Log Periodic Dipole Array: Everything You Need to Know

The log periodic array is a type of antenna that can function throughout a broad frequency range while still providing gain and directionality.

In addition to that, these antennas are used to gain high-frequency or ultra-high-frequency data. Compared to others not all antennas are as active as this one at any given frequency. One-third of this dipole antenna design can actively contribute to the radiation.

Till now if you already got interested in the dipole array then we’re sure that you want to know more. Then keep on reading to know the basics, and structure of this dipole array. Along with that, you’ll find the benefits and application.

What is A Log-Periodic Dipole Array?

It’s a high-frequency range antenna that receives data from a single direction. Compared to the standard antenna, the log periodic array has the ability to take data from a wide range of frequencies.

To build a log-periodic antenna, you’ll need a pair of single dipole and metal tubes. These settings will help in activating the antenna. You’ll also need a pair of reflectors and directors to direct radiated energy back toward the dipole.

A log periodic antenna uses a succession of dipole elements whose sizes and reception capabilities fluctuate in a logarithmic fashion to address this limitation.

Basics Of Log Periodic Antenna

To construct a log periodic antenna, one must first determine the maximum logarithm of frequency that must be received, and then determine the minimum number of dipole lengths or the shortest element required to achieve that frequency.

For the second group of dipoles, we derive a logarithmic formula that establishes their relative sizes so that their minimum frequency reception just touches the maximum frequency reception of the first group.

Each pair of dipole antenna elements is made larger with each repetition of this process until the antenna is able to receive all of the frequencies needed by the application.

Moreover, The resonant frequency range varies from 30 MHz to 3 GHz band for these antennas.

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One of the important facts about these antennas is that the impedance will vary according to the logarithmic function’s frequency. Radiation pattern, directive gain, beam width, and direction are only some of the electrical qualities that fluctuate in these antennas.

Those antennas may pick up signals from all around the place. Theoretical designs can be approximated to the point that bandwidths of up to 100:1 are achievable. Low to moderate gain radiation can be emitted in both straight lines and angled beams.

Why is Log-Periodic Dipole Antenna important?

As already said, LPDA (Log Periodic Dipole Antenna) can operate with a wide bandwidth of frequency. While in operation, this array design emits a pattern of radiation that is largely constant across the entire operating frequency range.

In addition to their occasional use as television antennas, log periodic antennas find widespread use among amateur radio enthusiasts who wish to access a wide band of frequencies.

These antennas have also been extensively researched for use in the transmission and receiving of electrical power in laboratory experiments.

How Do These Antennas Work?

The working procedure of these antennas is quite similar to the yagi antenna. One of the important facts of a log periodic antenna is that it maintains its shape and performance over a wide frequency range.

Additionally, their standing wave ratio will remain unchanged due to the same radiation resistance. Both the gain and the front-to-rear ratio remain constant.

However, the active region of the antenna elements changes as the operating frequency does, therefore not all of the elements will be actively conducting at the same frequency.

When examined closely, the physical structure and electrical characteristics reveal a pattern of consistency. The array is powered by a two-wire transmission line and is constructed from dipoles of varying lengths and separation. Any two dipoles next to one another will have this line swapped between them.

Here is the diagram of this antenna to give you an idea of its logarithm.

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Diagram Of Log Periodic Dipole Array
Diagram Of Log Periodic Dipole Array

Radiation Pattern Of Log-Periodic Antenna

One of the advantages of these arrays is their stable radiation pattern. You’ll see a directional antenna radiation pattern on log-periodic designs. It could be a unidirectional or bi-directional radiation pattern. However, it’ll depend on the periodic structure.

The radiation from a unidirectional Log-periodic antenna is strongest in the direction of the shorter element and weakest or nonexistent in the forward direction.

The radiation pattern for the uni-directional antenna is given below.

Radiation Pattern Of Log-Periodic Antenna
Radiation Pattern Of Log-Periodic Antenna
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Radiation Pattern

This is the structure pattern you’ll find in a bi-directional log-periodic antenna. Here you can see the pattern on the broad side which is the maximum radiation.

Types Of Log-Periodic Dipole Array Antenna

There are different types of log periodic dipoles you’ll find. However, the main variants of these antennas are given below.

  • Slot log periodic
  • V-log periodic
  • ZIg-zag-log periodic
  • Trapezoidal-log periodic

The only difference is the structure or the antenna design. For example, the v-log antenna has a v shape while the other one will be in a zig-zag shape.

Applications Of Log-Periodic Dipole Antennas

 Common applications of the periodic dipole arrays are given below.

  • High-frequency Communications

These antennas are used for collecting data HF bandwidths. Also, sometimes, these are efficient for ultra-high frequency wireless applications.

  • EMC Measurement

Electromagnet compatibility or EMC is a major concern for electronics. However,  log-periodic antennas Frequency scans across broad frequency bands while testing.

Advantages Of Log Periodic Array

Some advantages of log periodic are given below.

  • Design

The structure of the antenna is pretty simple. You’ll need some basic elements including reflectors, connectors etc to build the structure. Also, you can gain 10:1 bandwidth from the antenna. 

  • Gain and Radiation Pattern

You can obtain low moderate gain and the radiation pattern indicates directional characteristics of the antenna. Moreover, Its dual-way communication capabilities make it ideal for the use of a wide range of radio frequencies.

Disadvantages Of Log Periodic Array

Let’s look at some of the side effects of the antenna arrays.

  • Expensive
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The mounting and different parts of the antenna make it expensive compared to other dipole antennas.

  • Maintenance Of These Antenna Arrays

There are no such maintenance steps for these antennas. However, you should clear the external parts of the array so that it might not affect the internal parts.

Log-Periodic Dipole Array (LPDA)


Does the frequency affect the performance of a log-periodic antenna?

Antennas with a log periodic period are immune to frequency changes. The antenna’s geometry adapts to the relevant wavelength. Its electrical efficiency is solely frequency-dependent.

What’s the reason behind the name log periodic?

The gain or impedance of a log periodic varies periodically with the input frequency and that is one of the reasons. The working principle can be described by thinking of a log periodic dipole array. 

What is the input characteristic impedance of this array?

The input antenna impedance of some HF LPDAs is deliberately made to be 200; a 4/1 current arrow-shaped balun structure can change this to 50 ohms. At very high frequencies (VHF) and above, LPDAs typically have a 50 ohms or 75 ohms characteristic antenna impedance for direct connection.

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So, you now have ideas about what a log periodic dipole array is, how it works, its structure and design, and where this antenna is mostly used.

These are most popular for their usage with a wide frequency range. Radiation resistance and reflected power, as measured by the standing wave ratio, are two more relevant parameters that affect the overall performance of the array.

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