I could not get the equation for calculating imaginary part of the input impedance of half wavelength dipole.
@ Sajeed Mulla
Let me just notice that the complex number 73 + j 42,5 = 84,47 e^{j 30,2deg}, which means the the phase shift equals approximately \pi/6 - pretty round number :) This cannot be accidental! And is nor! Such a shift is related to the lenth of the antenna related to the wave length.
About the values - they are caused by interaction of the antenna due to the need to emit energy into the air, which for the feeding circuit means to do electrical work. Generally this is a feature of the electromagnetic fields. The non-full wavelenth dipols' impedance is a result of the fact that in such cases some part of the emitted energy returns to the system by inducing back the current in the antenna (obviously, with some delay). More exact explanations are to be saught in special books. Some of the advanced material is presented by MsWiki at
https://en.wikipedia.org/wiki/Dipole_antenna
Good luch in studying em fields!
Joachim
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