One possible limitation for automotive collision avoidance radar applications is unwanted antenna beam squinting over frequency. To circumvent this problem, this paper studies a novel K-band automotive radar that improves transmitted power distribution over the horizontal plane using a substrate-integrated waveguide (SIW) 4x4 Butler matrix (BM) beamforming network. The 24 GHz system, which is scalable to 77 GHz, uses frequency modulated continuous-wave (FMCW) transmission and scans the horizontal plane by switching the four input ports of the BM in time. The radar system has been calibrated and measured in an anechoic chamber and angular target position estimates have been completed using digital beamforming. These tests are also compared to a more conventional single-input multiple-output (SIMO) and multiple-input multiple-output (MIMO) FMCW radar configurations and it is shown that the proposed BM radar offers improvements in terms of higher return powers, improved signal-to-noise ratios, and enhanced field-of-view.