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Because of its good beam coverage and beam scanning abilities, the Luneburg lens (LL) is a promising multibeam antenna for the fifth-generation (5G) wireless communications. However, the conventional LL has a spherical formfactor, exhibiting a large volume, large weight, and curvature surface, all of which limit the adoption of an LL in practice. To alleviate the problem, a flat LL is proposed, with transformation optics to convert the conventional spherical structure into a flat one. However, a high permittivity distribution is usually required in a transformed flat LL, causing of server reflections, which further degenerates the performance of the LL in terms of both gain and efficiency. In this article, a millimeter-wave dual-polarized flat Luneburg lens antenna (FLLA) is proposed following the transformation of optics, and implemented using multilayer PCBs, where a reflection cancellation method is introduced to optimize the multilayer structure to improve its gain and efficiency. The designed FLLA is exemplified in the Ka-band and fed using a dual-polarized patch antenna. The measured results show that the designed FLLA has an impedance bandwidth (|S11| ≤ −10 dB) of 27.5–32.6 GHz, a gain of 16.8–18.8 dBi over the operating band, and a beam scanning range up to ±25°/±24° with a gain loss of 1.72 dB/1.7 dB in either E- or H-plane, respectively. [ABSTRACT FROM AUTHOR]

Because of its good beam coverage and beam scanning abilities, the Luneburg lens (LL) is a promising multibeam antenna for the fifth-generation (5G) wireless communications. However, the conventional LL has a spherical formfactor, exhibiting a large volume, large weight, and curvature surface, all of which limit the adoption of an LL in practice. To alleviate the problem, a flat LL is proposed, with transformation optics to convert the conventional spherical structure into a flat one. However, a high permittivity distribution is usually required in a transformed flat LL, causing of server reflections, which further degenerates the performance of the LL in terms of both gain and efficiency. In this article, a millimeter-wave dual-polarized flat Luneburg lens antenna (FLLA) is proposed following the transformation of optics, and implemented using multilayer PCBs, where a reflection cancellation method is introduced to optimize the multilayer structure to improve its gain and efficiency. The designed FLLA is exemplified in the Ka-band and fed using a dual-polarized patch antenna. The measured results show that the designed FLLA has an impedance bandwidth (|S11| ≤ −10 dB) of 27.5–32.6 GHz, a gain of 16.8–18.8 dBi over the operating band, and a beam scanning range up to ±25°/±24° with a gain loss of 1.72 dB/1.7 dB in either E- or H-plane, respectively.

A planar asymmetric substrate integrated wave¬guide leaky wave antenna is proposed with open stop band suppression and radiation efficiency equalization through broadside for the Ku-band. The stop-band behavior exhib¬ited at broadside in the 1-D periodic structure is signifi¬cantly reduced using reflection cancellation technique by placing the two slots at a quarter distance within the unit cell. Furthermore, asymmetric technique is applied. The asymmetry is introduced with respect to both axial and transversal axis of the structure so as to match the at-broadside Bloch impedance and off-broadside Bloch im¬pedance. This provides total open stop band suppression and radiation efficiency improvement as well as equaliza-tion through broadside. The problem is analyzed with the help of Bloch impedance behavior. For illustration of the above techniques; single slot, double slot and asymmetric designs are developed for the proposed leaky wave an¬tenna. The final asymmetric design after optimization is fabricated. Measured results are almost consistent with the simulation results with complete suppression of open stop band, efficiency improvement and equalization through broadside providing continuous beam scanning from –32° to +27° with constant gain of ~12.5 dBi.

A planar asymmetric substrate integrated waveguide leaky wave antenna is proposed with open stop band suppression and radiation efficiency equalization through broadside for the Ku-band. The stop-band behavior exhibited at broadside in the 1-D periodic structure is significantly reduced using reflection cancellation technique by placing the two slots at a quarter distance within the unit cell. Furthermore, asymmetric technique is applied. The asymmetry is introduced with respect to both axial and transversal axis of the structure so as to match the atbroadside Bloch impedance and off-broadside Bloch impedance. This provides total open stop band suppression and radiation efficiency improvement as well as equalization through broadside. The problem is analyzed with the help of Bloch impedance behavior. For illustration of the above techniques; single slot, double slot and asymmetric designs are developed for the proposed leaky wave antenna. The final asymmetric design after optimization is fabricated. Measured results are almost consistent with the simulation results with complete suppression of open stop band, efficiency improvement and equalization through broadside providing continuous beam scanning from -32° to +27° with constant gain of ~12.5 dBi. [ABSTRACT FROM AUTHOR]