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Effects of antenna mount on a spherical scanning measurement of the radiation efficiency of a wire antenna.

Loh, T H; Meng, D*; Huang, Y* (2011) Effects of antenna mount on a spherical scanning measurement of the radiation efficiency of a wire antenna. In: International Conference on Electromagnetics in Advanced Applications (ICEAA) 2011, 12-16 September 2011, Torino, Italy.

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It is well known that the antenna directivity function gives information about its capacity to concentrate the radiation in a desired direction and together with the acquired antenna gain function the antenna radiation efficiency can be calculated. The crucial point in the directivity evaluation is the accurate full spherical radiation pattern acquisition for the computation of the total radiated power, which is obtained by integrating the radiation intensity on the far-field spherical surface.

The most common antennas used for communication systems, broadcasting, and measurements of electric fields are dipole and monopole linear wire antennas. Their radiation pattern is generally shaped like a toroid symmetrical about their antenna axis and is considered to be omni-directional in the plane perpendicular to the axis of the antenna, but have deep nulls in the directions of the axis.

Accurate measurement of radiation pattern, gain, and directivity of these antennas involves the consideration of a number of factors, such as electrical and physical size of the antenna, its operational frequency band, and the environment in which it is to operate [1]. It is critically important to be able to measure only the direct wave from the antenna under test and avoid any reflected wave affecting the result. This requires them to be measured in a very low reflection environment and have very well matching with the antenna-to-range interface [2] - [3]. Since reflections from the spherical scanner can contribute substantial errors in the measurement this poses additional challenges in accurate directivity evaluation and therefore the radiation efficiency calculation.

We present in this work a study on the effects of a roll-over-azimuth spherical scanner to the radiation pattern measurement of a linear wire antenna and therefore its antenna radiation efficiency. Various setups such as the orientation of the antenna under test, and the spherical scanner fully covered with and without the RF absorber are investigated. It is noted that, for the scenario that the spherical scanner fully covered with RF absorber, only the semi-sphere radiation pattern for which the antenna is facing the source when allocated between the source and tower is used, where the other semi-sphere are obtained by rotating the antenna under test 180 degree in azimuth direction. The work aims to mitigate these effects by proposing solution to reduce them.

The linear wire antenna used throughout this study was a European half-wave dipole antenna (Model No.: EVD-2-1920-2175/548). This is a narrow band antenna operating from 1.92 - 2.17 GHz. The measurement was performed in a small antenna radiation test range at the UK, National Physical Laboratory. The test range is built in a screen room 7.15 m long, 6.25 m high and 6.25 m wide with a frequency range from 400 MHz to 26.5 GHz. It contains a roll-over-azimuth positioner system, with software to acquire radiation patterns. Both the E-plane and H-plane of the antenna were measured. The numerical results for the radiation pattern of an ideal half-wave dipole antenna are compared with the measured results.

(1) J. S. Hollis, T. J. Lyon, and L. Clayton, Microwave antenna measurements, Scientific-Atlanta, Inc., Atlanta, Ga., Tech. Rep., 1970.
(2) T. H. Loh, M. Alexander, P. Miller, T. Palmer, "Small Antenna Pattern Testing - The Antenna-to-Range Interface", 2nd European Conference on Antenna and Propagation (EuCAP 2007), Edinburgh, Nov. 2007.
(3) T. H. Loh, M. Alexander, P. Miller, and Andrés López Betancort, "Interference Minimisation of Antenna-to-Range Interface for Pattern Testing of Electrically Small Antennas", 4th European Conference on Antennas and Propagation (EuCAP 2010), Barcelona, Spain, 11th - 16th April 2010.

Item Type: Conference or Workshop Item (UNSPECIFIED)
Subjects: Electromagnetics
Electromagnetics > Wireless Communications
Identification number/DOI: 10.1109/ICEAA.2011.6046517
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5357

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