Numerical Investigation of the System-Matrix Method for Higher-Order Probe Correction in Spherical Near-Field Antenna Measurements

Thorkild B Hansen

doi:10.1155/2012/493705

Abstract

The system-matrix method for higher-order probe correction in spherical near-field scanning is based on a renormalized least-squares approach in which the normal matrix closely resembles the identity matrix when most of the energy of the probe pattern resides in the first-order modes. This method will be “stressed-tested” in the present paper by employing probes for which up to 49% of the pattern energy resides in the higher-order modes. The condition number of the resulting normal matrix will be computed, and its “distance” from the identity matrix displayed. It is also shown how the condition number of the normal matrix can be further reduced.

Highlights

The standard theories for spherical near-field scanning of electromagnetic fields [1,2,3,4,5] hold for first-order probes that have e±iφ azimuthal pattern dependence only
A truncated M corresponds to computing the spherical expansion coefficients Anm and Bnm of the antenna under test (AUT) only up to n = Ntr ≤ N based on data sampled at the original rate
We evaluated the system-matrix method for higher-order probe correction in spherical scanning using probes with varying higher-order mode pattern energy

Summary

Introduction

The standard theories for spherical near-field scanning of electromagnetic fields [1,2,3,4,5] hold for first-order probes that have e±iφ azimuthal pattern dependence only. Through χ-scanning, the standard method [3] can deal with higher-order probes in special situations. This approach does not work in the situation of highest practical importance where the data consists of the output of a twoport higher-order probe.) first-order probes have been preferred in spherical near-field scanning over the past 30 years. First-order probes are inherently narrowbanded, and a large number of different probes (each covering a narrow frequency band) are needed to measure the AUT over a broadband of frequencies. This means that wide-band characterizations become very time consuming because the spherical scan must be repeated many times. It takes a considerable amount of time to calibrate and change probes because precise alignment procedures are required

Objectives

Results

Conclusion