What is phase delay through tapered microstrip line? (simulation vs reality)

[Terminator3]

Hello all!
My current design requires use of T-power dividers and very phase sensitive.
But for simplicity I ask a simpler case, but with the same problem. Just a straight microstrip line with two two quarterwave tapers.

Imagine we have a tapered microstrip line, total length is one wavelength. This line consist of four quarterwave sections:
[port1]-[quarterwave 50 Ohm]-[ quarterwave X Ohm ]-[ quarterwave Y Ohm]-[ quarterwave 50 Ohm]-[port2]

The problem is S21 angle of this simple line is varies from 0 degrees to around -20 degrees (fdtd, rf simulator with spice support, etc.).
I expect it to be near 0 degrees. Because I have many such sections in my design, -20 and even - 10 degrees shift is unnacceptable.

How to solve this problem before actual fabrication?

 

[FvM]

Unclear question. What are you varying? Frequency or other parameters? What's the frequency range? How are you measuring phase? With port extension according to the line length or without?

 

[ferdem]

Did you consider the effect of effective dielectric constant on the wavelength i.e. guided wavelength? Simulators may not simulate the materials perfectly.
Examine its sensitivity, introduce an error of 10% on the dielectric constant and calculate what it causes on the amount of phase shift. 10 degree of shift is not looking high to me.

 

[Terminator3]

FvM, i use constant frequency value.
The only thing I change is line configuration:
4 quarterwave 50-ohm sections in series
1 quarterwave 50-ohm + 1-Y ohm + 1-X ohm + 1 quarterwave 50-ohm sections in series
X,Y around 30...40 ohm.
Each time it is a full-wavelength line, also I put them in repeating series.

 

[FvM]

I would expect S21 0 degree total phase and varying magnitude caused by different standing wave patterns. If the phase is different, the electrical length of each line is probably not λ/4.