Phase-Only Pattern Synthesis for Imaging Beams Using NURBS

The ability of PARs to synthesize spoiled transmit beams for imaging with minimal sensitivity losses is becoming increasingly crucial for achieving high-temporal resolution requirements for polarimetric weather observations. Spoiled beams can be achieved by significant amplitude tapering or using fewer elements, leading to significant sensitivity reduction. This paper introduces a novel phase-only beam pattern synthesis method using a Non-Uniform Rational B-Spline (NURBS) parameterization scheme in conjunction with the Particle Swarm Optimization (PSO) algorithm and the sequential quadratic programming algorithm SLSQP. When those phases are used to excite PAR antenna elements, they result in the desired imaging beam shape. The parameterization scheme's resulting spoiling beams are evaluated using six quality metrics, including peak sidelobe level, cost function value, mainlobe efficiency, mainlobe ripple, integrated contamination, and mainlobe leakage. The performance of the NURBS scheme is then compared to the existing Bezier scheme's performance in four scenarios: performance as a function of steering angle, as a function of control points, as a function of spoiling factor, and performance as a function of phase noise. Preliminary results suggest that the proposed NURBS scheme can generate phase-only imaging beams closely matching the desired beam shape with minimal sensitivity losses. Furthermore, quantitative performance results suggest that the NURBS parameterization scheme outperforms the Bezier scheme in all four proposed scenarios. Likewise, when imaging beams are spoiled at certain factors, the resulting patterns better resemble the desired ideal pattern for both Bezier and NURBS parameterization schemes.

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