Bandpass filters out of metal tubes? (Bird electronics)

[Phil1977]

Hi,

I was wondering how the bandpass filters shown in this video are working:



I have no need to know it, I´m just curious. I can roughly imagine how a waveguide works, but just have no idea how a set of tubes creates a well defined and mostly flat frequency response.

[madires]

They are called stub filters. When the stub is lambda/4 long and reflects the wave you'll get a lambda/2 delay (180° phase shift).

[Phil1977]

Thank you madires, that wording leads to the right explanations!