UGCPW Structure-Based Embedded Resonator with High Quality Factor for Microwave Substrate Characterization

In this paper, an ungrounded coplanar waveguide-based embedded resonator method for microwave substrate characterization was presented. The effective dielectric constant of the structure and the dielectric constant of microwave substrates can be calculated by the measured resonant frequency. The measured insertion losses at resonant frequencies and the 3 dB bandwidth can be used to determine the loaded and unloaded quality factors, including the dielectric quality factor which is related to dielectric loss tangent. The radiation loss and the extra length due to fringing effect caused by the open-end structure were taken into account to improve the extraction accuracy. The experimental unloaded quality factor of the proposed resonator at resonance order 1 reaches 211.3. The extracted dielectric constant and dielectric loss tangent of Taconic TLY at resonance order 1 are, respectively, 2.218 and 9.286×10−4, which are only 0.018 (relatively 0.82%) and 0.286×10−4 (relatively 3.18%) deviations from the datasheet values, respectively. The proposed resonator method is especially suitable for dielectric characterization of newly developed materials with the difficulty of realizing metal via holes, in which case substrate-integrated-waveguide (SIW) resonator methods are not applicable. When comparing with microstrip resonator methods, the proposed method is of higher quality factor, and it is more reliable and economical as well.

Enhancement of microwave ring resonator based on poly-lactic acid thermoplastic substrate

In this paper, the development of a single-port microwave ring resonator (MRR) sensor based on a thermoplastic material, which is poly-lactic acid (PLA), is presented. The open-ended coaxial probe method was applied to identify the dielectric properties of PLA in terms of dielectric constant (2.25) and loss tangent (0.0001). The PLA substrate was fabricated using a hot press machine and with the same thickness (1.6 mm) as FR4. Hence, to consider the PLA as microwave substrate, microwave ring resonator (MRR) operating at 1.1 GHz resonance frequency was designed, simulated, and measured. Based on the observation, the return loss of MRR for the simulation and the measurement of the conventional design are -5.37 dB and -5.02 dB, respectively. The quality factor (Q-factor) for both are 122.22 and 183.33, respectively. Then, the enhanced coupling gap method was applied to improve the performance of MRR sensitivity in terms of return loss and Q-factor. It is observed that the return loss of the enhanced design for the simulation and the measurement are -26.67 dB and -20.23 dB, respectively, and the Q-factor are 122.22 and 200, respectively. Thus, the performance of the MRR based on different designs were compared in order to validate the sensor’s sensitivity and PLA can be recognized as a substrate material for RF and microwave applications.

Surface-modified Zn0.5Ti0.5NbO4 particles filled polytetrafluoroethylene composite with extremely low dielectric loss and stable temperature dependence

Polymer-ceramic composites are widely applied in microwave substrate materials due to the excellent dielectric properties and simple preparation process recently. Polytetrafluoroethylene-based (PTFE) composites filled with Zn0.5Ti0.5NbO4 (ZTN) ceramic particles were fabricated by hot-pressing. The particles were modified by C14H19F13O3Si to enhance the interface compatibility between PTFE and ZTN powders, which was characterized by X-ray photoelectron spectroscopy (XPS) and contact angle. The surface characteristic of particles transformed into hydrophobicity and tight microstructure as well as better dielectric properties were obtained after the surface modification. The microstructure, dielectric, thermal, mechanical properties, and water absorption of the composites concerning ZTN content were investigated. Modified ZTN/PTFE composites with 50 vol% ZTN particles exhibit excellent dielectric properties with a high dielectric constant of 8.3, an extremely low dielectric loss of 0.00055 at 7 GHz, and a stable temperature coefficient of the dielectric constant of −12.2 ppm/°C. All the properties show modified ZTN particles filled PTFE composite is the potential material for microwave substrate application.