Performing EMC antenna calibrations in open area, site validation and measurement uncertainty

It is so important to determine the level of electromagnetic interferences (EMI) which an electric/electronic device produces or the level of the resistance of a device to the electromagnetic interferences, since electromagnetic interferences can be harmful to devices, ambients or people. This can be determined by electromagnetic compatibility (EMC) tests. EMC antennas are an important part of EMC Tests, especially for radiated emission and immunity tests. EMC Antennas have various parameters such as polarization, beamwidth, gain, Voltage-Standing-Wave-Ratio (VSWR), phase center, impedance, antenna factor etc. Antenna factor is one of the important parameters among these parameters.of EMC antennas, also. It is crucial to know antenna factors exactly and clearly to maintain EMC test quality, accuracy and reliability. At this point, the calibration of EMC antennas is critical. The antenna factor values of manufacturers are often inadequate. Using manufacturer antenna factor values may cause some errors in EMC tests, since some changes may occur for antenna between manufacturing time and using time. So, periodic calibrations of EMC antennas are critical to obtaining current antenna factor values. Actually, "the calibration of an antenna" means measuring the antenna factors of that antenna. In addition to obtaining current antenna factor values, the long-term behaviour of an antenna can be revealed by periodic calibrations. For calibration quality, calibration staff qualifications, calibration laboratory and its infrastructure are very substantial. In the introduction part of this thesis, some basic information about Open-Area Test Site (OATS), Turkish Standard Institute, EMC tests, metrology, calibration, the uncertainty of measurement, the importance of EMC antenna calibration and measurement units is available. Review of the literature and standards on the subject takes place in this part, also. In this study, it is aimed that EMC antenna calibrations to be performed in Open-Area Test Site of Turkish Standard Institute with measurement uncertainty calculations. Initially, it was important to determine the convenience of the site for calibrations. To determine this, ANSI C63.4-2014 standard was used. Normalized Site Attenuation (NSA) tests were performed over a volume of the site. Normalized Site Attenuation values are basically obtained by subtracting antenna factors of antennas from site attenuation values. After determining normalized site attenuation values by measurements and calculations, the theoretical normalized site attenuation values and measured normalized site attenuation values are compared. At the end of the tests, it was revealed that the site was convenient for the calibration of EMC antennas. It was so crucial, because a calibration in an inconvenient site is inaccurate. After NSA tests and determining the convenience of the site, antenna calibration studies were initiated. Antenna calibrations were performed for biconical, log-periodic and tuned dipoles and for a frequency band from 30 MHz to 1 GHz. ANSI C63.5-2006 standard was used for calibration studies. "Standard Site Method" of ANSI C63.5-2006 Standard is the main method in this study. The applied points which differ from the standard in the scope of this study are expressed in the related parts of this study. All site attenuation measurements were taken in the same measurement geometry (horizontal distance between antennas: 10 m, transmitting antenna height : 2 m, receiving antenna height : 1 m-4 m, horizontal polarization). To determine site attenuation values, discrete frequency method was used. Standard Site Method was implemented with its sub-methods. These sub-methods are specifically named in the scope of this study as "Standard Site Method with Three Antennas", "Standard Site Method with Known Antenna", "Standart Site Method with Identical Antennas". These methods were compared and some comments were made on the results. In the study, the results of Standard Site Method with Three Antennas and Standard Site Method with Known Antenna were compared on both biconical and log-periodic antennas. The results showed some differences with each other. It is thought to have originated from the antenna factor changes of "the known antenna" between last calibration time and working time. This shows Standard Site Method with Three Antennas is more accurate and reliable than Standart Site Method with Known Antenna. When Standart Site Method with Identical Antennas was implemented with half-wave dipole sets, the results and the manufacturer values were so similar although it has been many years since the production. Air temperature and relative humidity in Open-Area Test Site (OATS) were measured and stored by digital temperature and humidity gauge during the calibration processes. In addition, air pressure and wind speed were measured by digital pressure gauge and anemometer. In the control room, temperature and relative humidity were measured and stored by analogue temperature and relative humidity gauge during the calibration process. The uncertainty of measurement study is an important part of this study. There are a lot of uncertainty parameters because of open area conditions and a control room without air conditioning system. These parameters were analyzed in detail and the measurement uncertainty was calculated for Standart Site Method with Three Antennas. The measurement uncertainty budget has been built. Overall calculations of measurement uncertainty were made in accordance with GUM and EA-4/02 documents. Warm-up times of all devices are taken into account. The calculations showed that the most dominant factor was site and system effects. Therefore, it can be said that site qualifications have significant effect on the calibration of antennas in open field. The other dominant factor of measurement uncertainty was spectrum analyzer amplitude based factors. The calculated uncertainty contribution of the frequency characteristics of the devices that were used in the measurements were very small comparing to other uncertainty components. So, it was determined that it can be neglected. Three site attenuation measurement uncertainty values were very close to each other. The components which have negligible effect on measurement uncertainty were explained in the study. The calibration certificates of the antennas which calibrated in this study are located in Annex-A. Also, the calibration certificates of some devices that were used in calibration processes are located in Annex-B.