Actually I am not sure if the formula is correct or wrong since this research article (Page 4) uses the formula from the website - microstrip calculator , to find the Rin|y=0Hi,
Perhaps you can get the formula from the first website and compare it to the other formula and see if they are similar. One possibility is that the web site did not set up the formula right so you could try that.
by Jake Hertz
by Aaron Carman
by Jake Hertz
by Duane Benson