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Log Periodic Antenna: Advantages and Disadvantages

log periodic antenna antenna rf radiation pattern dipole array

This page covers the advantages and disadvantages of Log Periodic Antennas. It outlines the benefits and drawbacks of using this type of antenna. It also provides a basic overview of Log Periodic Antennas.

What is a Log Periodic Antenna?

Introduction:

The Log Periodic Antenna is composed of an array of dipoles, each with varying lengths and spacings.

The array is fed by a two-wire line that is transposed between each dipole pair. Feeding occurs from the narrower end, resulting in maximum radiation, as illustrated in Figure 1.

Log Periodic Antenna structure

Log Periodic Antenna structure

The following mathematical equation is used in the design of a Log Periodic Antenna:

  • R1/R2 = R2/R3 = R3/R4 = τ = l1/l2 = l2/l3 = l3/l4

Where:

  • τ is the design ratio and is less than 1.

Two lines drawn connecting the opposite ends of the dipoles are straight and convergent, forming an angle α.

Typical values for τ and α are 0.7 and 30 degrees, respectively.

LPDA (Log Periodic Dipole Array) antennas come in two types:

  • LPDA Straight type
  • LPDA Vee type

Benefits (Advantages) of Log Periodic Antennas

The following are the benefits or advantages of Log Periodic Antennas:

  • The radiation resistance and pattern of the antenna do not depend on frequency.
  • A 10:1 Bandwidth can be achieved with a simple design. This wide bandwidth is a significant advantage compared to YAGI and other antenna types.
  • Low to moderate gains can be obtained.
  • It offers unidirectional and bidirectional radiation patterns. It is a highly directional antenna.
  • It can be used for HF/VHF/UHF communication as well as for TV reception.
  • It is available in a wide variety of shapes.
  • It is used for two-way communication requiring multiple frequencies.

Drawbacks (Disadvantages) of Log Periodic Antennas

The following are the disadvantages of Log Periodic Antennas:

  • Log Periodic antennas require a higher number of elements for lower frequencies in the HF/VHF bands.
  • The antenna offers lower gain compared to YAGI antennas of the same size.
  • They are not used for omnidirectional applications.
  • They have a low polarization ratio.