2003 Technical Papers

A Highly Automated Approach to Obtaining Accurate Circularly Polarized Antenna Gain

Author: Marion C. Baggett

Publication: AMTA 2003

Copyright Owner: NSI-MI Technologies

At a Department of Defense antenna measurement laboratory, an important measurement is the accurate measurement of gain for circularly polarized antennas. An additional requirement is that a wide population of engineers and technicians that do not spend a significant amount of time using the facility make the measurements as they test the antennas for their projects. The objective was to create a highly automated, accurate test structure that was easily used by visiting engineers to make high quality measurements. Consistency of results across the user population was a paramount requirement. This paper describes the instrumentation and software used to meet this objective.

Alignment of a Large Spherical Near-Field Scanner using a Tracking Laser Interferometer

Authors: Scott Pierce, Charles Liang

Publication: AMTA 2003

Copyright Owner: NSI-MI Technologies

In this paper, we describe the process used to align a large spherical near-field test system. The probe positioner consists of a cantilevered arc design with a probe path radius of five meters and a scan angle of 180°. The AUT positioner consists of an MI Technologies Model 51230 azimuth positioner with a high-precision encoder. The system is aligned using an SMX Tracker 4000 tracking laser interferometer.

Alignment into a spherical system is achieved by initially defining two cylindrical systems; a primary probe positioner based system and a secondary, AUT positioner based system. Sources of mechanical error in each of these systems are identified and techniques used to control these error sources are described.

An Augmented Three-Antenna Probe Calibration Technique for Measuring Probe Insertion Phase

Authors: Aksel Frandsen, Doren W. Hess, Sergey Pivnenko, and Olav Breinbjerg

Publication: AMTA 2003

Copyright Owner: NSI-MI Technologies

Probe calibration is a prerequisite for performing high accuracy near-field antenna measurements. One convenient technique that has been used with confidence for years consists of using two auxiliary antennas in conjunction with the probe-to-be-calibrated. Inherent to this technique is a calibration of all three antennas. So far the technique has mostly been applied to calibrate for polarization and gain characteristics. It is demonstrated how the technique can be extended to also measure an antenna’s phase-versus-frequency characteristic.

Antenna Pattern Comparison between an Outdoor Cylindrical Near-Field Test Facility and an Indoor Spherical Near-Field Antenna Test Facility

Authors: Jeffrey Fordham, Mike Scott

Publication: AMTA 2003

Copyright Owner: NSI-MI Technologies

A new spherical near-field probe positioning device has been designed and constructed consisting of a large 5.0 meter fixed arc. This arc has been installed in a near-field test facility located at Alenia Marconi Systems on the Isle of Wight, UK. As part of the near-field qualification, testing was performed on a ground based radar antenna. The resultant patterns were compared against measurements collected on the same antenna on a large outdoor cylindrical near-field test facility also located on the Isle of Wight. These measurements included multiple frequency measurements and multiple pattern comparisons.

This paper summarizes the results obtained as part of the measurement program and includes discussions on the error budgets for the two ranges along with a discussion on the mutual error budget between the two ranges.

Evaluation of Radome Performance from Cylindrical Near-Field Measurements

Authors: W.C. Dixon, Daniël Janse Van Rensburg

This paper describes the installation and implementation of a Cylindrical Near-field Test Facility at Chelton Radomes Ltd, Stevenage, (formerly British Aerospace Systems and Equipment Ltd.), in the UK for the testing of large radome/antenna combinations. Test site commissioning and validation activities to determine measurement accuracy & repeatability for the radome performance parameters of transmission loss and boresight error, are discussed. Test data from actual measurements are presented.

Estimating the Uncertainties due to Position Errors in Shperical Near-Field Measurements

Authors: Allen C. Newell, Daniël Janse van Rensburg

Publication: AMTA 2003

Copyright Owner: NSI-MI Technologies

Probe position errors, specifically the uncertainty in the theta and phi position of the probe on the measurement sphere, are one of the sources of error in the calculated far-field and hologram patterns derived from spherical near-field measurements. Until recently, we have relied on analytical result for planar position errors to provide a guideline for specifying the required accuracy of a spherical measurement system. This guideline is that the angular error should not result in translation along the arc of the minimum sphere of more than λ/100.

As a result of recent simulation and analysis, expressions have been derived that relate more specifically to spherical near-field measurements. Using the dimensions of the Antenna Under Test (AUT), its directivity, the radius of the sphere (the minimum sphere) enclosing all radiating surfaces and the frequency we can estimate the errors that will result from a given position error. These results can be used to specify and design a measurement system for a desired level of accuracy and to estimate the measurement uncertainty in a measurement system.