Perry F. Wilson

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

Techniques for measuring the electromagnetic shielding effectiveness of materials. II. Near-field source simulation

Shielding effectiveness relates to the ability of a material to reduce the transmission of propagating fields in order to electromagnetically isolate one region from another. Because the shielding capability of a complex material is difficult to predict, it often must be measured. A number of approaches to simulating far-field source are studied, including the use of coaxial transmission-line holders and a time-domain system. In each case, the system frequency range, test sample requirements, test field type, dynamic range, measurement time required, and analytical background are considered. Data taken on a common set of materials are presented. >

On determining the maximum emissions from electrically large sources

This paper examines the use of measurements of the total radiated power from an arbitrary source, combined with theory-based estimates of directivity or quality factor, to accurately predict the maximum electric field radiated by the source either at a line-of-sight distance or in a resonant volume. The approach using total radiated power avoids source rotations during testing and is an efficient alternative to current emission test methods. Examples of simulated (random source set) and measured (box with holes) planar-cut radiation-patterns for electrically large sources are presented. Both simulated and measured data agree well with theoretical estimates.

Simple Approximate Expressions for Higher Order Mode Cutoff and Resonant Frequencies in TEM Cells

Simple approximate expressions for determining the cutoff frequencies of the first few higher order modes and the associated resonant frequencies in transverse electromagnetic (TEM) cells are presented. Both symmetric (seven TE and two TM modes) and asymmetric (three TE modes) cells are discussed.

Shielding-Effectiveness Measurements with a Dual TEM Cell

Small-aperture theory is used to investigate the dual transverse electromagnetic (TEM) cell. Analyzing coupling through an empty versus loaded aperture leads to a simple model of dual-TEM-cell material shielding-effectiveness (SE) measurements. Experimental data are compared to theory with good agreement in the case of an empty aperture. Some of the difficulties in analyzing a loaded aperture are discussed.

Fields radiated by electrostatic discharges

The problem of electrostatic discharge (ESD) radiated fields problem is examined, both theoretically and experimentally. Measurements indicate that the electric fields can be quite significant (>150 V/m at a distance of 1.5 m), particularly for relatively low-voltage sparks (<6 kV). A theoretical dipole model for the ESD spark is developed to compute the radiated fields. The agreement between theory and experiment is good. The model can be used to predict the fields for a wide range of possible discharge configurations.<<ETX>>

A Study of Techniques for Measuring the Electromagnetic Shielding Effectiveness of Materials

Abstract: Shielding effectiveness relates to a materials ability to reduce the transmission of propagating fields in order to electromagnetically isolate one region from another. Because a complex materials shielding capability is difficult to predict, it often must be measured. A number of measurement approaches are studied including the use of a shielded room, coaxial transmission line holders, time domain signals, the dual TEM cell, and an apertured TEM cell in a reverberation chamber. In each case, we consider the systems frequency range, test sample requirements, test field type, dynamic range, time required, analytical background, and present data taken on a common set of materials.

Emission and immunity standards: replacing field-at-a-distance measurements with total-radiated-power measurements

This paper examines the use of total radiated power measurements, combined with theory-based directivity estimates, to generate accurate estimates for the maximum radiation and reception from a device. This approach may be a useful alternative to present test methods for emission and immunity as frequencies above 1GHz become necessary for EMC standards. Radiation-pattern data for theory-based estimates, Monte Carlo simulations of an arbitrary device, and measurements on a sample device are presented, and good data agreement is demonstrated.

A comparison between near-field shielding-effectiveness measurements based on coaxial dipoles and electrically small apertures

The near-field shielding effectiveness (SE) of a material can be measured by placing it between two closely spaced dipoles (electric or magnetic) and noting the resulting insertion loss. An alternative approach is to cover an electrically small aperture with the test material and measure the resulting loaded aperture polarizability (electric or magnetic), as is done in a dual TEM (transverse electromagnetic) cell. The author develops approximations leading to simple closed-form SE expressions by developing expressions that relate these two configurations. Small-aperture theory is discussed first, followed by a development of approximate dipole coupling expressions. The results are then compared with an experimental example. >

Radiation patterns of unintentional antennas: Estimates, simulations, and measurements

Electronic devices designed for purposes other than transmitting and receiving electromagnetic fields can act as unintentional antennas. Measurement methods are needed to characterize these antennas for electromagnetic compatibility tests; however, the rigor of precision antenna measurements is typically too costly and time consuming for electromagnetic compatibility applications. Alternate approaches are needed. This paper presents analytical estimates for the directivity of unintentional antennas based on the assumption that unintentional antennas will only randomly (and not coherently) excite the available propagating spherical modes at a given frequency. This directivity estimate is then compared to simulated and measured data. Good agreement is shown. Directivity estimates combined with simple total radiated power measurements represent a useful alternative to direct antenna measurements for electromagnetic compatibility tests.