A high precision 24-GHz FMCW radar based on a fractional-N ramp-PLL

A 24-GHz FMCW radar system is presented using a fractional-N phase-locked loop ramp generator. This fractional-N ramp generator achieves relative ramp nonlinearities below 10/sup -8/. Among others linear frequency ramps are important tools in high precision FMCW radar systems. Highly linear frequency ramps make post measurement error correction feasible. Other important aspects of the high performance FMCW radar system are the design of the microwave circuit and the digital signal processing of the IF signals. Furthermore, a large RF bandwidth of more than 3 GHz obtained by thorough simulations results in a high range resolution and a good potential measurement accuracy. To maintain this high potential accuracy, a phase slope algorithm is used to calculate the precise range value leading to a significantly better precision with absolute range errors below 0.8 mm, compared to the commonly used spectral center algorithm.