Advanced Spherical Near-field Postprocessing Techniques

Spherical near-field measurements are regarded as the most accurate antenna testing technique. This accuracy comes with the cost of very strict requirements in terms of near-field sampling density, the measured point distribution, and phase coherence. The fulfillment of such conditions can lead to time-consuming, impractical or expensive measurements. Specially at high frequencies, the required number of points for a successful far-field transformation grows excessively, whereas maintaining a stable phase reference becomes challenging. This paper presents a series of postprocessing techniques which enable to relax these requirements. It is shown how antenna symmetries and a priori knowledge can be exploited to reduce the sampling rate below the Nyquist criterion. In addition, phase coherence can also be avoided by combining measurements in multiple surfaces and proper phase retrieval algorithms. All presented techniques aim to provide faster and cheaper alternatives, while maintaining the accuracy and reliability of near-field spherical measurements.