Quasi-Gregory Antenna for Subnanosecond Impulse Radiation

A quasi-Gregory antenna was designed for subnanosecond impulse radiation. It consists of an ellipsoidal feed, a mirror plane, and a paraboloidal reflector. The second focal point (F₂) of the ellipsoidal dish can be regarded as the radiation center of the feed because electromagnetic waves launched from the first focal point of the ellipsoidal dish (F₁) are in phase when arriving at point F₂, according to geometric optics. The equivalent radiation angle at point F₂ is a spherical sector; therefore, it can be designed to geometrically cover the paraboloidal reflector precisely. Gaussian pulses with widths of 200 and 330 ps are used to test the performance of this proposed impulse-radiating antenna (IRA). The 3-dB beamwidth of this proposed IRA with a 1.5 m aperture diameter for the paraboloidal reflector is less than ±3° in the H-plane and less than ±5° in the E-plane. Compared to some existing IRAs, this quasi-Gregory antenna is also suitable for radiating pulses in the subnanosecond regime.