A finite amount of time is required for a signal to travel from one place to another. In a vacuum, electromagnetic
energy travels at 2.9979*105 km/s (186,282 mi/s). The following equation holds for signal propagation time in a vacuum
(and in the air),
where the relative dielectric constant (εr) is 1. In keeping with a radar theme, 'R' is used for
range rather than the more common 'd' for distance. Be sure to keep dimensional units consistent across all values.
If a radar system is being evaluated where a round trip out and back needs to be accounted for, then double
the range figure. A "radar mile," which is a nautical mile out and a nautical mile back, is 12.36 μs.
Note: When using these formulas, be sure to keep dimensional units consistent; i.e.,
do not mix kHz with MHz, mm with inches, etc. It is safer to use base units (e.g., Hz, m)
for calculation, then convert result to desired units.
Only enter values in the yellow cells or risk overwriting formulas!
Two charts of propagation time vs. distance are provided below - one for units of km and one for units of
Here is information on Doppler, radar equation and path loss.
A 1-Way and 2-Way Path Loss Calculator is included in
RF Cafe Calculator Workbook for FREE.