Multilayer frequency-selective surfaces as artificial substrates for broadband conformal arrays

Antenna bandwidth is determined by the antenna structure itself and the surrounding environment. Although many approaches exist for designing broadband antennas, attention in recent years has been on developing radiating elements for conformal vehicle installation. In these cases, bandwidth is limited by the characteristics of the substrate rather than the antenna element itself.; Recent efforts have been directed towards the development of bandgap or high impedance substrates to increase conformal antenna bandwidth. This thesis proposes and develops a new class of broadband substrates aimed at enhancing conformal array bandwidth performance. The proposed substrates are based on the well-understood frequency selective surfaces (FSS), possibly multilayered, and their design is intended to emulate a magnetic ground plane that generates a reflected field which enhances antenna gain. In contrast to previous FSS applications where the focus was on the amplitude of the reflected field, here the emphasis is on phase control and a class of novel FSS elements is introduced to increase design control and bandwidth performance. Both dipole and slot arrays designs are developed which demonstrate that significant bandwidth enhancements are possible using the proposed artificial substrates. A challenge in the analysis of these structures is a requirement to concurrently model periodic structures, each associated with different periodicities. To accomplish this, a new analysis method is introduced and employed to allow for full flexibility in the design of such non-commensurate array/FSS structures.; For even greater bandwidth enhancements, loading of the substrate and/or reconfiguration of the antenna element can be employed. Substantial effort is therefore placed on trade-off studies relating to gain vs. substrate loss, and a design is proposed which demonstrates a 2:1 bandwidth for a dipole array on a resistively loaded substrate. Similar designs are also proposed for slot arrays on a resistively loaded FSS and measured data are included for validation purposes. When the individual array elements are also reconfigured using switches (PIN diodes or Micro-Electro-Mechanical-Systems) to increase or decrease antenna element length, slot array operation from 800–3200 MHz can be achieved on a substrate that is 1.65&inches; thick. Novel slot designs are proposed for achieving even 10:1 impedance bandwidths.