Generic Ka band link Budget : Return link from VSAT remote to the Teleport

This is a generic simulation of a satellite with Ka band spot beams, with multiple inbound carriers from the VSAT remotes..

The default figures refer to a 4MHz wide carrier from a remote site to the hub.

Adjust all parameters to match your particular satellite and circumstances. You need to know satellite G/T, PFDsat and EIRP for your two sites. Coverage maps for all three parameters are needed. You also need to know the transponder operating point for multi-carrier operation (back off in and back off out).

Example satellite design (per carrier, 50 MHz TDM from hub, 5 MHz TDMA from remotes)

Direction	Frequency	Antenna dia	Gain (on axis)	Beamwidth (-3 dB)	Watts	EIRP
Hub to satellite	29.5	6.1	63
Satellite to remotes	19.7	1	41	1	100	60
Remotes to satellite	30	1.2	49		4	55
Satellite to hub	19.2	1	44	1

(per carrier, 50 MHz TDM from hub, 5 MHz TDMA from remotes)

Do the following manual preparatory calculations:

Uplink:
Input PFDsat= -85 dBW/m2 at beam edge (-3 dB) per transponder
Back off in = -4.5 dB
5 MHz share of 300 MHz transponder = -17.8 dB
Input PFD for our carrier = -85 -4.5 -17.8 = -107.3 dBW/m2
Adjust your uplink dish diameter and Watts to achieve this.

Downlink:
Transponder saturated EIRP = +59 dBW beam edge (-3dB) per transponder
Back off out = -2.5 dB
5 MHz share of 300 MHz transponder = -17.8 dB
EIRP down for our carrier = 38.7 dBW
Adjust the transponder 'gain' figure to achieve this.

Uplink:
Uplink frequency GHz
Uplink antenna diameter m	Try 0.7m, 1m, 1.2m, 1.8m
Uplink antenna transmit gain dBi
Uplink antenna, power at the feed W	Try 1W, 3W, 5W and 10W
Uplink EIRP dBW
Range (35778 - 41679) km
Uplink path loss dB
Uplink pfd at satellite dBW/m^2
Bandwidth Hz
Satellite uplink G/T dB/K
Uplink C/N dB
Satellite:
Transponder "gain" input PFD to output EIRP	Try 140, 145, 150
Downlink:
Downlink frequency GHz
Downlink receive antenna diameter m	Try 6m, 9m, 11m, 13m
Downlink system noise temperature(antenna+LNA) K
Downlink receive antenna gain dBi
Downlink receive antenna G/T dB/K
Downlink satellite EIRP dBW
Downlink path loss dB
Downlink C/N dB
Summary link budget:
Uplink C/interference dB
Uplink C/N dB
Satellite C/intermod dB
Downlink C/N dB
Downlink C/interference dB
Total link C/N dB

Instead of using a big teleport hub dish, try the effect of reducing the hub size to say 1.8m diameter to evaluate possible low bit rate point to point VSAT to VSAT links.

You now need to do the outlink link budget from the hub to the remote VSAT sites. The hub will need to transmit several very large carriers. To avoid impossibly large power amplifiers it will be necessary to have a large dish. Adjust the dish size and earth station HPA size to minimise overall capital and running costs.

Any problems or comments please e-mail me

Last Revision: 26 July 2018, 31 July 2024, 2025-03-02.