Abstract:In this article, a compact branch-line hybrid coupler (BLC) which can suppress upper order harmonics of the conventional BLC is proposed. By adding a radial stub in the center of each branch, a compact BLC which can suppress the upper order harmonics are achieved. The proposed BLC is designed and simulated at 0.93 GHz. The proposed structure is 27% of the conventional BLC, while maintaining the characteristics of the conventional BLC at the center frequency. There are two transmission zeroes at 3.6 and 5.6 GHz. The third upto seventh harmonic are suppressed at least 20 dB. Keywords: branch-line hybrid coupler, compact size, harmonic suppression, microstrip transmission line, radial stub Classification: Microwave and millimeter wave devices, circuits, and systems
References[1] S. Jung, R. Negra, and F. M. Ghannouchi, "A design methodology for miniaturized 3-db branch-line hybrid couplers using distributed capacitors printed in the inner area," IEEE Trans.
An important part of radar processor is CFAR detector. In this paper, we propose a new cell-averaging constant false alarm rate (CA-CFAR) detector that uses local minimum of cells in sub-reference windows (SRW) and then it uses the general cell averaging technique to detect the target. Subreference sliding windows have been selected among reference cells in both sides of the test cell. We have improved the results obtained from the method of minimum selected cell averaging (MSCA)-CFAR [1] in the situations in which the distance between adjacent targets in the reference window is proportional to the length of SRW. This novel CFAR detector has been analyzed under Swerling II target fluctuating model, and compared with traditional cell averaging (CA) and minimum selected cell averaging (MSCA)-CFAR detectors. The simulation results indicate that, when the distance between adjacent targets in range cells equals to the length of the sub-reference windows, the local minimum selected cell averaging (LMSCA)-CFAR detector will provide more robust detection performance than CA-and MSCA-CFAR in homogeneous background with strong interfering targets.
An up to 25% power conversion efficiency and performance improvement of perovskite solar cells (PSCs) have made them promising products in photovoltaic technology. This study numerically investigates the light trapping and broadband light absorption enhancement of a PSC by introducing bismuth selenide (Bi2Se3) as shell material for Cu nanospheres (NSs) to achieve a “core/shell” configuration (Cu/Bi2Se3NSs) in the absorber layer of the PSC. The optimal values of Cu NS radius, Bi2Se3 thickness, periodicity of NSs, and the thickness of the absorber layer of PSC are equal to 40, 35, 172.5, and 410 nm, respectively. This structure has a photocurrent density (JL) of 33.01 mA cm−2 and a maximum normalized absorbed power () of 0.89 compared to the bare PSC with = 21.8 mA cm−2 and = 0.87. The results indicate that the increase in the Bi2Se3 thickness up to 35 nm at a fixed Cu NS radius of 40 nm can enhance the absorption in the whole spectrum. However, this enhancement is greater at longer wavelengths. The extinction cross‐section is improved by about 3.5 times in comparison with the bare Cu NSs. The results for the PSC with Cu/Bi2Se3 NSs show a 51.3% absorption enhancement compared to the PSC without NSs.
The improvement of light trapping inside the active layer of perovskite solar cells (PSCs) was numerically investigated. The light absorption probability was improved by incorporating periodic arrays of mesoscopic electron‐transporting layer into the absorber layer (CH3NH3PbI3) of the PSCs. Accordingly, chalcopyrite (CuInSe2) and bismuth selenide (Bi2Se3) were introduced in the form of hexagonal pillars with an optimum radius of 35 nm and a height of 292 nm. It was found that the proposed PSCs can significantly extend the broadband light absorption from the visible spectrum to the near‐infrared (NIR) region compared to planar PSCs that have an identical active layer thickness. After optimization, the PSCs based on MP‐CuInSe2 and MP‐Bi2Se3 showed the best performance with an enhancement of respectively 32% and 54 % in the photocurrent density, (with values of 29.94 and 34.93 mA.cm−2), as compared to the planar PSC (with a photocurrent density of 22.69 mA.cm−2). This enhancement resulted from a more effective carrier transport due to the mesoscopic structures.
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