H. Salehi

Analysis and design of Superconducting left-handed transmission lines

In this paper, for the first time, we study the properties of a superconductive-based left-handed transmission line (SLHTL). The effect of the kinetic inductance on the propagation constant of the left-handed transmission line is analyzed. It is shown that increasing the kinetic inductance decreases both the bragg frequency and the negative index frequency band of a distributed LHTL. A Coplanar waveguide structure is proposed to realize the LHTL. It is shown that the CPW structure has the capability of increasing the kinetic inductance of the TL by narrowing the spacing between the line and the ground plane because they are deposited on the same side of the substrate. This was not possible in a microstrip line as the spacing between the line and the ground is equal to the substrate thickness and is usually fixed. Furthermore, the dependency of the kinetic inductance to the bias current has been employed to design a tunable SLHTL. Possible applications of the tunable SLHTL in the design of miniaturized tunable resonators and filters are discussed.

Modified conductor loaded cavity resonator with improved spurious performance

The paper introduces a new resonator configuration to realize conductor-loaded cavity filters with improved spurious performance. Theoretical results are presented for the field distribution and resonant frequencies of the proposed structure. The results show that shaping the metal resonator inside the cavity can considerably improve its spurious performance. Experimental results are presented to verify the concept presented in this paper.

Analysis, modeling, and applications of coaxial waveguide-based left-handed transmission lines

In this paper, a new realization of left-handed transmission lines (LHTLs) is presented. The proposed structure employs a coaxial waveguide structure to host periodic arrays of split-ring resonators (SRRs) and capacitively loaded strips (CLSs). The SRRs and CLSs are radially mounted on the inner conductor of the coaxial waveguide structure, which provides the necessary polarization for the periodic arrays of SRRs and CLSs to exhibit a negative index of refraction over a specific frequency band. The structure of the proposed coaxial waveguide-based LHTL (CW-LHTL) is optimized by studying the effect of inductive and capacitive couplings on the performance of the structure. The properties of CW-LHTL are studied by analyzing the dispersion diagram and extracting its effective permittivity and permeability. The analysis shows that the proposed CW-LHTL exhibits negative effective permittivity and permeability around the resonant frequency of the SRRs. The inductive and capacitive couplings of the SRRs and CLSs of a CW-LHTL unit cell are related to the periodicity of left-handed material (LHM) in free space. Therefore, the proposed CW-LHTL provides a reliable measurement setup to study the behavior of LHM in free space without the need to use a large number of unit cells. The coaxial waveguide measurement setup is also used to analyze different modified SRRs, which have a smaller size while operating at the same resonant frequency. A coaxial waveguide structure housing a unit cell of the proposed SRR is fabricated and tested. The measurement results show that the proposed modified SRR is up to 46% smaller in size in comparison with the traditional SRR. The applications of CW-LHTL in guided microwave systems are also discussed.

A new realization of left-handed transmission lines employing a coaxial waveguide structure

The paper proposes the use of a coaxial waveguide structure to realize a left-handed transmission line (LH-TL) structure. The structure consists of periodic arrays of split-ring resonators (SRRs) and capacitively loaded strips (CLSs) mounted radially on the inner conductor. The coaxial waveguide structure provides a suitable guided environment to measure the characteristics of negative index materials (NIMs). The paper also presents a modified SRR structure that offers more than 45% size reduction in comparison with the traditional SRR. A coaxial waveguide structure housing a unit-cell of the proposed SRR is fabricated and tested. The experimental results confirm the validity of the proposed concept.

Lumped-element conductor-loaded cavity resonators

In this paper, we present a novel conductor-loaded cavity resonator having the form of L and C lumped-element resonators. The resonator is derived by modifying traditional split-ring resonators. The proposed lumped-element resonator offers more than 85% size reduction in comparison with split-ring resonators. In addition, the proposed resonator eliminates the need to use the dielectric support that is typically required for split-ring resonators. An 800 MHz 3-pole Chebyshev function filter was designed, built and tested. The experimental results obtained verify the validity of the proposed concept.

Unusual mode propagation characteristics of negative index slab waveguides

We study the unusual properties of the guided modes of negative index slab waveguides (NI-SWs). It is shown that for specific frequency bands, the structure can excite guided modes with similar field distributions but different propagation constants, which we refer to as dual-wavenumber modes (DWMs). The characteristics of evanescent fields of DWMs are studied. It is shown that when interfering destructively, the evanescent fields of the DWMs grow temporarily before they decay permanently.

Triple mode conductor loaded cavity filter

In this paper, a new triple mode conductor loaded cavity resonator is presented. The resonator consists of a cubic shape metallic structure mounted in a metallic enclosure. A low loss, low dielectric constant support structure is used to hold the metallic resonator inside the cavity. The proposed resonator, operating at the TM01δ mode, is similar to the triple mode dielectric resonator, where the dielectric constant of the resonator approaches infinity. The triple mode conductor loaded cavity resonator is considerably cheaper, easier to design and manufacture, and offers a significantly wider spurious free response in comparison to the triple mode dielectric resonator. A six-pole filter employing the proposed resonator is design using full wave EM simulator. Introducing asymmetry in the structure of the metallic resonator in the form of chamfers provides the required coupling between the degenerate modes inside each block to realize the desired filter response. The six-pole triple mode conductor loaded cavity filter is fabricated and tested. The measurement results verify the validity of the proposed concept. The triple mode conductor loaded cavity resonator can be combined with higher Q-factor triple mode ceramic resonators to realize a small size, high Q-factor filter with wide spurious free response.

A novel quasi lumped-element resonator using a left-handed transmission line section

The paper presents a novel miniaturized resonator configuration that employs a left-handed transmission line (LHTL) section. It is shown that combining right-handed and left-handed TLs can result in a compact resonator with a remarkable spurious performance. The paper employs the LHTL concept as a design tool to combine distributed TLs and lumped element components to realize a novel resonator structure. The proposed resonator consists of two distributed TLs that are connected through a 1-unit cell LHTL. The resonant frequency and quality factor of the proposed structure are measured. In comparison with the conventional /spl lambda//2 resonator, the proposed resonator offers 5 times size reduction. A three-pole filter is designed, fabricated and tested employing the proposed resonator.

A miniaturized ring resonator using a left-handed transmission line section

In this paper, we present a novel miniaturized ring resonator configuration that employs a combination of right-handed and left-handed transmission lines. It is shown that combining right-handed and left-handed transmission lines can result in a miniaturized resonator configuration whose resonant frequency is independent of its length. The proposed concept allows the realization of considerably smaller resonators in comparison with traditional ring resonators. Moreover, it offers a remarkable wide spurious free window. In practice, the maximum miniaturization of the proposed ring resonator is limited by the maximum achievable capacitance and inductance per unit area. The proposed concept can also be extended to other planar resonator configurations. Practical considerations to realize these structures are also discussed.

Anisotropic Left-Handed and μ-Negative Slab Waveguides: Physics and Device Applications

We study the properties of various anisotropic left-handed slab waveguides. The analysis is extended to anisotropic μ-negative slab waveguides. The possible existence of the plasmon modes in various anisotropic slab waveguide configurations is discussed. An FDTD program is developed to investigate the potential device applications of these anisotropic structures. A new signal detector and a two-channel harmonic separator multiplexer are designed employing the μ-negative slab waveguide.