Log-Periodic Antenna: Structure, Radiation, And More

A log-periodic antenna is a device that helps to establish a communication medium for high frequencies. Beyond that, it can also work best in solar monitoring and testing frequency bandwidth. 

The antenna provides great directives and a good radiation pattern with some amazing benefits. It can be used for domestic and commercial purposes.   

Don’t you want to know about the design implementation of the antenna? How does it work? Are there any advantages to using it? Keep reading to find your queries. 

What is Log-Periodic Antenna?

Log-Periodic antenna is a broadband directional antenna with a wide frequency band that follows logarithms and is also known as a log-periodic array or log periodic aerial.

Moreover, these antennas have a number half wave dipole active electricity characteristics that provide directivity and gain.

The log periodic antenna works with both impedance and radiation pattern. This antenna can be used at HF(high frequency), VHF (very high frequency), and UHF (ultra high frequency) that increase length.

Hence, it’s quite similar to Yagi-Uda antennas. While it’s best for domestic purposes, log periodic antennas tune better in commercial needs. Nonetheless, the average frequency range of this antenna is around 30 MHz to 3GHz.

Basics of Log-Periodic Antenna

A popular American physicist John Dunlavy invented a log-periodic antenna in 1952 while working in the United States Air Force.

He was a remarkable loudspeaker designer who patented several improvement innovations in antenna theory and wave movements. Dunlavy was the founder of Duntech, a prominent audio standard in Texas, USA.

Along with that, he invented an advanced speaker system and specialized control system for signal emissions. 

One of its well-known inventions of Dunlavy is the periodic log antenna. After that, it was structured at the University of Illinois in 1955.

Why is Log-Periodic Antenna Important?

The log-Periodic antenna has the highest frequency band compared to Yagi-Uda antennas. It can collect and transmit short-wave broadcasting bands of frequencies within a wide bandwidth.

Additionally, the log periodic is a frequency-independent antenna, and it can cover wider bandwidth without any limits.

However, it provides multi-elements in a single antenna. Log Periodic antennas are necessary for setting up TV signals, communicating through different regions and radio stations, and testing wireless frequency.

These antennas improve bandwidth with the dipoles number. Next up, it can receive signals better than omnidirectional antennas and operates in a single direction, increasing the frequency length.

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Types of Log-Periodic Antenna

Knowing the types of log periodic antenna will help to understand the wires’ purpose. Such as – 

  • Planer

The planar antenna helps to receive and transmit high-frequency gain. It also improves impedance and radiation patterns. Hence, these antennas can operate from 230 to 1600GHz.

Planar antennas are suitable to receive VHF(very high frequency) or UHF (ultra high frequency). Generally, it has been used in indoor and non-professional uses. But take it for professional use. 

It can be perfect for surveillance, pre-testing, and monitoring with better impedance. This increases the lowest frequency to the highest.

  • Zigzag

If the dipoles have an array of various spacing and lengths, then it is a zigzag antenna. These antennas might have straight or wavy wires of zigzag shape in the middle of walls and trees.

The zigzag antenna has been structured with more than 16 sections. Beyond that, it can operate from 6 to 26 MHz. It has teeth-like wires to transmit electricity elements between two sides.

  • V-type

One of the better version antenna types is the V-type. However, it includes two planar arrays at a 45° dihedral angle and feed lines at the bottom. This antenna operates in a unidirectional radiation system. 

Two parallel feed lines are constructed by finite integration and conformal mapping techniques. It’s usually used as a TV satellite antenna. Thus, it provides vertical polarization with a frequency rate of 140 to 470MHz.

  • Slot

Organizing a nine-electricity element in log periodic style to operate the microstrip-fed slots of broadband is known as a slot log periodic antenna. It consists of a triangle shape with a circular shape.

Therefore, this antenna analyzes the folded slot arrays with the Design of the Experiments method.

The circular fractal slots are probed to develop the gain and bandwidth with the DGS (Defective Ground Structure).

Thus, it operates from 12GHz to 18GHz consisting of the Ku-band. These lightweight antennas work better in communicating and military transmissions.

  • Dipole

The dipole Array is the most popular type of log periodic antenna. It’s also known as LPDA, which means Log Periodic Dipole Array.

Interestingly, these antennas contain half-wave dipoles with active elements to promote bandwidth length through two parallel metal rods. The dipole array antenna can cover 760MHz to 18GHz.

Structure of Log-Periodic Antenna

These antennas have circular polarization. Some types are dual or vertically polarized for different frequency bandwidths. The structure of the antenna promotes the highest directivity.

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Structure of Log-Periodic Antenna
Structure of Log-Periodic Antenna

In vertical polarization, the axle ratio can be at zero. If circular polarization occurs, then the axle ratio is at one. Beyond that, the linear horizontal polarization occurs the radiation on the way to a small axle ratio at a decent amount.

Radiation Pattern of Log-Periodic Antenna

The radiation pattern of the log periodic antenna is similar through band operation. Hence, it operates in unidirectional and bidirectional movement. It has a radiation range between 30MHz to 3GHz.

Radiation Pattern of Log-Periodic Antenna
Radiation Pattern of Log-Periodic Antenna

Properties of Log Periodic Antenna

If you want to measure the properties of this antenna, you should analyze the operational process. Luckily, a log periodic antenna works effectively in normal radiation mode.

It doesn’t require radiating in multiple modes. Balancing the dipole antenna helps to increase impedance and radiation resistance. 

Keep the antenna radiating in one direction at a time. Moving the feed lines can interrupt the impedance and radiation pattern. Nonetheless, it manifests the periodic contrast with the input frequency band. 

Designing of Log-Periodic Antenna

The design is a log periodic antenna consisting of basic design, mathematical models, SWR (Standing Wave Radio) calculation, and parameter calculation. After measuring the logarithm, it comes to the design implementation stage. 

However, the antenna consists of a triangular shape with two parallel metal rods, settling a support boom and antenna axis into the middle. 

Each electrical element in the antenna is active, and the wire design between metal rods can vary with the type of antenna. Besides, the metal rods are covered with aluminum and titanium wires. 

Designing of Log-Periodic Antenna
Designing of Log-Periodic Antenna

Its scaling factor is 1.05 in design parameters. The visible periodic logarithm is,

𝑳𝒊+𝟏 = 𝛕𝑳𝒊 

𝑹𝒊+𝟏 = 𝛕𝑹𝒊 

 𝝈 = 𝑹𝒊 – 𝑹𝒊−

In the mathematical equation, 𝛕 refers to periodicity (0 < τ < 1), 𝝈 refers to the parallel spacing of electrical characteristics, R refers to radiation, and L refers to logarithm. Hence, the antenna mathematical model follows the periodical logarithm.   

After calculating the math equation, the SWR calculation is necessary for designing the antenna. Then, structure a final antenna design and check the settings. Set the antenna in unidirectional radiation. 

Advantages of Log-Periodic Antenna

There are many advantages to these antennas. For example, 

  • Consistent Radiation Mode 

One of the most helpful features of this antenna is the normal radiation mode. Unlike other antennas, the wave propagation of a log periodic antenna is consistent. 

  • Multiple Polarization 
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A log periodic antenna is polarized in circular, horizontal, vertical, and dual patterns.

  • Broad Frequency Range 

The most essential advantage of LPA is that it can receive and transmit high, ultra-high, and very high frequencies. 

  • Versatile 

This antenna is categorized into five types. These different types of antenna are suitable for various purposes. 

Disadvantages of Log-Periodic Antenna

The disadvantages of log periodic antennas are: 

  • Low Gain

A log periodic antenna consists of a lower gain of each weight unit or wind load than a Yagi antenna. 

  • No Omnidirectional Uses

These antennas are unidirectional or bidirectional. It can’t operate in an omnidirectional way, which limits the bandwidth in some applications. 

Application of Log-Periodic Antenna

This antenna has versatile applications for domestic and commercial purposes. Such as, 

  • Protecting frequency effectiveness, pre-compliance testing, site surveying, and commercial electromagnetic simulation. 
  • Broadcasting radio and TV stations 
  • Perfect for solar monitoring in wavelength 
  • Used for analog TV, communicating high-frequency range 
  • Transmits and receives ultra-high frequency and very high-frequency range
Create Log Periodic Antenna 


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

Yagi antennas have higher gain and smaller sizes than log-periodic antennas. A log periodic antenna can cover commercial applications. Whereas Yagi antennas are better for residential applications. 

What is the bandwidth ratio of a log-periodic antenna?

The average bandwidth ratio of the log-periodic antenna is 2:1. 

What is the gain of a log-periodic antenna?

Generally, the gain of this antenna is 6.5 dBi with a frequency range of 290 MHz to 2000 MHz. 

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Final Thoughts 

That’s all about a log periodic antenna. Now you know this antenna’s basics, design, structure, applications, advantages, and disadvantages. The remarkable antenna types are zigzag, slot, and dipole. It’s used in television broadcasting stations. These antennas have excellent directivity, impedance and radiance method, and multiple polarization systems. 

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