Abstract
The gradient-index (GRIN) Luneburg lens antenna offers significant benefits, e.g. high aperture efficiency, low-power, minimal cost, wide beam scanning angle and broad bandwidth, over phased array antennas and reflector antennas. However, the spherical shape of the Luneburg lens geometry complicates the integration of standard planar feed sources and poses significant implementation challenge. To eliminate the feed mismatch problem, the quasi-conformal transformation optics (QCTO) method can be adopted to modify the lens’ spherical feed surface into a planar one. However, Luneburg lenses designed with QCTO method are limited to poor performance due to the presence of the reflections and beam broadening arising from the quasi-conformal mapping. In this paper, we present a new method of implementing QCTO-enabled modified Luneburg lens antenna by designing a broadband anti-reflective layer along with the modified lens’s planar excitation surface. The proposed anti-reflector layer is inherently broadband in nature, has a continuously tapered inhomogeneous dielectric permittivity profile along its thickness, and ensures broadband impedance matching. To show the new QCTO modified Luneburg lens antenna, an example lens antenna was designed at Ka-band (26–40 GHz) and fabricated using fused deposition modeling (FDM) based additive manufacturing technique. Electromagnetic performance of the lens antenna was experimentally demonstrated.
Highlights
Modern wireless communication systems are increasingly focusing on high gain, agile, wide-angle, multiband and multibeam beamscanning antenna elements for applications in radar, electronic warfare, wireless and satellite communication systems[1,2,3,4]
As quasi-conformal transformation optics (QCTO) method is restricted in two-dimensional geometry, here, we conducted a quasi-conformal mapping of the two-dimensional Luneburg lens to modify it into a two-dimensional flat-bottom lens
We have showed the design and implementation of a flat-bottom modified Luneburg lens antenna for practical beam scanning antenna applications
Summary
Modern wireless communication systems are increasingly focusing on high gain, agile, wide-angle, multiband and multibeam beamscanning antenna elements for applications in radar, electronic warfare, wireless and satellite communication systems[1,2,3,4]. While the QCTO method offers significant benefits to implement a modified Luneburg lens antenna with a planar feed surface using all-dielectric materials, this technique is offset by the presence of r eflections[6] and these reflections arise from the permittivity mismatches between the lens’s planar feed surface and air. To minimize the reflections of the QCTO modified Luneburg lens and improve the antenna gain over a broad frequency band, the feed sources of the modified lens antenna need to be designed very carefully, e.g. implementing dielectrically loaded antenna feed array, to ensure uniform impedance matching and high gain. Implementing an array of dielectrically loaded antenna feeds will be very difficult due to the inhomogeneous nature of the antenna feed surface’s permittivity profile
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