A Compact Vivaldi-Shaped Array Using Antipodal Vivaldi Antennas to Stabilize the High-Frequency Radiation Pattern

In this study, a novel ultra-wideband antipodal Vivaldi antenna with a Chebyshev tapering profile and exponential slots is designed and measured. The dimensions of the proposed antenna are 95mm $ \times 100$ mm $ \times 0.127$ mm and the relative dimensions are $0.31\lambda _{0} \times 0.327\lambda _{0} \times 0.0004\lambda _{0}$ where $\lambda _{0}$ is the free space wavelength at the lowest operating frequency at 0.98 GHz for a $VSWR \leq 1.9$ . Several array configurations are proposed and all elementary array sources are combined in a mirror configuration, including the feeding part, to drastically reduce cross-polarization. First, a planar array is created at a distance $d=150mm$ between elementary sources. Then, from this primary source, an oblique array is created by inclining the two antennas at an angle $\theta $ , which cancels the ambiguity lobes in the upper frequency band. Finally, the single antenna is bent along a Vivaldi curvature, creating a mechanical tilt depending on the curvature parameters in H-plane. An array is formed by two curved Vivaldi antennas and exhibits a tilting effect with better compactness than the oblique array. For measurements, several foams with Vivaldi curvatures were created, allowing us to shape the Vivaldi antennas along various array distances, resulting in various beam shapes depending on the configuration used. The optimal distance $d=50mm$ provides a more stable radiation pattern across frequencies and cancels out ambiguity lobes for distances > $2\lambda _{0}$ . These Vivaldi-shaped arrays are measured and show good agreement with simulations.