a) Photograph of the array module with the horn apertures visible. Conical horns are used to couple the incoming radiation to the detectors. b) Cross-sectional view of the horn array. Each horn feeds a cylindrical waveguide. At the waveguideexit a choke is used to optimize the coupling between the horn and the detector, as shown in (c). The LEKIDs are front-side illuminated. The detectors are fabricated on a 160 μm thick silicon wafer. The wafer thickness sets the λ/4 backshortdistance and the back side of the wafer is covered with 100 nm thick Al, which acts as a backshort and ground plane. There are pockets between the waveguides into which the spring-loaded pins that press down on the detector array are epoxied. c) Cross-sectional view of the coupling between the horn and one LEKID array element.