Seeing microstrip geometry in the TDR plot

[yefj]

Hello, I have built and simulated in CST a microstrip line with two discontinuetues.
looking form port 1 we have one discontinuety at 8.25mm the second one is at 36.25mm=8.25+10+18
given velicity factor 36mm and 8.25 mm roundtip where calculated at 740ps and 170ps.
few questions:
1.could you please say if you recognise the microstip geometry in the TDR?

2.I should have 3 sections of 50ohms why do you this I dont have them?

3.the plot is changing impedance graually unlike spice simulation ,what whould you reccomend to recognise start and stop of individual unique part of the microstrip?
Thanks.

 

[Baluncore]

1.could you please say if you recognise the microstip geometry in the TDR?

Yes. It is the same from each direction, only with a different length connection = time delay.

Did you terminate the unused port in 50 ohms when simulating the TDR ?
If so, why does it show only 26 ohms at Tmax ?

2.I should have 3 sections of 50ohms why do you this I dont have them?

Because the design of the narrow track is for about 32 ohms.
The design of the wide track is for 20 ohms.
Did you use the equations for a single or double sided PCB ?
The simulated instrument has output Zo = 47 or 48 ohms at T=0.

3.the plot is changing impedance graually unlike spice simulation ,what whould you reccomend to recognise start and stop of individual unique part of the microstrip?

What you have built is a transmission line filter. The wide tracks will resonate at some λ/2 frequency, I suspect you are seeing multiple reflections.

Give it another try.
Fix the track width calculations to restore Zo = 50 ohm.
Terminate the simulated track in 50 ohms.