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Electrical Engineering/measuring antanna impedance in 2.4 ghz spectrum

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Question
Hi, I am trying to build an external antanna for a 2.4 ghz wifi reciever. Can you help me understand how to match impedance between a 2.4 ghz wifi device and a home made 2.4 ghz antenna?  Is there a relatively cheap device one can build, or can a digital multimeter be used measuring ohms?

Answer
The 'cheapest' way to proceed is by trial and error; that is, by setting up a controlled reception area and a transmission system which allows you to make comparison readings of reception strength. Then by testing variations of antenna size, shape, length, etc. converge on the best performing design.

For impedance matching the easiest way to measure it is to put it at the end of a short transmission line (of several wavelengths long) and feed the line with a generator of the test frequency and compare the reflection or standing wave against a perfect resistive loading of the design frequency.  Sound difficult but really is simple if you have the right generator and dummy load.  You can find text book methods on how to do this.

But, I recommend the first approach from a practical point of view.  If you are designing for professional purposes then you need the testing and measurement method.

For antenna design I suggest you consult antenna design texts and monograms.

And, of course all depends on what you want the antenna to do. For example if you are wanting best range to a specific far away point you want a staged or yagi type design, perhaps; one that will reach hundreds of feet or yards like this one:

http://www.instructables.com/id/Easy-to-Build-WIFI-24GHz-Yagi-Antenna/

Here is another calculation idea:

http://www.nodomainname.co.uk/Omnicolinear/2-4collinear.htm

And so on and so on:

http://www.dxzone.com/catalog/Antennas/WiFi/

Good luck.  Hope this helps.  

Electrical Engineering

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