Loaded and Load-Less Supergain Parasitic End-Fire Arrays

This paper introduces a compact three-bent-dipole end-fire array operating at 916 MHz, exhibiting remarkably high realized gain in relation to its electrical size. The optimization process focuses on feeding the array elements to maximize directive properties in a chosen direction while upholding high efficiency as a constraint. Complex excitation coefficients are subsequently transformed into equivalent impedance loads for implementing a parasitic array. Two antennas are designed, fabricated, and characterized. For the first prototype (loaded), the central element is actively fed, and the external elements are loaded with reactive components. A second prototype (load-less) is designed to incorporate the required complex excitations by adjusting the imaginary parts of the dipoles through modifications in their vertical length. Both array versions are matched with a T-match on the active elements. Experimental results from differentially-fed fabricated prototypes reveal outstanding agreement between simulated and measured radiation properties. In the differential mode, a peak realized gain of 8.9 dBi at 910 MHz is achieved for the parasitic loaded array, and 8.3 dBi at 911 MHz for the load-less array.