What Is the Coaxial Cable Cutoff Frequency & Attenuation Calculator?
A coaxial cable consists of an inner cylindrical conductor surrounded by a concentric tubular conducting shield separated by an insulating dielectric.
It supports TEM wave propagation without lower frequency cutoff, shielding the internal signal from external electromagnetic interference.
How Does the Coaxial Cable Cutoff Frequency & Attenuation Calculator Work?
Characteristic impedance Z₀ depends purely on the ratio of diameters D/d and dielectric constant εr.
At very high frequencies, when the mean circumference π(D+d)/2 approaches the guided wavelength, non-TEM waveguide modes (TE₁₁) propagate, causing multimode distortion.
Losses comprise conductor skin effect resistance (scaling as √f) and dielectric molecular relaxation loss (scaling as f).
Coaxial Cable Cutoff Frequency & Attenuation Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Evaluates standard logarithmic coaxial impedance, higher-order modal cutoff threshold, and combined ohmic skin and dielectric dissipation losses.
How to Use the Coaxial Cable Cutoff Frequency & Attenuation Calculator
- Input the dimensions of the core and shield.
- Specify the dielectric material properties and operating frequency.
- Verify that the operating frequency remains well below the TE₁₁ cutoff frequency (typically < 0.9·fc).
Step-by-Step Example Calculation
50-Ohm PTFE Semi-Rigid Coax at 2.4 GHz
Input Values:
Understanding Your Result
Z₀ indicates the characteristic impedance (typically 50 Ω for RF, 75 Ω for broadcast video).
Total attenuation in dB/m and dB/100ft gives signal power insertion loss.
Factors That Affect the Result
- Diameter ratio: For 50 Ω with PTFE (εr=2.1), D/d must be approximately 3.3.
- Cable diameter: Larger diameter cables have lower attenuation but lower cutoff frequencies.
When Should You Use This Calculator?
- Sizing RF interconnect cables for transmitters, antennas, and test equipment.
- Determining link budget margins in telecommunications installations.
Assumptions & Limitations
- Assumes concentric conductors without eccentric displacement or braiding leakage.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard IEEE coaxial cable analytical equations.