Quarter-wave impedance transformer
![The lumped element low-pass filter (top) can be converted to a design that eliminates the inductors and contains capacitors only by the use of J-inverters, resulting in a mixed lumped element and distributed element design.](/Images/godic/202502/05/LC_to_J-inverter_filter.svg2125.png")
![Quarter-wave transformers are illustrated in an impedance Smith chart. Looking towards a load through a length l of lossless transmission line, the normalized impedance changes as l increases, following the blue circle. At l=λ/4, the normalized impedance is reflected about the centre of the chart.](/Images/godic/202502/05/SmithChartLineLength.svg2125.png")
![Standing waves on a transmission line with an open-circuit load (top), and a short-circuit load (bottom). Black dots represent electrons, and arrows show the electric field. A quarter-wavelength away from the open-circuit, the current and voltage oscillations are exactly the same as at a short-circuit, and vice versa. This reflects the fact that open circuit (Z=∞) is dual to short circuit (Z=0).](/Images/godic/202502/05/Transmission_line_animation_open_short22125.gif")
A quarter-wave impedance transformer, often written as λ/4 impedance transformer, is a component used in electrical engineering consisting of a length of transmission line or waveguide exactly one-quarter of a wavelength (λ) long and terminated in some known impedance. The device presents at its input the dual of the impedance with which it is terminated.