antenna-theory.com

[Rfdesign]

I don't understand what's the relation between the Q and the input impedance of an antenna as mentioned in the following link:
http://www.antenna-theory.com/definitions/q.php
why "The higher the value of Q, the more sensitive the input impedance is to small changes in frequency." this is true?
Regards.

[admin]

Yeah I should probably add more details to that page. But here's another common definition of Q:

Q = 2*pi*(energy stored)/(energy lost)

Now, for lumped components like capacitors or inductors, you want high Q, which is the same as saying low loss.

For antennas, energy lost is not resistive losses but radiated energy. For a given antenna with a fixed radiation resistance, say 50 Ohms, the higher the Q the more reactive the antenna input impedance is. This reactive component causes the impedance to vary more quickly with frequency, so the bandwidth is lower.

What do you think?