C.-C. Chang

Full-wave verification of the fundamental properties of left-handed materials in waveguide configurations

The fundamental electromagnetic properties of left-handed materials (LHMs) are reviewed and verified by finite-element method full-wave analysis using rectangular waveguide structures loaded by a LHM and adopting an effective medium approach. The negative phase velocity, positive intrinsic impedance, and modified boundary conditions at an interface with a right-handed medium are verified by loading a waveguide section with a LHM that has edges perpendicular to the waveguide axis. In addition, the negative angle of refraction is demonstrated by loading the junction of a T-junction waveguide with a LHM having one edge 45° with respect to the waveguide axis. These properties are shown by the evolution of wave fronts in the LHM and by analysis of the S-parameters of the waveguide structures.

Forward coupling phenomena between artificial left-handed transmission lines

Coupling phenomena between artificial left-handed (LH) transmission lines are explored on the basis of a transmission line approach of LH materials. A LH forward coupler in the form of an ideal lumped-element ladder network is presented and is shown to exhibit strong forward coupling that increases with decreasing of frequency. A quasi-lumped element microstrip implementation of a LH coupler is proposed. It is demonstrated that this coupler requires a shorter coupling length in comparison with the conventional right-handed coupled-line forward couplers, and hence makes the device much more compact.

ANALYSIS AND APPLICATIONS OF UNIPLANAR COMPACT PHOTONIC BANDGAP STRUCTURES

This paper reviews recent advancements in the research and development of Uniplanar Compact Photonic Bandgap (UCPBG) structures for microwave and millimeter-wave applications. These planar periodic structures are particularly attractive and have been intensively investigated due to their easy fabrication, low cost, and compatibility with standard planar circuit technology. In this paper, basic properties of UC-PBG will be studied such as the slowwave effect, distinct stopband and passband, leakage suppression of surface waves, and realization of a magnetic surface. Owing to the different features of UC-PBG, these structures have been applied to microwave circuits to improve microstrip filters and patch antennas, to perform harmonic tuning in power amplifiers, to suppress leakage in conductor-backed coplanar waveguide, to realize TEM waveguides, and to implement low-profile cavity-backed slot antennas.

Enhanced forward coupling phenomena between microstrip lines on periodically patterned ground plane

Strong forward coupling and slow-wave effects have been observed between two parallel microstrip lines on a periodically patterned ground plane, even though the two lines are separated with very large gap spacing. The even- and odd-mode effective dielectric constants have been calculated using the FDTD method to investigate this phenomenon. The slow-wave effects and enhanced coupling will help in the design of forward-wave directional couplers with reduced line lengths and relaxed gap spacing requirements.

An improved low-profile cavity-backed slot antenna loaded with 2D UC-PBG reflector

A slot antenna loaded with 2D UC-PBG pattern as the back reflector is demonstrated. The cavity height of this slot antenna with UC-PBG lattice is 16 times thinner than that of a regular /spl lambda//4 wavelength cavity slot antenna. The radiation patterns of this antenna show well defined unidirectional characteristics, and its gain is 1 dB higher than that of a conventional slot antenna at 5.28 GHz.

A reconfigurable leaky-wave/patch microstrip aperture for phased-array applications

A novel reconfigurable leaky-wave/patch microstrip aperture is introduced and characterized. The structure consists of a long leaky-wave microstrip antenna that has been segmented into several smaller patch antennas. The multimode structure can be reconfigured into a patch antenna anywhere along the aperture of the leaky-wave antenna with two degrees of freedom. p-i-n-diode switches are utilized to switch between the different aperture configurations. The structures unique field profile is utilized to minimize insertion loss in the leaky-wave mode and also to maximize isolation between the different aperture ports. Radiation patterns demonstrate excellent radiation characteristics consistent with standard leaky-wave and patch-antenna patterns. The reconfigurable leaky-wave/patch concept is applied to realize some unique multimode array configurations offering wide scan coverage and enhanced flexibility over traditional phased-array systems.

Analysis of a compact slot resonator in the ground plane for microstrip structures

A novel slot resonator in the ground plane for microstrip structures is proposed for filters and periodic structures. The resonant frequencies for one resonator are designed utilizing transmission line models with a lumped-element model extracted from the full-wave simulation. When these resonators are cascaded in a ground plane, the lumped-element model is used to simulate the frequency response with significant reduction of simulation time and good agreement with measurements.

A Novel Anisotropic Uniplanar Compact Photonic Band-Gap (UC-PBG) Ground Plane

A novel anisotropic UC-PBG structure, presenting a propagation direction and an attenuation direction and characterized by a period much smaller than wavelength, is introduced as a ground plane for a microstrip line. Simulated and measured transmission parameters of the resulting structure show good transmission in the propagation direction and strong rejection in the attenuation direction over a bandwidth of about 35%, an excelent insensitivity to the line position in both directions, a classical line and slow-wave behavior for the effective wavenumber in the propagation and attenuation directions, respectively, and a progressive variation of the transmission characteristics as a function of the angle of the line on the PBG. The gaps in the attenuation direction are shown to be very deep and to exhibit a very sharp cutoff despite the extremely small size of the overall structure.

A novel multilayer photonic band-gap (PBG) structure for microstrip circuits and antennas

The concept of the uniplanar compact PBG (UC-PBG) is extended to a novel architecture, which consists of several UC-PBG plates stacked up in the direction perpendicular to the plane of the substrate. This novel multilayer PBG is introduced here as the substrate for a microstrip line, and the resulting configuration builds a low-pass filter. In this design, the multilayer PBG includes two UC-PBGs with different periodicities. Simulated and measured transmission parameters in comparison with the corresponding monolayer UC-PBG show that the introduction of a second UC-PBG drastically enhances the width of the stop-band, as a result of the overlap of stop-bands associated with each UC-PBG layer.

Numerical and experimental characterization of slow-wave microstrip line on periodic ground plane

A low loss//spl lambda/ slow-wave microstrip transmission line structure is numerically and experimentally investigated. The structure is based on a microstrip line on periodically etched ground plane. Dependency of the slow-wave factor on lattice dimensions is investigated. The slow-wave factor has also been simulated by the FDTD method as numerical verification of the accuracy of the results. Numerical results reveal that the slow-wave microstrip structure can reduce the attenuation//spl lambda/ by 6/spl times/ compared to conventional planar slow-wave structures.