Wenhua Huang

Single and repetitive short-pulse high-power microwave window breakdown

The mechanisms of high-power microwave breakdown for single and repetitive short pulses are analyzed. By calculation, multipactor saturation with electron density much higher than the critical plasma density is found not to result in microwave cutoff. It is local high pressure about Torr class that rapid plasma avalanche and final breakdown are realized in a 10–20 ns short pulse. It is found by calculation that the power deposited by saturated multipactor and the rf loss of protrusions are sufficient to induce vaporizing surface material and enhancing the ambient pressure in a single short pulse. For repetitive pulses, the accumulation of heat and plasma may respectively carbonize the surface material and lower the repetitive breakdown threshold.

Combining gigawatt level X-band high power microwave beams with an overmoded circular waveguide diplexer

The high power microwave (HPM) beam combining results at X-band with an overmoded waveguide diplexer are presented. As the key device for the beam combining experiments, the diplexer is designed, fabricated, and tested. Then the beam combining experiments under short and long pulses are performed at HPM source, respectively. The experiment results reveal that short and long pulse HPM beams have been successfully operated without microwave breakdown at 3-GW with pulse duration of 25 ns and 1.3-GW with pulse duration of 96 ns. According to the experiments, conservative breakdown thresholds for the diplexer are concluded to be 800 kV/cm and 550 kV/cm, respectively, under the short and long pulse HPM conditions.

Dual-cavity mode converter for a fundamental mode output in an over-moded relativistic backward-wave oscillator

A dual-cavity TM02–TM01 mode converter is designed for a dual-mode operation over-moded relativistic backward-wave oscillator. With the converter, the fundamental mode output is achieved. Particle-in-cell simulation shows that the efficiency of beam-wave conversion was over 46% and a pureTM01 mode output was obtained. Effects of end reflection provided by the mode converter were studied. Adequate TM01 mode feedback provided by the converter enhances conversion efficiency. The distance between the mode converter and extraction cavity critically affect the generation of microwaves depending on the reflection phase of TM01 mode feedback.

A Compact Four-Way Power Combiner

A compact 8-port waveguide network is proposed in this letter. It is constructed by cascading two compact coaxial magic-Ts and one coplanar coaxial waveguide magic-T in series. Based on the 8-port waveguide network, a four-way power combiner is realized with three matching ports connected to loads. Measurements show that from 7.8 to 10.3 GHz, the return loss is greater than 18 dB, the isolation is greater than 21 dB, the insertion loss is less than 0.4 dB, and the amplitude and phase imbalance are less than 0.3 dB and 3°, respectively. Its cross section areas are approximately

A compact five-port waveguide structure and its application as a three-way power divider

1.1\lambda \times 1.1\lambda

Research on the honeycomb restrain layer application to the high power microwave dielectric window

for the central frequency of 9 GHz. The measurements agree well with the simulations.

A novel high power X-band ferrite phase shifter

A compact five-port waveguide structure consisting of three rectangular ports, one coaxial port, and one circular waveguide port is proposed. The three rectangular waveguides are uniformly distributed in space at angles of 120°, and the coaxial and circular waveguides are located at the top and bottom, respectively, of the rectangular waveguides. The ideal scattering matrix is derived from the symmetry properties of the structure. If the circular and coaxial ports are matched, then the entire five-port waveguide structure is automatically matched. Two connected inserted coaxial probes, a frustum, and a coaxial transition are used to match the five-port waveguide structure with a relatively wide bandwidth. The theoretical and experimental results are generally consistent with each other. With the circular port connected to the load, the five-port waveguide structure becomes a reciprocal TEM mode-to-three-way TE10 mode power divider. Measurements indicate that from 8 to 9.6 GHz, the return losses at the three rectangular ports and the coaxial port are greater than 20 dB and 17 dB, respectively. The isolation among the three rectangular ports is higher than 20 dB. The amplitude and phase imbalances in the division of power are less than 0.1 dB and 2°, respectively. The volume of the five-port waveguide structure is as small as 1.5 λ × 1.5λ × λ.

A compact two-way power divider based on five-port structure

Dielectric window breakdown is an important problem of high power microwave radiation. A honeycomb layer can suppress the multipactor in two directions to restrain dielectric window breakdown. This paper studies the effect of the honeycomb restrain layer on improving the dielectric window power capability. It also studies the multipactor suppression mechanism by using the electromagnetic particle-in-cell software, gives the design method, and accomplishes the test experiment. The experimental results indicated that the honeycomb restrain layer can effectively improve the power capability twice.

A novel two-way TM01 mode combiner for high power microwave applications

A novel high power X-band ferrite phase shifter (PS) employing the structure of several waveguides connected in parallel is proposed. Each of the waveguides is a phase shift unit utilizing a dual-toroid structure. First, the phase shift unit is designed, manufactured, and tested. The results indicate that the power capacity reaches 115 kW. At this power, the maximum magnetic field strength of ferrite is 7.9 kA/m, beyond which the nonlinear effect of ferrite will occur. On this basis, the PS that consists of four units connected in parallel is designed. According to the threshold of ferrite, the power capacity of the PS can theoretically reach 430 kW. Limited by the maximum output power of the microwave source, the preliminary high-power test results demonstrate that the PS can operate properly at 270 kW. The PS exhibits an insertion loss of 0.82 dB and a maximum differential phase shift of approximately 300° at 9.3 GHz. The return loss of the PS is more than 16 dB from 9.0 to 9.5 GHz.

An X band 5-way multiplexer for high power microwave combination

A novel compact five-port waveguide power divider based on the single-ridge waveguide and three-ridge waveguide structure is proposed. It is realized by the coupling of the TE10 and TE30 modes. At the central coupling section, the single-ridge and three-ridge waveguides are used to constitute the conventional rectangular waveguide to reduce the sectional sizes. It consists of one input port, two output ports, and two isolated ports. For validation, a compact five-port power divider is designed, fabricated, and measured. The measured results show that, from 8 to 9 GHz, the return loss of the input port and output ports is higher than 18 dB, the isolation between the output ports is higher than 15 dB, the insertion loss is less than 0.3 dB, and the amplitude and the phase imbalance between the output ports are less than ±0.05 dB and ±1°, respectively. The simulated results basically agree with the simulations. Its sectional sizes are 1.1 λ × 0.4 λ which are more compact than most of the two-way isolated waveguide power dividers.