AMERICAN NATIONAL STANDARD

Transcription

1 ENGINEERING COMMITTEE Inteface Pactices Subcommittee AMERICAN NATIONAL STANDARD ANSI/SCTE Test Method fo Measuing Shielding Effectiveness of Passive and Active Devices Using a GTEM Cell

2 NOTICE The Society of Cable Telecommunications Enginees (SCTE) Standads and Recommended Pactices (heeafte called documents) ae intended to seve the public inteest by poviding specifications, test methods and pocedues that pomote unifomity of poduct, intechangeability, best pactices and ultimately the long tem eliability of boadband communications facilities. These documents shall not in any way peclude any membe o nonmembe of SCTE fom manufactuing o selling poducts not confoming to such documents, no shall the existence of such standads peclude thei voluntay use by those othe than SCTE membes, whethe used domestically o intenationally. SCTE assumes no obligations o liability whatsoeve to any paty who may adopt the documents. Such adopting paty assumes all isks associated with adoption of these documents, and accepts full esponsibility fo any damage and/o claims aising fom the adoption of such Standads. Attention is called to the possibility that implementation of this document may equie the use of subject matte coveed by patent ights. By publication of this document, no position is taken with espect to the existence o validity of any patent ights in connection theewith. SCTE shall not be esponsible fo identifying patents fo which a license may be equied o fo conducting inquiies into the legal validity o scope of those patents that ae bought to its attention. Patent holdes who believe that they hold patents which ae essential to the implementation of this document have been equested to povide infomation about those patents and any elated licensing tems and conditions. Any such declaations made befoe o afte publication of this document ae available on the SCTE web site at All Rights Reseved Society of Cable Telecommunications Enginees, Inc Philips Road Exton, PA i

3 TABLE OF CONTENTS 1.0 SCOPE INFORMATIVE REFERENCES COMPLIANCE NOTATION DEFINITIONS AND ACRONYMS EQUIPMENT CHAMBER VERIFICATION TEST METHOD TEST METHOD ERROR ANALYSIS RECORDING RESULTS...10 APPENDIX A: RFI/EMI SHELDING CALCULATIONS AND METHODOLOGY...13 APPENDIX B: GTEM CELL QUALIFICATION METHOD...17 APPENDIX C: FIELD UNIFORMITY VERIFICATION METHOD...19 LIST OF FIGURES FIGURE 1 EQUIPMENT SETUP FOR INGRESS SHIELDING TEST (METHOD 2) 7 FIGURE A.1 RECEIVE PATH BLOCK DIAGRAM 14 FIGURE B.1 GTEM QUALIFICATION TEST CONFIGURATION 17 FIGURE C.1 GTEM QUALIFICATION TEST CONFIGURATION 19 LIST OF TABLES TABLE 1 LEVELS OF UNCERTAINTY 9 TABLE B.1 GTEM CELL QUALIFICATION DATA 18 TABLE C.1 TEST CHAMBER CALIBRATION DATA 20 1

4 1.0 SCOPE The pupose of this test is to detemine the shielding effectiveness against Electomagnetic Intefeence (EMI) of components. This method subjects the component to an electic field of known stength. 2.0 INFORMATIVE REFERENCES The following documents may povide valuable infomation to the eade but ae not equied when complying with this standad. 2.1 Standads fom othe Oganizations - Electonics Enginees Handbook, 2nd Edition, McGaw-Hill, ISBN EMC fo Poduct Designes, Tim Williams, 3d Edition, Newnes, ISBN LAB 34, Edition 1, August 2002, The Expession of Uncetainty in EMC Testing, United Kingdom Acceditation Sevice 3.0 COMPLIANCE NOTATION SHALL This wod o the adjective REQUIRED means that the item is an absolute equiement of this specification. SHALL NOT This phase means that the item is an absolute pohibition of this specification. SHOULD This wod o the adjective RECOMMENDED means that thee may exist valid easons in paticula cicumstances to ignoe this item, but the full implications should be undestood and the case caefully weighted befoe choosing a diffeent couse. SHOULD NOT This phase means that thee may exist valid easons in paticula cicumstances when the listed behavio is acceptable o even useful, but the full implications should be undestood and the case caefully weighed befoe implementing any behavio descibed with this label. MAY This wod o the adjective OPTIONAL means that this item is tuly optional. One vendo may choose to include the item because a paticula maketplace equies it o because it enhances the poduct, fo example; anothe vendo may omit the same item. 2

5 4.0 DEFINITIONS AND ACRONYMS E Electic field stength ƒ Fequency in MHz G Shielding Effectiveness K The sum of all losses and gains between the DUT and the test equipment GA The gain of any amplifie between the signal geneato and GTEM cell P Powe eceived by the DUT (ingess) Pm Powe measued at the measuement equipment MHz Megahetz (1 x 10 6 Hz) GTEM cell Gigahetz Tansvese Electic Field Mode Cell khz Kilohetz (1 x 10 3 Hz) RF Radio Fequency DUT Device Unde Test 5.0 EQUIPMENT 5.1 Measuement Device The measuement device may be a spectum o netwok analyze with the following chaacteistics: - 75 o 50 Impedance Input and connecto - Capable of measuing a fequency ange of 5 MHz to 1002 MHz - Noise floo that is 10 db o bette than the DUT at 1002 MHz (minimum 10 Hz esolution bandwidth), which can be achieved with o without amplification at the input of the GTEM. 5.2 Signal Geneato Depending on the method chosen, the signal geneato may be a tacking geneato associated with the spectum o netwok analyze. The output powe must be sufficient to ceate a field stength of at least 10 V/m acoss a test volume occupied by the DUT ove the fequency ange of 5 MHz to 1002 MHz. The signal geneato 3

6 may be combined with a powe amplifie to geneate the equied field stength. See section 5.6 fo details of the amplifie. 5.3 GTEM Cell The GTEM must have a test volume that is lage enough to accommodate the DUT. The GTEM cell must be able to povide unifom electic field stength ove the aea of the DUT. The field is consideed unifom if it vaies by less than 6 db ove the aea of the DUT 5.4 Adaptes 75 o 50 min-loss pads, adaptes teminations and cables as equied to connect the test system and DUT. 5.5 Field Stength Monito The field stength-monitoing pobe shall be an isotopic pobe with an accuacy of 3 db fom 5 MHz to 1002 MHz. 5.6 Powe Amplifie The powe amplifie shall have sufficient powe output to geneate at least 10 V/m fom 5 MHz to 1002 MHz and have the following chaacteistics: - Input VSWR: 2.0:1 max - Output VSWR: 2.0:1 max - Hamonic distotion: -15dBc max 4

7 6.0 CHAMBER VERIFICATION 6.1 Befoe any testing commences, the chambe must be veified. The veification should be pefomed evey six month unless the chambe has been modified. 6.2 Follow any pe-calibation equiements using the appopiate calibation kit as ecommended by the manufactue of the test equipment, including adequate wamup and stabilization time. 6.3 Follow the pocedue in Appendix C to veify the field unifomity of the GTEM cell. If the cell does not meet the equiements then it is unsuitable fo any of the test methods descibed in this document. 6.4 Follow the pocedue in Appendix B to pefom a GTEM cell qualification. If the GTEM does not meet the equiements, then test method 2 must be used. If the GTEM cell meets the equiements, eithe method 1 o 2 may be used. 7.0 TEST METHOD Place the DUT centeed in the test volume inside the GTEM cell. Connect one pot of the DUT to the measuement device and teminate all othe pots. All connections to the DUT, including powe cables, must be sufficiently shielded so that thei Shielding Effectiveness (G) is geate than the anticipated G of the DUT to ensue the accuacy of the test. 7.2 Follow any pe-calibation equiements using the appopiate calibation kit as ecommended by the manufactue of the test equipment, including adequate wamup and stabilization time. 7.3 Adjust the amplifie gain into the GTEM cell to achieve a minimum of 10 V/m (20 db V/m). Recod the loss/gain of the eceive path between the device unde test (DUT) and the measuement device at the fequencies of inteest. Recod this data fo futue calculations. (Note: Data should be ecoded in db with losses ecoded as db and gain ecoded as +db.) The combined loss/gain at each fequency shall be ecoded as K. 7.4 Select a esolution bandwidth (minimum 10 Hz) to ensue that the measuement device has a noise floo that is 10 dbm o bette than the DUT at 1002 MHz, which can be achieved with o without amplification at the input of the GTEM. 7.5 If the signal geneato is a tacking geneato o netwok analyze, sweep the signal fom 5 MHz to 1002 MHz and ecod the powe eceived at the measuement device. 5

8 7.6 If the signal geneato is only capable of poviding discete fequencies then measue and ecod the powe on the measuement device at 5, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1002 MHz. 7.7 Recod the pot tested and powe level as the X-axis oientation on the test epot. 7.8 Repeat steps 7.5 to 7.7 fo each input and output pot on the DUT. Teminate all unused pots. 7.9 Rotate the DUT though 90 to the Y axis oientation Make sue that the DUT emains centeed inside the test volume of the GTEM cell afte otation. Repeat steps 7.5 though Rotate the DUT though 90 to the Z axis oientation Make sue that the DUT emains centeed inside the test volume of the GTEM cell afte otation. Repeat steps 7.5 though At each fequency measued, detemine the wost-case measued powe fom each of the axes and pots. Recod the fequency and the wost case powe Pm. Calculate the shielding effectiveness using the following fomula: G ( db) P ( dbm) K 30 20Log ( f ) P ( dbm) 20Log ( d ) Whee: m G = Shielding effectiveness of DUT (db) Pm = Powe eceived at measuement device (dbm) K = Total loss o gain between DUT and measuement device (db) (see A.3) ƒ = Fequency (MHz) PIN = Powe into GTEM cell (dbm) = POUT + GA GA = The gain of any amplifie between the signal geneato and GTEM cell (db) POUT = The powe level out of the signal geneato (dbm) d = Septum height (m) See Appendix A fo the deivation of this equation. IN 6

9 8.0 TEST METHOD Follow any pe-calibation equiements using the appopiate calibation kit as ecommended by the manufactues of the test equipment, including adequate wamup and stabilization time. 8.2 Connect the equipment as shown in Figue 1. This diagam assumes the use of a tacking geneato, extenal RF amp, and a calibated field stength-monitoing pobe. 8.3 Set the measuement device and signal geneato to 5 MHz. Connect the geneato output though the powe amplifie (if equied) to the GTEM cell. Place the theeaxis field pobe in the cente of the test volume inside of the GTEM cell. Adjust the signal geneato output powe fo an E-field stength of 10 V/m + 1 V/m (+20 db V/m). Recod field stength, and signal geneato output powe level (o level on powe mete) fo futue testing. Figue 1 Equipment Setup fo Ingess Shielding Test (Method 2) 8.4 Repeat step 8.3 fo all of the fequencies of inteest including but not limited to: 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1002 MHz. 8.5 Measue the loss/gain of the eceive path between the device unde test (DUT) and the measuement device at the fequencies of inteest. Recod this data fo futue 7

10 calculations. (Note: Data should be ecoded in db with losses ecoded as db and gain ecoded as +db.) The combined loss/gain at each fequency shall be ecoded as K (see Appendix A fo an example). 8.6 Replace the field pobe with the DUT centeed in the test volume inside of the GTEM cell. Connect one pot of the DUT to the measuement device (see figue 1) and teminate all of the othe pots. Adjust the signal geneato fo the selected test fequency and the coesponding output powe measued in step 8.3. All connections to the DUT, including powe cables, must be sufficiently shielded to ensue the accuacy of the test. All cables and connections equied inside the GTEM should be placed and outed in a manne that will minimize any field petubations. 8.7 Select a esolution bandwidth (minimum 10 Hz) to ensue that the measuement device has a noise floo that is 10 dbm o bette than the DUT at 1002 MHz, which can be achieved with o without amplification at the input of the GTEM. Measue the ingess level on the spectum analyze and ecod this level as the X-axis oientation in the test epot. 8.8 Repeat steps 8.6 though 8.7 at the fequencies specified in 8.3 and Repeat steps 8.6 though 8.8 fo each enty and exit on the DUT Rotate the DUT 90 to the Y-axis oientation. Make sue that the DUT emains centeed inside the test volume of the GTEM cell afte otation. Repeat step 8.6 though Rotate the DUT 90 to the Z-axis oientation. Make sue that the DUT emains centeed inside the test volume of the GTEM cell afte otation. Repeat step 8.6 though Calculate the shielding effectiveness of the DUT fom the following fomula. Use the wost case ingess/egess signal powe measued in the X, Y, o Z-axis as Pm. Replace K with the Loss/Gain data measued in step 8.5 at the test fequency. Use E(dBV /m) measued in step 8.4 at the test fequency. Calculate the RF shielding fom the following fomula and ecod in the test epot. G = Pm(dBm)- K(dB) dB + 20Log(ƒ)- E(dBV / m) See Appendix A fo the deivation of this equation, (ƒ is in MHz) 8

11 9.0 ERROR ANALYSIS The accuacy of measuements taken using this test method is limited by seveal factos, including: - The vaiation between calculated and measued field stength (Method 1) o accuacy of field pobe (Method 2) - The vaiations in the field at the DUT as it is otated in the test volume - Resonance between the GTEM cell and the DUT - The accuacy of the measuement device ove a lage dynamic ange - The accuacy of the eceive path gain / loss measuements The estimated accuacy fo this test method can be calculated by detemining the uncetainty values fo each elevant component. The following table can be used as a template fo detemining the oveall uncetainty. Table 1 Levels of Uncetainty Facto Vaiation between calculated and measued field stength / Field Pobe Accuacy Field Vaiation ove test volume 1 Receive path / gain loss accuacy Spectum Analyze measuement accuacy Accuacy of amplifie between signal geneato and GTEM cell Accuacy 2.0 db / 1.0 db 5.0 db 0.5 db 1.7 db 2.0 db Assuming each component has a ectangula distibution then Best Eo Estimate (Method 1) 6.94 db 1 Typical manufactue specification of ± 4dB plus ± 1dB septum height vaiation in espect to depth of the DUT 9

12 Fo a ectangula distibution, the standad uncetainty fo each component ui (x) can be calculated fom the fomula: ai ui ( x), whee ai is the accuacy of the measuement (eg ai =2.0 if accuacy is db) Fo a 95% confidence level, the best estimate eo can be calculated by taking the squae oot of the sum of the squaes of ui (x) and multiplying the esult by 2, i.e. Best Eo Estimate = 2 u ( ) n i 1 2 i x 10.0 RECORDING RESULTS 10.1 While the exact fom of data ecoding will be application dependent, esults as a minimum should include: - Fequencies Tested - Type of device and identity of the specific sample tested - Identity of the peson pefoming the test - Date of the test - Values of ingess measued at each fequency - Calculation of the measuement accuacy - List of equipment used - Calibation due date of the test equipment 10.2 Typical test esult foms fo method 1 and method 2 ae shown on the next two pages 10

13 TEST RESULTS: SHIELDING EFFECTIVENESS (Method 1) IDENTITY OF DEVICE TESTED Type of device: Manufactue: Seial o Lot numbe Model Numbe: Pot identification: Ingess Data (Measued Powe at Measuement Device) Fequency (MHz) P in (db m) K (db) P m (X) (db m) P m (Y) (db m) P m (Z) (db m) Shielding Effectiveness G (db) G ( db) P ( dbm) K 30 20Log ( f ) P ( dbm) 20Log ( d ) m Accuacy Estimate Facto Accuacy Vaiation between calculated and measued field db Field Vaiation ove test volume db Receive path / gain loss accuacy db Spectum Analyze measuement accuacy db Accuacy of amplifie between signal geneato and GTEM cell db Wost Case Eo db IN Tested By Technician: Date 11

14 TEST RESULTS: SHIELDING EFFECTIVENESS (Method 2) IDENTITY OF UNIT TESTED Type of device: Manufactue: Seial o Lot numbe Model Numbe: Pot identification: Ingess Data (Measued Powe at Measuement Device) Fequency (MHz) E (dbv / m) K P m (X) P m (Y) P m (Z) Shielding Effectiveness G (db) G = Pm(dBm)- K(dB) dB + 20Log(ƒ)- E(dBV / m) Accuacy Estimate Facto Accuacy Field Pobe Accuacy db Field Vaiation ove test volume db Receive path / gain loss accuacy db Spectum Analyze measuement accuacy db Accuacy of amplifie between signal geneato and GTEM cell db Wost Case Eo db Tested By Technician: Date 12

15 APPENDIX A: RFI/EMI SHELDING CALCULATIONS AND METHODOLOGY A.1 E-Field Stength in the GTEM cell calculations The field inside the GTEM cell is calculated fom the powe applied to the cell and the impedance of the cell. The voltage in the GTEM cell is calculated fom the powe equation: V [1] Z P IN 2 V P Z o 2 2 V PIN Z [2] IN Taking 20Log of both sides gives us: 20LogV 10Log( P ) IN 10Log( Z) [3] Given that Z = 50Ω, then V ( dbv ) PIN ( dbw ) 17 [4] 1 The electic field stength in the cente of the GTEM cell is calculated fom the voltage on the cell septum (V) and the distance between the septum and the bottom of the GTEM cell in metes (d), ie: V E [5] d again, taking 20log of both sides gives 20Log( E) 20Log( V ) 20Log( d) [6] o E( dbv / m) V ( dbv) 20Log( d) [7] Substituting equation [4] in [7], gives E( dbv / m) PIN ( dbw ) 17 20Log( d) [8] 1 o E( dbv / m) PIN ( dbm) 13 20Log( d) [9] A.2 Example of an E-field Stength Calculation Calculate the E-Field stength in the GTEM cell if a powe amplifie with a +30dBm output level is used to dive the cell (P IN =+30). The input impedance of the cell is 50 Ω and the septum height is 0.63m (25 inches) (20Log(0.63) = -4 db) E ( 4) E = 21 dbv / m 13

16 A.3 Ingess Powe Calculation Figue A.1 Receive Path Block Diagam K is equal to the losses o gain between DUT and measuement device. Recod a loss as a negative numbe and a gain as a positive numbe. Example: Suppose that between the DUT and Measuement device thee is a cable with a loss of 2dB and an amplifie with a 30 db gain, and a 75Ω to 50Ω adapte with a loss of 5.7 db then: K = K = 22.3 db If the amplifie wee emoved then K would equal -7.7 db P ( dbm) P ( dbm) K( db) [10] m The elationship between the electic field inside the GTEM cell and the powe eceived P can be deived fom the following equations: P P A [11] d e Pd = Powe Density (W/m 2 ) P = Received Powe at output of DUT Ae = Antenna Effective Aea (m 2 ) P d PT GT o 2 4 d 2 E P d [12] 120 PT = Powe Tansmitted into Tansmit Antenna (Watts) GT = Gain of Tansmitting antenna (dbi) d = distance between tansmit antenna and DUT (m) 14

17 E = Field Stength at DUT (V/m) Ae 2 2 G fo an isotopic antenna and thus Ae fo any othe antenna [13] 4 4 G = Gain of Receiving antenna = Wavelength (m) P G G E G E G P [14] T T 2 2 ( 4 d ) Equation [14] is known as the FRIIS Equation It can be assumed that the gain of the eceiving antenna is equal to the shielding effectiveness and theefoe G is equal to the shielding effectiveness of the DUT. If the electic field at the DUT is known, then: P G Shielding Effectiveness [15] 2 2 E given c = ƒ x, then if ƒ is in MHz, equation 15 becomes G 480 P f E 300 Shielding Effectiveness [16] Multiplying both sides by 10Log10 gives: P f 10Log( G ) 10Log( ) [17] 2 2 E 300 the tems in backets may be expanded giving: 10Log( G 2 ) 10Log(480 ) 10Log( P ) 20Log( f ) 20Log( E) 10Log(300 2 ) [18] Given that 10Log(P) is the db equivalent, then the equation may be e-witten as: G ( db) P ( dbw) 20Log( f ) E( dbv / m) 49.5 [19] e-aanging gives: G ( db) P ( dbw) Log( f ) E( dbv / m) [20] 15

18 Whee E is in dbv/m and ƒ is in MHz Finally, substituting equations [9] and [10] into [20] gives: G ( db) P ( dbw ) K Log( f ) P ( dbm) 13 20Log( d) [21] m which is appoximately equal to: G ( db) P ( dbm) K 30 20Log( f ) P ( dbm) 20Log( d) [22] m G = Shielding effectiveness of DUT (db) Pm = Powe eceived at measuement device (dbm) ƒ = Fequency (MHz) PIN = Powe into GTEM cell (dbm) d = Septum height (m) K = Total loss o gain between DUT and measuement device (db) IN IN 16

19 APPENDIX B: GTEM CELL QUALIFICATION METHOD B.1 Connect the equipment as shown in Figue B.1 Figue B.1 GTEM Qualification Test Configuation B.2 Measue the insetion loss/gain between the signal geneato and the GTEM cell and ecod this value as K. A gain will be ecoded as a positive value and a loss shall be ecoded as a negative value. See A.3 fo an example. B.3 Set the fequency of the signal geneato to 5 MHz and ecod the field on the isotopic field pobe (in db(v/m)) and the powe into the GTEM cell (PGTEMIN). (PGTEMIN = POUT - K). Table B.1 may be used to ecod the data fo futue use. B.4 Repeat B.3 fo the following fequencies: 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1002 MHz B.5 Use the following fomula (equation [9]) to calculate the pedicted Electic field stength inside the GTEM cell: E( dbv / m) PGTEMIN ( dbm) 13 20Log( d) whee d is the septum height of the GTEM cell in metes. B.6 Compae calculated Electic field and actual electic field measuements fom the isotopic field pobe 17

20 B.7 If the calculated field stength is equal to the ecoded field stength ± 2dB then the chambe is qualified fo futhe use without the use of an isotopic field pobe. Table B.1 GTEM Cell Qualification Data Fequency (MHz) Powe Out of Sig Gen (P OUT ) Loss/Gain (K) Powe into GTEM (P OUT K) Recoded E-Field(dB) (A) Calculated E-Field(dB) (B) Delta (A B) 18

21 APPENDIX C: FIELD UNIFORMITY VERIFICATION METHOD C.7 Connect the equipment as shown in figue C.1. If the amplifie is calibated and stable, the diectional couple and powe mete may be omitted. Figue C.1 GTEM Qualification Test Configuation C.2 Detemine the maximum dimension of likely DUT s and fom these dimensions detemine the position of the eight cones inside the GTEM cell. C.3 Place the field pobe in the cente of the test volume inside the GTEM cell. C.4 Set the fequency on the analyze to 5 MHz, and adjust the amplitude until the level on the field pobe eads 10 V/m 1 V/m (+20 dbv/m). C.5 Recod the field stength and eithe the level on the powe mete o the signal geneato output level (if diectional couple not used). Table C.1 may be used to ecod the field stength data. C.6 Move the field pobe and measue the E-field stength at each of the eight cones of the equied test volume. If the maximum height of the DUT is less than that of the field pobe, it is acceptable to measue only the fou cones at the level of the DUT. 19

22 C.7 If the field vaies by moe than 5 db, then educe the volume if possible. If this citeion cannot be met due to the size of the DUT, adjust the test level such that the field is within 5 db. Note the test level within the test epot. C.8 Repeat steps C.4 to C.7 fo each of the following fequencies: 50, 100, 200, 400, 700 and 1002 MHz Table C.1 Test Chambe Calibation Data Pobe Location Cente Cone 1 Cone 2 Cone 3 Cone 4 Cone 5 Cone 6 Cone 7 Cone 8 MAX MIN DELTA (MAX-MIN) Field Stength V/m dbv/m V/m dbv/m V/m dbv/m V/m dbv/m V/m dbv/m V/m dbv/m V/m dbv/m V/m dbv/m V/m dbv/m dbv/m dbv/m db Fequency (MHz)