Reflection Suppression In Large Spherical Near-Field Range

Reflections in antenna test ranges can often be the largest source of measurement errors, dominating all other error sources. This paper will show the results of a new technique developed by NSI to suppress reflections from the radome and gantry of a large hemi-spherical automotive test range developed for Nippon Antenna in Itzehoe, Germany. The technique, named Mathematical Absorber Reflection Suppression (MARS), is a post-processing technique that involves analysis of the measured data and a special filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical near-field test range. It has also been applied to extend the useful frequency range of microwave absorber in a spherical near-field system in an anechoic chamber. The paper will show typical improvements in pattern performance and directivity measurements, and will show validation of the MARS technique using data measured on antennas in a conventional anechoic chamber.

Introduction
This paper describes a proprietary technique developed by NSI to suppress reflections in a spherical near-field test range.

The initial development of the MARS technique was done to support operation in a hemi-spherical automotive near-field test system that NSI recently installed for Nippon Antenna in Itzehoe Germany. The system is a combination spherical near-field and far-field test facility with a 11.5 m radius dielectric gantry provided by the Howland company, and 6.5 m diameter in-ground turntable provided by NSI. The radome is 14 m high and 24 m in diameter. The facility uses the continuous ground plane approach, rather than use of any absorber on the turntable or ground surface. Reflections from the dielectric gantry and the radome do affect the measured antenna performance, and the MARS technique is used to suppress the majority of these reflections.

NSI has also extended the MARS technique for operation with other spherical near-field test systems with limited or no absorber, as well as for use in improving the reflection performance in a traditional anechoic chamber.

© Copyright 2005 Nearfield Systems, Inc.