A Practical Approach to Generating First-Order Rician Channel Statistics in a RC plus CATR Chamber at mmWave

TL;DR

The paper presents a practical RC‑HARC hybrid chamber to generate first-order Rician channel statistics for mmWave OTA testing in the FR2 band ($24.25$–$29.5$ GHz). By mixing RIMP and LOS contributions through RC and CATR excitation and tuning with absorbers and polarization control, it achieves a controllable $K$-factor across $-9.2$ to $40.8$ dB with ~1.3 dB granularity, validated via a bootstrap Anderson–Darling GoF test against Rician or Rayleigh distributions. The methodology relies on a stationary horn reference, independent sample confirmation, and robust power/SNR estimations to extract $K$, $P_s$, $P_d$, and $\Omega$, revealing inverse frequency trends for the power components while $K$ remains frequency-insensitive on average. The approach offers a cost-efficient, repeatable OTA testing pathway for directional mmWave devices and active antenna systems, enabling controlled fading environments for beamforming and MIMO studies.

Abstract

This paper explores a novel hybrid configuration integrating a Reverberation Chamber (RC) with a Compact Antenna Test Range (CATR) to achieve a controllable Rician K-factor. The focus is testing directive antennas in the lower FR2 frequency bands (24.25-29.5 GHz) for 5G and beyond wireless applications. The study meticulously evaluates 39 unique configurations, using a stationary horn antenna for consistent reference K-factor characterization, and considers variables like absorbers and CATR polarization. Results demonstrate that the K-factor can be effectively adjusted within the hybrid setup, maintaining substantial margins above the noise level across all configurations. Sample independence is confirmed for at least 600 samples in all cases. The Bootstrap Anderson-Darling goodness-of-fit test verifies that the data align with Rician or Rayleigh distributions. Analysis of total received power, stirred and unstirred power and frequency-dependent modeling reveals that power variables are inversely related to frequency, while the K-factor remains frequency-independent. The hybrid RC-CATR system achieves a wide range of frequency-averaged K-factors from -9.2 dB to 40.8 dB, with an average granularity of 1.3 dB. Notably, configurations using co-polarized CATR signals yield large K-factors, reduced system losses, and improved frequency stability, underscoring the system's efficacy for millimeter-wave over-the-air testing. This research offers a cost-efficient and repeatable method for generating complex Rician fading channels at mmWave frequencies, crucial for the effective OTA testing of advanced wireless devices.

Figures (8)

• Figure 1: From left to right, Bluetest RTS65 with the CATR option and without any absorbers installed, corresponding to the "NoAs" case, depicting the RHA and the dual-polarized CATR feed. Then we have the Stirrer 1 and the LOS blocking plate, which hides the mmWave RIMPMA, depicted in the next picture, which is a ceiling shot taken from behind the LOS blocking plate, where the Stirrer 2 can be seen. Then, we have the front panel of the RC, with the three used ports highlighted: RIMP port, CATR port, and reference antenna port. Finally, the 1:4 splitter goes outside the chamber and indicates where each port is connected. Note the terminations in the unused ports. Note also that the splitter configuration shown is for the RaC case. In R and C cases the port of the splitter going to the CATR or RIMP ports, respectively, would be terminated too.
• Figure 2: CAD render showing geometry and signal flow (in green). The "quiet zone" is located within the lightest green volume. Notice how all absorbers are installed in the chamber, corresponding to the "AAs" case, including the back absorber, depicted in red, which intercepts the signal flow.
• Figure 3: Experiment setup for calibrating the VNA.
• Figure 4: $95\%$CI for the $K$-factor estimator used in this work (from KFEmulRician) and $600$ samples or stirrers' positions.
• Figure 5: DR and CV of $\Omega$, $K$, $P_\mathrm{s}$ and $P_\mathrm{d}$. Split into cases in which only RIMP is excited (red and magenta), cases in which the CATR is excited, along or not with RIMP, co-polarized with the RHA or "PS1" (green and black), and cases in which the CATR is excited, along or not with RIMP, cross-polarized with the RHA or "PS2" (blue and cyan). The purpose of these plots is to help identify trends in terms of DR and CV of $\Omega$, $K$, $P_\mathrm{s}$ and $P_\mathrm{d}$ depending on the frequency-averaged values of $\Omega$, $K$, $P_\mathrm{s}$ and $P_\mathrm{d}$, respectively. The split between "RIMP", "PS1" and "PS2" cases is made because they showed different behaviors among them while being similar for the cases they comprise, i.e., "PS1" cases behave in a relatively consistent manner, which is different to how "RIMP" and "PS2" behave.