Aytaç Alparslan

A small-sized reflectarray antenna array with compact production specifications is designed and fabricated for high-speed Ka-band communication systems. In the design phase, firstly, the reflection characteristics of unit cells used in the reflective surface are obtained by the full wave computational analysis tool, CST Microwave Studio. Secondly, an aperture efficiency analysis is carried out to determine the physical size of the reflectarray and the distances between the feeding antenna and the individual unit cells. Then, the entire reflectarray antenna is analyzed by array theory to obtain geometrical dimensions to be used in the fabrication phase. These results are verified by CST Microwave Studio and similar fabrication guidelines are obtained for both TE and TM polarizations. In the fabrication phase, the carefully tailored design parameters of the unit cells are used to build the antenna and measure important parameters such as radiation patterns, gain, cross polarization levels and S11 parameters, which agree with the results obtained in the design phase. The proposed reflectarray antenna makes it possible to support dual-polarized multi-beams in the range 18-20 GHz with stable gain behavior, which makes it possible to use it in high speed 5G satellite communication systems.

A dual-band, dual-polarized frequency selective surface (FSS)-backed multilayer reflectarray antenna is designed for 5G high-speed satellites operating at Ka-band uplink and downlink frequencies (20/30 GHz). A reflectarray antenna system consists of two reflectarrays that are separated from each other by an FSS layer that behaves as a planar bandpass filter at Ka-band satellite uplink frequencies. Each reflectarray antenna is designed with dual-polarized unit cells. In order to achieve a uniform phase distribution across the reflectarray surface, physical dimensions and positions of the unit cells with a fixed periodicity are carefully chosen. The FSS conductor is etched to the bottom layer of the 30 GHz reflectarray substrate to save cost and weight. The reflectarray performance is analyzed by using CST Microwave Studio and array theory. A prototype is fabricated, and the results are experimentally verified. The gain of the reflectarray is measured as 21.13 dBi and 26.94 dBi at 20 and 30 GHz, respectively. A crosspol level of more than 35 dB is observed at both frequencies. The simulated and measured results show that the proposed reflectarray is suitable for high-speed Ka-band satellites.

In this paper, a fast and simultaneous integration routine tailored for obtaining results of multiple numerical integrations is introduced. In the routine, the same nodes are used when integrating different functions along the same integration path. In the paper it is demonstrated by several examples that if the integrands of interest are similar on the integration path, then using the same nodes decreases the computational costs dramatically. While the method is introduced by updating the popular Gauss-Kronrod quadrature rule, the same steps given in the paper can be applied to any other numerical integration rule.

Layered media Green's functions (LMGFs) are obtained for line sources with complex longitudinal wavenumbers in planarly layered media by numerically evaluating Sommerfeld integrals. The results obtained in this article can be applied to the numerical analysis of structures in layered media composed of any combination of right-handed materials (RHMs) and left-handed materials (LHMs). In the derivation, due to the complex-valued longitudinal wavenumber values, two different boundary conditions are used to include plane waves with: (i) decaying and (ii) outgoing Poynting vectors in the LMGFs. As a result, two completely different LMGFs are obtained by using two different radiation conditions and corresponding Sommerfeld integration paths (SIP) that are rigorously tailored on the complex integrand plane. In this work, all the necessary numerical tools for calculating the 2-D LMGFs are provided to be implemented in a computer program from scratch.

Spectral properties of the modes supported by plasmonic waveguides in planarly layered media are studied by the method of Multiple MultiPoles (MMP). It is shown that the most important entities in the mode analysis are the wavenumbers of the upper and lowermost layers and the wavenumbers of the guided waves supported by the layered medium. These wavenumbers introduce branch points and associated branch cuts on the complex plane where the out-of-plane wavenumbers of the modes are searched. These branch points and associated cuts make the mode analysis in layered media more demanding than the mode analysis in homogeneous media, where there is only one branch point and associated branch cut related to the wavenumber of the homogeneous medium. Several numerical examples are given to address the differences introduced by the layered media in the mode analysis and guidelines that can be used in any well-known computational electromagnetics method are provided.

Spectral properties of line sources carrying electric or magnetic current placed in a planarly layered medium are analyzed. It is shown that when the current along the line varies in the longitudinal direction by an exponential function with a complex exponent, classical Sommerfeld radiation condition that ensures outgoing and decaying fields simultaneously cannot always be used. Instead, depending on the exponent and the material properties of the layered medium, outgoing and exponentially increasing or incoming and exponentially decreasing waves are generated. This property is not observed when the exponent is real where the classical Sommerfeld radiation condition is fulfilled. In this article, an in-depth analysis of layered media is first performed in spectral domain as a function of the longitudinal dependence of the line sources. Then, the fields generated by the line sources are obtained by Sommerfeld integrations using two different radiation conditions separately. The effect of the radiation condition on the fields are discussed both in the spectral and spatial domains. In addition, field patterns are compared with the results obtained by finite element method (FEM) combined with perfectly matched layers (PMLs) and several guidelines for increasing the efficiency of simulations by FEM are introduced.