Microwave microstrip simulation

[Leiser]

Hi,

I'm trying to simulate a 0.114pF shunt capacitor using a short circuit stub at 1.5GHz microstrip.

Doing the calculation it turns that a 51.7mm 50R transmission line is needed. I have compared the S11 parameters of the lumped capacitor to the transmission line and are the same.

Then I have calculated the microstrip length and thickness for a 1mm thickness PCB with Er=4.7 and 35um Cu thickness using the Txline application from MW, thickenss is 1,79mm.

I am not sure about what physical lenght I have to put in the TX line application.

Doing a tunning in MW I have found that for L=27.55mm the S11 of the microstrip is the same as the capacitor.

I do not understand why if I use a 51.7mm length microstrip with a short circuit I do not have the same result than for the 51.7mm transmission line.

Any suggestions?

Attached a doc file with MW sch.

 

[Higgler]

Was your original 51.7 mm length of transmission line in AIR? You didn't mention how you made your original transmission line, i.e. did you use the same dielectric 4.7?

The length is shortened to sqrt(diel. value) to get the same result as air.