Dennis G. Camell

Radiated emissions and immunity of microstrip transmission lines: theory and reverberation chamber measurements

The increasing complexity of electronic systems has introduced an increased potential for electromagnetic interference (EMI) between electronic systems. We analyze the radiation from a microstrip transmission line and calculate the total radiated power by numerical integration. Reverberation chamber methods for measuring radiated emissions and immunity are reviewed and applied to three microstrip configurations. Measurements from 200 to 2000 MHz are compared with theory, and excellent agreement is obtained for two configurations that minimize feed cable and finite ground plane effects. Emissions measurements are found to be more accurate than immunity measurements because the impedance mismatch of the receiving antenna cancels when the ratio of the microstrip and reference radiated power measurements is taken. The use of two different receiving antenna locations for emissions measurements illustrates good field uniformity within the chamber.

Radio-Wave Propagation Into Large Building Structures—Part 1: CW Signal Attenuation and Variability

We report on our investigation into radio communications problems faced by emergency responders in disaster situations. A fundamental challenge to communications into and out of large buildings is the strong attenuation of radio signals caused by losses and scattering in the building materials and structure. Another challenge is the large signal variability that occurs throughout these large structures. We designed experiments in various large building structures in an effort to quantify continuous wave (CW) radio-signal attenuation and variability throughout twelve large structures. We carried radio frequency transmitters throughout these structures and placed receiving systems outside the structures. The transmitters were tuned to frequencies near public safety, cell phone bands, as well as ISM and wireless LAN bands. This report summarizes the experiments, performed in twelve large building structures. We describe the experiments, detail the measurement system, show primary results of the data we collected, and discuss some of the interesting propagation effects we observed.

Electrically short dipoles with a nonlinear load, a revisited analysis

We reexamine the characteristics of electrically short dipoles with nonlinear loads and, specifically, the early work of Motohisa Kanda (1980, 1983). Although this topic has been examined in great detail in the past, some inconsistencies between numerical and analytical results are apparent, and these have not been previously addressed. We show that these inconsistencies were due to only periodic sampling of the analytic solution, and an insufficient number of iterations in the numerical solutions, and we give corrected results. Additionally, some of the more significant analytical results, which were once thought to be impractical due to their complexity, are numerically implemented. We also show that a simple approximation accurately describes the behavior of these electrically short dipoles over a wide range of frequency and amplitude.

Radio-Wave Propagation Into Large Building Structures—Part 2: Characterization of Multipath

We report on measurements that characterize multipath conditions that affect broadband wireless communications in building penetration scenarios. Measurements carried out in various large structures quantify both radio-signal attenuation and distortion (multipath) in the radio propagation channel. Our study includes measurements of the complex, wideband channel transfer function and bandpass measurements of a 20 MHz-wide, digitally modulated signal. From these, we derive the more compact metrics of time delay spread, total received power and error vector magnitude that summarize channel characteristics with a single number. We describe the experimental set-up and the measurement results for data collected in representative structures. Finally, we discuss how the combination of propagation metrics may be used to classify different propagation channel types appropriate for public-safety applications.

Measurements in Harsh RF Propagation Environments to Support Performance Evaluation of Wireless Sensor Networks

Purpose – The purpose of this paper is to describe common methods for evaluating the performance of wireless devices such as wireless sensors in harsh radio environments.Design/methodology/approach – The paper describes how measurements of real‐world propagation environments can be used to support the evaluation process, then presents representative measurement data from multipath environments where sensor networks are likely to be deployed: a fixed‐infrastructure, process‐control environment (here an oil refinery), and a heavy industrial environment (here an automotive assembly plant).Findings – Results on the characterization of multipath in the propagation channel are summarized and how these results may be used in the performance evaluation of sensor networks is discussed.Originality/value – The paper describes measurement results from environments where little open‐literature data exists on point‐to‐point propagation, specifically high‐multipath environments. These highly reflective scenarios can pre...

Across-the-road photo traffic radars: new calibration techniques

We discuss simulator units for calibrating across-the-road Doppler traffic radar transceivers used in enforcement of highway speed limits. Two units of very similar design were developed, one operating at K-band (24 GHz) and the other at Ka-band (35 GHz). The signal received from the radar transmitter is frequency-modulated at rates that correspond to the expected Doppler shift for approaching and receding vehicles travelling at speeds of 25 to 200 km/h. The modulated signal is subsequently retransmitted back to the radar receiver, which demodulates it and then displays the simulated speed. The required calibration accuracy is 1.6 km/h at 90 km/h.

Free-Space Antenna Factors through the Use of Time-Domain Signal Processing

This paper demonstrates the usefulness of time- domain processing to determine free-space antenna factors (FSAF) for electromagnetic compatibility (EMC) antennas. Our procedures are explained and data are provided for frequencies from 30 MHz to 9 GHz. We investigate time gating of dense frequency packed insertion loss data obtained with an ultrawideband measurement system. These results show the advantage of time-domain gating to provide reliable results for free-space antenna factors of EMC antennas.

Improvements in the CW evaluation of mode-stirred chambers

The authors present methods for improving the reliability of measurements made in a mode-stirred chamber. The combination of improved instrumentation and a larger paddle resulted in measurements that were significantly more reproducible (/spl plusmn/1 dB) than previous measurements. They also give a simple model that is capable of describing the characteristics of a mode-stirred chamber at any frequency using only two parameters.

NBS calibration procedures for horizontal dipole antennas (25 to 1000 MHz)

The theoretical basis and test procedures for calibrating horizontally polarized dipole antennas at the National Bureau of Standards are discussed. Two different techniques and two different test sites are used. In the standard antenna method, a field-strength level is calculated from the response of a simple half-wave dipole. This method is used at an open-field site in the frequency range of 25 to 1000 MHz. In the standard-field method, the theoretical gain equations of waveguides and horn antennas are used to determine the field-strength level. This latter method is used in an anechoic chamber in the frequency range of 200 to 1000 MHz. Procedures for both techniques are explained and measurement setups are illustrated. Measurement uncertainties are discussed.<<ETX>>

Calibration of antenna factor at a ground screen field site using an automatic network analyzer

Two approaches are described that permit automatic stepped-frequency data acquisition and rapid calculation of several antenna parameters. These parameters include antenna factor, intrinsic gain, realized gain, antenna input impedance, voltage standing wave ratio and site attenuation. The effects of antenna impedance on the meaning and accuracy of antenna measurements are emphasized throughout. The technique now used at the National Institute of Standards and Technology for calibrating the antenna factor at frequencies from 25 to 1000 MHz uses a standard open-circuit half-wave receiving dipole to measure the electric field strength. This approach is compared with a three-antenna method that uses an accurate automatic network analyzer with 120 dB dynamic range to measure insertion loss between the transmitting and receiving antennas. A field site having a 30*60 m ground screen, which acts as a good reflector, is used. Thus, the effects of ground reflection are calculated and compensated for. The new insertion loss technique permits faster measurements with greater repeatability and reduction in calibration uncertainty, especially at frequencies above 75 MHz.<<ETX>>