Biconical Antenna Calculator
Calculate wavelength, characteristic impedance and lowest operating frequency of a biconical antenna.
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Inputs
Live
Math
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Enter parameters and click Calculate to view results
Formula & Theory
λ = 300/f, Z₀ = 120 × ln(cot(α/4)), fmin = 75/LThis formula is used to calculate antenna parameters for biconical antenna calculator.
Overview
The Biconical Antenna Calculator computes fundamental physical and electrical design parameters for broadband biconical antennas. Instantly calculate characteristic input impedance ($Z_0$), operating wavelength ($lambda$), and lower cut-off frequency ($f_{\text{min}}$) based on cone length ($L$) and flare angle ($\alpha$).
Input Guide
Enter Operating Frequency, Cone Length, Cone Angle exactly in the units shown by this biconical antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Operating Frequency — use MHz.
- Cone Length — use m.
- Cone Angle — use °.
Output Guide
The results describe the calculated biconical 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 Biconical Antenna uses λ = 300/f, Z₀ = 120 × ln(cot(α/4)), fmin = 75/L. Supply Operating Frequency (MHz), Cone Length (m), Cone Angle (°) 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 biconical antenna consists of two conductive cones sharing a common apex. Because its boundary conditions scale geometrically with frequency, it acts as a broadband transmission line with a frequency-independent characteristic impedance given by $Z_0 = 120 \ln(\cot(\alpha/4))\;\Omega$. The minimum operating frequency ($f_{\text{min}} \approx 75/L\text{ MHz}$) is reached when cone slant length $L$ equals approximately a quarter-wavelength ($0.25\lambda$).
Build and Tuning Notes
Biconical antennas are widely used as omnidirectional broadband standards for EMC/EMI compliance testing (typically $30\text{--}300\text{ MHz}$). Solid sheet metal cones can be approximated using a wire-cage structure consisting of 6 to 12 skeletal rods per cone without significant performance loss. Use a high-quality 1:1 or 4:1 broad-spectrum balun at the apex feedpoint to match the unbalanced coaxial line to the balanced biconical elements.
Frequently Asked Questions
Why are Biconical Antennas popular in EMC/EMI testing?
Biconical antennas offer an exceptionally wide impedance bandwidth and stable omnidirectional radiation pattern, allowing engineers to measure radiated emissions across a broad spectrum without changing antennas.
How does Cone Angle (α) influence Characteristic Impedance?
Increasing the cone flare angle ($\alpha$) lowers the characteristic impedance ($Z_0$). For instance, an angle of around $60^{\circ}$ yields a characteristic impedance close to $120\;\Omega$, whereas wider angles bring $Z_0$ closer to $50\;\Omega$.
How is the minimum operating frequency (fmin) determined?
The lowest usable frequency occurs when the slant length ($L$) of each cone is approximately $\lambda/4$. The cut-off frequency formula is $f_{\text{min}} \approx 75 / L$ (where $L$ is in meters and $f$ is in MHz).
Can skeletal wire rods replace solid metal cones?
Yes. Replacing solid sheet metal cones with a skeletal cage of wire elements (usually 8 to 12 rods evenly spaced radially) significantly reduces wind load and physical weight while maintaining identical RF broadband behavior.
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.