Inductively-loaded wire monopole antenna

Image of the Inductively-loaded wire monopole antenna.

The inductively-loaded monopole antenna is a linearly polarised low gain antenna with an omnidirectional radiation pattern. The antenna uses a series inductor to tune out the large capacitive reactance introduced by shortening the traditional quarter-wavelength long wire.

Radiation pattern of the inductively loaded monopole illustrating the familiar omnidirectional pattern of a conventional monopole.

The benefit of the shorter structure comes at a price - a very low input impedance and a narrow bandwidth. A conventional monopole may provide 10% usable bandwidth in a 50 Ohm impedance system, while the inductively loaded monopole may require matching to a real impedance below 10 Ohm and achieve a bandwidth as low as 0.5%!

The inductively loaded monopole antenna has a very low input impedance.