S. Yarga

Degenerate Band Edge Crystals for Directive Antennas

We present an experimental demonstration of the degenerate band edge (DBE) behavior in anisotropic photonic crystals. Specifically, we present the design of a DBE crystal using a full-wave analysis method, its realization using laminate layers of printed strips emulating anisotropy, and experimental verification of field amplitude growth using field probe measurements. Although the DBE and magnetic photonic crystal theory has been presented before, this work is the first experimental demonstration of such anisotropic assemblies.

Degenerate Band Edge Crystals and Periodic Assemblies for Antenna Applications

Artificially manufactured materials such as periodic band gap structures are of growing interest because of their extraordinary characteristics. Regular band gap (RBG) photonic crystals have already been considered for RF applications, such as filters, waveguides, etc. [1]. One of the fundamental properties of photonic crystals is the vanishing group velocity, ω ∂ / 0 = ∂k of the supported propagating mode at the band edge (Fig. 1a). Such wave slow down results in the accumulation of electromagnetic energy leading to field amplitude growths. However, the transmittance of the ordinary band gap crystals vanishes at the band edge. Therefore, ordinary photonic crystals are not suited for operation close to the band edge for radiating structures.

A Directive Resonator Antenna Using Degenerate Band Edge Crystals

A new small antenna formed by a periodic assembly of two-tone dielectrics (Barium-titanate and Alumina) emulating an anisotropic medium is presented. Directive radiation characteristics are achieved when operated close to the band edge frequencies of a class of anisotropic photonic crystals supporting degenerate band edge (DBE) modes. Unique aspects of the antenna design are its smaller size (0.79 lambda0 times 0.80 lambda0 times 0.28 lambda0) and nearly optimum aperture efficiency. The subject 3-D assembly, fed by a slot on a ground plane, achieved a directivity of 10.17 dBi. This communication presents the design of the 3-D assembly using full-wave simulations and provides experimental verification of the overall antenna performance.

Multilayer Dielectric Resonator Antenna Operating at Degenerate Band Edge Modes

A multilayer rectangular dielectric resonator antenna (DRA) operating at a new hybrid mode is presented. The DRA is formed by a dispersion engineered combination of isotropic/anisotropic dielectric layers. These layers are optimized to operate at a degenerate band edge (DBE) mode with the introduction of misaligned anisotropic layers. A prototype DBE-DRA antenna is realized by emulating the anisotropic medium with a periodic assembly of two-tone dielectrics (barium-titanate and alumina).

Degenerate Band Edge Crystals and Periodic Assemblies for High Gain Antennas

Periodic arrangements of metallo-dielectric structures have been shown to exhibit novel phenomena that can be exploited for microwaves. Among them, regular band edge (RBE) structures are known for their high Q properties, and left handed materials lead to much smaller phase shifters and couplers. More recently, a new class of periodic arrangements, referred to as magnetic photonic crystals (MPCs) and degenerate band edge crystals (DBEs) have been shown to significantly improve matching of the incoming fields and support slow wave phenomena (frozen modes) leading to very large wave fields within the crystal over a relatively wide bandwidth. Thus, they can be used for much greater sensitivity antennas. In this paper, we experimentally demonstrate for the first time the support of such phenomena using a newly designed crystal from very low cost materials. We demonstrate that the purported slow wave and high amplitude phenomena can be observed using on periodic cells with a finite aperture. These experiments are corroborated with numerical data, making the utilization of these new class crystals for high gain and narrow beam scanning antennas a practical possibility.

Finite degenerate band edge crystals using barium titanate-alumina layers emulating uniaxial media for directive planar antennas

Electromagnetic band-gap (EBG) structures have been used to realize highly directive antennas either by using them as substrates and utilizing defect resonances or as a host medium when operating near band edge frequencies. As an alternative, it was recently proposed that degenerate band edge (DBE) crystals can achieve the required resonances using fewer number of unit cells, resulting in low profile structures.

Non-reciprocal radiation using magnetic photonic crystals

Magnetic photonic crystals (MPCs) were previously shown to support novel modes exhibiting spectral non-reciprocity and stationary inflection points (SIP) within their band diagram [1]. The latter implies a unidirectional frozen mode exhibiting wave slowdown and concurrent amplitude growth [3]. In [4], it was demonstrated that the frozen mode can be realized using available materials yielding highly directive radiation from small dipoles embedded within the MPC layers. However, only the receiving pattern was presented without emphasis on the non-reciprocal radiation characteristics. In this paper, we analyze the receiving and transmitting patterns of Hertzian dipoles embedded within MPC unit cell ensemble. We demonstrate that a rather thin MPC assembly achieves unidirectional radiation with non-reciprocal receiving/transmitting patterns. We also propose a simpler unit cell structure to realize the aforementioned phenomena.

Highly directive dielectric resonator antennas operating at higher order degenerate band edge modes

In recent years, there is a growing interest in compact high-gain antennas with a single feed for civil/tactical wireless communication systems. Electromagnetic band-gap (EBG) structures with embedded antennas/feeds present an attractive solution due to their high directivity and feeding ease. EBGs have been used to obtain highly directive radiation in two forms: (a) as a substrate utilizing defect resonances (Brown et al., 1993) (b) as a host medium near the band edge frequencies (Bulu et al., 2003). The first group requires comparatively large physical sizes for practical applications (e.g. thicknesses of larger than lambdao/2). For the latter, one must be careful to operate at the Fabry-Perot (F-P) transmission peak closest to the band edge. The degenerate band edge (DBE) resonances (see Fig. 1c) are of this type, but also have the unique property of exhibiting narrower F-P peaks in the vicinity of the band edge leading to better directional selectivity (Figotin and Vitebskiy, 2006). Consequently, DBE crystals can achieve required levels of high directivity using fewer number of unit cells, resulting in low profile structures.

Frozen modes in bounded photonic crystals for high gain antennas

Photonic crystals have been the subject of extensive research for almost twenty years. More recently, the physical nature of the constitutive components was diversified to include anisotropic, magnetic, metallic, and nonlinear materials. Greater diversity of physical properties, along with more sophisticated space arrangement of the constituents, can result in qualitatively new features and novel phenomena, such as electromagnetic unidirectionality and the frozen mode regime. The resulting structures are referred to as magnetic photonic crystals (MPCs). This presentation provides analysis that demonstrates the benefits and potential applications of MPCs and degenerate bandgap structures (DBEs) from a numerical and experimental point of view. Three dimensional realizations of antennas and conformal arrays within MPCs are presented using frequency domain and time domain techniques, and preliminary experimental data are given for validation purposes

Chiro-ferrites for low-loss magnetic photonic crystals

Summary form only given. Magnetic photonic crystals (MPCs) display exotic propagation characteristics in the form of a frozen mode (Figotin, A. and Vitebskiy, I., Phys. Rev. E, vol.63, 066609, p.1-17; Phys. Rev. B, vol.67, 165210, p.1-20). At microwave frequencies, ferrites are associated with losses which are further exacerbated due to resonant wave behavior (frozen mode) within the crystal. To minimize losses, it is therefore necessary to minimize the ferrite layer thickness while still attaining sufficient Faraday rotation to preserve the frozen mode phenomenon. We investigate the performance of: (1) chiral inclusions within a ferrite medium; (2) chiral (handed) ferrite inclusions within a possibly non-magnetic host medium. Our preliminary analysis demonstrates that much thinner periodic MPC layers can be designed using chiro-ferrite layers. Concurrently, the MPC frozen mode and reflectivity properties are maintained. More specifically, the inflection point in the band diagram is achievable using only a fraction (lower than 1%) of the original ferrite material, implying a significant loss reduction in practice.