Deconvolution of target signature for a scene with bistatic impulse radiating antennas and a sphere
A model for an impulse radiating antenna (IRA) has been developed in WIPL-D. A scene using a bistatic pair of these IRAs is modeled with a sphere target and is simulated in the frequency domain. The input to the antenna is a Gaussian pulse, and the current on the receive antenna is plotted vs. frequency. This receiver response is proportional to the scattered field from the sphere. The frequency domain data are processed to give the time domain response. The objective of this work is to deconvolve the signature of the scatterer from the receiver transient response. Additional separate simulations for each scene component and electromagnetic interaction were needed and were performed using WIPL-D. The process is successful for this scene, which does not include a ground plane. The analysis of the simulated data and deconvolution of the target signature are done in Matlab.
Optimization of the TEM feed structure for four-arm reflector impulse radiating antennas
This paper considers the optimization of the feed arm geometry of four-arm crossed-coplanar plate impulse radiating antennas (IRAs) when the angular position and extent of the arms are taken as free parameters. Previously, optimization of this class of antenna considered only the symmetric case where the two pairs of crossed feed arms were perpendicular to each other. Comparison is made using the prompt aperture efficiency, and the results indicate that the efficiency of four-arm IRAs can be increased from /spl sim/25% for the perpendicularly crossed arms to /spl sim/35% for the optimum configuration. In addition to the optimization, the feed impedance of coplanar feeds is presented for general values of feed arm angle and plate width, and the optimum feed impedance is computed for each feed arm angle. The results can be used to design the optimal four-arm IRA with an arbitrary specified input impedance.
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.<<ETX>>