I know this my sound a little bit basic but I know spiral antennas either planar or conical were developed by Rumsey,J Dayson,and et al;at the same time Raymond DuHamel and Dwight Isbell were developing log periodic antennas.But looking at the structure of spiral antennas you might think that they are also log periodic.I might be wrong,anyone with thought or suggestion?Any reading suggestion will also be appreciated.
Thank you
i am not expert on it. From my knowledge, the spiral antenna is a case for babinet principles and self-complementary antenna. The antenna and its complementary is the same. Hence, from Babinet principle, the product of input impedances of the antenna and its complementary counterpart is constant. Hence, for a self-complementary antenna, the input impedance is constant and not dependent on frequency. This is a reason why it can serve as a broadband antenna. I think it is not the same as log antenna.
An Archimedean spiral is not log periodic - it has a constant pitch, the track and gap stay the same width, the radius increases by a constant distance each turn, and the angle of the spiral decreases every turn.
Spiral antennas with constant angle are log periodic, they increase by a constant proportion each turn, and the tracks and gaps get thicker every turn.
Both types are used, I am not sure how the performance differs between them, but I expect it does.
@Malcolm Thanks a lot for your response,that is exactly what I have been thinking but I couldn't get my mind around it so easily.
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