How Do Chokes in Microwave Waveguides Function?

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Discussion Overview

The discussion revolves around the functioning of microwave chokes, particularly in the context of waveguides. Participants seek to clarify the principles behind chokes, their applications in microwave circuits, and specific design considerations for high-frequency ranges, particularly between 20 to 40 GHz.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants inquire about the specific frequencies and propagation mechanisms relevant to microwave chokes, suggesting that the context of use is crucial for understanding their function.
  • One participant proposes that a choke can function similarly to an inductor, acting as a short circuit at DC while presenting high impedance at microwave frequencies, emphasizing the importance of considering parasitic effects due to physical dimensions.
  • A participant expresses interest in understanding the operation of chokes in axially segmented waveguides with circumferential slots, noting a desire to grasp the principles before applying them to cylindrical waveguides.
  • There is mention of the relationship between choke stub length and wavelength, with a participant questioning the reasoning behind the 1/4 wavelength length and the design of multiple stubs with small gaps to minimize leakage.

Areas of Agreement / Disagreement

The discussion does not appear to reach a consensus, as participants express varying levels of understanding and seek clarification on different aspects of microwave chokes and their applications.

Contextual Notes

Participants highlight the need for specific details regarding frequency ranges and the physical context of microwave chokes, indicating that assumptions about their function may depend on these factors. There are also unresolved questions about the design choices for choke stubs and their effectiveness.

MadScience
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Does anyone know how microwaves chokes work?

Or have any references with simple explanations?
 
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MadScience said:
Does anyone know how microwaves chokes work?

Or have any references with simple explanations?

Welcome to the PF.

Can you be more specific? What frequencies are you asking about? And what is the microwave propagation mechanism you are addressing? Do you mean inductive impedance on a PCB microwave frequency circuit? Or are you referring to something in a waveguide structure?
 
What are you trying to do? Need more info. Are you referring to using it as a dc source to supply power to say collector of a transistor but like an open circuit at the microwave frequency? Also it serve as isolation from the other stages.

From circuit I've seen, in theory, it is same as an inductor that is short circuit at dc and high impedance at desired rf frequency. There is no difference between rf or lf, a choke is a choke. You just need to worry a lot about parasitic and distributing effect due physical dimension.
 
Some more details:

I'm trying to understand how a choke would work for an axially segmented wave guide (with circumferential slots) in the 20 - 40 GHz region. Eventually I want to do it for a cylindrical wave guide but to start just understanding the cartesian version would be good.

I had a look at some of the original papers on chokes but the best understanding I was able to get was that they work something like lecher lines.

For instance, I can see intuitively why a choke stub should be about 1/4 wavelength long, but I don't know concretely why. Also, why have many stubs with small gaps between them? And how is the dimension of the slot chosen to minimize leakage?
 

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