Reflector Impulse Antenna of High Electrodynamic Potential

A few versions of impulse antennas are studied with the aim of suggesting an optimal design of the feed line and radiator for the reflector-based antenna and ensuring operation of the facility at high voltages and under field conditions. The high-voltage system described as the final choice is intended for shaping and radiating electromagnetic pulses of ultrashort duration, while maintaining the proper electric strength of its components. It is characterized by an electrodynamic potential (field-range product) W = 1.2 MV. The system is a variant of the half-reflector impulse antenna design, involving a half-circular parabolic reflector that is excited through a nonuniform dual-line feeder of simple geometry.

I. Introduction

Live tests of electronics for electromagnetic compatibility and resistance to ultrashort pulsed (USP) electromagnetic fields require availability of sources and antennas that are capable of producing radiated electric fields of a few 100 kV/m in intensity [1]. The class of emitting structures that are best suited for the purpose includes the reflector impulse antenna (IRA) and half-IRA (HIRA), i.e., reflector and half-reflector-based impulse radiating antennas [2]–[5]. The far-field boundary of USP signals can be estimated as a few tens of meters, taken the characteristic antenna size and maximum frequency from the spectral content of the pulsed signal . Hence, the corresponding electrodynamic potential (a.k.a. field-range product) of the appropriate antennas, , should be in excess of 1 MV, where is the absolute value of the field strength on bore sight and is range from the aperture plane. Their radiation efficiency depends essentially on the pulse shape as provided by the primary source of the electric impulse and parameters of the antenna. An analog of the gain parameter, in the case of an impulse antenna, is the factor of merit (FOM) defined as , where is the pulse amplitude at the antenna input [4]. The radiated field strength at a distance in the far-field region can be estimated from

$$E(r,t)=\bigg ({{h_{A}}\over{2\pi c\eta}}\bigg)(r)^{-1}\bigg ({{{dU}_{0}}\over{dt}}\bigg)\eqno{\hbox{(1)}}$$ where is the effective antenna height, is the speed of light, and is the feeder-to-free space impedance ratio [5]. Thus, the FOM can be written as $$F_{W}={{h_{A}}\over{2\pi c\eta t_{R}}}\eqno{\hbox{(2)}}$$ implying that output parameters of an impulse antenna are determined, for a specified feed voltage , by the pulse rise time, , and design of the antenna. (The characteristic pulse frequencies are , where and are the higher and the lower frequency, respectively, in the spectral content of the pulse [3].)