Damir Senic

Absorption Cross-Section Measurements of a Human Model in a Reverberation Chamber

We provide the results of human body absorption cross-section (ACS) measurements. The setup was based on the reverberation chamber as a well-known measurement environment capable of performing ACS measurements. The approach was supported by reference measurements on canonically shaped objects which were convenient for analytical (Mie scattering theory) ACS calculations. Measured ACS of canonical objects was in excellent agreement with calculated values. The ACS measurements of a human model were performed: 1) on an actual human body in an upright posture and 2) on a cylindrical water model made of vertically stacked water-filled jugs. The cylindrical model had the same water content as an average human body. Comparison between these two models showed a small difference in measured ACS within the measurement uncertainty of our setup. Thus, the cylindrical water model proved to be a useful artifact, especially for time-consuming broadband ACS measurements.

Estimating and Reducing Uncertainty in Reverberation-Chamber Characterization at Millimeter-Wave Frequencies

This contribution provides techniques for accurately characterizing uncertainty when measuring total radiated power (TRP) at millimeter-wave frequencies. The setup is based on the reverberation chamber as a well-known measurement environment capable of performing TRP measurements of wireless devices. We show that by applying various stirring techniques, we can reduce the random component of measurement uncertainty to around 2%. We use a model for estimating the uncertainty for TRP measurements based on the K factor, which is compared with uncertainties calculated from relative power measurements and we show excellent agreement. We perform a significance test to confirm that the uncertainty due to the limited number of mode-stirred samples dominates over the uncertainty due to the lack of spatial uniformity. The observed uncertainty is also compared with an ideal chamber situation and shows good agreement.

Improved Antenna Efficiency Measurement Uncertainty in a Reverberation Chamber at Millimeter-Wave Frequencies

We provide results of antenna radiation and total radiation efficiency at millimeter-wave frequencies gathered with a new open-ended waveguide-plate method that is compared to a well-known two-antenna method. The new method yields improved uncertainty in antenna efficiency measurements. Both methods are based on use of a reverberation chamber. Measurement results are compared to numerical simulations and good agreement (~3% maximum difference) is achieved. Before performing the efficiency measurements, the chamber configuration was assessed with respect to the Rician

High efficiency carbon nanotube thread antennas

K

Radiated power based on wave parameters at millimeter-wave frequencies for integrated wireless devices

-factor, number of uncorrelated paddle orientations, and coherence bandwidth. We calculated the uncertainty using the NIST microwave uncertainty framework capable of performing parallel sensitivity and Monte Carlo analyses. The framework enables us to capture and propagate the uncertainties in the S-parameter measurements to the final efficiency result. The expanded uncertainty that we achieved for these antenna efficiency measurements is 2.60%.

Estimating and Correcting the Device-Under-Test Transfer Function in Loaded Reverberation Chambers for Over-the-Air Tests

Although previous research has explored the underlying theory of high-frequency behavior of carbon nanotubes (CNTs) and CNT bundles for antennas, there is a gap in the literature for direct experimental measurements of radiation efficiency. These measurements are crucial for any practical application of CNT materials in wireless communication. In this letter, we report a measurement technique to accurately characterize the radiation efficiency of λ/4 monopole antennas made from the CNT thread. We measure the highest absolute values of radiation efficiency for CNT antennas of any type, matching that of copper wire. To capture the weight savings, we propose a specific radiation efficiency metric and show that these CNT antennas exceed coppers performance by over an order of magnitude at 1 GHz and 2.4 GHz. We also report direct experimental observation that, contrary to metals, the radiation efficiency of the CNT thread improves significantly at higher frequencies. These results pave the way for practical a...

Whole-Body Specific Absorption Rate Assessment of Lossy Objects Exposed to a Diffuse Field Inside a Reverberant Environment

We provide total radiated power measurements at millimeter-wave frequencies using a reverberation chamber and a power-calibrated vector network analyzer capable of measuring wave parameters. We compare total radiated power results obtained from two different approaches. In the first approach, applicable when the terminals of the antenna under test are accessible, the total radiated power is calculated directly from forward and reflected waves. In the second approach, when we cannot access the terminals of the antenna under test, the total radiated power is calculated from measured forward and reflected waves at the receive antenna taking into account chamber loss. The results from the two different approaches have excellent agreement, and are within the measurement uncertainty. The uncertainty in our total radiated power measurements is below 2%.

Measurement Challenges for 5G and Beyond: An Update from the National Institute of Standards and Technology

We assess the potential error in measurements of the power transfer function corresponding to a reverberation chamber set-up when different antenna types are used for the reference and device-under-test measurements. We derive a mathematical description of the transfer function that accounts for differences in the amount of unstirred energy, represented by the spatially averaged K factor, arising from various antenna types. Our results show that loaded chamber configurations, combined with reference/device antenna pairs having significantly different radiation patterns, can result in statistically significant errors in the prediction of the transfer function. If it is possible to obtain an estimate of the K factor associated with the device antenna, this correction can improve the estimate of the transfer function that would be experienced by the device under test. Finally, we develop a method that could be used in standardized test methods to bound the uncertainty associated with the unknown K factor for common antenna types.

Use of Absorption Cross Section to Predict Coherence Bandwidth and Other Characteristics of a Reverberation Chamber Setup for Wireless-System Tests

In this study, we provide a novel approach for exposure assessment in terms of whole-body average specific absorption rate (<italic>WBSAR</italic>) due to the electromagnetic fields inside reverberant environments. The approach utilizes <italic>power balance theory</italic> and the lossy objects absorption cross section (<italic> ACS</italic>). We use this to present a noninvasive technique for determining the <italic>WBSAR</italic> in reflective environments. Measurements were performed inside a reverberation chamber on spherically-shaped phantoms filled with lossy liquids. The approach was verified by performing invasive temperature measurements and showed excellent agreement (within 5%). This approach can be used for human exposure assessment inside reverberant environments since human body <italic>ACS</italic> has been well studied in the literature. The main advantage of the proposed approach is that it overcomes the need for complex invasive measurements in order to determine <italic>WBSAR</italic>.

Isotropy study for over-the-Air measurements in a loaded reverberation chamber

In less than a decade since the mainstreaming of cellular wireless technology, spectrum has become saturated by data-intensive smartphones, driving the so-called spectrum crunch. As a solution, the wireless community is pursuing the use of alternatives to current wireless technologies, including multiple-input/multipleoutput (MIMO) antenna arrays that allow increased simultaneous transmission capacity; the millimeter-wave (mmW) spectrum (30-300 GHz) to alleviate the spectrum crunch in current frequency bands; and ultradense networks transmitting wide-band modulated signals to allow short-range, high-speed data transfer.