I want to know the answer to the following question:
What can be used in place of  a standard transmission line?
All the background I'm provided with is that "In a so-called aperture antenna, such as a horn or parabolic dish, the "feed" may also refer to a basic antenna inside the entire system (normally at the focus of the parabolic dish or at the throat of a horn) which could be considered the one active element in that antenna system.". Is that enough to answer the question?
Answer: no