Estimation of Antenna Factor of Wire Antenna as Emi Sensor

Abstract

The ratio of incident electric field at the surface of receiving antenna to the received voltage at the antenna terminal when terminated in 50 ohms load is known as the antenna factor. It is an important parameter of a sensor used for EMI measurements. To determine electromagnetic radiation from an electronic component it is required to evaluate the field strength at a certain distance from it using the sensor. If the antenna factor of the receiver and the received voltage are known then the field can be found out applying simple relations. In this paper a simple and useful Method of Moment-based theoretical technique is described to evaluate the antenna factor of wire antenna. The wire is considered as perfectly conducting with radius much less compared to the wavelength of operation. The wire is divided in large number of small segments. A point matching technique is applied to evaluate the surface current distribution due to the incident electric field. The output impedance is found out from the short circuit current and the open circuit voltage of the wire. The received voltage and hence the antenna factor is evaluated from the equivalent circuit diagram of the antenna. The data for current distribution on the antenna in receiving and transmitting mode and input impedance for transmitting mode are well comparable to the results available in literature. Studies have been extended for off-centered antenna and for oblique incidence of electric field.