# What is the impedance of two transmission lines in parallel?

Lets say we have two transmission lines in parallel as shown in the figure below, what will be the total impedance of their combination? That rectangle is the way I am representing TL and Z is the characteristic impedance and theta is the electrical length.

I was thinking whether I can use the same formula as for the case of resistors. So, the characteristic impedance of two parallel transmission lines will be as shown below and electrical length is the same, theta: $$Z_{total} = \frac{Z_1*Z_2}{Z_1+Z_2}$$ Is this correct?

• It's not clear, from your diagram how the transmission lines are connected at the sending end and receiving end. There is more than one way of doing this. – Chu Jul 14 '19 at 0:07
• Is the length of both transmission lines the same? – Eduardo1992 Jul 14 '19 at 0:11
• Yes, they have similar electrical length. – BGA Jul 14 '19 at 5:37