What Is the Rectangular Waveguide Cutoff Frequency & Propagation Calculator?
A rectangular waveguide is a hollow metallic pipe of cross section a × b that guides high-frequency electromagnetic waves via repeated internal reflections.
Unlike TEM coaxial cables, waveguides cannot propagate DC or frequencies below the cutoff frequency fc; each mode behaves as a high-pass filter.
How Does the Rectangular Waveguide Cutoff Frequency & Propagation Calculator Work?
The dominant mode with the lowest cutoff frequency is TE₁₀, where the electric field is polarized vertically across the narrow wall b.
Inside the waveguide, waves travel at an angle, making phase velocity vp > c and guide wavelength λg > λ₀, while information travels at group velocity vg < c.
Rectangular Waveguide Cutoff Frequency & Propagation Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Determines the modal cutoff boundary and the dispersive phase/group velocities inside hollow metallic wave guides.
How to Use the Rectangular Waveguide Cutoff Frequency & Propagation Calculator
- Input the broad and narrow wall dimensions (e.g. standard EIA WR-numbers).
- Enter the operating frequency to check if it lies in the clean single-mode operating band.
- Read the guide wavelength λg for component impedance matching.
Step-by-Step Example Calculation
WR-90 X-Band Waveguide at 10.0 GHz
Input Values:
Understanding Your Result
If operating frequency is below fc₁₀, the wave is evanescent and attenuates exponentially.
The recommended single-mode operating window spans 1.25·fc₁₀ to 1.90·fc₁₀ to prevent multi-mode dispersion.
Factors That Affect the Result
- Broad dimension a sets the fundamental TE₁₀ cutoff.
- Narrow dimension b is typically a/2 to maximize single-mode bandwidth and prevent premature TE₀₁ / TE₁₁ excitation.
When Should You Use This Calculator?
- Designing radar transmitter feeds, horn antennas, and satellite communications links.
- Verifying WR-standard dimensions (WR-284, WR-90, WR-42).
Assumptions & Limitations
- Assumes perfectly conducting smooth walls and uniform dielectric filling.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Exact Maxwell equation analytical solutions.