Jason B. Coder

On the Use of Reverberation Chambers to Simulate a Rician Radio Environment for the Testing of Wireless Devices

With the proliferation of wireless devices in recent years, there is a growing need to test the operation and functionality of these various devices in different multipath environments, ranging from line-of-sight environment to a pure Rayleigh environment. In this paper we discuss how a reverberation chamber can be used to simulate a controllable Rician radio environment for the testing of a wireless device. We show that by varying the characteristics of the reverberation chamber and/or the antenna configurations in the chamber, any desired Rician K-factor can be obtained. Expressions for the desired K-factor as a function of the chamber and antenna characteristics will be presented. Experimental results are presented to illustrate the validity of these expressions, to show how the reverberation chamber can be used to simulate different multipath environments, and to show the realization of a controlled K-factor test facility. We present both a one-antenna and a two-antenna test configuration approach

Use of Reverberation Chambers to Determine the Shielding Effectiveness of Physically Small, Electrically Large Enclosures and Cavities

With the proliferation of small electric devices in recent years, along with various other applications, there is a growing need to test and determine the shielding properties or shielding effectiveness (SE) of physically small (but electrically large) enclosures or cavities. In this paper, we discuss how a reverberation chamber technique can be used to measure the SE of such enclosures. The approach consists of placing the small enclosure inside a reverberation chamber and using frequency stirring to excite the reverberation chamber. A small surface probe (i.e., a monopole) is mounted on the inside wall of the small enclosure to measure the power level inside the small enclosure. We present measured data from various other reverberation chamber approaches obtained from various enclosure configurations. The data from these other reverberation chamber approaches are used to validate the proposed approach. We also compared measured data to theoretical calculations of the SE for two small enclosures with circular apertures. These various comparisons illustrate that the proposed technique is a valid approach for determining the SE of physically small (i.e., cubic enclosure dimensions of the order of 0.1 m and smaller), but electrically large enclosures (that support several modes at the lowest frequency of interest).

Measuring the Shielding Effectiveness of Small Enclosures/Cavities with a Reverberation Chamber

For various applications, there is a growing need to determine the shielding effectiveness (SE) of physically small (but electrically large) enclosures or cavities. In this paper, we present a reverberation chamber technique for measuring the SE of such enclosures. We present data from four different reverberation chamber approaches obtained from various enclosure configurations. These four different sets of measurements are used to validate the proposed approach.

Using Nested Reverberation Chambers to Determine the Shielding Effectiveness of a Material: Getting Back to the Basics With a "Lei"-Person's Approach

We examine an existing method for determining the shielding effectiveness of a material using nested reverberation chambers and then present an alternate derivation based on measurement intuition. Included in our examination is a discussion of the purpose for using a four antenna measurement system and a simplification of the equations used in the data processing portion of the measurement. The result of this approach will be a measurement process that is more intuitive and makes use of S-parameters along with power ratios in all portions of the measurement effort. To validate our simplifications and data processing methods, we provide an experimental demonstration and verification.

Characterizing a Device's susceptibility to broadband signals: A case study

Electronic devices are commonly tested for their susceptibility to radiated signals which they may be exposed to during normal operation. A reverberation chamber is well suited to perform this type of testing because it can expose the device under test to a radiated signal from all polarization and incidence angles. Testing devices by exposing them to a narrow-band or CW signal has been well documented. However, with the increase in broadband communication signals, device manufacturers and users are becoming more interested in the devices performance when exposed to a broadband signal. In this case study, measurements of cable television/telecommunications equipment (i.e., set-top boxes, modems) are used to examine the potential for interference from 4G/LTE signals. We show that several difficulties arise when testing with broadband signals, particularly when measuring the incident electric field. We also examine how different device configurations (i.e., cabling and/or the use of splitters) can significantly change device performance.

On lower bound antenna efficiency measurements in a reverberation chamber

This paper addresses a few specific aspects of measuring the lower bound of antenna efficiency in a reverberation chamber. While the initial method for measuring the lower bound of efficiency has been presented, three key revisions are discussed here: (1) an updated notation, (2) a revised method for calculating the lower bound of efficiency, and (3) a new method for combining stirring techniques. The updated antenna model notation is designed to be more general and applicable to situations with n antennas. The revised efficiency calculation targets an issue of the original method where the minimum bounding circle exceeded the unit circle. Introducing a new method of combining stirring techniques addresses a weakness of the original model. For the model to work well, it needs a very large number of paddle positions that generate a good statistical approximation of the environment (in this case, a reverberation chamber). As a possible remedy to this weakness, we propose a different way of combining stirring techniques.

A review of wireless coexistence test methodologies

This paper discusses several wireless coexistence test methods in-practice and proposed for industry standards such as ANSI C63.27 The test methods include conducted and radiated setups, and utilize a range of technologies at various levels of sophistication, including consumer electronics, laboratory grade test equipment, and anechoic test chambers. Some key parameters associated with the testing environments are outlined, and the benefits and limitations of the different test methods are discussed. Finally, some ideas on research needed to reconcile the outputs from the various tests are explored.

A novel method for determining the lower bound of antenna efficiency

Determining absolute transmitting efficiency has been a difficult task since the inception of the antenna itself. While methods that can measure transmitting efficiency do exist, most are complicated and prone to high uncertainties. A new method is presented for determining the lower bound of absolute transmitting efficiency by use of a reverberation chamber. This method is able to characterize both the transmitting and receiving efficiency of an antenna. After the method is derived, numerical simulations are presented. These simulations can provide insight into the behavior of the equations and necessary assumptions. Then, by use of measurement data, the method for transmitting efficiency is compared to efficiency data obtained from another reverberation chamber method. Data for this comparison will come from two different types of antennas: a wide band dual-ridged horn, and a narrow-band meta-material inspired antenna. Following the measurement data, possible areas for improvement of the method and its optimization are discussed.

Coexistence analysis of LTE and WLAN systems with heterogenous backoff slot durations

To enable constructive coexistence with wireless local area networks (WLANs), unlicensed long-term evolution (LTE) systems use listen before talk (LBT) as a major candidate technique. The LBT has a flexible backoff idle slot duration, which can be significantly larger than the WLAN counterpart. To our knowledge, however, available analytical results on the LTE and WLAN coexistence have considered only identical idle backoff slot durations. There is a formidable technical difficulty to coexistence analysis for different backoff slot durations. In this paper, we develop a new technical approach to address this open issue. First, we point out an LBT backoff slot jamming effect, and propose a modified LBT backoff scheme to address this problem. Second, for our proposed LBT scheme, we develop a new analytical framework to address system interactions with non-equal backoff slot durations, model the LTE backoff process as super-counters, and provide a thorough analysis on the throughput, backoff counter hold time, and successful transmission probabilities of LTE-LBT and WLAN systems. Finally, we program the algorithms and use computer simulation to validate the analysis. This result fills a major gap and provides practical value for LTE-LBT and WLAN coexistence performance analysis with heterogeneous sensing and backoff slot durations.

Spectrum sensing with WLAN access points

With wireless communication becoming increasingly common in simple everyday devices, the available spectrum is quickly filling up and the risk of interference is increasing. This interference could be a slight nuisance or a disruption to critical services. To better understand the quantity and type of traffic in congested environments, a potential spectrum sensing solution in the ISM bands is discussed. By using a commercially available wireless access point we may be able to monitor the spectrum within range of the access point. If the electromagnetic environment is better understood, device manufacturers should be better able to test their products before deployment, ensuring they can still perform in a crowded electromagnetic environment.