2005 Technical Papers

A Hemi-Spherical Near-Field System for Automotive Antenna Testing

Authors: Pieter N. Betjes, Dieter Pototzki, Daniël Janse van Rensburg

Publication: AMTA 2005

Copyright Owner: NSI-MI Technologies

A hemi-spherical near-field test system with added far-field capability is described. The facility has been constructed for the characterization of automotive antennas. The test system consists of an 11m tall dielectric gantry, a 6.5m diameter in-ground turntable and a 28m-diameter radome enclosure. Special software required to compensate for the reflectivity in the facility and the hemi-spherical truncation was developed and forms an integral part of this test system. The characteristics of this facility are described in this paper and measured data is presented.

An Apparent Discrepancy Between Impedance Mismatch Factors for Near-Field and Far-Field Measurements

Author: Doren W. Hess

Publication: AMTA 2005

Copyright Owner: NSI-MI Technologies

In making accurate measurements of antenna gain one must correct for the impedance mismatches between (1) the signal generator and transmitting antenna, (2) between the receiving power sensor and the receiving antenna and (3) between the signal generator and receiving power sensor. This is true for both far-field gain measurements and near-field gain measurements. It has recently come to our attention that there is a lack of clarity as to the form the mismatch factor should take when correcting near-field measured data. We show that a different form of impedance mismatch factor is to be used with the voltage domain equations of near-field than has been used with the power domain Friis transmission equation.

Application of a Circular Arch for Spherical Near-Field Antenna Measurements from 1 to 60 GHz

Authors: Doren W. Hess, Jeffrey A. Fordham, Scott Pierce, Evan Langman

Publication: 28th ESA Antenna Workshop

Copyright Owner: NSI-MI Technologies

MI Technologies has developed and constructed two of a new generation of spherical near-field ranges that expand the regime of measurement requirements to which the spherical near-field technique can be applied. This evolutionary design permits measurements to be made on large apertures -- up to 10.0 m (32 ft) and at frequencies up to 60 GHz under conditions of constant gravity loads over 4π SR of coverage. Here we report on developments leading to a spherical near-field scanning system that has been built and realized for apertures up to 3.66 m (12 ft) and frequencies between 2.0 and 45 GHz which corresponds to an electrical size of 550 wavelengths.

Electromagnetic Performance of a Carbon Composite Compact Range Reflector

Authors: Doren W. Hess, David Smith

Publication: AMTA 2005

Copyright Owner: NSI-MI Technologies

This paper describes the first experience gained with a new carbon composite compact range reflector (C³R²). The reflector’s backup structure is made entirely of carbon fiber reinforced composite material. An outstanding advantage of this design is its superior mechanical and thermal-environmental stability. This yields improvement in the overall performance. We have revised the process by which compact range reflectors are designed and modeled, making use of professionally authored software. We describe the results of electromagnetic field probe measurements made at the factory. Special attention is given to new results at W-band – in the 75 to 100 GHz regime.

Low Cost and High Accuracy Alignment Methods for Cylindrical and Spherical Near-field Measurement Systems

Author: John Demas

Publication: AMTA 2005

Copyright Owner: NSI-MI Technologies

Precise mechanical alignment of motion axes of both cylindrical and spherical near-field systems is critical to producing accurate data. Until recently the only way to align these types of systems was to employ traditional optical tooling (i.e. jig transits, theodolites). Alignment by these methods is difficult, time consuming, and requires specialized training. More recently, laser trackers have been used for this type of alignment. Unfortunately, these devices are expensive and demand an even higher level of operator training.

This paper describes the use of low cost alignment tools and techniques that have been developed by Nearfield Systems, Inc. (NSI) that greatly simplify the alignment process. Setup and alignment can be performed in a very short period of time by technicians that have been given minimal training. Suitable optical alignment procedures when followed by the use of electrical alignment techniques [7] yield sufficient alignment accuracy to permit testing up to Ku-band.

Reflection Suppression in Large Spherical Near-Field Range

Authors: Greg Hindman, Allen C. Newell

Publication: AMTA 2005

Copyright Owner: NSI-MI Technologies

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.