ECE 590 Microwave Transmission for Telecommunications

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

11. Ref: Krauss

12. Conduction Current  H x Dipole

14. Antennas Beam Area or Beam Solid Angle, 

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

17. Receiving Antennas

18. Antenna Polarization Ref: Krauss

19. Antenna Polarization

20. Antenna Polarization

21. Ref: Krauss

27. Arrays of Point Sources Ref: Krauss

28. Arrays of Point Sources Ref: Krauss

29. Ref: Krauss

30. Ref: Krauss

31. Ref: Krauss

32. 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.

41. Ref: Krauss

42. Ref: Krauss

49. Ref: Krauss

50. Ref: Krauss