EMC FLEX BLOG A site dedicated to Automotive EMC Testing for Electronic Modules

RF Boundary in automotive EMC for electronic components

RF Boundary is the element of an EMC test setup that determines what part of the harness and/or&nbsp

RF Boundary is the element of an EMC test setup that determines what part of the harness and/or peripherals is included in the RF environment and what is excluded. It may consist of, for example, ANs, BANs, filter feed-through pins, RF absorber coated wire and/or RF shielding.


RF Boundary is also an RF-test-system implementation within which circulating RF currents are confined


  • to the intended path between the DUT port(s) under test and the RF-generator output port, in the case of immunity measurements (ISO 11452-2, ISO 11452-4, ISO 1145-9), and
  • to the intended path between the DUT port(s) under test and the measuring apparatus input port, in the case of emissions measurement (CISPR 25),


and outside of which stray RF fields are minimized.


The boundary is maintained by insertion of BANs, shielded enclosures, and/or decoupling or filter circuits. The ideal RF boundary replicates the circuitry of the device connected to DUT in vehicle.

The standard test harness lenght for automotive EMC electronic components is (1700mm -0mm / +300mm). This 1.7m test harness runs between the DUT and the Load Simulator (Shielded Enclosure) that plays the role of RF Boundary.


If the Load Simulator enclosure does not include all DUT loads and activation/monitoring support equipment, additional support devices may be placed directly on the ground plane. The connection of additional devices to LS enclosure must be done via short wiring running on the ground plane.


Testing at subsystem level is preferable to any simulation. Whenever possible, use production intent representative loads.


Running long coax cables directly from DUT outside the chamber via SMA bulk filter panel would violate the 1.7m test harness length rule invalidating the test result. Ideally is to use Fiber Optic to exchange data with devices placed outside the test chamber.


Running long coax cables between Load Simulator and a support device placed outside the chamber is acceptable as long as the I/O line in question is not just an extension from DUT without proper RF boundary at the end of maximum 2-meter length of standard test harness.


It is critical to use the test harness length as defined by CISPR-25, ISO 11452-2, ISO 11452-4, and ISO 11452-9 to achieve valid compliance for your product. The length of the test harness as well as the grounding method (remote vs local) can result in different RF emissions level. Longer the test harness, higher RF emissions above 100 MHz due to its resonance pattern. The local grounding would show less magnitude variation across resonance peaks above 100MHz.


Christian Rosu



Antenna Factor

19. December 2020 06:25 by Christian in Troubleshooting, Test Equipment, Calibrations
Antenna factor when properly applied  to a field strength meter reading yields the electric fie

Antenna factor when properly applied to a field strength meter reading yields:

  • electric field intensity (V/m)
  • magnetic field intensity (A/m).

The field intensity in the far-field radiation pattern of an antenna:

  • Is proportional to the square root of the effective radiated power. Increasing the effective radiated power four times , the field intensity will be doubled.
  • Is direct proportional to antenna current. If the far-field intensity in the far-field antenna pattern is doubled the antenna current will increase 2 times. 


16. December 2020 06:35 by Christian in EMC/EMI, Troubleshooting, Test Equipment
ANTENNA TYPE FREQUENCY RANGE USAGE NOTES LOOP 1 KHz TO 30 MHz Magnetic Field 20 dB dynamic range f
LOOP1 KHz TO 30 MHzMagnetic Field20 dB dynamic range for 1 KHz
ROD1 KHz TO 30 MHzRadiated Emissions41 inches long, uses ground plane and active amplifier
BICONICAL20 MHz to 200 MHzRadiated EmissionsRequired by automotive standards
DIPOLE100 MHz to 1 GHzShielding Effectivenessmore efficient above 400 MHz 
LOG PERIODIC200 MHz to 1 GHzRadiated EmissionsCISPR 25
BICONLOG20 MHz to 1 GHzRadiated EmissionsEuropeean requirements
LOG SPIRAL200 MHz to 10 GHz Shielding EffectivenessCone-shaped. Can't distiguish between horizontal and vertical polarization
HORNabove 1 GHzRE, RI ALSEHighly efficient, directional, can be harmful causing blindness, glaucoma
RIDGED HORN1 GHz to 10 GHzRI ALSEBroadband
HOOD RI ALSEHorn antenna with a metallic hood around it for safety.
HAND-HELD Shielding Effectiveness 
DISCONE  Shielding Effectivenessnot directional
YAGIbelow 100 MHz Shielding Effectiveness 


16. December 2020 06:17 by Christian in Troubleshooting
Wavelength at 1 GHz = 1 foot

Rule of thumb: Wavelength at 1 GHz = 1 foot

(3 * 10meter/second)/(109 cycles/second) = 3 * 10-1 meters = 0.3 meters = 30cm

30 cm / 2.54 cm/inch = 11.81 inches

1 GHz1 ft
100 MHz10 ft
200 MHz5 ft
400 MHz2 1/2 ft
10 GHz1/10th feet = 1 1/4 inch
18 GHz1/20th feeth = 5/8 inch

Common Impedance Coupling, Common Power Supply

15. December 2020 17:01 by Christian in Grounding, Noise Coupling, Troubleshooting
When two circuits share a common ground, the ground voltage of each one is affected by the ground cu

See Ground Return & Common Impedance Coupling

When two circuits share a common ground, the ground voltage of each one is affected by the ground current of the other circuit.

When two circuits share a common power supply, current drawn by one circuit affects the voltage at the other circuit.