Page 19

EETE JANUARY 2013

sion of the antenna and λ is the wavelength. If we increase the The near field plotting is available in Sigrity’s tool (Power SI), distance from 2D2/λ we will get waves with the same phase so which provides a convenient way to study the hotspots on a there will be less measurement errors. Because the radiation given structure. We defined a box where the near field is going pattern doesn’t change in this region, we can keep the receiver to be plotted. Similarly far field radiations can also be measured antenna at a long distance, which is taken as λ by FCC. As the using this tool. In this measurement tool, the user defines a test probe gets closer to the source, the nature of the electro- receiver antenna at a specified distance and then measures the magnetic field changes because we are in the Reactive Near radiation. Radiation patterns in the form of Ev , Eh, Eθ and Eφ field region where E and H fields are in quadrature. can be plotted using this facilities. The electromagnetic field is characterized by its wave imped- The Near field radiation has been observed for the whole fre- ance which is the ratio of transverse component of electric and quency band (30 Mhz – 1 Ghz) and it is found that it is maximal magnetic fields i.e. at 200 MHz as shown in figure1. The far field has been mea- z = E/h sured by following the same limitation given in FCC regulation. The wave impedance or the intrinsic impedance of free To cross check the property we have obtained the result for far space is 120π or 377 ohms where the measurement is done. field measurement. We noticed that the radiation is maximal at 200 MHz as shown in figure 2. Simulation & result We simulated a board using the Power SI tool of Sigrity for the We can conclude that the standard far field compliance test analysis of near field and Far field radiation following the FCC for radiated emission is not well suited for the early stages of regulations. In this setup, the board has been excited using product development. The near field can be used to locate a source and the probable radiation sources like traces and the source of EMI which is useful in early stage of design as it edges have been selected to check the level of emission. an can reduce the cost. Early knowledge of radiation can tell the FCC test condition is already available in the tool with the given designer where to shield the radiating bodies. Besides this the regulations for class A and class B. As we know that the far field far field setup requires an anechoic chamber vector network measurements do not help in locating the source of problem, analyzer, VSWr meter etc which is a costly setup. on the other we also perform a near field analysis. One thing which is certain hand near field probes are cheap. Hence, one can perform a is that if the radiation is more important in some frequency band near field test to modify the design in the early stages of devel- of the near field band it will also be more important in the far opment to limit the probabilities of radiated emissions. field for the same band. When 4 channels are not enough… A unique 8 channel Mixed Signal Oscilloscope which provides comprehensive measurement and analysis capabilities for embedded, automotive, power and mechatronics applications NEW NEW DLM4000 Series 8 analogue channels Up to 24 digital inputs Up to 500 MHz bandwidth Up to 125M points long memory Solve your complex measurement requirements faster and easier than ever before Watch the video at: http://bit.ly/T1gLUn and contact us to see how the DLM4000 can help you. YOKOGAWA EUROPE B.V. Tel.: + 3188 464 1429 tmi@nl.yokogawa.com http://tmi.yokogawa.com www.electronics-eetimes.com Electronic Engineering Times Europe January 2013 19


EETE JANUARY 2013
To see the actual publication please follow the link above