Measurement of Substrate High-Frequency Complex Dielectric Constant With 2-D Spatial Distribution

A high-frequency (HF) S-matrix-based measurement of complex permittivity with a microstrip resonant ring (MRR) and coplanar waveguide (CPW) transmission line (TL) is developed. The permittivity characterization technique exploring the MRR resonance frequency and CPW TL insertion loss enables originally to consider the spatial distribution uniformity. The MRR is coupled with access TL and the CPW integrates hole and transition section to improve the transmission performance. The MRR and CPW parameter theoretical influences around 2 and 10 GHz are examined from 3-D electromagnetic (EM) simulation. As a proof of concept (POC), different batches of domestic and RO4350B substrates are tested and compared. Due to the domestic substrate instability, the CPW and CPW physical parameter effects need to be compared by RO4350B substrate test. High-precision dielectric constant $\varepsilon (x$ , $y$ ) and loss tangent $\tan \delta (x$ , $y$ ) at 2- and 10-GHz frequencies are measured with respect to the dielectric surface coordinates ( $x$ , $y$ ). The measured differences between $\varepsilon (x$ , $y$ ) and $\tan \delta (x$ , $y$ ) at various coordinate positions compared to the average values are assessed. The precision of dielectric constant testing can reach 0.004. The domestic substrate relative permittivity presents inhomogeneous property at the considered test frequencies.

I. Introduction

The dielectric characterization technique is an important test engineering to guarantee the radio frequency (RF) and microwave device performance [1]. Different dielectric property measurement techniques for microwave devices were overviewed in [2]. The most popular measurement techniques of dielectric material permittivity were developed in the frequency domain [3]. The measurement adaptability with respect to the material nature, shape, and size constitutes the main challenge. According to the material types, permittivity measurement techniques of solid [4], [5] and liquid [6], [7], [8] materials were introduced. An innovative dielectric constant microwave sensor operating with highly sensitive phase variation was designed with capacitively loaded transmission line (TL) [4] and rat-race coupler pair [5]. Moreover, radio frequency identification (RFID) wireless [6] and planar [7], [8] microwave sensors were tested to characterize liquid permittivity. By using substrate integrated waveguide (SIW) sensor structure, a nontrivial semisolid dielectric material characterization was investigated to realize high -factor microwave resonator [9]. Some of the measurement techniques are particularly dedicated to the characterization of nanostructured dielectric material property [10], [11], [12]. Microwave method sensors were also designed to characterize thin dielectric samples [13], [14], [15]. By using on-chip coplanar waveguide (CPW) circuit, an innovative in vivo dielectric analysis was proposed [16]. The dielectric measurements of liquids media in capillaries are also very important, as presented in some literature [17], [18].