Shiou-Li Chen

Effective electromagnetic parameters of novel distributed left-handed microstrip lines

The novel one-dimensional left-handed microstrip lines (LHMLs) consisting of the arrays of thin wires and two-layer split-ring resonators are investigated theoretically and experimentally in this paper. Unlike the conventional left-handed metamaterials for waveguides or microstrip lines, which are bulky three-dimensional constructions or require the lumped elements for high-pass configuration, this distributed structure can be directly implemented on a substrate by photolithographic techniques without soldering any chip inductors or capacitors. Moreover, it can also be easily realized at a higher frequency region by scaling the dimensions of the structure, making it highly efficient and flexible in millimeter-wave applications. To characterize the inhomogeneous LHML, the effective medium description is developed for extracting the effective electromagnetic parameters, i.e., the complex effective permittivity and permeability, as well as the refractive index. Results show that not only the simultaneously negative real permittivity and permeability, but also the antiparallel phase and group velocities may be achieved in the design passband region. In contrast to the antenna array using the conventional microstrip delay line, the LHML is incorporated in the series-fed microstrip combline array to exhibit the leading phase between the successive elements.

Characterization and modeling of left-handed microstrip lines with application to loop antennas

This study investigates in detail the left-handed (LH) properties of the two-layer microstrip line, periodically loaded with broadside-coupled split ring resonators (BC-SRRs) and vias. The mechanism of the left-handed microstrip line (LHML), which includes the diamagnetic response, the backward-wave propagation and the proportionality of the guided wavelength on frequency, is discussed in terms of the field and current distributions and the dispersion diagram. To examine the resonance of the BC-SRR, both the full-wave eigenmode analysis and the closed-form formula based on the quasistatic approach are developed. The effects of the BC-SRR shape on the resonant frequency are evaluated. To facilitate the computer-aided-design (CAD) applications of the LHML, the equivalent-circuit model, which comprises the three-conductor coupled microstrip line for the coupling section, the series LC for the BC-SRR, and the shunt inductance for the via, is established. Good agreement among the results of the full-wave simulation, equivalent-circuit model, published data, and measurement supports the usefulness of the proposed modeling methodology and also validates the analytical expressions. The application of the LHML in the microstrip rectangular loop antenna fed by the conductor-backed coplanar waveguide-to-conductor-backed coplanar stripline (CBCPW-to-CBCPS) transition is presented to highlight the unique features of the LHML. Compared with the conventional loop antenna, the LHML-loaded loop antenna achieves a 50% area reduction and the 52% of main beam steering.

Frequency- and Time-Domain Characterizations of Ultrawideband Tapered Loop Antennas

A novel ultrawideband (UWB) antenna that consists of a tapered loop radiator and a coplanar waveguide-to-coplanar stripline (CPW-to-CPS) transition is investigated in both frequency- and time-domain. Contrary to the conventional monopole/dipole-like UWB antennas, this tapered loop antenna has predominately magnetic near fields and hence the coupling due to nearby dielectric objects is less significant. The antenna possesses a wide impedance bandwidth from 3.1 to 10.6 GHz under the |S11| < -10 dB criterion, and shows similar radiation patterns and 3.3-7 dBi antenna gain in its operating band. The time-domain characteristic of the transmitting/receiving antenna system is described by antenna transfer function. The propagation channel considering reflection effect is represented as the sum of the contributions of different multipath components. The calculated time-domain pulse response of the UWB antenna-channel system is validated by measurement. Results indicate that the proposed antenna with broad bandwidth and low pulse distortion is a good candidate for UWB applications.

Broadband series-fed printed dipole arrays with conductor-backed coplanar waveguide-to-coplanar stripline transitions

A novel printed antenna composed of a series-fed dipole array and a planar-type conductor-backed coplanar waveguide-to-coplanar stripline (CBCPW-to-CPS) transition in a uniplanar configuration is presented. According to careful design and optimization, the CBCPW-to-CPS transition possesses 120% bandwidth (for the 10 dB return loss criterion), which facilitates an antenna with a very broad bandwidth. The measured results of the antenna indicate an operating bandwidth of 100%, an end-fire radiation pattern with a front-to-back ratio greater than 15 dB, and cross-polarization radiation less than -16 dB across the frequency band of interest.

Frequency- and time-domain modeling of tapered loop antennas in ultra-wideband radio systems

The time-domain as well as frequency-domain characteristics of the UWB tapered loop antennas have been investigated theoretically and experimentally. A good agreement between the measured and simulated results is observed and thus validates the proposed impulse response technique for the joint antenna-channel system. This antenna offers high-fidelity and low-deltagd transmission and reception of UWB impulse signals with minimal distortion. The wavelet transform is used to determinate the dispersion and transient behavior of the radiated signal, which is useful for the UWB antenna array and receiver design