Antennas slideshare part 2
- 1. Dr. S.MUTHUMANICKAM Associate Professor Department of ECE 1 EC8701 ANTENNAS AND MICROWAVE ENGINEERING PART 2
- 2. 2 ANTENNA FIELD ZONES (NEAR AND FAR FIELD REGION) RADIATION RESISTANCE LINK BUDGET AND FRIIS TRANSMISSION FORMULA ANTENNA APERTURES ANTENNA NOISE TEMPERATURE AND G/T RATIO ANTENNA IMPEDANCE AND IMPEDANCE MATCHING T O P I C S
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- 6. 6 Five-hundred-meter Aperture Spherical Telescope (FAST) size of 30 football fields CHINA LARGEST APERTURE TELESCOPE IN THE WORLD
- 9. 9 GMRT PUNE
- 10. 10 ANTENNA SETUP IN SAMSUNG MOBILE
- 12. 12 ANTENNA FIELD ZONES Types 1. Reactive Near Field Region 2. Radiating Near Field Region 3. Far Field Region Antenna D is diameter of parabolic dish L is length of a wire antenna Area surrounding the antenna, where EM field is produced
- 13. 13 Reactive Near Field Region Radiation Pattern This region is immediately surrounding the antenna For most of the antenna the outer boundary of this region is R < 0.62 𝑫³/𝝀 For short dipole radiator R < 𝝀/2п Objects with in this region will result coupling with the antenna and distortion of the ultimate far field antenna pattern Large conductor within this region will couple with the antenna and ‘detune’ it. This affects the following antenna parameters resonant frequency radiation resistance radiation pattern
- 14. 14 Radiating Near Field Region The field region of the antenna between the reactive near and far field region, the distance from the antenna R is 0.62 𝑫³/𝝀 < R < 2D²/ 𝝀 The region is also called as Transition region(antenna holds its radiation shape) Properties: The antenna pattern is taking shape but is not truly formed The radiation field predominates the reactive field The radiated wave front is still clearly curved The E and H field vectors are not orthogonal Radiation Pattern
- 15. 15 Far Field Region The angular field distance is essentially independent of the distance from the antenna R > 2D²/ 𝝀 Properties of this region are The wave front becomes approximately planar The radiation pattern is completely formed and does vary with distance E and H field vectors are orthogonal to each other Radiation Pattern
- 16. 16 Comparison of the Radiation patterns Reactive near field patteRadiative near field pattern Far field pattern
- 17. 17 Radiation Resistance The value of resistance that would dissipate the same amount of power when an input current passing through it
- 18. 18 RADIATION RESISTANCE Rr Antenna radiation is associated with radiation resistance. If we supply I current to antenna, then power dissipated by antenna P = I² x R The energy supplied to antenna is dissipated in two ways 1. Radiated power Prad = I² Rr 2. Due to ohmic loss Ploss = I² RL Total power P = Prad + Ploss = I² Rr + I² RL = I² (Rr + RL) Because of Rr the antenna radiates power in free space P ∞ Rr when Rr increases P increases Rr decreases, P decreases HOW? Radiation Efficiency ϵrad = Rr Rr + RL For example Case i: If Rr is 50 Ω and RL is 10 Ω Then ϵrad = 50 50 + 10 = 50 60 = 83% Case ii: If Rr is 10 Ω and RL is 10 Ω Then ϵrad = 10 10 + 10 = 10 20 = 50%
- 19. 19 Radiation Resistance Depends upon Configuration of antenna It depends upon corona discharge Ratio of length to diameter of conductor used in antenna Location of antenna with respect to ground and other objects Depends upon point where radiation resistance is considered Rr
- 20. 20 When High Voltage applied When High Frequency Applied
- 21. 21 LINK BUDGET Accounting of power gain and losses
- 22. 22 1. Then the power density p (in Watts per square meter) of the plane wave incident on the receive antenna a distance R from the transmit antenna is given by: 2. If the transmit antenna has an antenna gain in the direction of the receive antenna given by GT, then the power density equation above becomes: 3. Assume now that the receive antenna has an effective aperture given by AER. Then the power received by this antenna PR is given by: 4. Since the effective aperture for any antenna can also be expressed as: 5. The resulting received power can be written as: 6. Since wavelength and frequency f are related by the speed of light c , we have the Friis Transmission Formula in terms of frequency f : Derivation of FRIIS Transmission Formula 7. If the antennas are not polarization matched, the above received power could be multiplied by the Polarization Loss Factor (PLF) If we consider Tx antenna as isotropic source, Then power density at Rx antenna is P = PT/A = Transmitted power/Area PR = P x AER Gain of Tx antenna, GT = 4п 𝐴𝑒𝑇 λ² Then PR = PT 4п𝐴𝑒𝑇 4п𝑅²λ² x AER slly. gain of Rx antenna GR = 4п 𝐴ᴇ𝑅 λ²
- 24. 24 ANTENNA APERTURE (Ap) The area or part of the antenna which extracts power from the wave Describes the power capturing characteristics of antenna Types: 1. Physical aperture 2.Effective aperture 3.Scattering aperture 4.Loss aperture 5.Collecting aperture
- 25. 25 Rectangular Horn antenna with dimensions a and b is given Ap = a x b(m²) The area of opening is called as physical aperture If the incident wave has power density W, then the received power P = W x Ap (watts) where P is power received W is power density of the plane wave (watts per m²) Ap is physical aperture in m² Physical Aperture (Ap)
- 26. 26 EFFECTIVE APERTURE (Ae) The effective area simply represents how much power is captured from the plane wave and delivered by the antenna. This area factors in the losses intrinsic to the antenna (ohmic losses, dielectric losses, etc.). A general relation for the effective aperture in terms of the peak antenna gain (G) of any antenna is given by: Ae = λ² 4п G
- 27. 27 Antenna Apertures Scattering Aperture Loss Aperture
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- 31. 31 Antenna Effective Height/Length lef = 𝑉𝑜𝑐 𝐸
- 32. 32 ANTENNA NOISE TEMPERATURE AND G/T CALCULATION Antenna gain in decibels Noise temperatureFigure of Merit
- 33. 33 Antenna noise temperature is a parameter that describes how much noise an antenna produces in a given environment The temperature is not the physical temperature of the antenna
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- 36. 36 The temperature appearing at the terminals of antenna is given by TA = antenna noise temperature at output terminals of antenna (K) To = physical temperature of transmission line (K) Ta = antenna temperature at receiver terminals (K) TA = antenna noise temperature at the antenna terminals (K) TAP = antenna temperature at the antenna terminals due to physical temperature(K) G = gain pattern of antenna(dB), Tm = molecular temperature (K) Γ= reflection coefficient of surface, ϵ = emissivity (dimensionless) Brightness temperature (K)
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- 38. 38 Tp = Antenna physical temperature (K) α = attenuation coefficient of transmission line l = length of transmission line eA = Thermal efficiency of antenna(dimension less) Antenna Noise Temperature (TA)c Antenna temperature at receiver terminals Antenna temperature at the antenna terminals due to physical temperature
- 39. 39 Antenna Noise Temperature (TA)c TB = brightness temperature (K) TA = antenna noise temperature at output terminals of antenna(K) Ps = system noise power (W) Ta = antenna noise temperature at receiver terminals (K) Tr = receiving noise temperature at receiver terminals (K) Δf = bandwidth (Hz) k = Boltzmann’s constant (k = 1.38x10‾²³ J/K)
- 40. 40 ANTENNA IMPEDANCE (ZA) Transmitting antenna Receiving antenna
- 41. 41 ANTENNA IMPEDANCE Transmitting antenna and its Thevenin equivalent circuit
- 42. 42 Transmitting antenna and its Norton equivalent circuit To find the amount of power delivered to Rr for radiation and amount dissipated RL as heat
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- 47. 47 IMPEDANCE MATCHING WHY? Maximize the power transfer to load or Minimize signal reflection from the load
- 48. 48 Pair of AC&E 120 Ω twisted pair (Krone IDC) to 75 Ω coaxial cable balun transformers. Actual length is about 3 cm A 75-to-300-Ω balun built into the antenna plug Impedance matching device
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- 51. 51 PROBLEM
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