Transmission Line Calculator
Calculate ideal transmission-line wavelength, electrical length, phase shift, propagation delay and velocity factor from frequency, physical length and phase.
RF-009 covers fundamental line propagation only. It does not calculate cable loss, Smith chart impedance transformation, microstrip geometry, stripline geometry or matching networks.
Engineering tool
Transmission Line Calculator
Calculate transmission-line wavelength, electrical length, phase shift, propagation delay, physical length and velocity factor.
Result console
- Wavelength
- 2.997925 m
- Physical Length
- 1 m
- Physical Length mm
- 1,000mm
- Electrical Length
- 120.083074°
- Phase Shift
- 120.083074° modulo 360
- Propagation Delay
- 3.335641 ns
- Propagation Velocity
- 299,792,458 m/s
- Velocity Factor Used
- 1
- Formula Used
- λ = c × VF / f; θ = 360° × Length / λ
This transmission line calculator uses an ideal lossless propagation model.
Formula reference
Transmission Line Formulas
Electrical length depends on frequency, physical length and velocity factor.
λ = c × VF / fθ = 360° × Length / λLength = θ / 360° × λt = Length / (c × VF)f = (θ / 360°) × (c × VF) / LengthVariable definitions
- λ
- wavelength in the selected line medium
- c
- speed of light, 299,792,458 m/s
- VF
- velocity factor
- f
- frequency
- θ
- electrical length or phase shift in degrees
- Length
- physical line length
- t
- propagation delay
Worked Examples
100 MHz, 1 m, VF = 1
Wavelength is 2.9979 m, so a 1 m line is about 120.08 electrical degrees with 3.34 ns delay.
433 MHz quarter-wave
At VF = 1, 90 degrees corresponds to about 173.09 mm.
915 MHz half-wave
At VF = 1, 180 degrees corresponds to about 163.82 mm.
2.4 GHz, 100 mm
At VF = 1, a 100 mm line is about 288.20 electrical degrees.
5.8 GHz, VF = 0.66
At 10 mm physical length, electrical length is about 105.53 degrees.
Propagation delay, 10 m, VF = 0.66
Delay is about 50.54 ns.
Electrical length 90 degrees
Length = 90 / 360 × λ, so the physical line is one quarter wavelength in the selected medium.
Compare VF = 1 vs VF = 0.8
At the same frequency, VF = 0.8 produces 80% of the wavelength and more delay per meter.
Length to frequency
A 0.25 m line that is 90 degrees with VF = 1 corresponds to about 299.79 MHz.
Velocity factor from measured phase
If 0.5996 m is 90 degrees at 100 MHz, calculated VF is about 0.8.
Engineering Notes
- Electrical length is not the same as physical length.
- Velocity factor determines propagation speed inside the line.
- Higher frequency means greater electrical length for the same physical line.
- A quarter-wave line is 90 electrical degrees.
- A half-wave line is 180 electrical degrees.
- A full-wave line is 360 electrical degrees.
- Different cable dielectrics and PCB transmission lines have different velocity factors.
- Characteristic impedance matters for reflections, but this calculator does not synthesize geometry.
- Standing waves appear when the line is not terminated in its characteristic impedance.
- Use measured cable or PCB data for precise RF timing and phase work.
Common Mistakes
- Treating physical length as electrical length.
- Ignoring velocity factor.
- Entering MHz as Hz or millimeters as meters.
- Confusing phase shift with propagation delay.
- Assuming the same cable length has the same phase at every frequency.
- Using free-space wavelength for coax or PCB line calculations.
- Assuming characteristic impedance is calculated from length alone.
- Using ideal delay when dispersion, connectors or layout discontinuities matter.
Support reference
FAQ
What is electrical length?
Electrical length is the phase length of a physical transmission line at a given frequency. It is usually expressed in degrees or wavelengths.
What is transmission line phase?
Transmission line phase is the signal phase shift caused by propagation along the line. A quarter-wave line is 90 degrees and a half-wave line is 180 degrees.
How do I calculate propagation delay?
Use t = Length / (c × VF), where c is the speed of light and VF is the velocity factor of the line.
Why does velocity factor matter?
Velocity factor reduces propagation speed in a dielectric or cable, shortening wavelength and increasing delay compared with free space.
How do I calculate quarter-wave length?
Calculate wavelength with λ = c × VF / f, then divide by four. A quarter-wave section is 90 electrical degrees.
Does cable type change electrical length?
Yes. Different cable dielectrics and transmission line structures have different velocity factors, so the same physical length can have different electrical lengths.
What is characteristic impedance?
Characteristic impedance is the impedance a long uniform transmission line presents to a traveling wave. This calculator references it conceptually but does not synthesize line geometry.
Why is electrical length frequency dependent?
For a fixed physical length, wavelength decreases as frequency rises, so the same line occupies more degrees at higher frequency.
Does this calculator include cable loss?
No. RF-009 models ideal propagation length, phase and delay. Cable loss belongs to a dedicated coaxial cable loss calculator.
Can this replace a Smith chart?
No. This calculator does not solve complex input impedance or matching. It is for fundamental line length, delay and phase calculations.
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Future Engineering Guide Topics
Transmission Line Basics
In_DevelopmentElectrical vs Physical Length
In_DevelopmentVelocity Factor Explained
In_DevelopmentPropagation Delay
In_DevelopmentDisclaimer
This calculator provides ideal lossless transmission-line estimates. Final RF designs should use measured cable, PCB, connector, termination and instrument data.