A novel and low-cost method for slot-crossing differential line to reduce GHz common-mode radiation in advanced PCB

By symmetrically placing a pair of open stubs (ground resonators) between the slot-crossing differential line, the radiated emission induced by common-mode noise is greatly reduced around the designed frequency. Under proper design, these ground resonators can provide a shorting path for the common-mode return current around the resonant frequency of slotline, and thus avoid the noise to excite the slotline. Also, the equivalent model is established to validate the proposed idea. Based on the proposed idea, solution and reference board are fabricated by typical PCB process. The simulated results indicate that the radiated emission caused by the slot-crossing common-mode noise is effectively reduced at least 5 dB in frequency range from 2.2 GHz to 3.3 GHz by the connected ground resonators. It is a low-cost and useful solution to reduce the radiated emission caused by the slot-crossing common-mode noise around GHz frequency range on high-density package or PCB.