Fourier transformation for circular apertures

QuarkDecay
Messages
43
Reaction score
2
Homework Statement
Find the Resolution of a circular aperture with a radius of a
Relevant Equations
Fourier transformations noted below
My notes say that the Resolution of the Aperture(in the Electric field of the wave) is the Fourier transformation of the aperture.
Then gives us the equation of the aperture:

1659133442407.png

and says that for the circular aperture in particular also:

1659133647684.png


My attempt at solving this:

We know that the Fourier transformation in general is :
1659133738649.png


For circular aperture we have G(x)=Π(r/2a). So I thought that if I manage to turn the θ/λ inside the H(θ) equation into an s, (θ/λ=s or θ=λs), then I could say G(x)=Π(r/2a) ⊃ aJ1(2πas)/s, therefore H(θ)= aJ1(2πas)/s, but not this one exactly, because I need to change the s inside the H(θ) equation.

So H(θ=λs)=∫∫G(x)e-i2πsxdx
But now we have an H(λs) instead of an H(θ), so we need to use this Fourier property
1659135074015.png

and this is where I stop because I don't know which is which, and I don't know how this ⊃ works much.
I tried replacing the s with s=θ/λ and say
H(λ*θ/λ)=Η(θ)=aJ1(2πa(θ/λ))/(θ/λ) But I always get a result of
H(θ)=DλJ1(πDθ/λ)/(2θ) and the result is supposed to be this:
1659135029572.png

I always get the λ on the top. And again, when I tried using the
1659135566936.png

I still got the same result, although I'm not sure if I'm appliying this to the H(λs) right, but the book does say that I need to use the property above somewhere.
My main problem is that I can't really solve Fourier transformation and don't understand very well how this ⊃ symbol works
 
Physics news on Phys.org
I've no idea what \supset is supposed to mean in this context.

Start from <br /> H(\boldsymbol{\theta}) = \iint_{\mathbb{R}^2} G(\mathbf{x}) e^{-2\pi i \boldsymbol{\theta} \cdot \mathbf{x}}\,dA where so far as I can tell from googling the aperture function G(\mathbf{x}) is equal to 1 if \|\mathbf{x}\| \leq a and 0 otherwise. By symmetry we can orient the coordinate axes such that \boldsymbol{\theta} = (0,\theta). Now change to plane polar coordinates (r, \phi) to obtain <br /> H(\mathbf{\theta}) = \int_0^a r \int_{-\pi}^{\pi} e^{-2\pi i r \theta \sin \phi / \lambda}\,d\phi\,dr. The integral over \phi can be done by making use of the integral representation J_0(z) = \frac 1{2\pi} \int_{-\pi}^{\pi} e^{-iz\sin\phi}\,d\phi and the resulting integral over r can be done by substitution, noting that <br /> \frac{d}{dz} (zJ_1(z)) = zJ_0(z).
 
  • Like
Likes vanhees71, PhDeezNutz, Delta2 and 1 other person
pasmith said:
I've no idea what \supset is supposed to mean in this context.

Start from <br /> H(\boldsymbol{\theta}) = \iint_{\mathbb{R}^2} G(\mathbf{x}) e^{-2\pi i \boldsymbol{\theta} \cdot \mathbf{x}}\,dA where so far as I can tell from googling the aperture function G(\mathbf{x}) is equal to 1 if \|\mathbf{x}\| \leq a and 0 otherwise. By symmetry we can orient the coordinate axes such that \boldsymbol{\theta} = (0,\theta). Now change to plane polar coordinates (r, \phi) to obtain <br /> H(\mathbf{\theta}) = \int_0^a r \int_{-\pi}^{\pi} e^{-2\pi i r \theta \sin \phi / \lambda}\,d\phi\,dr. The integral over \phi can be done by making use of the integral representation J_0(z) = \frac 1{2\pi} \int_{-\pi}^{\pi} e^{-iz\sin\phi}\,d\phi and the resulting integral over r can be done by substitution, noting that <br /> \frac{d}{dz} (zJ_1(z)) = zJ_0(z).
Thanks a lot...! I'm quite desperate over this problem and I couldn't find the solution anywhere over the web. Been searching for it for three days. Now I hope I can solve the rest of it lol
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top