Spherical coverage from planar, conformal and volumetric arrays

Many current radar and communication systems make use of planar arrays. These antennas offer the capability for rapid electronic beam scanning with phase only control, low sidelobes, and low cross-polar operation. However, the scan volume is limited by grating lobes with a maximum practical scan limit of 60 degrees from boresight. To achieve this an element spacing of half a wavelength is required, which for an active array is costly in terms of the number of active devices required. The array beamwidth increases and the gain decreases with scan due to the change in effective aperture. To achieve coverage beyond 60 degrees from boresight, a multifaceted planar array may be used, but this adds significantly to overall system volume and complexity. A useful alternative which addresses these problems is provided by spherical conformal arrays or volumetric arrays. Both these give spherical coverage. The paper compares the performance of these arrays to that of planar arrays.