Collinear Antenna Calculator
Calculate wavelength, element lengths, total antenna length, and estimated gain for a collinear antenna.
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Inputs
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Math
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Enter parameters and click Calculate to view results
Formula & Theory
λ = 300 / f, Half-wave = (λ × VF) / 2, Quarter-wave = (λ × VF) / 4, Gain ≈ 2.15 + (10 × log₁₀(N))This formula is used to calculate antenna parameters for collinear antenna calculator.
Overview
The Collinear Antenna Calculator computes physical element lengths, phasing section dimensions, total stack height, and estimated omnidirectional gain for collinear antenna arrays. Popular in VHF/UHF amateur radio repeaters, ADS-B receivers, and cellular base stations, collinear antennas stack multiple half-wave dipole elements vertically to flatten radiation toward the horizon and boost gain.
Input Guide
Enter Frequency, Number of Half-wave Elements, Velocity Factor exactly in the units shown by this collinear antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Frequency — use MHz.
- Number of Half-wave Elements.
- Velocity Factor.
Output Guide
The results describe the calculated collinear 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 Collinear Antenna uses λ = 300 / f, Half-wave = (λ × VF) / 2, Quarter-wave = (λ × VF) / 4, Gain ≈ 2.15 + (10 × log₁₀(N)). Supply Frequency (MHz), Number of Half-wave Elements, Velocity Factor 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 collinear array aligns multiple $\lambda/2$ radiating elements vertically in a single line. To ensure currents in adjacent elements flow in phase rather than canceling each other out, phasing sections—such as quarter-wave coaxial stubs, phasing coils, or inverted coaxial delay lines—are inserted between active elements. Stacking $N$ elements narrows the elevation beamwidth toward the horizon, scaling ideal omnidirectional gain according to $G \approx 2.15 + 10 \log_{10}(N)\text{ dBi}$.
Build and Tuning Notes
When constructing coaxial collinear (Coco) antennas from RG-58 or RG-8X, strictly apply the coaxial cable velocity factor ($VF \approx 0.66\text{ to }0.82$) when calculating element cut lengths. Encase the fragile coaxial stack inside a rigid fiberglass radome for weather protection and structural stability. Tune and verify the feedpoint VSWR ($< 1.5:1$) across the target operating frequency using a Vector Network Analyzer (VNA).
Frequently Asked Questions
What is a Collinear Antenna and how does it increase gain?
A collinear antenna stacks multiple half-wave radiator elements vertically in a straight line. By forcing currents across all elements to oscillate in-phase, it compresses the vertical radiation pattern toward the horizon, providing high omnidirectional gain without directivity bias.
Why are phasing sections required between collinear elements?
Without phasing stubs or delay lines, current phase reverses every half-wavelength along a continuous wire, causing adjacent sections to cancel out each other's far-field radiation. Phasing sections delay the signal by $180^{\circ}$, maintaining in-phase currents across all elements.
How does coaxial cable Velocity Factor affect a Coaxial Collinear (Coco) antenna?
In a coaxial collinear array, the RF signal travels inside the coaxial dielectric insulator, where velocity is reduced ($VF = 1/\sqrt{\epsilon_r}$). Physical element lengths must be multiplied by $VF$ to achieve true electrical half-wave resonance.
What happens to elevation beamwidth as more elements are added?
Adding more stacked elements narrows the vertical (elevation) half-power beamwidth, focusing RF energy tighter to the horizontal plane. Extremely tall collinear arrays require careful mast alignment to prevent overshooting nearby receivers on ground level.
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.