Folded dipole antenna

A type of aerial, widely used with television and VHF radio receivers, consisting of two parallel dipoles connected together at their outer ends and fed at the center of one of them. The length is usually half the operating wavelength.

1. FOLDED DIPOLE ANTENNA PRESENTED BY: NAVIN MANDAL (700415) 1 01

2. CONTENT Introduction Folded Dipole Basis Types Of Folded Dipole Design Properties Radiation Pattern Polar Diagram Advantage Application Reference 2 02

3. INTRODUCTION dipole antenna, with the ends folded back , and connected to each other width ‘ d’ of the folded dipole is much smaller than the length ‘ L’ 3 00 03 Fig. Folded Dipole

4. FOLDED DIPOLE ANTENNA BASIC Basic Format is shown in fig consists of a basic dipole with an added conductor 4 030 04 Fig. Folded Dipole Antenna Basis

5. TYPES OF FOLDED DIPOLE: Unequal conductor folded dipoles Multi-conductor folded dipoles 5 05 Fig. Folded Dipole

6. 1.Unequal Conductor Folded D ipoles varying the effective diameter of the two conductors : top and bottom, different ratios can be obtained. 6 06 Fig. Unequal Conductor Folded Dipole

7. T he impedance step up ratio provided by the folded dipole is: Where, d1 = conductor diameter for the feed arm of the dipole. d2 = conductor diameter for the non-feed arm of the dipole s =distance between the conductors r is the step up ratio 7 07 Impedance  

8. 2.Multi-conductor folded dipoles folded dipole antenna often implies the use of one extra conductor concept can be extended further by adding additional 'folds' or conductors 8 08 Fig. Multi-Conductor Folded Dipole

9. I mpedance of Multi-conductor folded dipoles special case where all the conductors have the same diameter then the impedance is increased by a factor of three squared, i.e. 9 . 9 00 09

10. DESIGN The Length of folded dipole * La = 145 / freq ( MHz ) Length of coil * for 75 ohm cable : Lb = La x 0.8 * for 50 ohm cable: Lb = La x 0.66 10 10 Fig. Folded Dipole Design

11. PROPERTIES OF FOLDED DIPOLE Impedance properties Ease of construction Structural rigidity Wider bandwidth than λ/2 dipole 11 11

12. Radiation P attern 12 12 Fig. Radiation Pattern

13. Radiation Pattern reflects the 'sensitivity' of the antenna in different directions knowledge of this allows the antenna to be orientated in the optimum direction to ensure the required performance 13 13

14. Fig: Antenna polar diagram concept P olar D iagram P lot that indicates the magnitude of the response in any direction 14 14

15. ADVANTAGES: Increase in impedance:   Wide bandwidth:   15 1 15

16. APPLICATION folded dipoles find more uses when a dipole is incorporated domestic television VHF FM broadcast antennas 16 16

17. Reference John D Kraus, Ronald J Marhrfka & Ahmed S Khan Ch.6-24 Martin E. Meserve - K7MEM - Folded Dipole Design.html Dipole Radiation Patterns _ Antenna Polar Diagram _ Tutorial.html Dipole antenna/Folded Dipole Antenna _ Folded Dipole Aerial _ Tutorial.html visited on: August 2,2016 17 16 17

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