Spurline

The spurline is a type of radio-frequency and microwave distributed element filter with band-stop (notch) characteristics, most commonly used with microstrip transmission lines.

Only one of the input ports of the coupled lines is connected to the feed microstrip, as shown in the figure below.

The orange area of the illustration is the microstrip transmission line conductor and the gray color the exposed dielectric.

is the wavelength corresponding to the central rejection frequency of the bandstop filter, measured - of course - in the microstrip line material.

The additional resonances can be designed to widen the antenna bandwidth or to create multiple bands, for instance, for a tri-band mobile phone.