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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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Presentation Transcript
slide2

Radio

An Antenna is :

An effective interface between the radio and free space:

Free space

Antenna

For Terrestrial Communications, antennas must be directional:

Radio

terrestrial microwave antennas for point to point communication
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…
electrical performance parameters
Electrical Performance Parameters

Cross-Polar Discrimination (XPD)

Gain

Radiation Pattern Envelope

Interport Isolation (IPI)

Front to Back Ratio (F/B)

Return Loss (VSWR)

parabolic antenna directive gain
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)

slide6

Typical ParabolicAntenna Gain in dBi

Antenna Diameter

Frequency

radiation pattern concept
Radiation Pattern Concept

Antenna Under Test

Antenna Test Range

Source Antenna

slide10

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
co polarization and cross polarization
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

slide12

Inter-port Isolation (IPI)

Feed Horn

  • Leakage of Signal Between Antenna Ports
  • Internal Noise
  • Expressed in dB

Towards Reflector

Transmit Signal

Leakage Signal

voltage standing wave ratio vswr
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)

return loss the amount of energy lost due to reflected returned signal
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)

slide15

Basic Antenna Types

Standard Parabolic Antenna

Focal Plane Antenna

Shielded Antenna

GRIDPAK® Antenna

slide16

GRIDPAK® Antenna

  • Grid Reflector
  • Low Wind load
  • Single Polarized
  • Below 2.7GHz
  • Shipped in Flat, Lightweight Package
slide17

Standard Parabolic Antenna

  • Basic Antenna
  • Comprised of
    • Reflector
    • Feed Assembly
    • Mount
slide18

Focal Plane Antenna

  • Deeper Reflector
  • Edge Geometry
  • Improved F/B Ratio
  • Slightly Lower Gain
slide19

Shielded Antenna

  • Absorber-Lined Shield
  • Improved Feed System
  • Planar Radome
  • Improved RPE
antenna efficiency
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%
antenna f d ratio
Antenna f/D Ratio

f

f

D

D

f/D = 0.333

f/D = 0.250

Standard & Shielded Antennas

Focal Plane Antennas

slide22

Unwanted Signals

Scattering

Spillover

Diffraction

slide23

Front to Back Ratio

Direction of Signal

Direction of Signal

Direction of Signal

Standard Parabolic Antenna

Focal Plane Antenna

Shielded Antenna

parabolic reflector beamwidth

3dB

Parabolic Reflector Beamwidth

Diameter

Frequency

Beamwidth in Degrees

radiation pattern envelope
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

radomes
Radomes
  • Reduce Windloading on Tower
  • Protection Against Ice, Snow and Dirt
other antenna options
Other Antenna Options

High XPD antennas

Dual beam antennas

Dual band antennas

Low profile antennas

Integrated antennas