Design, fabrication and measurement of hybrid frequency selective surface (FSS) radomes

Abstract

In modern military platforms such as ships, aircrafts and missiles, frequency selective surfaces (FSS) are widely used for antennas and radar cross section (RCS) reduction. The RCS of complicated objects such as antennas are difficult or impossible to control over a wide frequency range. The most efficient and cost-effective approach in these situations is to shield the scattering object from the threat radars by making use of wide-band radar absorbing material (RAM) coating. If the object is an antenna, then obviously, the system served by this antenna cannot operate when it is stowed. An alternate approach is to cover the antenna with an FSS that is transparent at the antenna operating frequency, yet opaque at the threat radar frequencies. In this thesis, different types of FSS structures comprising slot elements and modified loop elements, namely single polarized loop FSS, have been investigated intensively with their applications to hybrid FSS radomes. Their resonance mechanisms and transmission properties are examined in detail. The main focus of the thesis is to design a hybrid FSS radome based on different unit element types. Complex dielectric constant measurements are conducted as aninput to the FSS radome design. Experimental results based on measuring the transmission curves of fabricated radome prototypes are supported by computer simulations. Transmission properties of the slot FSS structures and the single polarized loop FSS structures have been compared and discussed. In contrast with most of the published work in literature, transmission measurements are supported by the radiation performance measurements. Adaptation of the single polarized loop FSS radome to the slotted waveguide antenna has been achieved without any significant reduction in the radiation performance. The antenna with this metallic radome has the advantage of superior mechanical durability as well as reduced out-of-band RCS.