1514 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 55, NO. 6, JUNE 2007 Molding Left- or Right-Handed Metamaterials by Stacked Cutoff Metallic Hole Arrays Miguel Beruete, I. Campillo, Miguel Navarro-Cía, Francisco Falcone, Member, IEEE, and Mario Sorolla Ayza, Senior Member, IEEE Abstract—A novel periodic structure, made of an arbitrary number of stacked subwavelength hole arrays, exhibiting simul- taneously electromagnetic band gap, extraordinary transmission and a longitudinal left handed propagation is presented in this paper. If the longitudinal period of the stacked structure is chosen adequately, it is possible under normal incidence to mold the electromagnetic wave properties inside the structure from right- handed to left-handed wave propagation passing through a zero- group velocity band. The transmission response of the fabricated prototype has been measured with a Millimeter Wave Quasioptical Vector Network Analyzer in the range between 40 GHz and 110 GHz confirming the possibility to tune the left- or right-handed char- acteristics of the propagating waves. These results can give rise to interesting applications such as novel lenses and other quasioptical structures. Index Terms—Electromagnetic bandgap (EBG), extraordinary transmission, left-handed metamaterials. I. INTRODUCTION E LECTROMAGNETIC band-gap (EBG) structures were originally proposed to inhibit the spontaneous emission in semiconductor lasers as an initial application. However, these structures have exhibited additional properties that allow the control of the flow of light and its confinement, which is resulting in important technological advances [1]. In turn, the discovery of extraordinary transmission (ET) phenomenon through subwavelength hole-arrays [2] has stim- ulated the research activities in this new topic opening up, simultaneously, novel technological applications [3]. Initially, the phenomenon was reported at optical wavelengths [2], but it has been also proven in the millimeter wave range [4]–[6]. A key role in the explanation of this effect are leaky waves and the so-called Wood anomalies, which may occur at an interface that supports a slow wave [7]–[11]. In [12], an alternative explanation can be found. Manuscript received April 1, 2006; revised November 13, 2006. This work was supported by the CICYT and E.U. FEDER under Contracts UNPN00-33- 008, TEC2005-06923-C03-01 and TEC2005-06923-C03-02. M. Beruete, M. Navarro-Cía, and M. Sorolla Ayza are with the Millimeter Wave Laboratory, Departamento de Ingeniería Eléctrica y Electrónica, Uni- versidad Pública de Navarra, Campus Arrosadía, E-31006 Pamplona, Spain (e-mail: mario@unavarra.es). I. Campillo is with the Center for Construction Applications of Nanostruc- tured and Intelligent Materials (NANOC), Labein-Tecnalia, c/ Geldo ed. 700, Parque Tecnológico de Bizkaia, 48160-Derio, Spain. F. Falcone is with Telefónica Móviles España, Madrid 199112, Spain and also with the Millimeter Wave Laboratory, Departamento de Ingeniería Eléctrica y Electrónica, Universidad Pública de Navarra, E-31006 Pamplona, Spain. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2007.897324 Finally, the newest breakthrough in electromagnetism has been the experimental demonstration of the possibility to build novel left-handed metamaterials (LHM) which exhibit a nega- tive refractive index (NRI) [13], [14] and envisage a new class of devices with unconventional properties [15]. Besides, interesting evanescent growth and tunnelling effects have been proposed in paired complementary frequency selec- tive surfaces [16]. Relations among several pairs of these three phenomena have been proposed, i.e., photonic crystals exhibit negative refrac- tion effects [17] and electromagnetic and photonic band gaps have been reported in stacked subwavelength hole-arrays [18]. Very recently the first fabrication and experimental verification of a transversely structured metal-dielectric-metal bi-layer ex- hibiting a negative refractive index around 2 microns has been reported, see [19]. A numerical demonstration of the negative index of refraction achievable with this structure is presented in [20]. Similar results have been published in [21]. The full connection among the three phenomena has been shown only very recently with periodically stacked metallic plates perforated with an array of subwavelength holes to form a structure showing left-handed propagation at the ET frequencies [22]. It has to be noted that transversal periodicity is of the order of free space wavelength but it is the longitudinal periodicity which determines the left-handed propagation. In the latter case, the longitudinal periodicity can be made much smaller than the wavelength as it will be presented in this paper. In this sense, we can homogenize along the longitudinal dimension allowing the use of the Metamaterial term in this dimension. This is different of the case of left-handed propaga- tion observed in standard EBGs [17]. This structure [22] is apparently similar to those of [19] and [21]. The key difference is that the structure introduced in [22] is a real tunable EBG, whereas the structures presented in [19], [21] consist of an isolated period. Moreover, one of the drawbacks of such structures [19], [21] are the losses, even for a minimal size structure due to the op- erating wavelength. The conductor losses are relevant at optical frequencies but not so important in our case of millimeter waves or even in the infrared frequencies. Dielectric losses are less rel- evant and can be overcome by using air as a dielectric insulator provided membranes are employed as described in [22]. In this way, our structure is optimal regarding losses. Recently, magnetic photonic crystals (MPCs) constructed from periodic arrangements of available (possibly anisotropic) homogeneous material layers have been proposed. These struc- tures, can exhibit the phenomena of minimal reflection at their interface, large amplitude growth of the harmonic wave within the crystal, and concurrent group velocity slow-down [23]. 0018-926X/$25.00 © 2007 IEEE