Distributed collaborative reconnaissance and positioning of radar radiation sources within a certain target area using mounted electronic reconnaissance payloads is an important application scenario for multiple unmanned aerial vehicle platforms, especially small-scale unmanned aerial vehicle platforms. This article is based on the principle of distributed multi-station collaborative reconnaissance and positioning, and analyzes the impact of factors such as baseline length between drone platforms, time difference between radiation sources and drone platforms on collaborative positioning accuracy. In addition, for the application scenario of multiple drone collaborative reconnaissance, simulation analysis is conducted to investigate the impact of increasing or decreasing the number of drones on collaborative positioning accuracy. The simulation results show that the longer the baseline distance between drone platforms, the higher the accuracy of arrival time difference measurement, and the higher the positioning accuracy of ground radar radiation sources; Research on the robustness of distributed drone collaborative positioning shows that the more drones there are, the higher the collaborative positioning accuracy. However, when the number of drones exceeds 6, the collaborative positioning accuracy tends to a certain value. On the contrary, the fewer drones there are, the lower the collaborative positioning accuracy. When the number of drones is less than 3, the three-station time difference positioning cannot be performed. The research results of this article can provide theoretical guidance for the practical application of collaborative reconnaissance and positioning of multiple unmanned aerial vehicle platforms.
A GaN surface emitting laser (SEL) based on angular-symmetry-breaking concentric-ring surface grating (ASB-CRSG) is proposed in this paper. The second-order CRSG located in the p-contact and p-cladding of an EPI wafer of GaN FP laser is adopted to select the radial mode and couple the optical power vertically out of the laser cavity. As the zero-order azimuthal CRSG with a two-lobe far field has the lowest mode loss in the angular-symmetric CRSG, the first-order ASB is adopted by the removal of two circular sections of GaN epitaxial layers to break the angular symmetry of the lasing modes. The simulation results show that degenerate modes in angular-symmetric CRSG have different mode losses with the help of the first-order ASB and the bigger breaking angles of CRSG results to higher loss difference between the first-order and other azimuthal modes. The loss and divergence angle decrease with the increasing area of CRSG, and the deeper CRSG results to the higher out-plane coupling. The first-order azimuthal mode has the lowest mode loss whose value is ~ 84% of that of the second-lowest-loss mode. A single-lobe far-field with a divergence angle of 1.33° in the wavelength of 450nm will be realized by an ASB-CRSG with the diameter of 10.6μm, the breaking angles of 12° and the depth of 325nm. Therefore, the single-mode operation of the first-order azimuthal mode which has a single-lobe far field is expected with the combination of the second-order CRSG and the first-order ASB.
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