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[Roberto]

I would like to know ....How can I calculate the feed point position where I have to feed the PIFA with a coaxial feed?

In the book "Antenna theory" of Balanis, It's showed how you can feed a MICROSTRIP ANTENNA, but in a microstrio antenna the slots are spaced lambda/2 (λ/2). Nevertheless in PIFA the slots are spaced lambda/8 (λ/.
The formula that is showed in Balanis for a MICROSTRIP ANTENNA is:

Rin(y=yo)=Rin(y=0)cos2(Yo pi/L)

Yo: Position of the feed point
Rin(y=yo): Impedance at feed point
Rin(y=0):Impedance at slot #1
L: patch length
pi=3.14....

Besides I have to feed in the middle of W (patch width)

THIS FORMULA OF THE POSITION OF THE FEED POINT IS FOR MICROSTRIP ANTENNA


But, Does it work in PIFA? because PIFA is smaller and the slots or resonators are spaced lambda/8 unlike microstrip where the slots are spaced lambda/2. On the other hand PIFA is short circuited

Could somebody tell me if the formula for the FEED POINT FOR MICROSTRIP work for a PIFA ANTENNA?

or is there any other formula??

Thanks so much for your help

Robert[/url]

[bigSteve]

Yeah the same basic formula applies:

Half-Wavelength Patch:
Rin(y=yo)=Rin(y=0) [ cos(y0 * pi/L) ]^2

However, if the PIFA is L_pifa=1cm long, you would use L=2cm in the above equation. Hence:

Rin(y=yo)=Rin(y=0) [ cos(y0 * pi/[2*L_pifa]) ]^2

This is because you basically still assume a sinusoidal voltage/current distribution, with the current and voltage a 90 degrees out of phase. [And the ratio of voltage and current is impedance]