High Power Microwave Applications Research Articles

Electron mobility enhancement by electric field engineering of AlN/GaN/AlN quantum-well HEMTs on single-crystal AlN substrates

To enhance the electron mobility in quantum-well high-electron-mobility transistors (QW HEMTs), we investigate the transport properties in AlN/GaN/AlN heterostructures on Al-polar single-crystal AlN substrates. Theoretical modeling combined with experiment shows that interface roughness scattering due to high electric field in the quantum well limits mobility. Increasing the width of the quantum well to its relaxed form reduces the internal electric field and scattering, resulting in a binary QW HEMT with a high two-dimensional electron gas (2DEG) density of 3.68×1013 cm–2, a mobility of 823 cm2/Vs, and a record-low room temperature (RT) sheet resistance of 206 Ω/□. Further reduction of the quantum well electric field yields a 2DEG density of 2.53×1013 cm–2 and RT mobility > 1000 cm2/V s. These findings will enable future developments in high-voltage and high-power microwave applications on the ultrawide bandgap AlN substrate platform.

A Low-Reflection Tuning Strategy for Three-Stub Waveguides

In high-power microwave applications, the reflection of energy can be effectively reduced by adjusting the three-stub waveguide. However, most of the existing tuning algorithms do not make an arrangement for the adjustment sequence of stubs, and accurately calculating the depth of the stubs requires a great deal of time via electromagnetic (EM) simulations, which may cause large reflection in the matching process. To solve these problems, we first propose an improved calculation method that can accurately calculate the input impedance of a three-stub waveguide. Then, an impedance matching algorithm is designed based on the equivalent circuit model that can quickly and accurately calculate the optimal depth of the stubs. Finally, we present a low-reflection tuning strategy to suppress the large reflection during the adjustment of the stub process. An experimental system is built to verify the calculation method and the tuning strategy. The results show that the strategy can avoid large reflection in the case of load mutation and can maintain low reflection when the load changes continuously. The algorithm meets the needs of the industry and can be used for automatic and real-time adjustment of three-stub waveguides of different specifications.

Experimental Investigation of Reflectarray Antennas for High-Power Microwave Applications.

The power capacity of reflectarray antennas (RAs) is investigated through full-wave simulations and high-power microwave (HPM) experiments in this paper. In order to illustrate the results in detail, two RA elements are designed. The simulated power handling capacity of two RA elements are 7.17 MW/m2 and 2.3 GW/m2, respectively. To further study the HPM RA, two RA prototypes operating at 2.8 GHz are constructed with the aperture size of 1 m × 1 m. Simulations and experimental measurements are conducted for the two prototypes. The experimental results demonstrate that, even when subjected to 1 GW of power, the radiation beam of the RA with the second elements can still propagate in the intended direction. This research will establish a basis for advancing the practicality of RAs in HPM applications.

Pulsed High-Power Radio Frequency Energy Can Cause Non-Thermal Harmful Effects on the BRAIN.

High-power microwave applications are growing for both military and civil purposes, yet they can induce brain-related risks and raise important public health concerns. High-power sub-millisecond radio frequency energy pulses have been demonstrated to be able to induce neurological and neuropathological changes in the brain while being compliant with current regulatory guidelines' limits, highlighting the necessity of revising them.

Cascaded Oscillators for High-Power Microwave Applications

Cascaded Oscillators for High-Power Microwave Applications

Miniaturised element frequency selective surface design for high power microwave applications

AbstractA third‐order miniaturised element frequency selective surface (MEFSS) for high‐power microwave (HPM) systems is proposed. The MEFSS design is characterised by the excellent capability to handle high‐power waves and the stable frequency response at large incidence angles. Through combining the particle swarm optimisation algorithm and the equivalent circuit method to improve the efficiency, the design has low resonant temperature while maintaining a low maximum field enhancement factor. A theoretical guide for the selection of substrate parameters in high‐power systems is provided. Instead of being as small as possible, the loss tangent should be properly selected to reach a balance between metal loss and dielectric loss. To the author's best knowledge, it is the first time in‐band low temperature and out‐of‐band high temperature suppression at various incidence angles are realised. The results show that the frequency response remains stable for incident angles up to 60°, and the maximum temperature is reduced from 148°C to 44°C for incident power density of 10 kW/m2. A MEFSS prototype was fabricated, and the transmission coefficients were measured. The full‐wave simulation and measurement results agree well. It has significance to the engineering progress of FSS as radomes for HPM antenna systems.

An L-Band Leaky-Wave Array Antenna for High-Power Microwave Applications

This work seeks a novel design for a compact leaky-wave array antenna for high-power microwave (HPM) applications. The leaky-wave antenna is made of a rectangular waveguide with closely spaced non-resonant slots in the broad-wall of the waveguide. By this means, more slots can be set within a unit length and less energy will radiate from each slot, then higher power-handling capacity can be achieved. An L-band leaky-wave waveguide antenna centered at 1.57 GHz is designed and experimentally studied. The results show that the radiation efficiency of the antenna is 97% and the power-handling capacity of a single waveguide exceeds 1.3 GW. In addition, a 5-waveguide array antenna is also designed. The antenna array has an aperture efficiency of 76.6% and the beam scanning range can reach ±40° in H-plane, which would be suitable for many HPM applications.

Performance Analysis of Slotted Waveguide Antenna for High Power Microwave Applications

Performance Analysis of Slotted Waveguide Antenna for High Power Microwave Applications

Исследование тепловых характеристик беспроволочной интеграции мощных СВЧ кристаллов

This paper presents the results of thermal analysis evaluation of two assembly techniques for high power microwave applications: conventional integration on metal carrier using solder preform and flip-chip mounting using Au-Sn system for SLID bonding as an interconnect layer to dielectric substrate. A high power GaN HEMT on SiC substrate with fabrication technology of 0.15 μm and total gate width 1.2 mm are used. The results of the flip-chip approach showed a 7.2% reduction in the overall thermal resistance of the assembly compared to conventional integration approach. Dependences of individual circuit elements on thermal parameters are determinated. Electrical equivalent circuit of thermal models of investigated constructions are obtained.

A Compact Gigawatt Pulsed Power Generator for High-Power Microwave Application

Nanosecond square voltage pulse is of wide interest because of its potential military and industrial applications, such as high-power microwave (HPM). In this article, a gigawatt pulsed power generator (PPG) for HPM based on the multistage pulse forming networks (PFNs) with a voltage superposition using the Marx scheme, i.e., PFN-Marx generator, is proposed through the theory analysis, numerical simulation, processing manufacturing, and performance experiment. The PPG consists of the main subsystems of the primary power and pulse modulation subsystems. The primary power subsystem is a modular bipolar dc high-voltage generator based on the ac–dc–ac, high-frequency transformer, and voltage multipliers by using the power electronics switches. It can generate bipolar dc high 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">$\pm$</tex-math> </inline-formula> 42 kV to charge the PFN-Marx generator. As for the pulse modulation subsystem, the PFN-Marx technique is preferred, which consists of 24-stage and six <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> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{C}$</tex-math> </inline-formula> sections. To verify the PPG, an experimental prototype is fabricated and tested. It has a characteristic impedance of about 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol\Omega$</tex-math> </inline-formula> and can deliver square voltage wave with an output voltage pulse of about 500 kV, full-width at half-maximum (FWHM) of 94 ns, and 10%–90% rise time of fewer than 35 ns, indicating its ability to deliver peak power beyond 6.25 GW. In addition, a transit-time oscillator was connected and can radiate microwave power of 0.8 GW at 12.89 GHz for the cathode voltage of 372 kV and the beam current of 9.3 kA.

Development and Test of 500 kV Repetitive Pulsed Power Source for HPM Application

A compact peaking capacitor-based 500 kV, 10 kA, 100 Hz repetition rate pulsed power source has been designed and developed for high-power microwave applications. This system utilizes a 500 kV, 1.9 nF peaking capacitor to deliver the nanosecond pulse with a peak current of 10 kA. An eight-stage bipolar Marx generator (MG) with 35 kV charging voltage is used for driving this peaking capacitor. The design was carried out by an analytical approach and confirmed by simulation for the MG with and without peaking capacitors using PSpice software. The simulated results were compared to study the enhancement of voltage pulse using a peaking capacitor. The system was developed and tested experimentally with and without a peaking capacitor with different load impedances. The experimental results show the merits of peaking capacitor implementation. The system is suitable for driving HPM load at a high repetition rate with less input energy than similar systems.

Analysis of Trapping Effect on Large-Signal Characteristics of GaN HEMTs Using X-Parameters and UV Illumination.

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave (X21FB) and small-signal forward gain (X2111S) at fundamental frequency increased, whereas the large-signal second harmonic output wave (X22FB) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X21FB and X2111S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors.

Design of low profile wideband high power waveguide to substrate integrated waveguide coupler

AbstractThis paper presents a new wideband waveguide substrate integrated waveguide (SIW) coupler with maximum deviation of ±0.5 dB in a 7.5–12.25 GHz bandwidth (48% fractional bandwidth). Proposed coupler consists of the standard WR90 waveguide and single layer/double clad SIW printed circuit board (PCB) which is placed crosswise on the waveguide. Proposed three port coupler (isolated port was ended with match load) has a two coupling level (average of coupling in 8–12 GHz frequency range) of 43.2 and 58.3 dB, which is correspond with the hole diameter of 3.5 and 3 mm, respectively. The main contribution of this work is based on the hybrid techniques of SIW and RWG for coupler design in the high power microwave application. Validation of the simulation results with measurement one proves that the proposed X‐band waveguide to SIW coupler is a good candidate for use in high power industrial/commercial applications.

Coaxial Beam Rotating HPM Mode Converter Using Dielectrics Plates

The incorporation of the dielectric plates to produce phase delay for propagating waves is a widely employed technique in phase shifters and mode converters. In this article, a compact dielectric plate loaded coaxial beam rotating (CBR) mode converter having high gain and co-polarized (CP) pattern has been proposed for high-power microwave (HPM) applications at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band. Here, the input transverse magnetic (TM), i.e., TM01 mode, is converted to CP transverse electric (TE), i.e., TE11 likeness mode. The proposed design consists of a circular waveguide (WG) loaded with 12 dielectric polytetrafluoroethylene (PTFE) plates in a radial-azimuthal direction. For 5-mm plate thickness, the proposed design yielded a reflection loss of −20.01 dB with a radiation efficiency of 98.34% and a 17.9 dB gain at 10.084 GHz. Also, the power handling capacity of the proposed structure is predicted as 3.20 GW. Furthermore, the mode conversion is verified by measuring the far-field radiation pattern. Besides, the simulation studies of the thermal behavior of the proposed design are also discussed with the aid of CST Studio Suite.

Design and Experiments of a Beam-Steerable Wideband Reflectarray Antenna for High-Power Microwave Applications

A beam-steerable wideband reflectarray antenna (WRA) is presented in this communication. The WRA element operated at 3.3–5.5 GHz (relative bandwidth 50%) exhibits a continuous 360° phase coverage, and its power handling capacity (PHC) is estimated to exceed 4.5 GW/m2 in simulation, indicating its potential in high-power microwave (HPM) applications. Moreover, to verify the wideband performance of the WRA, a prototype was successfully designed, simulated, fabricated, and measured in the S- and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$ </tex-math></inline-formula> -bands. The WRA prototype is composed of an ultrawideband helical feed antenna, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25\times25$ </tex-math></inline-formula> antenna elements, and a dielectric plate as a radome. The results show that in the frequency band of 3.3–5.5 GHz, the WRA can achieve an arbitrary direction of reflection beam within ±60° (120° conical region). Additionally, at the center frequency of 4.4 GHz, its sidelobe level is consistently below −15 dB, while the maximum gain loss is 3.3 dB during beam steering, and the maximum aperture efficiency reaches 67.89% in the direction of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta _{0}=0$ </tex-math></inline-formula> ° and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi _{0}=0$ </tex-math></inline-formula> °.

Design, Analysis and Fabrication of an Inside-Grooved Slotted Waveguide Array Antenna for HPM Applications

In this paper, a slotted waveguide array antenna (SWAA) is designed for S-band high-power microwave (HPM) applications. The single element of the array consists of ten Gaussian distributed slots on the broad wall of the waveguide, integrated with inside grooves. The 4-element SWAA configuration is designed to achieve a relatively high gain (24.6 dB) along with highly isolated (−24 dB) radiating elements. The gain enhancement and mutual coupling (MC) reduction is achieved by optimizing inside-grooved regions. An efficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> power divider (PD) of identical phase and magnitude (−6 dB) at its output ports, is designed to feed the array elements. The radiation performance of SWAA is further improved by developing a dielectric radome. The proposed design is compact having dimensions <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.46\lambda _{0}\times 4.3\lambda _{0}\times 1.47\lambda _{0}$ </tex-math></inline-formula> , and offers return loss (RL) better than −25 dB with side lobe level (SLL) of −15 dB and −20 dB in E and H-plane, respectively. The designed array has 95.78% antenna efficiency over 3.8% measured bandwidth with 63% aperture efficiency. It has been demonstrated that the developed system, because of effective suppression of unwanted surface current, provides ±22° beam scanning without causing a significant reduction in its gain. The technique, without adding any complexity in the system, offered a 7% improvement in the gain when compared with a similar design.

Coaxial Low-Pass Filter Design and Manufacture

In this study, a low-pass filter with coaxial transmission lines is designed and produced. The objective for designing a coaxial low-pass filter was to utilize both low loss transmission and high breakdown voltage capability for high power microwave applications to enable the suppression of the second harmonic of the 4.4-6 GHz C-Band ( C-Band was selected as a proof of concept ) signals with minimal insertion loss. Microwave and 3D electromagnetic simulators were used in the filter design. The design was started by establishing an 11 th order Chebyshev low-pass filter prototype giving 0.05 dB ripple. Based on this prototype, a filter circuit consisting of capacitors and inductors as lumped elements was designed. The low and high impedances to be selected for the stepped impedance method, which is the basis of the transition to coaxial transmission lines, were decided and the most suitable impedances for manufacturing was determined. The filter using these impedances and designed with stepped impedance lines was transformed into the filter in which coaxial transmission lines are used. Coaxial transmission lines in the low-pass filter circuit consist of conductors with an insulating material in between. While the insulating material is selected as air in the high impedance sections of the transmission lines, it is PTFE (Polytetrafluoroethylene) with an insulating constant of 2.1 in the low impedance sections. The designed filter was manufactured. The basic properties of the manufactured filter were characterized by using RF measuring devices and compared with the designed filter. The measurements results prove that the frequency responses of the designed filter and the produced filter are very close to each other. Namely, a low-pass filter with a cutoff frequency of 6 GHz, a sharp suppression of about 45 dB at the stopband of 9 GHz and a return loss of 20 dB was designed and produced by using coaxial transmission lines. The novelty in our work can be stated that the power handling capability is increased by two techniques. The first one is that the highest transmission line radius preventing the higher order mode excitations is used to decrease the conductor loss. Teflon is covered around the low impedance lines to enhance the dielectric breakdown capability. Teflon inclusion is also used to decrease the practical low impedance level that improves the filter characteristics.

X-Band Active Phased Array Antenna Using Dual-Port Waveguide for High-Power Microwave Applications

An X-band active phased array horn antenna with high power capacity and high peak power is proposed in this paper. At the horn aperture, the baffles are loaded to suppress higher-order modes and eliminate blind spots during beam scanning. Straight walls are added to improve impedance matching. Considering that the peak power that T/R modules can provide is very limited, the proposal of a dual-port waveguide breaks through the bottleneck of the power capacity of a single-port input for the first time. The proposed curved dual-port waveguide is used to connect the horn antenna and the T/R module, which is verified to improve the power capacity of the overall internal structure. Simulated and measured results show that VSWR ≤ 2 in the frequency range of 7.5–8.5 GHz. There is no grating lobe in the ±10° scanning range and the maximum gain drop does not exceed 0.4 dB. The power capacity of the proposed HPM array is 56.34 MW. The phased array antenna has the characteristics of flexible scanning, small size, and high gain, and can be applied in high-power microwave systems.

Tunability Behavior of (Ba, Ca)(Zr, Ti)O Ceramic Capacitors Powered by Thermally Induced Phase Transitions With Applications to Nonlinear Transmission Lines

Ferroelectric ceramics with low loss dielectric, high permittivity, and nonlinear behavior are essential in capacitive nonlinear transmission lines (NLTLs) for radio frequency (RF) generation. NLTLs have the potential to generate soliton waves for high-power microwave (HPM) applications in mobile defense platforms and satellite communications. In this work, we synthesize, characterize, and investigate the nonlinear behavior of (Ba,Ca)(Zr,Ti)O3 ceramics system to be applied as nonlinear elements in capacitive NLTLs. The ceramics were structurally and microstructural characterized. Anomalies in dielectric and pyroelectric curves access the temperatures of phase transitions. The permittivity tunability was studied as a function of electric field and frequency in temperatures near phase transitions. The phase transitions of materials are identified by temperature where the permittivity and percentage of nonlinear tunability factor (NTF) are higher, which are required to produce RF on NLTLs.

Short-Length, High-Efficiency S-Band Coaxial Cavity Relativistic Multibeam Klystron Amplifier for Potential High Power Microwave Application

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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$= {14} \times {230}$ </tex-math></inline-formula> 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.