In this paper, a broadband double balanced mixer is presented using a wideband Marchand balun implementation by vertical coupler. Frequency is selected as $1.0{sim}3.7GHz$ for RF, $1.14{sim}3.84GHz$ for LO, and 140 MHz for IF signals. When LO signal with 7 dBm at 2.64 GHz is injected, a conversion loss of 7.5 dB and RF to LO isolation of -45 dB are obtained. Also, an average conversion loss of 9 dB and RF to LO isolation of -25 dB are obtained for frequency band of $1.0{sim}3.7GHz$.