Optical-delay-based wide-range FMCW radar altimeter

The design of a frequency-modulated continuous wave (FMCW) radar altimeter with wide altitude range and low measurement errors is presented. Wide altitude range is achieved by employing the optical delay in the transmitting path to reduce the dynamic range of the measuring altitude. Transmitting power and receiver gain are also controlled to enable the dynamic range of the received power to be reduced. In addition, low measurement errors are obtained by improving the sweep linearity using the direct digital synthesiser (DDS) and minimising the phase noise employing the reference clock (Ref_CLK) as the offset frequency of the phase-locked loop (PLL).