Post by aeffejr on Mar 24, 2009 13:48:34 GMT -5
Hi there,
I am drafting a report on how to superpose EM fields from multiple RF sources to estimate the composite human exposure level. This can be quantified in terms of SAR (specific absorption rate) or power density (flow). Both quantities depend on the rms E-field squared magnitude.
Since the total field is the vector superposition of the fields from the individual sources, the rms squared operation produces self and mutual power terms. For instance:
|E1+E2|^2=|E1|^2+|E2|^2 + 2 Re[E1* x E2]
where * is complex conjugate and x is the scalar product in the mutual power term.
Since these are rms terms, the mutual power terms would vanish if the fields are uncorrelated in time.
Suppose that two CDMA sources emit two signals occupying the same band and featuring distinct aligned Walsh codes; then these signals would be uncorrelated in time. Now, suppose that the delay of these signals to the observation point where the E-field is measured is different for the two signals (for instance, they could have been emitted by separate antennas). So the Walsh sequences embedded in the respective time waveforms are not aligned in time anymore.
Q1: would the received signals (fields) at the observation point be still uncorrelated in time?
Q2: if not, would the degree of correlation be negligible? In other words, would the aforementioned mutual power terms be much smaller than the self power terms, in typical CDMA systems?
Thanks, I hope these questions make sense to you.
Antonio
I am drafting a report on how to superpose EM fields from multiple RF sources to estimate the composite human exposure level. This can be quantified in terms of SAR (specific absorption rate) or power density (flow). Both quantities depend on the rms E-field squared magnitude.
Since the total field is the vector superposition of the fields from the individual sources, the rms squared operation produces self and mutual power terms. For instance:
|E1+E2|^2=|E1|^2+|E2|^2 + 2 Re[E1* x E2]
where * is complex conjugate and x is the scalar product in the mutual power term.
Since these are rms terms, the mutual power terms would vanish if the fields are uncorrelated in time.
Suppose that two CDMA sources emit two signals occupying the same band and featuring distinct aligned Walsh codes; then these signals would be uncorrelated in time. Now, suppose that the delay of these signals to the observation point where the E-field is measured is different for the two signals (for instance, they could have been emitted by separate antennas). So the Walsh sequences embedded in the respective time waveforms are not aligned in time anymore.
Q1: would the received signals (fields) at the observation point be still uncorrelated in time?
Q2: if not, would the degree of correlation be negligible? In other words, would the aforementioned mutual power terms be much smaller than the self power terms, in typical CDMA systems?
Thanks, I hope these questions make sense to you.
Antonio