Development of metamaterials for wideband antenna applications

Abstract

Many low-profile, broadband antennas that operate in the relatively low frequency ranges desired for certain mobile RADAR and electronic warfare (EW) applications radiate bi-directionally. Thus, a low-profile, ultrawideband ground plane is clearly necessary to back these antennas and provide for enhanced performance. To achieve the desired performance with minimal limitations, it is logical to lean towards a hybrid design that implements a combination of ground plane options. With a hybrid approach ultrawideband operation can be achieved in a low-profile package. This dissertation presents the design and analysis of a low-profile, ultrawideband hybrid EBG/ferrite structure. The hybrid structure consists of an EBG structure implemented with a slab of ferrite absorber resting on the backing of the structure. Reflectivity and phase simulation analyses indicate that the hybrid structure offers ultrawideband operation beginning in the hundreds of megahertz, achieving an operational bandwidth exceeding 40:1 starting at 120 MHz. Simulation analyses of the hybrid structure implemented with Raytheon's ultrawideband long slot array antenna further validate the performance of the hybrid structure. An equivalent circuit model of the hybrid structure was developed to provide a more in-depth understanding of the operation of the structure in regards to its dimensions and material properties. It is shown that unlike the circuit models for traditional EBG structures, the circuit model developed for the hybrid structure contains a resistance representing the permeability losses due to the ferrite. Additionally, it is shown that the inductive and resistive circuit components are frequency dependent and depend on the frequency dependent characteristics of the ferrite. A transverse electromagnetic (TEM) cell was designed and fabricated to experimentally analyze the performance of the hybrid structure. Presented experimental results of the reflectivity and phase analyses show good correlation with the simulated results. Experimental analyses of the surface-wave suppression capabilities of the hybrid structure indicate suppression of at least 20dB across the band and suppression exceeding 60dB in the "EBG structure" region of operation compared to an electric conductor. Thus, the implementation of the hybrid EBG/ferrite structure as a ground plane will allow for the practical and effective implementation of new ultrawideband antenna systems.