Dual frequency broadband reflectarray element design

Abstract

The bandwidth limitation of a reflectarray is a consequence of the non-linear and high Q variation in the reflection phase which occurs when the element size is changed to produce the required progressive phase distribution across the antenna aperture. A significant increase in the bandwidth is shown to occur when the periodic structure of a grounded stacked rings or concentric rings generates two resonances which are closely spaced. This paper presents the reflection phase response of a two-layer array of orthogonally oriented concentric split rings for dual frequency broadband reflectarray. The concentric split ring concept is discussed in this chapter and the validity of the approach at X-band is confirmed by comparing the computed results, which is simulated by Micro-stripesTM simulator, and experimental results from waveguide simulator experiment. Good agreement is shown between the two sets of result. Simply by inserting gaps in the ring elements, it will suppress the interlayer coupling and produce polarisation sensitive scattering. The results demonstrate that these properties enable the reflection phase coefficients of a reflectarray to be independently optimised at two closely different frequencies.