Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia MITIGATION OF CROSS-POLAR INTERFERENCE IN POLARIMETRIC WEATHER RADAR James J. Stagliano E. Jeff Holder Propagation Research Associates 1275 Kennestone Circle, Suite 100 Marietta, Georgia

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Immediate Motivation SBIR RFP 8.3.3R SUBTOPIC: Cross Polarization Isolation Techniques for Phased Array Weather Radars Modern Doppler weather radars are being designed with polarimetric capability to provide hydrometeor classification and improved precipitation estimation performance. Providing sufficient polarization isolation is challenging for active phased array radars as it is difficult to develop low-cost transmit/receive modules that maintain sufficient cross polarization isolation for hydrological use. In addition, the unique ability of phased array radars to steer the beam off array broadside creates additional isolation challenges that are not encountered with today’s weather radars utilizing parabolic antennas. We seek novel and innovative approaches leading to the design, development and implementation of technology that can be employed by phased array weather radars to provide sufficient cross polarization isolation and matching beams (in all directions) at the two orthogonal polarizations for the next generation Multifunction Phased Array Radar (MPAR) system. We request a Phase I study that might lead to the development of an approach to maximize cross- polarization isolation while minimizing design costs for the next generation MPAR system. Phase I would include investigation into approaches for cross-polarization isolation to achieve the necessary end-system isolation requirement (-35dB). A cost-benefit trade study of various approaches in terms of implementation costs, impact to system, and overall performance gain would also be expected. If successful, a Phase II activity might include the development of a prototype architecture for the isolation techniques developed in Phase I.

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Motivation NRC (2008) notes the viability of MPAR for weather surveillance rests with ability to mitigate cross-polar interference. Orientation Project –January 2008 finished a project that needed accurate measure of field analogous to L DR –Very sensitive to error

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Review Measuring L DR in Simultaneous Mode L DR can be measured in simultaneous mode if polarimetric channels modulated with orthogonal waveforms (Stagliano (2006), Chandrasekar (2007), and Chandrasekar (2008))

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Measuring L DR Simultaneously Transmit Signal Received Signal

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Decoding the Channels Horizontal Vertical Chandrasekar (2007, 2008) demonstrated the ability to measure L DR simultaneously limited by the cross-polar isolation of the antenna

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Updated Signal Model Signal model of Stagliano (2006) ignored cross-polar interference, so now add the inteference term. Transmit Signal Received Signal

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Received Signal Model

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Decoding the Channels 4 Linear Equations and 4 Unknowns

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Solution of Linear System

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Future Work Implementation –Constructing bistatic polarimetric system Multi – Element (“Phased Array”) X-band Transmit antenna elements have 30 dB cross- polar isolation –45 dB Xpol isolation measured Receive antenna elements have 20 dB cross- polar isolation –30 dB Xpol isolation measured Evaluation begins 2010

Paper 8A.3, 34 th Conference on Radar Meteorology, 5-9 October 2009, Williamsburg, Virginia Questions