antenna resonance

i am having some doubts about the antenna resonance and its impedance behaviour when its resonating?

when we say antenna is resonating it means its impedance is apprximately real with no imaginary part.
my question at which point of antenna structure this impedance will be only real?
for example for half wavelenth dipole which is fed at the centre , i know this impedance will be the centre . but what about at other part of the dipole? will it be real all over the dipole???

and similary the same question is for micrsotrip antennas as well?


any comments would be highly appreciated

regards

Hello,
feeding the center of a half wave dipole antenna will not yield a purely resistive load. It will be around 72ohm + j*something(?). If you examine the current/voltage distribution on the conductors you'll see a current maxima at the dipole's center and a voltage maxima at the ends of the dipole. Hence, Z=V/I will vary across the dipole accordingly.
I think it is the same with microstrip antenna, you find the optimal feeding point according to the voltage/current distribution.

P.

hi pushhead
thanks for your reply to my question

do you know how we can see the variation of the impedance along the length of dipole or micrstrip antenna using CST MWS?

regards

Well, a quick way to do it will be to use a discrete port and "slide" it along the dipole or under the patch antenna.
In other words, you change the feeding point coordinates and see the variation referenced to your line impedance.

P.