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2001 APCO/NENA State Training Conference

2001 APCO/NENA State Training Conference January 19, 2001 Radio An Antenna is : An effective interface between the radio and free space: Free space Antenna For Terrestrial Communications, a ntennas must be directional: Radio

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2001 APCO/NENA State Training Conference

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  1. 2001 APCO/NENA State Training Conference January 19, 2001

  2. Radio An Antenna is : An effective interface between the radio and free space: Free space Antenna For Terrestrial Communications, antennas must be directional: Radio

  3. Terrestrial Microwave Antennas for Point-To-Point Communication • Terrestrial microwave antennas generate a beam of RF signal to communicate between two locations. • Point-To-Point communication depends upon a clear line of sight between two microwave antennas. • Obstructions, such as buildings, trees or terrain interfere with the signal. • Depending upon the location, usage and frequency, different types can be utilized. • We will address the basic characteristics of these various types…

  4. Electrical Performance Parameters Cross-Polar Discrimination (XPD) Gain Radiation Pattern Envelope Interport Isolation (IPI) Front to Back Ratio (F/B) Return Loss (VSWR)

  5. Parabolic AntennaDirective Gain Ga (dBi) = 10 log10h [ 4 p Aa / l2 ] Where: Ga = Antenna Directive Gain (Catalog spec) h = Aperture Efficiency (50-55%) Aa = Antenna Aperture Area l= Wavelength (speed of light / frequency)

  6. Typical ParabolicAntenna Gain in dBi Antenna Diameter Frequency

  7. Radiation Pattern Concept Antenna Under Test Antenna Test Range Source Antenna

  8. Radiation Patternabout Bore sight

  9. Cut Through Radiation Pattern at Boresight

  10. Front to Back Ratio • Ratio of the signal level at beam peak to that directed behind the antenna • Considered in intra-system interference calculation (hop overreach) • Expressed in dB

  11. Co-Polarization and Cross-Polarization • Co-Polarization • Where Transmit & Receive Antennas have the Same Polarization • Either Horizontal or Vertical (HH or VV) • In your System, The Wanted Signal Co-polarized antenna pattern XPD Relative Power • Cross-Polarization • Where Transmit & Receive Antennas have Different Polarizations • Either HV or VH. • In your System, The Unwanted Signal X-polarized patttern Azimuth Angle

  12. Inter-port Isolation (IPI) Feed Horn • Leakage of Signal Between Antenna Ports • Internal Noise • Expressed in dB Towards Reflector Transmit Signal Leakage Signal

  13. Voltage Standing Wave Ratio (VSWR) Incident Signal • VSWR : 1.30 Reflection Coefficient : 13% (0.13) • VSWR : 1.20 Reflection Coefficient : 9.1% (0.091) • VSWR : 1.10 Reflection Coefficient : 4.7% (0.047) • VSWR : 1.08 Reflection Coefficient : 3.8% (0.038) • VSWR : 1.06 Reflection Coefficient : 2.9% (0.029) Reflected Signal VSWR = 1 + (Reflection Coefficient) 1 - (Reflection Coefficient)

  14. Return Loss The Amount of Energy Lost due to Reflected (Returned) Signal • RL : 17.8dB Reflection : 13% (0.13) VSWR : 1.30 • RL : 20.8dB Reflection : 9.1% (0.091) VSWR : 1.20 • RL : 26.7dB Reflection : 4.7% (0.047) VSWR : 1.10 • RL : 28.4dB Reflection : 3.8% (0.038) VSWR : 1.08 • RL : 30.7dB Reflection : 2.9% (0.029) VSWR : 1.06 RL = -20 x log (Reflection Coefficient)

  15. Basic Antenna Types Standard Parabolic Antenna Focal Plane Antenna Shielded Antenna GRIDPAK® Antenna

  16. GRIDPAK® Antenna • Grid Reflector • Low Wind load • Single Polarized • Below 2.7GHz • Shipped in Flat, Lightweight Package

  17. Standard Parabolic Antenna • Basic Antenna • Comprised of • Reflector • Feed Assembly • Mount

  18. Focal Plane Antenna • Deeper Reflector • Edge Geometry • Improved F/B Ratio • Slightly Lower Gain

  19. Shielded Antenna • Absorber-Lined Shield • Improved Feed System • Planar Radome • Improved RPE

  20. Antenna Efficiency Well-designed antennas have efficiency ratings of 45 - 65% • Efficiency Factor Affected By : • Feed Illumination • Aperture Blockage • Reflector Surface Tolerance • Efficiency can never be 100%

  21. Antenna f/D Ratio f f D D f/D = 0.333 f/D = 0.250 Standard & Shielded Antennas Focal Plane Antennas

  22. Unwanted Signals Scattering Spillover Diffraction

  23. Front to Back Ratio Direction of Signal Direction of Signal Direction of Signal Standard Parabolic Antenna Focal Plane Antenna Shielded Antenna

  24. 3dB Parabolic Reflector Beamwidth Diameter Frequency Beamwidth in Degrees

  25. Radiation Pattern Envelope 0 10 20 30 40 50 Antenna Directivity dB down from Main Lobe 60 70 80 90 100 0 5 10 15 20 40 60 80 100 120 140 160 180 Azimuth - Degrees from Main Lobe

  26. Radomes • Reduce Windloading on Tower • Protection Against Ice, Snow and Dirt

  27. Other Antenna Options High XPD antennas Dual beam antennas Dual band antennas Low profile antennas Integrated antennas

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