Cantenna Design Calculator
Enter your target frequency and (optionally) your can's inner diameter. The calculator returns practical dimensions for a basic circular waveguide cantenna build.
Assumptions: air-filled can, dominant TE11 mode, standard quarter-wave probe feed.
What this cantenna calculator does
A cantenna is a simple directional antenna made from a cylindrical metal can acting as a waveguide. If the dimensions are close to the right values, performance can be surprisingly good for Wi-Fi and other microwave experiments.
This calculator helps you size the most important geometry:
- Free-space wavelength at your chosen frequency
- Single-mode diameter range for circular waveguide operation
- Cutoff frequencies for TE11 and TE21 modes
- Quarter-wave probe length
- Probe placement from the back wall (quarter guide wavelength)
- Practical can length targets
How the math works
1) Wavelength in free space
The basic RF wavelength is:
λ = c / f
where c is the speed of light and f is frequency.
2) TE11 cutoff for a circular can
The dominant circular waveguide mode is TE11. Its cutoff frequency is:
fc,11 = (1.8412 × c) / (π × D)
For propagation, your operating frequency must be above this value.
3) Staying near single-mode behavior
The next important mode (TE21) has:
fc,21 = (3.0542 × c) / (π × D)
For cleaner pattern behavior, many builders aim to keep operating frequency below TE21 cutoff. This calculator shows the resulting diameter window.
4) Feed dimensions
- Probe length: approximately
λ/4 - Probe offset from back wall: approximately
λg/4
Guide wavelength is:
λg = λ / sqrt(1 - (fc,11/f)^2)
Practical build advice
- Measure inner diameter carefully. Wall thickness and rolled lips can change effective dimensions.
- Keep the N-type connector and probe mechanically rigid to preserve tuning.
- Smooth interior surfaces generally give more predictable results.
- If your can diameter is near the upper single-mode limit, pattern quality may degrade as higher modes appear.
- Tune by small probe length and position adjustments while watching RSSI/SNR.
Example use case
At 2.4 GHz, a typical cantenna often lands in roughly the 75–120 mm diameter range, with many hobby builds around 80–100 mm. This is why common food cans are frequently used for DIY Wi-Fi experiments.
At 5.8 GHz, dimensions get much smaller and mechanical precision matters more. Small drilling errors become a larger fraction of wavelength, so careful construction has a bigger impact.
Limitations
This tool is for first-pass design, not full EM simulation. Real performance depends on connector quality, probe diameter, material conductivity, mounting alignment, and nearby objects. For critical links, validate with antenna measurements or simulation software.