When I studied elementary antenna's theory, I saw that the resistance (for simplicity let's consider only the resistive terms) of an antenna Ra is made of:
1) a parasitic resistance Rl, which causes antenna losses.
2) a radiation resistance Rr which is in practice the free space resistance, and it is like a load resistance if for instance we think at a transmitting antenna.
Now I have two questions:
about 2), from its definition it seems to me that the radiation resistance should depend on the space conditions (rain, humidity, temperature, presence of turbulences etc). If it is true, how can we design a correct matching network between an antenna and a transmission (since it is not a fixed value)?
how can I physically evaluate the impedance of an antenna? For instance a stylus antenna (I must connect it to a coaxial cable and so I thought that its knowledge is important to choice the correct matching network)?