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