Open circuit resonator not acting by theory

[yefj]

Hello, I have tried to implement an open circuit microstrip resonator .
I got the microstrip resonating at 5Ghz as shown below.
However the S-parameters is very bad.
Is there a way to improve the matching so It will have a better dip in 5GHz.

 

[Baluncore]

However the S-parameters is very bad.
Is there a way to improve the matching so It will have a better dip in 5GHz.

If you measure S11 at one end of the resonator you will be loading it with 50Ω. That will kill any resonance.

You need to excite the resonator with a lightly coupled input signal, then view the output from a lightly coupled load. That requires three spaced strips on the PCB, one input, one resonator, and one output probe. The resonance will appear as a dip of the input, and a peak in the load on the output.
The input and output will be λ/4 long, which makes them quarter wave transformers.
The resonator will be λ/2, and so is usually bent into a 'U'.

https://en.wikipedia.org/wiki/Distributed-element_filter
Google: 'hairpin resonator'