Microwave link budget
35 GHz Power Beaming Link Budget
How much DC power lands at the rectenna after travelling through free space? Friis equation, all loss terms exposed.
// parabolic-dish gain, free-space path loss, EIRP, rectification efficiency. far-field assumption; near-field warning surfaces automatically when violated.
How this model works & what it omits
Microwave power transmission is a 50-year-old idea recently dragged back into engineering relevance by orbital power. The basic physics is short: a transmitter radiates a beam of microwave energy through a directional antenna, a receiver (a rectenna — rectifying antenna) captures the beam, rectifies it back to DC, and delivers power to a load. The arithmetic between Tx and DC is the link budget.
This tool implements the Friis transmission equation with explicit terms for parabolic-dish gain (G = η(πD/λ)²), free-space path loss (FSPL = (4πR/λ)²), pointing loss, polarisation mismatch, and atmospheric absorption. EIRP is Tx-power times Tx-gain; received signal is EIRP times Rx-gain over FSPL, minus all the loss terms; DC delivered is received signal times rectenna conversion efficiency.
Defaults model HawkLogic's orbital-power case: a 1 kW transmitter, 5 m dishes at both ends, 1000 km range (a generator at ~500 km beaming up to a collector at ~1500 km), 35 GHz Ka-band. Three preset scenarios cover orbital-to-orbital, short-range densification, and ground-to-LEO with realistic atmospheric loss. Wavelength and FSPL update live as you change inputs.
Two warnings surface automatically when relevant: the Fraunhofer near-field boundary (Friis is invalid for ranges shorter than 2D²/λ), and beam spill when the Tx beam diameter at the Rx exceeds the Rx aperture diameter. Both are real failure modes for the orbital-power link design.
What this tool does not model: rain attenuation at 35 GHz (significant for ground-to-space links in storm cells; ITU-R P.838), beam steering and tracking dynamics, sidelobe interference, regulatory power-density limits on the ground, and non-uniform aperture illumination. For flight design, defer to ITU-R P.676 / P.838, the SPS-ALPHA reference architecture (NASA 2012), and Brown's MTT history (1984).
// try a scenario, then dial the loss budget for your link.
Frequency + range
// 35 GHz Ka-band is the orbital-power default; tunable across 0.1-300 GHz.
Transmitter
// parabolic dish; gain = η × (πD/λ)².
Receiver + rectenna
// DC efficiency captures Schottky rectification + matching losses.
Loss budget
// margins; sum into the link equation in dB.
Link budget
// 35 GHz · 1,000 km · far-field
63.7 dBi
Tx antenna gain
63.7 dBi
Rx antenna gain
93.7 dBW
EIRP
183.3 dB
Free-space path loss
-26.7 dBW
Received signal
2.1 mW
Rx power (linear)
1.5 mW
DC delivered
0.000%
End-to-end η
4.18 km
Beam diameter at Rx
187.3 µW/m²
Isotropic power density
5.84 km
Near-field boundary
// beam spill
The Tx beam diameter at this range (4.18 km) is larger than the Rx aperture. Most of the radiated power misses the rectenna; the link calculation here uses the Friis equation with the configured Rx gain, which captures this loss implicitly through the smaller Rx capture area. To recover more power, increase Tx dish diameter (tighter beam) or move the Rx closer.
// shareable URL encodes every input. no backend.
// ai-generated breakdown of what these numbers mean — with diagrams.
References
- // Friis, H. T. (1946). A note on a simple transmission formula. Proc. IRE 34, 254-256.
- // Brown, W. C. (1984). The history of power transmission by radio waves. IEEE Trans. MTT 32(9), 1230-1242.
- // Mankins, J. C. (2012). SPS-ALPHA: The First Practical Solar Power Satellite via Arbitrarily Large Phased Array. NASA NIAC report.
- // ITU-R Recommendation P.676 — atmospheric gaseous absorption.
- // ITU-R Recommendation P.838 — rain attenuation models.
- // For the power-budget context, see the Spacecraft Power Budget tool's beamed-mode toggle.