RFI Estimation for Multiple Noise Sources Due to Modulation at a Digital Mic Using Diople Moment Based Reciprocity

Non-ideal ground structures in flexible printed circuit board, such as the meshed ground or discrete ground nets, can cause severe RFI to the nearby antennas. Those RF radiators can be modeled as a set of equivalent dipole moment(s) when they are electrically small. Then, the dipole moment based reciprocity theorem can be applied to estimate the noise coupling level. In this article, a practical methodology using the dipole moment based reciprocity is proposed to identify multiple radiation sources of a real cellphone product. Multiple equivalent dipole moments are constructed with one-to-one correspondence to the physical structures. The reciprocity calculations can eventually provide the noise contributions of each noise source.