I am trying to come up with an equivalent circuit for a structure that I'm working on. The response is shown below:



The modelling of the structure hasn't incorporated any loss, therefore the real part of the impedance is 0. I am not a circuit expert, and would like some pointers on what kind of circuits would be capable in producing a response like this.

I was pointed to this circuit:

However, it generates a different response as shown below:



Where the imaginary impedance first increases near resonance, then decreases.

I tried a few simple LC circuit configurations but wasn't able to find one that matches my expectation, I was wondering if anyone could give me some pointers.

Thanks!

 

How about a simple LC series circuit.
The impedance of that reduces near resonance and then increases after resonance.

 

Try replacing C2 in the crystal equivalent circuit with a 3nH inductor.

 

How about a simple LC series circuit.
The impedance of that reduces near resonance and then increases after resonance.

This is the first thing I tried and I don't think it behaves as what I observed on the graph.

 

Try replacing C2 in the crystal equivalent circuit with a 3nH inductor.

I have and it didn't seem to work, does it also depend on other factors (frequency, value of L and C, etc.?)

 

The response I got is as below

Try replacing C2 in the crystal equivalent circuit with a 3nH inductor.

 

How about a simple LC series circuit.
The impedance of that reduces near resonance and then increases after resonance.

Response I got for a series LC circuit:

 

Here's the LTspice simulation of an arbitrary series, ideal LC circuit.
I drove it with a current source (1Aac) so V(in) is a measure of the circuit impedance.
As you can see, below resonance, the impedance steadily drops until going to a very low value at resonance, and then steadily rises above resonance.

 

Here's the LTspice simulation of an arbitrary series, ideal LC circuit.
I drove it with a current source (1Aac) so V(in) is a measure of the circuit impedance.
As you can see, below resonance, the impedance steadily drops until going to a very low value at resonance, and then steadily rises above resonance.

View attachment 129863

But the *impedance* response that I am expecting is

Y axis is impedance, not current.

 

Maybe some negative resistance will give you a range of Z at resonance.

 

T

Maybe some negative resistance will give you a range of Z at resonance.

The Z I'm plotting is imaginary.

 

I am trying to come up with an equivalent circuit for a structure that I'm working on.

Why do you want this response?

 

Why do you want this response?

I'm trying to map the antenna I designed to a circuit model so I could have a systematic way of analyzing it....

 

But the *impedance* response that I am expecting is...

Here's the plot in of my simulation in ohms.
The difference is that yours has the ohms scale magnitude reversed in direction from mine.