EMF measurements from 100 kHz to 40 GHz ... - Rohde & Schwarz

EMC / FIELD STRENGTHMeasurement systemsReactive near field Radiated near field Far fieldLimit distance* 0 to λ λ to 2D² / λ >2D² / λE perpendicular to H? No Almost YesE, H ~ 1 / r No No YesZ F = E / H ≠ 377 Ω ≈ 377 Ω = 377 ΩTo measure E and H E or H E or HFIG 2Differences between near andfar field;* heavily dependent on thetype of transmit antenna(D = largest antenna dimension,e. g. diameter of a parabolicreflector).FIG 3 Configuration of the R&S ® TS-EMF with the R&S ® FSP / FSU / ESPI. FIG 4 Configuration of the R&S ® TS-EMF with the R&S ® FSH3.More information and data sheet atwww.rohde-schwarz.com(search term: TS-EMF)FIG 5The R&S ® TS-EMF with the Radio Network Analyzer R&S ® TSMU.44064 / 10REFERENCES[1] prEN54000, February 2002[2] Bochtler / Eidher / Wuschek: GroßräumigeErmittlung von Funkwellen in Baden-Württemberg, July 2003 (“ www.lfu.baden-wuerttemberg.de / lfu / abt3 / funkwellen”)[3] SAEFL: Mobilfunk-Basisstationen (UMTS-FDD), Messempfehlung (draft of 17 Sept.2003)[4] Radio Network Analyzer R&S ® TSMU:Performance giant in compact formatsets new standards. News fromRohde & Schwarz (2003) No. 180, pp 4–740News from Rohde & Schwarz Number 181 (2004 / I)

Measurement of UMTS emissionsWhile the construction of UMTS networksis progressing at a fast pace, norules or regulations regarding UMTS andEMF measurements were establishedyet. The Swiss Agency for the Environment,Forests and Landscape (SAEFL)is now the first civil authority to publisha measurement recommendation [3].Other countries are expected to adopt asimilar form of the measurement methodsdescribed therein.A (simplified) comparison with GSMshows the conditions of EMF measurementsin UMTS emissions. With GSM,fixed frequencies are assigned to eachbase station. A continuous signal istransmitted at constant power at one ofthese frequencies, which makes it possibleto simply extrapolate to the maximumfield strength generated by a basestation. The measured field strengthcan be assigned to the base station bymeans of the frequency.In the case of UMTS, however, all basestations of a network operator transmitat the same frequency. The basestations are differentiated by means ofscrambling codes with which each basestation encodes its own signal. With thistype of coding, the signal is simultaneouslyspread, creating a noiselike signalwith a bandwidth of 5 MHz. The transmissionpower depends on the amountof transmitted data and is betweenapprox. 10% for the organization channelsand the maximum output power atfull capacity utilization.Frequency-selective measurementwith UMTSFrequency-selective measurements,which are standard practice for measuringelectromagnetic fields in the environment,can also be performed for UMTS –but with the following restrictions:◆ Assignment to a base station notpossible◆ Statement only regarding themomentary value◆ Restricted sensitivity caused by abroadband, noiselike signalThe measurements obtain only the currentsummed value of all UMTS basestations in the vicinity. The worst-casescenario for extrapolation to the maximumpossible field strength presupposesthat only the organization channelswere active at the time of the measurement.However, the result of thisextrapolation can be as much as 10 dBtoo high if data was also transmitted atthe time of the measurement. This measurementuncertainty can be minimizedby performing long-term measurementswith the R&S ® TS-EMF.The measurement is made using theRMS detector and at a signal-matchedbandwidth. Channel power measurementmust be set if the Spectrum AnalyzerR&S ® FSH3 is used. The measurementparameters for UMTS arestored in a predefined measurementpacket that comes with the test system.Rohde & Schwarz verified the measurement-packetsettings on real and syntheticUMTS signals.Code-selective measurementwith UMTSUMTS emissions must be decoded soas to avoid the restrictions of frequencyselectivemeasurements and to be ableto use a measurement method that iscomparable to GSM. Decoding must beprecise and reproducible, even undercomplex reception conditions involvingstrong reflections, no line of sight tothe transmitting antenna and simultaneouslyseveral base stations. Importantfactors for this measurement are highsensitivity and wide dynamic range, highmeasurement speed for mobile measurements(stirring method) and the possibilityto process many codes in parallel(due to the time offset, each reflection isprocessed as a separate code).Rohde & Schwarz has acquired widerangingexperience with UMTS radiatedemission measurements with its coveragetest systems for measuring networkquality. Owing to this experience,an option for decoding the UMTS organizationchannel (CPICH) has been addedto the R&S ® TS-EMF, allowing the testsystem to comply with the preferredmeasurement method described in theSwiss recommendation. The systemallows the field strength to be accuratelymeasured and extrapolated to themaximum emission and assigned to thebase station. The sensitivity is greaterthan with a spectral GSM measurement.Decoding by means of the R&S ® RFEXsoftware can be implemented in connectionwith a Spectrum Analyzer R&S ® FSPor R&S ® FSU or the Precompliance TestReceiver R&S ® ESPI. Alternatively, theRadio Network Analyzer R&S ® TSMU(FIGs 4 and 5) can be used for performingpure UMTS measurements or as acompact addition to the R&S ® FSH3 [4].Existing test systems can be retrofittedwith this option. A version without anisotropic antenna is available for userswho apply only the stirring method.SummaryThe expanded frequency range of30 MHz to 3 GHz and the option for preciseUMTS measurements provide thePortable System for EMF MeasurementsR&S ® TS-EMF with the greatest possibleflexibility in EMF measurements. Additionalantennas and spectrum analyzersfor the range from 100 kHz to 40 GHzare available for more exacting measurementrequirements. Frequency-selectivemeasurements involving UMTS systemsare subject to restrictions. CPICHchannel decoding, available as an optionto the R&S ® TS-EMF, yields an accuratemeasurement method comparable to thetechnique used with GSM.Jürgen Kausche; Gerd Mielke41News from Rohde & Schwarz Number 181 (2004 / I)