Answer
Two antennas driven by the same electrical signal emit coherent radio waves because the signal from both antennas is in phase and has the same frequency. However, it is not possible for two antennas driven by independent signals to emit radio waves that are coherent with each other. This is because if two antennas are driven by independent signals, the phase and frequency of the signals will be different, and the radio waves emitted by each antenna will not be in phase with each other.
Work Step by Step
Coherence means that the waves have a consistent phase relation between each other, the waves must have the same frequency and the same phase. If the antennas are driven by independent signals, the phase and frequency may vary and the radio waves emitted by each antenna will not have a consistent phase relation, therefore they will not be coherent.
Additionally, the radio waves emitted by each antenna will not interfere constructively, but destructively, resulting in a reduced amplitude of the overall signal.
In summary, it is not possible for two antennas driven by independent signals to emit radio waves that are coherent with each other because the phase and frequency of the signals will be different, and the radio waves emitted by each antenna will not be in phase with each other. Therefore, the radio waves will not interfere constructively, but destructively, resulting in a reduced amplitude of the overall signal.
