Introducing magnetism into topological insulators (TIs) can tune the topological surface states and produce exotic physical effects. Rare earth elements are considered as important dopant candidates, due to their large magnetic moments from heavily shielded 4f electrons. As the first element with just one 4f electron, cerium (Ce) offers an ideal platform for exploring the doping effect of f-electron in TIs. Here in this work, we have grown cerium-doped topological insulator Bi2Te3 thin films on an Al2O3(0001) substrate by molecular beam epitaxy (MBE). Electronic transport measurements revealed the Kondo effect, weak anti-localization (WAL) effect and suppression of surface conducting channels by Ce doping. Our research shows the fundamental doping effects of Ce in Bi2Te3 thin films, and demonstrates that such a system could be a good platform for further research.
An E-band antenna module and corresponding beam sharpening method is proposed to achieve high azimuth resolution for front-looking real aperture radar application. To achieve high angular resolution with a small antenna aperture size, a solution involving real beam and super-resolution is investigated. A monopulse antenna is developed to produce two coprime channels, which are essential for the subsequent beam sharpening in digital domain. A dual-aperture horn antenna and a monopulse comparator that make up the monopulse antenna are designed respectively, and the experimental prototypes are fabricated and tested. Experimental results show the antenna module can operate in the 75 to 80 GHz band, more than 20 dBi gain and 12 half power azimuth beamwidth can be maintained in the sum-patterns, and the null-depths are lower than -20 dB in the difference-patterns. Based on the measured sum and difference patterns, an azimuth super-resolution processing based on two-channel deconvolution is implemented. The simulation results show the sharpening ratio can achieve 12 dB with 0 dB signal-noiseratio and truncated half power beamwidth. Theoretically, the azimuth super-resolution of 0.8° can be achieved with 20 mm aperture size. The corresponding achievements are valuable in the follow-up E-band civil front-looking imaging system.INDEX TERMS E-band antenna, monopulse comparator, high angular resolution, super-resolution.
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