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An Introduction to RF Anechoic Chamber Technology

An Introduction to RF Anechoic Chamber Technology. Vicente Rodriguez, Ph.D. ETS-Lindgren 1301 Arrow Point Dr. Cedar Park, TX, 78613 Vicente.Rodriguez@ets-lindgren.com. SUMMARY. The Chamber Family Absorber Materials The EMC Chamber The antenna Chamber Tapered and Rectangular.

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An Introduction to RF Anechoic Chamber Technology

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  1. An Introduction to RF Anechoic Chamber Technology Vicente Rodriguez, Ph.D. ETS-Lindgren 1301 Arrow Point Dr. Cedar Park, TX, 78613 Vicente.Rodriguez@ets-lindgren.com

  2. SUMMARY • The Chamber Family • Absorber Materials • The EMC Chamber • The antenna Chamber • Tapered and Rectangular. • RCS chambers • References

  3. EMC testing Properties: Semi-free space or half free space Absorber: FS-1500,1000,600,400 (polyurethane) and FS-1250,600,400 PS and EMC-24, (for High frequency applications other absorber may be used). Design tools: In-House Software Std. Doc: ANSI C63.4-1992/1998; EN50147-2 (semi-anechoic),-3(fully anechoic),-1(shielding test); VCCI V98.3 (Japanese); RCS and Antenna. Properties: Fully anechoic. Absorber: EHP series absorbers RCS: mostly military applications, is a chamber to measure radar cross section of a target Antenna: military and commercial, these are chambers to measure the radiation pattern of a radiator, could be an antenna or an antenna plus other system. Chamber Types: Two Main Families

  4. The Absorber Family 1 Microwave Pyramidal absorber. EMC and EHP series Electric Losses Preferred technology for High frequencies It can be used for low frequencies if size (length) is increased

  5. The Absorber Family 2 Ferrite Tile . Magnetic Losses Preferred technology for Low frequencies (up to 1GHz), it has low profile. It cannot be used for high frequencies

  6. The Absorber Family 3 Hybrid Absorber . Electric and Magnetic Losses Preferred technology for EMC Applications. foam has to have special formula for good matching with ferrite tile at the bottom. At High frequencies its performance is not as good as MW pyramid of equal size. Flat top causes undesired reflections at MW range.

  7. The Absorber Family 4 Flat laminate . Electric Losses Preferred technology for laboratory set ups. It is a sandwich of different foams. About 20dB absorption as frequency increases.

  8. The Absorber Family 5 Wedge and pyramid Electric Losses A variant of pyramidal absorber wedge does not show backscattering. Preferred technology for QZ treatment and for RCS chambers.

  9. Pyramidal Absorber Theory (Example) This material is volumetrically loaded having the same constitutive parameters through the volume of the pyramid Popular types of absorber have constitutive parameters of: Non magnetic material Low permittivity with losses We will study how the electromagnetic wave behaves as is incident on to a wall of this type of absorber.

  10. Pyramidal Absorber Theory (Example) At the tip of the absorber The wave impedance is that of air NO SUDDEN CHANGE IN WAVE IMPEDANCE = LOW REFLECTIVITY Along the length of the pyramid the wave impedance falls between those two values. At the base of the pyramid The wave impedance becomes

  11. Pyramidal Absorber Theory (Example)

  12. Pyramidal Absorber Theory (Example) Let’s approximate by saying that the pyramid is equivalent to a solid medium of 1/3 the height Let’s assume a length of 30cm The wavelength at 3GHz is 10cm And at 10GHz is 30mm For 3GHz Wavelength at 3GHz Approximate thickness of equivalent solid material

  13. Pyramidal Absorber Theory (Example) Let’s approximate by saying that the pyramid is equivalent to a solid medium of 1/3 the height For 10GHz Wavelength at 3GHz Approximate thickness of equivalent solid material In practice the reflection coefficient may not be as small as this but it will be significantly Smaller than at 3GHz

  14. 4m 1m 1,3,5,10m EMC Chamber • Design is guided by the standards and the test that the customer is going to perform. Frequency range is from 30 to 1000MHz • At what distance is the measurement (3m, 5m,10m)? Are we testing immunity or emissions? • The chamber must perform as if it was an infinite ground plane in an infinite open space • NSA is a measurement of how close we are to this goal. • Std.Docs call for NSA being within +- 4dB of the theoretical.

  15. abs Rx2 D Tx1 Dsin() a B Qzd Qzs Rx1 Tx2 abs abs A EMC Chamber There are some rules that can be applied when sizing an EMC Chamber once the test distance and the quiet zone size are known Rx1 can be a minimum of 1.5m It is desirable that  > 0 so that reflections from the side walls Do not arrive in phase to the test area.

  16. abs Tx1 H 1 – 4 meter scan 2m 1.5m abs D 1m A EMC Chamber The FCC asks that the performance of that anechoic chamber matches that of an out door range. The Normalize Site Attenuation (NSA) is measured. Another common measurement for qualification is the field uniformity measurement

  17. EMC Chamber Chamber Validation Requirements • A typical standard will have wording similar to this: • ANSI C 63.4-1992 § 5.4.2, Alternate test Sites: Measurements can be made at a location other than an OATS, ... Provided that the alternate site meets the site attenuation requirements of 5.4.6 over the volume occupied by the EUT, … and the ground plane requirements of 5.4.3 What this means is that it must be shown that the chamber performs like an infinite ground plane with no obstructions anywhere.

  18. EMC Chamber Vertical Polarization VNSA

  19. EMC Chamber Horizontal Polarization HNSA

  20. Testing the Uniform Area according EN 61000-4-3. For chambers where immunity measurements will be performed it may be required to test the FU according to a given standard. this will show that the reflections from the wall do not affect the field. EMC Chamber This plane includes the uniform area, 12 from 16 points of E-Field are within +6/-0 dB.

  21. EMC Chamber: Partially lined chambers • Mil Std chambers and some other aircraft and SAE EMC standard documents call for partial absorber treatment chambers. • Frequencies for use start in the 100 of MHz. • Not looking for a half free space. • Absorber is loading the cavity (chamber) to reduce any resonant behavior. • EMC24 absorber is enough for these applications.(A pyramidal specially loaded absorber) EUT Bench 1m

  22. EMC Chamber: Mil Std Chamber • Mil Std 461 Defines the size of the chamber in terms if the EUT being measured, EUT size determines the size of the chamber. The sketches bellow show the standard MIL-STD chamber offered by ETS-Lindgren.

  23. Mil Std 461E • What is it? • “Department of Defense: Requirements for the control of electromagnetic interference characteristics of subsystems and equipment” • So it is a complete Standard for all different EMC measurements

  24. Mil Std 461E Mil Std 461 E came to be in August 20 1999 It superseding both Mil Std 461D and Mil Std 462D Which passed away (rest in peace)

  25. Mil Std 461E Emissions Conducted Susceptibility Mil Std 461E Is made of many parts (which one are YOU interested in) Emissions Radiated Susceptibility

  26. Mil Std 461E Conducted CE 101 Emissions CE 102 CE 106 Conducted CS 101 CS 114 CS 103 CS 115 CS 104 Susceptibility CS 105 CS 116 CS 109

  27. Mil Std 461E Conducted Emissions CE 101 Conducted Emissions, power leads 30HZ-10KHz No chamber required Shielded room recommended. LISN, receivers, O’cope, data recorders, sig gens, Current probe, etc are part of the required Equipment CE CE 102 Conducted Emissions, power leads 10KHz-10MHz CE 106 Conducted Emissions, Antenna terminal, 10KHz to 40GHz

  28. Mil Std 461E Conducted Susceptibility (Immunity) CS 101 Conducted Susceptibility, Power leads, 30Hz, to 150KHz CS 103 Conducted Susceptibility, Antenna Port, Intermodulation, 15KHz to 10GHz CS 104 Conducted Susceptibility, Antenna Port, rejection of Undesired signals, 30Hz to 20GHz CS 105 Conducted Susceptibility, Antenna Port, Cross-modulation, 30Hz to 20GHz CS CS 109 Conducted Susceptibility, Structure Current, 60Hz to 100KHz CS 114 Conducted Susceptibility, Bulk Cable Injection, 10kHz to 200Mhz CS 115 Conducted Susceptibility, Bulk Cable Injection, Impulse excitation CS 116 Conducted Susceptibility,Damped Sinusoidal transients, cables and power leads, 10KHz to 100MHz

  29. Mil Std 461E Radiated RE 101 Emissions RE 103 RE 105 More details about equipment and facilities will be given Radiated RS 101 RS 103 Susceptibility RS 105

  30. Mil Std 461E Radiated Emissions RE 101 Radiated Emissions, Magnetic Field, 30Hz to 100KHz RE RE 102 Radiated Emissions, Electric Field, 10KHz to 18GHz RE 105 Radiated Emissions, Antenna Spurious and harmonic Outputs, 10KHz to 40GHz

  31. Mil Std 461E Radiated Susceptibility (Immunity) RS 101 Radiated Susceptibility, Magnetic Field, 30Hz to 100KHz RE RS 103 Radiated Susceptibility, Electric Field, 2MHz to 18GHz RS 105 Radiated Susceptibility, Transient Electromagnetic field

  32. Mil Std 461E Where do we test? Paragraph 4.3.2 “To prevent interaction between the EUT and the outside environment, SHIELDED ENCLOSURES will be usually required for testing” Paragraph 4.3.2.1 “RF absorber material… shall be used when performing RE and RS testing inside a shielded enclosure… The RF absorber shall be placed above, behind and on both sides of the EUT, and behind the radiating or receiving antenna”

  33. The Absorber Family EMC-24 Mil Std 461E requirements TABLE I page 10 6dB absorption 80Mhz to 250Mhz 10dB absorption 250Mhz and above

  34. Mil Std Chamber side view • Mil Std 461 Defines the size of the chamber in terms if the EUT being measured, EUT size determines the size of the chamber. The sketches bellow show the standard MIL-STD chamber offered by ETS-Lindgren.

  35. Mil Std Chamber Side View • Mil Std 461 Defines the size of the chamber in terms if the EUT being measured, EUT size determines the size of the chamber. The sketches bellow show the standard MIL-STD chamber offered by ETS-Lindgren.

  36. Mil Std Chamber RE and RS Equipment RE101 RECOMMENDED REQUIRED Current Probe EMCO 3725-2M CHAMBER EMCO 7604 EMCO 4-TR

  37. Mil Std Chamber RE and RS Equipment RE103 REQUIRED EMCO 3725-2M CHAMBER EMCO 4-TR EMCO 7-TR EMCO 3115 EMCO 3110B EMCO 3301B EMCO 3106 MIL STD 461E does not longer accept Log Periodic and spiral Logs only double ridge horns above 200MHz

  38. Mil Std Chamber RE and RS Equipment RS101 RECOMMENDED REQUIRED Current Probe EMCO 3725-2M CHAMBER EMCO 7605/7606 EMCO 4-TR

  39. Mil Std Chamber RE and RS Equipment RS103 REQUIRED EMCO 3725-2M CHAMBER EMCO 4-TR EMCO 7-TR EMCO 3115 EMCO 3109 EMCO 3301B EMCO 3106 MIL STD 461E does not longer accept Log Periodic and spiral Logs only double ridge horns above 200MHz

  40. Mil Std Chamber RE and RS Equipment RS103 paragraph 5.19.4, states that an accepted method is the mode tuned reberveration chamber, the range is 200MHz to 40GHz, for the reverb log periodics can be used since pattern is no longer an issue

  41. CISPR 25 • “Limits and methods of measurement of radio disturbance characteristics for the protection of receivers used on board vehicles” • This means that we measure the emissions that would affect any receiver in the vehicle. Is another self immunity standard, of how vehicle receivers are immune to radiated emissions from its own systems • SAE J 551-4 and SAE J 1113-41 are equivalent standards

  42. CISPR 25 • “Covers the frequency range from 150KHz- 1000MHz • When an absorber lined chamber is used the absorption of the material has to be better than 6dB for the range 70MHz and up. • For the chamber testing of subsystems a monopole is used for the range 150KHz to 30MHz, for 30MHz to 200MHz a biconical antenna is used, the log periodic is used for the range 200MHz-1000MHz. For equipment testing a TEM cell can be used.

  43. EMC Chamber: CISPR 25 Chamber • The CISPR-25 calls for reflectivity in the EUT area to be better than 6dB. • There is no method for testing this. • Normal incidence performance of absorber is the best way to determine the reflectivity in the area given the test geometry

  44. EMC Chamber: CISPR 25 Chamber • A recommended practice is to map the field along the cable harness although the standard does not mentions anything about any chamber validation method. This method can help compare the results in two different chambers.

  45. CISPR 25 Chamber Side View (Bicon)

  46. CISPR 25 Chamber Side View (Bicon)

  47. CISPR 25 Chamber Monopole Testing

  48. EMC Chamber: CISPR 25 Chamber • Apart from component testing the CISPR 25 rooms could accommodate some vehicle testing if the floor is reinforced.

  49. CISPR 25 TEM Cells • Additionally CISPR 25 allows for testing of equipment in TEM cells and other TEM like devices

  50. Every manufacturer has its own requirements (usually very difficult to meet). Automotive standards are actually rather simple. The most common are SAE, ISO and 95/54 EC. These usually are copies of each other with small difference. The previous slides look at the FACT 25 chamber which can be used for automotive component testing for all these standards. A short introduction to emission testing of whole vehicles is presented now Automotive Testing: A Short Introduction 50

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