Reduction of Cross Polarization Level in Connected Slot Arrays using Artificial Dielectric Layers with Vertical Metallic Inclusions

Abstract

The interest for phased array antennas has increased over the past years along with the need for wide bandwidth arrays. Connected arrays are becoming more prevalent as a well suited solution to achieve the desired bandwidth. In order to increase the bandwidth and the scan angle of this type of array, horizontal artificial dielectric supersaturates have been used with good results. However, those superstrates come with an increase in cross polarization. The cross polarization of connected arrays with isotropic dielectric substrates and superstrates is thoroughly investigated in this thesis, along with an analysis on the cross polarization of the connected array with artificial dielectrics. In order to reduce the cross polarization as a result of that superstrate, a novel artificial dielectric is introduced which implements vertical vias to form a wire medium. For this medium a method of moments analysis is performed and a closed form expression is found. Additionally, the wire medium is implemented in the horizontal artificial dielectric to form the top-hat loaded wire medium as a solution to the restricted height between layers of the artificial dielectric slab. The wire medium increases only the z-component, since the wire is oriented vertically, of the effective permittivity without impacting the other effective constitutive parameters. The increase of the refraction index for transverse magnetic wave reduces the cross polarization level and aids in the matching for E-plane scanning, while maintaining a decay over the scan angle. However, a trade off between the reduction in cross polarization and the E-plane scanning is observed. This trade off is a result of the large z-component of the effective permittivity which promotes the propagation of the TM0 surface wave mode. The effectiveness of this novel structure is shown by considered a satellite communication application for simultaneous operation in the Ku- and Ka-transmit bands with a scan angle up to 60 degrees . A design for this application is performed with good matching, -10dB for broadside and -6dB for scanning in both E- and H-plane, and with a low cross polarization level of < −10dB. An evolved design with the manufacturing necessities, such as bonding layers and support layers, is obtained which exhibits a cross polarization level < −15dB with the use of the introduced wire medium, however, the layer height restriction set by the manufacturer and the feeding structure still provide a challenge at the frequency bands which are considered.