# I Transmission in Single Mode Waveguide

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1. Jul 18, 2017

### TinaTina

Hello there,

I was wondering if the power profile of a single mode waveguide can be changed? I mean, a wave that travels through the waveguide will have a harmonic shape, right? Is it possible to get a different shape of the power profile?

Thank you :)

2. Jul 18, 2017

### tech99

The cross sectional shape of the 'guide can be changed, for instance, to a dumb bell, or from round to rectangular. The walls can be loaded with dielectric, or by inserting screws. But essentially, a waveguide guides a wave, and its contents will be wave-like!

3. Jul 18, 2017

### sophiecentaur

What exactly do you mean by "power profile'?
Is there some reference you can give us to help get some context here?

4. Jul 19, 2017

### TinaTina

Thank you for your replies. Well, when I simulate a waveguide, I can look at the input over the output profile. Does that make sense?

5. Jul 19, 2017

### sophiecentaur

Do you mean the Field distribution over the end? Do we have a translation problem here?

6. Jul 20, 2017

### TinaTina

So, the field distribution would be a cross section of the waveguide, right? What I meant with the "output profile" was more like the Power Profile. So the question is: can I have a power profile of a single mode waveguide that is for example rectangular shaped?

7. Jul 20, 2017

### davenn

your term power profile still doesn't really make sense
do you understand how the electric and magnetic fields look inside a waveguide ?

have you seen these diagrams before ? ......

..

8. Jul 20, 2017

### TinaTina

Thank you for your reply, daevnn. Sorry, I might have labelled it wrong. It is probably a basics problem. Yes, I have seen these before. I think I understand how the waves propagate. What I tried to say is: when I "cut" the waveguide (like a cross section), I will get a sinusoidal function for the E-field for example. Because this is how the waves propagate, just like in the pictures you send. But if I simulate a device, I can also plot the input-output profile of this device, which is like the spectral response, right?

9. Jul 20, 2017

### TinaTina

So, if I for example have a single mode waveguide coming into a multimode wavguide this will create an interference pattern and self-imaging, right? At some points, I will get an overlap of two images, which creates a "rectangular" shape of the crosssection, instead of a sinusoidal function (because it is two sinusoidal functions overlapping and creating a broader, flattened function). Can I transfer this flat image into a single mode waveguide if I put a single mode waveguide behind the multimode waveguide?

10. Jul 20, 2017

### davenn

when you say device, are you referring to the waveguide or something else ?

The waveguide, like all RF components has a frequency response. That is you can plot how it responds to a change in applied frequency

Waveguide is basically a high pass filter. It will only pass frequencies above a certain frequency ( for a given size waveguide)
that lower frequency is called the cutoff frequency.
A note to be made .... although the WG will pass all higher frequencies, above a certain point multi-moding will occur and this will
lead to losses ( greater attenuation) of the signal.
As a result, WG has a stated lower freq of use ( the cutoff frequency) and a high end freq limit before which moding occurs

Dave

11. Jul 20, 2017

### sophiecentaur

@TinaTina Why do you insist on using a term that no one but you understands? "Power Profile" means absolutely nothing to anyone else but you. If you want to take Physics seriously, you should be prepared to use a common language. If nothing else, it would be polite and would show some respect for the subject.
For a simulation to be valid, it has to represent a real world item. (Garbage in = Garbage out, remember) Dave has shown you field distributions for real waveguides and those fields are there because of the boundary conditions with the wall of the guide. Are you proposing that you can change the fields at the walls? How would you achieve that?
?????