$4\mathrm{.}23.$ A center$-$fed electric dipole of length $l$ is attached to a balanced lossless transmission line whose characteristic impedance is $50$ ohms. Assuming the dipole is resonant at the given length, find the input VSWR when

$R_r=\frac{2P_{\text{r}\text{a}\text{d}}}{|I_0{|}^2}=\frac{}{2}\{\begin{array}{c}C+ln(kl)-C_i(kl)\end{array}$

$+\frac{1}{2}sin(kl)[S_i(2kl)-2S_i(kl)]$

$\{$:$+\frac{1}{2}cos(kl)[C+ln(k\frac{l}{2})+C_i(2kl)-2C_i(kl)]\}$

$(((((((((((((((($If $L=1,3$