Hybrid OTA Chamber for Multidirectional Testing of Wireless Devices: Plane Wave Spectrum Generator Design and Experimental Demonstration

This article investigates practical implementation aspects of a novel hybrid chamber concept that has been recently introduced for over-the-air (OTA) testing of wireless devices. The chamber allows to synthesize a spectrum of plane waves (PWs) incident on a device under test (DUT) from a wide range of angles of arrival (AoAs) through exploiting multiple field scattering inside the overmoded waveguide (WG) chamber. An optimal design approach for the plane wave spectrum generator (PWSG) array inside the chamber is presented considering: 1) array antenna impedance matching for the desired test zone (TZ) quality and AoAs' range; 2) an operational frequency bandwidth of the test environment and an instantaneous signal bandwidth; and 3) the impact of PWSG excitation errors. A robust linearly constrained minimum variance (LCMV) beamformer is formulated to realize the desired test environment over a wide frequency band, while accounting for the varying number of the WG propagating modes as excited by PWSG array. Numerical simulations and measurements with the first prototype of the hybrid chamber for FR1 frequency band (~3.5 GHz) are presented. This prototype includes a {7\times 7} bowtie antenna element PWSG array, a 1.00 m \times1.25 m \times1.75 m metal WG chamber, an off-line optimal array beamforming setup, and a planar scanner for TZ characterization.