Accredited Standards Committee C63® - EMC

Accredited Standards Committee C63® - EMC
Draft C x Annex N Site-Specific Qualification Procedure for Hybrid Antennas (intended to be used for the making of ANSI C x Final Compliance Measurements) Harry H. Hodes, NCE Principal EMC Engineer ACIL Corporation for EMC Proficiency Testing, Inc. [ACE-PT Inc.] 18 April 2012

Summary of this Presentation Observations, Current Situation, & Problem-Requirement Statement Ground Rules for Selecting the Technical Approach Overall Technical Approach - Pre-requisites Dimensional, Frequency, and VSWR [Return Loss] Restrictions Required Equipment - Qualification Test Setup, Qualification Test Procedure, and Analysis of the Test Data Qualification Criteria (Pass/Fail Limits) Some Antennas that meet all of the Annex N Restrictions Some Antennas that do not meet all of the Annex N Restrictions.

Observations - I EMC PT data strongly indicate that, in some cases, the use of hybrid antennas results in excellent, highly repeatable measurements. (Note: variations of +/- 5 dB or better from the “assigned value” have repeatedly occurred).

Observations - II In contrast, EMC PT data also strongly indicate that, in some cases, the use of hybrid antennas has resulted in gross measurement errors. (Note: variations of +/- 23 dB from the “assigned value” have repeatedly occurred, in cases that were not obviously caused by test operator egregious error).

Observations - III In contrast, EMC PT data strongly indicate that the use of biconical and LPDA antennas has resulted in much smaller gross measurement errors. (Note: variations of +/- 9 dB to +/- 12 dB from the “assigned value” have repeatedly occurred, in cases that were not obviously caused by test operator egregious error).

Observations - IV Possible causes for these conflicting results: - Use of large or very large hybrids (especially in small semi-anechoic chambers at 3 m distances). some hybrids have an extremely high VSWR (> 500:1 or more, especially in the 30 MHz to 70 MHz range). every manufacturer of hybrid antennas uses a different BALUN design and a different arrangement of antenna elements. The coupling responses of each model of hybrid antenna will vary significantly with: test site size (i.e., 3 m, 5 m, or 10 m); test site style (e.g., non wx-protected OATS, partially wx-protected OATS, full wx- protected OATS, symmetric semi-anechoic chambers, non-symmetric semi-anechoic chambers, fully anechoic rooms); and, with varying RF Absorber floor laydown pattern and wall/ceiling treatments. Hybrid Antennas have a significantly greater calibration MU than biconicals and LPDAs (cf. CISPR :2010).

Current Situation ANSI C : - Section refers to ANSI C for the list of acceptable antennas. ANSI C contains the following broadband antennas for MHz (cf. Sections 15 and ): biconical antenna, log periodic antenna, double-ridged guide horn. There is no mention of hybrid antennas. However, ANSI C Section further states that linearly polarized broadband antennas are allowed, with the biconical and log periodic as the recommended types. Since a hybrid is classified as a linearly polarized antenna, it is accepted provided it is calibrated using the latest edition of ANSI C63.5 or SAE-ARP- 958:1992, and, can be shown to be correlated with measurements made with a tuned dipole with an “acceptable” degree of accuracy. - Does NOT allow the use of hybrid antennas for making NSA measurements. (Note: only Roberts-type Tuned Dipoles, Biconicals, and LPDAs are allowed when making NSA measurements).

ANSI C Current Situation - I Table 1 does not include hybrid antennas. The intent of the ANSI C maintenance team was to prohibit the use of hybrid antennas for making final compliance measurements. Notwithstanding this fact, ANSI C states that CISPR : is a normative reference. Per CISPR : , a broadband antenna may be used provided it meets the requirements in CISPR : Clause ( MHz) and Clause ( MHz). CISPR : Clause refers to the CISPR : Clause requirements, which are summarized as: 1) Linearly polarized antenna, 2) Main lobe and reflected lobe within 1 dB; i.e. broad beam or pointed antenna, 3) Antenna with a 2:1 SWR at receiver, 4) Antenna calibration to meet the requirements in 4.1 of CISPR : The above is subject to the ANSI C Clause requirement that an antenna is acceptable “provided that the measurement can be correlated with that made with a tuned dipole with an acceptable degree of accuracy”.

ANSI C Current Situation - II In addition, ANSI C also states that ANSI C is a normative reference. ANSI C , in turn, specifies an undated reference to CISPR as its only normative reference, and notes that the sensor specifications in Table 1, Note 2 of CISPR , CISPR , and CISPR Measurement Procedures are applicable. CISPR Clause states that antennas need to conform to CISPR In CISPR : Clause it is stated that: “The antenna shall be a dipole-like antenna designed to measure the E-field, and the free-space antenna factor shall be used. The antenna types include: a) tuned dipole antennas, whose element pairs are either straight rods or conical in shape; b) dipole arrays such as the log-periodic dipole array (LPDA) antennas, comprising a series of staggered sets of straight rod elements; c) and hybrid antennas.” However, CISPR : Clause also imposes conditions that are summarized here: - The antenna must be linearly polarized, - The antenna must meet balance test of Clause for frequencies below 200 MHz, - The antenna must meet the conditions for beam width described in Clause 4.5.3(c), - The antenna must have a Return Loss of 10 dB or more, The antenna calibration factors must meet the Clause 4.1 requirements. Regardless, the use of hybrid antennas is subject to the ANSI C Clause requirement that an antenna is acceptable “provided that the measurement can be correlated with that made with a tuned dipole with an acceptable degree of accuracy”.

ANSI C Current Situation - III In addition, ANSI C also states that ANSI C is a normative reference. ANSI C , in turn, specifies an undated reference to CISPR as its only normative reference, and notes that the sensor specifications in Table 1, Note 2 of CISPR , CISPR , and CISPR Measurement Procedures are applicable. CISPR Clause states that antennas need to conform to CISPR In CISPR : Clause it is stated that: “The antenna shall be a dipole-like antenna designed to measure the E-field, and the free-space antenna factor shall be used. The antenna types include: a) tuned dipole antennas, whose element pairs are either straight rods or conical in shape; b) dipole arrays such as the log-periodic dipole array (LPDA) antennas, comprising a series of staggered sets of straight rod elements; c) and hybrid antennas.” However, CISPR : Clause also imposes conditions that are summarized here: - The antenna must be linearly polarized, - The antenna must meet balance test of Clause for frequencies below 200 MHz, - The antenna must meet the conditions for beam width described in Clause 4.5.3(c), - The antenna must have a Return Loss of 10 dB or more, The antenna calibration factors must meet the Clause 4.1 requirements. The above is subject to the ANSI C Clause requirement that an antenna is acceptable “provided that the measurement can be correlated with that made with a tuned dipole with an acceptable degree of accuracy”.

ANSI C Current Situation - IV - ANSI C does NOT allow the use of hybrid antennas for making NSA measurements. (Note: only Roberts-type Tuned Dipoles, Biconicals, and LPDAs are allowed when making NSA measurements).  Note that CISPR : specifically allows (but does not recommend) the use of hybrid antennas for making NSA measurements (cf. Clause Note 2).

ANSI C Current Situation - V Unfortunately, if you are a user of hybrid antennas, and, you want to perform final compliance tests on products, none of this really is of any practical help because: - almost no one has the required data needed to show compliance with all of the requirements of CISPR : Clause 4.5.3; - the CISPR : Clause requirement to meet the “antenna having a 2:1 SWR at the receiver” will be difficult or impossible unless a “pad” attenuator AND a pre-amplifier are used (which will create many other problems); - there is no clear statement in ANSI C of what “an acceptable degree of accuracy” actually is (w.r.t. measurement correlation with those made with a tuned dipole).

Problem-Requirement Statement What is required is a technically reasonable, practical, test-site-specific qualification test procedure that can be used to objectively determine whether or not a given hybrid antenna is acceptable (or not acceptable) for use in making final compliance measurements on products in accordance with ANSI C63.4.  “technically reasonable” means that appropriate hybrid antenna designs should be acceptable. “practical” means that the procedure can be accomplished at reasonable cost with regularly-available test equipment. “objectively determined” means that the acceptance criteria are based on the actual measurement uncertainties of the actual qualification test procedure, and not on arbitrary criteria.

Ground Rules for Selecting the Technical Approach - I Must contain a definition of what a “hybrid antenna” is for the purpose of the Qualification Test Procedure. Achieve a reasonable balance between best technical practices and the concerns of economic operators. Qualification Test Procedure must be both test-site specific and antenna-specific. Use the “funnel approach” to minimize the lab workload. Funnels are wide at the top and narrow at the bottom. The notion was to eliminate antennas that are obviously unacceptable from consideration at the outset so as to avoid wasting time and money on futile testing.

Ground Rules for Selecting the Technical Approach - II Acceptance Criteria must be based upon the actual measurement uncertainties of the actual Qualification Test Procedures used, not on an arbitrary (e.g., +/- 1 dB) “acceptability” criteria. Hybrid antennas are not permitted to be used for Test Site Validation measurements  Note that CISPR :2010 allows, but does not prefer the use of hybrid antennas for Test Site Validation measurements.

Overall Technical Approach - I Pre-requisites: Site must meet NSA / VSA [30 MHz – 1000 MHz] (Section N.1) Site must meet SVSWR [1 GHz – 18 GHz] (if hybrids are to be used > 1GHz) (Section N.1) Hybrid Antennas must be designed for Emissions measurements (dual use emissions/immunity hybrids can be used if the “bat-wing” or “grid” elements are removed). (Section N.3) Dimensional, Frequency and VSWR [Return Loss] Restrictions Restricts maximum Hybrid Antenna dimensions to max length x 1.5 m width x 1.5 m height. (Section N.3) Restricts minimum nominal frequency of operation of Hybrid Antennas to MHz, and the maximum nominal frequency of operation of Hybrid Antennas to 6 GHz. (Section N.3) From 30 MHz to 200 MHz, the free-space VSWR of the Hybrid Antenna must be :1 or better; if not 10:1 or better, an impedance matching “pad” attenuator must be installed on the antenna so as to make it 10:1 or better. (Section N.3)

Overall Technical Approach - II Required Equipment (Section N.4.2): the Hybrid Antenna to be investigated, and if necessary, its Hybrid Impedance-Matching Pad Attenuator [HAIMP]. Free-Space Antenna Factors (obtained per ANSI C63.5) must be available for the hybrid. quantity = 2 biconical antennas, each having the same nominal balun impedance (i.e., both must have 200 Ohm baluns or both must have 50 ohm baluns). One bicon is to be designated as the transmit antenna, and the other as the “reference” (receive) bicon Free-Space Antenna Factors (obtained per ANSI C63.5) must be available for the “reference” (receive) Bicon. quantity = 2 nominally identical LPDA antennas. One LPDA is to be designated as the transmit antenna, and the other as the “reference” (receive) LPDA. Near-Free-Space Antenna Factors (obtained per ANSI C63.5) must be available for the “reference” (receive) LPDA. quantity = 2 nominally DRG Horn antennas. One DRG Horn is to be designated as the transmit antenna, and the other as the “reference” (receive) DRG Horn. Free-Space Antenna Factors (obtained per ANSI C63.5) must be available for the “reference” (receive) DRG Horn. [Note: applicable only if the hybrid to be investigated is to be used above 1 GHz].

Overall Technical Approach - III Required Equipment (Continued) (Section N.4.2): Test Site to be investigated (i.e., OATS or Semi-Anechoic Chamber [SAC] or Fully Anechoic Room [FAR]) Lab’s Antenna Mast and Controller, and lab’s standard coaxial range cable(s) EMI Receiver or Spectrum Analyzer-based EMI Measurement System. Tripod or Mast (or other antenna mounting system) for transmit antennas Quantity = two 10 dB impedance matching “pad” attenuators are required. One 10 dB attenuator is required to be installed on the input connector of each transmit antenna, and the other 10 dB attenuator is required to be installed on the input connector of the EMI Receiver or Spectrum Analyzer-based EMI Measurement System. Signal Generator(s) covering the frequency range from 30 MHz to the maximum frequency of the hybrid that is to be investigated (but not exceeding 6 GHz). High-quality coaxial cable(s) to connect the Signal Generator(s) to the 10 dB Pad installed on the Transmit Antennas.

Overall Technical Approach (Section N.4.3) - IV Test Setup: a) Place the transmit biconical antenna in horizontal polarization at a height of 1 m at the center of the turntable. Install a 10 dB attenuator on the input connector of the transmit biconical antenna. b) Place the receiving biconical antenna on the antenna mast in horizontal polarization at a height of 1 m at a distance of 3 m, as measured from the reference point of the transmit biconical antenna to the reference point of the receive biconical antenna. Do NOT use an attenuator on the output connector of the receiving biconical antenna. Use a high quality coaxial cable to connect the transmit biconical antenna (with the 10 dB attenuator installed) to a signal source. Use the coaxial cable that is used for regular product testing to connect the receiving antenna to the EMI receiver or spectrum analyzer via a 10 dB attenuator that shall be installed directly onto the input port of the EMI receiver or spectrum analyzer.

Overall Technical Approach (Section N.4.3) - V Test Setup & Test Procedure: c) Scan the receiving biconical antenna from 1 m to 4 m while simultaneously scanning or stepping the EMI Receiver or Spectrum Analyzer over the frequency range 30 MHz to 200 MHz. Use a maximum resolution bandwidth of 120 kHz. Use either linear frequency steps with maximum step-size equal to one-half of the chosen resolution bandwidth, or use a linear scan. Ensure that the received signal is at least 20 dB above the system noise floor. Record the maximum received signal levels. The results recorded are the reference values for the two biconical antennas at 3 m in horizontal polarization and are designated as S21,BB3H. Without moving the transmit biconical antenna, remove the receiving biconical antenna and replace it with the hybrid antenna to be qualified, such that the reference point on the hybrid is at the 3 m distance, as measured from the reference point of the transmit biconical antenna. d) If required in accordance with N.3 c), install the impedance matching "pad" attenuator at the output connector of the hybrid antenna. Reconnect the receiving coaxial cable, and repeat step c), making certain that the EMI Receiver or Spectrum Analyzer settings are not changed. The results are the “antenna under test” [AUT] values of the transmit biconical antenna and the receiving hybrid antenna at 3 m in horizontal polarization. These results are designated as S21,BH3H.

Overall Technical Approach (Section N.4.3) - VI Test Data Analysis: Compute the reference and AUT horizontally polarized field strength measurement results (in dBV/m) as follows: Compute the difference between the reference and AUT horizontally polarized field strength results (in dB) as follows: Compare the E3mH results obtained with the acceptance criteria given in N.5.1 a).

Overall Technical Approach (Section N.4.3) - VII Repeat the above procedure and computations with the biconical antennas and the hybrid antenna under test in vertical polarization at the 3 m measurement distance. Denote the reference and AUT vertically polarized field strength measurement results (in dBV/m) as follows: Compute the difference between the reference and AUT horizontally polarized field strength results (in dB) as follows: Compare the E3mV results obtained with the acceptance criteria given in N.5.1 a).

Overall Technical Approach (Section N.4.3) - VIII Repeat the above process using LPDAs and the hybrid antenna under test at the 3 m measurement distance, as measured from the reference point of the transmit LPDA to the reference point of the receive LPDA and the reference point of the hybrid, respectively. Compute the reference and AUT horizontal and vertical polarization field strength measurement results (in dBV/m) as follows: Compute the differences between the reference and AUT horizontally and vertically polarized field strength results (in dB) as follows: Compare the E3mH and E3mV results obtained with the acceptance criteria given in N.5.1 b).

Overall Technical Approach (Section N.4.3) - IX If necessary, repeat the above procedure using DRG horn antennas and the hybrid antenna under test at the at the 3 m measurement distance, as measured from the reference point of the transmit DRG Horn to the reference point of the receive DRG Horn and the reference point of the hybrid, respectively. Compute the reference and AUT horizontal and vertical polarization field strength measurement results (in dBV/m) as follows: Compute the differences between the reference and AUT horizontally and vertically polarized field strength results (in dB) as follows: Compare the E3mH and E3mV results obtained with the acceptance criteria given in N.5.1 c).

Overall Technical Approach (Section N.4.3) - X If applicable, repeat the entire process using the biconicals, LPDAs, DRG horns and the hybrid antenna under test at the 10 m measurement distance. (Alter the subscript notation used in equations accordingly, perform the required computations, and compare the results with the applicable acceptance criteria given in N.5.2 a) or b) or c)

Acceptance Criteria (Section N.5.1, 3 m distance) N.5.1 a): In the frequency range 30 MHz to 200 MHz, for a given polarization, at the 3 m measurement distance, on a specific test site, a hybrid antenna shall be deemed acceptable for use in making final compliance measurements if the difference in results of measurement performed in accordance the procedures in the previous slides at each polarization meets the following requirements: - the results of the E3mH calculations are less then or equal to  2.5 dB at all measured frequencies in the range 30 MHz to 200 MHz (inclusive); and, - the results of the E3mV calculations are less then or equal to  2.5 dB at all measured frequencies in the range 30 MHz to 200 MHz (inclusive). NOTE: The above criteria are based upon the Expanded Uncertainty Values for a k=2 Coverage Factor that were computed for the exact measurement procedure (at the 3 m measurement distance) detailed in Section N.4.3.

Acceptance Criteria (Section N.5.1, 3 m distance) N.5.1 b): In the frequency range 200 MHz to 1000 MHz, for a given polarization, at the 3 m measurement distance, on a specific test site, a hybrid antenna shall be deemed acceptable for use in making final compliance measurements if the difference in results of measurement performed in accordance the procedures in the previous slides at each polarization meets the following requirements: - the results of the E3mH calculations are less then or equal to  2.9 dB at all measured frequencies in the range 200 MHz to 1000 MHz (inclusive); and, - the results of the E3mV calculations are less then or equal to  2.9 dB at all measured frequencies in the range 200 MHz to 1000 MHz (inclusive). NOTE: The above criteria are based upon the Expanded Uncertainty Values for a k=2 Coverage Factor that were computed for the exact measurement procedure (at the 3 m measurement distance) detailed in Section N.4.3 .

Acceptance Criteria (Section N.5.1, 3 m distance) N.5.1 c): In the frequency range 1000 MHz to 6000 MHz, for a given polarization, at the 3 m measurement distance, on a specific test site, a hybrid antenna shall be deemed acceptable for use in making final compliance measurements if the difference in results of measurement performed in accordance the procedures in the previous slides at each polarization meets the following requirements: - the results of the E3mH calculations are less then or equal to  3.2 dB at all measured frequencies in the range 1000 MHz to 6000 MHz (inclusive); and, - the results of the E3mV calculations are less then or equal to  3.2 dB at all measured frequencies in the range 1000 MHz to 6000 MHz (inclusive). NOTE 1: The above criteria are based upon the Expanded Uncertainty Values for a k=2 Coverage Factor that were computed for the exact measurement procedure (at the 3 m measurement distance) detailed in Section N.4.3. NOTE 2: A hybrid antenna that satisfies the above criteria may be used up to its maximum operating frequency or to 6000 MHz, whichever is less.

Acceptance Criteria (Section N.5.2, 10 m distance) N.5.2 a): In the frequency range 30 MHz to 200 MHz, for a given polarization, at the 10 m measurement distance, on a specific test site, a hybrid antenna shall be deemed acceptable for use in making final compliance measurements if the difference in results of measurement performed in accordance the procedures in the previous slides at each polarization meets the following requirements: - the results of the E3mH calculations are less then or equal to  2.4 dB at all measured frequencies in the range 30 MHz to 200 MHz (inclusive); and, - the results of the E3mV calculations are less then or equal to  2.4 dB at all measured frequencies in the range 30 MHz to 200 MHz (inclusive). NOTE: The above criteria are based upon the Expanded Uncertainty Values for a k=2 Coverage Factor that were computed for the exact measurement procedure (at the 10 m measurement distance) detailed in Section N.4.3.

Acceptance Criteria (Section N.5.2, 10 m distance) N.5.2 b): In the frequency range 200 MHz to 1000 MHz, for a given polarization, at the 10 m measurement distance, on a specific test site, a hybrid antenna shall be deemed acceptable for use in making final compliance measurements if the difference in results of measurement performed in accordance the procedures in the previous slides at each polarization meets the following requirements: - the results of the E3mH calculations are less then or equal to  2.9 dB at all measured frequencies in the range 200 MHz to 1000 MHz (inclusive); and, - the results of the E3mV calculations are less then or equal to  2.9 dB at all measured frequencies in the range 200 MHz to 1000 MHz (inclusive). NOTE: The above criteria are based upon the Expanded Uncertainty Values for a k=2 Coverage Factor that were computed for the exact measurement procedure (at the 10 m measurement distance) detailed in Section N.4.3 .

Acceptance Criteria (Section N.5.2, 10 m distance) N.5.2 c): In the frequency range 1000 MHz to 6000 MHz, for a given polarization, at the 10 m measurement distance, on a specific test site, a hybrid antenna shall be deemed acceptable for use in making final compliance measurements if the difference in results of measurement performed in accordance the procedures in the previous slides at each polarization meets the following requirements: - the results of the E3mH calculations are less then or equal to  3.2 dB at all measured frequencies in the range 1000 MHz to 6000 MHz (inclusive); and, - the results of the E3mV calculations are less then or equal to  3.2 dB at all measured frequencies in the range 1000 MHz to 6000 MHz (inclusive). NOTE 1: The above criteria are based upon the Expanded Uncertainty Values for a k=2 Coverage Factor that were computed for the exact measurement procedure (at the 10 m measurement distance) detailed in Section N.4.3. NOTE 2: A hybrid antenna that satisfies the above criteria may be used up to its maximum operating frequency or to 6000 MHz, whichever is less.

How were the Acceptance Criteria determined? A set of Measurement Uncertainty calculations were developed specifically for the test processes specified in Section N.4. The MUC calculations were mechanized using four Microsoft Excel® 2010 workbooks, with three sheets per workbook for each of two measurement distances (i.e., 3 m and 10 m). Four spreadsheets: bicon frequency range ( MHz) at 3 m & 10 m; Liberty Labs & ETS-Lindgren; Four spreadsheets: LPDA frequency range ( MHz) at 3 m & 10 m; Liberty Labs & ETS-Lindgren; Four spreadsheets for the DRG Horn frequency range (1 GHz – 6 GHz) at 3 m & 10 m; Liberty Labs & ETS-Lindgren.

Example Spreadsheet

Qualification Interval (Section N.6) For any given hybrid antenna used at a given measurement distance, on a specific test site, the qualification process detailed in N.4 and N.5 shall be performed when the hybrid antenna is first taken into service at the given measurement distance on the specific test site, and subsequently at intervals of not more than three years. If damage to or degradation of the antenna is known or suspected to have occurred, a re-qualification is to be performed as well.

Some Hybrid Antennas that meet all of the Annex N Restrictions Schaffner (Chase) CBL 6116C Schaffner (Chase) CBL 6112B Teseq CBL 6112D Teseq CBL 6111D Electrometrics 6917C-1 ETS-Lindgren 3143B ETS-Lindgren 3149 Sunol JB1 Sunol JB2 Sunol JB6 Schwarzbeck VULB 9162

Some Antennas that do NOT meet all of the Annex N Restrictions Electrometrics 6917B-1 (does not meet the minimum low frequency restriction) Schaffner CBL 9140A (does not meet the dimensional restrictions and the minimum frequency restrictions) Teseq CBL 6143A (does not meet the “Emissions only/Dual Use” restriction) EMCO 3142B (does not meet the dimensional restrictions and the minimum frequency restrictions) EMCO 3142C (does not meet the dimensional restrictions and the minimum frequency restrictions) ETS-Lindgren 3142D (does not meet the dimensional restriction) Rohde & Schwarz HL562 (does not meet the dimensional restriction) A.H. Systems SAS (does not meet the minimum frequency restrictions)

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