Log-periodic antenna

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Log-periodic dipole array

In telecommunication, a log-periodic antenna (LP, also known as a log-periodic array) is a broadband, multielement, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. The individual components are often dipoles, as in a log-periodic dipole array (LPDA).

It is normal to drive alternating elements with a circa 180^o (π radian) phase shift from the last element. This is normally done by wiring the elements alternatingly to the two wires in a balanced transmission line.

The length and spacing of the elements of a log-periodic antenna increase logarithmically from one end to the other.

1 Coverage example
2 Popular Amateur radio variations
- 2.1 HB9CV
- 2.2 ZL special
3 Sources

[edit] Coverage example

[edit] Popular Amateur radio variations

[edit] HB9CV

The HB9CV is a very popular two-element beam which can be considered as a log-periodic dipole array with only two elements.

[edit] ZL special

This is a beam antenna which for a given boom length gives a higher gain than a Yagi antenna, it is a log-periodic where only two elements are driven with a series of parasitic elements (directors) in front of the smaller of the two driven elements.

The driven elements are folded dipoles which are linked by a length of balanced twin-lead feed line. The polar plot of the ZL special and the HB9CV is a heart shape (cardioid) while the typical Yagi antenna has a large forward lobe and a smaller back lobe.