All-metal beam steering antenna based on the concept of Risley prism is presented in this communication. The antenna is composed of a feed antenna and two metal lenses. Mechanically rotate two lenses along the same axis independently can steer the radiation beam in both azimuth and elevation planes. Simulations and measurements were carried out in X-band to verify its performance, and the results agree each other well, which are also in agreement with the theoretical results. Furthermore, the power handling capability of the lens antenna with a dimension of $1~\text {m} \,\, \times \,\, 1 \,\, \text {m}$ is estimated about 4 GW, which indicates the all-metal beam steering antenna has the application potentials for high-power microwave applications.

All-Metal Beam Steering Lens Antenna for High Power Microwave Applications

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.

Progress in narrowband high-power microwave sources

https://aip.scitation.org/doi/pdf/10.1016/j.mre.2016.04.001

Research progresses on Cherenkov and transit-time high-power microwave sources at NUDT

This paper describes a new design of a relativistic Cherenkov oscillator with strong modulation of the e-beam current at the input of two-sectioned slow-wave structure, as well as numerical and experimental results on generation of few gigawatt-level $X$ -band pulses with pulse duration of up to 35 ns. Due to special phase shift between two sections and electrodynamic coupling between $E_{01}$ surface wave and $E_{02}$ volume mode, the first one is locked at the upper boundary of the passband and the second one gains more transparency. An electron beam can interact simultaneously with two waves with higher power conversion efficiencies, which in simulations amount up to 47% and 30% for high (~4 T) and low (~1 T) guiding magnetic fields, correspondingly. The tests of the geometry optimized in simulations were performed on the base of SINUS-7 high-current electron accelerator in the diode voltage range of 400–850 kV and current from 7 to 16 kA. The repeated and full-pulsewidth generation of about 1.5-GW microwave power is achieved only in the low magnetic field. The pulse shortening and the mode competition took place in the strong magnetic field. The results are considered as preliminary for creation of the efficient relativistic millimeter-wave oscillators at magnetic fields below the cyclotron resonance.

Two-Wave Cherenkov Oscillator With Moderately Oversized Slow-Wave Structure

A klystron-like relativistic backward wave oscillator with a ratio of transverse dimension to free-space wavelength being about four is presented. In the beam-wave interaction region, the electron beam interacts with surface wave and volume wave simultaneously. The cathode holder plays an important role in the reflection of backward waves. A guard electrode, an electron collector ring, and a reflection ring are used to optimize the beam-wave interaction. The particle in cell simulation results reveal that microwaves with a power of 2 GW and a frequency of 12.3 GHz are generated with an efficiency of 42% when the diode voltage is 400 kV, the beam current 12 kA, and the magnetic field 0.48 T.

A high-efficiency overmoded klystron-like relativistic backward wave oscillator with low guiding magnetic field

A klystronlike relativistic backward wave oscillator (RBWO) with a dual-cavity extractor is presented. The phase of the axial electric field component E z varies by 0° in the dual-cavity extractor, and a larger electric field appears in the second extraction cavity, in comparison with a single-cavity extractor. Such an improved field distribution is beneficial for converting modulated beam power into microwave power. The particle in cell simulation results reveal that microwaves with power of 10 GW, frequency of 4.3 GHz are generated, and conversion efficiency is 48% when diode voltage is 1.2 MV and beam current 17.3 kA.

A high-power high-efficiency klystronlike relativistic backward wave oscillator with a dual-cavity extractor

A dual-mode operation mechanism in an overmoded relativistic backward wave oscillator is presented. The electron beam interacts with the −1st space harmonic of TM01 mode synchronously in the slow wave structure. Then the backward propagating TM01 mode is converted to the forward propagating TM02 mode. As the phase velocity of the volume harmonic of TM02 mode is about twice that of the surface harmonic of TM01 mode, the TM02 mode also plays an important role in the high-power microwave generation. Particle-in-cell simulation shows that an efficiency of 48% and a significant improvement of the power capacity have been obtained.

An overmoded relativistic backward wave oscillator with efficient dual-mode operation

To realize power combination of two phase-locked relativistic backward wave oscillators (RBWOs), a compact power combiner is designed and investigated by 3-D particle-in-cell (PIC) simulation and experiment. The power combiner consists of two TM01-TE11 serpentine mode converters with a common output. When the two incident ports are fed with TM01 modes with a relative phase of 180° and power of 2.5 GW at each port, the conversion efficiency from the incident TM01 modes to the combined TE11 mode is 95.2% at 9.3 GHz, and the maximum electric field in the combiner is 714 kV/cm. The PIC simulation shows that the output power from the common port is 4.2 GW when the power combiner is connected to the two RBWOs with input signals, both producing 2.2 GW microwave, corresponding to a combination efficiency of 95.4%. In the high power microwave test, a method is proposed to obtain the combination efficiency without breaking the vacuum, which is 94.1% when the two phase-locked RBWOs output 1.8 GW and 2.2 GW. The power capacity of multi-gigawatts has been demonstrated.

Power combiner with high power capacity and high combination efficiency for two phase-locked relativistic backward wave oscillators

An oversized mode-selective relativistic backward wave oscillator is proposed. This device operates using the pure TM02 mode in the beam-wave interaction area and transmits a pure TM01 mode in the output waveguide. In the beam-wave interaction area, mode selection is well realized through oversized slow-wave structures with a coaxial inner conductor that provides perfect boundary conditions for the TM02 mode and simultaneously eliminates other modes. A large proportion of the TM02 mode field is eventually exported into the output waveguide in the form of a pure TM01 mode. With the large diameter and high mode purity, the device can be expected to have high power capacity. With a 770 kV, 11.0 kA beam guided by a 3.5 T magnetic field, a 3.2 GW microwave at 9.42 GHz has been obtained in our simulation. The device efficiency is 38%.

Over-Sized Mode-Selective Relativistic Backward Wave Oscillator

Experimental demonstration of improving resonant-multipactor threshold by three-dimensional wavy surface

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