2008 Technical Papers

An Ethernet Based Controller for Managing Complex Antenna Measurements with a Vector Network Analyzer

Authors: Marion Baggett, James Langston

Publication: AMTA 2008

Copyright Owner: NSI-MI Technologies

Vector Network Analyzers (VNA’s) are finding increasing utilization in antenna measurement ranges. At the same time, complex measurement scenarios involving many data channels in the antenna under test along with integration to beam steering computers for phased array antennas require management of the data collection beyond the VNA. Traditional methods have added control cards in the measurement control computer, increasing software complexity and reducing measurement throughput. The MI-788 Networked Acquisition Controller is designed to manage the hardware handshakes between position controllers, external sources and VNA’s, control up to 16 channels of multiplexed data from the antenna under test and/or interface with a beam steering computer. The MI-788 tremendously increases system throughput, particularly in these more complex measurement scenarios by removing real time data collection responsibilities from the measurement control computer. In addition, this unit makes all instrument communication Ethernet based, eliminating the spacing and operational limitations of GPIB based measurement systems. This paper will describe the operation of the MI- 788 and demonstrate the increased measurement capabilities while using VNA’s in antenna measurements.

An Overview of Near-field Sub-millimeter Wave Antenna Test Applications

Authors: Daniёl Janse van Rensburg, Greg Hindman

Publication: COMITE Conference, Czech Republic, 23-24 April 2008

Copyright Owner: IEEE

This paper provides an overview of planar nearfield antenna test systems developed for sub-millimeter wave applications used for earth observation and radio astronomy. Examples are shown of some of these test systems and methods described to overcome technical restrictions, limiting performance at very high RF frequencies. Aspects like thermal structural change, RF cable phase instability and scanner planarity are addressed. These methods have been implemented and validated on practical real-world applications up to 660 GHz and 950 GHz. These extreme cases have lead to the development of low cost commercial test systems, making antenna testing in the V and W-bands cost effective and viable today.

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Compensation for Probe Translation Effects in Dual Polarized Planar Near-Field Antenna Measurements

Author: Daniël Janse van Rensburg

Publication: AMTA 2008

Copyright Owner: NSI-MI Technologies

In this paper a technique is described that allows for the determination and correction of probe translation during polarization rotation in planar near-field measurements. The technique, which relies on the independent translation of coordinate systems for the two orthogonally polarized data sets, has significance for mm-wave testing, where bulky RF components makes probe alignment difficult. Measured data is presented to demonstrate the success of the technique.

Conical Near-Field Antenna Measurements

Author: Stuart F. Gregson, Greg E. Hindman

Publication: AMTA 2008

Copyright Owner: NSI-MI Technologies

A near-field measurement technique for the prediction of asymptotic far-field antenna patterns from data obtained from a modified cylindrical, or plane-polar, near-field measurement system is presented. This technique utilises a simple change in facility alignment to enable near-field data to be taken over the surface of a conceptual right cone [1, 2], or right conic frustum [3, 4] thereby allowing existing facilities to characterise wide-angle antenna performance in situations where hitherto they would perhaps have been limited by truncation.

This paper aims to introduce the measurement technique, describe the novel probe-corrected near-field to far-field transform algorithm which is based upon a cylindrical mode expansion of the measured fields before presenting preliminary results of both computational electromagnetic simulations and actual range measurements. As this paper recounts the progress of ongoing research, it concludes with a discussion of the remaining outstanding issues and presents an overview of the planned future work.

Cross Polarization Uncertainty in Near-Field Probe Correction

Author: Allen Newell

Publication: AMTA 2008

Copyright Owner: NSI-MI Technologies

The probe correction of near-field measured data can be considered as being composed of two parts. The first part is a pattern correction that corrects for the effects of the aperture size and shape of the probe and can be analyzed in terms of the far-field main component pattern of the probe. The second part is due to the non-ideal polarization properties of the probe. If the probe responded to only one vector component of the incident field in all directions, this correction would be unnecessary. But since all probes have some response to each of two orthogonal components, the polarization correction must be included. The polarization correction will be the focus of the following discussion. Previous studies have derived and tested general equations to analyze polarization uncertainty12. This paper simplifies these equations for easier application. The results of analysis and measurements for Planar, Cylindrical and Spherical near-field measurements will be summarized in a form that is general, easily applied and useful. Equations and graphs will be presented that can be used to estimate the uncertainty in the polarization correction for different AUT/Probe polarization combinations and measurement geometries. The planar case will be considered first where the concepts are derived from the probe correction theory and computer simulation and then extended to the other measurement geometries.

Evaluation of IsoFilter^TM Fidelity in Selected Applications

Authors: Doren W. Hess, Scott McBride

Publication: AMTA 2008

Copyright Owner: NSI-MI Technologies

The IsoFilter^TM technique was originally demonstrated to operate by rejecting secondary signals that derive from reflections off of a nearby metallic object – namely, the ground plane surface supporting a small pyramidal horn. The aperture of the horn was located several wavelengths above the ground plane and the sidelobes and backlobes of the horn illuminated the ground plane itself. The success of this demonstration has been sufficient to encourage us to pursue further the question of how well the IsoFilter^TM technique will work to suppress other types of secondary signals– such as signals coming from other elements of an array antenna or another individual first-order primary radiator nearby.

Here we report on some of the results of that investigation. We have calculated the far-field patterns of a sparsely populated array and applied the IsoFilter^TM technique. The goodness of the suppression is judged by how well the “IsoFiltered” result agrees with the calculated pattern of the individual radiator.