Optimizing the Feed Impedance of Impulse Radiating Antennas Part I: Reflector IIUs

., When designing a reflector Impulse Radiating Antenna, one must choose an appropriate feed impedance. Using the simplest approximations valid for high feed impedances, one finds that lower feed impedances are always prcfcrablc. However, low feed impedances imply thick feed arms, which incrcasc feed blockage for many designs, thus reducing the radiated field. Low feed impedances also lead to a breakdown of the approximation that the cffcctivc aperture height is equal to the radius of an aperture for circular apertures. Thus, even when there is no feed blockage, there is a reduced aperture height at low feed impedances. We calculate here the radiated field based on a contour integration technique that takes into account feed blockage. With these calculations, one can find the optimal feed impedance for a given configuration of feed arms. The analysis is valid in the limit of fast risetimes, and is carried out for three different feed structures. ..