1 EMLAB Chapter 9. Broadband dipoles and matching techniques

2 EMLAB Contents 1.Introduction 2.Biconical antenna 3.Triangular sheet, Bow-tie, and wire simulation 4.Cylindrical dipole 5.Folded dipole 6.Discone and conical skirt monopole 7.Sleeve dipole 8.Matching techniques

3 EMLAB Fundamental limit of BW The bandwidth of an antenna (which can be enclosed in a sphere of radius r) can be improved only if the antenna utilizes efficiently, with its geometrical configuration, the available volume within the sphere

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5 9.2 Bi-conical antenna Dominant TEM mode

6 EMLAB Electric and magnetic fields, and associated voltages and currents, for a bi-conical antenna.

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8 The input impedance is independent of frequency.

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11 EMLAB 9.3 Triangular sheet, bow-tie, wire simulation Triangular sheet Bow-tie Wire-simulation

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13 EMLAB 9.4 Cylindrical dipole Thick dipole has broad band characteristics.

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15 EMLAB Equivalent radii

16 EMLAB Dielectric coating 1.Increasing Re{P} or Re{Q} a.Increases the peak input admittance b.Increase the electrical length (lowers the resonant frequency) c.Narrows the bandwidth 2. Increasing Im{P} or Im{Q} a.decreases the peak input admittance b.decrease the electrical length (lowers the resonant frequency) c.increase the bandwidth d.Accentuate the power dissipated (decreases the radiation efficiency) e.Accentuate the traveling wave component of the current distribution

17 EMLAB 9.5 Folded dipole 1.FM broadcasting receiving (88~ 108MHz). 2.TV antenna (54~ 216MHz)

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22 EMLAB Equivalent circuit of folded dipole

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25 EMLAB 9.6 Discone and conical skirt monopole

26 EMLAB 9.7 Matching techniques

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30 EMLAB Balun and transformers

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