This paper presents 77-GHz CMOS radar transmitter and receiver chips equipped with monopole feeders for use in frequency-modulated continuous-wave radar systems. The on-chip monopole feeder can feed not only the aperture of waveguides but also the slots on planar circuits by simply attaching the chips to a printed circuit board using a low-cost non-conductive epoxy. With the aid of a high ratio multiplier and the proposed on-chip feeder, a radar system can easily be integrated without needing to use precise and expensive millimeter-wave packaging technologies. In order to experimentally confirm this, the chips integrated with waveguides are first measured and a full radar system integrated on the planar circuit is evaluated using the microstrip patch antennas. Finally, with the benefit of compact integration technology, the design of a five-channel 3-D environmental sensing radar for small-unmanned aerial vehicles is presented. INDEX TERMS Radar, CMOS, frequency multiplier, millimeter-wave (mm-wave) packaging, on-chip feeder.