Huijun Huang

Suppressing high-power microwave dielectric multipactor by the sawtooth surface

This paper theoretically and experimentally researches the effect of a periodic sawtooth surface on vacuum multipactor. Dynamic calculation and particle-in-cell simulation are applied to analyze the electron impact energy and multipactor scenario on the periodic isosceles triangular surface with different slope angles and heights. It has been discovered that, with the slope angle increasing, the impact energy significantly decreases to be lower than the first crossover energy of the secondary yield curve, leading to suppressed multipactor. S-band high power microwave dielectric breakdown experiment, with microsecond pulse length, was conducted. It is confirmed by experiment that the periodic sawtooth surface with sufficiently large slope angle (such as 45°) can effectively increase the breakdown threshold of about 2 compared to the flat surface.

DESIGN AND EXPERIMENTS OF THE GW HIGH- POWER MICROWAVE FEED HORN

Design and optimization of high-power microwave (HPM) feed horn by combining the aperture fleld with radiation patterns are presented in the paper. The optimized feed horn in C band satisfles relatively uniform aperture fleld, power capacity higher than 3GW, symmetric radiation patterns, low sidelobes, and compact length. Cold tests and HPM experiments were conducted to investigate the radiation patterns and power capacity of the horn. The theoretical radiation patterns are consistent with the cold test and HPM experimental results. The power capacity of the compact HPM horn has been demonstrated by HPM experiments to be higher than 3GW.

A Novel X-Band Diplexer Based on Overmoded Circular Waveguides for High-Power Microwaves

On the basis of mode-matching techniques and numerical optimization, a novel X-band diplexer based on overmoded waveguides for high-power microwaves is presented in this paper. Two ridged overmoded circular waveguides are proposed as bandpass filters operating at TM01 mode and through mode-matching techniques, filters are designed with central frequency of 9.7 and 9.3 GHz and ±100-MHz bandwidth, respectively. The radial waveguide structure with six rectangular ports is used as diplexing manifold. Moreover, one radial waveguide structure placed between two filters efficiently extracts the microwave after filtering. The other radial waveguide structure is placed coaxially, which is connected with the first one through six rectangular waveguides and whereafter combines and outputs the microwave after extraction. For practical integration with two high power microwave (HPM) sources, a high efficiency 90 ° circular waveguide bend operating at TM01 mode is designed. Simulation results show that the designed diplexer can handle gigawatt-class HPM with transmission efficiency up to 97% for each channel in ±100 MHz.

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.

Experimental study of dielectric window breakdown suppression technology under HPM in vacuum

In order to restrain surface breakdown of dielectric window in HPM (High Power Microwave) devices, experimental research of surface breakdown suppression technology for PTFE is performed under an S-band HPM experimental system in this paper. Different suppression technologies are employed, such as surface polishing, surface notching and surface coating technologies, etc. Experimental results show that polishing treatment on dielectric surface can increase surface breakdown threshold. The surface grooves parallel to the direction of electric field can reduce surface breakdown threshold, while the grooves perpendicular to the direction of electric field can suppress surface breakdown, and the effect is influenced by the depth and width of groove. The surface breakdown experiment of TiN coating on PTFE surface is performed, and the results are also discussed. A new machinable ceramic material is proposed, and the main electrical characteristics of which are introduced. This new material will be promising as dielectric window material of HPM devices.