Engineered materials, such as new material composites, electromagnetic bandgap and periodic structures have received strong interest in recent years due to their extraordinary and unique electromagnetic behavior. Recently, a new class of magnetic photonic crystals (MPCs) and Double Band Edge (DBE), displaying spectral nonreciprocity, were introduced. Studies of these crystals have demonstrated that MPCs exhibit interesting phenomena which can be readily understood from the k-w diagram of the propagating Bloch modes. Specifically, waves entering the MPC or DBE crystal exhibit (a) drastic wave slow down, (b) significant amplitude growth and (c) minimal reflection at the interface of the crystal with free space. The latter makes them attractive for antennas applications, high sensitivity microwave detectors, and very small microwave devices due to inherent miniaturizations afforded by the high contrast dielectrics. This property also distinguishes them from other photonic or periodic structures associated with bandgap phenomena.

This presentation will cover the basic microwave properties [1] of these crystals both mathematically and experimentally. Two dimensional and three dimensional models will be presented demonstrating the very high sensitivity and field growth associated with these crystals. However, a major part of the presentation will be on the development of realistic anisotropic periodic structures using a combination of layers constructed from thin film Frequency Selective Surfaces (FSS), Alumina, Titanate and CVG materials. Measurements of these for antenna applications will be also presented demonstrating and validating the theoretical performance of the MPC and DBE crystrals.

The latter part of the paper will present an exciting and promising development relating to microwave circuit applications. Specifically, a novel dual-line printed circuit will be presented to emulate propagation in anisotropic media. As such, the MPC and DBE phenomena can thus be created using very simple printed circuits (couple lines). The development of high sensitivity circuits, miniature couplers are among the several applications to be considered.

1. G. Mumcu, K. Sertel, J.L. Volakis, and A. Figotin, "Propagation in Magnetic Non-reciprocal crystals," IEEE Antennas and Propagation Trans., Vol. 53, pp. 4026-4034, Dec. 2005.
2. G. Mumcu, K. Sertel and J.L. Volakis, "Miniature Antennas and Arrays Embedded within Magnetic Photonic Crystals" IEEE Antennas and Wireless Propagation Letters, 2006
3. C. Locker, K. Sertel and J.L. Volakis, "Emulation of propagation in bulk layered anisotropic media with equivalent coupled line microstrip circuits," submitted to IEEE Microwave and Guided Wave Letters.

Electronic steerable antennas have received during last years a great deal of attention and an increasing interest from industries in the key areas of space and terrestrial communications, remote sensing, radar systems. These antennas in fact can potentially meet exceptional performance in scanning/tracking rapidity, vibration tolerances, and interference robustness.

Electronic steering of array antennas is typically accomplished by using tuning components (diodes, FET) that modify the phase of the signal transmitted/received by each radiating element. The recent advance in the area of RF-MEMS (Micro Electro Mechanical Systems) eventually enables the use of such component in RF (Radio Frequency) systems. Thanks to their low-cost and high performance, RF MEMS switches are indeed a very attractive solution for beam steerable antennas, particularly at high frequencies where the semiconductor-based counterparts present unavoidable limitations. Additionally, RF MEMS offer unique features that make them employable not only as switching components replacing PIN diodes or FETs, but also as moving mechanical parts that can physically alter the structure of the antenna or the feeding circuit itself.

In this talk, the potential advantages of RF-MEMS in steerable antennas will be illustrated, and a review of state-of-the-art reconfigurable antennas will be presented. Particular attention will be devoted to the on-going research activities within the European networks of excellence AMICOM (Advanced MEMS for RF and MIllimeterwave COMmunications) and ACE (Antenna Centre of Excellence). Cooperation between the two networks has been in fact recently established, aimed to take advantage of the respective expertises in RF MEMS and antennas. This activity has led so far to different design topologies of printed MEMS reflectarrays. Reflectarray antennas have been chosen because of a number of advantageous inherent features, such as: flat-profile, low weight, low loss; the last being especially important at mm-wave frequencies where the loss associated to the feeding network become excessive in conventional phased-arrays.

The proposed architectures are essentially of two classes: single or multi-layer patches slot-coupled to tunable loads in microstrip or coplanar Silicon-based technology; dual-slotted tuneable patches in LTCC (Low Temperature Cofired Ceramic) or Silicon technology. Both solutions are meant to achieve the following objectives: low-cost integration of hundreds of RF MEMS required for beam steering; simple packaging procedure; mass production.

Limitations and future of this technology will be discussed.