Ku-Band Feed – Feeds Are Adjusted, No Antenna Movement

Ku-Band Feed – Feeds Are Adjusted, No Antenna Movement

Major Earth Station Equipment 6/10/5244 - 1 Major Earth Station Equipment . ANTENNA – Types – Parameters . Uplink – Modulation – Up-converters – Transmitters – Inter Facilities Link . RF Downlink – LNA / LNB – Down-converters – Demodulation – Inter Facilities Link 6/10/5244 - 2 Antenna . A satellite earth station antenna – An effective interface between the uplink equipment and free space – Must be directional to beam an RF signal to the satellite – Requires a clear line of sight between the antenna and the satellite Free space HPA Antenna Free space HPA 6/10/5244 - 3 Antenna 6/10/5244 - 4 ANTENNA . ANTENNA PARAMETERS: . GAIN . G (dBi) = 20.4 + 20 Log f + 20 Log D + 10 Log h . f = frequency in GHz . D = diameter in meters . h = antenna efficiency in decimal format . What should be the gain of a 9.3 m C-band antenna at 6.4GHz that is 62% efficiency ? . G = 20.4 + 20 Log 6.4 + 20 log 9.3 + 10 Log 0.62 . G = 20.4 + 20 ( .806179) + 20 ( .968482) + 10 ( -0.2076) . G = 20.4 + 16.12 + 19.37 - 2.08 . G = 53.81 dBi 6/10/5244 - 5 ANTENNA BEAMWIDTH: . For a given antenna, the higher the frequency the narrower the 3dB beamwidth. Therefore the receive band will be broader than the transmit. For a given frequency band the larger the antenna aperture the smaller or narrower the beamwidth. θ (deg.) = 21 f D f = frequency in GHz D = diameter in meters 6/10/5244 - 6 ANTENNA BEAMWIDTH: 6/10/5244 - 7 Antenna . Full Motion – Motorized o – Azimuth ± 180 from antenna center line (CL) – 5 - 90o – Tracking satellites in transfer orbit . Limited Motion – Typically Motorized o – Azimuth ± 60 from center line (CL) – 5 – 90o Elevation – Full time service – Occasional use on multiple satellites . Fixed – Manual movement – Provides coverage of the entire satellite arc – Peaked on satellite with no further adjustments 6/10/5244 - 8 Antenna . Antenna Position Controllers (APC) – Installed at base of the antenna (“Jog Controller”) – Toggle switches for AZ (CW/CCW), EL (UP/Down) and Polarizer – Serial data link for remote control with a computer – Transducers provide AZ & EL and Polarizer angle readouts . Antenna Control Unit (ACU) – Manually position and polarize the antenna – Preset satellite locations stored in memory – Step Track • Requires a suitable receiver to provide signal level to the ACU • Back and forth movement in AZ and EL to ensure peak signal level – Memory Track • Creates a model of satellite motion for a twenty-four hour period • Uses this model to track the satellite – Computer Track • Predict data from computer controls antenna movement 6/10/5244 - 9 Antenna . Antenna Control Unit (ACU) – Mono-pulse • Relative signal phase and the sharp slope of a tracking null is used to determine peak position • It is not necessary to step the antenna to determine satellite target orientation relative to the antenna’s RF axis • Utilizes an electrical means (phase comparison) rather than a mechanical means (antenna stepping) to determine satellite orientation • Responds more accurately and faster to satellite dynamics • Primary use is for tracking transfer orbits 6/10/5244 - 10 Antenna Efficiency . Well-designed antennas have efficiency ratings of 50 - 70% – 60 – 65 % typical . Efficiency is affected by: – Spar and feedhorn blockage – Subreflector alignment and placement – Subreflector surface tolerance and design – Main reflector surface tolerance or deviation – Feed horn loss – On axis alignment – Polarization purity . Efficiency can never be 100% 6/10/5244 - 11 Antenna Types . Prime Focus parabolic reflector – Center Feed – Feed & strut blockage can be large – High feed line loss RF – Both TX and RX – Poor G/T performance Feed OMT SPAR MAIN REFLECTOR RF 6/10/5244 - 12 Antenna Types . Parabolic reflector Cassegrain – Typical use 5m or larger – Parabolic main reflector – Hyperboloidal subreflector – Subreflector and strut blockage small – Small feed line loss – Good G/T 6/10/5244 - 13 Antenna Types . Parabolic reflector Gregorian – Typical use 5m and larger – Parabolic main reflector RF – Ellipse subreflector – Subreflector and strut blockage small – Small feed line loss SPAR – Good G/T SUBREFLECTOR OMT Ellipse Feed SPAR RF MAIN REFLECTOR 6/10/5244 - 14 Antenna Types . Parabolic reflector offset feed – Typical 3.7m and smaller – No feed blockage – Small feed line loss R F – VSAT applications MAIN REFLECTOR R F Feed OMT SPAR 6/10/5244 - 15 Antenna Types . Simulsat – Receive Only – Captures signals across a 70° view arc – Up 35 satellites are received with uniform performance – Each satellite illuminates a specific area – Signals reflect to their corresponding C or Ku-Band feed – Feeds are adjusted, no antenna movement 6/10/5244 - 16 Antenna Types . In a direct feed reflector, the feed horn is located at the focus or may be offset to one side of the focus . Large earth station antennas have a subreflector at the focus – The subreflector permits the antenna optics to be located near the base of the antenna – Reduces losses because the length of the waveguide between the transmitter or receiver and the antenna feed is reduced – The system noise temperature is also reduced because the receiver looks at the cold sky instead of the warm earth 6/10/5244 - 17 Antenna Subreflector . Cassegrain – The subreflector is convex with an hyperboloidal surface – Hyperboloidal? A mathematical surface whose sections parallel to one coordinate plane form ellipses and those parallel to the other two coordinate planes form hyperbolas . Gregorian – The subreflector is concave with an ellipsoidal surface – Ellipsoidal? A geometric surface or a solid figure shaped like an oval. Any section through an ellipsoid is either an ellipse or a circle. 6/10/5244 - 18 Antenna Focal Distance (f/d) . Focal Distance (f/d) – To calculate: f/d = D2/16d • D = Antenna Diameter • d = Depth of Parabola f/d f/d d = 0.6m d = 0.8m D = 3.8m D = 3.8m 2 2 f/d = D /16d f/d = D /16d D = 3.8 m D = 149.6 in D = 3.8 m D = 149.6 in d = 0.8 m d = 31.5 in d = 0.6 m d = 23.63 in f/d = 1.128 m f/d = 44.42 in f/d = 1.504 m f/d = 59.23 in 6/10/5244 - 19 Antenna . Shallow dish antenna – Long focal length increases the feedhorn’s ability to illuminate the entire reflector area providing good gain – More susceptible to: • Earth noise at low elevation angles • Terrestrial interference – Affects antenna noise temperature . Deep dish antenna – Short focal length decreases the feedhorn’s ability to illuminate the entire reflector area providing less gain – Can provide advantages • Low elevation angles • Terrestrial interference – Better antenna noise temperature 6/10/5244 - 20 Antenna De-Ice . Freezing perception will impact antenna performance – Snow or ice on the reflector surface • Attenuates the signal • De-focus the antenna . Area’s with freezing perception require antenna de-icing . Electric – Blankets glued to the back of the reflector – Forced hot air with the back structure enclosed . Natural gas – Forced hot air with the back structure enclosed . Fabric Cover – Prevent snow/ice accumulation in the dish . Rain Blower – Blows air across feed input to prevent water buildup 6/10/5244 - 21 Antenna Feed Assembly 6/10/5244 - 22 Antenna Feed System . 1 Port – Receive Only . 2 Port – Two Receive – One Transmit and One Receive . 3 Port – One Transmit and Two Receive . 4 Port – Two Transmit and Two Receive . Polarization adjustment – Single plane, transmit and receive are fixed and both rotate – Dual plane, transmit and receive rotate separately . Rain Blower – Blows air across feed input to prevent water buildup 6/10/5244 - 23 OMT and TRF . Ortho Mode Transducer (OMT) – Changes feeds circular W/G to two rectangular W/G’s – Separates and directs signals of two different polarities – Determines isolation for Circular Polarization V Feed H Transmit .Transmit Reject Filter (TRF) – Blocks transmit power from the Low Noise Amplifier TRF . 4 port feed will have an OMT and TRF LNA for each polarity Receive 6/10/5244 - 24 Antenna Patterns 6/10/5244 - 25 Antenna Pattern •3D Radiation Pattern 6/10/5244 - 26 Antenna Pattern •Cut Through Radiation Pattern 6/10/5244 - 27 Antenna Pattern . FCC / ITU requirements for transmit patterns – 29-25log θ from 1 to 7o from – 8 dBi from 7 to 9.2o Deg 29-25 log θ peak o – 32-25log θ > 9.2 1 29.0 15.2 2 21.5 22.7 . How are the curves applied? 3 17.1 27.1 4 13.9 30.3 – Calculations are subtracted from 5 11.5 32.7 antenna gain 6 9.5 34.7 – i.e. antenna gain = 44.2 dBi 7 7.9 36.3 – Higher gain antenna will provide 8 8.0 36.2 more discrimination 9 8.0 36.2 – i.e. 50 dBi – 29 = 21 dB 10 7.0 37.2 11 6.0 38.2 6/10/5244 - 28 Antenna Pattern from Deg peak 1 15.2 2 22.7 3 27.1 4 30.3 5 32.7 6 34.7 7 36.3 8 36.2 9 36.2 10 37.2 11 38.2 6/10/5244 - 29 Antenna Pattern Co-pol pattern Cross-pol pattern 6/10/5244 - 30 Uplink 6/10/5244 - 31 Uplink Components . Uplink Block Diagram – Modulator / Modem – Up-Converter – Power Amplifier – Antenna – Inter Facility Link (IFL) • Fiber Optics • Co-axial cable • Patch Panels • Combiners / Splitters • Waveguide Antenna Modem IFL Up-Converter IFL Transmitter IFL Feed Simplified Uplink Block Diagram 6/10/5244 - 32 Up-Converter (U/C) 6/10/5244 - 33 Up-Converter (U/C) . A device that converts an input signal known as the intermediate frequency (IF) to a desired higher frequency without disturbing the intelligence (modulation) on the incoming signal .

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