An investigation on the reduction technique of radiated emission from chassis with PCB

Correlation between radiated emission from chassis with PCB and the junction current which is the current flowing through screws connecting PCB GND to chassis GND was investigated, and new technique to reduce the junction current was proposed. The measurement results of the junction current frequency spectra showed strong correlation with the emission from chassis with PCB. Also investigation using meshed LCR network SPICE model of PCB and chassis was performed. The calculation results of the junction current showed good correlation with measurement results for frequency spectrum and it suggested that the closer to screw bypass capacitor is placed, the lesser current flows through junction. That new concept was validated by actual measurement and the results of radiated emission showed 19 dB improvements at 320 MHz.