Antennas in electromagnetic compatibility

The analysis of sources of uncertainty, or more simply, the understanding of physical phenomena encountered in electromagnetic compatibility (EMC) measurements, often requires consultation of electromagnetic treatises. This article takes up this preoccupation by endeavoring to synthesize knowledge borrowed from the study of antennas. Antennas are used in EMC metrology on a number of occasions, for example to emit strong fields during immunity tests, or to measure weak fields emanating from an electronic device in operation. We should point out that the frequency range under consideration extends from 30 MHz to 1 GHz, that a strong electric field can reach an amplitude of 1 V/m to 10 V/m or more, and that a weak field is around 100 µV/m.

The article is divided into three distinct parts, but linked by common physical properties. First and foremost, it deals with the concept of the elementary dipole. The term dipole used here differs from its electrokinetic equivalent, however, as we are dealing with the radiation of a conducting element of dimension Δl through which a uniform current flows, animated by sinusoidal amplitude variations.

This first part is mainly dedicated to the calculation of near and far fields acting at a distance r from the dipole. The investigation is then extended to calculations of other relevant parameters, including the active power transmitted into space and the concept of radiation resistance.

The second part, devoted entirely to transmitting antennas, focuses on the symmetrical dipole made up of two quarter-wave-tuned conductors of dimensions L ₀ . We'll see that this operation, widely used in metrology, gives the symmetrical antenna properties akin to a transmission line. The assimilation to lines greatly facilitates the calculation of the current variation on the conductors, as well as the determination of the far field. It is also shown that another remarkable feature of the quarter-wave resonant dipole is its radiation resistance of 73 Ω. The study of the symmetrical dipole is then completed by other parameters specific to EMC metrology and antennas, such as input impedance, power gain, effective area and antenna factor. In this second part, the descriptive and physical analysis of antennas, transmitting or receiving signals over a wide frequency band, is briefly outlined.

The third part of the article is mainly concerned with receiving antennas subjected to electromagnetic field inductions, locally assimilated to a plane wave. The calculation of the fem collected on a monopole-type antenna, consisting of a conductor of dimension L ₀ and perpendicular to a metallic plane, is undertaken. Developments...