Open Stub Calculator
Calculate input reactance, equivalent capacitance/inductance, and physical length for a lossless open-circuited transmission line stub.
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Inputs
Live
Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
Z_in = -j Z₀ cot(βl) | X_in = -Z₀ / tan(θ) | C_eq = -1 / (ω X_in) | L_eq = X_in / ωThis formula is used to calculate antenna parameters for open stub calculator.
Overview
Open Stub helps you calculate design values for a transmission lines project from Characteristic Impedance (Z₀), Electrical Length (θ), Frequency (f), Velocity Factor (VF). Calculate input reactance, equivalent capacitance/inductance, and physical length for a lossless open-circuited transmission line stub. Use the result to make an informed first design decision before choosing hardware, setting dimensions, or evaluating the RF system in its final environment.
Input Guide
Enter Characteristic Impedance (Z₀), Electrical Length (θ), Frequency (f), Velocity Factor (VF) exactly in the units shown by this open stub. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Characteristic Impedance (Z₀) — use Ω.
- Electrical Length (θ) — use °.
- Frequency (f) — use MHz.
- Velocity Factor (VF).
Output Guide
The results describe the calculated open stub values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Open Stub uses Z_in = -j Z₀ cot(βl) | X_in = -Z₀ / tan(θ) | C_eq = -1 / (ω X_in) | L_eq = X_in / ω. Supply Characteristic Impedance (Z₀) (Ω), Electrical Length (θ) (°), Frequency (f) (MHz), Velocity Factor (VF) in the displayed units, then use the calculated values as the first engineering target for this transmission lines design or analysis.
Design Notes
This transmission lines calculation is based on Z_in = -j Z₀ cot(βl) | X_in = -Z₀ / tan(θ) | C_eq = -1 / (ω X_in) | L_eq = X_in / ω. Real-world accuracy depends on factors such as material properties, losses, mounting, nearby conductors, ground interaction, feed-line effects, and construction tolerance. Confirm the final system with measurement or simulation.
Build and Tuning Notes
Apply the open stub result as an initial target, then validate it in the intended installation. Keep the physical layout and feed arrangement consistent while testing, change one parameter at a time, and record the measured outcome before making another adjustment.
Frequently Asked Questions
What does the Open Stub calculate?
Calculate input reactance, equivalent capacitance/inductance, and physical length for a lossless open-circuited transmission line stub. The calculation provides an initial design value based on Characteristic Impedance (Z₀) (Ω), Electrical Length (θ) (°), Frequency (f) (MHz), Velocity Factor (VF).
Which inputs are needed for the Open Stub?
Enter Characteristic Impedance (Z₀) (Ω), Electrical Length (θ) (°), Frequency (f) (MHz), Velocity Factor (VF) using the displayed units. Each value directly affects the calculated result, so confirm the unit and operating conditions before running the calculation.
How accurate is this open stub?
It follows Z_in = -j Z₀ cot(βl) | X_in = -Z₀ / tan(θ) | C_eq = -1 / (ω X_in) | L_eq = X_in / ω. It is accurate for the formula assumptions, but installed performance can change because of materials, loss, environment, mounting, nearby objects, and measurement uncertainty.
What should I do after using the Open Stub?
Compare the result with the practical constraints of your transmission lines system, then validate the completed design with appropriate measurement equipment or simulation.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.