== Designing Two Sets of Coupled Microstrip Lines ==
In this part of the tutorial lesson, you will design and test a microstrip realization of the coupled line bandpass filter you simulated in the previous part. For this purpose, you will use a substrate of thickness h = 1.6mm with ε<sub>eff</sub> = 3.4. You will assume a lossless substrate (tand = 0). Remember that in the previous section, TEM line segments with ε<sub>eff</sub> = 1 were assumed and the length of the coupled line segments were set to be a quarter free-space wavelength at 2GHz. For this part, first you need to design coupled microstrip lines with the given even and odd mode impedances. Then, you have to calculate the guide wavelengths of the couple microstrips at 2GHz. You will do these using [[RF.Spice]]'s Device Manager.
Open the '''Coupled Microstrips Designer''' dialog from the Tools Menu of Device Manager. Enter the substrate parameters: h = 1.6mm and er = 3.4. Enter the Z0e and Z0o values for the two types of coupled line segments from the previous section and calculate width and spacing of the coupled microstrip lines for each case. Then, open the '''Coupled Microstrips Calculator''' dialog from the Tools Menu of Device Manager. Enter the calculated microstrip width and spacing values to verify your design and also find the corresponding guide wavelengths λ<sub>g</sub> at 2GHz. The lengths of the coupled microstrip segments are chosen to be a quarter of the corresponding guide wavelength at 2GHz. The following table summarizes the parameters of the coupled microstrip segments L1, L2, L3 and L4.