Geoffrey S. Mendelson wrote:
If you have a resonant antenna, supposedly all of the power is radiated.

(SWR 1:1)

If you have a nonresonant antenna, some of the power is reflected back to
the transmitter.

(SWR 1:1)

If you connect a tuner and it is "tuned", none of the power is reflected
back to the transmitter.

(SWR at transmitter 1:1, at antenna still 1:1)

Obviously it has to go somewhere.
Differentiate between an antenna that happens to present the wrong
non-reactive resistance... the tuner is just a transformer (whether done
with linked magnetic fields, or by a narrow band matching network of Ls
and Cs)

and an antenna that presents a reactive feedpoint impedance.
In this case: energy circulates between the tuning network and the antenna.

Say your antenna presents a Z that is inductive and you put a parallel
capacitor across the feed to exactly cancel the "inductance". What's
really happening is that you have the equivalent of an LC tank where the
energy moves back and forth between L and C every cycle. In the classic
LC, the energy moves between the magnetic field of the L and the
electric field of the C. In the antenna case, it's somewhat more
complex: the antenna stores energy in the near field in both electric
and magnetic fields.

That answers the question...
The problem is that nothing is lossless, so as it moves, there's a loss.
If it's a resistive loss, it goes as I^2, so doubling the current
results in 4 times the loss. And, if you have an antenna with high
stored energy (about which more, later), this square of the current
means bad news.




Many antennas don't have an explicit separate matching network, but do
the cancelling by doing it within the antenna structu say by
changing element lengths, etc... so now that "circulating current" is
circulating between different parts of the antenna.

In fact, the ration between that stored energy and the amount flowing
"through" (i.e. radiated away) is related to the directivity of the
antenna: high directivity antennas have high stored energy (large
magnetic and electric fields): the ratio of stored to radiated energy
is "antenna Q" (analogous to the stored energy in a LC circuit leading
to resonant rise).

So, high directivity = high stored energy = high circulating energy =
high I2R losses.

It circulates between tuner and antenna.




Where?

If you are designing a tuner, where would you design it to go?

Thanks in advance

Geoff.