Matching to imperfect antennas

RE: Matching to imperfect antennas

Bret Foreman — Tue, 17 May 2016 17:59:29 GMT

From my perspective, the important behavior is power transfer, not reflection. And I think we can all agree that a conjugate match will optimize power transfer from the output of the matching network to the (perfect) antenna. The question, then, is what figure of merit can I use to evaluate the degradation of power transfer as the impedance of the manufactured (imperfect) antenna varies? VSWR seems like the wrong metric, since the magnitude of gamma can easily be bigger than 1, which results in nonsensical (often negative) values for VSWR.

At the end of the day, I want to numerically evaluate how many dB of matching loss I will suffer for a given variation in antenna impedance, and then I want to calculate the statistics of this loss for hundreds of simulated impedances at a given frequency.

RE: Matching to imperfect antennas

RK — Sat, 14 May 2016 03:43:09 GMT

Conjugate matching and reflectionless matching aren't the same thing, except in the case where the matched impedence is resistive only (which is the usual case for a transmission line and one of the reasons matching is almost always done to a resistive component).

So if you match with the Zl == Zo you get no reflection at all, but not max power transfer (I have a problem with some part of that statement but I'm working on it), if you match conjugates you get max power transfer but a purely imaginary reflection, which just means the reflection itself has a phased component, ie it changes, however over the cycle it consumes no power.

Here's one paper which tries explain the difference, there are better ones, however discussion of complex reflection coefficients is fairly rare and often heated (and complicated)