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Antenna PARAMETERS
Antenna PARAMETERS
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FUNDAMENTAL PARAMETERS OF ANTENNA

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FUNDAMENTAL PARAMETERS OF ANTENNA

  1. 1. PNF, radiated=Re(E x H*)=|E||H|Cos(90o) Watts=0 PNF, stored=Im(E x H*)=|E||H|Sin(90o) Watts=Max PRNF, radiated=Re(E x H*)=|E||H|Cos(0≤theta≤90o) Watts>0 PRNF, stored=Im(E x H*)=|E||H|Sin(0≤theta≤90o) Watts<Max
  2. 2. PFF, radiated=Re(E x H*)=|E||H|Cos(0o) Watts=Max PFF, stored=Im(E x H*)=|E||H|Sin(0o) Watts=0
  3. 3. Largest dimension of the antenna Patten is flat (no main lobes are formed) Main lobe begins to develop Pattern is well formed with dominant Main lobe
  4. 4. infinite distances are not realizable in practice, the most commonly used criterion for minimum distance of far-field observations is 2D2/λ.
  5. 5. One radian is defined as the plane angle with its vertex at the center of a circle of radius r that is subtended by an arc whose length is r.
  6. 6. One steradian is defined as the solid angle with its vertex at the center of a sphere of radius r that is subtended by a spherical surface area equal to that of a square with each side of length r.
  7. 7. Radiation Power Density The power radiated per unit surface area from the antenna surface (in spherical coordinates system) is called Radiation Power Density (in W/m2). Instantaneous Poynting vector
  8. 8. The poynting vector can also be expressed as: Average poynting vector or Average power density Real (calculated over one time period): Imaginary part is eliminated Radiation Power Density Peak Values (not RMS) Analogous to Ohm’s law : P=1/2 VI*
  9. 9. Instanatious Total Power = Integration of normal component of poynting vector (power density) over the entire surface Average (total) radiated power
  10. 10. (Radial component of radiated power density) Given
  11. 11. Radiation intensity (W/unit solid angle) in a given direction is defined as “the power radiated from an antenna per unit solid angle.” Obtained by multiplying radiation density (in W/m2) with square of distance r.
  12. 12. Radiation is equal in all directions, i.e. U will be independent of the angles θ and φ,
  13. 13. The beamwidth of a pattern is defined as the angular separation between two identical points on opposite side of the pattern maximum. Half-Power Beamwidth (HPBW ) is defined as: “In a plane containing the direction of the maximum of a beam, the angle between the two directions in which the radiation intensity is one-half value of the beam.” The angular separation between the first nulls of the pattern is referred to as the First-Null Beamwidth (FNBW )
  14. 14. Directivity, D •directivity of an antenna defined as “the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions. •The average radiation intensity is equal to the total power radiated by the antenna divided by 4π. •If the direction is not specified, the direction of maximum radiation intensity is implied.”
  15. 15.  directivity of a nonisotropic source is equal to the ratio of its radiation intensity in a given direction over that of an isotropic source.
  16. 16. Radiation power density of infinitesimal linear dipole of length l <<λ.
  17. 17. General Formulation of Radiation Power Density & Radiation Intensity
  18. 18. General Formulation of Directivity Let,
  19. 19. The values of directivity will be equal to or greater than zero and equal to or less than the maximum directivity (0 ≤ D ≤ D0).
  20. 20. Normalised Radiation intensity The beam solid angle ΩA is defined as the solid angle through which all the power of the antenna would flow if its radiation intensity is constant (and equal to the maximum value of U, i.e. Umax) for all angles within ΩA.
  21. 21. Instead of using the exact expression of (2-23) to compute the directivity, it is often convenient to derive simpler expressions, even if they are approximate, to compute the directivity. These can also be used for design purposes. For antennas with one narrow major lobe and very negligible minor lobes, the beam solid angle is approximately equal to the product of the half-power beamwidths in two perpendicular planes Symmetrical and
  22. 22. Approximate Methods to Calculate Directivity
  23. 23. The total antenna efficiency e0 is used to take into account losses at the input terminals and within the structure of the antenna. 1. reflections because of the mismatch between the transmission line and the antenna 2. I 2R losses (conduction and dielectric)
  24. 24. Gain •Gain of an antenna (in a given direction) is defined as “the ratio of the intensity, in a given direction, to the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically. •The radiation intensity corresponding to the isotropically radiated power is equal to the power accepted (input) by the antenna divided by 4π.” •gain of the antenna is closely related to the directivity, it is a measure that takes into account the efficiency of the antenna as well as its directional capabilities. •directivity is a measure that describes only the directional properties of the antenna, and it is therefore controlled only by the pattern.
  25. 25. Relative Gain •the ratio of the power gain in a given direction to the power gain of a reference antenna (a lossless isotropic source).” The power input must be the same for both antennas. Partial Gains
  26. 26. Ps=Pg+Pr+PL ( Conjugate Matching)
  27. 27. Receiving Mode
  28. 28. Antenna in Receiving Mode…
  29. 29. Vector Effective Length of Antenna
  30. 30. Definition: the ratio of the available power at the terminals of a receiving antenna to the power flux density of a plane wave incident on the antenna from that direction, the wave being polarization-matched to the antenna.
  31. 31. 2
  32. 32. RT (load) Rr RL Finally the capture area is defined as the equivalent area, which when multiplied by the incident power density leads to the total power captured, collected, or intercepted by the antenna.
  33. 33. Aem=? Emf induced= VT= E* length of dipole

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