ultra narrow band antennas?

[CopperCone]

What is the most narrow band antenna that can be made? Is it a thin dipole? Are there any tricks?

[T3sl4co1l]

Superconducting resonators have Q up in the 10^7 range, open a pinhole on that and you'll have an antenna with mediocre efficiency and a more than uselessly narrow bandwidth.

Presumably such a structure could be miniaturized, as a small helical resonator open to space (a Tesla coil as it were), rather than a nearly-closed Helmholtz resonator; at significant cooling cost, of course, given present technology.

Tim

[hagster]

The trouble with very narrow band antennas is that they are very easily detuned. This could be because of nearby materials(or people) or even temperature/humidity changes.

Typically electrically small antennas are narrow band. Much of this is due to the matching network needed to maximise efficiency.

An easy to envisage example is the small tuned loop. You can add more turns to the loop to increase the radiation resistance, but also increases the inductance and the required shunt capacitor size needed to match. The LC circuit becomes more and more narrow band and susceptible to slight changes in L or C.

[HB9EVI]

For the practical, everydays use us radioamateurs normally use short loop-antennas with a variable capacitor as tuning element. In case of an environment with a lot of QRM, such a loop can give a better S/N-ratio than a dipole