Cage Antenna Calculator
Calculate wavelength, half-wave and quarter-wave dimensions, and recommended cage dimensions for a cage antenna.
2
Inputs
Live
Math
3
Related
Enter parameters and click Calculate to view results
Formula & Theory
λ = 300 / f, Half-wave Length = (λ × VF) / 2, Quarter-wave Length = (λ × VF) / 4This formula is used to calculate antenna parameters for cage antenna calculator.
Overview
The Cage Antenna Calculator computes physical element lengths, cage diameter, wire spacing, and bandwidth expansion factors for cage dipole and monopole antennas. Cage antennas simulate a thick cylindrical conductor using a ring of parallel wires, significantly broadening SWR impedance bandwidth on HF and VHF bands.
Input Guide
Enter Frequency, Velocity Factor exactly in the units shown by this cage antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Frequency — use MHz.
- Velocity Factor.
Output Guide
The results describe the calculated cage antenna 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 Cage Antenna uses λ = 300 / f, Half-wave Length = (λ × VF) / 2, Quarter-wave Length = (λ × VF) / 4. Supply Frequency (MHz), Velocity Factor in the displayed units, then use the calculated values as the first engineering target for this specific antenna types design or analysis.
Design Notes
A cage antenna replaces a single thin wire conductor with multiple parallel wires arranged in a cylinder using circular spreaders. This increases the effective conductor radius ($r_{\text{eff}}$), which lowers the antenna radiation Quality Factor ($Q$) and flattens the input reactance curve. The resulting broadband behavior allows the antenna to cover full amateur radio bands (such as 80m, 40m, or 160m) without requiring an antenna tuner (ATU).
Build and Tuning Notes
Construct the cage framework using 4 to 8 parallel copper or copper-clad steel wires held in shape with lightweight, UV-resistant non-conductive ring spreaders (e.g., PVC or fiberglass rings). Connect all parallel wires together at the feedpoint and element ends. Install a $1:1$ or $4:1$ current balun at the feedpoint to prevent common-mode currents and maintain a symmetrical radiation pattern.
Frequently Asked Questions
What is a Cage Antenna and why is it used?
A cage antenna is a dipole or monopole variant that uses multiple parallel wires arranged in a cylindrical cage layout. It acts as an electrically thick conductor, providing up to 2–3 times broader SWR bandwidth than a thin single-wire dipole.
How does cage diameter affect antenna bandwidth?
Increasing the cage cylinder diameter (typically around $1\%$ of operating wavelength) increases equivalent conductor radius, lowering the antenna's Quality Factor ($Q$) and providing a much flatter SWR response across the band.
How many parallel wires are needed to form a cage antenna?
Most practical cage antennas use between 4 and 8 evenly spaced wires. Using 6 wires is widely considered the optimal balance between electrical performance, mechanical weight, and wind load.
Does a cage dipole require a different tuning length than a wire dipole?
Yes. Because of the increased equivalent diameter and higher tip capacitance, a cage dipole is physically slightly shorter than a thin-wire dipole for the same resonant frequency ($VF \approx 0.92\text{--}0.95$).
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.