Everything you need to Know about Log Periodic Antennas

Log Periodic Antenna is a kind of antenna that offers gain and directivity. It offers wide bandwidth and it is larger than Yagi Antenna. Apart from that, the antenna also works on several frequencies. It is also used for UHF terrestrial TV reception. It is used in several other applications where wide bandwidth and directivity are required.

Now, let us discuss more on this antenna in this blog. We will also discuss the various benefits of using a log-periodic antenna with its working style.

What is a Log Periodic Antenna?

The term Log Periodic Antenna is not new. It is a kind of antenna that works on a wide frequency bandwidth. It offers good gain and directivity and performs better than other kinds of antennas. Log periodic antenna has impedance and radiation characteristics that work as a logarithmic function of the excitation frequency.

Another term for this antenna is a log-periodic beam antenna or a long-period array. It is a fractal antenna or self-similar array.

What is a Log periodic Antenna Used For?

Log periodic antenna is developed in the year 1955 at the University of Illinois. It can operate at a frequency range of 2:1. These antennas are used in the HF band of the spectrum and even at ultra-high frequency (UHF) and very high frequency (VHF) bands.

Normally, an LPDA antenna is used for high-frequency communication. Besides, it is also used for signal monitoring appliances and TV signal reception. This antenna makes communication clear.

How Does a Log periodic Antenna Work?

In the case of a log-periodic antenna, the impedance works as the logarithmically periodic function of the frequency of operation. These LPDAs have many electrical properties such as beam direction, radiation pattern, beam width, and directive gain. These electrical properties also vary from period to period.

This antenna has various elements. They increase gradually from point of feed to the other end with the angle a constant in a log-periodic antenna.

There should be enough gaps between these elements to keep a particular ratio in the dimensions of diploes. The relation between the spacing and the length of the antenna elements is called the scale factor or design ratio. It is represented by T. It is also known as the periodicity factor with a value lower than 1.

There is a constant repetitiveness in the working of this antenna that shows similar kinds of behavior or characteristics. 

A log-periodic antenna is a standard antenna just like a Yagi antenna. However, the working style of this antenna is different. Unlike Yagi Antenna, A log-periodic antenna works in an active region and not in the full area.

There are different regions of a high gain log periodic antenna such as:

1. Transmission Line region

In a transmission line region, the length of half-wavelength is more than the length of elements. These elements offer high capacitive impedance. There is also less spacing between all these elements.

A small magnitude current flows through these series of elements and gives voltage by 90 degrees. Small current results in small radiation in the backward directions.

2. Active region

In the case of the active region, the length of elements is equal to the half wavelength. It also gives resistive impedance. In this region, there is a larger flow of current. There is a large spacing between the dipoles in the active region.

Additionally, the active region offers maximum radiation by producing a large resultant field to both left and right. The phase center in LPDA moves from one end to another according to the change in the frequency from low to high.

3. Reflective region  

This is the third region of a log-periodic antenna. In this region, the length of elements is larger than the resonant length. So, the impedance is inductive which produces a current that lacks supplied voltage.

The reflective region in this directional antenna gets very less voltage from the transmission line. The main reason for this is the active region that radiates and attracts more radiation.

Benefits of Log periodic Antenna

Log periodic antennas are outdoor antennas used for several purposes.  They have various benefits such as:

1. More bandwidth than other types of antennas

Log periodic antenna works better than other kinds of antennas such as Yagi antennas and other indoor antennas. Log period antenna has a wide bandwidth which is not present in other kinds of antennas. Because of the wide bandwidth, you will get low to moderate gains.

2. Different radiation patterns

Unlike other types of antennas, Log periodic antenna provides both bi-directional and unidirectional radiation patterns. It offers both patterns according to the log-periodic structures. When there is only one active region, the antenna offers a unidirectional radiation pattern. On the other hand, the antenna offers a bidirectional radiation pattern when there are 2 active regions. 

3. Compact design

These military antennas are small and compact. It is easy to install and fit this antenna in any small space. Besides, it is also a time-saving task to install this antenna on both residential and commercial buildings.

4. No loss of power

When you terminate a dual-polarized log periodic antenna, there is no power loss. You can save loads of power even after terminating this antenna. It is also an affordable antenna to get precise communications at home or the workplace.

How Do I Aim for a Log Periodic Antenna?

A Military log periodic dipole antenna is a type of directional antenna. It can be used for many purposes such as a survey of the site and tracking interference or for RF and EMC analysis applications.

It works in areas with high frequency to ultra-high frequency ranges. You will get LPDAs in the market with 380 MHz to 35 GHz for RFI detection applications.

A unique feature of a log-periodic antenna is the dipole elements put close to one another. The relationship between the positioning of diploe elements and graduated length helps a log periodic antenna to work in different directions.