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In this paper, a gain-increased method of cavity-backed slot antennas based on excitation of high-order substrate-integrated waveguide cavity resonance has been proposed. To this end, the metallic posts are introduced in a main cavity to excite the cavity's TM220 mode. Then the properties of the modified cavity's TM220 mode are used to feed an array of 2 × 2 slot antenna. Moreover, to acquire insight of modified cavity's field distribution, a comprehensive modal study was performed on the modified cavity to fully understand the effects of the dividing walls on the cavity's field distribution. Also, compared with HFSS, the modal solution that is proposed in this paper provide a considerable time and storage saving. To validate the simulated results, two types of the proposed antenna forming two different polarizations (horizontal and vertical) are analyzed, simulated, and fabricated. The proposed antennas exhibit relatively gain of 8.2 dBi at resonant frequency and high front-to-back ratio. In addition, the gain-enhanced method proposed in the present paper can be extended for using even higher-order cavity resonances, such as TM440, TM660 etc., if higher gain is desirable. The proposed antennas are suitable for using in many wireless communication systems and some radar systems.

The analysis and synthesis of metasurfaces are important because of their emerging applications in a broad range of the operational wavelengths from microwaves to the visible light spectrum. Moreover, in many applications, like optical nanoantennas, absorbers, solar cells, and sensing, the presence of a substrate is apparent. Therefore, understanding the effects of substrates upon the metasurfaces is important, as the substrates typically affect the resonance behaviors of particles, as well as the interactions between them. In order to consider the impacts of substrates, this paper develops a method for the characterization and homogenization of substrated metasurfaces. This approach is based on independent studies of the electromagnetic behavior of the constituting nanoparticles, and the interactions between them. It uses image theory to calculate the interaction constant tensors in the presence of a dielectric substrate. Then, the contributions of the quasi-static interaction fields of the primary and image dipoles are considered as a homogeneous sheet of surface polarization currents. Finally, the closed-form expressions for the interaction constant tensors are derived. To show the accuracy of our proposed approach, the numerical results of the method are compared to other approaches, as well as with those generated by a commercial EM solver, which are all found to be in good agreement. Moreover, the effects of the refractive index of the substrate, the geometric characteristics of the particle, and periodicity of the array are also investigated on the interaction constants. We believe that this methodology is general and useful in the design and analysis of substrated metasurfaces for various applications.

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