Olof Lundén

Experimental Investigation and Mathematical Modeling of Design Parameters for Efficient Stirrers in Mode-Stirred Reverberation Chambers

In this paper, we have investigated the design parameters for efficient stirring in reverberation chambers. We have measured the efficiency of the stirrer in terms of the lowest possible frequency for which it gives a certain number of uncorrelated samples. Rotating stirrers, when rotated about their axes, generate cylindrical volumes. The impact of a change of the stirrer diameter is approximately cubic compared with the change of the stirrer height. The efficiency of stirrers that are translated is proportional to the stepping increment and to the square root of the area of projection of the stirrer on a plane orthogonal to the direction of translation

Vulnerability of European Rail Traffic Management System to Radiated Intentional EMI

In this paper, the vulnerability of the future electrified railway system in Europe from a high-power microwave (HPM) source is investigated. The scenario of in-band disturbances radiated toward a GSM-R antenna and damaging the connected communications system is evaluated for different classes of HPM sources and situations. The minimum realistic distances for the different HPM sources from the antenna to cause permanent damage is shown, and the severity of threat from the different sources is discussed.

Susceptibility of Civilian GPS Receivers to Electromagnetic Radiation

Civilian handheld global positioning system receivers were tested for their susceptibility against radiated electromagnetic disturbances of different characteristics and field levels. This susceptibility data were compared to the existing electromagnetic compatibility (EMC) immunity requirements for electronic devices. Some of the receivers were disrupted by continues waves at in- as well as out-of-band frequencies, at field levels far below the existing EMC requirements. The possible reason for this is discussed. In general, due to the ever-growing use of commercial-off-the-shelf equipment even for critical functions, certificates of conformity to current EMC requirements may be inadequate.

Numerical simulations as a tool for optimizing the geometrical design of reverberation chambers

The finite difference time domain (FDTD) method is used to simulate the electro-magnetic field in a reverberation chamber. By including conductivity and thickness of the walls in our model a good agreement with measurements is found. With help of the FDTD numerical computation program it is shown that by introducing wall mounted diffusers the minimum operating frequency of the reverberation chamber could be lowered.

Microwave breakdown in slots

The properties of microwave-induced breakdown of air in narrow metallic slots are investigated, both theoretically and experimentally, with emphasis on factors important for protection against transmission of incident high-power microwave radiation. The key factors investigated are breakdown power threshold, breakdown time, peak-leakage power, and total transmitted energy, as functions of incident pulse shape and power density. The theoretical investigation includes estimates of the electric field intensification in narrow slots and basic breakdown plasma modeling. New results important for application to the high-power microwave field, such as the influence of pulse shape on breakdown time and peak-leakage power, are presented. The experimental investigation comprises a set of slot breakdown experiments at atmospheric pressure, which are analyzed to extract key parameters, such as transmission cross section, breakdown time, peak leakage power, and transmitted energy. The experimental data is compared and shown to be in good agreement with results obtained in the theoretical investigation.

How to Avoid Unstirred High Frequency Components in Mode Stirred Reverberation Chambers

A goodness of fit test of the assumed Chi-Squared distribution, of the power received by an antenna in a Reverberation Chamber, is a very efficient way to reveal the presence of unstirred components at frequencies above the lowest usable frequency. To reduce the risk of having an unstirred component, in RS-testing, the transmitting antenna has to be directed towards the stirrer. The distance between the transmitting antenna and the stirrer has to be so close that the main lobe of the antenna is enclosed by the geometry of the stirrer. In RE- testing this will hold also for the reference antenna. Unstirred components are not possible to reveal and correct for in RS- and RE-testing which might lead to erroneous testing.

The maximum value distribution in a reverberation chamber

The maximum over mean distribution of received power in the FOI reverberation chamber is analyzed. The experimental results are compared with the theoretical distribution for a chi squared distributed power. For the theoretical distribution the confidence intervals are given as functions of the number of independent measurements for the maximum over mean values. The minimum number of required samples to obtain an acceptable estimate of the maximum over mean is discussed. It turns out that the number of samples should be at least greater than 20. Further the relation between statistical independence and linear correlation coefficients of measured data are discussed and analyzed. The authors make a chi square goodness of fit test to reject data that are statistically dependent. These results are compared with linear correlation coefficient evaluations.

Absorber loading study in FOI 36.7 m 3 mode stirred reverberation chamber for pulsed power measurements

A feasibility study was conducted to gain better understanding of the influence of different Q-values of a 36.7 m3 reverberation chamber. The chamber was loaded with different types and numbers of microwave absorbers. For different chamber Q-values, the lowest usable frequency for 200 uncorrelated stirrer positions the agreement with the expected exponential power distribution, the chamber time constant and field build up process, has been studied.

Stirrer Blade Separation experiment in reverberation chambers

It is often claimed that it is the volume swept by the stirrers in relation to the reverberation chamber volume that is of importance for the efficiency of the stirrers. The impact of a change of the stirrer diameter is however approximately cubic compared with the change of the stirrer height. In this paper it is shown that it is mainly the periphery of the stirrers that contribute in the tuning of reverberation chambers.

A factorial designed experiment for evaluation of mode-stirrers in reverberation chambers

A factorial designed experiment at two levels was applied to investigate the performance of stirrers in reverberation chambers. The goal has been to quantify the sensitivity of the design parameters for the mode-stirrer. The focus has been to investigate single rotational stirrers. The experiment shows that the effect of changing the diameter of the stirrer is much greater than changing the height, and that the effect of changing the chamber volume is small