Log Periodic Antenna Calculator

A Log Periodic Antenna Calculator helps estimate the basic dimensions and characteristics of a log-periodic dipole array (LPDA) from three inputs: center frequency, tau ratio, and number of elements. The calculator determines wavelength, longest and shortest element lengths, estimated boom length, estimated gain, and an estimated bandwidth ratio.

Log-periodic antennas are directional antennas made from multiple elements whose dimensions progressively change along the boom. This scaling allows the antenna to operate over a broader range of frequencies than many conventional single-frequency directional antennas.

The calculator is designed as a preliminary antenna design and estimation tool. Enter the center frequency in MHz, choose a tau ratio, and specify the number of elements. The calculator then applies its predefined formulas to estimate the antenna's physical dimensions and selected performance parameters.

For example, with a center frequency of 144 MHz, a tau ratio of 0.85, and 10 elements, the calculator estimates a wavelength of approximately 2.0833 m, a longest element of approximately 1.0417 m, a shortest element of approximately 0.251 m, an estimated boom length of approximately 0.791 m, an estimated gain of 8 dBi, and an estimated bandwidth ratio of approximately 4.60:1.

These values should be treated as starting-point estimates rather than guaranteed physical antenna performance. A practical LPDA design also depends on element spacing, element diameter, feed arrangement, conductor characteristics, mechanical construction, installation environment, and electromagnetic optimization.

What Is a Log Periodic Antenna?

A log periodic antenna is a directional antenna whose physical dimensions follow a repeating geometric relationship. One common implementation is the log-periodic dipole array (LPDA), which uses multiple dipole elements arranged along a boom.

Unlike an antenna designed around only one resonant frequency, an LPDA uses elements of progressively different lengths. At a particular operating frequency, some of the elements become more electrically active than others. As the operating frequency changes, the active region shifts along the array.

The result is a directional antenna structure that can cover a relatively broad frequency range.

The dimensions of adjacent elements are commonly related using a scaling factor known as tau (τ). In the simplified calculation used by this calculator, each successive element is reduced according to the relationship:

Ln = L0 × τⁿ

Where:

• Ln = length of the selected element
• L0 = reference element length
• τ = tau scaling ratio
• n = element index

The calculator uses the center frequency to determine wavelength and then uses approximately half a wavelength as the longest element. The remaining element dimensions are obtained by repeatedly applying the tau ratio.

What does a log periodic antenna do?

A log periodic antenna provides directional radiation while being designed to operate over a broader frequency range than many narrowband directional antenna designs. It can therefore be useful for applications where both directionality and frequency coverage are important.

However, the actual operating bandwidth, gain, impedance, and radiation pattern of a physical antenna depend on its complete geometry and construction. The calculator provides simplified estimates rather than a complete electromagnetic model.

How the Log Periodic Antenna Calculator Works

The calculator requires three inputs:

1. Center Frequency
2. Tau Ratio
3. Number of Elements

It then performs several calculations.

1. Calculate Wavelength

The first step is calculating the wavelength from the entered frequency.

The calculator uses:

λ = 300 / f

Where:

• λ = wavelength in meters
• f = frequency in MHz

For example, at 144 MHz:

λ = 300 / 144

λ ≈ 2.0833 m

This wavelength becomes the basis for estimating the longest element.

2. Calculate the Longest Element

The calculator estimates the longest element as half of the wavelength:

Longest Element = λ / 2

For 144 MHz:

Longest Element = 2.0833 / 2

≈ 1.0417 m

This is a simplified half-wavelength reference used by the calculator.

3. Calculate the Shortest Element

The calculator applies the tau ratio repeatedly according to the number of elements:

Shortest Element = Longest Element × τ^(N−1)

Where:

• τ = tau ratio
• N = number of elements

As the number of elements increases, the exponent increases and the final element becomes progressively smaller when tau is below 1.

4. Estimate Boom Length

The calculator uses a simplified boom-length estimate:

Estimated Boom Length = Longest Element − Shortest Element

This provides a quick dimensional reference based on the two calculated endpoint element lengths.

It is important to understand that this is not a complete mechanical or electromagnetic calculation of an LPDA boom. Actual element spacing and boom geometry require additional design parameters.

5. Calculate Estimated Bandwidth Ratio

The calculator calculates:

Bandwidth Ratio = 1 / τ^(N−1)

The result is displayed in the format:

X : 1

For example, a result of 4.60:1 indicates that the mathematical ratio calculated from the selected tau and element count is approximately 4.60 to 1.

This should not automatically be interpreted as a guaranteed measured SWR bandwidth.

6. Estimate Gain

The calculator uses a simplified element-count-based gain estimate:

This is an intentionally simplified approximation implemented in the calculator. Actual LPDA gain cannot be determined from element count alone.

Log Periodic Antenna Calculator Inputs

Center Frequency

The center frequency is the frequency used to determine the wavelength and initial element dimension.

The calculator accepts frequency in MHz.

For example:

• 50 MHz
• 88 MHz
• 144 MHz
• 222 MHz
• 432 MHz
• 900 MHz
• 1200 MHz

The frequency has a direct effect on antenna size.

As frequency increases, wavelength decreases. Therefore, the calculated element dimensions also become smaller.

For example, a 144 MHz signal has a substantially longer wavelength than a signal at several hundred MHz, so a half-wavelength reference element at 144 MHz is physically longer.

Tau Ratio

The tau ratio (τ) controls the scaling relationship between successive elements.

The calculator supports tau values from 0.6 to 0.95 through its input configuration, while the calculation itself requires tau to be greater than zero and less than one.

A value such as:

τ = 0.85

means that the next scaled element is approximately 85% of the preceding reference dimension under the calculator's simplified geometric model.

Changing tau can significantly change the calculated shortest element and bandwidth ratio.

A lower tau produces more aggressive scaling between elements. A higher tau produces more gradual scaling.

There is no single tau value that is universally correct for every LPDA design. Practical antenna optimization requires consideration of additional design parameters.

Number of Elements

The calculator accepts between 5 and 50 elements.

The number of elements influences several calculated outputs.

Increasing the element count:

• Extends the sequence of scaled element dimensions.
• Produces a smaller calculated shortest element.
• Increases the calculated bandwidth ratio.
• Can move the simplified gain estimate into a higher category.

The calculator's gain model changes at 8, 13, and 20 elements.

It is important not to interpret this as meaning that every physical LPDA automatically gains a fixed amount of gain simply by adding elements. Real antenna gain depends on the entire electromagnetic structure.

Log Periodic Antenna Formulas

Understanding the formulas behind the calculator makes it easier to interpret the results.

Wavelength

The calculator uses:

λ = 300 / f

For frequency in MHz, the resulting wavelength is expressed in meters.

Example:

f = 144 MHz

λ = 300 / 144 = 2.0833 m

Longest Element

The calculator uses:

Lmax = λ / 2

For the 144 MHz example:

Lmax ≈ 1.0417 m

Shortest Element

The calculator uses:

Lmin = Lmax × τ^(N−1)

For:

• Lmax = 1.0417 m
• τ = 0.85
• N = 10

the result is approximately:

Lmin ≈ 0.251 m

Estimated Boom Length

The calculator uses:

Boom Length ≈ Lmax − Lmin

For the example:

Boom Length ≈ 1.0417 − 0.251

≈ 0.791 m

Again, this is a simplified estimate based on the calculator's implementation.

Estimated Bandwidth Ratio

The calculator uses:

Bandwidth Ratio = 1 / τ^(N−1)

With τ = 0.85 and N = 10:

Bandwidth Ratio ≈ 4.60 : 1

This is a calculated frequency ratio and should not be confused with a guaranteed impedance or SWR bandwidth.

Estimated Gain

The calculator uses element-count categories rather than a detailed electromagnetic gain equation.

For 10 elements, the calculator returns:

8.0 dBi

The value should therefore be described as estimated gain, not measured or guaranteed antenna gain.

Real-Life Example: 144 MHz Log Periodic Antenna

Consider an amateur radio experimenter who wants to explore a directional antenna design around 144 MHz.

The user selects:

• Center Frequency: 144 MHz
• Tau Ratio: 0.85
• Number of Elements: 10

The calculator can be used to quickly estimate the initial geometry.

Step 1: Calculate Wavelength

Using:

λ = 300 / f

we get:

λ = 300 / 144

λ ≈ 2.0833 m

The calculated wavelength is approximately 2.0833 meters.

Step 2: Calculate the Longest Element

The calculator uses:

Lmax = λ / 2

Therefore:

Lmax ≈ 2.0833 / 2

Lmax ≈ 1.0417 m

The estimated longest element is therefore approximately 1.04 meters.

Step 3: Calculate the Shortest Element

The calculator uses:

Lmin = Lmax × τ^(N−1)

With:

• Lmax = 1.0417 m
• τ = 0.85
• N = 10

the resulting shortest element is approximately:

0.251 m

So the calculator predicts a large difference between the first and last element dimensions.

Step 4: Estimate Boom Length

The simplified boom calculation is:

1.0417 − 0.251 ≈ 0.791 m

Therefore, the estimated boom-length value is approximately:

0.791 m

Step 5: Calculate Bandwidth Ratio

The calculator determines:

1 / 0.85⁹ ≈ 4.60

Therefore:

Estimated Bandwidth Ratio ≈ 4.60:1

Step 6: Estimate Gain

Because the design contains 10 elements, it falls into the calculator's 8–12 element category.

Therefore:

Estimated Gain = 8 dBi

Complete Example

This example demonstrates how the calculator converts a small set of design inputs into a useful preliminary set of antenna parameters.

However, these numbers should not be treated as a complete construction blueprint. Before building an actual LPDA, an engineer or antenna experimenter should consider element spacing, element diameter, feed arrangement, mechanical constraints, impedance behavior, and electromagnetic performance.

Practical Use Cases for a Log Periodic Antenna Calculator

Amateur Radio Projects

One practical application is preliminary planning for directional amateur radio antennas.

An operator can enter a target frequency, experiment with different tau ratios, and compare different element counts before deciding which configuration is worth modeling or constructing.

For example, an operator interested in VHF experimentation can compare 8-, 10-, and 13-element configurations and see how the calculator's estimated dimensions and gain category change.

RF Engineering Prototyping

Engineers can use the calculator as an early-stage design aid.

Instead of manually repeating wavelength and exponential scaling calculations, the calculator produces the basic estimates immediately.

This can be useful during:

• Concept development
• Early geometry selection
• Design comparisons
• Educational prototypes
• Preliminary mechanical planning

Wideband Directional Receiving

A log periodic structure can be attractive when a receiving system requires directionality over a relatively broad frequency range.

Potential areas include:

• RF monitoring
• Spectrum observation
• Experimental receiving systems
• Antenna measurement setups
• Technical education

The calculator helps determine whether a proposed design is physically practical before more detailed work is performed.

Antenna Education

The tool is also useful for learning antenna concepts.

Students and beginners can change one input at a time and observe how it affects the calculated results.

For example:

• Increase frequency → wavelength decreases.
• Increase element count → calculated shortest element decreases.
• Change tau → element scaling changes.
• Increase element count → calculated bandwidth ratio increases.

This makes the relationship between frequency, wavelength, scaling, and antenna dimensions easier to visualize.

How Tau Ratio Affects a Log Periodic Antenna

Tau is one of the most important variables in the calculator because it controls how quickly the element dimensions shrink.

Suppose the longest element remains fixed while the tau ratio changes.

With a lower tau, each successive element becomes significantly smaller than the previous one.

With a higher tau, successive elements remain closer in size.

For example, compare conceptual values such as:

• τ = 0.70
• τ = 0.85
• τ = 0.90

With the same number of elements, the 0.70 configuration produces much more aggressive geometric scaling than the 0.90 configuration.

The calculator's shortest-element formula makes this relationship explicit:

Lmin = Lmax × τ^(N−1)

Because tau is raised to a power, even relatively small changes in tau can have a substantial effect when many elements are used.

The bandwidth-ratio calculation is also directly affected:

Bandwidth Ratio = 1 / τ^(N−1)

Consequently, tau and element count should be considered together rather than independently.

What does tau mean in a log periodic antenna?

Tau is the geometric scaling ratio used to determine how the dimensions of successive antenna elements change. In this calculator, it is used to progressively reduce element length from the longest element toward the shortest element.

How Number of Elements Affects LPDA Calculations

The number of elements has a major effect on the calculator's results.

Suppose the center frequency and tau remain constant while the number of elements increases.

The exponent in:

τ^(N−1)

becomes larger.

Because tau is less than one, the resulting shortest-element value becomes smaller.

At the same time, the calculated bandwidth ratio:

1 / τ^(N−1)

becomes larger.

The calculator also changes its estimated gain category as the number of elements increases:

• 5–7 elements → 6 dBi
• 8–12 elements → 8 dBi
• 13–19 elements → 10 dBi
• 20 or more → 12 dBi

These values are specific to the calculator's simplified model.

They should not be interpreted as a universal LPDA gain relationship. Actual gain is influenced by much more than the number of elements.

Log Periodic Antenna vs. Other Directional Antennas

Log periodic antennas are one option among several directional antenna architectures.

A log periodic antenna can be attractive when frequency coverage is an important requirement.

A Yagi can be preferable when the design objective is strongly focused on a narrower frequency range and high directional performance.

A dipole can be attractive when simplicity, low cost, and ease of construction are more important than directional gain.

There is no universally "best" antenna. The appropriate architecture depends on frequency range, gain requirements, available space, mechanical limitations, and system requirements.

How to Use the Log Periodic Antenna Calculator

Using the calculator is straightforward.

Step 1: Enter the Center Frequency

Enter the desired frequency in MHz.

Make sure the value is greater than zero.

Step 2: Enter the Tau Ratio

Enter a tau value within the calculator's supported input range.

A common test value for experimentation is:

0.85

You can change this value to investigate how scaling affects the results.

Step 3: Enter the Number of Elements

Specify the number of elements.

The calculator supports:

5 to 50 elements

Step 4: Calculate

The calculator returns:

• Wavelength
• Longest element length
• Shortest element length
• Tau ratio
• Number of elements
• Estimated boom length
• Estimated gain
• Estimated bandwidth ratio
• Polarization

Step 5: Evaluate the Results

Use the results to determine whether the preliminary antenna concept is physically practical.

If the dimensions are unsuitable, change the frequency, tau ratio, or element count and calculate again.

Step 6: Validate the Design

Before constructing a final antenna, use more detailed electromagnetic analysis and physical measurements where appropriate.

Understanding the Calculator Results

Wavelength

Wavelength represents the distance associated with one cycle of the electromagnetic wave.

The calculator expresses wavelength in meters.

It is the fundamental dimension used to establish the longest element.

Longest Element Length

The longest element is calculated as approximately half the wavelength.

This provides the starting dimension for the calculator's geometric scaling.

Shortest Element Length

The shortest element is determined by applying the tau ratio across the number of elements.

A larger element count or smaller tau generally produces a smaller final element under this mathematical model.

Estimated Boom Length

The calculator subtracts the shortest element from the longest element.

This provides a simplified estimate:

Boom Length ≈ Lmax − Lmin

It does not represent a complete LPDA boom-spacing calculation.

Estimated Gain

Gain is estimated from element count using the calculator's predefined categories.

Because the model is simplified, actual antenna gain can differ significantly.

Estimated Bandwidth Ratio

The calculator provides a ratio based on tau and element count.

It is important to distinguish this mathematical ratio from the actual impedance bandwidth of a constructed antenna.

Polarization

The calculator reports:

Linear

The actual physical polarization orientation depends on how the antenna is installed.

For example, rotating a linear antenna structure changes its polarization orientation relative to the surrounding system.

Common Log Periodic Antenna Design Mistakes

Mistake 1: Treating Calculator Results as Final Construction Dimensions

A calculator can provide a useful starting point, but a complete LPDA design requires additional geometry.

Element spacing, diameter, feed structure, and other parameters are not represented in the simplified calculator.

Mistake 2: Assuming the Estimated Gain Is Guaranteed

The calculator's gain estimate is based only on element-count categories.

A physical antenna should not be expected to produce exactly the displayed dBi value without measurement or more detailed analysis.

Mistake 3: Confusing Bandwidth Ratio With SWR Bandwidth

A calculated bandwidth ratio is not automatically the same as the range over which a physical antenna maintains an acceptable SWR.

This distinction is particularly important when using the calculator for practical antenna construction.

Mistake 4: Ignoring Element Spacing

The length of an element is only one part of an LPDA design.

Spacing between elements influences electromagnetic behavior and must be considered in a complete design.

Mistake 5: Ignoring the Feed Structure

The feed system can have a significant impact on practical antenna behavior.

A physical LPDA requires a suitable feed arrangement rather than simply placing independent dipoles along a boom.

Mistake 6: Building Without Measurement

After construction, antenna measurements can help determine how closely the real antenna matches the intended design.

Depending on the project, useful measurements may include:

• SWR
• Impedance
• Resonant behavior
• Radiation pattern
• Gain

Factors That Affect Real-World LPDA Performance

The calculator intentionally focuses on a small number of variables. Real antennas are more complicated.

Element Diameter

The diameter of conductive elements affects their electrical behavior and can influence bandwidth and impedance.

Element Spacing

Actual spacing between elements is a fundamental part of LPDA geometry.

The simplified calculator does not calculate a detailed element-spacing schedule.

Feedline Geometry

The feed arrangement affects how energy is distributed among the elements.

A real design therefore needs an appropriate feed structure.

Conductive Material

The electrical and mechanical properties of the conductors can influence practical performance.

Boom Construction

The physical boom supports the antenna elements and may also become part of the electromagnetic environment.

Installation Environment

Nearby objects can affect antenna behavior.

Buildings, towers, cables, metallic structures, terrain, and other objects can influence the resulting radiation pattern and impedance.

Manufacturing Accuracy

A physical antenna can differ from calculated dimensions because of cutting tolerances, mounting hardware, element bending, connector dimensions, and construction variations.

These effects become increasingly important as wavelengths become shorter.

Using the Calculator for Frequency Planning

The calculator can be particularly useful during early frequency planning.

Start by identifying the target center frequency.

Next, calculate the wavelength and inspect the longest-element dimension.

Then select a preliminary tau ratio and number of elements.

Try several combinations and compare:

• Longest element
• Shortest element
• Estimated boom length
• Estimated bandwidth ratio
• Estimated gain

This lets you quickly explore the design space.

For example, instead of immediately constructing a 10-element antenna, you can compare 8, 10, 12, and 15 elements and determine which configuration appears physically manageable.

The next step should be detailed antenna modeling and optimization.

Example Use Case: Wideband VHF/UHF Antenna Experiment

Imagine an antenna experimenter needs a directional antenna concept that can cover more than one operating frequency.

Instead of designing a separate narrowband antenna for every frequency, the experimenter investigates a log periodic structure.

The first step is selecting a center frequency.

The user then chooses an initial tau value such as 0.85 and tests several element counts.

For example:

• 8 elements
• 10 elements
• 12 elements
• 15 elements

The calculator provides a quick comparison of the resulting element dimensions and estimated bandwidth ratios.

The experimenter can then select a configuration based on physical size and project requirements.

The workflow could be:

1. Define the target frequency range.
2. Select an initial center frequency.
3. Enter a preliminary tau ratio.
4. Test different element counts.
5. Compare calculated dimensions.
6. Select a candidate configuration.
7. Develop the detailed LPDA geometry.
8. Simulate the antenna.
9. Construct a prototype.
10. Measure its impedance and radiation behavior.
11. Refine the design if necessary.

This is where the calculator provides the most value: rapid early-stage design iteration.

Limitations of the Log Periodic Antenna Calculator

The calculator is intentionally simplified and should not be treated as a complete electromagnetic design program.

It calculates:

• Wavelength
• Longest element
• Shortest element
• Estimated boom length
• Estimated gain
• Estimated bandwidth ratio
• Linear polarization

It does not directly calculate:

• Detailed element spacing
• Element diameter
• Feedpoint impedance
• Exact SWR
• Exact radiation pattern
• Front-to-back ratio
• Measured gain
• Exact usable bandwidth
• Manufacturing tolerances
• Environmental effects
• Detailed feed-system geometry

The simplified boom calculation is particularly important to understand.

The calculator uses:

Boom Length = Longest Element − Shortest Element

This is useful as a quick estimate based on the calculator's defined model, but it should not be interpreted as a complete mechanical layout for an LPDA.

Similarly, the estimated gain is based on element-count categories rather than a complete electromagnetic simulation.

For a production-quality antenna, these estimates should be followed by more detailed design work.

Frequently Asked Questions

What is a log periodic antenna calculator?

A log periodic antenna calculator is a tool used to estimate important parameters of a log-periodic antenna from design inputs such as frequency, tau ratio, and number of elements. This calculator estimates wavelength, longest and shortest element lengths, boom length, gain, bandwidth ratio, and polarization.

What does tau mean in a log periodic antenna?

Tau (τ) is a geometric scaling ratio that describes how successive antenna elements change in size. In this calculator, tau is used to calculate the progressively smaller element dimensions.

What is a good tau ratio for a log periodic antenna?

There is no single tau value that is universally optimal for every LPDA design. The appropriate value depends on the desired frequency range, geometry, number of elements, gain, impedance characteristics, and other design objectives. This calculator allows users to experiment with tau values within its supported range.

How do you calculate a log periodic antenna element length?

This calculator uses the relationship:

Ln = L0 × τⁿ

The longest element is first estimated from half the wavelength, and subsequent dimensions are scaled using the tau ratio.

How do you calculate wavelength from MHz?

The calculator uses:

λ = 300 / f

where frequency is entered in MHz and wavelength is returned in meters.

For example, at 144 MHz:

λ = 300 / 144 ≈ 2.0833 m

How long should a log periodic antenna element be?

In this calculator, the longest element is estimated as approximately half the wavelength. The shortest element is then calculated by applying the tau ratio according to the number of elements.

Actual LPDA element dimensions may require further optimization.

Does adding more elements increase LPDA gain?

The calculator's estimated gain increases when the element count crosses predefined thresholds. However, actual antenna gain depends on the complete antenna geometry, so adding elements does not guarantee a specific real-world gain increase.

What is the bandwidth of a log periodic antenna?

A log periodic antenna is designed to provide operation across a relatively broad frequency range. This calculator reports an estimated bandwidth ratio using:

1 / τ^(N−1)

That mathematical ratio should not automatically be interpreted as the physical antenna's measured SWR bandwidth.

Are log periodic antennas directional?

Yes. Log-periodic dipole arrays are directional antenna structures. Their radiation characteristics depend on the complete antenna design and operating frequency.

Is a log periodic antenna horizontally or vertically polarized?

The calculator reports the polarization as linear. Whether the physical antenna produces horizontal or vertical polarization depends on its orientation and installation.

Can I use this calculator for VHF?

Yes. The calculator accepts frequency in MHz and can be used to generate preliminary dimensions for VHF frequencies. The resulting physical antenna should be further analyzed before construction.

Can I use this calculator for UHF?

Yes. The calculator can provide preliminary estimates for UHF frequencies as well. At higher frequencies, physical construction accuracy and electromagnetic effects become increasingly important because the wavelength is shorter.

Can this calculator design a complete log periodic antenna?

No. It provides preliminary calculations rather than a complete electromagnetic design. A complete LPDA design requires additional parameters such as element spacing, element diameter, feed arrangement, impedance characteristics, and detailed geometry.

What is the difference between a log periodic antenna and a Yagi antenna?

Both can provide directional radiation, but they are designed with different approaches. A log periodic antenna uses progressively scaled elements to support broader frequency operation, while a Yagi is generally optimized around a more limited frequency range.

Neither antenna is universally better. The appropriate choice depends on the application's frequency coverage, gain, size, and design requirements.

Log Periodic Antenna Calculator vs. Manual Calculation

Calculating LPDA dimensions manually requires repeated mathematical operations.

A user would need to:

1. Convert frequency into wavelength.
2. Calculate half wavelength.
3. Apply the tau ratio repeatedly.
4. Determine the shortest element.
5. Calculate the estimated boom length.
6. Calculate the bandwidth ratio.
7. Determine the calculator's estimated gain category.

The calculator automates these steps.

This makes it useful for quickly testing multiple configurations.

For example, an antenna designer can keep the frequency constant while changing tau from 0.80 to 0.85 or 0.90, then compare how the shortest element and bandwidth ratio change.

Likewise, the designer can compare different element counts without manually recalculating every value.

Key Takeaways

The Log Periodic Antenna Calculator provides a fast way to estimate the basic characteristics of a log-periodic dipole array.

The calculator uses three primary inputs:

• Center frequency
• Tau ratio
• Number of elements

From these inputs, it calculates:

• Wavelength
• Longest element length
• Shortest element length
• Estimated boom length
• Estimated gain
• Estimated bandwidth ratio
• Polarization

The key formulas are:

λ = 300 / f

Longest Element = λ / 2

Shortest Element = Longest Element × τ^(N−1)

Estimated Boom Length = Longest Element − Shortest Element

Bandwidth Ratio = 1 / τ^(N−1)

The calculator's gain estimate is based on predefined element-count categories rather than a detailed electromagnetic model.

For that reason, the results are best used for preliminary planning, education, prototyping, and design comparison.

A physical LPDA should be evaluated using a more complete design process that considers element spacing, element diameter, feed structure, impedance, construction tolerances, installation environment, and electromagnetic performance.

If you are exploring a new LPDA design, enter your target frequency, tau ratio, and number of elements into the calculator to quickly estimate the starting dimensions and key parameters for your antenna project.