Reduction of Errors in Antenna Radiation Patterns Using Optimally Truncated Spherical Wave Expansion

Abstract

Abstract-This paper demonstrates how the error of a measured or simulated antenna radiation pattern can be decreased by calculating a spherical wave expansion (SWE) with an optimised truncation mode index. Four radiation pattern examples are examined for which the analytical expression of the electrical field is known. Upon adding random and φ-alignment errors to the exact electric fields, the SWEs are determined and compared with the corresponding ones for the exact fields. These comparisons show that the accuracy of the calculated SWE is much better than the accuracy of the original inaccurate field. Resting on the calculated examples, a method is created which can be used to determine the optimal truncation index from the modal power distribution of a SWE without knowing the exact field. Finally, the method developed is applied to measured antenna radiation patterns.

Overview of Novel Post-Processing Techniques to Reduce Uncertainty in Antenna Measurements

“…Increasing the signal-to-noise ratio by reducing the noise power was also proposed in (Koivisto, 2004) and (Foged, 2009). The technique described in these studies can be applied to measurements performed in spherical near-field, and it is based on oversampling to obtain a higher number of spherical modes than required (Jensen, 2004), and thus, to be able to apply a modal filtering.…”

The Far Field Transformation for the Antenna Modeling Based on Spherical Electric Field Measurements

“…The superscript (1) in (9) and (10) denotes that in (7) and (8) B n (kr) = h (2) n (kr), which represents outgoing waves; otherwise, B n (kr) = j n (kr) for standing waves when r → 0. In the far field region, approximations can be made as follows [20] …”

On the Comparison of the Spherical Wave Expansion-to-Plane Wave Expansion and the Sources Reconstruction Method for Antenna Diangostics

“…From the measured near-field and the knowledge of the probe response, the probe-corrected Q coefficients of the spherical wave expansion were calculated and the far-field pattern was determined [3,4,18]. From the Q coefficients the power spectrum was then computed (1): The Q coefficients determined from the near-field measurement and the obtained far-field were used as input to the SWE-PWE and SRM algorithms, respectively, in order to compute the extreme nearfield on the reference aperture plane (z meas = 0.5 cm).…”