Antipodal Vivaldi antenna for sum and difference radiation patterns with reduced grating lobes

Abstract

A new design of an E-plane double-element Vivaldi antenna with sum and difference radiation patterns is presented in this letter. The antenna operates in the frequency range of 2.3–15 GHz (ratio of 6.5:1) with the highest grating lobe level of −10 dB at 15 GHz and competitive gain performance from 6.8 dBi at 2.3 GHz up to 14.7 dBi at 15 GHz. The grating lobes are reduced effectively by decreasing the distance between the two input ports to one wavelength at the highest operating frequency. The active S-parameters of the antenna are improved using modifications of the geometry, including a new method consisting of an increased length of the internal flares, as well as combinations of known methods such as elliptical corrugations on the outer edges, and optimal shaping of inner edges of the antenna. The gain is also improved by the addition of a dielectric lens, which also provides extra space for lengthening the internal flares. The proposed double-element antenna satisfactorily provides the sum and difference radiation patterns when fed by a wide band rat-race coupler. To warrant a near-ideal beam symmetry, the antenna is designed so that the directive radiation pattern occurs when the antenna elements are fed by out-of-phase signals, i.e., when the difference (Δ) port of the coupler is excited.