National University of Defense Technology

About: National University of Defense Technology is a education organization based out in Changsha, China. It is known for research contribution in the topics: Radar & Synthetic aperture radar. The organization has 39430 authors who have published 40181 publications receiving 358979 citations. The organization is also known as: Guófáng Kēxuéjìshù Dàxué & NUDT.

Scanning Rate Enhancement of Leaky-Wave Antennas Using Slow-Wave Substrate Integrated Waveguide Structure

Abstract: In this communication, we propose a high scanning rate leaky-wave antenna (LWA) based on a slow-wave substrate integrated waveguide (SIW) structure. The slow-wave effect is introduced by etching periodical slots on the top surface of SIW. The LWA radiation is subsequently realized by introducing sinusoidal modulation to the slots profile. Such a structure significantly improves the scanning rate of LWA due to the small group velocity at the slow-wave region. Simulation and measured results indicate that the proposed LWA scans a wide angle in a narrow bandwidth near the cutoff frequency of surface plasmon polariton. Within the frequency band 13.5–13.9 GHz (3% relative bandwidth), the measured scanning angle is from 2° to 37° with the measured gain all above 9.2 dBi.

Effects of pyrolysis processes on the microstructures and mechanical properties of Cf/SiC composites using polycarbosilane

Abstract: Three-dimensional braided carbon fiber reinforced silicon carbide composites (3D-B Cf/SiC) were prepared through eight cycles of vacuum infiltration of polycarbosilane (PCS) and subsequent pyrolysis under an inert atmosphere. The influences of heating rate and pyrolysis temperature on the microstructure and mechanical properties of Cf/SiC were discussed. It was found that the heating rate had great effect on the mechanical properties of Cf/SiC composites. With the increase of heating rate, the density of Cf/SiC composites increased and the interfacial bonding was weakened. As a result, the flexural strength of Cf/SiC was enhanced from 145 to 480 MPa when the heating rate was increased from 0.5 to 15 °C/min. The results showed that the flexural strength of the Cf/SiC composites fabricated at a heating rate of 15 °C/min could be increased from 480 to 557 MPa if the pyrolysis temperature of the sixth cycle was elevated from 1200 to 1600 °C, which was also attributed to the desirable interfacial structure and increased density. When tested at 1300 °C in vacuum, the Cf/SiC showed higher flexural strength (680 MPa) than that (557 MPa) at room temperature.

Application of metamaterials to ultra-thin radar-absorbing material design

Abstract: A novel ultra-thin radar-absorbing material (RAM) using metamaterials is presented, and the absorption performance is examined. Owing to the high-impedance property of the metamaterials, the thickness of the RAM is about several tenths of the centre wavelength of the absorption band, considerably thinner than conventional absorbers. The absorption bandwidth of the RAM is about several hundred megahertz.