Practical way to measure the microstrip impedance

[surfing]

Here is my method to measure the ustrip impedance

Step1. Perform a one-port calibration at the end of the test cable
Step2. connect the fixture and measure the 50-ohm load
Step3. analyze the S11 data, is the middle point of that circle present
the ustrip char. impedance.?

(this method ignored the effect of the connector)

here are 2 jpg. to illustrate the method

Are there any problem in my method?

 

[flyhigh]

Hi,

I think it is a very straightforward way to determine the Zc of a microstrip. Alternatively, you can measure the response of a trough line (2 ports, not terminated with resistors). Then you can transfer the measured 2 port S paremeter file to a microwave circuit simulator and change the impedance of both port simulatneously to get the S11 (and S22 in the same time) to become the spot in the center of a Smith chart. The characteristic impedance of ports is the characteristic impedance of your line. You can even use TDR (Time Domain Reflectometry) feature on your NA to eliminate the influence of connector discontinuity form measured S pars by applying time gateing. The advantage of this is that you don't need to care about resistor accuracy, grounding effect, parasitics etc.

I use this method from time to time to get the charactheristic impedance from some funny lines that I analize in EM simulator without port parameter calculation option.

flyhigh

 

[surfing]

Flyhigh,

Thanks your opinion.

I am a little surprised why few people are interesting in testing microstrip's impedance?

would they rather believe software simulator than
measurement by themself?