The progress in developing metallic metamaterial lenses founded on stacked subwavelength hole arrays is reported.
Before, the lens was studied when it emulates a medium with effective index of refraction -1. Here, the lens is
investigated at higher frequencies, where it behaves like a near-zero index of refraction. We show that exploiting both
regimes, dual-band capabilities are attainable. Moreover, a zoning technique is applied to the initial design to reduce the
lens in terms of volume and weight, while the performance is maintained.
Novel antennas exhibiting directivity enhancement by using a short focal length plano-concave lens engineered by
stacked subwavelength hole arrays in such a way that an effective negative index of refraction is obtained. An additional
unexpected property of this design is that it opens the possibility to achieve an index close to zero, n → 0, arisen from ε-
and μ-near-zero extreme values. Our original design works with evanescent modes in comparison with the well known
classical metallic lenses operating with propagating modes. In our case, this leads to a negative index of refraction,
whereas metallic lenses exhibit a positive but less than one index of refraction. It is demonstrated by means of a simple
design based on dispersion diagram and ray tracing an easy and correct method for rather accurate results. Also, an
optimization of the hole diameter or longitudinal lattice constant to achieve not only n = -1, but also free space matching
is possible simultaneously. A power enhancement up to 24 dB with cross-polarization below -30 dB with regards to co-polar,
when the lens is applied as antenna radiation beamforming has been measured. For the case of index close to zero,
n → 0, the power enhancement is 27 dB whereas the cross-polarization remains -17 dB with regards to co-polar. New
improvements are under analysis in order to determine if this technology could be competitive with current state of the
art of waveguide lenses and Fresnel zone plate lenses.
In this paper, a novel structure in coplanar waveguide (CPW) technology which exhibits an equivalent negative magnetic permeability is described. Such a structure consists in a conventional coplanar waveguide that is loaded with split ring resonator (SRR) cells. Due to the configuration of the magnetic field components in the coplanar waveguide, by adequately placing the SRR cells, quasi-static resonance occurs. In the vicinity of such resonance frequency, the magnetic permeability exhibits a negative value in a certain frequency range. Full wave simulation results as well as measurement from fabricated prototypes validate initial assumptions, providing a new method to implement band rejection filters with very small size.
The use of Electromagnetic Bandgap (EBG) structures has proven to be effective in the implementation of many devices in planar circuit technology, such as filters, couplers and antenna design. In this paper, a low pass filter based in EBG structures in coplanar waveguide (CPW) technology is proposed. The device consists in a periodically loaded CPW with shunt capacitive elements. This way, a low pass frequency response is obtained. The capacitive elements are formed by t-shaped fingers that extend from the central conductor strip to both ground planes. Further enhancement is achieved by introducing a second periodicity in the central conductor strip, modulating the width of the strip. By doing so, effective rejection of undesired frequency harmonics is achieved. Full wave simulation results as well as measurement from fabricated prototypes confirm the performance of the proposed low pass filter, which exhibits low insertion losses in the passband, high rejection slope and effective rejection of undesired harmonics. Another advantage is the small footprint, due to the inherent slow-wave nature of the device.
In this paper, electromagnetic bandgap structures are applied to a conventional coplanar waveguide. The EBG is obtained by etching a continuous sinusoidal perturbation pattern either on the central conductor strip or the both ground planes of the CPW. By doing so, a rejected frequency band appears. Since the frequency response of the device can be approximated by the Fourier Transform of the perturbation function, the application of a sinusoidal perturbation gives allows in principle a unique rejected band, without the presence of frequency harmonics. Full wave simulation results are presented for simple reflectors as well as for combination of several simultaneous perturbation functions, tailoring the desired frequency selective behavior.
In the paper, electromagnetic bandgap (EBG) structures in coplanar waveguide (CPW) technology are presented. In order to design this type of circuits, a custom Finite Difference Time Domain (FDTD) code is employed. Due to the fact that simulation is performed in the time domain, a wide frequency response can be obtained in a reasonable amount of time, being a numerically efficient technique. Simulation of several proposed designs are presented and these results are validated with measurements from fabricated prototypes. The results show that the use of FDTD techniques is adequate for the design of EBG devices in planar circuit technology in general.
A simple and fast fiber-grating model for the simulation and design of 1D photonic bandgap structures consisting of a row of circles etched in the ground plane of microstrip lines is proposed. It is based on the relationship found between the parameters of the photonic bandgap structure and those for an equivalent fiber Bragg grating with the same frequency- response shifted to the optical wavelength range.
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