Dipole Antenna Calculator
Calculate wavelength, practical dipole dimensions, feed-point impedance, gain, and recommended mounting height.
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Inputs
Live
Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
Wavelength = 300/f, Total Length ≈ 143/f, Each Arm ≈ 71.5/fThis formula is used to calculate antenna parameters for dipole antenna calculator.
Overview
The Dipole Antenna Calculator computes resonant half-wave dipole dimensions, quarter-wave individual arm lengths, nominal feed-point impedance, directional gain ($2.15\text{ dBi}$), and recommended ground clearance. The half-wave dipole is the fundamental building block for many complex RF antennas and serves as a primary reference standard in radio engineering.
Input Guide
Enter Frequency exactly in the units shown by this dipole antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Frequency — use MHz.
Output Guide
The results describe the calculated dipole 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 Dipole Antenna uses Wavelength = 300/f, Total Length ≈ 143/f, Each Arm ≈ 71.5/f. Supply Frequency (MHz) in the displayed units, then use the calculated values as the first engineering target for this dipole antennas design or analysis.
Design Notes
In free space, an ideal thin-wire half-wave dipole measures $\lambda/2$ in length. However, because real conductors exhibit finite thickness and tip end-effects, RF wave velocity along wire elements is reduced by a velocity factor ($VF \approx 0.95$). Practical total dipole length is calculated using the standard empirical formula $L_{\text{total}} = 143 / f_{\text{MHz}}\text{ meters}$ ($468 / f_{\text{MHz}}\text{ feet}$). In free space, its theoretical center feed-point impedance is approximately $73\;\Omega$, which matches well with standard $50\;\Omega$ or $75\;\Omega$ coaxial feedlines.
Build and Tuning Notes
To achieve optimal low-angle radiation and prevent ground-reflection impedance detuning, elevate the horizontal dipole at least one-half wavelength ($lambda/2$) above the ground. Feed the balanced dipole elements through a $1:1$ current balun to isolate the outer coaxial shield and prevent feedline common-mode radiation. Trim each dipole arm symmetrically in small increments ($1\text{--}2\text{ cm}$) while monitoring $S_{11}$ return loss or VSWR ($< 1.5:1$) using a Vector Network Analyzer (VNA).
Frequently Asked Questions
How do I calculate the physical length of a Half-Wave Dipole antenna?
Total physical length in meters is estimated using $L_{\text{total}} = 143 / f_{\text{MHz}}$. Each individual arm (quarter-wave section) measures half of that: $L_{\text{arm}} = 71.5 / f_{\text{MHz}}$ meters.
Why is a 1:1 Balun required at the feedpoint of a dipole antenna?
A dipole is a balanced antenna, whereas coaxial cable is an unbalanced feedline. Connecting coaxial cable directly to a dipole induces RF common-mode currents on the outer shield, causing line radiation, pattern distortion, and local noise pickup. A $1:1$ current balun converts unbalanced coax to balanced dipole terminals.
What is the typical feed-point impedance of a half-wave dipole?
In free space at resonance, a half-wave dipole has a pure resistive feed-point impedance of approximately $73\;\Omega$. Placing the dipole close to lossy ground lowers this impedance toward $50\;\Omega$.
How does antenna mounting height affect dipole performance?
Mounting a dipole at a height of $\lambda/2$ or higher minimizes ground interaction, restores its characteristic $73\;\Omega$ input impedance, and focuses radiated energy at lower elevation angles suitable for long-distance (DX) communication.
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.