting down its operational frequency.

This paper presents the use of machine learning (ML) to facilitate the design of dielectricfilled Slotted Waveguide Antennas (SWAs) with specified sidelobe level ratios (SLR). Conventional design methods for air-filled SWAs require the simultaneous solving of complex equations to deduce the antenna's design parameters, which typically requires further manual simulation-based optimization to reach the desired resonance frequency and SLR. The few works that investigated the design of filled SWAs, did not optimize the design for a specified SLR. For an accelerated design process in the case of specified SLRs, we formulate the design of dielectric-filled SWAs as a regression problem where based on input specifications of the antenna's SLR, reflection coefficient, frequency of operation, and relative permittivity of the dielectric material, the developed ML model predicts the filled SWA's design parameters with very low error. These parameters include the unified slots length and the non-uniform slot displacements required to achieve the desired performance. We experiment with several regressive ML algorithms and provide a comparative study of their results. Our numerical evaluations and validation experiments with the best performing ML models demonstrate the high efficiency of the proposed ML approach in estimating the dielectric-filled SWA's design parameters in only a few milliseconds. A comparison to the design obtained through conventional optimization using the Genetic Algorithm also indicates superiority of the ML models in computation time and resulting antenna performance. INDEX TERMS Antenna design, slotted waveguide antennas, dielectric-filled SWA, sidelobe level ratio, machine learning, neural networks.

This paper presents antenna designs with improved performance and characteristics for applications requiring high levels of microwave power. One such application is in the remote neutralization of landmines and unexploded ordnance, which is part of a wide research program on Humanitarian Demining. A description of this program is included in this paper. Two types of antennas are dealt with in this work: Vlasov and the slotted waveguide antennas. A Vlasov antenna with a curved cut is first introduced. This novel cut shape is more suitable for high power microwave (HPM) applications and results in increased antenna gain and good sidelobe level and half-power beamwidth. Bevel-cut and step-cut Vlasov antennas with optimized reflector position and angle are also reported. The optimized reflector is directly attached to the waveguide making the Vlasov antenna, which gives a simpler design. It also offers the advantages of a better control over the direction of maximum radiation, an increa...

This paper presents a Vlasov antenna with optimized re∞ector position and angle suitable for high power microwave applications. With the proposed conflguration, the re∞ector is directly attached to the waveguide, which is an advantage and makes it simpler to radiate in the direction of the axis of the waveguide. Bevel-cut and Step-cut Vlasov antennas, designed for operation at 3GHz, are used to validate the efiect of the re∞ector. In addition to proper radiation of the direction of maximum radiation, the optimized re∞ector results in increased antenna gain and reduced half-power beamwidth. 1. INTRODUCTION High Power Microwave (HPM) sources, such as the Backward-Wave Oscillator (BWO), the gy- rotron, and the vircator (virtual cathode oscillator), generate power in cylindrically symmetric transverse electric TE0n or transverse magnetic TM0n modes. The side lobe generation, gain re- duction, and ine-cient power loading on the antenna aperture, make these modes unsuitable for driving co...

This paper presents antenna designs with improved performance and characteristics for applications requiring high levels of microwave power. One such application is in the remote neutralization of landmines and unexploded ordnance, which is part of a wide research program on Humanitarian Demining. A description of this program is included in this paper. Two types of antennas are dealt with in this work: Vlasov and the slotted waveguide antennas. A Vlasov antenna with a curved cut is first introduced. This novel cut shape is more suitable for high power microwave (HPM) applications and results in increased antenna gain and good sidelobe level and half-power beamwidth. Bevel-cut and step-cut Vlasov antennas with optimized reflector position and angle are also reported. The optimized reflector is directly attached to the waveguide making the Vlasov antenna, which gives a simpler design. It also offers the advantages of a better control over the direction of maximum radiation, an increa...