Design of a side-band-separating heterodyne mixer for band 9 of ALMA

A side-band-separating (SBS) heterodyne mixer has been designed for the Atacama Large Millimeter Array (ALMA) 602-720 GHz band, as it will present a great improvement over the current double-side-band configuration under development at the moment. Here we present design details and the results of extensive computer simulations of its performance. The designed SBS mixer exploits waveguide technology. At its core it consists of a quadrature hybrid, two LO injectors, and three dumping loads. The entire structure has been analyzed in a linear circuit simulator with custom code written to accurately (verified by HFSS finite element simulations) model the hybrid structures. This technique permitted an optimization of the dimensions and the study of the consequences of deviations from the ideal situation. It is estimated that the tolerances in several of the components should be kept at less than 3 mu m.