Antenna Antenna RadomeRadome

Effects onEffects on High Performance SATCOMHigh Performance SATCOM Antenna SystemsAntenna Systems

Dr. D. J. KozakoffConsultant and Chief ScientistUSDigiComm

Corp. ‐

Marietta, GA

R. CianoSenior Antenna Systems EngineerGeneral Atomics Corp. ‐

San Diego, CA

Presentation GoalsPresentation Goals

� Discuss Special Problems Encountered When Enclosing a SATCOM, and in Particular a Satellite on the Move (SOTM) Antenna within a Radome

� Investigate Considerations of Utilizing a SOTM Phased Array Antenna as Opposed to a Mechanically Gimbaled Antenna with the Dome

Uplink/Downlink Frequency Bands Uplink/Downlink Frequency Bands Commonly Used for SATCOMCommonly Used for SATCOM

RadomeRadome

Bandwidth Needs to Extend Bandwidth Needs to Extend from Downlink to Uplink Frequenciesfrom Downlink to Uplink Frequencies

Problem Worsens as Uplink Frequency Increases

� Dual Frequency (Uplink & Downlink) Requirements Pushes Design Towards Multilayer Wall Concepts Since Monolithic Typically Cannot Provide Suitable Bandwidths

� The Most Common Types Use 3-Layers (A-Sandwich) or 5-Layers (C-Sandwich) Consisting of Higher Dielectric “Skin”

Materials and Alternating Layers of Very Low Dielectric Core Materials

Design ConsiderationsDesign Considerations

Monolithic Monolithic RadomeRadome

ApproachApproach (0.15(0.15””

Thick Fiberglass Wall Example)Thick Fiberglass Wall Example)

� Transmission Peaks Seldom Correspond to Uplink and Downlink Frequency Segments

� Insufficient Bandwidth to extend from uplink to downlink frequencies

� Excessive Loss for most SATCOM applications

Cross Section of an“A-Sandwich”

3

Layer Wall

Cross Section of a“C-Sandwich”

5

Layer Wall

Some Popular Multilayer WallsSome Popular Multilayer Walls

Example of Effect of IncreasingExample of Effect of Increasing Number of Wall LayersNumber of Wall Layers

(Thickness = 0.5(Thickness = 0.5””, Epoxy Quartz), Epoxy Quartz)

� Select Low Loss Tangent Materials

� Determine Number of Wall Layers and Stackup (Core Thicknesses & Number of Prepreg Plies per Skin Layer)

� Computerized Optimization Can Greatly Improve Development Time and Radome Design Efficiency

� Initial Wall Design Best Achieved by a Flat Plate Analysis, Then Fine Tune the Design Using a full 3D Radome Analysis Approach.

Multilayer Wall Design MethodologyMultilayer Wall Design Methodology

Selection of Material Based on Loss Selection of Material Based on Loss Tangent ValueTangent Value

� The Power Loss in Propagation Through the Radome Wall is Proportional to the Loss Tangent Value and the Wall Thickness in Wavelengths

� What a Radome Does in Transmitting it Also Does in Receiving:

Receive Loss = Transmitting Loss

� Only Materials with a Loss Tangent of ≤

0.01 Should be Considered

Calculation of Loss Tangent EffectCalculation of Loss Tangent Effect (Thickness = 0.3(Thickness = 0.3””, Permittivity = 3), Permittivity = 3)

Radome WALL OptimizationRadome WALL Optimization (Computer Modeling Approach)(Computer Modeling Approach)

Output Data

Example of Optimized CExample of Optimized C--SandwichSandwich (for 20GHz to 30GHz Bandpass)(for 20GHz to 30GHz Bandpass)

� Antenna Noise Temperature

� Radome Effect on Decreasing Antenna Gain

� Radome Effect on Decreasing Antenna G/T Ratio

� Increase in Link Bit Error Rate (BER) Due to Effect

Other Considerations inOther Considerations in Specifying Radome PerformanceSpecifying Radome Performance

Sky Temperature vs FrequencySky Temperature vs Frequency (Antenna EL Angle is a Parameter)(Antenna EL Angle is a Parameter)

Ref: www.antetec.com

Sky Temperature vs FrequencySky Temperature vs Frequency (Plot Assumptions)(Plot Assumptions)

� Plot Assumes a Lossless Antenna

� Plot Doesn’t Include Hot Earth Contribution through Antenna Sidelobes

� At Near Zenith Antenna Pointing the Sky Noise Temperature is Less Than 10°K

Effect of Radome Loss onEffect of Radome Loss on Ku Band Antenna Noise TemperatureKu Band Antenna Noise Temperature

Effect of Radome Loss onEffect of Radome Loss on Ku Band Antenna Noise TemperatureKu Band Antenna Noise Temperature

Eb

/ NO

= Pt + Gt

- Lsp

- La

- k – fb + (Gr

/ T)

Where:

Eb

/ NO

= Energy per bit to noise density at receive antenna (dB)

Pt

= Transmit power (dBW) at satelliteGt

= Transmit antenna gain (dB) on satelliteLsp

= Free space loss (dB)k

= Boltzman’s constant (dB/K)

fb = Bit rate (dBHz)Gr

/ T

= Receive antenna gain to antenna/receiver noise temperature ratio (dB/K)

SATCOM Receive Link BudgetSATCOM Receive Link Budget

Ku Band Change in G/T Due to Ku Band Change in G/T Due to Radome LossRadome Loss

G/T  Decreases 

Faster  Than the 

Radome  Loss 

Increases

G/T  Decreases 

Faster  Than the 

Radome  Loss 

Increases

Ka Band Change in G/T Due to Ka Band Change in G/T Due to Radome LossRadome Loss

QPSK BER Related to EQPSK BER Related to Eb b / N/ Noo

� The Antenna Beam can Track a Satellite and Compensate for the Motion its Platform. On Ships for Example, a Specialized Pitch and Roll Stabilized Antenna Pointing Gimbal is Used to Eliminate the Effect of a Ship’s Motion.

� The Beam can be Configured to Operate in a Monopulse Mode for Autotrack

� Multiple Simultaneous Beams can be Used toTrack Multiple Satellites

� Aperture Weightings for Very Low Sidelobes can be Employed (i.e. –

Taylor or Chebychev Distributions

Benefits for SOTM PhasedBenefits for SOTM PhasedArray AntennasArray Antennas

� Must Populate a Single Aperture with Both Uplink Band and Downlink Band Antenna Elements

� Must Increase Aperture Size for Needed Effective Area so That Antenna Gain is Achieved Over the Entire Scan FOV

� Radome Design is More Complicated Because the Ray AOI’s are Different Than a Mechanically Steered Antenna

� Prove That Regulatory Requirements Such as Antenna Sidelobes are Satisfied for All Possible Pointing Angles

� Transmit and Receive Beams Must Point in Same Direction (Called “Registration Error”, the Difference Between the Uplink & Downlink Band BSE’s

Problems for SOTM PhasedProblems for SOTM PhasedArray AntennasArray Antennas

Thank You for ViewingThank You for Viewing Our PresentationOur Presentation

Have a Nice Day!Have a Nice Day!R. Ciano

ron.ciano@gmail.comDr. D. J. Kozakoff

dr.kozakoff@usdigicomm.com