# Showing Resonant Frequency

1. Jun 27, 2012

### fereshteh

So I have this PEC cylinder that I am illuminating with a plane wave. As we know it should resonate when lambda is twice the length of the cylinder.
My adviser suggested to examine the phase of surface current, but I do not understand how it is relevant. Maybe I didn't get it right....

2. Jun 27, 2012

### Simon Bridge

Welcome to PF.
It helps to describe the experiment setup - do not assume everyone knows the same exact setup that your course uses.

Did you examine the relative phase of the current anyway?
To understand what the phase has to do with it, consider how the wave you are using interacts with the PEC: why would you expect resonance of any kind at all anyway?

3. Jun 27, 2012

### fereshteh

You are right. I should try to describe it.
I have a plane wave, z-polarized, illuminating a thin PEC wire along z-direction.
I am doing a frequency sweep in such a way that the wavelength corresponding to central frequency is twice the length of the wire. So at that frequency we should see bigger RCS due to resonance. My adviser mentioned I should examine the phase of the surface current on PEC to show this resonance at this frequency but I do not understand how this is relevant.

4. Jun 27, 2012

### fereshteh

I did examine it. At the resonance frequency it is 180 degrees.

5. Jun 27, 2012

### Simon Bridge

OK. So clearly there is a relationship between the current phase and resonance.
(Did you check what happens to the current phase as you went off resonance?)

6. Jun 27, 2012

### fereshteh

It just continues to increase!

7. Jun 27, 2012

### Simon Bridge

What? Is it always greater than 180 degrees?
(That would be pi radiens - hint: useful to start thinking in radiens.)
Can you think of other resonant situations which behave like this?
What do you think happens at 2$\pi$?