Bandwidth enhancement of a double-element Vivaldi antenna with sum and difference radiation patterns

Abstract

A two-port double-element Vivaldi antenna with enhanced bandwidth and two different radiation patterns in the E-plane is presented herein. The achieved bandwidth ranges from 2.6 GHz to 18 GHz, with a gain increasing from 7.3 dBi at 2.6 GHz up to 15.1 dBi at 18 GHz. The bandwidth extension is obtained in the base double-element Vivaldi antenna by reducing the distance between the two elements and elongating the inner flares, thus delaying the emergence of grating lobes. The mutual coupling level between the ports is further decreased by introducing two vertical metal slabs between the antenna elements. Some well-known methods are also adopted to improve the scattering parameters and enhance the radiation performance including etching elliptical corrugations on the outermost edges of the antenna, abruptly bending the inner edges, and incorporating a semicircle dielectric substrate lens into the antenna boresight. In order to realize the pattern diversity function, an ultrawideband 180° hybrid coupler is utilized to excite the antenna elements with in-phase and out-of-phase signals. For improved beam symmetry the antenna is designed such that the differential feeding results in the directive radiation pattern and the in-phase feeding yields a null in the main direction of the radiation.