K-factor Evaluation in a Hybrid Reverberation Chamber plus CATR OTA Testing Setup

TL;DR

This work addresses how to realize diverse $K$-factors in mmWave OTA testing using a hybrid Reverberation Chamber and Compact Antenna Test Range (RC+CATR) setup across $24.25$–$29.5$ GHz. It compares six configurations combining Rich Isotropic Multipath (RIMP) and CATR plane-wave excitations, with and without a back absorber, and analyzes the envelope distributions via GoF testing, estimating the $K$-factor using an unbiased KFEmulRician approach that relies on complex $S_{21}$ data. The findings show that RIMP-only scenarios favor a Rayleigh envelope while CATR-excited scenarios exhibit Rician envelopes with higher and more stable $K$-factors, though no universal method to achieve a target $K$ is found; back absorbers modify stirred versus unstirred energy and influence overall losses. The results demonstrate the feasibility of commercial mmWave OTA testing with controlled $K$-factors and provide baseline insights into how absorber placement and excitation mode affect channel statistics, informing future design of controllable mmWave channel emulators.

Abstract

This paper investigates achieving diverse K-factors using a Reverberation Chamber (RC) with a Compact Antenna Test Range (CATR) system. It explores six hybrid "RC plus CATR" configurations involving different excitations of the Rich Isotropic Multipath (RIMP) field and CATR-generated plane waves, with some setups including absorbers. A fixed horn antenna points towards the CATR in all configurations. The study found that the null hypothesis of Rayleigh or Rician probability distributions for the received signal envelope could not be rejected, with RIMP setups primarily conforming to Rayleigh distribution and all setups showing Rician distribution. Various K-factors were obtained, but no generalizable method for achieving the desired K-factor was identified. The paper also estimates the K-factor as a function of frequency in the 24.25-29.5 GHz band. Smaller K-factors exhibit larger fluctuations, while larger K-factors remain relatively stable, with consistent fluctuations across the frequency range.

Figures (4)

• Figure 1: Bluetest RTS65 with the CATR option and the back absorber installed. The dimensions of the chamber are $1945$x$2000$x$1440$ mm (WxHxD).
• Figure 2: CAD render showing geometry and signal flow (in green). The test zone is located within the lightest green volume. Source: BluetestCATR.
• Figure 3: Experiment setup for calibrating the VNA.
• Figure 4: $K-$factor for different SW and $|S_{21}|^2$, as a function of the frequency; where only $|S_{21}|^2$ belongs to the right y-axis.