Twin Orthogonally Polarized UWB Aperture Antenna Elements With Optimized Profile Feed for Optimal Adaptation

The objective of this letter is the design of twin orthogonally polarized ultrawideband (UWB) antenna elements with the lowest return losses posible, low mutual coupling between both polarizations, frequency-stable radiation pattern, and suitability for integration into an array. In order to satisfy the array integration and low mutual coupling criteria, two 2-cm radius circular apertures with perpendicular feeds were chosen as the starting point of the design. The profile of the feed for both apertures was optimized in order to minimize the return losses in the 3-11-GHz frequency band using a simulated annealing algorithm together with the finite element method (FEM) as the analysis tool. After the design and optimization procedure, a prototype was built and measured. Return losses of less than 15 dB were measured in the entire UWB band starting from 3.4 GHz for each port, while mutual coupling fell below the -20-dB limit for the same frequency band. Measured radiation patterns show 15 dB of difference between the copolar and cross-polar components and the pattern stability in directions with maximum radiation. Finally, good agreement between simulated and measured results serves to validate the optimization method.