A double balanced mixer includes a local oscillator balun, a radio frequency balun and four diodes. The local oscillator balun has a transmission line, a half wavelength transmission line and a quarter wavelength transmission line mounted on a printed circuit board. The radio frequency balun has a transmission line, a half wavelength transmission line and a printed circuit line mounted on a printed circuit board. The four diodes are mounted to the printed circuit board and connected between the local oscillator balun and the radio frequency balun.