A Highly Accurate Multi-Target Microwave Ranging System for Measuring Liquid Levels in Tanks

A microwave multi-level gauging system employing a FSCW radar measurement technique is described. Conventional FMCW radar technique is normally employed to find only the level of the liquid surface in storage tanks. The system described here also detects a second level, caused by the tank floor for example. If this second reflection dominates the distance measurement with the inverse Fourier transform (IFT) results in a poor resolution and shows a very high range error for small gaps between these two scatterers. For estimating the exact time delay and amplitude of each reflection from each scatterer an optimal signal processing algorithm is derived, based on a reference model Performance of the multiple target detection reference model is illustrated using measured data obtained from an HP-8510 network analyzer. It is demonstrated that the reference model offers a significant enhancement of resolution and is insensitive to noise and clutter signals approach over the standard processing IFT algorithm. The described system achieves a time delay accuracy with a bandwidth of ¿F=1 GHz which corresponds to a range error of ± 0.2 mm.