Log periodic antenna

A brief explanation of Log Periodic Antenna,it's types ,Advantages & Disadvantages and Applications.

1. LOG-PERIODIC ANTENNA BY : H.P Anush 1560547 6BTEC

2. CONTENTS INTRODUCTION LPDA STRUCTURE OF LP ANTENNA WORKING OF LP ANTENNA RADIATION PATTERN POINT OF EXCITATION TYPES OF LP ANTENNA ADVANTAGES & DISADVANTAGES APPLICATION CONCLUSION

3. INTRODUCTION A log-periodic antenna (LP), also known as a log-periodic array or log-periodic aerial, is a multi-element, directional antenna designed to operate over a wide band of frequencies. It was invented by  Dwight Isbell  and Raymond DuHamel at the University of Illinois in 1958. It is a broadband, multi-element, unidirectional, narrow-beam antenna.

4. LPDA (Log – Periodic Dipole Array ) The most common form of log-periodic antenna is the  log-periodic dipole array  or  LPDA. The LPDA normally consists of a series of dipoles known as " elements " positioned along a support boom lying along the antenna axis LPDA antennas look somewhat similar to Yagi antennas, in that they both consist of dipole rod elements mounted in a line along a support boom. Both LPDA & Yagi Antenna work in a different manner.

5. STRUCTURE OF LP ANTENNA Log periodic antenna has an array of dipole which has their length according to logarithmic scale. The elements at the back of the array where the elements are the largest is a half wavelength at lowest frequency of operation. It is basically a wideband antenna due to the presence of many dipole elements which are of different length, radiating in a different frequency.

6. WORKING OF LP ANTENNA The construction and operation of a log-periodic antenna is similar to that of a Yagi- Uda antenna. The major difference with this antenna when compared to other antenna’s is that it exhibits constant characteristics over a desired frequency range of operation. It has the same radiation resistance and therefore the same SWR. The gain and front-to-back ratio are also the same.

7. RADIATION PATTERN From the Radiation pattern one can say that it has less directivity than compared to other antennas like Yagi- uda . But we can obtain wide frequency response than any other antenna‘. Here the radiation pattern is shown at 2GHz frequency.

8. RADIATION PATTERN @ 2 GHZ

9. POINT OF EXCITATION The single element is provided excitation via these cross connection lines. Here in the example taken only one element has provided excitation and other element has no separate excitation. By varying the point of excitation we can change the radiation pattern of log periodic antenna.

10. TYPES OF LP ANTENNA There are several forms of log periodic antenna. The exact type that is most applicable for any given application will depend upon the requirements. The main types of log periodic antenna include: Log periodic dipole array, LPDA Slot log periodic Zig zag log periodic array Trapezoidal log periodic V log periodic

11. ADVANTAGES & DISADVANTAGES ADVANTAGES The antenna design is compact. Gain and radiation pattern are varied according to the requirements. DISADVANTAGES External mount. Installation cost is high.

12. APPLICATIONS Used for HF communications. Used for particular sort of TV receptions. Used for all round monitoring in higher frequency bands.

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