This paper presents a sub-6 GHz cost-effective wideband dual-polarized plane wave generator (PWG) design for 5G base station (BS) over-the-air (OTA) test. The proposed nonuniform PWG design is composed of 256 elements and has a dimension of 1.7 m×1.7 m. Several novel strategies are proposed and implemented to reduce the cost and complexity. To reduce feeding network complexity and mutual coupling among PWG elements, a novel tapered amplitude-only excitation method (i.e. with the same relative phase excitations among all PWG elements) is proposed. To reduce the number of channels in the phase and amplitude control network, a 4-element subarray is applied. Furthermore, wideband PWG element design and non-uniform configuration are applied to support for ultra-wideband operations from 2 GHz to 5 GHz. The proposed PWG design is numerically simulated and experimentally validated. A cylindrical quiet zone of a diameter of 0.9 m and a depth of 0.9 m, with 2.1 m distance to the PWG, is achieved in the measurement for the considered bandwidth, with typical peak-to-peak (PP) E-field amplitude and phase variations less than ±1.25 dB and ±7.5º, respectively, which demonstrated its effectiveness and robustness.
Plane Wave Generator (PWG) has recently attracted great attention from industry and academia for over-the-air (OTA) testing of base station (BS) antennas in the fifth-generation (5G) wireless communication systems. This paper aims to reduce the scattering from the PWG to the antenna under test (AUT), which might be problematic in the near-field OTA testing. First, we introduce a low monostatic radar cross section (RCS) PWG array element design. The PWG is also loaded with pyramidal microwave absorbing material (MAM) to suppress the multi-reflections between the AUT and the PWG. Furthermore, unlike coplanar PWG design generally reported in the literature, a novel non-coplanar design is proposed to realize the destructive interference of the scattered signals from the PWG, thereby significantly reducing the multiple reflections. PWG elements in the non-coplanar design are placed in the propagation direction according to planar and non-planar field distribution on the PWG radiated from the BS AUT. To validate our proposed design, a 4×4 PWG array with a 108 mm element spacing and a non-coplanar structure is developed and experimentally validated. The measured results show that the second incident wave of the proposed non-coplanar PWG array structure based on non-planar field distribution is 7.9 dB lower than that of the classical coplanar PWG design from 2.3 GHz to 3.8 GHz, and 1.9 dB lower than that of the proposed non-coplanar PWG array structure based on planar field distribution, which demonstrates the effectiveness and robustness of our proposed design. INDEX TERMS 5G, OTA testing, PWG, low scattering design, probe antenna design, non-coplanar PWG structure. I. INTRODUCTION ASSIVE multiple-input multiple-output (MIMO) is one of the key technologies employed at the base stations (BSs) in the sub-6 GHz 5G wireless communication systems [1], [2]. Accurate measurement of the massive MIMO BS antenna systems is essential in the performance and conformance testing. Over-the-air (OTA) testing is a competitive method to evaluate BS antennas due to its advantage of convenient operation and cost savings, compared to conventional cable conducted testing [3], [4]. The plane-wave generator (PWG), which aims to approximate a plane wave in the quiet zone with a nearfield distance, has attracted great interest recently [5]-[10]. Compared with the traditional antenna measurement methods (e.g., near-field to far field transformation, direct far-field and compact antenna testing range (CATR)), the PWG has the advantages of compact size, fast measurement, low-cost, and support for both continuous wave (CW) and modulated signal measurement. The PWG has a good potential to support for massive MIMO BS antenna parameter measurement, array calibration, radio frequency (RF) transmit and receive performance measurements. Extensive works have been reported on the PWG design in the literature, e.g. algorithms to determine the complex excitation coefficients for the PWG element [11]-[13], and guidance to design a good PWG [14]. Multiple refle...
A high channel consistency subarray of plane-wave generators (PWG) is described for fifth-generation (5G) base station (BS) over-the-air (OTA) testing. Firstly, the variation of the near field radiation characteristics of the subarray based on the feed amplitude and phase errors of the traditional power divider network is analyzed. The recommended amplitude and phase errors between channels are given. After that, a novel subarray which combines four pyramidal horn antennas and a compact 1:4 waveguide power divider is designed. The optimized perfectly symmetrical zigzag waveguide transmission lines are used to realize consistent power allocation among antenna elements. No intermediate pins are employed, which avoids the significant deterioration of channel consistency caused by assembly errors. The size of the subarray is 4.89 λ0 × 4.97 λ0 × 1.23 λ0 (λ0 is the working wavelength corresponding to the subarray center frequency at 3.5 GHz). The VSWR < 1.5 impedance bandwidth covers 3.4 GHz to 3.6 GHz. The amplitude difference between the four elements of the subarray is less than 0.5 dB, and the phase difference is less than 3°. The simulated and measured results agree well in this design.
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