Millimeter-wave passive circuits that are designed and fabricated in the form of substrate-integrated waveguide (SIW) are presented in this paper. A W-band SIW 90° hybrid coupler and multiport SIW circuit are made and synthesized on alumina substrate using metallized slot arrays. In order to connect the SIW circuits with WR-10 standard rectangular waveguides for measurement purposes, a new transition is also proposed and developed. Such millimeter-wave integrated passive circuits are developed for applications in radar sensors operating at 94 GHz. Performances of these circuits are evaluated and discussed on the basis of a series of S-parameter simulations and measurements. Excellent agreement between simulated and measured results is observed.