Hayrettin Odabasi

Electrically small, complementary electric-field-coupled resonator antennas

We study the radiation properties of electrically small resonant antennas (ka<1) composed of electric-field-coupled (ELC) and complementary electric-field-coupled (CELC) resonators and a monopole antenna. We use such parasitic ELC and CELC “metaresonators” to design various electrically small antennas. In particular, monopole-excited and bent-monopole-excited CELC resonator antennas are proposed that provide very low profiles on the order of λ0/20. We compare the performance of the proposed ELC and CELC antennas against more conventional designs based upon split-ring resonators.

Impedance-matched absorbers and optical pseudo black holes

We investigate the design of metamaterial blueprints for impedance-matched (reflectionless) absorbers over nonplanar surfaces in connection with optical pseudo black holes. The presence of some fundamental constraints on the existence of reflectionless absorber media at nonplanar surfaces are discussed based on analytical properties of the associated constitutive tensors on the complex ω (angular frequency) plane. In view of such constraints, some new metamaterial blueprints of near-reflectionless absorbers are suggested for integration into optical pseudo black hole devices.

Electric-field-coupled resonators as metamaterial loadings for waveguide miniaturization

We show that a rectangular metallic waveguide loaded with metamaterial elements consisting of electric-field-coupled (ELC) resonators placed at the sidewalls can operate well below the cutoff frequency of the respective unloaded waveguide. For the example considered of a waveguide with square cross-section and original TE-mode cut-off frequency at 16.67 GHz (under no loading), a TE-mode passband is obtained around 8.6 GHz once the waveguide is loaded with ELC resonators. Similarly, for TM-mode excitation with original cut-off at 23.57 GHZ, TM-mode passbands are obtained around 8.5 GHz and 11.3 GHz, for two different orientations of ELC resonators. The dispersion diagrams indicate that propagating modes in ELC-loaded waveguides are of forward-type for both TE and TM modes. We also study the dispersion diagram and transmission characteristics of rectangular metallic waveguides simultaneously loaded with both ELCs and split ring resonators. Such “doubly”-loaded waveguides can support both forward wave and ba...

Impedance analysis of extremely low-profile antennas using metamaterial substrates

Low-profile antennas are desirable in personal communications due to attractive features such as low cost, light weight, conformability, and ease of integration. A major challenge in low-profile antenna design is the trade off between the (reduced) antenna profile and performance. This trade-off can be ameliorated by loading the antennas with properly designed metamaterials. In this paper, we explore the use of a new anisotropic metamaterial as antenna substrate and examine its effect on the input impedance of two types of low-profile antennas. We have shown that height reduction can be achieved without significant change on the antenna input impedance.

Metamaterial claddings for waveguide miniaturization

Summary form only given. The study of waveguides loaded with metamaterials has become quite popular in recent years (R. Marques et al., PRL, 89-18, 183901, 2002, S. Hrabar et al., IEEE Trans. Antennas Propag., vol. 53, no. 1, pp.110-119, 2005). It was pointed out that a rectangular waveguide below cut-off behaves as a 1-dimensional electric plasma for TE modes (R. Marques et al., PRL, 89-18, 183901, 2002). Likewise it behaves as magnetic plasma for TM modes (J. Esteban et al., IEEE Trans. on Microwave Theory and Techniques, vol. 53, no. 4, 2005). Since the rectangular waveguide naturally provides negative permittivity below cut-off, when combined with negative permeability materials, such loaded waveguide mimics the double negative materials in the frequency range where the negative permeability and permittivity overlaps. Backward waves in such waveguide were also experimentally verified. It is also of interest to investigate what happens when the waveguide is loaded with negative permittivity medium. It turns out that negative permittivity medium provides a pass band below cut-off inside the negative permittivity region (Y. Dong and T. Itoh, IEEE Microwave Magazine, 2012). The waves in such waveguide are forward waves unlike the former.

Analysis of cylindrically conformal patch antennas on isoimpedance anisotropic substrates

We numerically investigate the performance of cylindrically conformal patch antennas on isoimpedance anisotropic substrates. These substrates are specifically designed to increase the effective (electrical) height without producingsurface waves.

Analysis of metamaterial absorber blueprints for optical ‘black holes’

We investigate the design of metamaterial blueprints for reflectionless (impedance-matched) absorbers over non-planar surfaces in connection with optical ‘black holes’. New metamaterial blueprints of near-reflectionless absorbers are suggested for integration into optical ‘black hole’ metamaterials.