Order of magnitude of Grating Spacing!

[aama100]

1. The problem statement, all variables and given/known data

Some microowaves (EM radiation) have wavelength of 3 cm. What would be the order of magnitude of grating spacing needed to observe these ?

2. Relevant equations

n\lambda = d sin\theta

3. The attempt at a solution

First of all, I am not really sure if I was using the correct equation for that question but all what I am doing is about the diffraction grating spectrometer, gas spectra wavelength of light. In that question there was no angle so I can find n. The only thing is the wavelength given. I do not want you to solve it. I just want you to lead me to where should I go ?

[merryjman]

I once saw this video of a guy making ball lightning in a microwave oven, and he used a graphite 'antenna' that was 1/4 the 110-cm wavelength of the microwaves, and a circular 'focusing' bowl that was 1/2 the wavelength. If that gives you any idea.

So I think this problem is easier than you're making it. In order to resolve light, you need a grating which approximately matches the wavelength of the light. So for visible light, you need small spacing (like 10,000 slits per cm), and for radio waves (like those "very large array" dishes they use for stars) you need large spacing, like several meters between dishes.