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  • "學萃講壇”第970期—Incident Angle-Stable Spatial Filters for Wireless Communication

    “學萃講壇”秉承學名家風范、萃科技精華的理念,以學術為魂,以育人為本,追求技術創新,提升學術品位,營造濃郁學術氛圍,共品科技饕餮盛宴!
    報告題目:(1)Incident Angle-Stable Spatial Filters for Wireless Communication;
    (2)Angle of Incidence-Stable FSS with DSRS Elements;
    (3)Scattering from thin Conducting Strips with/without Impedance Loaded Edges天吉论坛手机app;
    (4)RCS Reduction of Coated Dielectric/Conducting Objects;
    (5)High Frequency Analysis of Sea Winds Reflector Antenna;
    (6)Scattering from Impedance Loaded Cylindrical Shells of Arbitrary Cross Section.
    報  告 人:Dr. Tekao WU
    報告時間:2019年06月12-15日 09:40-11:30,17日13:30-15:30,18-19日09:40-11:30
    報告地點:21B教學樓3樓306教室
    主辦單位:科學技術研究院
    承辦單位:信息與通信工程學院
    報告人簡介:He received B.S.E.E. from National Taiwan University in 1970, M.S. and Ph.D. degree in Electrical Engineering from University of Mississippi in 1973 and 1976, respectively. He has 46 years professional experience as the Research & Development (R&D) Engineer of Electromagnetics, FSS, and Antennas, in Northrop Grumman, JPL, and Hughes Aircraft companies. Back then he worked on various government or internal research and development (IR&D) sponsored satellite communication, user terminal, and radar antenna systems. He is currently consulting in the field of FSS and metamaterials for low volume, low mass, and low cost applications in wireless communication. He has published more than 200 technical papers, 27 U.S. patents, 1 book, and 2 book chapters. He was awarded fourteen NASA Certificates of Recognition for technical innovation research works in antennas.
    報告內容:
    1. Incident Angle-Stable Spatial Filters for Wireless Communication
     Resonant frequency stability has been an issue for both band-stop and band-pass spatial filters to perform over varying incident angles and polarizations. In this presentation, the resonant frequency stability in a band-stop filter over varying incident angles and polarizations is designed, fabricated, and tested/ demonstrated by the miniature fractal-patch-element FSS. The design and analyses of the patch FSS filters are based on the accurate integral equation formulation (IEF) combined with the method of moments (MOM). This analytical approach is also known as the full wave analysis technique. To facilitate the fractal FSS measurement, a 24”x18” proof-of-concept test sample was fabricated on a Duroid 5880 PCB board. This sample was also tested in a precision Free-Space Transmission Measurement test setup [8-9] with thin Gaussian beam lenses. Since the FSS sample is illuminated by the small spot beam of the test setup, the edge diffraction effect is reduced significantly. Therefore, large-incident-angle (i.e. 45°- 60°) tests can be readily conducted with this approach. The measured results show much improved resonant frequency stability near 10 GHz for incident angle varying from normal to 60° incidence.
    2. Angle of Incidence-Stable FSS with DSRS Elements
    In the past, a single screen cross-dipole FSS] was shown to have a 7:1 stop-to-pass-band-ratio or band-separation-ratio. The reason why such a large band-separation-ratio is the cross-dipole being an inferior element. Furthermore, in modern communication, radar, or EMC/EMI applications, better FSS element, such as the square-loop or fractal element is often required to have a dual band spatial filter exhibiting closely separated pass and stop bands. To reduce this band-separation-ratio, a thin screen FSS with the double square ring slot (DSRS) element is proposed and demonstrated . The design and analyses of this DSRS FSS filters are based on the accurate integral equation formulation (IEF) combined with the method of moments (MOM). This analytical approach is also known as the full wave analysis technique. The calculated band-separation-ratio is 1.15. Most important, the predicted FSS transmission performance shows excellent stability with the incident angle from normal to 45° and for both TE and TM polarizations. One may further reduce the band-separation-ratio by cascading two or three DSRS screens together.
    3. Scattering from thin Conducting Strips with/without Impedance Loaded Edges
    An integral equation formulation is developed for the scattering from a thin conducting strip with/ without impedance loaded edges. The unknown surface currents on the strip are next solved using the method of moments. Once the surface current is determined, the far-zone scattered fields and radar scattering section are readily calculated. Numerical results will be presented with and without edge impedances. Namely, the radar cross section (RCS) reduction with impedance loaded strips is demonstrated.
    4. RCS Reduction of Coated Dielectric/Conducting Objects
    The cloaking (or electromagnetic invisibility) of a dielectric or conducting cylinder or sphere was first investigated via the transformation-optics method. It requires complex metamaterials with sub-wavelength structured inclusion to realize high unisotropy/inhomogeneity of the material parameters. To substitute the unisotropy materials, a concentric multi-layered structure of alternating homogeneous isotropic materials was introduced. However, it still requires materials with very low (close to zero) or high permittivity, which are only available at infrared and visible light frequencies. Recently, a single or five-layered (with linear profile) isotropic lossless dielectric/magnetic cladding was shown to partially cloak an electrically small sized conducting cylinder. Further, electromagnetic scattering is purposely suppressed by a thin layer of FSS (or patterned metasurface) conformal to a planar (or cylindrical, or spherical) object . In this presentation, electromagnetic scattering (or RCS) reduction of a dielectric or conduction cylinder is more closely examined with a thin coating of metamaterial or plasmon with high permittivity or εr close to zero.
    5. High Frequency Analysis of SeaWinds Reflector Antenna
    Antennas are often mounted among many other instruments on the spacecraft (S/C) platform. The electromagnetic interference (EMI) and compatibility (EMC) issues are of great concern to the antenna and S/C system design engineers. Considering the rotating reflector antenna of the NASA SeaWinds Scatterometer on the Japanese ADEOS II S/C, it is desirable to determine the antenna's field of view (FOV) performance. In other words, how far should the other instrument boxes be kept away from this reflector antenna to minimize the blockage/diffraction effects on the antenna's performance requirements. Since the antenna is rotating around an axis parallel to the z-axis, the problem may now be interpreted as determining a limiting FOV cone angle such that no boxes should be placed inside. In this presentation, the efficient high-frequency technique of shooting and bouncing rays is implemented to determine this antenna’s FOV cone angle. Extensive numerical results obtained with this approach indicated that the boxes should be kept 5° outside the rotating antenna’s projected aperture in order to meet the gain and beam-width stability requirements.
    6. Scattering from Impedance Loaded Cylindrical Shells of Arbitrary Cross Section
    In the previous presentation, the scattering from a multi-layered circular cylinder was analyzed via the separation of variable (or mode expansion) method. The scattering from general, two dimensional, finitely conducting (or impedance loaded) shells with vanishingly thin walls are analyzed and examined in this presentation by the integral-equation method. For the circular cylinder case, a field plot throughout the shield interior reveals that, at the 'no shielding' frequencies found by Schieber, fields are attenuated greatly, except near the center. The influence of slots in the shell walls is also assessed for both circular and rectangular cylinders. Due to focusing effects, the field at the shield center is even stronger than the incident field at certain resonant frequencies for the slotted cylindrical shells.

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