Normalized Site Attenuation Measurements Research Articles

Calculation of Normalized Site Attenuation for Calculable Dipole Antennas

When a pair of calculable dipole antennas (CalDAs) with a 3-dB hybrid balun is used for a validation test of a constructed open area test site (OATS), the theoretical normalized site attenuation (NSA) curves of an ideal OATS for the CalDAs are required. This paper presents a method to calculate this theoretical NSA in the frequency range of 30 MHz to 1 GHz. The theoretical NSA was directly derived using the power mismatch and dissipative loss concepts of an NSA measurement system. Accurate antenna factors (AFs) above the ground plane were also needed and calculated to obtain the theoretical NSA. When free-space AFs are used to determine the measured NSA, AF correction factors known as mutual impedance correction factors are needed. Both free-space AFs and AF correction factors were also considered.

Proper Antenna Factors for the Normalized Site Attenuation Above a Ground Plane

The antenna factor (AF) above the ground plane changes with respect to the height and obtaining a height pattern of the AF with a sufficient resolution is time consuming. In this paper, a novel method is proposed to obtain an accurate AF at an arbitrary height by a single site insertion loss (SIL) measurement. A ratio of the E-field strength at the location of the antenna under calibration (AUC) to the current amplitude at the transmitting antenna port is introduced. By using this ratio, the AF of the AUC at the height can be obtained by only one SIL measurement. Unlike the conventional method, the multiple SIL measurements are no longer necessary and the proposed method remarkably reduces the measurement time. By using the AFs properly calibrated by the proposed method, the effects of antenna characteristics are significantly reduced in the normalized site attenuation measurement.

A Numerical Investigation of Finite Ground Planes and Reflector Effects on Monopole Antenna Factor using FDTD Technique

An accurate antenna factor (AF) is highly desirable for radiated emission and/or normalized site attenuation measurements. An AF is often measured in the presence of a perfectly conducting ground plane and reflectors. For a receiving antenna; the ground plane or reflectors affects the electromagnetic field by altering the magnitude and distribution of the incident field. It also introduces mutual coupling between the antenna and its image beneath the ground. These effects can cause a different measured AF when the same antenna is polarized horizontally or vertically in respect with ground, or calibrated at a different height. Using a monopole antenna: we conduct a numerical analysis to quantify the influence of the ground and reflector on the AF.

Correction factors for normalized site attenuation

EMI standards require test sites to be validated by measuring the normalized site attenuation (NSA) instead of the classical site attenuation (CSA). Theoretical investigations are, therefore, carried out on the general formulation of NSA and CSA, where chain matrices are introduced to account for the effects of antenna circuits. It is found that the theoretical NSA values given by the standards are based on three assumptions inappropriate to measurements using tuned dipole antennas. Thus, correction is considered requisite for every NSA measurement when tuned dipoles are used. In this connection, new correction factors are proposed for various measurement configurations at 3-, 10-, and 30-m test sites. In addition, numerical evaluations are made on the correction factors applicable to the NSA measurements with antenna factors calibrated at 2 or 3 m above a metal plane.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Formulation of normalized site attenuation in terms of antenna impedances (EMI measurement applications)

General formulas for normalized site attenuation (NSA) are derived in terms of antenna impedances by using the two-port circuit theory to show the effects of mutual coupling. The investigations focus on the antenna factors and antenna calibration procedures that are appropriate for NSA, and the validity of the NSA concept is discussed on the basis of these theoretical investigations. The NSA measurements are found to be appropriate for site validation when using broadband antennas having constant antenna factors. It is theoretically concluded, however, that the original concept of the NSA may not be applicable to the use of tuned dipole antennas, even after adopting the correction factors specified in the existing ANSI standard. NSA is shown to require different correction factors if the antennas have changeable antenna factors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>