Waveform design for CASA X-band radars

The Center for Collaborative Adaptive Sensing of the Atmosphere (CASA), an engineering research center established by the National Science Foundation (NSF) will deploy its first generation network of four low-power, short-range, X-band, dual-polarized Doppler weather radars  known as NETRAD. Each radar node is a pulsed Doppler radar with the maximum unambiguous range (r_max) and maximum unambiguous velocity (v_max)  determined by the pulse repetition time and the wavelength. There is always a conflicting trade off between r_max and v_max  and their product  is fixed for a given wavelength. This trade off is more stringent for X-band radars due to the shorter wavelength. NETRAD is primarily for “targeted applications” such as tornado detection, flash flood monitoring, and hydrological applications. Such applications will have range overlay and velocity folding problems with conventional pulse-pair processing. This paper will describe the adaptive pulsing schemes for the individual radar nodes based on NETRAD operational requirements such as scan speeds, volume coverage pattern and system/hardware limitations to resolve range and velocity ambiguities. The pulsing schemes considered here will include phase coding and multi-PRF waveforms for X-band implementation. The first generation NETRAD systems are magnetron based systems and can only support random phase processing. The advent of high-speed digital processor with IF sampling and extensive computational power with the ability of real time spectral processing makes such schemes possible.