Excitation of TEM mode through a slot

[yefj]

Homework Statement: TEM mode
Relevant Equations: TEM mode

Hello, I have built a TEM mode resonator closed from bothe sides and added a source.
E-field is attached.how can i excite such mode threw that slot?
Hope this the correct forum.

 

[marcusl]

How did you get a modal E field without an excitation?

 

[yefj]

eigen mode solver in CST, it shows possible modes that could be created.
AM i in the correct section of the forum?
Thanks.

 

[marcusl]

Is this a school assignment?

 

[yefj]

no its not, where is the more suitable place?

 

[berkeman]

I will move it to the EE forum for you now.

 

[berkeman]

and added a source.

eigen mode solver in CST, it shows possible modes that could be created.

So you don't actually have a source inside the structure? It's a little hard to tell from the plots you've uploaded.

 

[yefj]

I need to ecite the fillowing structure so it will create the E-field H-field shown below.
Any intuitions?
Thanks.
Structure:

E-field:

H-field:

 

[berkeman]

What is the application?

 

[yefj]

Its a resonator.

 

[marcusl]

You can excite that mode with a small loop inserted in the slot. The plane of the loop should lie in the z-r plane.
EDIT: corrected the plane.
RE-edit: no, it was ok at first.

 

[yefj]

Hello Marcus, I cannot put a loop inside the coax.
I used another method which is using a coax probe as shown below.
It excited the TEM mode in my resonator as shown in the photos below.
Currently the coax probe is very very under coupled as shown in the S params and smith chart.
Is there a way to see how can i improve the coupling threw the E-field genrated?
Thanks.

 

[marcusl]

Yes, an electric probe also works but I suggested a loop because it gives you more adjustability (loop area, position and orientation). It looks like you are using air coupling, BTW. This is a mistake. Drill a hole through the cylinder's wall opposite the slot and insert the probe, soldering the coax shield to the cylinder. Changing how far the center conductor extends into your resonator adjusts the coupling. You might even be able to connect it to the center rod of the resonator (maximal coupling), although it may really mess with the impedance presented to the source.
The impedance match is very important, because you can have good coupling to the resonator but the incident power reflects back to the source due to a bad match. Consult books on waveguides and resonators for guidance.

 

[tech99]

Yes, an electric probe also works but I suggested a loop because it gives you more adjustability (loop area, position and orientation). It looks like you are using air coupling, BTW. This is a mistake. Drill a hole through the cylinder's wall opposite the slot and insert the probe, soldering the coax shield to the cylinder. Changing how far the center conductor extends into your resonator adjusts the coupling. You might even be able to connect it to the center rod of the resonator (maximal coupling), although it may really mess with the impedance presented to the source.
The impedance match is very important, because you can have good coupling to the resonator but the incident power reflects back to the source due to a bad match. Consult books on waveguides and resonators for guidance

For the case of the slot, radiation arises because of currents flowing around the cylinder. Therefore the exciting voltage must be connected across the slot. The impedance can be altered by choosing the position of the two connections, which are usually near one end of the slot. This is called an Alford Slot antenna and will provide an approximately circular radiation pattern (Antennas, by J D Kraus, page 643).

 

[marcusl]

Is the goal to maximally excite the TEM mode or to maximize radiation? They may require different excitations.

 

[yefj]

Hello,the goal is maximally excite TEM.
my question regarding the coupling between the probe and the coax.
How can i see visually at the fields and currents the coupling ,not just looking at the smith chart.

"Is the goal to maximally excite the TEM mode or to maximize radiation."