Low-pass electronic filter:
The capacitors and inductors are the reactive elements of the filter. The number of elements ascertains the order of the filter. In this situation, an LC tuned circuit being employed in a band-pass or band-stop filter is considered a single element although it contains two components.
At high frequencies (above approximate 100 megahertz), sometimes the inductors contains single loops or strips of sheet metal, and the capacitors contain adjacent strips of metal. These inductive or capacitive pieces of metal are termed as stubs.
Single element types
A low-pass electronic filter realised through an RC circuit
The very simple passive filters, RC and RL filters, involve only one reactive element, except hybrid LC filter that is characterized by inductance and capacitance integrated in one element.