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.
Note: 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 miles.
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.