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In this article, absorbers with open boundary condition are analyzed theoretically. First, a complex analysis method is used to obtain integrations of the reflection and transmission over the whole frequency band for slab with general boundary condition, which can be regarded as a general extension of Rozanov’s discussion. Second, integration relations with open boundary condition for single-layer slab and multilayer slab are obtained successively. Third, theoretical limitations for the absorbers with open boundary condition are deduced. As an application, complete analytic limitations between the reflection, transmission, operating band, and thickness are provided for single-layer nonmagnetic absorber with small reflection and transmission required. Finally, after presenting optimal design method for single-layer nonmagnetic slab, several absorbers are designed as examples. [ABSTRACT FROM AUTHOR]

An ellipsoidal Luneburg lens (LBL) binary array is proposed and implemented for wide-angle scanning. In order to solve the occlusion problem between the lens elements in the array, the spherical LBL is transformed into the ellipsoidal LBL based on the transformation optics. The permittivity distribution of the LBL is revised to increase the lens’ aperture efficiency when the lens is not particularly large compared with the feed. Further, by introducing the local-beam shifting method, the number of feeds under each lens and the mutual coupling between the feeds can be reduced with the scanning characteristics remained. To validate the proposed design, a ${1 \times 2}$ ellipsoidal LBL array has been designed, fabricated, and tested. Each ellipsoidal LBL with 110 mm long-axis radius and 88 mm short-axis radius is fabricated by means of 3-D printing technology. Patch antennas operating at 2.25 GHz are employed as feeds. The measured results show that the proposed ellipsoidal LBL binary array can realize the maximum gain of 15.5 dB at zenith direction and 13.3 dB at 62°. The maximum scanning angle of ±68° can be achieved with a 3 dB gain reduction and −8 dB sidelobe. [ABSTRACT FROM AUTHOR]

A novel antenna integrated the advantages of the Yagi–Uda and the dielectric rod antenna (DRA) is presented in this communication. The antenna mainly consists of a tapered printed Yagi–Uda, a tapered dielectric cover, and a periodic dielectric rod. First, a tapered printed Yagi is designed as the primary feeder and embedded inside a tapered dielectric rod to improve the directive gain, radiation efficiency, and sidelobe levels. The influence of the dielectric cover to the Yagi is discussed. Then, a dielectric rod with triangular periodic surface is also loaded to the end of the dielectric cover to obtain higher gain and better front-to-back ratio. Finally, a sample of the antenna working at 8.5–9.7 GHz with 18 dBi maximum gain and −23.37 dB sidelobe level is designed. A prototype is fabricated and tested; the measured results match well with the simulated. Compared with the traditional Yagi–Uda antenna and DRA with the same length, the presented integrated antenna has higher gain with lower sidelobe level. [ABSTRACT FROM AUTHOR]