This paper presents millimeter wave propagation measurements at 28 GHz for a typical suburban environment using a 400-megachip-per-second custom- designed broadband sliding correlator channel sounder and highly directional 22-dBi (15° half-power beamwidth) horn antennas. With a 23-dBm transmitter installed at a height of 27m to emulate a microcell deployment, the receiver obtained more than 5000 power delay profiles over distances from 80m to 1000m at 50 individual sites and on two pedestrian paths. The resulting basic transmission losses were compared with predictions of the over-rooftop model in recommendation ITU-R P.1411-9. Our analysis reveals that the traditional channel modeling approach may be insufficient to deal with the varying site-specific propagations of millimeter waves in suburban environments. For line-of-sight measurements, the path loss exponents obtained for the close-in (CI) free space reference distance model and the alpha-beta-gamma (ABG) model are 2.00 and 2.81, respectively, which are close to the recommended site-general value of 2.29. The root mean square errors (RMSEs) for these two reference models are 9.93dB and 9.70dB, respectively, which are slightly lower than that for the ITU site-general model (10.34dB). For non-line-of-sight measurements, both reference models, with the resulting path loss exponents of 2.50 for the CI model and 1.12 for the ABG model, outperformed the site-specific ITU model by around 14dB RMSE.