This paper presents an improved approach for the synthesis of sparse planar arrays using density-weighted method and chaos sparrow search algorithm (CSSA) with multiple constraints. The approach consists of two stages and has an efficient way in dealing with multiple constraints, including the array aperture, number of elements, and minimum spacing between adjacent elements. In the first step, a density-weighted method is implemented to generate a thinned array structure by introducing the weighted coefficient based on the distribution function of a uniform full array to the elements, which can reduce the time and improve the efficiency of the optimization of sparse matrices. On the basis of a density-weighted array, tent chaotic mapping is introduced to initialize the population, then sparrow search algorithm (SSA) is used to further optimize the location of each element of the array antenna to search for the global optimal solution. As a consequence, the proposed method exhibits improved flexibility with respect to other analytical techniques, and reduces the computational cost of the optimization algorithm. Numerical validation results demonstrate the effectiveness and reliability of the proposed method, showing that it can achieve better results than existing methods in the design of sparse planar array arrangements.

This paper presents a multiple-resonance technique that sought to achieve a wide bandwidth for printed wide-slot antennas with fork-shaped stubs. By properly appending an extra fork-shaped stub onto the main fork-shaped stub, the impedance bandwidth was able to be clearly broadened. To validate this technique, two designs where the extra stubs were added at different positions of the main stub were constructed. The measured impedance bandwidths of the proposed antennas reached 148.6% (0.9–6.1 GHz) for S₁₁ < −10 dB, indicating a 17.9% wider bandwidth than that of the normal antenna (0.9–4.3 GHz). Moreover, a stable radiation pattern was observed within the operating frequency range. The proposed antennas were confirmed to be much-improved candidates for applications in various wireless communication systems.

High power vacuum electronic devices of the millimeter wave to terahertz regime are attracting extensive interest due to their potential applications in science and technologies. In this paper, a novel sheet beam (SB) folded waveguide (FWG) slow-wave structure (SWS) is applied and studied for enhanced output power of oscillators. Through the analysis of high-frequency characteristics of the SB FWG-SWS, the selection of an appropriate beam–wave interaction point on the dispersion curve and beam position is determined for an SB folded waveguide oscillator (FWO) operating near the 2π stopband point. The fundamental mode operation of the SB FWO was verified by the particle-in-cell simulation results, which also indicate that the SB FWO exhibits a better outstanding performance (84.6 W with a beam voltage and current of 25.1 kV and 200 mA, respectively) than the conventional circular beam FWO. The transmission stability of the SB was analyzed by observing the interception beam current in the FWO. The voltage and frequency tuning performance of the SB FWO were discussed in combination with clutter suppression. A preliminary experiment was conducted by fabricating a 220 GHz SB FWG-SWS and measuring the S parameter.

The X-ray fast imaging beamline at SSRF is a new beamline under construction and will provide X-ray micro-imaging on multiple time-scale from 100 ps, s and ms to study the following fast processes such as deformations and invalidations of materials under strong dynamic load and the high pressure/speed spray process of fuel in automobile engines. The beamline will have the capability of about 100 ps temporal resolution and micrometer scale spatial resolution. Including the researches of dynamic impact of materials, high speed fluid dynamics and the calibration of the streak camera could be done on this beamline. In addition, X-ray dynamic micro-CT is also available on the beamline, which is a powerful tool for the researches of the deformation mechanism in the invalidation dynamics processes of light-weight high-strength alloys and the formation mechanism of the defects in the solidification processes of these alloys. Using the dynamic micro-CT technique, the research of soft matter system including granule, foam and colloid also could be carried out to establish the links between its microscopic structure, kinematics and macroscopic appearance. A cryogenic permanent magnet undulator (CPMU) cooled by liquid nitrogen will be selected as the light source providing the X-ray photons with energy range of 8.7-30 keV, whose smallest magnet gap is 6 mm. With the periodic length of 18mm and 170 periods, the total length of the undulator is 3.06 m. The beamline will provide pink beam mode and monochromatic beam mode with a liquid nitrogen cooled double-crystal monochromator. The first crystal of DCM can be moved in or out of the beam, making the monochromatic or pink beam available. For the fast imaging, a millisecond-shutter (water cooled) and a microsecond-shutter are used to control the exposure time of imaging detectors and reduce unwanted heat of the pink beam. The experimental endstation will provide multiple X-ray imaging detectors to meet the different requirements of spatial and temporal resolution. In-situ devices include small gas gun, compression/tension Hopkinson bar, high speed spray set-up, furnace with electric/magnetic field and stretching devices. Up to now, the construction of the beamline and two-turn small beam current commissioning has been completed. The test results show the the design technical indexes have been reached. The beamline will be in test operation in 2022.