Open circuit resonator not acting according to 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'

 

[sophiecentaur]

You need to excite the resonator with a lightly coupled input signal,

That could be achieved with a very high impedance source feeding in parallel with (across) the transmission line ('injecting from a Current Source'.)

 

[sophiecentaur]

@yefj
Re S parameters: The way the (Complex) S parameters are measured is by measuring the forward and reflected waves in a 'good' 50Ohm matched system. If you want to design a circuit with a resonator in it with an S Parameter tester then I think you should be looking at the S Parameters of the whole circuit or a part of the planned circuit. The point of the resonator will be frequency selective (obvs). The S parameter could reveal the presence of a resonator by an amplitude blip or a rapid phase change with frequency, depending.

 

[Baluncore]

in a 'good' 50Ohm matched system.

Units police here. 50Ohm has problems.
Ohm was a person, so ohm is the unit.
50 ohm is spaced, 50Ω is not.
47 kilohm is contracted, 47 kilo ohm is not. 47kΩ is also correct.

 

[sophiecentaur]

Units police here. 50Ohm has problems.
Ohm was a person, so ohm is the unit.
50 ohm is spaced, 50Ω is not.
47 kilohm is contracted, 47 kilo ohm is not. 47kΩ is also correct.

Low hanging fruit, officer.
Have a lovely day.