Windsurfer reflective surface considerations

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#1
Many of the threads on the Windsurfer type antenna booster talk about the kind and arrangement of the metallic material used as the reflector. Typically aluminum or copper tape or sheet is used. One area of concern is how smooth the surface needs to be in order to prevent losses from spurious reflection.

I've been doing some research on microwave antennas and came across this paragraph in the ARRL Antenna Book, 22cd edition (page 15-59). The specific discussion is for parabolic reflectors but the passive element reflector design of the Windsurfer should follow the same physics.

Gain is dependent on good surface accuracy, which is more difficult to achieve with increasing frequency. Surface errors should not exceed 1/8 λ {wavelength} in amateur operation.
At 2.4 GHz that comes out to 1.25 cm / 8 = .15 cm = 1.5 mm. That is a comfortably large number for smoothness. So, assuming no other factors are involved, any reasonably smooth surface should be adequate.

Any thoughts?
 
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#2
I think they're referring to how close to a mathematical parabola the reflector is, with the radiating element at the focus of the parabola, not to the smoothness of the surface.
 
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#3
I think they're referring to how close to a mathematical parabola the reflector is, with the radiating element at the focus of the parabola, not to the smoothness of the surface.
There is certainly that concern - I'm working on that now in terms of optimization, but there are a number of threads were folks obsess about the need for surface smoothness. At least what I can determine, you needn't worry about that unless you are particularly clumsy.
 
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#4
Many of the threads on the Windsurfer type antenna booster talk about the kind and arrangement of the metallic material used as the reflector. Typically aluminum or copper tape or sheet is used. One area of concern is how smooth the surface needs to be in order to prevent losses from spurious reflection.

I've been doing some research on microwave antennas and came across this paragraph in the ARRL Antenna Book, 22cd edition (page 15-59). The specific discussion is for parabolic reflectors but the passive element reflector design of the Windsurfer should follow the same physics.



At 2.4 GHz that comes out to 1.25 cm / 8 = .15 cm = 1.5 mm. That is a comfortably large number for smoothness. So, assuming no other factors are involved, any reasonably smooth surface should be adequate.

Any thoughts?
Looks like there's an error of one order of magnitude for the initial wavelength @ 2.4 GHz.

It should be 125 mm or 12.5 cm (4.92"), not 1.25 cm.

Thus 1/8 wave would be 15.6 mm (.615").
 
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#5
Looks like there's an error of one order of magnitude for the initial wavelength @ 2.4 GHz.

It should be 125 mm or 12.5 cm (4.92"), not 1.25 cm.

Thus 1/8 wave would be 15.6 mm (.615").
****. Hate that. But that makes it even more tolerant....

Thanks for the pickup.
 
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#6
Ever make one of those homemade windsurfers? I did - and the surface can be described a lot of ways, but smooth isn't one of them. Yet it seems to work okay.
 
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#7
Ever make one of those homemade windsurfers? I did - and the surface can be described a lot of ways, but smooth isn't one of them. Yet it seems to work okay.
Yes, that's the point. Doesn't really need to be a mirror.
 

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