Mixer block details. (a) Photograph of the bottom part of the mixer block. The following components are marked: 1 – outputs from the LO power divider; 2 – LO directional couplers; 3 – the 90° RF hybrid; 4 – mixer circuits; 5 – the IF circuitry; 6 – the IF hybrid. (b). Detailed photograph of the mixer circuitry. The following components are marked: 1 – SIS junctions; 2 – the landing capacitor. The SIS mixer chip is placed in the mixer channels and is bonded to the IF extraction point through the landing capacitor, and to the ground at the choke structure.