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  1. #1
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    L vs IF antenna, which to pick

    I need to pick a PCB trace antenna.

    From my understanding, the only advantage of the inverted F over an L antenna is that the inverted F antenna can be matched by choosing the feed point.
    Either way I was going to use a pie matching network, so given this fact is there still any advantage to choosing the inverted F antenna?

    •   Alt5th January 2017, 15:53

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  2. #2
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    Re: L vs IF antenna, which to pick

    Let me add what my understanding is and put forth some assumption(s), so someone can tell me if I'm wrong.
    how3.png

    Looking at point B from the feedline, to the left (C) is a overall capacitive load (parallel to ground i guess) and to the right (A) is an overall inductive load (parallel to ground i guess). By moving the feed point, one can do a decent amount of impedance matching without requiring extra components. I bet that a perfectly designed antenna will be matched to 50 Ohm without requiring any matching components. The manufacturer would save up to two components on the board, thus safe cost. I almost want to assume that this is the only reason to use the inverted F style.

    In my case, I don't care about the cost. If segment A represents nothing other than a parallel inductor to ground, then I propose the second picture that has this stub removed and instead has an equivalent parallel discrete inductor to ground.
    I'm a little hesitant to assume that the 2nd picture is better. On the one hand the actual antenna becomes physically larger but on the other hand I wonder if the inductor through some mechanism that I don't know about loses energy, that would otherwise be radiated via the stub (A).

    Something makes me wonder if there is some other benefit to the inverted F antenna aside from saving on matching components.



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