In this paper, we have presented millimeter-wave high conversion gain quadruple subharmonic mixers adopting the cascode structure. The subharmonic mixers were successfully integrated by using 0.1 mum GaAs pseudomorphic HEMTs (PHEMT's) and the coplanar waveguide (CPW) structures. From the measurement at LO power of 13 dBm at 14.5 GHz, it shows that conversion gain is 3.4 dB which is one of the best conversion gains at 60.4 GHz. Isolations of LO-to-IF and LO-to-RF were -53.6 dB and -46.2 dB, at a frequency of 14.5 GHz, respectively. (C) 2004 Elsevier B.V. All rights reserved.