Takehiro Morioka

Uncertainty Analysis of Dipole Antenna Calibration Above a Ground Plane

A thorough analysis of the uncertainty for dipole antenna calibration is presented. The primary standard of the antenna factor (AF) is obtained by the three-antenna method (TAM), and an ordinary calibration service is performed using the reference-antenna method (RAM). As the AF of the standard antenna is necessary for the RAM, the uncertainty analysis of TAM with the specified antenna setting is presented first, followed by the analysis of RAM. The Guide to the Expression of Uncertainty in Measurement (GUM) shows how to analyze and express the measurement uncertainties. According to the GUM, the uncertainty analysis of the calibration procedure is formulated by expressing AF as a function of other quantities, and every source of uncertainty that affects the result of the measurement is evaluated. An example of the uncertainty budget at 400 MHz is shown, and uncertainties at 24 frequencies in the range of 30 to 1000 MHz for TAM and RAM are summarized. To validate the uncertainty analyses, the differences between the calibrated and calculated AFs are shown to be smaller than the expanded uncertainties with the coverage factor of 2(k=2)

Measurements of antenna characteristics above different conducting planes

Measurement of dipole antennas by three-antenna method is evaluated by the comparison of the different types of open-area test site. These results show that the repeatability of the derived antenna factors is within /spl plusmn/0.3 dB for the fixed element dipole antennas in the case of the same height measurement.

Uncertainty of Free-Space Dipole Antenna Factor From 1 GHz to 2 GHz

The free-space antenna factor (AF) of a dipole antenna above 1 GHz using the three-antenna method (TAM) and associated uncertainty is presented. Theoretical site insertion loss containing antenna alignment and terminal impedances is newly given for the TAM and the uncertainty analysis. Higher order terms of Taylor series expansion are considered to include the effect of the alignment angle on uncertainty. Finally, the AFs are obtained with an expanded uncertainty of 0.4 dB (k = 2) in the entire frequency range.

A Field Uniformity Study of a TEM Cell by Using a Short Wire Scatterer

TEM cells are widely used for EMC/EMI measurements. However, the electric field strength only at the center point of the cell is roughly estimated. By introducing a passive scatterer into the cell, such as a straight wire, the echo fields can be detected by the deviation of the reflection coefficient from that of the empty cell. This deviation is related to the incident electric field at the location of the scatterer. In this paper, the electric field uniformity of a TEM cell for the dominant and orthogonal polarizations is investigated by the measurement.

MoM Calculation of the Properly Defined Dipole Antenna Factor With Measured Balun Characteristics

A new method is proposed to calculate the properly defined antenna factor (AF) of a dipole antenna including environmental and terminal conditions. The original definition of the AF can be easily obtained by combining 1) the numerical method to calculate interaction between incident fields and the antenna element and 2) measured characteristics of the attached circuit. The AF obtained by the proposed method is free from the mutual coupling effects and the imperfect applied plane wave due to the finite separation from the transmitting antenna.

Probe response to a non-uniform E-field in a TEM cell

An ordinary calibration of an E-field probe using a TEM waveguide is carried out by assuming an ideal plane E-field incidence onto the probe. However, the E-field of a TEM cell does not have such an ideal field uniformity. In the present paper, the field distribution of a TEM cell is simulated by using a numerical method and responses of a short dipole probe to the calculated non-uniform E-field are investigated.

Antenna factors of an off-resonant dipole antenna

An off-resonant antenna, such as a shortened dipole is widely used in electromagnetic compatibility measurements due to compactness. The antenna factor of the shorten dipole antenna is ordinary calibrated by comparing that of the standard antenna. However, considerable errors are introduced by applying this method with an insufficient separation due to the coupling with the transmitting antenna and the field distribution along the element. In the present paper, errors in calibrating the off-resonant dipole antenna by the reference antenna method are discussed for the successful measurement.

Tracing E-field probe responses to the dipole antenna factor

A well-defined E-field is often generated in an anechoic chamber by using the gain of the transmitting antenna, and E-field probes are calibrated by applying that field. However, the gain at a finite separation is no longer the same as that in the far-field region. In the present paper, a simple calibration method for E-field probes using dipole antenna factors (AF) is proposed. An E-field generated at a location is directly calibrated by using the AF of a dipole antenna. This method has considerable advantages in simplicity and compactness. In addition to analysis of the through performance of the method, uncertainty associated with this method is overviewed.

Response of a Short-Dipole Probe to a Nonuniform

A transverse electromagnetic cell is often used as a standard field generator since the E-field strength can be predicted using a simple formula. However, the E-field of the cell varies with respect to the location, and the estimated E-field strength is valid only at the center of the cell. Accordingly, the probe size should be sufficiently small compared with the field variation to ignore the nonuniformity of the field. Although the nonuniformity of the incident field can be improved by using a large cell, the usable upper frequency becomes low. In this paper, probe responses to the nonuniform E-field of a cell are investigated by a sequentially combined numerical method. The proposed method is validated by the comparison of the calculated results with the measured ones.

E

Free space dipole antenna factor above 1 GHz and associated uncertainty are presented. Theoretical site insertion loss containing the antenna alignment and terminal impedances is given for the uncertainty analysis. Antenna factors are obtained with uncertainty of 0.4 dB in the entire frequency range.