Antenna Measurement

Antennas as the indispensable transducer between guided waves and free space wave propagation are a key element for every high-frequency wireless system, be it mobile communications, radar sensors, or nuclear magnetic resonance imaging. Therefore, theoretical and practical investigations of novel antenna concepts form one focus of research at IHF. Assessing the characteristics of antennas and antenna systems calls for dedicated measurement techniques inside an electromagnetically anechoic chamber allowing high precision results. Consequently, measurement techniques as such are also of central interest to our researchers.

 


Far-Field Measurements

Compact Range

Compact Antenna Test Ranges provide an efficient means of obtaining the plane wave illumination of an Antenna Under Test (AUT) over a specified test zone (“Quiet Zone”) normally provided by a long far-field range in a relatively short distance. This is achieved by conversion of the spherical wave produced by the feed antenna to a high-quality plane wave by a parabolic reflector assembly.


Near-Field Measurements

Near-field measurement systems provide an alternative to conventional far-field measurement systems for characterizing the radiation properties of an antenna. Three main system types, namely planar, cylindrical and spherical, exist. The general method is based on the Huygens principle: From the measured tangential components on a defined surface in the near-field of the antenna, the far-field is determined by numerical calculation. The near-field of the antenna further transformed to modes in the corresponding coordinate system. From the mode spectrum the different antenna parameters such as the radiation pattern can be calculated.

 

Planar Near-Field Measurements

In planar near-field measurements the radiated field is measured on a flat rectangular surface in front of an antenna (AUT). This geometry allows a simple and inexpensive mechanical setup. Moreover, the transformations are mathematically simple to describe and easy to implement. However, it provides the radiation pattern only in a limited range of solid angles and is therefore only suitable for antennas with high gain.

Spherical Near-Field

Sphärische Nahfeldmesstechnik

Sphärische Nahfeldmesssysteme messen die räumliche Verteilung des elektrischen Nahfeldes auf einer Kugeloberfläche um eine Testantenne. Numerische Nachbearbeitungsverfahren, auf Basis der Zerlegung in vektorielle Kugelwellen, werden verwendet um die Transformation ins Fernfeld durchzuführen. Der mechanische Aufwand ist bei der sphärischen Geometrie am größten, hat aber den Vorteil, dass eine geschlossene Fläche um die Testantenne herum gemessen wird. Damit liefert sie die komplette drei-dimensionale Strahlungscharakteristik.