saturation flux density
The power flux density at the satellite's receive antenna aperture required to drive the transponder's travelling wave tube amplifier to its saturation point.
Full Definition
Saturation flux density (SFD) is a key transponder parameter that specifies the uplink signal strength, measured in dBW/m², needed to push the satellite's HPA to full (saturated) output power. Ground stations use SFD in conjunction with the link budget to calculate the required uplink EIRP. Setting EIRP too high relative to SFD causes the transponder to saturate, introducing intermodulation distortion; setting it too low results in reduced downlink EIRP and degraded C/N at receive terminals. Adjustable attenuators (flux density limiters) in some transponders modify the effective SFD. Editors will encounter SFD in ITU satellite network filings, transponder data sheets, and link budget tables; the unit expression 'dBW/m²' must be preserved accurately.
Usage
Usage note: The unit is dBW/m²—retain the superscript '2' and solidus; do not write 'dBW per m2' in running text without the superscript. Distinguish from PFD (power flux density), a general term of which SFD is a specific threshold value.
In Context
- "The transponder datasheet lists a saturation flux density of −87.5 dBW/m² at beam centre." — Transponder specification sheet
- "The uplink EIRP was calculated to drive the transponder to 3 dB output back-off from saturation flux density." — Link budget worksheet