BROADSIDE-COUPLED COPLANAR WAVE-GUIDE - STUDIES OF HYBRID MODES AND DOMINANT-MODE OPERATION

Hybrid modes in the broadside-coupled coplanar waveguide (CPW) are examined for the first time using the full-wave spectral-domain method. Various numerical results for the characteristic impedances and effective dielectric constants are obtained to study the behaviors of the dominant and higher-order modes as well as to assess the operating range of the dominant propagation modes in this structure. Criteria to enhance the dominant-mode frequency range are also discussed Over the dominant-mode frequency range, the dispersion is low. However, variation of the characteristic impedances is more pronounced than that of the effective dielectric constants, indicating the need for dynamic characteristic impedances for accurate circuit designs. The results in the low-frequency limit agree well with those obtained using a quasistatic approach. Also, the calculated effective dielectric constants of the dominant odd mode match closely the existing data for the effective dielectric constants of a shielded conductor-backed CPW. (C) 1995 John Wiley & Sons, Inc.