Answer 7—A transmission line that is an electrical quarter-wavelength long at a particular frequency can be used to transform impedance from one value to another. This can be used, for example, to match a given transmission line to an antenna at a different impedance. This approach usually has lower losses and greater simplicity than using wound transformers; but, because of the size, it’s more suitable for higher frequencies.

In extreme cases, a quarter-wave matching section will transform a short into an open circuit and vice versa, allowing simple notch and band-pass filters to be constructed.

Contributor: David Tweed