Electromagnetic crystals, also called Electromagnetic Band-Gap (EBG) materials, show an enormous potential in manipulating the propagation of electromagnetic waves [1]. Their technology is advancing rapidly and they are used in a lot of microwave and optical applications such as waveguides, filters, antennas, high- and low-Q resonators, reflectors, integrated circuits. In particular, EBGs can be employed to improve the performances of antennas, enhancing their directivity. An electromagnetic crystal can be used as a planar reflector, as a substrate, or as a high-impedance ground plane, and it is able to eliminate the drawbacks of conducting ground planes, to prevent the propagation of surface waves, to lower the device profiles, and to increase radiation efficiency [2]. Otherwise, an EBG can be employed as a superstrate, and its effect is a considerable reduction of the angular range of the field emitted by the antenna [3], [4]. Both an electromagnetic-crystal substrate and a cover can be simultaneously used [5]. Moreover, it has been demonstrated that, embedding sources in EBGs working near their band-gap edges, it is possible to obtain highly directive antennas [6] thanks to the limited angular propagation allowed within the crystal. In this work, attention is paid to different classes of radiating devices employing EBGs in accordance to the operating mechanisms. In particular the study of directivity enhancement due to the insertion of an antenna source in a bulk dielectric electromagnetic crystal, working near a band-gap edge, or due to EBG layers used as substrate/superstrate is presented. We attempt to highlight the role of the EBG, clarifying in which way it succeeds in improving the performances of the emitting devices. Electromagnetic crystals can be periodic in one, two, and three dimensions. In one- and two-dimensional EBGs it is possible to obtain no propagating modes in one direction or in all directions lying in a plane of directions, respectively. Only a three-dimensional (3D) periodicity can support an omnidirectional stop-band. However, the electromagnetic characterization of a 3D EBG is a difficult task. A fast and accurate modeling of the transmission and reflection properties of 3D-EBGs can be performed by exploiting a Fourier Modal Method (FMM) [7], which in the literature is regarded as the most efficient and prevailing rigorous technique for the analysis of doubly-periodic gratings. A 3D-EBG can be considered as a stack of periodic diffractive optical elements. We implemented the 3D-FMM in Matlab, by using the correct Fourier factorization rules for discontinuous functions. For a numerically-stable treatment of the evanescent waves at the interfaces between different dielectric media, we used the S-matrix algorithm in the solution of the boundary problem. Our technique allows us to study implants with an arbitrary shape which can be arranged in whatever kind of lattice. Moreover, the approach is suitable to analyze EBGs with periodic defects. The introduction of a periodicity interruption in an electromagnetic crystal may cause the occurrence of a sharp transmission peak in its stop-bands. While in one- and two-dimensional EBGs the transmission peak of the electromagnetic field, caused by the presence of a defect, occurs in all directions or in a plane of directions, respectively, with 3D crystals it is possible to confine the transmission peak in one direction. The ensemble constituted by perfectly conducting planes, 3D-EBGs, and homogeneous dielectric substrates, can be schematized by means of an equivalent resonating all-dielectric structure: we can therefore design it by using our FMM tool. Comparisons with results obtained by using other numerical approaches are shown.
Frezza, F., Pajewski, L., Ponti, C., Schettini, G. (2007). Band properties and directivity enhancement in 3d electromagnetic crystals for antenna applications. In Proc. Metamaterials 2007: First International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (pp.355-356).
Band properties and directivity enhancement in 3d electromagnetic crystals for antenna applications
PAJEWSKI, LARA;SCHETTINI, Giuseppe
2007-01-01
Abstract
Electromagnetic crystals, also called Electromagnetic Band-Gap (EBG) materials, show an enormous potential in manipulating the propagation of electromagnetic waves [1]. Their technology is advancing rapidly and they are used in a lot of microwave and optical applications such as waveguides, filters, antennas, high- and low-Q resonators, reflectors, integrated circuits. In particular, EBGs can be employed to improve the performances of antennas, enhancing their directivity. An electromagnetic crystal can be used as a planar reflector, as a substrate, or as a high-impedance ground plane, and it is able to eliminate the drawbacks of conducting ground planes, to prevent the propagation of surface waves, to lower the device profiles, and to increase radiation efficiency [2]. Otherwise, an EBG can be employed as a superstrate, and its effect is a considerable reduction of the angular range of the field emitted by the antenna [3], [4]. Both an electromagnetic-crystal substrate and a cover can be simultaneously used [5]. Moreover, it has been demonstrated that, embedding sources in EBGs working near their band-gap edges, it is possible to obtain highly directive antennas [6] thanks to the limited angular propagation allowed within the crystal. In this work, attention is paid to different classes of radiating devices employing EBGs in accordance to the operating mechanisms. In particular the study of directivity enhancement due to the insertion of an antenna source in a bulk dielectric electromagnetic crystal, working near a band-gap edge, or due to EBG layers used as substrate/superstrate is presented. We attempt to highlight the role of the EBG, clarifying in which way it succeeds in improving the performances of the emitting devices. Electromagnetic crystals can be periodic in one, two, and three dimensions. In one- and two-dimensional EBGs it is possible to obtain no propagating modes in one direction or in all directions lying in a plane of directions, respectively. Only a three-dimensional (3D) periodicity can support an omnidirectional stop-band. However, the electromagnetic characterization of a 3D EBG is a difficult task. A fast and accurate modeling of the transmission and reflection properties of 3D-EBGs can be performed by exploiting a Fourier Modal Method (FMM) [7], which in the literature is regarded as the most efficient and prevailing rigorous technique for the analysis of doubly-periodic gratings. A 3D-EBG can be considered as a stack of periodic diffractive optical elements. We implemented the 3D-FMM in Matlab, by using the correct Fourier factorization rules for discontinuous functions. For a numerically-stable treatment of the evanescent waves at the interfaces between different dielectric media, we used the S-matrix algorithm in the solution of the boundary problem. Our technique allows us to study implants with an arbitrary shape which can be arranged in whatever kind of lattice. Moreover, the approach is suitable to analyze EBGs with periodic defects. The introduction of a periodicity interruption in an electromagnetic crystal may cause the occurrence of a sharp transmission peak in its stop-bands. While in one- and two-dimensional EBGs the transmission peak of the electromagnetic field, caused by the presence of a defect, occurs in all directions or in a plane of directions, respectively, with 3D crystals it is possible to confine the transmission peak in one direction. The ensemble constituted by perfectly conducting planes, 3D-EBGs, and homogeneous dielectric substrates, can be schematized by means of an equivalent resonating all-dielectric structure: we can therefore design it by using our FMM tool. Comparisons with results obtained by using other numerical approaches are shown.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
