Design and Test of a Half Reflector Impulse Radiating Antenna with Feed-Point Lens

A feed-point lens is used to match an electrically large, oil filled, coaxial waveguide to the feed arms of a high-voltage half reflector impulse radiating antenna (HIRA). Theory and designs are for rotationally symmetric lens and transmission line systems feeding reflectors having focal-length-to-diameter ratios (F/D) of 1/4. Also developed are theory and designs for systems feeding reflectors having larger F/D ratios by retaining a rotationally symmetric lens design while moving the inner feed conductor off axis. A scale-model HIRA was built to confirm the theory and design. Complex permittivity measurements were performed on the lens material. Finally, a full-size HIRA with a 24 cm diameter titanium dioxide/epoxy lens feeding a 1.83 m diameter reflector with F/D of 114 was built. The step response was an impulse with full width half maximum of 70 Ps. The measured aperture height of the antenna was 0.36 m.