A novel type of hybrid measurement facility comprising a chamber antenna array (CAA) inside an overmoded waveguide (WG) is proposed and analyzed numerically. The reflecting walls of the metal rectangular WG are used in conjunction with a CAA to synthesize obliquely incident plane-wave (PW) fields at the device under test (DUT). This enables increased flexibility in emulating almost any PW multipath testing conditions in the WG chamber without the high cost and complexity of classical anechoic measurement systems employing relatively large phase-steered PW generators (PWGs).A modeling framework is proposed that has been used to devise first-order design rules (e.g., the number of independent propagating modes, dimensions of the WG, CAA, and DUT). Afterward, an optimally beamformed CAA example is presented to numerically validate the quality of the on-and off-axis PW fields in the test zone (TZ). This study shows design tradeoffs between the amplitude ripple in the DUT region, the total power focused in this region, the DUT size, and the angle of incidence.

We investigate the use of a hybrid over-the-air (OTA) measurement chamber to emulate far-field testing conditions. The focus has been on the generation of a plane wave arriving at an arbitrary angle-of-arrival (AoA) to the device-under-test (DUT) without mechanical steering. The chamber consists of an oversized waveguide (WG) and a planar array antenna with adaptive beamforming. A modified linear constrained minimum variance (LCMV) beamforming algorithm is used to form a quiet zone (QZ) in the DUT region by using the reflections from the WG's metal walls. The LCMV beamformer formulation has been extended to achieve a volumetric QZ with the desired amplitude and phase uniformity. Numerical studies for the QZ size corresponding to an FR1 base station demonstrate promising results with the low levels of amplitude and phase variation. The AoA coverage of this chamber meets 3GPP specification requirements for OTA conformance testing of base stations with active antenna systems.

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This paper investigates practical implementation aspects of a novel hybrid chamber concept that has been recently introduced for over-the-air testing of wireless devices. The chamber allows to synthesize a spectrum of plane waves (PWs) incident on a device under test from a wide range of anglesof-arrival (AoAs) through exploiting multiple field scattering inside the overmoded waveguide chamber. An optimal design approach for the plane wave spectrum generator (PWSG) array inside the chamber is presented considering: (i) array antenna impedance matching for the desired test zone (TZ) quality and AoAs range; (ii) an operational frequency bandwidth of the test environment and an instantaneous signal bandwidth; and (iii) the impact of the 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 waveguide propagating modes as excited by the 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 × 7 bowtie antenna element PWSG array, a 1.00 × 1.25 × 1.75 m metal waveguide chamber, an off-line optimal array beamforming setup, and a planar scanner for the TZ characterization.

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