Closed-Form Expressions of the Axial Prompt Responses of a Defocused Parabolic Reflector Antenna

In a previous paper, closed-form time-domain expressions of the prompt responses along the axis of such an antenna have been derived, assuming a focused primary point source. In this communication, the formulas are generalized to a defocused primary point source laying on the axis. The new closed-form expressions are valid along the axis, near and far from the reflector. A closed-form expression of the impulse duration is also given. The analytical results show that defocusing may produce significant transient electromagnetic field on the axis.