Voir la source de User Manual 3.3 Properties and models: Link budget



== Introduction ==
=== Scope ===
This section contains the description of the RF properties associates to an antenna (which is represented by a part of an Assembly) and the RF link budget computation model.

=== Javadoc ===
The classes described in this section are available in the packages :

{| class="wikitable"
|-
! scope="col"| Library
! scope="col"| Javadoc
|-
| Patrius
|[{{JavaDoc3.3}}/fr/cnes/sirius/patrius/assembly/models/package-summary.html Package fr.cnes.sirius.patrius.assembly.models]
|-
| Patrius
|[{{JavaDoc3.3}}/fr/cnes/sirius/patrius/assembly/properties/package-summary.html Package fr.cnes.sirius.patrius.assembly.properties]
|-
| Patrius
|[{{JavaDoc3.3}}/fr/cnes/sirius/patrius/groundstation/package-summary.html Package fr.cnes.sirius.patrius.groundstation]
|}

== Features Description ==
=== RF properties for a satellite antenna ===
These properties represent the features of the transmitter; they are used when calculating the RF link budget between the satellite antenna and a ground station.<br>
If <math>\theta</math> is the polar angle related to +Z axis of antenna frame [0, PI], and <math>\phi</math> is the azimuth angle from X to Y [0, 2PI] of the vector representing the direction of the ground station in the frame of the transmitter antenna, the properties are the following:
* <math>PT</math>: the amplifier output power [dB];

* <math>GT</math>: the antenna gain diagram. Gain is a function of <math>\theta</math>and <math>\phi</math> [dB];

* <math>r_{1}</math>: the factor of ellipticity. The factor of ellipticity is a function of <math>\theta</math> and <math>\phi</math> [dB];

* <math>L_{rt}</math>: the technological losses by the satellite transmitter [dB];

* <math>LT</math>: the losses between TX and antenna [dB];

* <math>R_{b}</math>: the bit rate for nominal mode [bps];

* <math>freq</math>: the emission frequency [Hz];

The class <code>RFAntennaProperty</code> contains all these parameters; the associated property type is <font color="green">'''RF'''</font>.

The value of the gain or the factor of ellipticity for given <math>\theta</math> and <math>\phi</math> are obtained by interpolation by spline of the input values; as this type of interpolation can not be perfomed for less than three values for <math>\theta</math> and <math>\phi</math>, an exception will be raised when the size of the <math>\theta</math> and/or <math>\phi</math> arrays is less than three; however, this does not apply if their size is equal to 1 (in that case the interpolation is not necessary).

=== RF model for a ground station antenna ===
These properties represent the RF antenna model for a ground station; this antenna is described by a topocentric frame (which coincides with the ground station frame) and the following parameters:

* <math>G/T</math>: the factor of merit of the ground antenna (Gain / noise temperature) [dB/K];

* <math>L_{rg}</math>: the technological losses by the ground antenna [dB];

* <math>r_{2}</math>: the factor of ellipticity, used to calculate the polarisation losses of the antenna [dB];

* <math>L_{23}</math>: the atmospherical losses (iono+tropo+rain) as function of the elevation [dB];

* <math>L_{4}</math>: the pointing losses as function of the elevation [dB];

* <math>PC</math>: the loss due to the combiner of the antenna [dB];

The class <code>RFStationModel</code> contains all these parameters.

=== Computation of the link budget ===
The link budget is the accounting of all of the gains and losses from the transmitter (the satellite), through the medium to the receiver (the ground station).<br>
To compute the link budget at a given date one must know the direction of the ground antenna in the satellite antenna frame and the transmitter and ground receiver RF parameters.<br>
The class <code>RFLinkBudgetModel</code> contains the algorithm to compute the link budget; a detector (<code>RFVisibilityDetector</code>) can also be used during the propagation in order to know when the link budget value exceeds a certain threshold value (see the [[User Manual 3.3 Events: ground stations and satellites|satellite/ground station event detectors page]]).

The RF link budget value is computed as follows:

* <math>KdB</math>: Boltzmann constant (in decibels);

* <math>distance</math>: distance between the spacecraft and the ground station;

* <math>dr_{1}</math>: factor of ellipticity of the satellite antenna (in the decimal numeral system) at the current polar angle and azimuth;

* <math>dr_{2}</math>: factor of ellipticity of the ground station antenna (in the decimal numeral system);

<math>L1 =- \left [  \frac{(dr_{1} + dr_{2})^{2}}{(1 + dr_{1}^{2})(1 + dr_{2}^{2})}\right ]_{decibel}</math>

<math>L = L1 + L23 + L4;</math>

<math>L_{fs} = \left [ \left (\frac{4 \Pi*distance*freq}{lightSpeed}\right )^{2}\right ]_{decibel}</math>

<math>RF_{link budget} = PT + GT- LT + G/T - KdB - L_{fs} - R_{b} - L_{rg} - L_{rt} - L - PC;</math>

== Getting Started ==
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== Contents ==
=== Interfaces ===
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=== Classes ===
{| class="wikitable"
|-
! scope="col"| Class
! scope="col"| Summary
! scope="col"| Javadoc
|-
|'''RFStationAntenna'''
|This class represents an RF antenna model for a ground station; it is used when calculating the RF link budget.
|[{{JavaDoc3.3}}/fr/cnes/sirius/patrius/groundstation/RFStationAntenna.html ...]
|-
|'''RFAntennaProperty'''
|This class represents an RF antenna property for a part of the assembly; it is used when calculating the RF link budget.
|[{{JavaDoc3.3}}/fr/cnes/sirius/patrius/assembly/properties/RFAntennaProperty.html ...]
|-
|'''RFLinkBudgetModel'''
|This class contains the algorithm to compute the link budget knowing the satellite transmitter and ground receiver parameters
|[{{JavaDoc3.3}}/fr/cnes/sirius/patrius/assembly/models/RFLinkBudgetModel.html ...]
|}

[[Category:User_Manual_3.3_Spacecraft]]

== Tutorials ==
=== Tutorial 1 ===
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=== Tutorial 2 ===
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== [[File:lightBulb.png]] Tips & Tricks ==
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