Electromagnetic pulses radiated by parabolic antennas and similar structures are needed in many applications like air and ground penetrating radar or high power microwaves (HPM) weapons. In this paper, an approach based on Skulkin and Turchin's work and on physical optics approximation in the time domain is developed to determine the radiated fields. Closed-form time-domain expressions of the electromagnetic step and impulse responses, along the axis of a classical parabolic reflector antenna, are derived. A closed-form expression of the impulse response duration is also given. The obtained E-field and H-field formula are valid along the axis, both near and far from the reflector. Using these closed-form expressions, the radiated fields are computed by means of a convolution product of the primary source excitation and the impulse response. Numerical results have been obtained in the case of a causal sine and a generalized Gaussian impulse excitations to illustrate some specific transients effects which occur with such an antenna

Closed-Form Expressions of the Axial Step and Impulse Responses of a Parabolic Reflector Antenna

A time-domain (TD) analysis of ellipsoidal reflector antennas is presented to predict the transient scattered fields when it is illuminated by a cosine-tapered and transient-step feed radiation whose phase center is located at the nearby focus. A transient-step function of the feed's radiation is considered because it will produce an impulsive response near the second focus of the reflector as interested in the applications of impulse-radiating antennas. This TD solution is in a closed form and remains valid both near and far from the reflector, and can be used via the convolution theorem to efficiently obtain the early time transient fields generated by the same ellipsoidal reflector antenna when it is illuminated by a realistic finite-energy pulse which emanates as a spherical wave from the focus. Numerical results are presented for the transient fields both near and far from the reflector.

Analytic Transient Analysis of Radiation From Ellipsoidal Reflector Antennas for Impulse-Radiating Antennas Applications

Cet article decrit une methode semi-analytique du calcul du champ electromagnetique rayonne par une antenne a reflecteur parabolique. Basee sur l’approximation de l’optique geometrique dans le domaine temporel, la methode s’appuie sur les travaux de Skulkin et Turchin sur le rayonnement de reflecteurs plans. Elle tient compte de la polarisation de la source primaire ainsi que de sa defocalisation possible. Les resultats numeriques presentes illustrent son egale capacite a simuler en regime impulsionnel ou frequentiel, en regime transitoire ou etabli, le rayonnement electromagnetique dans la zone eclairee, en tout point proche ou eloigne du reflecteur. Avec cette methode, quelques secondes de calculs sur un ordinateur disposant d’un processeur Rise a 400 MHz suffisent pour simuler le comportement electromagnetique d’une telle antenne. La methode a ete validee par comparaison avec les resultats de la litterature sur le sujet et par verification du bilan de puissance.

Le Rayonnement D’une Antenne Parabolique Par Une Approche Temporelle Semi-Analytique

Due to the development of ultra wide band systems or high power microwave weapons, the parabolic reflector antenna operating in pulsed mode remains an interesting case of study. Usually, methods for evaluating the electromagnetic field radiated are performed in the frequency domain and numerous computer codes are available for calculating this field. Then, the time domain behaviour is investigated by means of a Fourier transform. The inconvenience of this approach is that, for the particular case of the parabolic reflector operating in pulsed mode, this leads to a prohibitory CPU time. To cure partially this issue, we propose a full analytical formulation of the impulse response field of such an antenna. The E-field and the H-field formulas are valid along the axis both near and far the reflector. These analytical expressions are based on the Skulkin and Turchin?s work and on physical optics approximation in the time domain. Numerical results are given to illustrate some specific transients effects of such an antenna.

A full analytical formulation of the impulse response of the parabolic reflector antenna along its axis

http://ieeexplore.ieee.org/iel1/2213/3475/00122011.pdf

E. Kramer

Papers

Correction to “Short-pulse excitation of reflector antennas”