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Teori Medan Elektromagnet (5 - 7) pandu_gelombang
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Teori Medan Elektromagnet (5 - 7) pandu_gelombang

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Teori Medan Elektromagnet (5 - 7) pandu_gelombang Teori Medan Elektromagnet (5 - 7) pandu_gelombang Presentation Transcript

  • Pertemuan 5 - 7 PANDU GELOMBANG Umiatin, M.Si Jurusan Fisika Fakultas Matematika dan Ilmu Pengetahuan Alam
    • Pandu gelombang :
    • modus TE, TM, dan TEM pada pandu gelombang berbentuk persegi
    • modus TE, TM, dan TEM pada pandu gelombang berbentuk silinder
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • CAHAYA, light
    • Aliran partikel yang dalam pemancarannya memenuhi hukum optik  reflection & refraction, snell law .
    • Radiasi gelombang elektromagnetik (fresnel, maxwell) dengan diffraction, interference dan pengubahan polarisasi selain mengalami reflection & refraction.
    • Pendekatan “ray” yang juga dapat mengalami diffraction, interference dan pengubahan polarisasi selain mengalami reflection & refraction.
    • Arah rambat cahaya dari sumbernya dapat diasumsikan gelombang spheric ataupun plane
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Rambatan Cahaya Gelombang merambat secara spheric If didekat sumber Gelombang merambat secara planar If relatif jauh dari sumber 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Matematika Gelombang
    • Cahaya dapat dianggap gelombang yang mempunyai polarisasi linear ataupun elliptik. Polarisasi tergantung pada kondisi vektor medan E dan H.
    • Sebagaimana gelombang EM, cahaya mempunyai konstanta propagasi, dengan notasi k.
    • Agar merambat, medan E dan H membentuk vektor yang orthogonal agar terjadi transverse wave.
    • Mode perambatan cahaya di serat optik, secara umum mengikuti hukum perambatan gelombang EM yang diturunkan oleh MAXWELL.
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Rambatan GEM Polarisasi bisa linear ataupun elliptical / circular tergantung nilai medan E dan H. 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Polarisasi
    • Dengan asumsi bahwa cahaya merupakan gelombang EM, maka ada phenomena “POLARISASI”
    • LINEAR (Vertical - Horizontal)
    • ELLIPTICAL (circular, RHCP, LHCP)
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Mode
    • Pattern atau bentuk pola rambatan sinyal EM atau cahaya terhadap penampang lintang saluran transmisi.
    • Contoh :
    • Mode TE dan TM terjadi pada saluran transmisi dan WG
    • Mode TEM hanya terjadi di udara
    • Dalam fiber hitungan TE, merupakan pendekatan termudah
    • Monomode dan multimode merupakan istilah yang mengacu pada jumlah gelombang yang merambat dalam setiap “kanal”.
    • Laser Multimode adalah laser yang dapat mengirim banyak “lambda” dalam waktu yang sama.
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Penampang WG 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Modes
    • Waves can propagate in various ways
    • Time taken to move down the guide varies with the mode
    • Each mode has a cutoff frequency below which it won’t propagate
    • Mode with lowest cutoff frequency is dominant mode
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Propagasi Multimode 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Mode Designations
    • TE: transverse electric
      • Electric field is at right angles to direction of travel
    • TM: transverse magnetic
      • Magnetic field is at right angles to direction of travel
    • TEM: transverse electromagnetic
      • Waves in free space are TEM
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Rectangular Waveguides
    • Dominant mode is TE 10
      • 1 half cycle along long dimension (a)
      • No half cycles along short dimension (b)
      • Cutoff for a =  c/2
    • Modes with next higher cutoff frequency are TE 01 and TE 20
      • Both have cutoff frequency twice that for TE 10
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Mode TE transverse electric (TE) mode: A mode whose electric field vector is normal to the direction of propagation . Note: TE modes may be useful modes in waveguides. In an optical fiber , TE and TM modes correspond to meridional rays . meridional ray: In fiber optics , a ray that passes through the optical axis of an optical fiber (in contrast with a skew ray , which does not). 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Cutoff Frequency
    • cutoff mode: The highest order mode that will propagate in a given waveguide at a given frequency .
    • For TE 10 mode in rectangular waveguide with a = 2 b
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Cutt0ff wavelength cutoff wavelength: 1. The wavelength corresponding to the cutoff frequency . ( 188 ) 2. In an uncabled single-mode optical fiber , the wavelength greater than which a particular waveguide mode ceases to be a bound mode . ( 188 ) Note 1: The cutoff wavelength is usually taken to be the wavelength at which the normalized frequency is equal to 2.405. Note 2 : The cabled cutoff wavelength is usually considered to be a more functional parameter because it takes into consideration the effects of cabling the fiber. 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Usable Frequency Range
    • Single mode propagation is highly desirable to reduce dispersion
    • This occurs between cutoff frequency for TE 10 mode and twice that frequency
    • It’s not good to use guide at the extremes of this range
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Mode TM transverse magnetic (TM) mode: A mode whose magnetic field vector is normal to the direction of propagation . Note: TM modes may be useful in waveguides. In an optical fiber , TE and TM modes correspond to meridional rays . 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Mode TEM transverse electric and magnetic (TEM) mode: A mode whose electric and magnetic field vectors are both normal to the direction of propagation . Note: The TEM mode is the most useful mode in a coaxial cable or Radio propagation. 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • Example Waveguide
    • RG-52/U
    • Internal dimensions 22.9 by 10.2 mm
    • Cutoff at 6.56 GHz
    • Use from 8.2-12.5 GHz
    02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |
  • TERIMA KASIH 02/02/11 © 2010 Universitas Negeri Jakarta | www.unj.ac.id |