λ/4 Transformer

A λ/4 microstrip rotates the impedance in the Smith chart by 180 degrees. The center of the rotation is at the characteristic impedance of the microstrip.

In this example, R_L=25Ω is transformed to Rin=50Ω at f=0.5GHz. The characteristic impedance of the microstrip should be Z0=(R_LRin)^1/2=35.355Ω. The effective dielectric constant is assumed to be ε_eff=4, so the velocity factor is 1/(ε_eff)^1/2=0.5, the wavelength is λ=0.5×2.998e8/0.5e9=299.8mm, λ/4=74.95mm.