Chapter 22 Fundamentalfundamental Propertiesproperties Ofof Antennasantennas

Chapter 2 Fundamental Properties of Antennas ECE 5318/6352 Antenna Engineering Dr. Stuart Long 1. IEEE Standards . Definition of Terms for Antennas . IEEE Standard 145-1983 . IEEE Transactions on Antennas and Propagation Vol. AP-31, No. 6, Part II, Nov. 1983 2. Radiation Pattern (or Antenna Pattern) “The spatial distribution of a quantity which characterizes the electromagnetic field generated by an antenna.” 3. Distribution can be a . Mathematical function . Graphical representation . Collection of experimental data points 4. Quantity plotted can be a . Power flux density W [W/m²] . Radiation intensity U [W/sr] . Field strength E [V/m] . Directivity D 5. Graph can be . Polar or rectangular 6. Graph can be . Amplitude field |E| or power |E|² patterns <ul style="display: flex;"><li style="flex:1">(in linear scale) </li><li style="flex:1">(in dB) </li></ul>7. Graph can be . 2-dimensional or 3-D most usually several 2-D “cuts” in principle planes 8. Radiation pattern can be . Isotropic Equal radiation in all directions (not physically realizable, but valuable for comparison purposes) . Directional Radiates (or receives) more effectively in some directions than in others . Omni-directional nondirectional in azimuth, directional in elevation 9.Principle patterns . E-plane . H-plane Plane defined by H-field and direction of maximum radiation Plane defined by E-field and direction of maximum radiation (usually coincide with principle planes of the coordinate system) 10 Coordinate System Fig. 2.1 Coordinate system for antenna analysis. 11 . Radiation pattern lobes . Major lobe (main beam) in direction of maximum radiation (may be more than one) . Minor lobe - any lobe but a major one . Side lobe - lobe adjacent to major one . Back lobe – minor lobe in direction exactly opposite to major one 12 . Side lobe level or ratio (SLR) . (side lobe magnitude / major lobe magnitude) . - 20 dB typical . < -50 dB very difficult Plot routine included on CD for rectangular and polar graphs 13 Polar Pattern Fig. 2.3(a) Radiation lobes and beamwidths of an antenna pattern 14 Linear Pattern Fig. 2.3(b) Linear plot of power pattern and its associated lobes and beamwidths 15 .Field Regions . Reactive near field energy stored not radiated D3 R 0.62 λ = wavelength D= largest dimension of the antenna 16 .Field Regions . Radiating near field (Fresnel) radiating fields predominate pattern still depend on R radial component may still be appreciable <ul style="display: flex;"><li style="flex:1">D3 </li><li style="flex:1">D2 </li></ul>0.62  R  2 <ul style="display: flex;"><li style="flex:1"></li><li style="flex:1"></li></ul>λ = wavelength D= largest dimension of the antenna 17 .Field Regions . Far field (Fraunhofer) field distribution independent of R field components are essentially transverse D2 R  2 18 .Radian 2 radians in full circle arc length of circle  r  Fig. 2.10(a) Geometrical arrangements for defining a radian 19 .Steradian one steradian subtends an area of A  r2 4π steradians in entire sphere dA  r2 sin d d dA d   sin d d r2 Fig. 2.10(b) Geometrical arrangements for defining a steradian. 20

Chapter 22 Fundamentalfundamental Propertiesproperties Ofof Antennasantennas

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