Ungrounded Coplanar Waveguide Based Straight Line Methods for Broadband and Continuous Dielectric Characterization of Microwave Substrates

Abstract

This work presents a novel method for fast characterization of broadband and continuous dielectric properties of microwave substrates based on an ungrounded coplanar waveguide (UGCPW) structure containing two simple straight lines. The proposed method could, to some extent, alleviate the derivation error due to connector soldering and device fabrication. To verify this point, theoretical analysis and result comparisons are carried out. By considering both the conductor loss and radiation loss, the dielectric loss tangent can be retrieved with a high precision. The deviation of the measured dielectric constant and dielectric loss tangent are found to be within 0.03 (0.68%, 4.37 vs 4.40) and 0.0013 (6.5%, 0.0213 vs 0.02), respectively, in the range from 12 to 20 GHz, which is more accurate than the results reported in the literature, all while the proposed extraction approach is simpler than other methods such as the wave cascading matrix (WCM) algorithm. Due to the UGCPW configuration, this method is suitable for property evaluation of emerging synthesized dielectric materials, as a single round of electroplating process is required for device design, which can eliminate possible consistency error in conductor thickness and roughness caused by multiple electroplating process. INDEX TERMS Dielectric properties, ungrounded coplanar waveguide (UGCPW), dielectric constant, dielectric loss tangent, FR4.

Broadband Measurement of Substrate Complex Permittivity Using Optimized ABCD Matrix

“…UGCPW straight transmission lines are used as an example to investigate the proposed algorithm. As described in [15], it is very suitable to use the UGCPW structure for electroplating circuit on newly developed dielectric materials, avoiding excessive fabrication cost and difficulty, as well as the problem and error of inconsistent conductor thickness and roughness caused by multiple electroplating steps. High Frequency Structural Simulator (HFSS) software is employed for theoretical simulation and calculation.…”

“…In order to acquire the dielectric loss (see equation ( 7)), the corresponding radiation loss and conductor loss also need to be calculated. For UGCPW straight transmission line structures, the radiation loss is very small, which can be roughly described by equation ( 9) [15], [19]. In equation ( 9), ( ) and are the radiation form factor and dielectric wavelength, respectively.…”

“…In equation ( 9), ( ) and are the radiation form factor and dielectric wavelength, respectively. The conductor loss of UGCPW straight transmission lines can be expressed as equation (10), which is related to the characteristic impedance , the distributed series resistance of center strip conductor , and the distributed series resistance of the ground planes [15]. The characteristic impedance could be determined by the effective dielectric constant and the complete elliptic integral of the first kind K, which is associated with UGCPW structure dimensions, including the signal line width , gap , and substrate thickness .…”

“…The study in [14] proposed a covered transmission-line method to determine substrate complex permittivity. Our previous work proposed a line-line method for characterizing dielectric parameters by utilizing the transmission coefficients [15]. In [16], a hybrid covered-and two-ML method for extracting dielectric properties was proposed.…”

“…In order to investigate the proposed extraction method, we choose ungrounded coplanar waveguide (UGCPW) transmission line as an example, which is well suited for electroplating circuits on newly developed dielectric materials, avoiding excessive fabrication cost and difficulty, as well as the problem and error of inconsistent conductor thickness and roughness caused by multiple electroplating steps. Compared to our previous work of characterizing dielectric parameters by utilizing the transmission coefficients [15], this study makes use of all scattering parameters ( 11 / 22 / 12 / 21 ) which are included in the expression of ABCD parameters, and it could provide more comprehensive and reliable extraction results. ABCD matrix is a link between the four scattering parameters and total line attenuation/phase number of transmission lines.…”