Physical optics uses things that can be measured. We can measure both currents and fields, but auxiliary vector potentials have no physical reality, only mathematical artifacts that simplify Maxwell’s equations. Nevertheless, the auxiliary vector potentials provide simple models for problems that enable simple mental pictures, as shown earlier, but we cannot easily formulate them into a systematic analysis tool for antenna problems.
The physical optics analysis method combines the use of Green’s functions to calculate fields radiated by a given distribution of currents and then uses boundary conditions to determine the currents induced on objects due to incident fields. We compute the effects of a mounting structure by inducing currents on it and adding their radiation to the antenna pattern. The method assumes that radiation from the induced currents on the structure does not change the initial currents.
We start analyses from either currents or incident fields and work from those. The resonant structure of many antennas determines the approximate current distribution that we normalize to the radiated power.We calculate the fields from these currents. Physical optics can use an iterative technique to calculate incremental currents induced on the original radiators and improve the solution, but we usually just sum the radiation from the original currents to the radiation from the induced currents. The second starting point for physical optics can be incident fields. These could be plane waves or could be fields found from the measured radiation patterns of antennas: for example, the pattern of a reflector feed. We add the radiation from the induced currents to the incident waves. |
