This work proposes a symmetrical offset stack coupled lines balun and a dual balun for a single balanced mixer and a star mixer, respectively. To achieve a minimum insertion loss and a maximum bandwidth, the design formulas are derived by properly selecting the width of coupled lines and the offset width between two coupled lines. The measured results of the proposed single and dual baluns achieve the bandwidths of over 110% and 90%, and insertion losses less than 4.4 dB and 7.4 dB at 38 GHz. These two baluns occupy chip sizes of 0.07mm2. Two balanced diode mixers are further proposed and implemented in tsmc™ 0.18-μm CMOS processes. These mixers utilize a stack balun feature wide bandwidth with very compact size. The measured results of the single balanced and star mixer achieve over 115% and 100% bandwidth for a conversion loss of < 15 dB. The isolations are better than 24 dB from 10 to 65 GHz of the single balance mixer and better than 31 dB from 20 to 65 GHz of the star mixer.