lect 05© 2012 raymond p. jefferis iii1 satellite communications link budget analysis transmitted...

Lect 05 © 2012 Raymond P. Jefferis III 1

Satellite Communications

Link budget analysis• Transmitted power• Transmitting antenna gain• Path loss• Receiving antenna gain• Receiver sensitivity


Tx Down-Link Budget Analysis• Starting with transmitter link loss factors:

– Power is reduced by system loss factors• detuning losses, cabling losses, coupling losses, etc.

– Power is reduced by antenna inefficiency, from beam sidelobes, for instance

• Dynamic losses – Backoff, beamwidth, and pointing losses

• Path loss factors– Free space loss– Atmospheric losses– Precipitation losses

Rx Down-Link Budget Analysis

• Receiver factors:– Receiver antenna gain – efficiency loss– Coupling, cabling, and detuning losses– Receiver sensitivity

• Noise factors– Input noise (natural factors)– Antenna, RF amplifier, and mixer noise



Transmitted Power• Usually specified in Watts• Can be converted to dBW by,

PtdB =10 logPt1.0⎛⎝⎜

⎞⎠⎟

where,Pt db = Transmitter power [dB-Watts]Pt = Transmitter power [Watts]


Transmitted Power• Usually specified in Watts• Can be converted to dBm by,

Pt dBm =10 logPt

1* 10−3

⎛⎝⎜

⎞⎠⎟

where,Pt dbm = Transmitter power [dB-milliWatts]Pt = Transmitter power [Watts]


Examples 05-01, 05-02• Transmitter power = 20 Watts• Pt db = 10 log(20) = 13 dBW• Pt dbm = 10 log(20/10-3) = 43 dBm

• Transmitter power = 75 Watts• Pt db = 10 log(75) = 18.75 dBW• Pt dbm = 10 log(75/10-3) = 48.75 dBm


What does this specification mean?

Intelsat GALAXY-11 at 91W (NORAD 26038)

• 39.1 dBW on C-Band (20W, 24 ch, Bw: 36 MHz)

• 47.8 dBW on Ku-Band (75/140W, 40 ch, Bw: 36 MHz)

• Transmitter power, is simultaneously distributed across all the available channels (CDMA)

• The satellite has four antennas, two for each band, and sequential channels are transmitted on one antenna in a band and received on the other. Shared channel (TDMA)

Two possible interpretations (CDMA vs. TDMA)


Transmitter Antenna Gain

For a circular antenna (parabolic dish),

Ae =ηAπ(d / 2)2

G=4πλ2 Ae

G=ηA

πdλ

⎛⎝⎜

⎞⎠⎟

2

where,Ae = Effective aperture [m2]η= aperture efficiencyd = aperture diameter [m]G = aperture antenna gainλ= operating wavelength [m]

LECT 04 © 2012 Raymond P. Jefferis III 9

Circular Aperture Antenna

• The electric field of a circular aperture antenna can be calculated from:

E[φ] =2λπD

J 1[(πD / λ)sinφ]sinφ

where, D/λgives the aperture diameter in wavelengths and ϕ is the angle relative to the normal to the plane of the aperture.


Example 05-03 - Ku-Band antenna

• 3dB beamwidth = 3˚

• D/λ= 25η= 0.63

• G = 3886

• GdBi = 36

Beamwidth – Circular Aperture

Show demo.

Lect 05 © 2012 Raymond P. Jefferis III Lect 00 - 11

E-Field of a Circular Aperture Antenna


eps = 0.001;Diam = 20;

Manipulate[e2 = (2.0/p*Diam)*(BesselJ[1, p*Diam*Sin[theta]])/Sin[theta]; Plot[Abs[e2], {theta, -p/6, p/6}, PlotRange -> {{-0.5, 0.5}, {0, 600}}, PlotStyle -> {Directive[Thick, Black]}], {Diam, 1, 25} ]


Antenna Gain vs Beamwidth Calculation

eff = 0.63;beamw = 1;f = 12*10^9;c = 2.99792458*10^8;lam = c/f;Plot[app = 75.0/beamw; diam = app*lam; G = eff*p^2*app^2; lG = 10*Log[10, G]; lG, {beamw, 1, 5}, AxesLabel -> {Beamwidth [deg], Gain}]

Antenna Gain vs Beamwidth Result


Link Budget – General Information

• The accounting of gains and losses over a link• Other effects that can be considered

– Fading– Reflections (multipath interference)– Ground absorption

• Excessive power losses can reduce a transmitted signal to levels below the receiver sensitivity in the presence of noise



Link Budget Calculation (Downlink)

• Calculate power density of isotropic antenna• Calculate effective radiated power (EIRP)

using transmitter antenna gain and efficiency• Calculate path loss• Calculate receiving antenna aperture and gain• Calculate received power at the earth station

Link Budget Calculation (continued)

• Compare receiver input specifications with the calculated power levels at the receiver

• Add noise factors• Calculate receiver input Signal/Noise ratio• If this is inadequate, change accessible link factors


The Isotropic (Ideal) Antenna

• The gains of antennas can be stated relative to an isotropic ideal antenna as G [dBi], where G > 0.

• This antenna is a (theoretical) point source of EM energy

• It radiates uniformly in all directions• A sphere centered on this antenna would exhibit

constant energy per unit area over its surface• The gain of an isotropic antenna is 0 dBi


EIRP

• Equivalent Isotropic Radiated Power

• – the equivalent power input that would be needed for an isotropic antenna to radiate the same power over the angles of interest

LECT 04 © 2012 Raymond P. Jefferis III Lect 00 - 19


Equivalent Isotropic Radiated Power - EIRP

EIRP =GtPtWhere: (in the far-field only),EIRP = Equiv. isotropic rad. power [W]Pt = Transmitted power [W]Gt = Gain of lossless transmitting antenna (Gt = 1 for lossless isotropic antenna)or, in dB units,EIRPdBW = Pt dBW + Gt dBi


Isotropic Radiated Flux Density

ψ =1

4π r2

⎛⎝⎜

⎞⎠⎟EIRP

where (in the far-field only),ψ = Transmitted power flux density (W/m2)EIRP = Equiv. isotropic rad. power [W]r = Distance from transmitter

Note: This is the EIRP per unit area of a sphere at radius r from an isotropic antenna.


Actual Transmitting Antenna Gain

Gte =ηtGt

EIRPeff =ηtGtPtwhere (in the far-field only),EIRPeff = Effective EIRP [W]Pt = Transmitted power [W]Gt = Gain of a lossless (ideal) transmitting antennaηt = Transmitting antenna efficiency Gte = Effective gain of transmitting antenna


Example 05-04: Ku-Band Satellite• Pt: 75 [W] => 18.75 [dBW]

• Antenna diam: 1.8 [m]• Frequency: 12 [GHz]• Wavelength: 0.025 [m]• Antenna Eff.: 0.62 [-2.1 dBW]• Antenna Gain: 45.02 [dBi]

• EIRPeff 63.77 [dBW]

EIRP Calculation for Ku-band Example

c = 2.99792458*10^8; (* m/sec *)

freq = 12.0*10^9; (* Hz *)

pt = 75.0;(* Watts *)

ptdbW = 10*Log[10, pt]; (* dBW *)

eff = 0.62; (* efficiency *)

lam = c/freq; (* m *)

diam = 1.8; (* m *)

dl = diam/lam;

gain = eff*(p*diam/lam)^2;

loggain = 10*Log[10, gain];(* dB *)

eirp = gain*pt;(* W *)

dBW = 10*Log[10, eirp];(* dBW *)

Print["EIRP = ", dBW, " [dBW]"]



Free Space Path Loss Calculation

• Due to the spreading of transmitted energy• Other losses will be accounted separately

Lp =λ

4πr⎛⎝⎜

⎞⎠⎟

2

where,λ= wavelength [m]r = transmission-reception distance [m]


Received Power (Gain & Losses)Pr =EIRP ⋅Lp ⋅Gr

Gr =ηr

πdrλ

⎛⎝⎜

⎞⎠⎟

2

where,EIRP = Effective Isotropic Radiated Powerηr = Antenna efficiencyGr = Antenna gain (G = 1 for isotropic)dr = Antenna diameter [m]Lp = Path lossλ= wavelength [m]


Net Received Power CalculationPr =EIRP ⋅Lp ⋅Gr _ eff

EIRP =Gt_ effPt

Gt_ eff =ηt

πdtλ

⎛⎝⎜

⎞⎠⎟

2

Lp =λ

4πr⎛⎝⎜

⎞⎠⎟

2

Gr _ eff =ηr

πdrλ

⎛⎝⎜

⎞⎠⎟

2

EIRP = Eff. Isotropic Radiated Powerηt/r = Antenna efficiencyGt/r = Antenna gain Dt/r = Antenna diameter [m]Lp = Path lossλ = wavelength [m]R = transmitter-receiver distance [m]


Another Received Power Interpretation

Pr =ψ r ⋅Aeff

Where,Pr = Received power [W]ψr = Received flux density [W/m2]Aeff = Effective receiving antenna aperture [m2]


Path Loss Summary Diagram


Power Ratio over Path Calculation

where,ηt = Efficiency of receiving antenna [-]ηr = Efficiency of receiving antenna [-]Gt = Antenna gain (G=1 for isotropic antenna)Gr = Antenna gain (G=1 for isotropic antenna)λ = wavelength [m]d = distance between antennas [m]


Path Loss [dB]

Pr dB =PtdB +10 log(ηtGt) +10 logλ

4πr⎛⎝⎜

⎞⎠⎟

2

+10 log(ηrGr )


Example 05-05: Ku-Band Satellite• Receiving antenna diameter: 0.9 [m]• Frequency: 12 [GHz]• Wavelength: 0.025 [m]• Path length: 42000 [km]• Antenna Eff.: 0.62• Receiving Antenna Gain: 39 [dBi]• EIRPeff 63.8 [dBW]• Path gain (-loss): -206.5 [dBW]• Received power: -103.7 [dBW]

Class Activity

• Compute the path loss of the previous example in dBW.

• Compute the received power of the previous example in dBW.


Activity Results

• f = 12 GHz [12000 MHz]

• λ= 0.025 [m] => (-32 dBW)

• Pt = 18.75 dBW

• ηtGt = 45.02 dBW

• ηrGr = 39.0 dBW

• r = 42,000 km => (-206.5 dBW)

• Pr = 18.75 + 45.02 - 206.5 + 39 = -103.7 [dBW]



Activity Calculationc = 2.99792458*10^8; f = 12.0*10^9; lam = c/f;r = 42.0*10^6;pwrTx = 75.0; dAntTx = 1.8; effAntTx = 0.62;gAntTxEff = effAntTx*(p*dAntTx/lam)^2;gAntTxEffdB = 10 Log[10, gAntTxEff];EIRPdB = 10 Log[10, pwrTx] + gAntTxEffdB;Lp = (lam/(4*p*r))^2;LpdB = 10 Log[10, Lp];dAntRx = 0.9; effAntRx = 0.62;gAntRxEff = effAntRx*(p*dAntRx/lam)^2;GAntRxEffdB = 10 Log[10, gAntRxEff];PrdB = EIRPdB + LpdB + GAntRxEffdB;Print["Path Loss ", LpdB, " [dB]"];Print["Rcv pwr = ", PrdB, " [dBW]"];


Example: Ku-Band Link• Tx power: 10 [Watts]• Rx and Tx antenna diameters:3.0 [m]• Frequency: 12 [GHz]• Path length: 35,900 [km]• Antenna Efficiencies 0.55• Antenna Gains: 48.93[dBi]• EIRPeff 58.93 [dBW]• Path gain (-loss): -205.1 [dBW]• Received power: -97.24

[dBW]

Example Ku-Band Calculationf = 12.0*10^9; Bw = 36.0*10^6; c = 2.99792458*10^8;lam = c/f;r = 35.9*10^6;(* Tx EIRP CALC. *) pwrTx = 10.0;pwrTxdB = 10 Log[10, pwrTx];dAntTx = 3.0; effAntTx = 0.55;gAntTxEff = effAntTx*(p dAntTx/lam)^2;gAntTxEffdB = 10 Log[10, gAntTxEff];EIRPdB = 10 Log[10, pwrTx] + gAntTxEffdB;(* Path Loss *) Lp = (3.0*10^8/(4*p*f*r))^2;(* Path Loss [DB] *) LpdB = 10 Log[10, Lp];(* Rx Antenna CALC. *) dAntRx = 3.0; effAntRx = 0.55;gAntRxEff = effAntRx*(p dAntRx/lam)^2;GAntRxEffdB = 10 Log[10, gAntRxEff];(* Received Power [DB] *) PrdB = EIRPdB + LpdB + GAntRxEffdB;(* Received Power [W] *) PrWatts = 10^(PrdB/10);



Conversion to Frequency Baseλ =c / f

Pr = Pt3*108

4π fR

⎛

⎝⎜⎞

⎠⎟

2

GtGr

Lp =c

4π fR

⎛⎝⎜

⎞⎠⎟

2

Pr( )dB

= Pt( )dB

+ (Gt )dB + (Lp )dB + (Gr )dB

where,(Pt)dB = Transmitted power [dBW](Pr)dB = Received power [dBW](Lp)dB = Path loss power [dBW](Gt/r)dB = Transmitting or receiving antenna gainf = frequency [Hz]R = distance [m]


Example Calculation: Ku-Band• f = 12 GHz [12000 MHz]• Pt = 18.7 dBW• Gt = 45 dBi• Gr = 39 dBi• R = 42, 000 km• Pr = 18.7 + 45 - 206.49 + 39 = - 103.8 dBW

Note:Considering free space loss only

Workshop 05

• Please do all work indicated on the Workshop 05 handout.

• You may use a spreadsheet or a mathematics package (Mathematica®is recommended) for your calculations

• Document ALL work and calculations

• Submit as a written Workshop report.



Workshop 05 Calculationsc = 2.99792458*10^8; f = 12.0*10^9;lam = c/f; r = 42.0*10^6;pwrTx = 75.0; pwrTxdB = 10 Log[10, pwrTx];dAntTx = 1.8; effAntTx = 0.62;gAntTxEff = effAntTx*(p dAntTx/lam)^2;gAntTxEffdB = 10 Log[10, gAntTxEff];EIRPdB = 10 Log[10, pwrTx] + gAntTxEffdB;Lp =(3.0*10^8/(4*p*f*r))^2; LpdB =10 Log[10, Lp];dAntRx = 0.9; effAntRx = 0.62;gAntRxEff = effAntRx*(p dAntRx/lam)^2;GAntRxEffdB = 10 Log[10, gAntRxEff];PrdB = EIRPdB + LpdB + GAntRxEffdB;

End


lect 05© 2012 raymond p. jefferis iii1 satellite communications link budget analysis transmitted...

Documents

circular aperture antenna

transmitter power watts

aperture antenna gain

dbm slide

receiver antenna

dbm transmitter power

jefferis iii3 slide

transmitter power dbwatts