Aperture efficiencies for IRAs

The IRA (impulse radiating antenna), consists of a special kind of conical TEM (transverse electromagnetic) feed launching a step-rising wave on an aperture after conversion of the spherical wave to a plane wave via a paraboloidal reflector (or a lens if desired). The radiated field has an important part which is a narrow impulse, although there is a comparatively low-amplitude, slow undershoot to give a net zero time integral in the far field. The feed arms are terminated (primarily resistive) at the reflector to minimize multiple reflections and to improve the limited low-frequency performance by balancing the electric and magnetic dipole moments for forward (from the reflector) radiation. There are various possible configurations of the TEM conical feed and feeding coaxial cables (and possible baluns as well) to allow for a variety of characteristic impedances. Aperture efficiencies for IRAs are evaluated.<>