The properties and characteristics of a recently proposed anisotropic metamaterial based upon layered arrays of tightly coupled pairs of "dogbone" shaped stripe conductors have been explored in detail. It has been found that a metamaterial composed of such stacked layers exhibits artificial magnetism and may support backward wave propagation. The equivalent network models of the constitutive conductor pairs arranged in the periodic array have been devised and applied to the identification of the specific types of resonances, and to the analysis of their contribution into the effective dielectric and magnetic properties of the artificial medium. The proposed "dogbone" configuration of conductor pairs has the advantage of being entirely realizable and assemblable in planar technology. It also appears more prospective than simple cut-wire or metal-plate pairs because the additional geometrical parameters provide an efficient control of separation between the electric and magnetic resonances that, in turn, makes it possible to obtain a fairly broadband left-handed behaviour of the structure at low frequencies.

The design of a thin microwave absorber which exhibits a −10 dB reflectivity bandwidth of 108% at normal incidence and 16% for simultaneous suppression of TE and TM polarised waves over the angular range 0-45°is presented. The structure consists of a 3 mm-thick metal backed frequency selective surface (FSS) with four resistively loaded hexagonal loop elements in each unit cell. The surface resistivity and width of the loops are carefully chosen to maximise the bandwidth by merging the reflection nulls that are generated by the multi-resonant absorber. Measurement and simulation results are in good agreement over the broad frequency range 7.8-24 GHz.Introduction: Microwave absorbers based on resistively loaded high impedance surfaces [1] are an attractive option for providing radar cloaking where the main design drivers are weight and thickness. However, the reflectivity bandwidth of this class of absorbers is proportional to the structure thickness [2-6], which is determined by the gap between the frequency selective surface (FSS) and the ground plane. In [2], a −10 dB reflectivity bandwidth of 109% was obtained from a 5 mm-thick metal backed resistively loaded single square loop FSS array. This was designed to resonate at the two frequencies where the imaginary component of the FSS impedance is cancelled by the inductance and capacitance presented by the ground plane with gap widths of <λ/4 and >λ/4 at the lower and upper frequencies, respectively. The FSS absorber studied in this Letter is shown to give a similar bandwidth; however, the ground plane spacing is < λ/4 at all frequencies where the reflectivity is below −10 dB. Moreover, because the structure is 40% thinner, the figure of merit (FOM), which is defined as the common (TE/TM) bandwidth divided by the physical thickness normalised to the centre working frequency, is significantly larger, 670 compared with 470 in [2]. For this arrangement, radar backscatter suppression occurs at four frequencies where the complex impedances of the individual hexagonal loops cancel the inductance which is presented by the ground plane. In [3,5,[7][8][9], the simulated backscatter suppression for various resistively loaded thin FSS absorbers based on single and nested square loop elements has been reported, but only for normal or small incidence angle operation. The structure depicted in Fig. 1 which was studied in this Letter, exhibits higher FOM values except for the arrangement reported in [7], where numerical results are presented for an FSS design with different surface resistances for the five individual nested elements in the range 4-1680 Ω/sq. In contrast, our methodology enables the use of the same surface resistance for all four hexagonal loops in the unit cell which significantly simplifies the construction and manufacture of the FSS. Bi-static measured results obtained for an absorber with an FSS that was fabricated by patterning a uniform thickness film of commercially available shielding paint [10] are shown to be in good agreement with numerical predictions...

Abstract-Entwining planar quadrifilar spirals arranged in doubly periodic arrays enables a strong subwavelength response of the unit cell smaller than 1/40 of wavelength. It is shown that interleaving counterwound spiral arms extended into adjacent unit cells dramatically increases the equivalent capacitance while reducing the inductance. The dielectric substrate enhances this effect of the unit cell miniaturization with concurrent bandwidth expansion. The proposed topology of compact planar spiral array exhibits excellent angular and polarization stability and circular polarization selectivity in a broad frequency band. Negligible variations of the resonance frequency are demonstrated for both TE and TM polarized waves at incidence angles up to 45 with a common fractional bandwidth over 40% at the level of 10 dB.

Abstract-We present a fully printable effective negative refractive index (NRI) metamaterial responsive to arbitrarily linearly polarized incident waves. The proposed metamaterial is composed of a periodic array of tightly coupled Jerusalem cross conductor pairs printed on the opposite sides of a dielectric substrate. Each pair supports both symmetric and antisymmetric resonance modes, whose superposition can lead to an effective NRI of the composite medium. A thorough characterization of the transmission properties of such metamaterial is performed, and conclusive evidences of the medium exhibiting effective NRI properties and impedance matching to free space are presented for a range of the structure parameters.Index Terms-Left-handed media, negative permeability, negative permittivity, negative refractive index (NRI), polarization independence.

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