Abstract
Abstract. The characterisation of antenna radiation patterns by measurements in the near-field and a following near-field far-field transformation require accurate amplitude and phase data. Especially at higher frequencies phase measurements are demanding in terms of instrumentation and measurement accuracy. Phaseless techniques which require amplitude only data on one or more measurement surfaces are therefore of special interest. In this paper a phaseless spherical algorithm based on spherical modal expansion is presented. The algorithm works with amplitude only near-field data measured on two spheres of different radii and is therefore not restricted to certain types of antennas as for planar measurements for example. Simulated as well as measured results of low and medium gain antennas are shown.
Highlights
The radiation characteristic of an antenna under test (AUT) is typically defined at far-field distance and is to be measured in the far-field region of the AUT
For electrically large AUTs which satisfy far-field conditions at a far distance (≈ 2D2/λ, D being the diameter of the minimum sphere enclosing the AUT and λ the wavelength), near-field measurements can be carried out much
Characteristics of medium gain antennas within the phaseless spherical algorithm are addressed considering the example of a simulated Narda standard gain horn
Summary
The radiation characteristic of an antenna under test (AUT) is typically defined at far-field distance and is to be measured in the far-field region of the AUT. The Iterative Fourier Technique (IFT) (Razavi and Rahmat-Samii, 2006) is known from planar phaseless measurements and requires amplitude only measurements on two planes. A more common approach for the measurement of medium and low gain antennas is the spherical measurement technique (Hansen, 1988), where the radiated fields of the AUT over a sphere are recorded and the radiation in backward direction is considered. To utilise the advantages of phaseless measurements, a phaseless spherical transformation algorithm based on a spherical modal expansion has been presented (Schmidt and Rahmat-Samii, 2009) and applied to a low gain patch antenna. The algorithm is suitable for low as well as medium gain antennas and utilises measured amplitude only near-field data on two spheres. Characteristics of medium gain antennas within the phaseless spherical algorithm are addressed considering the example of a simulated Narda standard gain horn
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