Phased Array Design for Biological Clutter Rejection: Simulation and Experimental Validation

Radar studies of the atmospheric boundary layer (ABL) have become widespread since the advent of relatively inexpensive and compact profiling radars [Ecklund et al., 1988], termed boundary layer radars (BLR). Arguably, one of the most sophisticated of these type of radar systems is the so-called Turbulent Eddy Profiler (TEP), which was developed at the University of Massachusetts [Mead et al., 1998; Pollard et al., 2000]. The TEP system is a volumetric radar designed for clear-air observations with high temporal and spatial resolution comparable to the grid size used in Large Eddy Simulation (LES) models [Lilly, 1967; Wyngaard et al., 1998]. The multi-receiver design of the TEP radar allows offline digital beamforming to construct volumetric images and is capable of acquiring measurements at altitudes up to 3 km, depending upon atmospheric conditions. Imaging radars, including the TEP radar, help researchers and scientists to enhance their understanding of small-scale structure of the atmosphere. In addition to lower atmospheric measurements, imaging radars are also important for studies of other regions of the atmosphere, such as the mesosphere [Yu et al., 2001; Hysell et al., 2002], stratosphere [Rao et al., 1995], and the ionosphere [Hysell, 1996; Hysell and Woodman, 1997]. For coherent radar imaging (CRI), signals from each of the receiver elements are combined to form a beam pointing in the direction of interest. The coherently combined signals allow spectral moments to be extracted from the beam pointing direction. This technique is known as beamforming. By changing the beamforming weights, signals from arbitrary directions can be extracted. The beamforming weights can also be data adaptive. This allows suppression of strong signals outside the region of interest. With a high spatial resolution radar system such as the TEP, many narrow beams can be formed over the field of view, providing tremendous detail in the imaging area. Pioneering work in spatial in-