Abstract
Abstract. Near-field far-field transformations (NFFFTs) are commonly performed for time-harmonic fields. Considering arbitrary in-situ measurement scenarios with given transmission signals, time-varying aspects of modulated signals have to be taken into consideration. We investigate and characterize two methods for the measurement of modulated fields, which work with a time-domain representation of the radiated fields and, at the same time, allow to employ the standard time-harmonic NFFFT. One method is based on the fact that the modulation signal can be assumed to be constant in a short enough measurement interval under the condition that the modulation and carrier frequencies are several decades apart. The second method performs long-time measurements in order to obtain the complete frequency spectrum in every single measurement. Both methods are verified by the NFFFT of synthetic field data.
Highlights
With the rise of wireless communication technologies, the demand for antenna characterization increases
We investigate and characterize two methods for the measurement of modulated fields, which work with a time-domain representation of the radiated fields and, at the same time, allow to employ the standard time-harmonic Near-field far-field transformations (NFFFTs)
We present two methods to measure or process the time-varying electromagnetic fields in a way that they can be used in a time-harmonic NFFFT algorithm
Summary
With the rise of wireless communication technologies, the demand for antenna characterization increases. A common method to obtain the radiation pattern involves near-field (NF) measurements of the antenna from which the FF can be calculated in the post-processing. Frequency domain NFFFTs are usually faster and more efficient than their time-domain counterparts To overcome this problem, we present two methods to measure or process the time-varying electromagnetic fields in a way that they can be used in a time-harmonic NFFFT algorithm. Two different techniques to measure modulated fields are described and compared In both cases, the NFFFT is based on the common time-harmonic NFFFT, in particular the FIAFTA. To cope with continuously modulated (i.e. continuously time-varying with a certain periodicity and without abrupt phase and magnitude changes) fields within the timeharmonic NFFFT, the field signals must be available in the frequency domain. The opening time of w(t) is directly related to the measurement time, which is relevant for the following subsections
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