Radio frequency (RF)-based sensors provide a direct measure of the particulate filter loading state. In contrast to particulate matter (PM) sensors, which monitor the concentration of PM in the exhaust gas stream for on-board diagnostics purposes, RF sensors have historically been applied to monitor and control the particulate filter regeneration process. This work developed an RF-based particulate filter control system utilizing both conventional and fast response RF sensors, and evaluated the feasibility of applying fast-response RF sensors to provide a real-time measurement of engine-out PM emissions. Testing with a light-duty diesel engine equipped with fast response RF sensors investigated the potential to utilize the particulate filter itself as an engine-out soot sensor. Measurements of the instantaneous change in the filter PM loading state using the fast response RF sensors were compared to measurements of engine-out PM emissions using conventional test cell instrumentation including the AVL micro soot sensor and tapered element oscillating micro-balance (TEOM). The results showed a high degree of correlation between the fast response RF sensor and test cell instruments. From a practical standpoint, the results indicate considerable potential for feedback control and engine diagnostics based on real-time measurements of engine-out PM emissions from a particulate filter equipped with a fast response RF sensor.