Design of an FMCW Radar Altimeter for Wide-Range and Low Measurement Error

This paper presents the design of a frequency-modulated continuous-wave radar altimeter with wide altitude range and low measurement error. A wide altitude range is attained by employing an optical delay in the path of transmission to reduce the dynamic range of the altitude being measured. The transmitter power and receiver gain are also controlled to facilitate a reduction in the dynamic range of the received power. In addition, low measurement error was obtained by improving the sweep linearity using a direct digital synthesizer and minimizing phase noise by employing a phase-locked loop with the offset frequency driven by a reference clock (Ref_CLK). The performance of the radar altimeter was experimentally verified using an optical-delay simulator, which provided a delay time corresponding to a 200-m radar distance. To assess the performance of the system in a realistic setting, the radar altimeter was tested using a crane setup. The crane test demonstrated that the design described in this paper resulted in a reduced measurement-error rate.