Question

If the radii of two conductors are r1 (feed arm), r2 (non feed arm) and separated by a distance,then the impedance transformation for a half folded dipole is given by _______

(a) \(\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2\)

(b) \(73\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2\)

(c) \(\left(1+\frac{log⁡(\frac{a}{r2})}{log⁡(\frac{a}{r1})}\right)^2\)

(d) \(73\left(1+\frac{log⁡(\frac{a}{r2})}{log⁡(\frac{a}{r1})}\right)^2\)

I had been asked this question in homework.

The above asked question is from Folded Dipole Antenna topic in chapter Folded Dipole & Yagi – Uda Antenna of Antennas

Answer 1

Correct answer is (b) \(73\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2\)

To elaborate: If the radii of two conductors are r1 (feed arm), r2 (non feed arm) and separated by a distance, then the impedance transformation for folded dipole is given by

\(Z = Z’\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2\)

For a half dipole Z’=73Ω

∴ \(Z = 73\left(1+\frac{log⁡(\frac{a}{r1})}{log⁡(\frac{a}{r2})}\right)^2\)