Wideband, stub-loaded cross-dipole reflectarray elements for Ku band

Bandwidth enhancement of reflectarray has drawn the attention of researchers towards the development of wideband elements. The design of these elements is largely based on methods such as (i) use of multi-resonant or sub-wavelength elements, (ii) modification of substrate parameters, and (iii) multilayer (stacked patches) configuration. In method (i), cross-dipole based single layer elements have been widely investigated to achieve wideband performance for FSS, microstrip printed antenna, and reflectarray antennas. In this work, five different stub-loaded cross-dipoles with rings on substrates of various thicknesses and dielectric constants are designed and analyzed for reflection phase performance in Ku band, by using infinite (unit cell) array approach of CST MW Studio 2016. Effect of element geometry and substrate parameters (thickness and dielectric constant) on reflection phase bandwidth is examined. For a given dielectric constant, increasing thickness is observed to result in enhanced reflection phase bandwidth for four of these elements. Besides, for these elements, for a given substrate thickness, decreasing dielectric constant is observed to result in enhanced bandwidth. Interestingly, for the fifith element, the bandwidth appears to decline with increasing thickness, for a given dielectric constant. Also, for this element, the reflection phase does not seem to vary significantly as a function of dielectric constant. Bandwidths (±90° reflection phase) observed for these elements are typically in the range of 34.5% to 48.3%.