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In this article, a design method for the reflectionless absorber (RLA) is proposed based on the principle of the band-stop reflectionless filter (RLF). Compared with the traditional absorbing structures, the RLA can effectively absorb the electromagnetic (EM) waves within its operating band with small out-band reflection. Besides, the RLA has layer-independent characteristics due to its small reflection. Therefore, multiband and wideband RLAs can be achieved by simply stacking several single-band RLAs. After theoretical analysis and discussion of the single-band RLA, multiband and wideband RLAs are designed. Finally, two samples are fabricated to verify the presented design method. The theoretical calculated, simulated, and measured results agree well. [ABSTRACT FROM AUTHOR]

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]

An X-band leaky waveguide antenna (LWA) with high aperture efficiency and high power capacity is investigated in this paper. The antenna is mainly composed of two parts: a sectorial waveguide power divider and an LWA array. First, in the design of the power divider, the magnitude uniformity and phase consistency are ensured by adjusting the channel central angles and introducing phase adjusting structures, respectively. Then, the analysis and design of the LWA array are carried out. New formulas and conditions have been proposed for realizing uniform radiation distribution and maximum aperture efficiency. Five supporting beams are introduced to increase the antenna gain and power capacity. An LWA array as a prototype is fabricated and tested to verify the analysis and simulation. Experimental results agree well with the simulation. The return loss is better than 17 dB at the center frequency 9.7 GHz, the gain is 38.75 dB, and the corresponding aperture efficiency is 80.7%. The power capacity of the LWA array reaches 1.5 GW. These characteristics demonstrate that the proposed LWA array is suitable for radiating high power microwaves. The analysis and design method proposed in this paper is a useful guide for designing the high-aperture efficiency antenna in the future. [ABSTRACT FROM AUTHOR]

In this paper, a full solid angle scanning cylindrical-and-conical (CYLCON) conformal phased array antenna (PAA) is designed. First, a microstrip Yagi antenna with low profile and small size is proposed and discussed. Second, a cylindrical conformal Yagi antenna array consisting of 24 aforementioned 8-element Yagi antennas is designed and optimized. Simulation results show that the Yagi antenna array can realize low-elevation beam scanning in the region of 0 ^\circ \le \theta \le 30 ^\circ , 30 ^\circ \le \varphi \le 150 ^\circ with low sidelobe levels and sharp beams. Third, CYLCON conformal microstrip antenna arrays are developed to realize the broadside beam scanning. Afterwards, an integrated PAA by combining the aforementioned conformal arrays along with feeding networks is constructed to achieve full solid angle scanning. Finally, a prototype is fabricated, the measured results show that it can realize beam scanning in the regions of 0 ^\circ \le \theta \le 30 ^\circ , 30 ^\circ \le \varphi \le 150 ^\circ , and 30 ^\circ \le \theta \le 180 ^\circ , 60 ^\circ \le \varphi \le 120 ^\circ , which meet well with those of the simulated. By arranging proper number of arrays along the perimeter accompanied with the switchable feeding configurations, a full solid angle scanning can be achieved. [ABSTRACT FROM AUTHOR]