Matched antenna impedance and reactance

[danesh]

antenna impedance

why the reactance when antenna is matched supposed to be close to 0 or negative at imagenary part example: 50-j0.1 ohm?
what happen if reactance is positive at imagenary part?

thanks for concern
thanks
danesh

 

[House_Cat]

Re: antenna impedance

A matched antenna is resonant at the frequency of concern. At resonance, the inductive reactance equals the capacitive reactance. The phase angles, hence the signs, of the two reactances are opposite. The reactance effects cancel, leaving just the real part of impedance.

Having just the real part of impedance remaining is just what you want to get the maximum power delivered. If there is a reactive component, part of the power will be reflected back down the transmission line rather than being coupled to the atmosphere by the antenna.

The reactance in the antenna shifts the phase of the current in relation to the voltage and affects both the incident and reflected current, and also the resultant voltage. When an antenna has inductive reactance, the point of maximum voltage and minimum current is shifted towards the antenna. When it is capacitive, the opposite occurs. Both conditions result in increased VSWR and decreased antenna efficiency.