Developments of a reflectarray and its element characterization at millimeter wavelengths

Abstract

We present design and simulations of a reconfigurable reflectarray suitable for use as a sub-reflector within a confocal millimeter-wave imaging system. The performance of various reflectarray designs for use within a confocal imaging system are evaluated, e.g. phase quantization, feeding field. A quantized-particle-swarm optimization algorithm is discussed and applied to the reflectarray phase distribution in order to circumvent common challenges, such as the effects of the periodic phase error across the aperture, in addition to the generation of grating lobes due to aperture discontinuities. The reflectarray elements are based on a microstrip structure integrated with MEMS-based phase shifters in order to yield dynamic reconfigurability of the aperture. Both 1- and 2-bit phase quantization is considered. A reflectarray is characterized in a near-field measurement range; reflections from individual reflectarray elements are imaged at a distance on the order of a wavelength. Both the realized reflection phase and magnitude of the specular reflection are measured, yielding accurate characteristics of reflectarray element performance when compared to standard beam pattern measurements. A near-field measurement system is configured and tested at 120 GHz. The lateral resolution and phase measurement accuracy were measured to be 0:56λ and ±4° respectively. A static reflectarray is tested in the measurement system, and the reflection coefficient of the individual elements measured.