Log Periodic Dipole Array Calculator
Calculate LPDA bandwidth ratio, element dimensions, estimated element count, boom length, and gain.
3
Inputs
Live
Math
3
Related
Enter parameters and click Calculate to view results
Formula & Theory
N ≈ 1 + log(BW Ratio)/log(1/τ)This formula is used to calculate antenna parameters for log periodic dipole array calculator.
Overview
The Log Periodic Dipole Array Calculator helps RF engineers, antenna designers, broadcast engineers, amateur radio operators, EMC specialists, researchers, and students design broadband Log Periodic Dipole Arrays (LPDAs). By entering the lowest operating frequency, highest operating frequency, and tau (τ) ratio, the calculator determines bandwidth ratio, wavelength limits, longest and shortest dipole element lengths, estimated number of elements, boom length, and expected antenna gain. It is widely used for HF, VHF, UHF, television broadcasting, spectrum monitoring, EMC testing, military communication, direction finding, and broadband wireless communication systems.
Input Guide
Enter Lowest Frequency, Highest Frequency, Tau Ratio exactly in the units shown by this log periodic dipole array. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Lowest Frequency — use MHz.
- Highest Frequency — use MHz.
- Tau Ratio.
Output Guide
The results describe the calculated log periodic dipole array 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 Log Periodic Dipole Array uses N ≈ 1 + log(BW Ratio)/log(1/τ). Supply Lowest Frequency (MHz), Highest Frequency (MHz), Tau Ratio in the displayed units, then use the calculated values as the first engineering target for this directional antennas design or analysis.
Design Notes
A Log Periodic Dipole Array (LPDA) is a frequency-independent directional antenna capable of maintaining relatively constant impedance, gain, and radiation characteristics across a very wide frequency range. The antenna consists of multiple dipole elements whose lengths and spacing decrease logarithmically according to the tau (τ) ratio. Lower tau values generally increase gain and directivity but require additional elements and a longer boom, while higher tau values reduce antenna size at the expense of bandwidth and gain. The bandwidth ratio determines the required frequency coverage, which directly influences the number of active dipole elements. Practical antenna performance also depends on the sigma (σ) spacing factor, conductor diameter, boom construction, balun performance, feed-line balance, mechanical accuracy, environmental conditions, and installation height.
Build and Tuning Notes
Use the calculated element dimensions and estimated boom length as the initial design values when constructing an LPDA. Position each dipole according to the required logarithmic progression while maintaining accurate alignment and spacing. Install a high-quality broadband balun or balanced feed system to minimise feed-line radiation and maintain impedance stability across the operating frequency range. After construction, verify return loss (S11), VSWR, impedance, gain, front-to-back ratio, beamwidth, and radiation pattern using a vector network analyser (VNA) and anechoic chamber measurements. Electromagnetic simulation using CST Studio Suite, Ansys HFSS, FEKO, NEC, or Altair Feko is recommended before fabrication to optimise broadband performance and minimise design iterations.
Frequently Asked Questions
What is a Log Periodic Dipole Array (LPDA)?
A Log Periodic Dipole Array is a broadband directional antenna composed of multiple dipole elements whose lengths and spacing follow a logarithmic progression. It provides consistent gain, impedance, and radiation characteristics across a wide frequency range.
How is the number of LPDA elements determined?
The required number of elements depends on the desired bandwidth ratio and the selected tau (τ) ratio. Wider bandwidths generally require more dipole elements and a longer boom structure.
What is the tau (τ) ratio in an LPDA?
The tau ratio defines the relationship between the lengths of adjacent dipole elements. It is one of the primary design parameters controlling antenna gain, boom length, operating bandwidth, and overall antenna size.
Where are Log Periodic Dipole Arrays commonly used?
LPDAs are widely used for television reception, amateur radio, HF, VHF and UHF communication, EMC testing, military communication, spectrum monitoring, radio direction finding, broadband wireless systems, and antenna measurement applications.
What advantages does an LPDA offer?
An LPDA provides wide operating bandwidth, relatively constant impedance, predictable radiation patterns, moderate to high gain, and stable performance across multiple frequency bands, making it ideal for broadband communication systems.
Why can measured LPDA performance differ from calculated values?
Actual antenna performance may vary because of boom construction, element alignment, balun quality, feed-line routing, conductor diameter, nearby conductive objects, manufacturing tolerances, environmental conditions, and measurement uncertainty. Practical testing and electromagnetic simulation should always be used to validate the final antenna design.
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.