Site Attenuation Measurements Research Articles

Symmetry Versus Balance in Balancing Networks for Dipolar Antennas

Imperfect balancing networks (baluns) have been identified as a source of error in emission and site attenuation measurements. For this reason, performance tests have been developed to characterize the symmetry of baluns. We draw a distinction between symmetry and balance as they relate to baluns and describe both quantitatively in terms of three-port network parameters. It is shown that a symmetric balun alone does not necessarily eliminate common-mode (CM) current on the feed transmission line. CM current on the feed transmission line is minimized by use of a current balun. However, for a given implementation, such as a transmission-line transformer, some types of baluns are more difficult to implement than others and an imperfect, asymmetric current balun may perform worse than another type of balun (e.g., voltage), which is more symmetric. The case of a vertically polarized biconical antenna situated over a ground plane and driven from a coaxial feed line via a balun is examined for three symmetric baluns: a voltage balun, a current balun, and a $180^{\circ }$ power divider. It is shown that although all three baluns are symmetric, only the current balun maintains the dipolar pattern under the asymmetrical influence of the ground plane.

Calculation of Site Attenuation for Calculable Dipole Antennas

This paper presents a method for calculating the site attenuation (SA) of an open-area test site (OATS) for a pair of calculable dipole antennas with a 3-dB hybrid balun in the frequency range of 30 MHz to 1 GHz. The SA was directly derived using the concept of power mismatch and dissipative loss from the SA measurement system instead of the concept of substitution loss. Two types of SA formulas using the power loss concept on the treatment of the OATS are presented. The first is the SA formula related to knowing only the value of the SA. The other is the SA formula that analyzed the effects of each part of the SA. Additionally, the constituent losses of the SA measurement system are discussed using the derived SA formula. The analysis of the results showed that the SA could be successfully characterized individually from the loss of the OATS. It also showed that SA is expressed as two kinds of losses: the balanced portmismatch losses of transmit and receive baluns and the half-space dissipative loss. The resultant SA showed good agreement with the results calculated from the S-parameters as well as with the measured results.

Time-Domain Mixed-Mode Site Attenuation Measurement

The mixed-mode S -parameters have become widely used for transmission line measurements on printed circuit boards. In this article, the mixed-mode S -parameter measurement is applied to the site attenuation measurement using a pair of dipole antennas. The proposed method requires no balance–unbalance transformer (balun) for the balancing antenna measurement and is free from the limitation of the antenna operating frequency caused by the balun. Compared with conventional methods, 20-dB smaller site attenuation between the dipole antenna pair was obtained. This results in expansion of the measurement frequency and enables us to carry out time-domain measurements with higher time resolution. Since no additional circuit, such as a matching circuit is necessary for the proposed method, the ring-down time of the main response is much shorter. These characteristics lead to significant advantages in carrying out precision measurements.

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.

Balancing networks for symmetric antennas .I. Classification and fundamental operation

Emphasis has been placed on the quality of a metrology antenna system that allows it to be represented accurately using analytical or numerical models. Central to this capability is the efficacy of the balancing networks, sometimes referred to as balanced to unbalanced transformers (baluns). In this paper, we classify three fundamental types of baluns and show that all three can be derived from the 180/spl deg/, four-port hybrid network. Balanced antennas driven from coaxial feed lines and operated in the presence of an asymmetric scatterer present an intrinsically unbalanced load to the balun. We show that in such situations the current balun is the only appropriate balun to employ. For numerous antenna metrology applications, in particular, site attenuation measurements, 180/spl deg/, four-port hybrid networks have been employed as baluns. Network relations are derived relating the so-called voltage and current baluns to the 180/spl deg/, four-port hybrid network. It is shown that, in addition to acting as a 0/spl deg/ or 180/spl deg/ power divider, the hybrid network can serve as either a voltage or a current balun depending on the termination at the isolated port. In contrast to the traditional approach, it is shown that when using a 180/spl deg/ hybrid as a balun, the isolated port should be terminated in such a way that the hybrid behaves as a current balun as opposed to a 180/spl deg/ power divider. This will yield experimental results that can be more readily reconciled with models.

Site attenuation measurements using shortened dipole antennas

Use of a shortened dipole with its element length fixed at the 80-MHz resonator length or a half-wavelength is studied for the site-attenuation measurement of the interference-wave measurement field. Since this shortened dipole antenna is specified as the standard antenna for interference wave measurement, the antenna factor and the impedance characteristics are investigated by numerical calculations and measurements. Next, in regard to the measurement of the site attenuation with this antenna, the theoretical values are derived by the method of moments. Further, actual measurement is carried out at three outdoor locations. It is confirmed that the obtained theoretical values agree well with the measured data. As a result, it is found that the theoretical values can be used sufficiently well as normalized values. Therefore, a measurement method of the site attenuation using a shortened dipole has been established. It is found that the use of the shortened dipole is better in terms of measurement error and labor than the conventional half-wave dipole in site attenuation measurements at these frequencies. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(8): 81–88, 1998

A comparison of electric field-strength standards for the frequency range of 30-1000 MHz

Published results about site attenuation and transmission loss measurements as well as antenna factor calculations and calibrations are summarized. The antenna types discussed are precision dipoles, a microstrip patch antenna, open-ended waveguides, and horn antennas as well as TEM-cells. The best values for agreement between theory and experiments that were reported for the transmission losses were in the range of 0.25-0.4 dB. An experimental comparison between precision reference dipoles and a TEM-cell that was performed in the Seibersdorf calibration laboratory is described with deviations of no more than 0.15 dB in the antenna factor or field-strength.

Modeling semi-anechoic electromagnetic measurement chambers

Previous studies developed a model to predict theoretically the low-frequency plane-wave reflection coefficient of an array of pyramid cone absorbers such as those used to line anechoic electromagnetic measurement chambers. The present authors apply this model in a geometrical optics approach to predict the electromagnetic field in a chamber lined with cone absorbers in the frequency range of 30-300 MHz. The results are compared with site attenuation measurements for two actual semi-anechoic chambers.

A low-frequency model for wedge or pyramid absorber arrays-II: computed and measured results

Based on the theoretical model developed in Part I of this two-part paper, we present numerical results for the plane-wave reflection coefficient from arrays of pyramid-cone absorbers when the period of the array is smaller than half a wavelength. Comparison is made with results of a moment-method calculation, as well as with experimental measurements. The model is then used to modify the design of some existing types of commercially available absorbers for reduced reflection in the frequency range of 30-300 MHz. These improved absorbers have been installed in an anechoic chamber used for electromagnetic compatibility and electromagnetic interference (EMC/EMI) measurements. Site attenuation measurements from this chamber are presented which show closer correspondence to an ideal open-field test site. >

Standard-Site Method for Determining Antenna Factors

A method for calibrating antennas from site attenuation measurements made on an open-field site is described. The method, termed the standard-site method because the accuracy of the results depends on the quality of the measuring site, requires neitller the use of a standard antenna nor the generation of a standard field. The antenna factors of a number of broad-band antennas calibrated by the standard-site method over the frequency range 30-1000 MHz show good agreement with the antenna factors found by the standard-antenna method.