Log Periodic Antenna

Keval Patel

100110111007

Introduction

• In telecommunication, a log-periodic antenna is a broadband, multi-element, directional, narrow-beam antenna thathas impedance and radiation characteristics that are regularlyrepetitive as a logarithmic function of the excitation frequency.

• The individual components are often dipoles.

• The lengths and spacings of the elements of a log-periodic antennaincrease logarithmically from one end to the other.

KEY POINTS: High bandwidth

Moderate directivity

Structure:

• Log periodic antenna has an array of dipolewhich has their length according tologarithmic scale.

• Log periodic antenna is basically a widebandantenna because it has many dipole elementswhich are of different length, radiatingdifferent frequency.

• The structure of log periodic antenna isshown on right side.

• In this the dipole array are cross connected toeach other.

Point of Excitation:

• The single element is providedexcitation via these cross connectionlines.

• Here only one element has providedexcitation and other element has noseparate excitation.

• By varying the point of excitation wecan change the radiation pattern of logperiodic antenna.

Radiation Pattern:

• The radiation pattern of log periodicantenna is shown here.

• From the pattern we can say that ithas less directivity than otherantennas like Yagi-uda.

• But we can obtain wide frequencyresponse than any other antenna‘.

• Here the radiation pattern is shownat 12MHz frequency.

Far Field Pattern:

In 3D:

Uses:

• This antenna design is used where a wide range of frequencies isneeded while still having moderate gain and directionality.

• It is sometimes used for a (VHF/UHF) television antenna.

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