There are two conditions to meet to have a correctly 'tuned' antenna (makes no difference what kind of antenna). The antenna should be resonant and there should be a good impedance match to the rest of the system (feed line and transmitter). That antenna's length or loading determines resonance. Resonance has nothing to do with impedance matching, it has to do with getting rid of any reactances in that antenna. Those reactances do not contribute to radiation efficiency so are detrimental to that antenna producing a good signal.
The other part, matching impedances, will have to be done with any and all antennas. There isn't any antenna that has a 50 ohm input impedance without some type of impedance matching being done at the antenna's feed point. Using the characteristics of particular types of coax to make that antenna's input impedance seem to be 50 ohms to the transmitter is certainly possible. It's called a 'conjugate match'. It is 'usable' but never efficient. You will have the same losses as without using that 'magic' length of coax. Your SWR meter may read a nicer number, but the mismatch is still there. Why? Cuz you are reading the SWR in the wrong place, at the transmitter end of the feed line instead of at the antenna feed point where the mismatch is.
What about changing the antenna's length to adjust impedance? You can find a length that will have a reactive component that in combination with some resistive component will make what that SWR thinks is 50 ohms impedance. But there are two things that length adjustment does. It introduces some reactive characteristics, and it destroys the resonance of the antenna. You got a nice SWR reading, but the efficiency of the antenna just flew out the window. Why does that sound sort of self defeating? It is self defeating, don't mistake that!
Nothing new in any of that, it's been a proven fact for a very, very long time. Don't agree with it? Fine, don't agree with it. It's still a fact though, not an opinion, but a fact.
- 'Doc