ND SatCom SKYWAN IDU 7000, Manual

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76 Network Design and Engineering Guide 2010-10-26
Outdoor Unit and Satellite Link Design
Fundamentals of Link Budget Calculation
3.3 Fundamentals of Link Budget Calculation
This section is not supposed to be an extensive description of the techniques of link budget
calculations. For that purpose we refer to the available text book literature covering this subject.
The reader should however have a qualitative understanding how earth station and satellite pa-
rameters affect the quality of a satellite link. For that purpose we present here some fundamen-
tal considerations concerning the principles of link budget calculations.
The following picture presents a satellite link including the most important link parameters
which are subsequently explained:
Figure 3-4 Up- and Downlink Link Budget
Uplink and Downlink
The uplink part of a satellite connection represents the signal propagation from the transmitting
earth station to the satellite whereas the downlink part represents the signal path from the sat-
ellite to the receiving earth station.
Equivalent Isotropic Radiated Power (EIRP) and Antenna Gain
The signal intensity (signal power per area) of the earth station or satellite signal in the main
beam direction of the antenna is determined by the output power of the amplifier P
amp
and the
focusing effect of the parabolic antenna which is represented by the antenna gain G
ant
. The
combination of both quantities is called the Equivalent Isotropic Radiated Power (EIRP) of the
station. In logarithmic quantities this is given by:
In this formula L
Ins
is the signal loss which occurs in the feed system of the antenna after the
amplifier’s wave guide flange. The antenna gain is proportional to the square of the antenna’s
diameter and the carrier frequency. Typical transmit antenna gains for a 2.4m parabolic anten-
na are 42 dBi for C-Band and 49 dBi for Ku-Band.
EIRP[dBW] = P
amp
[dBW] + G
ant
[dBi] – L
Ins
[dB]