A circuit includes a conductive layer, an insulation layer on the conductive layer, a transmission line on the insulation layer, the transmission line having a first end and a second end, and a stub on the insulation layer and having a first section of a first constant width connected to the transmission line at a location on the transmission line between the first and second ends, and a second section of a second constant width adjacent to the first section. The first constant width is less than the second constant width.