Rasmus Cornelius

A comparison of different methods for fast single-cut near-to-far-field transformation [euraap corner]

Near-field-to-far-field transformation algorithms have been developed during the last decades of the last century. Spherical near-field measurements are nowadays the most accurate technique for characterizing one antenna. However, one of the drawbacks is the requirement for a full spherical acquisition. This means a large number of scans, especially for very large antennas, requiring a long measurement time. This paper presents several techniques for performing a single-cut near-to-far-field transformation. An explanation of each algorithm, and a comparison among them for several antennas, are presented. The possibilities and limitations of the algorithms are discussed in the last section. This work was performed thanks to the mobility programs offered by the Antenna Networks in the European Union: European Association on Antennas and Propagation (EurAAP) and COST-VISTA action, allowing researchers from the three institutions to work together on this project.

Spherical Wave Expansion With Arbitrary Origin for Near-Field Antenna Measurements

The far-field radiation pattern of an antenna under test (AUT) can be derived via a spherical wave expansion of near-field antenna measurement data. The transformation as well as the measurement time scales with the number of spherical mode coefficients which depends on the radius of the sphere enclosing the antenna. In existing transformation procedures, the radius is measured from the center of the measurement sphere. Thus, the radius increases for an offset-mounted antenna so that more spherical mode coefficients are required to represent the electromagnetic field. In this communication, a procedure is proposed where the origin of the spherical wave expansion can be specified independently of the measurement sphere. With this procedure, the number of coefficients can always be minimized by selecting an expansion origin that minimizes the sphere enclosing the AUT. A translated expansion origin requires to include the probe pointing direction in the probe response constant calculation. This is achieved by Euler rotations of the probe receiving coefficients. The benefits of the procedure are demonstrated by measurements of an offset-mounted AUT.

Spherical Near-Field Scanning With Pointwise Probe Correction

Spherical wave expansion algorithms based on matrix inversion are flexible. They allow arbitrary sampling schemes and higher order probe correction. However, the probe correction technique assumes, up until now, the same measurement probe at every measurement point. This is a limitation, especially for dual-polarized measurement probes and multiprobe measurement systems. In this communication, a spherical near-field (SNF) far-field transformation procedure, including pointwise probe correction, is presented. For a measurement sphere with constant radius, the additional calculation time is small. Furthermore, varying but known measurement distances can be corrected using the same technique. The procedure is tested with a dual-polarized SNF measurement and a simulated measurement with varying measurement distances.

Calculating Arbitrarily Located Sampling Data From Quiet Zone Spherical Near-Field Scanning Measurements

Amplitude and phase distribution inside the quiet zone (QZ) of a far-field antenna measurement chamber are important indicators for the quality of antenna measurements therein. Both amplitude and phase can be further subdivided into intuitive quality parameters such as linear taper, parabolic taper, and ripple. In order to retrieve these parameters from QZ spherical near-field measurements, the transmission formula is adapted to the case where the output signal of a virtually positioned output probe-antenna can be calculated on arbitrary locations inside the QZ. The output probe-antenna can be a measured or theoretically defined antenna and can be rotated in any direction of interest. This paper will show that this method provides similar results as industry standard linear field-probing by comparing amplitude taper and ripple extracted from both measurements. Further the advantages of using QZ spherical near-field scanning (QZSNFS) in combination with the adapted output transmission formula will be shown by calculating multiple projections not available by standard field-probing.

Three antenna gain determination method in compact antenna test ranges

In this paper the well-known three antenna method for determining the antenna gain will be discussed in relation to a compact antenna test range. It will be shown that the applicability of such a method is possible and delivers quite accurate results if one carefully considers the different parameters that play a role in compact antenna test ranges.

Description and Results: Antenna Measurement Facility Comparisons [Measurements Corner]

In recent years, formalized facility comparison activities have become important for the documentation and validation of laboratory proficiency and competence and mandatory for achieving accreditation such as that of the International Organization for Standardization (ISO) 17025 or similar organizations [1]. Different intercomparison campaigns have been conducted on antenna measurements in the framework of various European activities. Such activities were initiated in 2004 with the Sixth Framework Program of the European Union (EU) Antenna Center of Excellence (ACE) [2]. The work continued under the management of the European Association on Antennas and Propagation (EurAAP), supported by the European Cooperation in Science and Technology (COST) in the programs Antenna Systems and Sensors for Information Society Technologies (ASSIST) IC0603 and Versatile, Integrated, and Signal-Aware Technologies for Antennas (VISTA) IC1102, including still ongoing campaigns [3]-[5]. Results of these activities have led to improvements in antenna measurement procedures and protocols in facilities and standards [6], [7]. Due to the direct benefits available to the participants, the activities have been very successful, and partial outcomes have been published in IEEEreferenced articles [8]-[18].

Effect of different truncation angles in spherical near-field measurements

In all antenna measurement scenarios the complete radiation pattern is not available or not measurable and this is mainly due to montage reasons, where the tower on which the antenna is mounted shadows the antennas back side; causing loss of information. Other scenarios might be that the operator is not interested in the complete radiation pattern of the antenna but in some specific solid angle or area. In this paper truncation effect will be investigated, in which the missing field range will simply be filled with zeros. It will be shown that the location at which one truncates has a direct effect on the accuracy of the reconstructed antenna pattern in the valid region.