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

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. 

ANTENNA TYPE

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
ANTENNAFREQ. RANGEUSAGENOTES
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 

Wavelength

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

FrequencyWavelength
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.

 

Differential Mode Current vs Common Mode Current (Transmission Lines)

15. December 2020 12:14 by Christian in EMC/EMI, Noise Coupling, Troubleshooting
Differential Mode Configuration Assuming 1A is propagated from the source to the load usin

See Ground Return & Common Impedance Coupling

Differential Mode Configuration

Assuming 1A is propagated from the source to the load using I1 to represent the current flow. The 1A current must return to the source represented by I2. If I1 = I2 then we have a perfectly balanced transmission line system, no loss in the network.
The EM filed that exists in the outgoing path will couple inductively to the RF return path (AC transmission while DC will always travel in the lowest rsistance path I2). Magnetic flux between these two transmission lines will cancel each other out, being of equal value and opposite in dirrection. Assuming that the spacing between opposite conductors is very small, there should be no radiated emissions. Differential-mode radiation is caused by the flow of RF current loops within a system 's structure.
Common Mode Configuration
Assuming tht 50% of the transmitted current is consumed within the load, it leaves 50% of current that must be returned to its source.  The Kirchhoff's Law states that the sum of all currents withinn a transmission line must equal zero.We have 50% loss. 
I'2 represents the a virtual return path through free space or metallic interconnect. Not all desired return current will flow in I2 due to inductance or loss in transmission line. The remaining of the desired return current will flow in I'2. A negative current flow will exist in I2, travelling in opposite direction to satisfy Ampere's Law. The undesired (negative) current flow in I2 is that portion that contributes to common-mode currents.
Common mode radiation results from unintentional voltage drops caused by a circuit rising above the 0V reference.
Cables connected to the affected reference system will act as dipole antenna when stimulated with a voltage source.
The only solution to resolve CM radiation is reducing the common path impedance for  the return current.
 
 
 
The total magnitude of imbalance in a DM transmission line system becomes the the total magnitude of CM current.
RF loss within a system or transmission line will result in CM energy, and this CM current is the reason for EMI problems.