In order to avoid the difficulties associated with waveguide and point contacts at frequencies above 100 GHz, a planar integrated circuit combining SIS junctions and a receiving antenna has been developed. The antenna pattern and a study of the quasi-optical coupling using an f/1 TPX lens are presented. Measurements of the direct detection performance of this device at 88 GHz agree well with quantum theory. The measured noise of the device gives an NEP of 5.6×10
-14W/

. The antenna can readily be scaled to higher frequencies where quasi-optical coupling is essential. Being planar, this device can be replicated into a multi-detector array for imaging.