Novel design approaches for ultra-high-order subharmonic self-oscillating mixers (SOMs) based on a multiple-element technique are presented. They are of high impact for high-end millimetre-wave systems as subharmonic operation reduces local oscillator frequency requirements. An outline of the basic theory and a design procedure for arbitrary high mixing orders are presented, and a sixth-order SOM is fabricated for the first time. The prototype exhibits a conversion gain of +2.8 dB at an RF input frequency of 7.4 GHz.