Changes
/* Designing a Quarter-Wave Impedance Transformer */
==Designing a Quarter-Wave Impedance Transformer==
Quarter-wave impedance transformer are often used for impedance matching between two transmission lines of different characteristic impedances Z<sub>o1</sub> and Z<sub>o2</sub>. In that case, a line segment of length L = 0.25λ<sub>g</sub> with a characteristic impedance of Z<sub>0</sub> = √( Z<sub>o1</sub> . Z<sub>o2</sub> ) is inserted between the two transmission lines. In this part of the tutorial lesson, we design a quarter-wave impedance transformer that matches your 100Ω resistive load to the voltage source with the 50Ω internal resistance.
<table>
<tr>
<td>
[[File:RF11.png|left|thumb|550px|The quarter-wave impedance transformer circuit.]]
</td>
</tr>
</table>
Quarter-wave impedance transformers are narrowband devices because they are designed based on a certain length at a specific frequency. You will design your quarter-wave impedance transformer to operate at 3GHz. At this frequency, the free-space wavelength is λ<sub>0</sub> = 3×10<sup>8</sup> / 3×10<sup>9</sup> = 0.1m = 100mm. Since your Generic T-Line is of the TEM-type (eeff = 1), therefore, λ<sub>g</sub> = λ<sub>0</sub> = 100mm. Also, Z<sub>0</sub> = √(100 . 50) = 70.71Ω. So you need a 25mm, 70.71Ω T-Line segment. Open the property dialog of your T-Line part and change its characteristic impedance to Z0 = 70.71 and its length to len = 25mm. Keep the default values of the other parameters: eeff = 1 and alpha = 0. Run a new AC Sweep test again as specified below:
