This article presents a method of antenna radiation pattern reconstruction for the planar near-field measurement system. The proposed method uses clustering analysis and Voronoi cell classification to realize reasonable regional interpolation according to the data characteristics of a small number of initial samples, leading to an expansion of the amount of effective data in the initial array. Meanwhile, the Gerchberg-Papoulis (GP) algorithm is used to reduce the truncation errors of the interpolated planar near-field data, and consequently improve the overall reconstruction accuracy. The proposed method can effectively reduce the number of initial sampling points and the planar near-field scanning time of the measurement process. Besides, it can be seen from the simulation and measurement results that the planar near-field data processed by the clustering interpolation and GP algorithm can effectively enhance the reconstruction accuracy of the far-field pattern of the antenna under test (AUT).

This article presents an effective E-field reconstruction method for the near-field measurement system. The spatial convolution and field similarity theory are used to form two observation planes with similar E-field distributions. Then the clustering analysis and Voronoi cell classification are introduced to interpolate the defective E-field dataset at the target frequency using the similar dataset at another frequency and observation plane, which improves the data utilization efficiency in the frequency domain. The key purpose of the proposed method is to effectively reconstruct the defective planar E-field influenced by the under-sampling in the multi-frequency test, saving the retesting time cost of the E-field at the target frequency point and improving the utilization efficiency of the multi-frequency data. From the simulation and measurement results, it can be known that the reconstructed correlation coefficients are greater than 0.98, implying the high accuracy and good effectiveness of the proposed method. More importantly, the measurement time cost of the proposed method, which is 70 minutes for the measured results, can be half of that of the two-time measurement under the same frequency and observation distance, greatly saving the time cost for the electrically large antenna.

It has been shown that the angular correlation of the antenna can be obtained by rotating it in a reverberation chamber (RC) and the radiation pattern of the antenna under test (AUT) can be reconstructed from the measured correlation coefficients using spherical wave decomposition. However, the correlation coefficient needs to be obtained by measuring the complex-valued S-parameters in an RC, which is no longer applicable to active antenna tests where the phase information is unavailable. To solve this problem, we propose an antenna radiation pattern reconstruction method based on phaseless measurement in an RC. In this method, the power correlation coefficient of AUT is calculated using the signal amplitude received by the antenna at different angles. According to the relationship between complex correlation coefficient and power correlation coefficient of the AUT, the nonlinear least squares method is used to reverse the spherical wave coefficients and reconstruct the antenna radiation pattern. Simulations and measurements are carried out in RC and anechoic chamber, which demonstrated the feasibility and applicability of the proposed method.

It has been experimentally demonstrated that the antenna pattern can be reconstructed using correlation coefficients and spherical wave expansion in a well-stirred large reverberation chamber (RC) when the antenna under test (AUT) has little impact on the testing environment, but the method becomes ineffective for loaded RCs. To solve this problem, we apply a compensation method to the pattern reconstruction process by using a reference antenna, enabling AUT pattern reconstruction in a loaded RC. In the proposed method, the original radiation pattern of the reference antenna is measured in an anechoic chamber (AC), and the transmission coefficients of the reference antenna are obtained according to the spherical wave coefficient expansion theory. Then, by rotating the reference antenna in the RC, the corresponding antenna correlation and autocorrelation coefficients are obtained, and the radiation pattern of the AUT is reconstructed by using the least square method. Finally, the near-field spherical scattering signals of the reference antenna are used to compensate for the reconstructed results of the AUT spherical wave coefficients, and an improved far-field radiation pattern of the AUT is obtained. The feasibility and effectiveness of the proposed method are verified by simulation and measurement in a loaded RC.

This letter presents a sparse non-uniform sampling method for planar near-field measurement system. First, the Igloo spherical sampling points are mapped into the near-field planar sampling points, which determines the positions and quantity of non-uniform sampling points. Then, the sparse non-uniform sampling points can accurately recover the near-field distribution through linear interpolation. Finally, the fast Fourier transform based near-to-far field transformation (NFT) is applied to derive the far-field radiation pattern of the antenna under the test (AUT). Simulations and measurements demonstrate that the near-field and far-field results agree well with those obtained through the existing half-wavelength uniform sampling method. Thus, the presented method can significantly reduce the sampling points without sacrificing the measurement accuracy.

Due to the special advantages of the reverberation chamber (RC), it has been recognized as a standardized over-the-air (OTA) testing methodology by the cellular telecommunications industry association (CTIA). Currently, OTA tests of the fifth-generation (5G) wireless terminals are usually performed in different testing environments, e.g., in a reverberation chamber for fast isotropic tests in the sub-6 GHz frequency band, and in an anechoic chamber for directional tests in the millimeter-wave (mm-wave) frequency band, which are inconvenient and costly. In this work, two multi-functional frequency selective absorbers (FSAs) are designed to realize absorption in the 5G mm-wave band and reflection/transmission in the sub-6 GHz band. By loading the FSAs to the RC, an integrated testing environment for 5G terminals can be established. Namely, a quasi-anechoic environment in the mm-wave band and a reverberation environment in the sub-6 GHz band can be simultaneously achieved in the RC loaded with the proposed FSAs. Experimental and simulated results are presented to demonstrate the effectiveness of the proposed scheme.