Free Space Environment Research Articles

Sensors for Electromagnetic Pulse Measurements Both Inside and Away from Nuclear Source Regions

For measuring transient electromagnetic fields and related quantities, one needs accurate broadband sensors with simple transfer functions. The various sensor designs developed to achieve this in an optimal manner are summarized. Such sensors are designed for use either in a free space environment (such as in an EMP simulator or on a system under test in such a simulator) or in a nuclear source region that includes local source current and perhaps conductivity. There are now numerous designs which have been iterated for improvements over the last decade.

Sensors for electromagnetic pulse measurements both inside and away from nuclear source regions

For measuring transient electromagnetic fields and related quantities, one needs accurate broadband sensors with simple transfer functions. The various sensor designs developed to achieve this in an optimal manner are summarized. Such sensors are designed for use either in a free space environment (such as in an EMP simulator or on a system under test in such a simulator) or in a nuclear source region that includes local source current and perhaps conductivity. There are now numerous designs which have been iterated for improvements over the last decade.

Experimental study of the radar cross-section of maritime targets

A comprehensive set of results are presented for a variety of surface targets. The targets chosen range from −40 dBm2 to + 70 dBm2 and results of the smaller ones have been compiled from trials that have taken place over a variety of environmental conditions. These illustrate the variability experienced at sea in the radar performance of targets, which, in a free-space environment, may exhibit neither fading nor variability with the aspect viewed. The necessary statistical treatment for fading targets has been used to describe the targets examined in a manner which is directly applicable to the estimation of radar range and detection probabilities. Most of the results are appropriate to the bulk of marine radars using a wavelength of 3.2 cm and horizontally-polarised transmission and reception

An Energy-Density Antenna for Independent Measurement of the Electric and Magnetic Field

An energy-density antenna which can measure both the E field and H field of a plane wave simultaneously has been developed, consisting of two small orthogonal semiloops over a ground plane. Hybrids were used to take the sum and difference of the loop outputs, giving voltages uniquely proportional to the E and H fields. The loop dimensions and optimum configurations were experimentally determined by measurements at a frequency of 836 MHz in a man-made free-space environment. Energy-density computation from the measured E and H fields of a standing wave in free space showed that the maximum-to-minimum range of the energy density is much less than that of either the E or H fields alone.

Statistical Determination of Electromagnetic Compatibility

A new approach to the prediction of electromagnetic compatibility between possible culprit and victim cases is introduced. It is shown that this approach, based on statistical descriptions of case emission and case susceptibility, leads directly to the determination of the probability of interference between randomly oriented equipments in operational situations. Results of tests made using a technique to statistically describe case emissions indicate that greater measurement accuracy and repeatability can be obtained with this technique than is inherent in the case emission measurement methods currently in use and recommended by most specifications. Measurements made on culprit sources in a typical laboratory work area using the statistical technique were found to routinely yield results within + 1.5 dB of corresponding values measured in a free space or anechoic chamber environment. When the technique was used with a hooded probe antenna, equally precise results were obtained in a shielded enclosure. Used in conjunction with appropriate statistical descriptions of case susceptibility, case emission data such as those accumulated with the statistical technique discussed could be used to predict the probability of electromagnetic compatibility in actual equipment lashups.