Finite-width Conductor-backed Coplanar Waveguides Research Articles

Characterization of uniplanar compact photonic-bandgap finite-width conductor-backed coplanar waveguide by using an electrooptic near-field mapping technique

An electrooptic near-field mapping system based on a gain-switched distributed-feedback pulsed laser and a CdTe electrooptic crystal was used for characterizing transient and stationary near-field patterns of conventional and uniplanar compact photonic bandgap (UC-PBG) finite-width conductor-backed coplanar waveguides (FW-CBCPWs). Comparison of transient and stationary near-field patterns of FW-CBCPWs visually shows that parasitic parallel-plate modes in the FW-CBCPW are effectively suppressed by the UC-PBG pattern on side-ground plates.

Investigation of microstriplike mode suppression in UC-PBG FW-CBCPW by using an electro-optic near-field characterization

Near-field patterns of uniplanar compact photonic bandgap (UC-PBG) and non-UCPBG finite-width conductor-backed coplanar waveguides (FW-CBCPWs) are characterized using an electro-optic near-field mapping system. This system is very effective in visually showing the role of the UC-PBG structure in the suppression of microstriplike (MSL) modes in the FW-CBCPWs. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 119–122, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21098

Propagation characteristics of finite-width conductor-backed coplanar waveguides with periodic electromagnetic bandgap cells

Wave propagation along the finite-width conductor-backed coplanar waveguide (FW-CBCPW) with periodically loaded one-dimensional electromagnetic bandgap (EBG) cells proposed earlier by the authors is investigated theoretically and experimentally in this paper. The full-wave simulation in conjunction with Floquet's theorem is employed to find the dispersion diagram for characterizing the guided and leaky waves over a wide frequency range. For examining the guided-wave mode, the equivalent-circuit model is established to obtain the analytical formula of the Bloch impedance. The remarkable slow-wave factor 1.9-2.9 times higher than that of a conventional FW-CBCPW is presented. When operating frequency is sufficiently high, the leaky-wave mode is emitted so that the structure radiates in the backward direction. Good agreement among the results of the full-wave simulation, equivalent-circuit model, published data, and measurement supports the usefulness of the proposed full-wave simulation and also validates the analytical formula. By properly adjusting the circuit configuration, the periodic EBG structure with controllable propagation characteristics, which include the bandgap zone, the slow-wave factor, and the Bloch impedance for the guided wave, as well as the radiation main beam for the leaky wave, may be achieved.

A novel periodic electromagnetic bandgap structure for finite-width conductor-backed coplanar waveguides

The one-dimensional (1-D) periodic electromagnetic bandgap (EBG) structure for the finite-width conductor-backed coplanar waveguide (FW-CBCPW) is proposed. Unlike the conventional EBG structures for the microstrip line and the coplanar waveguide (CPW), which are typically placed on one of the signal strips and the ground plane, this EBG cell is etched on both the signal strip and the upper ground plane of FW-CBCPW resulting in a novel circuit element. The equivalent circuit is also used to model the EBG cell. Measured and full-wave simulated results show that the cell exhibits remarkable stopband effect. The low-pass filter with lower cutoff frequency and wider rejection bandwidth is constructed from a serial connection of the EBG cells. The effect of back metallization on the guiding characteristic is also discussed. Compared to the published EBG cells, the proposed structure has the advantages of relative flexibility, higher compactness, lower radiation loss, and easier integration with the uniplanar circuits.

Non-leaky coplanar (NLC) waveguides with conductor backing

In this paper, we present a structure called a non-leaky coplanar (NLC) waveguide with conductor backing. It is a multilayered structure with two possible configurations. The spectral domain approach with a complex root searching procedure is used to investigate leakage phenomena. The simulation results confirm that the leakage in conductor-backed coplanar waveguide (CBCPW) occurs in the form of wave in the parallel plate waveguide with infinite width. The results show that the leakage in the multilayered structure can be removed if the geometrical and material parameters of the structure are chosen appropriately. Experiments were carried out to investigate the transmission of these structures. It was found that the resonance in the transmission of finite-width conductor-backed coplanar waveguide (FW-CBCPW) is caused by the energy leakage from the dominant CPW mode. The resonance is eliminated in the NLC waveguides. These NLC waveguides are feasible and practical in the uniplanar MMIC design due to their planar nature. >

Transmission characteristics of finite-width conductor-backed coplanar waveguide

This paper presents theoretical and experimental results for a finite-width conductor-backed coplanar waveguide (FW-CBCPW). The guiding characteristics of FW-CBCPW are investigated first by the rigorous method of mode matching. An FW-CBCPW through line is then placed within a test fixture commonly used in laboratories, and the scattering parameters of the through line are obtained theoretically by approximating the FW-CBCPW as a simple system of coupled transmission lines. Experimental results are shown to agree very well with the theoretical ones. In particular, the anomalous behavior observed in the transmission characteristic of the through line is related to the resonant phenomenon of the terminated side planes which are short-circuited at both input and output ends due to the test fixture. Finally, a technique of mode suppression in the side-plane regions is suggested for the improvement of signal transmission over a broad band of frequency spectrum. The effects of extra higher order modes on the transmission characteristics at high frequencies are also discussed. >

Effect of lateral walls on the propagation characteristics of finite-width conductor-backed coplanar waveguides

The connection of the side planes of finite-width conductor-backed coplanar waveguide (FW-CBCPW) to the ground through lateral walls suppresses the undesired microstrip-like (MSL) mode and provides a wide frequency range over which singlemode propagation occurs. The leakage or resonance phenomena of the higher-order modes can be avoided, if the distance separating the lateral walls is carefully designed.

Mode conversion at discontinuities in finite-width conductor-backed coplanar waveguide

The effect of overmoding in a conductor-backed coplanar waveguide is discussed, with special emphasis on mode conversion of discontinuities. The coplanar waveguide gap end and shorted end are studied by means of a fully electromagnetic application of the moment-method technique. Significant conversion occurs at the gap end. The results of a simple experiment which partially verify the analysis are described. >