antenna-theory.com

[scubasteve]

Hi.

First post here so if I've gotten any of the etiquette wrong please let me know.

In this page from the main site I believe there may be a mistake in the calculation of the 800 ohm input impedance, or if not a clarifying sentence could be made.

Looking at the second to last image, copied below:



In the last line, I believe what is happening is that the real parts of the second expression drop out as they are dominated by the tan(pi/2) terms which tend to infinity. So then the (j) terms drop out leaving you with just 200*inf/(-50*inf) and the infinities drop out. Thus I think the result should be 200*-200/50=-800 rather than positive 800. How could it be positive?

If I am incorrect somewhere can someone please explain where? Or if not could a clarifying statement be added to the tutorial page to explain why the answer is not negative?

Many thanks!

[admin]

You are right on the math that tan(beta*L) goes to infinity so it dominates. It looks like the minus sign in the denominator is correct, but there should also be a minus sign in the numerator. The net result though should be positive (you would know something is wrong if input impedance is negative 800 Ohms)

[scubasteve]