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ECE 590 Microwave Transmission for Telecommunications

ECE 590 Microwave Transmission for Telecommunications. Introduction to Antennas April 1. Generic Radar System. Display. Timing & Control. Digital signal Processor. A/D. Low-Pass. Recv’r Power Ampl. modulator. Duplexer. Trans. Ampl. Mode Conv. Ant. Source. Cavity. Servo

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ECE 590 Microwave Transmission for Telecommunications

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  1. ECE 590 Microwave Transmission for Telecommunications Introduction to Antennas April 1

  2. Generic Radar System Display Timing & Control Digital signal Processor A/D Low-Pass Recv’r Power Ampl. modulator Duplexer Trans. Ampl. Mode Conv. Ant. Source Cavity Servo Motor

  3. Ref: Krauss

  4. Antenna Systems • Conduction Current • Source of radiation is conduction current on metallic radiator surfaces • Center-fed dipoles, end-fed monopole loops, helix • Lower frequency, lower gain, wide-beam width • Displacement Current • Source- E&M fields at antenna aperture or slot • Horn, slot, parabolic reflector • No conduction current at radiation surface

  5. Ref: Krauss

  6. Ref: Krauss

  7. Antennas Radiation – produced by accelerated charges or time changing current radiates, perpendicular to the change in current Far-field: r >> 2D2/; where D = maximum dimension of antenna  = operating wavelength r > size of the antenna and r >  E(r,,)= (E + E )e-jkr / r H = E / 0 and H = - E / 0 where 0 = 377 , the wave or intrinsic impedance of free space.

  8. Antennas Far-field Radiation Pattern - most important, E (,) and E (,) - note independent of r - often normalized to the maximum values of E (,) and E (,) S(,) = Poynting vector = E x H* = (E2 + E2 )/ 0 Pnorm = S (,) / Smax (,) = radiation pattern which is a 3 dimensional pattern

  9. Ref: Krauss

  10. Ref: Krauss

  11. Conduction Current  H x Dipole

  12. Antennas Beam Area or Beam Solid Angle, 

  13. Example: Isotropic Antenna: radiates the same in all directions Example: Let HPBW = 20o

  14. Receiving Antennas

  15. Antenna Polarization Ref: Krauss

  16. Antenna Polarization

  17. Antenna Polarization

  18. Ref: Krauss

  19. Arrays of Point Sources Ref: Krauss

  20. Arrays of Point Sources Ref: Krauss

  21. Ref: Krauss

  22. Ref: Krauss

  23. Ref: Krauss

  24. Displacement Current Type Antennas • Source of radiation is E&M fields at antenna surface • Use Huygen’s principle: Use known field at time t as sources for fields later in time • Electromagnetic fields in space due to “sources” at the radiating surface, S, can be calculated by defining electric and magnetic surface currents on S mathematically equivalent to tangential H & E at radiating surfaces.

  25. Ref: Krauss

  26. Ref: Krauss

  27. Ref: Krauss

  28. Ref: Krauss

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