## Newbie question lambda g

• 1
Hi, im totally new to uw, but have a 4th Ed book by Pozar and am slowly plowing through it. I have an Elec Eng degree but been out if it for years doing IT, so Im learning a lot of this from scratch as a hobby.

My question is with a WR430 waveguide, for calculating where 1/4 wavelength locations should be along the waveguide - should i use the free air wavelength, or use the lamdba g ( waveguide wavelength)?
• 34
I believe you should use lambda guide, as described here

https://www.microwaves101.com/encyclopedias/waveguide-mathematics

But I would hold out for a second opinion!

Steve
• 5
Hi
Agreeing with the previous answer and from what I've learned, I would say wavelength in a waveguide is modified with regards to the wavelength in an unbounded medium by the m and n indexes of the mode that you consider, as the propagating wave is not a perfect plane wave unless you go very high in frequency...

You can also check your Pozar(MWEng, 4ed. p112), Balanis(Adv.Eng.Electromags,1ed. p354) or Ramo (Fields&Waves in CommElectr, 3ed. p418) or go to the classics: Marcuvitz (WaveguideHandbook, Ch1)

Hope this helps.

Regards

Iban
• 2
Also, from Feynman lectures, which are very easy to read through, you can see itÂ´s in line with Microwaves101: see formula (24.19), you can find the lecture on this link http://www.feynmanlectures.caltech.edu/II_24.html
• 8
You need to use lambda g which is the wave length inside the wave guide for a particular frequency
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