Consider an antenna as a 2-port reciprocal network such that you may have S11 reflection at the feedpoint, but also S22 reflection back into freespace.
S11 is well understood and measured because that is usually what you care about for transmission, but this question about S22: impedance mismatch between the antenna and freespace (376Ω) will reflect the signal you want to recieve, back into freespace away from the antenna.
- Are their known S22 freespace reflection values for different kinds of antennas?
- Helical, ...
- Preferrably, can S22 be inferred or calculated from S11?
- If not then can S22 be simulated or measured?
- Other considerations?